ARTICLE OF FOOTWEAR WITH BISTABLE COMPLIANT DEVICE FOR FOOT ENTRY

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001]This application claims the benefit of priority to U.S. Provisional Application No. 63/730,656 filed Dec. 11, 2024, which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

[0002]The present disclosure generally relates to an article of footwear including a bistable compliant device for raising and lowering the rear of a footwear upper during donning and doffing.

BACKGROUND

[0003]Traditionally, placing footwear on a foot often requires the use of one or both hands to stretch the ankle opening of a footwear upper and hold the rear portion open during foot insertion. The fit of the footwear upper is then adjusted following foot insertion, such as by tying laces. People with limited dexterity, including young children, may find donning and doffing of footwear challenging.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004]The drawings described herein are for illustrative purposes only, are schematic in nature, and are intended to be exemplary rather than to limit the scope of the disclosure.

[0005]FIG. 1 is a lateral side view of an article of footwear that includes a bistable compliant device shown in a first stable resting state.

[0006]FIG. 2 is a lateral side view of the article of footwear of FIG. 1 showing the bistable compliant device in a second stable resting state.

[0007]FIG. 3 is a perspective view of the bistable compliant device of FIG. 1.

[0008]FIG. 4 is a perspective rear view of the article of footwear of FIG. 1.

[0009]FIG. 5 is a perspective view of the bistable compliant device of FIG. 3 with the first and second arms shown prior to connection at their posterior portions.

[0010]FIG. 6 is another perspective view of the bistable compliant device of FIG. 5.

[0011]FIG. 7 is a front view of the bistable compliant device of FIG. 5.

[0012]FIG. 8 is a cross-sectional view of the arms of FIG. 3 taken at lines 8-8 in FIG. 3 in a first stable resting state as in FIG. 1.

[0013]FIG. 9 is a cross-sectional view of the bistable compliant device of FIG. 3 in the second stable resting state as in FIG. 2.

[0014]FIG. 10 is a lateral side view of another article of footwear that includes a bistable compliant device shown in a first stable resting state.

[0015]FIG. 11 is a lateral side view of another article of footwear that includes a bistable compliant device shown in a first stable resting state.

[0016]FIG. 12 is a lateral side view of another article of footwear that includes a bistable compliant device shown in a first stable resting state.

[0017]FIG. 13 is a lateral side view of another article of footwear that includes a bistable compliant device shown in a first stable resting state.

[0018]FIG. 14 is a lateral side view of another article of footwear that includes a bistable compliant device shown in a first stable resting state.

[0019]FIG. 15 is a lateral side view of another article of footwear that includes a bistable compliant device shown in a first stable resting state.

[0020]FIG. 16 is a lateral side view of another article of footwear that includes a bistable compliant device shown in a first stable resting state.

[0021]FIG. 17 is a perspective rear view of the article of footwear of FIG. 16.

[0022]FIG. 18 is a perspective view of a midsole and a base of a bistable compliant device for an article of footwear.

[0023]FIG. 19 is another perspective view of the base of FIG. 18.

[0024]FIG. 20 is a plan view of first and second arms securable to the base of FIGS. 18 and 19 as part of the bistable compliant device.

[0025]FIG. 21 is a medial side view of the midsole and bistable compliant device of FIGS. 18-20 with the bistable compliant device in a first stable resting state.

[0026]FIG. 22 is a cross-sectional view of the first and second arms of the bistable compliant device of FIG. 21 taken at lines 22-22 in FIG. 21.

[0027]FIG. 23 is a medial side view of the midsole and bistable compliant device of FIGS. 18-20 with the bistable compliant device in a second stable resting state.

[0028]FIG. 24 is a cross-sectional view of the first and second arms of the bistable compliant device of FIG. 22 taken at lines 24-24 in FIG. 23.

[0029]FIG. 25 is a perspective view of a bistable compliant device for an article of footwear with the bistable compliant device in a first stable resting state.

[0030]FIG. 26 is a perspective view of the bistable compliant device of FIG. 25 with the bistable compliant device in a second stable resting state.

[0031]FIG. 27 is a perspective view of another bistable compliant device for an article of footwear including first and second arms integral with a base with the posterior portions of the first and second arms shown prior to connection to one another.

[0032]FIG. 28 is a plan view of the bistable compliant device of FIG. 27.

[0033]FIG. 29 is a perspective view of another bistable compliant device for an article of footwear including first and second arms integral with a base with the posterior portions of the first and second arms shown prior to connection to one another.

[0034]FIG. 30 is a bottom view of the bistable compliant device of FIG. 29.

[0035]FIG. 31 is a side view of another bistable compliant device for an article of footwear including first and second arms integral with a base with the posterior portions of the first and second arms shown prior to connection to one another.

[0036]FIG. 32 is a plan view of the bistable compliant device of FIG. 31.

[0037]FIG. 33 is a perspective view of another bistable compliant device for an article of footwear including first and second arms integral with a base with the posterior portions of the first and second arms shown prior to connection to one another.

[0038]FIG. 34 is another perspective view of the bistable compliant device of FIG. 33.

[0039]FIG. 35 is a side view of the bistable compliant device of FIGS. 33-34.

[0040]FIG. 36 is a perspective view showing a top side of another bistable compliant device for an article of footwear including first and second arms integral with a base with the posterior portions of the first and second arms shown prior to connection to one another.

[0041]FIG. 37 is a closeup fragmentary perspective view of a bottom side of the arms of the bistable compliant device of FIG. 36.

[0042]FIG. 38 is a bottom view of another bistable compliant device for an article of footwear including first and second arms integral with a base with the posterior portions of the first and second arms shown prior to connection to one another.

[0043]FIG. 39 is a plan view of the bistable compliant device of FIG. 38.

[0044]FIG. 40 is a side view of the bistable compliant device of FIGS. 38-39.

[0045]FIG. 41 is a closeup fragmentary perspective view of a top side of the arms of the bistable compliant device of FIGS. 38-40.

[0046]FIG. 42 is a closeup fragmentary perspective view of a bottom side of the arms of the bistable compliant device of FIGS. 38-41.

[0047]FIG. 43 is a perspective view of another bistable compliant device for an article of footwear including first and second arms integral with a base with the posterior portions of the first and second arms shown prior to connection to one another.

[0048]FIG. 44 is another perspective view of the bistable compliant device of FIG. 43.

[0049]FIG. 45 is a side view of the bistable compliant device of FIGS. 43-44.

[0050]FIG. 46 is a closeup fragmentary perspective view of a bottom side of the arms of the bistable compliant device of FIGS. 43-45.

[0051]FIG. 47 is a perspective view of another bistable compliant device for an article of footwear including first and second arms integral with a base with the posterior portions of the first and second arms shown prior to connection to one another.

[0052]FIG. 48 is another perspective view of the bistable compliant device of FIG. 47.

[0053]FIG. 49 is a side view of the bistable compliant device of FIGS. 47-48.

[0054]FIG. 50 is a closeup fragmentary perspective view of one of the arms of the bistable compliant device of FIGS. 47-49.

[0055]FIG. 51 is a closeup fragmentary perspective view of another one of the arms of the bistable compliant device of FIGS. 47-50.

[0056]FIG. 52 is a fragmentary perspective view of an alternative arm for use in any of the bistable compliant devices disclosed herein.

[0057]FIG. 53 is a fragmentary perspective view of another alternative arm for use with the arm of FIG. 52 in any of the bistable compliant devices disclosed herein.

[0058]FIG. 54 is a fragmentary perspective view of an alternative arm for use in any of the bistable compliant devices disclosed herein.

[0059]FIG. 55 is a fragmentary perspective view of another alternative arm for use with the arm of FIG. 54 in any of the bistable compliant devices disclosed herein.

[0060]FIG. 56 is a perspective view of another bistable compliant device for an article of footwear including first and second arms integral with a base with the posterior portions of the first and second arms shown prior to connection to one another.

[0061]FIG. 57 is another perspective view of the bistable compliant device of FIG. 56.

[0062]FIG. 58 is a closeup fragmentary perspective view of one of the arms of the bistable compliant device of FIGS. 56-57.

[0063]FIG. 59 is a closeup fragmentary view of an arm for use in a bistable compliant device like that of FIGS. 56-57 as an alternative to the arm of FIG. 58.

[0064]FIG. 60 is a plan view of a sole structure for an article of footwear and a bistable compliant device including a base and first and second arms integral with the base with the posterior portions of the first and second arms shown prior to connection to one another.

[0065]FIG. 61 is a fragmentary lateral side view of a heel region of the sole structure of FIG. 60 and showing the bistable compliant device in a first stable resting state with the posterior portions of the arms connected to one another.

[0066]FIG. 62 is a perspective view of a base of a bistable compliant device including projections with ramped surfaces.

[0067]FIG. 63 is a side view of the base of FIG. 62.

[0068]FIG. 64 is a bottom perspective view of the base of FIGS. 62-63.

[0069]FIG. 65 is a perspective view of a sole structure for an article of footwear and a bistable compliant device including the base of FIGS. 62-64 and first and second arms secured to the base at the projections with the posterior portions of the first and second arms connected to one another and the bistable compliant device in a first stable resting state.

[0070]FIG. 66 is a perspective view of the sole structure of FIG. 65 with the bistable compliant device in a second stable resting state.

[0071]FIG. 67 is a cover for one of the projections of the base of FIGS. 62-66.

[0072]FIG. 68 is a perspective view of the sole structure of FIG. 66 with the bistable compliant device in the second stable resting state and covers like that of FIG. 67 over the projections.

[0073]FIG. 69 is a medial side view of an article of footwear including a sole structure and a bistable compliant device including first and second arms secured to a base with posterior portions of the first and second arms connected to one another and to a collar mount secured to a collar of a footwear upper, and the bistable compliant device in a first stable resting state.

[0074]FIG. 70 is a fragmentary perspective view of the article of footwear of FIG. 69.

[0075]FIG. 71 is a perspective view of the collar mount of FIGS. 69 and 70.

[0076]FIG. 72 is another perspective view of the collar mount.

[0077]FIG. 73 is a cross-sectional view of the collar mount taken at lines 73-73 in FIG. 72.

[0078]FIG. 74 is a medial side view of the sole structure and the bistable compliant device of FIG. 69 with a different collar mount and showing the bistable compliant device in a second stable resting state.

[0079]FIG. 75 is a perspective view of the collar mount of FIG. 74.

[0080]FIG. 76 is a lateral side view of an article of footwear including a footwear upper secured to the sole structure and bistable compliant device of FIG. 65 in a first stable resting state and showing posterior portions of the first and second arms secured to a tab extending at a rear of the footwear upper.

[0081]FIG. 77 is a lateral side view of the article of footwear of FIG. 76 with the bistable compliant device in a second stable resting state.

[0082]FIG. 78 is a perspective view of an article of footwear having a footwear upper, sole structure, and bistable compliant device with first and second arms all as a one-piece, unitary and monolithic component and showing posterior portions of the arms prior to connection to one another with complementary connecting features.

[0083]FIG. 79 is a perspective view of an article of footwear having a footwear upper, sole structure, and bistable compliant device having a single arm all as a one-piece, unitary and monolithic component and showing an anchor end of the arm prior to connection to the sole structure at a complementary connecting feature, and showing the anchor arm connected in phantom.

[0084]FIG. 80 is a perspective view of an article of footwear having a footwear upper and sole structure, as a one-piece, unitary and monolithic component, and having a separate one-piece arm shown prior to connection to the sole structure at anchor ends of the arm and complementary connecting features of the sole structure.

[0085]FIG. 81 is a perspective view of the article of footwear of FIG. 80 with the single arm of the bistable compliant device secured to the sole structure and in a first stable resting state, and showing a second stable resting state of the bistable compliant device in phantom.

[0086]FIG. 82 is a perspective view of an article of footwear having a footwear upper, sole structure, and bistable compliant device having first and second arms all as a one-piece, unitary and monolithic component and showing posterior portions of the arms prior to connection to one another.

[0087]FIG. 83 is a connecting sleeve configured to fit over posterior portions of the first and second arms of FIG. 82 to connect the first and second arms to one another to establish first and second stable resting states.

DESCRIPTION

[0088]The present disclosure generally relates to a footwear heel structure and an article of footwear that include a bistable compliant device that eases foot entry into and exit out of the article of footwear. The bistable compliant device has two stable resting states in which the device will remain absent application of an applied external force of at least a predetermined magnitude in a predetermined direction. One of the resting states is a state in which the ankle opening of the footwear upper is held relatively open for easy foot entry for example. Accordingly, a foot may be inserted without the wearer needing to apply force to hold the footwear upper open, and then the device may be moved to the other resting state, such as a use state (conducive for wearing the article of footwear during typical activities such as walking, etc.) by applying at least the threshold external force. The threshold external force applied to move from a first stable resting state to a second stable resting state may be in a different direction, such as an opposite direction, as the external force applied to move from the second stable resting state to the first stable resting state.

[0089]Accordingly, as used herein, a “bistable compliant device” means a device that has at least two independent minimal or low stress resting state positions at which the device can maintain a stable structure. An external force of at least a threshold magnitude applied to the device may move it from one minimal or low stress resting state position to another. In at least some examples, no external forces are needed to hold the bistable compliant device in any of its various stable positions.

[0090]In an example, an article of footwear includes a footwear upper, a sole structure, and the bistable compliant device. The sole structure is secured to the footwear upper. The footwear upper defines an ankle opening and a foot-receiving cavity over the sole structure. The bistable compliant device includes a first arm that has a first anchor end secured at a medial side of the article of footwear. The first arm has a first posterior portion remote from the sole structure and further rearward than the first anchor end. The bistable device also includes a second arm that has a second anchor end secured at a lateral side of the article of footwear. The second arm has a second posterior portion remote from the sole structure and further rearward than the second anchor end. The first posterior portion and the second posterior portion are connected with one another such that the bistable compliant device extends around a rear of the foot-receiving cavity and has a first stable resting state with the first and second posterior portions in a first position and a second stable resting state with the first and second posterior portions in a second position closer to the sole structure than in the first position. The footwear upper is secured to the bistable compliant device at the rear of the heel region.

[0091]As discussed in the various examples herein, the bistable compliant device is configured to remain in the first stable resting state in the absence of an applied external force of at least a threshold magnitude, and move to the second stable resting state upon application of the applied external force with the footwear upper moving with the bistable compliant device at the rear of the heel region and lowering a rear of the ankle opening. Accordingly, to ease foot entry into the ankle opening, the user may apply the external force to cause the bistable compliant device to move to the second stable resting state. The bistable compliant device is configured to remain in the second stable resting state in the absence of an applied external force of at least the threshold magnitude (e.g., of another application of such a force in a different direction). When such a force is applied (e.g., after the wearer has fully inserted their foot), the bistable compliant device is configured to move to the first stable resting state upon application of the applied external force with the footwear upper moving with the bistable compliant device at the rear of the heel region and raising the rear of the ankle opening. The first and second stable resting states are the only stable resting states of the bistable compliant device.

[0092]In one or more implementations, the bistable compliant device provides a tactile and/or an audible signal when moving from the first stable resting state to the second stable resting state and when moving from the second stable resting state to the first stable resting state. The user is thus easily alerted as to when the desired position of the device and the corresponding stable resting state (e.g., the first position or the second position) has been achieved after applying the external force.

[0093]The bistable device is configured to be movable between the two resting states and remain in a current resting state in the absence of the application of the applied external force of at least the threshold magnitude at least in part due to the geometry of the first and second arms. For example, each of the first arm and the second arm may have an anterior portion at the respective first or second anchor end and an intermediate portion between the anterior portion and the respective first or second posterior portion. The bistable compliant device may flex at the intermediate portion of each of the first arm and the second arm under a first applied external force of at least a threshold magnitude to move from the first stable resting state to the second stable resting state, and flex at the intermediate portion of each of the first arm and the second arm under a second applied external force of at least the threshold magnitude in a different direction than the applied external force used to move to the second stable resting state to move from the second stable resting state to the first stable resting state.

[0094]Notably, the applied external force is generally in a first direction (e.g., having at least a downward component) to move the bistable compliant device from the first stable resting state to the second stable resting state (e.g., such as closer to the sole structure at the rear of the article of footwear), and in a different second direction, such as an opposite direction (e.g., having at least a upward component) to move from the second stable resting state to the first stable resting state (e.g., such as further from the sole structure at the rear of the article of footwear).

[0095]In an aspect, the posterior portion of the first arm and the posterior portion of the second arm rotate about a pivot axis extending through a connection between the posterior portion of the first arm and the posterior portion of the second arm when the bistable compliant device moves from the first stable resting state to the second stable resting state and when the bistable compliant device moves from the second stable resting state to the first stable resting state.

[0096]The geometry of the arms that may enable such flexing may include the intermediate portion of each of the arms having a width and a thickness, with the width greater than the thickness. Stated differently, a ratio of a width to a thickness of the intermediate portion of each of the arms is greater than one in such an example. The width is generally in the transverse direction of the article of footwear and the thickness is generally in a vertical direction.

[0097]In an example, each of the first arm and the second arm may have a width and a thickness at a cross-section extending in a medial-lateral direction of the article of footwear perpendicular to a longitudinal axis of the article of footwear and the width may be greater than the thickness.

[0098]In an example, each of the first arm and the second arm may tilt inward and downward toward the foot-receiving cavity from an outer extent of the intermediate portion to an inner extent of the intermediate portion when the bistable compliant device is in the first stable resting state. In the same or a different example, the intermediate portion of each of the first arm and the second arm may have an inner wall that tilts inward toward the foot-receiving cavity from a bottom edge of the inner wall to a top edge of the inner wall when the bistable compliant device is in the first stable resting state. In the same or a different example, the intermediate portion of each of the first arm and the second arm may have an outer wall that tilts inward toward the foot-receiving cavity from a bottom edge of the outer wall to a top edge of the outer wall when the bistable compliant device is in the first stable resting state. In one or more implementations, the intermediate portion of each of the first arm and the second arm may have a quadrilateral transverse cross-section at the intermediate portion, such as a rectangular cross-section.

[0099]In an example, the first posterior portion may have a first distal end and the second posterior portion may have a second distal end. The first and second posterior portions may be coupled to one another in a connected state. The first and second arms are each internally biased to a disconnected state in which the first and second posterior portions are not connected to one another and the distal ends are further apart from one another than in the connected state. Stated differently, when connected, the posterior portions are pulled toward one another from the positions to which they are internally biased, which causes the bistable compliant device to store energy that biases posterior portions toward the disconnected state.

[0100]The disconnected state of the arms (e.g., the position the arms are biased to when not connected at their distal ends) may include any of various orientations within the scope of the disclosure. In one example, the first and second arms may extend parallel with one another from the first and second anchor ends to the first and second distal ends in the disconnected state.

[0101]In another example, the first arm may have a first anterior portion nearer to the first anchor end than the first posterior portion, the second arm may have a second anterior portion nearer to the second anchor end than the second posterior portion, the first posterior portion may be angled inward between 25 and 45 degrees along a longitudinal axis of the first arm relative to the first anterior portion in the disconnected state, and the second posterior portion may be angled inward between 25 and 45 degrees along a longitudinal axis of the second arm relative to the second anterior portion in the disconnected state.

[0102]In a specific example, the first posterior portion may be angled inward at 36 degrees along a longitudinal axis of the first arm relative to the first anterior portion in the disconnected state, and the second posterior portion may be angled inward at 36 degrees along a longitudinal axis of the second arm relative to the second anterior portion in the disconnected state.

[0103]In yet another example, the first posterior portion may be angled inward between 10 and 20 degrees along the longitudinal axis of the first arm relative to the first anterior portion in the disconnected state, and the second posterior portion may be angled inward between 10 and 20 degrees along the longitudinal axis of the second arm relative to the second anterior portion in the disconnected state.

[0104]In still another example, the first posterior portion may be angled inward between 10 and 80 degrees along a longitudinal axis of the first arm relative to the first anterior portion in the disconnected state, and the second posterior portion may be angled inward between 10 and 80 degrees along a longitudinal axis of the second arm relative to the second anterior portion in the disconnected state.

[0105]The bistable compliant device may include any of various complementary connecting features by which the first distal end and the second distal end are coupled to one another. In one example, a rivet or other fastener extends through aligned holes in the first and second distal ends.

[0106]In other examples, the complementary connecting features may include a slot and a peg. The slot may extend through the first arm and the peg may extend from the second arm and be configured to extend through the slot and engage with the first arm. Alternatively, the slot may extend through the second arm and the peg may extend from the first arm and be configured to extend through the slot and engage with the second arm.

[0107]In an example, the peg may have an interference fit with the respective first arm or second arm through which the slot extends.

[0108]In an implementation, the slot may have a first portion and a second portion extending from the first portion. The second portion may be smaller than the first portion and disposed closer to the first distal end of the first arm than the first portion in the example in which the slot extends through the first arm or disposed closer to the second distal end of the second arm than the first portion in the example in which the slot extends through the second arm.

[0109]The slot may have a perimeter with three sides at the second portion. The peg may have a stem with a square outer perimeter that fits in the second portion against the three sides. In another implementation, the slot may have an arced perimeter at the second portion and the peg may have a stem with a cylindrical outer perimeter that fits in the second portion against the arced perimeter. In still another example, the peg may be configured as a first hooked prong and the bistable compliant device may include a second hooked prong spaced from the first hooked prong. The first hooked prong and the second hooked prong may engage the respective first arm or second arm through which the slot extends at opposing ends of the slot.

[0110]In some implementations, the bistable compliant device may further include a base secured to the sole structure. The first and second anchor ends may be secured to the base and, in some examples, integral with the base. In an implementation, the bistable compliant device may include a base that is integral with and extends from the first anchor end and from the second anchor end and connects the first anchor end to the second anchor end. The bistable compliant device may define a gap between the first and second posterior portions and the base.

[0111]In an example, the base may have a first slot at a medial side of the base and a second slot at a lateral side of the base. The first anchor end of the first arm may be configured to engage with the base at the first slot to secure the first arm to the base. The second anchor end of the second arm may be configured to engage with the base at the second slot to secure the second arm to the base.

[0112]The base may define an inverted channel in some implementations. The sole structure may include a rim, and the base may fit to the sole structure with the rim in the inverted channel.

[0113]The base may have a first projection with a first ramped surface inclining in a rearward direction of the article of footwear at a medial side of the base. The base may have a second projection with a second ramped surface inclining in a rearward direction of the article of footwear at a lateral side of the base. The first anchor end of the first arm may be secured to the first projection. The second anchor end of the second arm may be secured to the second projection. The first arm and the second arm may extend rearwardly from the first ramped surface and from the second ramped surface, respectively.

[0114]In an example, the bistable compliant device may define a slot in each of the first projection and the second projection. The first anchor end may engage the base at the slot in the first projection, and the second anchor end may engage the base at the slot in the second projection.

[0115]The article of footwear may include a first cover engageable with the first projection to cover the first anchor end and the first ramped surface and a second cover engageable with the second projection to cover the second anchor end and the second ramped surface.

[0116]In an implementation, the first cover and the second cover may each be configured as an inverted channel that has an inner surface with one of a rail or a groove, and the first projection and the second projection may each have the other of the rail or the groove. The rail may be configured to interfit with the groove. Accordingly, the covers are held to the base by the interfitting of the rail and the groove.

[0117]In an example, the first anchor end and the second anchor end may be configured to be disposed at a midfoot region of the article of footwear. In another example, the first anchor end and the second anchor may be configured to be disposed at a forefoot region of the article of footwear.

[0118]At least one of the first arm or the second arm may include an elongated flange extending outward and configured to receive the applied external force to move the bistable compliant device from the first stable resting state to the second stable resting state.

[0119]In an aspect, the footwear upper may include a base layer defining the ankle opening and the foot-receiving cavity, and may further include foxing disposed between the base layer and the sole structure. At least one of the first arm or the second arm may be at least partially disposed between the foxing and the base layer, such as, for example, at an anchored end of the arm. Accordingly, the foxing may help to maintain the arm relative to the base layer and the sole structure. As used herein, foxing is a strip of material, separate from the sole structure and the footwear upper that helps to reinforce the biteline where the footwear upper and the midsole meet.

[0120]In an aspect, a shroud may be secured to the footwear upper and may at least partially cover the first and second arms, with the posterior portions extending above the shroud. The shroud thus helps to conceal and protect the flexing intermediate portions of the arms and thus may help to focus the user on manipulating the posterior portions (e.g., applying force at the posterior portions).

[0121]In an aspect, the footwear upper may include a collar extending at least partially around the ankle opening at the foot-receiving cavity. The bistable compliant device may be operatively secured to the collar (i.e., either directly or indirectly). As such, when the bistable component moves between the two stable resting states, the footwear upper will move with the bistable compliant device at the collar.

[0122]In an implementation, the article of footwear may include a collar mount extending around a rear of the ankle opening from the medial side to the lateral side and secured to the collar. The bistable compliant device may be secured to the collar mount. In an example, the first posterior portion may have a first distal end and the second posterior portion may have a second distal end connected to the first distal end. For example, a rivet may be used to connect the distal ends. The collar mount may have a hemispherical portion protruding at an exterior of the collar mount. More particularly, and outer surface of the hemispherical portion is a hemispherical surface. At least one of the first distal end and the second distal end may interface with the hemispherical portion. For example, a fastener such as a rivet may couple the first and second posterior portions to one another in a connected state, such as by extending through the distal ends and into the hemispherical portion. As the arms pivot about an axis through the rivet, one or both may interface with the hemispherical portion. By configuring the portion as hemispherical, the surface area of the interface with the arms is minimal in comparison to other shapes thus reducing any resistance to movement between the two stable resting states.

[0123]In an example, the hemispherical portion defines a hollow space at an inner side of the collar mount. The fastener extends into the hollow space and terminates outward of the collar. In this manner, the fastener does not extend into the upper or to the wearer's foot.

[0124]In an aspect, the collar mount may have a ledge with a surface that declines forwardly and downwardly toward the foot-receiving cavity, providing a foot entry ramp.

[0125]In an aspect of the disclosure, an article of footwear includes a one-piece footwear upper and sole structure that together define an ankle opening and a foot-receiving cavity over the sole structure. The article of footwear also includes a bistable compliant device including at least one arm having a first anchor end secured at a lateral side of the sole structure, a first posterior portion remote from the sole structure and further rearward than the first anchor end, a second anchor end secured at a medial side of the sole structure, and a second posterior portion remote from the sole structure and further rearward than the second anchor end. The first posterior portion and the second posterior portion are connected with one another such that the bistable compliant device extends around a rear of the foot-receiving cavity and has a first stable resting state with the first and second posterior portions in a first position and a second stable resting state with the first and second posterior portions in a second position closer to the sole structure than in the first position.

[0126]In an example, the at least one arm is a single arm, and the first posterior portion and the second posterior portion are integral. In some implementations, the first posterior portion and the second posterior portion define an obtuse angle when at least one of the first anchor end and the second anchor end is disconnected from the sole structure.

[0127]In some implementations, the single arm is also integral and unitary with the one-piece footwear upper and sole structure. That is, it is also part of the one-piece, monolithic component. For instance, the single arm may be integral and unitary with the one-piece footwear upper and sole structure at one of the first anchor end and the second anchor end. The other of the first anchor end or the second anchor end and the sole structure may have complementary connecting features at which the other of the first anchor end or the second anchor end is secured to the sole structure. In other implementations, the single arm is not part of the one-piece, monolithic component that is the footwear upper and sole structure. Instead, the sole structure and both of the first anchor end and the second anchor end of the single arm have complementary connecting features at which the first anchor end and the second anchor end are secured to the sole structure.

[0128]In other examples, the at least one arm includes both a first arm and a second arm. The first arm includes the first anchor end and the first posterior portion and the second arm includes the second anchor end and the second posterior portion. To connect the first and second arms in order to establish the configuration of the bistable compliant device that provides the first and second bistable states, the first posterior portion and the second posterior portion have complementary connecting features at which the first posterior portion and the second posterior portion are secured to one another.

[0129]In an example, the sole structure and both of the first anchor end and the second anchor end have complementary connecting features at which the first anchor end and the second anchor end are secured to the sole structure.

[0130]In another example, the first arm is integral and unitary with the one-piece footwear upper and sole structure at the first anchor end and the second arm is integral and unitary with the one-piece footwear upper and sole structure at the second anchor end. That is, both arms are part of the one-piece, monolithic component that is the footwear upper and sole structure. In one implementation of such a configuration, the article of footwear also includes a connecting sleeve fit over the first posterior portion and the second posterior portion and securing the first posterior portion to the second posterior portion.

[0131]In an implementation, a footwear heel structure for easing foot entry into and exit out of an article of footwear may include a bistable compliant device having a first stable resting state and a second stable resting state. The bistable compliant device may be configured to remain in the first stable resting state or in the second stable resting state in the absence of an applied external force of at least a threshold magnitude. The bistable compliant device may have a first arm and a second arm, each having an anterior portion, a posterior portion, and an intermediate portion between the anterior portion and the posterior portion. The posterior portion of the first arm may be connected with the posterior portion of the second arm, storing force urging the posterior portions in an outward direction. The anterior portion of the first arm and the anterior portion of the second arm may each be anchored and spaced apart from one another.

[0132]The above features and advantages and other features and advantages of the present teachings are readily apparent from the following detailed description of the modes for carrying out the present teachings when taken in connection with the accompanying drawings. It should be understood that even though in the following the embodiments may be separately described, single features thereof may be combined in additional embodiments.

[0133]FIG. 1 is a lateral side view of an article of footwear 10 that includes a bistable compliant device 12 shown in a first stable resting state. FIG. 2 is a lateral side view of the article of footwear 10 showing the bistable compliant device 12 in a second stable resting state. FIG. 3 is a perspective view of the bistable compliant device 12 of FIG. 1. FIG. 4 is a rear perspective view of the article of footwear 10 with the bistable compliant device 12 in a first stable resting state.

[0134]The article of footwear 10 is configured for a right foot and includes a sole structure 14 and a footwear upper 16. Although shown as applied in an article of footwear 10 for a right foot, a like bistable compliant device that is a mirror image of the bistable compliant device 12 may be used in an article of footwear for a left foot. For example, both the right and left foot may each include a bistable compliant device 12 as discussed. The footwear upper 16 is secured to the sole structure 14 to define a foot-receiving cavity 18 over the sole structure 14 and has an ankle opening 20 that permits a foot 17 to access the foot-receiving cavity 18. The footwear upper 16 is shown as including a base layer 16A that is configured as a lace-up type upper, but is not limited to such. The footwear upper 16 may include any materials having sufficient flexibility to allow the rear of the footwear upper 16 to move at the rear 20A of the ankle opening 20 with the bistable compliant device 12 as discussed herein. The sole structure 14 is shown as a unisole (e.g., a combined midsole and outsole), but could have other configurations within the scope of the disclosure.

[0135]The bistable compliant device 12 is configured to remain in the first stable resting state shown in FIG. 1 in the absence of an applied external force F1 of at least a threshold magnitude, and move to the second stable resting state of FIG. 2 upon application of the applied external force. A threshold external force F1 is shown in phantom applied to a rear of the bistable compliant device 12 in FIG. 1, which will cause the bistable compliant device 12 to flex and move to the second stable resting state of FIG. 2. The footwear upper 16 moves with the bistable compliant device 12 at the rear of a heel region 22 and lowers a rear 20A of the ankle opening 20 as shown in FIG. 2.

[0136]In addition to the heel region 22, the article of footwear 10 includes a midfoot region 24, and a forefoot region 26. The heel region 22 corresponds with rear portions of the foot, including the calcaneus bone. The midfoot region 24 generally includes portions of the article of footwear 10 corresponding with the arch area of the foot. The forefoot region 26 generally includes portions of the article of footwear 10 corresponding with the toes and the joints connecting the metatarsals with the phalanges of a wearer's foot.

[0137]The article of footwear 10 includes a lateral side 28 and a medial side 30 that extend through each of the heel region 22, the midfoot region 24, and the forefoot region 26 and fall on opposite sides of a longitudinal midline LM of the article of footwear 10. The longitudinal midline LM is a longitudinal axis shown in FIG. 1. The heel region 22, the midfoot region 24, the forefoot region 26, the lateral side 28, and the medial side 30 also refer to regions and sides of the individual components of the article of footwear 10, and are not intended to demarcate precise areas of footwear 10, but are instead intended to represent general areas of the article of footwear 10, the bistable compliant device 12, the sole structure 14, and the footwear upper 16, etc., to aid in the following discussion.

[0138]For example, the lateral side 28 and the medial side 30 are indicated in FIG. 3 with respect to the bistable compliant device 12. As shown in isolation in FIG. 3, the bistable compliant device 12 includes a first arm 40 and a second arm 42. The first arm 40 has an anterior portion 40A at a first anchor end 41 that is secured at the lateral side 28 of the article of footwear 10 as shown in FIG. 1. The first arm 40 has a posterior portion 40B remote from the sole structure 14 and further rearward than the anterior portion 40A and the first anchor end 41. The first arm 40 also has an intermediate portion 40C between the anterior portion 40A and the posterior portion 40B.

[0139]Similarly, the second arm 42 has an anterior portion 42A that includes a second anchor end 43 secured at the medial side 30 of the article of footwear 10 as indicated in FIG. 4. The second arm 42 has a second posterior portion 42B remote from the sole structure 14 and further rearward than the second anterior portion 42A and the second anchor end 43. The second arm 42 also has an intermediate portion 42C between the anterior portion 42A and the posterior portion 42B. In the example shown, the first and second anchor ends 41, 43 are at least partly in the heel region 22 of the article of footwear 10. The anterior portion 40A of the first arm 40 is spaced apart from the anterior portion 42A of the second arm 42 by the transverse width of the foot-receiving cavity 18 between the anterior portions 40A and 42A, for example.

[0140]The footwear upper 16 is also secured to the bistable compliant device 12 at the rear 18A of the foot-receiving cavity in the heel region 22 and, more specifically, at a rear of the base layer 16A of the footwear upper 16 as best shown in FIG. 4. The footwear upper 16 includes a collar 46 extending at least partially around the ankle opening 20 at the foot-receiving cavity 18 as shown in FIG. 1. The bistable compliant device 12 is secured to the collar 46 by stitches 44 shown in FIG. 4. In the example shown, the stitches 44 extend through the posterior portions 40B, 42B and to the collar 46. As such, when the bistable compliant device 12 moves between the two stable resting states (e.g., from one stable resting state to the other stable resting state), the footwear upper 16 will move with the bistable compliant device 12 at the collar 46 to help maximize lowering and raising of the rear 20A of the ankle opening 20.

[0141]The bistable compliant device 12 flexes at the intermediate portion 40C and 42C of each of the first arm 40 and the second arm 42, respectively under the first applied external force F1 of at least the threshold magnitude to move from the first stable resting state to the second stable resting state, and flexes at the intermediate portions 40C and 42C under the second applied external force F2 of at least the threshold magnitude to move from the second stable resting state to the first stable resting state. The first arm 40 is shown with the intermediate portion 40C in a different orientation relative to the anterior portion 40A and the posterior portion 40B in the second stable resting state of FIG. 2 relative to the first stable resting state of FIG. 1 after such flexing at the intermediate portion 40C.

[0142]Additionally, the footwear upper 16 includes foxing 48 disposed between the base layer 16A and the sole structure 14 at the lateral and medial sides 28, 30 (shown best at the lateral side 28 in FIGS. 1 and 4, and arranged in a symmetrical manner at the medial side 30). The anchor ends 41 and 43 of the first and second arms 40, 42 are at least partially disposed between the foxing 48 and the base layer 16A. Accordingly, the foxing 48 may help to maintain the anterior portions 40A and 42A of the arms 40, 42 relative to the base layer 16A and the sole structure 14.

[0143]With reference to FIG. 2, the first arm 40 and the second arm 42 each include an elongated flange 50A and 50B, respectively, that extends rearward and is configured to receive the applied external force to move the bistable compliant device 12 from the first stable resting state to the second stable resting state. When the posterior portions 40B and 42B of the respective arms 40 and 42 are secured to one another as discussed herein, the flanges 50A and 50B together establish a larger flange 50. In other examples, only one of the arms 40 or 42 may have the flange.

[0144]The posterior portions 40B, 42B are shown connected with one another in FIGS. 1-4 such that the bistable compliant device 12 extends around a rear 18A of the foot-receiving cavity 18. One example of complementary connecting features by which the posterior portions 40B and 42B are connected to one another are discussed with respect to FIGS. 5 and 6. FIG. 5 is a perspective view of the bistable compliant device 12 of FIG. 3 with the first and second arms 40 and 42 shown prior to connection at their posterior portions 40B and 42B. FIG. 6 is another perspective view of the first and second arms 40 and 42, FIG. 7 is a front view of the first and second arms 40 and 42, and FIG. 8 is a cross-sectional view of the first arm 40 taken at lines 8-8 in FIG. 7.

[0145]More particularly, the first posterior portion 40B has a first distal end 51 and the second posterior portion 42B has a second distal end 52. The first and second distal ends 51 and 52 are coupled to one another in a connected state shown in FIGS. 1-4. However, the first and second arms 40 and 42 are each internally biased to a disconnected state, shown in FIG. 5, in which the first and second distal ends 51 and 52 are not connected to one another and are further apart from one another than in the connected state. FIG. 5 represents the positions the first and second arms 40 and 42 would be in at the lateral and medial sides 28, 30 of the article of footwear 10 if the ends 41, 43 were anchored as described and the ends 51 and 52 were not connected.

[0146]Stated differently, the ends 51 and 52 are pulled toward one another from the positions to which they are internally biased when the ends 51 and 52 of the posterior portions 40B and 42B are connected to one another, which causes the bistable compliant device 12 to store energy that biases them toward the disconnected state. Connecting the posterior portions 40B and 42B at the respective distal ends 51 and 52 resiliently deforms the arms 40 and 42, storing force that urges the posterior portions 40B and 42B in an outward direction, although they are prevented from moving apart by the connected posterior portions 40B and 42B. This stored force, in combination with the geometry of the arms 40 and 42 discussed herein, creates the bistable nature of the bistable compliant device 12 (e.g., the first and second stable resting states which the bistable compliant device 12 will automatically adopt and stay in absent application of the force F1 or F2 as discussed herein).

[0147]The arms 40 and 42 are of a material that enables sufficient resilient deformation to connect the posterior portions 40B and 42B even when the ends 41, 43 of the anterior portions 40A, 42A are anchored, as well as to flex at the intermediate portions 40C and 42C. Example materials for the bistable compliant device 12 and particularly the arms 40 and 42 thereof include but are not limited to acetal homopolymer (Polyoxymethylene POM), available as Delrin® from DELRIN USA LLC, Wilmington, Delaware, carbon fiber, and spring steel. Other examples materials may include foam, as discussed herein.

[0148]Accordingly, to ease foot entry into or out of the foot-receiving cavity 18 through the ankle opening 20, the user may apply the external force F1 (shown in phantom in FIG. 1) of at least the predetermined threshold magnitude to cause the bistable compliant device 12 to move downward to the second stable resting state of FIG. 2. The bistable compliant device 12 will remain in the second stable resting state until a threshold external force F2 (which may be of the same magnitude as the threshold external force F1, but in a different direction, such as an opposite direction) is again applied to the posterior portions 40B, 42B of the bistable compliant device 12. This will cause the bistable compliant device 12 to move upward, back to the first stable resting state of FIG. 1. The applied external force F1 is generally in a first direction (e.g., having at least a downward component) to move the bistable compliant device 12 from the first stable resting state to the second stable resting state (e.g., such as closer to the sole structure 14 at the rear of the article of footwear 10), and the applied external force F2 is in a different direction, such as an opposite second direction (e.g., having at least an upward component) to move from the second stable resting state to the first stable resting state (e.g., such as further from the sole structure 14 at the rear of the article of footwear 10).

[0149]As such, a wearer could leave the article of footwear 10 in the second stable resting state of FIG. 2 for an extended period of time, until ready to don the article of footwear 10. The wearer's foot 17 can enter or be withdrawn from the foot-receiving cavity 18 through the ankle opening 20 as shown in FIG. 2 without any force being applied by the wearer or otherwise to the bistable compliant device 12. Stated differently, no application of force is required by the wearer to keep the bistable compliant device 12 in the second stable resting state while donning or doffing the article of footwear 10. When such a force F2 is applied (which should be after the wearer has fully inserted their foot), the bistable compliant device 12 is configured to move back to the first stable resting state upon application of the applied external force with the footwear upper 16 moving with the bistable compliant device 12 at the rear of the heel region and raising the rear of the ankle opening 20.

[0150]When in one of the stable resting states, the bistable compliant device 12 resists movement toward the other stable resting state under the applied external force until the intermediate portions 40C and 42C have flexed an intermediate amount, at which point the inner and outer edges of the intermediate portions 40C, 42C of the arms 40, 42 invert relative to one another, and the arms 40, 42 automatically travel the remainder of the path to the other stable resting state. In doing so, the bistable compliant device 12 may provide a tactile and/or an audible signal when moving from the first stable resting state to the second stable resting state and when moving from the second stable resting state to the first stable resting state. For example, the material of the arms 40, 42 may make a snapping noise. Alternatively or in addition, the wearer may feel the movement of the arms 40, 42 and the cessation thereof when the bistable compliant device 12 reaches a stable resting state. The user is thus easily alerted as to when the desired position of the bistable compliant device 12 and the corresponding stable resting state (e.g., the first position or the second position) has been achieved after applying the external force.

[0151]FIGS. 5 and 6 best show the complementary connecting features 60, 62 by which the first and second distal ends 51 and 52 are connected to one another. Specifically, the first arm 40 has a peg 60 at the first distal end 51 and the second arm 42 has a slot 62 at the second distal end 52. The slot 62 extends inward into the second arm 42, and opens at the distal end 52. The peg 60 extends outward from the distal end 51 of the first arm 40. The peg 60 and the slot 62 are sized so that the peg 60 can be inserted into the slot 62 and engage the second arm 42 with the first arm 40 by an interference fit with the second arm 42 at the slot 62. Alternatively, the slot 62 may extend at the distal end 51 of the first arm 40 and the peg 60 may extend from the distal end 52 of the second arm 42. It should be appreciated that any set of complementary connecting features described herein as having a first one of the features on a first arm and a second one of the features on a second arm could alternatively have the first feature on the second arm and the second feature on the first arm. Furthermore, any of the complementary connecting features described with respect to one bistable compliant device herein could instead be implemented on any of the other bistable compliant device described herein.

[0152]As shown, the distal ends 51 and 52 need to be rotated inward and toward one another in order for the peg 60 to be inserted into the slot 62. With the anterior portions 40A and 42A fixed at the anchor ends 41 and 43, this necessitates twisting the arms 40 and 42 inward along their lengths toward one another. As such, when the distal ends 51 and 52 are connected, the intermediate portions 40C, 42C of the first arm 40 and the second arm 42 may each tilt inward and downward toward the foot-receiving cavity 18 from an outer extent of the intermediate portion to an inner extent of the intermediate portion when the bistable compliant device 12 is in the first stable resting state.

[0153]More specifically, as shown in FIG. 8, the intermediate portion 40C of the first arm 40 tilts inward and downward from the outer extent 70C to the inner extent 70D which is toward the foot-receiving cavity 18 when installed in the article of footwear 10 of FIG. 1 and when the bistable compliant device 12 is in the first stable resting state. The inner wall 74D of the intermediate portion 40C tilts inward toward the foot-receiving cavity from a bottom edge 74E of the inner wall 74D to a top edge 74F of the inner wall 74D when the bistable compliant device 12 is in the first stable resting state. The outer wall 74C of the intermediate portion 40C tilts inward toward the foot-receiving cavity from a bottom edge 74G of the outer wall 74C to a top edge 74H of the outer wall 74C when the bistable compliant device 12 is in the first stable resting state.

[0154]The same geometry applies to the second arm 42. The intermediate portion 42C of the second arm 42 tilts inward and downward from the outer extent 72C to the inner extent 72D. The inner wall 74J of the intermediate portion 42C tilts inward toward the foot-receiving cavity 18 from a bottom edge 74L of the inner wall 74J to a top edge 74M of the inner wall 74J when the bistable compliant device 12 is in the first stable resting state. The outer wall 74K of the intermediate portion 42C tilts inward toward the foot-receiving cavity 18 from a bottom edge 74N of the outer wall 74K to a top edge 74P of the outer wall 74K when the bistable compliant device 12 is in the first stable resting state. Alternatively, the intermediate portions 40C, 42C could still tilt inward and downward in the second stable resting state, but to a lesser extent than when in the first stable resting state. The intermediate portions 40C, 42C of each of the first arm 40 and the second arm 42 have a quadrilateral transverse cross-section at the respective intermediate portions 40C and 42C. In the example shown, the quadrilateral transverse cross-sections are rectangular with a hollow center. In other examples, the arms 40, 42 are not hollow.

[0155]When the bistable compliant device 12 moves from one stable resting state to the other stable resting state, the inner edge and the outer edge of each arm 40 and 42 at the intermediate portion 40C and 42C change relative positions, with the inner edges above the outer edges at a given cross-section perpendicular to the length of the arms 40, 42 in one stable resting state, and the outer edges above the inner edges at the same given cross-section in the other stable resting state. Accordingly, in the second stable resting state, the tilt of the arms 40 and 42 at the intermediate portions 40C and 42C will change from that of the first stable resting state shown in FIG. 8. As shown in FIG. 9, the inner wall 74D of the intermediate portion 40C will move upward relative to the outer wall 74C and the inner wall 74J of the intermediate portion 4C will move upward relative to the outer wall 74K as the posterior portions 40B and 42B move downward closer to the sole structure 14. In order to go through this transition, the arms 40 and 42 will require the applied force (F1 or F2, depending upon whether moving from the first stable resting state to the second stable resting state or vice versa) to overcome resistance to movement as a portion of each arm 40, 42 closer to the respective inner wall 74D, 74J goes through compression and a portion of each arm 40, 42 closer to the respective outer wall 74C, 74K goes through tension (as it moves through a larger arc than the portion closer to the inner wall) up to a transition position somewhere between the first stable resting state and the second stable resting state after which the stored energy completes the movement of the inner and outer walls relative to one another and the movement of the arms 40, 42 as a whole to the other stable resting state. In other words, the applied force (F1 or F2) can be removed once the intermediate portions 40C, 42C of the arms 40, 42 reach the transition position, and the arms 40, 42 will complete the movement to the other stable resting state automatically via the stored energy.

[0156]Another aspect of the geometry of the arms 40 and 42 that will enable such flexing (e.g., change of tilt at the intermediate portions 40C and 42C) is the intermediate portions 40C and 42C of each of the arms 40 and 42 having a width W and a thickness T with the width W greater than the thickness T. Stated differently, a ratio of a width W to a thickness T of the intermediate portion 40C and 42C of each of the arms 40 and 42 is greater than one in such an example. The width W is generally in the transverse direction of the article of footwear 10 (from the inner wall 74D to the outer wall 74C of the intermediate portion 40C, for example) and the thickness T is generally in a vertical direction (from the bottom edge 74E to the top edge 74F of the inner wall 74D of the intermediate portion 40C, for example). Stated differently, each of the first arm 40 and the second arm 42 may have a width W and a thickness T at a cross-section extending in a medial-lateral direction of the article of footwear 10 perpendicular to the longitudinal midline LM of the article of footwear 10, and the width W is greater than the thickness T. In such examples, the cross-sections of the intermediate portions 40C, 42C would not be a circle or a square, for example.

[0157]FIG. 10 is a lateral side view of another article of footwear 110 that includes the sole structure 14 and a footwear upper 116 like footwear upper 16 of FIG. 1 except that the footwear upper 116 includes foxing 148 having a lower profile than the foxing 48 in FIG. 1. The article of footwear 110 includes a bistable compliant device 112 shown in a first stable resting state The bistable compliant device 112 is configured with first and second arms like first and second arms 40 and 42 (only first arm 140 shown), connected to one another at their posterior portions and to the collar 46, and functions as described with respect to the bistable compliant device 12, having two stable resting states (e.g., also having a second stable resting state in which the posterior portions of the bistable compliant device 112 are closer to the sole structure 14, as described with respect to the bistable compliant device 12). The bistable compliant device 112 has anterior portions with anchored ends. Only anterior portion 140A of the first arm 140 at the lateral side 28 is shown, and is slightly more elongated than the anterior portion 40A.

[0158]FIG. 11 is a lateral side view of another article of footwear 210 that includes a footwear upper 216 having a base layer 216A configured as a slip-in upper with an elastic band 217 over the instep, and including foxing 248 with a similar lower profile as the foxing 148. The article of footwear 210 includes a bistable compliant device 212 shown in a first stable resting state. The bistable compliant device 212 is configured with first and second arms like first and second arms 40 and 42 (only first arm 240 shown), connected to one another at their posterior portions and to the collar 46, and functions as described with respect to the bistable compliant device 12, having two stable resting states (e.g., also having a second stable resting state in which the posterior portions of the bistable compliant device 212 are closer to the sole structure 14, as described with respect to the bistable compliant device 12). The arms have anterior portions with anchored ends. Only anterior portion 240A of the first arm 240 at the lateral side 28 is shown, is slightly more elongated than the anterior portion 40A, and has an anchored end 241 disposed inward of an upper edge 14A of the sole structure 14. The anterior portion 240A is outward of the foxing 248. Stated differently, the anterior portion 240A is between the foxing 248 and the sole structure 14.

[0159]FIG. 12 is a lateral side view of another article of footwear 310 that includes the bistable compliant device 12 of FIG. 1 shown in the first stable resting state. The article of footwear 310 includes the sole structure 14, and a footwear upper 316 that is configured as a slip-in upper with an elastic band 217 over the instep, and including the foxing 248. The footwear upper 316 includes an outer base layer 316A and an inner base layer 316B (shown partially at the rear of the footwear upper 316). The bistable compliant device 12 is disposed between the outer base layer 316A and the inner base layer 316B except at the connected posterior portions (posterior portion 40B shown). The collar 46 is connected to the posterior portions. The anterior portions are disposed inward of not only the outer base layer 316A, but also inward of the foxing 248, as indicated at the anterior portion 40A.

[0160]FIG. 13 is a lateral side view of another article of footwear 410 that includes the footwear upper 216 as described with respect to FIG. 11 and the sole structure 14. The article of footwear 410 includes a bistable compliant device 412 shown in a first stable resting state. The bistable compliant device 412 functions as described with respect to the bistable compliant device 12 (e.g., also having a second stable resting state in which the posterior portions of the bistable compliant device 412 are closer to the sole structure 14, as described with respect to the bistable compliant device 12).

[0161]The bistable compliant device 412 includes a base 413B that is integral with and extends from a first anchor end to a second anchor end and connects the first anchor end to the second anchor end. The first anchor end 441 of the first arm 440 is indicated in FIG. 12 and the second anchor end is disposed in a like manner extending from the second arm at the medial side 30. The base 413B is secured to an upper extent of the sole structure 14 and/or to the base layer 216A of the footwear upper 216. One anchor end 441 is shown at an anterior portion 440A of the first arm 440 at the lateral side 28, and a like second arm is disposed at the medial side, similar to the first and second arms of the bistable compliant device 12. The base 413B includes a front base segment 413B1 that extends through the midfoot and forefoot regions 24, 26 and around the front of the article of footwear 410 to connect the anchor ends, and a rear base segment 413B2, that extends through the heel region 22 and around the rear of the article of footwear 410 to connect the anchor ends. The bistable compliant device 412 defines a gap 445 between the first and second posterior portions 440B, 442B and the base 413B (e.g., the rear base segment 413B2). The second posterior portion 442B is indicated with hidden lines as it is connected to the first posterior portion 440B at the medial side 30. The rear of the footwear upper 216 extends across the gap 445.

[0162]FIG. 14 is a lateral side view of another article of footwear 510 that includes a bistable compliant device 512 shown in a first stable resting state. The article of footwear 510 includes the footwear upper 216 and elastic band 217 as described with respect to FIG. 11 and the foxing 148 as described with respect to FIG. 10. The bistable compliant device 512 functions as described with respect to the bistable compliant device 12 (e.g., also having a second stable resting state in which the posterior portions of the bistable compliant device 512 are closer to the sole structure 14, as described with respect to the bistable compliant device 12).

[0163]The bistable compliant device 512 includes a base 513B that is integral with and extends from the first anchor end to the second ancho r end and connects the first anchor end to the second anchor end. The first anchor end 541 of the first arm 540 is indicated in FIG. 14 and the second anchor end is disposed in a like manner extending from the second arm at the medial side 30. The base 513B as well as the anterior portions are secured to the outer wall 14B of the sole structure 14. The anterior portion 540A of the first arm 540 is shown at the lateral side 28, and a like second arm is disposed at the medial side, similar to the first and second arms of the bistable compliant device 12. The base 513B extends through the heel region 22 and around the rear of the article of footwear 510 to connect the anterior portions. The base 513B also extends forward from the anchor ends through the midfoot region 24 and has a forward end disposed in the forefoot region 26 at each of the lateral side 28 and the medial side 30 (only forward end 512C at the lateral side 28 is shown). In other words, the base 513B does not extend around the front of the sole structure 14. The bistable compliant device 512 defines a gap 545 between the first and second posterior portions 540B, 542B and the base 513B. The second posterior portion 542B is indicated with hidden lines as it is connected to the first posterior portion 540B at the medial side 30.

[0164]FIG. 15 is a lateral side view of another article of footwear 610 that includes a bistable compliant device 612 shown in a first stable resting state. The article of footwear 610 includes the footwear upper 216 and elastic band 217 as described with respect to FIG. 11. The bistable compliant device 612 functions as described with respect to the bistable compliant device 12 (e.g., also having a second stable resting state in which the posterior portions of the bistable compliant device 612 are closer to the sole structure 14, as described with respect to the bistable compliant device 12). The bistable compliant device 612 includes first and second arms. An anterior portion 640A of a first arm 640 is shown at the lateral side 28, and a like second arm is disposed at the medial side 30. A first anchor end 641 of the first arm 640 may be considered to be where the first arm 640 secures to the sole structure 14 where it extends just below the upper edge 14A of the midsole, or may be considered the entire length of a base 613B that is secured to the outer wall 14B of the sole structure 14 and extends along the sole structure 14 to a forward end 612C in the forefoot region 26. A second arm and base are disposed in a like manner at the medial side 30. The second posterior portion 642B is indicated with hidden lines as it is connected to the first posterior portion 640B at the medial side 30.

[0165]FIG. 16 is a lateral side view and FIG. 17 is a rear perspective view of another article of footwear 710 that includes the bistable compliant device 12 described with respect to FIGS. 1-4 shown in the first stable resting state. The article of footwear includes the footwear upper 16 and the sole structure 14, with a relatively low profile foxing 148 of FIG. 10. The connected posterior portions 40B, 42B of the arms 40 and 42 are stitched to the collar 46 as described with respect to FIG. 4 and the anterior portions 40A, 42A of the arms 40, 42 are between the foxing 148 and the base layer 16A of the footwear upper 16. A shroud 16D is secured to the base layer 16A of the footwear upper 16 and covers the anterior portions 40A, 42A and the intermediate portions 40C, 42C of the first and second arms 40, 42, with the posterior portions 40B, 42B extending out from between the shroud 16D and the base layer 16A above the shroud 16D. The shroud 16D thus helps to conceal and protect the flexing intermediate portions 40C, 42C of the arms 40, 42 and thus may help to focus the user on manipulating the posterior portions 40B, 42B (e.g., applying force at the posterior portions). A rear strip 16E of flexible material may extend along a rear of the shroud 16D to the collar 46. The rear strip 16E may cover a seam in the shroud 16D, for example. Both the shroud 16D and the rear strip 16E are flexible material so as not to inhibit movement of the footwear upper 16 with the bistable compliant device 12 between the first and second stable resting states. For example, the shroud 16D and the rear strip 16E may be the same material as the base layer 16A.

[0166]FIG. 18 is a perspective view of a sole structure 814 and a base 813 of a bistable compliant device 812 for an article of footwear 810 shown in FIG. 21. The article of footwear 810 is shown configured for a right foot. A footwear upper 816 having an ankle opening 820 is shown in phantom in order to better view the entire bistable compliant device 812 in FIGS. 21 and 23 and is secured to the sole structure 814 and to the posterior portions 840B, 842B of first and second arms 840, 842 of the bistable compliant device 812. FIG. 19 is another perspective view of the base 813 of FIG. 18. FIG. 20 is a plan view of first and second arms 840, 842, respectively, securable to the base 813 of FIGS. 18 and 19 as part of the bistable compliant device 812 as shown in FIGS. 21 and 22, for example. The base 813 secures to the sole structure 814, as shown in FIGS. 21 and 22. The sole structure 814 has a bottom 814D integral with the side wall 814B that together form a top-opening cavity 814E that is a portion of the foot-receiving cavity 818 when the footwear upper 816 is secured to the sole structure 814.

[0167]The base 813 is generally U-shaped, having a lateral portion 813A, a medial portion 813B, and a rear portion 813C that connects the lateral portion 813A and the medial portion 813B. As best shown in FIG. 19, the base 813 defines an inverted channel 815 that extends under the lateral portion 813A, the medial portion 813B, and the rear portion 813C and opens at a front lateral edge 813AA and at a front medial edge 813BB. The upper extent of the sole structure 14 may also be referred to as a rim 814A. The base 813 fits to the sole structure 814 with the rim 814A in the inverted channel 815. Stated differently, the base 813 slips over the rim 814A and is seated on the rim 814A of the sole structure 814. A lower edge 813D of the base 813 may fit into a slot 814C at an outer side (e.g., exterior side) of the side wall 814B of the sole structure 814 to help position the base 813 on the rim 814A. Adhesive may be used to further secure the base 813 to the sole structure 814. Any of the bases described herein, such a base 813, may alternatively be referred to as a chassis. For examples in which the arms secure to the sole structure, such as arms 40, 42, the sole structure functions as a base and may be referred to as a chassis.

[0168]FIG. 20 shows the top sides of the first arm 840 and the second arm 842. The first arm 840 has an anterior portion 840A, a posterior portion 840B, and an intermediate portion 840C. The second arm 842 has an anterior portion 842A, a posterior portion 842B, and an intermediate portion 842C. The anterior portions 840A and 842A have respective anchor ends 841 and 843. The posterior portions 840B and 842B have respective distal ends 851 and 852. The first and second arms 840, 842 and their respective anterior, posterior, and intermediate portions function as described with respect to the first and second arms 40 and 42 and their respective anterior, posterior, and intermediate portions. The longitudinal axes of each of the posterior portions 840B, 842B are shown extending inward toward one another, each at an angle of about 25 degrees relative to a longitudinal axis extending along a length of the anterior portion 840A, 842A of the respective arm 840, 842 when the posterior portions 840B, 842B are disconnected as shown in FIG. 20, but the angle may be a different angle, such as an angle from about 10 degrees to about 80 degrees.

[0169]The first and second anchor ends 841, 843 are secured to the base 813. More specifically, the base 813 has a first slot 817A at the lateral side 28 of the base 813 and a second slot 817B at the medial side 30 of the base 813. The base 813 has a first projection 819A with a first ramped surface 821A inclining in a rearward direction of the article of footwear 810 at the lateral side 28 of the base 813 and a second projection 819B with a second ramped surface 821B inclining in the rearward direction of the article of footwear 810 at the medial side 30 of the base 813. The rearward direction of the article of footwear 810 is a direction from the forefoot region 26 toward the heel region 22 of the sole structure 14 as shown in FIG. 21. The slots 817A and 817B are in rear faces of the projections 819A, 819B respectively. The first anchor end 841 of the first arm 840 secures to the first projection 819A at the first slot 817A. The second anchor end 843 of the second arm 842 secures to the second projection 819B at the second slot 817B. In other words, the first anchor end 841 fits into the first slot 817A, the second anchor end 843 first into the second slot 817B, and the anchor ends 841 and 843 may have an interference fit with the base 813 at the slots 817A, 817B or may be secured to the base 813 at the slots 817A, 817B with adhesive, for example. The first arm 840 and the second arm 842 extend rearwardly from the first ramped surface 821A and from the second ramped surface 821B, respectively.

[0170]The posterior portions 840B and 842B have complementary connecting features 860 and 862, respectively, which are holes (e.g., through holes) that align with one another when the posterior portions 840B and 842B are pulled toward one another after the anchor ends 841 and 843 are secured to the base 813, creating stored energy in the arms 840, 842. The first and second distal ends 851 and 852 are connected to one another with a connector or other fastening device such as a rivet 863 (shown in FIGS. 21 and 23) that extends through the aligned holes 860, 862.

[0171]As shown in FIGS. 21 and 23, the bistable compliant device 812 defines a gap 845 between the first and second posterior portions 840B, 842B and the base 813 in both the first stable resting state shown in FIG. 21 and the second stable resting state shown in FIG. 23, with the gap 845 of a smaller size when the bistable compliant device 812 is in the second stable resting state with the posterior portions 840B, 842B closer to the sole structure 814. The footwear upper 816 is secured to the posterior portions 840B, 842B at a collar, as described with respect to the article of footwear 10, and to the sole structure 814, such as to the inner sides of the side wall 814B in the cavity 814E. The footwear upper 816 will move with the bistable compliant device 812 at the rear of the ankle opening 820 to ease foot entry and exit similarly as described with respect to the bistable compliant device 12.

[0172]FIG. 22 is a cross-sectional view of the first and second arms 840, 842 of the bistable compliant device 812 of FIG. 21 taken at lines 22-22 in FIG. 21. The connected posterior portions 840B, 842B rotate together about a pivot axis PA extending through a connection (the rivet 863) between the posterior portion 840B of the first arm 840 and the posterior portion 842B of the second arm 842 when the bistable compliant device 812 moves from the first stable resting state of FIG. 21 to the second stable resting state of FIG. 23 and when the bistable compliant device 812 moves from the second stable resting state of FIG. 23 to the first stable resting state of FIG. 21. As shown in FIG. 21, due to the position of the connected posterior portions 840B, 842B in the first stable resting state, the applied force F1 is initially a horizontal rearward force, and changes to a downward force as the arms 840, 842 flex toward the second stable resting state. The pivot axis PA extends in a plane perpendicular to the longitudinal axis of the article of footwear 810 (e.g., a vertical plane that includes the longitudinal axis). The connection of the arms 840, 842 with a rivet 863 through aligned holes 860, 862 allows the posterior portions 840B, 842B to rotate as needed separately from one another about the pivot axis PA as the bistable compliant device 812 moves between the first and second stable resting states.

[0173]Similar to the orientation of the arms 40, 42 described herein, the intermediate portions 840C, 842C of the first and second arms 840, 842 tilt inward and downward from their outer extent to their inner extent as shown in FIG. 22 when the bistable compliant device 812 is in the first stable resting state of FIG. 21, and tilt inward and upward from their outer extent to their inner extent as shown in FIG. 24 when the bistable compliant device 812 is in the second stable resting state of FIG. 23. Alternatively, the intermediate portions 840C, 842C could still tilt inward and downward, but to a lesser extent than when in the first stable resting state. The intermediate portions 840C and 842C of each of the first arm 840 and the second arm 842 have a quadrilateral transverse cross-section at the respective intermediate portion 840C and 842C. As described with respect to the bistable compliant device 12, the cross-section at the intermediate portions 840C, 842C could be shapes other than a quadrilateral as long as the ratio of width to thickness is greater than one. In such examples, the cross-sections of the intermediate portions 840C, 842C would not be a circle or a square, for example.

[0174]To move from one stable resting state to the other stable resting state, the inner edge and the outer edge of each arm 840 and 842 at the intermediate portion 840C and 842C must change relative positions, with the inner edges above the outer edges at a given cross-section perpendicular to the length of the arms in one stable resting state, and the outer edges above the inner edges at the same given cross-section in the other stable resting state. Accordingly, in the second stable resting state, the tilt of the arms 840 and 842 at the intermediate portions 840C and 842C will change, as shown in FIG. 24, as the inner wall 874D will move upward relative to the outer wall 874C and the inner wall 874J will move upward relative to the outer wall 874K as the posterior portions 840B and 842B move downward closer to the sole structure 814. In order to go through this transition, the arms 840 and 842 will require the applied force (F1 or F2, depending upon whether moving from the first stable resting state to the second stable resting state or vice versa) to overcome resistance to movement as a portion of each arm 840, 842 closer to the respective inner wall 874D, 874J goes through compression and a portion of each arm 840, 842 closer to the respective outer wall 874C, 874K goes through tension (as it moves through a larger arc than the portion closer to the inner wall) up to a transition position somewhere between the first stable resting state and the second stable resting state after which the stored energy completes the movement of the inner and outer walls relative to one another and the movement of the arms 840, 842 as a whole to the other stable resting state. In other words, the applied force (F1 or F2) can be removed once the intermediate portions 840C, 842C of the arms 840, 842 reach the transition position, and the arms 840, 842 will complete the movement to the other stable resting state automatically via the stored energy.

[0175]The geometry of the arms 840 and 842 that will enable such flexing (e.g., change of tilt at the intermediate portions 840C and 842C) include the intermediate portions 840C and 842C of each of the arms 840 and 842 having a width W and a thickness T with the width W greater than the thickness T. Stated differently, a ratio of a width W to a thickness T of the intermediate portion 840C and 842C of each of the arms 840 and 842 is greater than one in such an example. The width W is generally in the transverse direction of the article of footwear 810 (from the inner wall 874D to the outer wall 874C of the intermediate portion 840C, for example) and the thickness T is generally in a vertical direction (from the bottom edge to the top edge of the inner wall 874D of the intermediate portion 840C, for example). Stated differently, each of the first arm 840 and the second arm 842 may have a width W and a thickness T at a cross-section extending in a medial-lateral direction of the article of footwear 810 perpendicular to a longitudinal axis of the article of footwear 810 and the width W is greater than the thickness T.

[0176]FIG. 25 is a perspective view of another bistable compliant device 912 for an article of footwear, shown with the bistable compliant device 912 in a first stable resting state. The bistable compliant device 912 has first and second arms 940, 942 configured as described with respect to first and second arms 840 and 842, respectively, except that the first and second arms 940, 942 have anterior portions 940A, 942A with respective anchor ends 941, 943 that are integrally formed with a base 913. The arms 940, 942 include respective posterior portions 940B, 942B that are connected with the rivet 963 through aligned holes as described with respect to the bistable compliant device 812 of FIG. 20. The arms 940, 942 include respective intermediate portions 940C, 942C configured like the arms 840, 842 and which flex under the applied forces F1 and F2 to move between the first stable resting state of FIG. 25 and the second stable resting state of FIG. 26. As shown in FIG. 25, due to the position of the connected posterior portions 940B, 942B in the first stable resting state, the applied force F1 is initially a horizontal rearward force, and changes to a downward force as the arms 940, 942 flex toward the second stable resting state. The base 913 is relatively flat and does not form an inverted channel like base 813. Instead of being U-shaped, the base 913 extends transversely between and connects the anchor ends 941, 943 of the respective first and second arms 940, 942. The base 913 also extends fore and aft of the anchor ends 941, 943. The base 913 is thus configured to extend underfoot rather than connecting to a rim of the sole structure and extending around the rear of the foot as does the base 813 and any of the other bases described herein that have a U-shape and an inverted channel like the base 813. Accordingly, to provide cushioning between the foot and the base 913, the base 913 may be adhered to a foot-facing surface of a midsole layer and another midsole layer may overlie the base 913 between the arms 940, 942 to establish a foot-support surface and sandwich the base 913 between the foam midsole layers.

[0177]FIG. 27 is a perspective view of another bistable compliant device 1012 for an article of footwear. The bistable compliant device 1012 includes a first arm 1040, a second arm 1042, and a base 1013. The first and second arms 1040, 1042 are secured to the base 1013 as they are integral with the base 1013 (e.g., such that the bistable compliant device 12 is a one-piece, monolithic structure).

[0178]The base 1013 is configured like the base 813, and is generally U-shaped, having a lateral portion 1013A, a medial portion 1013B, and a rear portion 1013C that connects the lateral portion 1013A and the medial portion 1013B. The base 1013 defines an inverted channel 1015 that extends under the lateral portion 1013A, the medial portion 1013B, and the rear portion 1013C and opens at a front lateral edge 1013AA and at a front medial edge 1013BB. The base 1013 fits to a rim of a sole structure, like the rim 814A of the sole structure 814 discussed herein.

[0179]The first and second arms 1040, 1042 include respective anterior portions 1040A, 1042A with respective anchor ends 1041 and 1043 that are integral with the base 1013. The arms 1040, 1042 include respective posterior portions 1040B, 1042B shown prior to connection to one another. The arms 1040, 1042 include respective intermediate portions 1040C, 1042C at which the bistable compliant device 1012 flexes under a first applied external force of at least the threshold magnitude to move from a first stable resting state to a second stable resting state, and flexes at the intermediate portions 1040C and 1042C under a second applied external force of at least the threshold magnitude to move from the second stable resting state to the first stable resting state as described with respect to the arms 40, 42. Specifically, the arms 1040, 1042 may have inner and outer walls configured like those of the arms 40, 42 or the arms 840, 842, and connecting the posterior portions 1040B and 1042B at the respective distal ends 1051 and 1052 resiliently deforms the arms 1040 and 1042, storing force that urges the posterior portions 1040B and 1042B in an outward direction. The stored force, in combination with the geometry of the arms 1040 and 1042 creates the bistable nature of the bistable compliant device 1012 (e.g., the first and second stable resting states which the bistable compliant device 1012 will adopt and remain in upon application of the force F1 or F2 as discussed herein).

[0180]As is evident in the plan view of the bistable compliant device 1012 in FIG. 28, the first and second arms 1040, 1042 extend parallel with one another from the first and second anchor ends 1041, 1043 to the first and second distal ends 1051, 1052 in the disconnected state. The arms 1040, 1042 are formed to adopt the disconnected state shown (e.g., they are internally biased to extend parallel with one another). The further apart the posterior portions 1040B, 1042B of the arms 1040, 1042 are in the disconnected state will increase the outward bias of the arms 1040, 1042 when connected. Configuring the arms 1040, 1042 (or at least the posterior portions 1040B, 1042B thereof) to be parallel with one another in the disconnected state will result in a greater outward bias than if the bistable compliant device 1012 was molded or otherwise formed so that the arms 1040, 1042 (or at least the posterior portions thereof) extend inward toward one another in the disconnected state.

[0181]The bistable compliant device 1012 includes complementary connecting features 1060 and 1062 by which the first distal end 1051 and the second distal end 1052 are coupled to one another. Specifically, the complementary connecting features include a slot 1060 extending through the first arm 1040 and a peg 1062 extending from the second arm 1042 and configured to extend through the slot 1060 and engage with the first arm 1040. The peg 1062 has an interference fit with the respective first arm 1040 at the slot 1060.

[0182]FIG. 29 is a perspective view of another bistable compliant device 1012A for an article of footwear. The bistable compliant device 1012A is the same as and functions as described with respect to the bistable compliant device 1012, including base 1013, except that the first and second arms 1040, 1042 are replaced with first and second arms 1040D, 1042D that angle inward toward one another when disconnected rather than extending parallel with one another. By configuring the bistable compliant device 1012A so that the arms angle inward toward one another in the disconnected state, to which state they are internally biased, less tension is created in the arms when the posterior portions 1040B, 1042B are connected and there is therefore less force urging the posterior portions 1040B, 1042B in an outward direction in comparison to arms that extend parallel with one another in the disconnected state.

[0183]The arms 1040D, 1042D have anterior portions 1040A, 1042A, posterior portions 1040B, 1042B, and intermediate portions 1040C, 1042C, and the arms 1040D, 1042D are integral with the base 1013 (e.g., such that the bistable compliant device 1012A is a one-piece, monolithic structure). The first and second arms 1040D, 1042D and the respective portions are configured identically to first and second arms 1040, 1042 except that the posterior portions 1040B, 1042B angle inward toward one another rather than extending parallel with one another when in a disconnected state. More specifically, the longitudinal axes of the posterior portions 1040B, 1042B extend inward toward one another, each at an angle A1 of 15 degrees relative to a longitudinal axis extending along a length of the respective anterior portion 1040A, 1042A of the respective arm as shown in FIG. 30 when disconnected. The arms 1040D and 1042D are shown prior to connection of the posterior portions 1040B, 1042B at the complementary connecting features 1060, 1062. In other examples, the angle A1 could be an angle from about 10 degrees to about 80 degrees. In a specific example, the angle A1 may be 36 degrees.

[0184]FIG. 31 is a side view of another bistable compliant device 1012B for an article of footwear. The bistable compliant device 1012B is the same as described with respect to bistable compliant device 1012A except that the first and second arms 1040D, 1042D are replaced with first and second arms 1040E, 1042E. The longitudinal axes of each of the posterior portions 1040B, 1042B extend inward toward one another, each at an angle A2 shown as about 22 degrees, but may be 30 degrees relative to a longitudinal axis extending along a length of the anterior portion 1040A, 1042A of the respective arm 1040E, 1042E when the posterior portions 1040B, 1042B are disconnected as shown in FIG. 32. In other examples, the angle A2 could be an angle from about 10 degrees to about 80 degrees. In a specific example, the angle A2 may be 36 degrees. By configuring the bistable compliant device 1012B so that the arms 1040E, 1042E angle inward toward one another in the disconnected state, to which state they are internally biased, by a greater angle than the bistable compliant device 1012A, the tension created in the arms 1040E, 1042E when the posterior portions 1040B, 1042B are connected is less and there is less force urging the posterior portions 1040B, 1042B in an outward direction in comparison to arms with posterior portions that extend parallel with one another in the disconnected state (like arms 1040, 1042) and in comparison to arms with posterior portions that are angled inward toward one another at a smaller angle (like arms 1040D, 1042D) when in the disconnected state.

[0185]FIG. 33 is a perspective view of another bistable compliant device 1112 for an article of footwear The bistable compliant device 1112 includes the base 1013 as previously described with first and second arms 1140, 1142 secured to and integral with the base 1013 at their respective anterior portions 1140A, 1142A (e.g., such that the bistable compliant device 1112 is a one-piece, monolithic structure). The first and second arms 1140, 1142 are shown prior to connection with one another at their posterior portions 1140B, 1142B in FIG. 33. Like the bistable compliant device 1012A, the posterior portions 1140B, 1142B each angle inward toward one another at an angle A1 described with respect to FIG. 30.

[0186]The arms 1140, 1142 are connectable with one another by complementary connecting features and, once connected, function as described with respect to the bistable compliant device 12 to have two stable resting states in which the bistable compliant device 1112 will remain absent application of an applied external force of at least a predetermined magnitude at which the intermediate portions 1140C, 1142C of the arms 1140, 1142 flex to help raise and lower an ankle opening of a footwear upper. The complementary connecting features include a slot 1160 extending through the first arm 1140 near the first distal end 1151 of the first arm 1140, and a peg 1162 extending from the second arm 1142 near the second distal end 1152 of the second arm 1142. The peg 1162 is configured to extend through the slot 1160 and engage with the first arm 1140. In the example shown, the first arm 1140 has two slots 1160 and the second arm 1142 has two pegs 1162. The slots 1160 are spaced apart from one another and from the first distal end 1151 of the first arm 1140 such that the pegs 1162 are configured to engaged with the slots 1160. The slot 1160 has a first portion 1160A and a smaller second portion 1160B extending from the first portion 1160A. The second portion 1160B is disposed closer to the distal end 1151 of the first arm 1140 than the first portion 1160A. Each slot 1160 has a perimeter with three sides at the second portion 1160B. Each peg 1162 has a stem 1162A (perhaps best shown in FIG. 35) with a square outer perimeter that fits in the second portion 1160B and a head 1162B that is wider than the stem 1162A. Additionally, the upper side of the first arm 1140 forms a ledge 1163 and the lower side of the second arm 1142 forms a ledge 1165. The arms 1140, 1142 may be abutted at the ledges 1163, 1165 to help properly align the pegs 1162 with the first portions 1160A and, once the pegs 1162 are inserted through the first portions 1160A, the arms 1140, 1142 can be slid relative to one another so that the pegs 1162 move into and are secured in the second portions 1160B by an interference fit. The outward biasing force of the arms 1140, 1142 (the bias urging them outward toward the disconnected state of FIG. 33) will also tend to pull the pegs 1162 away from the first portions 1160A to remain in the second portions 1160B.

[0187]FIG. 36 is a perspective view showing a top side of another bistable compliant device 1112F for an article of footwear. The bistable compliant device 1112F includes the base 1013 and arms 1140 and 1142 as described with respect to the bistable compliant device 1112. The only difference is that the bottom side of the arm 1142 includes a slight square-shaped recess 1161 at the slot 1160, as shown in FIG. 37. The larger head 1162B of the peg 1162 is the same size as or slightly smaller than the first portion 1160A and can enter the slot 1160 at the first portion 1160A from the top side of the first arm 1140 and nests in the recess 1161 when the stem 1162A is received in the second portion 1160B of the slot 1160 and engaged with the first arm 1140.

[0188]FIG. 38 is a bottom view of another bistable compliant device 1212 for an article of footwear. The bistable compliant device 1212 includes first and second arms 1240, 1242, respectively, secured to the same base 1013 previously described (e.g., such that the bistable compliant device 1212 is a one-piece, monolithic structure). The arms 1240, 1242 have respective anterior portions 1240A, 1242A secured to and integral with the base 1013, respective intermediate portions 1240C, 1242C, and respective posterior portions 1240B, 1242B shown prior to connection with one another at their distal ends 1251, 1252. The first and second arms 1240, 1242 include respective anterior portions 1240A, 1242A with respective anchor ends 1241 and 1243 that are integral with the base 1013. The bistable compliant device 1212 flexes at the intermediate portions 1240C, 1242C under a first applied external force of at least the threshold magnitude to move from a first stable resting state to a second stable resting state, and flexes at the intermediate portions 1240C and 1242C under a second applied external force of at least the threshold magnitude to move from the second stable resting state to the first stable resting state as described with respect to the forces F1, F2 and the arms 40, 42. Specifically, the arms 1240, 1242 may have inner and outer walls configured like those of the arms 40, 42 or the arms 840, 842, and connecting the posterior portions 1240B and 1242B by complementary connecting features at the respective distal ends 1251 and 1252 resiliently deforms the arms 1240 and 1242, storing force that urges the posterior portions 1140B and 1142B in an outward direction. The stored force, in combination with the geometry of the arms 1240 and 1242 creates the bistable nature of the bistable compliant device 1212 (e.g., the first and second stable resting states which the bistable compliant device 1212 will adopt and remain in upon application of the force F1 or F2 as discussed herein).

[0189]Like the bistable compliant device 1012A, the longitudinal axes of the posterior portions 1240B, 1242B extend inward toward one another but each at an angle A3 shown as about 55 degrees but that may be 45 degrees relative to a longitudinal axis extending along a length of the anterior portion 1240A, 1242A of the respective arm 1240, 1242 when the posterior portions 1240B, 1242B are disconnected as shown in FIG. 39. In other examples, the angle A3 could be an angle from about 10 degrees to about 80 degrees. In a specific example, the angle A3 may be 36 degrees. The arms 1240 and 1242 are shown prior to connection of the posterior portions 1240B, 1242B at the complementary connecting features 1260, 1262.

[0190]The complementary connecting features include a slot 1260 extending through the first arm 1240 and a peg 1262 extending from the second arm 1242 and configured to extend through the slot 1260 and engage with the first arm 1240. In the example shown, the first arm 1240 has two slots 1260 and the second arm 1242 has two pegs 1262. The two pegs 1262 are spaced apart from one another and from the distal end 1252 of the second arm 1242 such that the pegs 1262 are configured to engage with the first arm 1240 at the slots 1260.

[0191]Like the slots 1160, each slot 1260 has a first portion 1260A and a smaller second portion 1260B extending from the first portion 1260A as best shown in FIG. 41. The second portion 1260B is disposed closer to the distal end 1251 of the first arm 1240 than the first portion 1260A. Each slot 1260 has a perimeter with three sides of equal length at the second portion 1260B such that the second portion 1260B forms a square shape opening into the first portion 1260A. Each peg 1262 has a stem 1262A with a square outer perimeter that fits in the second portion 1260B and a rectangular head 1262B that is wider than the stem 1262A. The arms 1240, 1242 do not have ledges configured to abut like ledges 1163 and 1165 of the bistable compliant device 1112. Once the pegs 1262 are inserted through the first portions 1260A, the arms 1240, 1242 can be slid relative to one another so that the pegs 1262 move into and are secured in the second portions 1260B by an interference fit. The outward biasing force of the arms 1240, 1242 (the bias urging them outward toward the disconnected state) will also tend to pull the pegs 1262 away from the first portions 1260A to remain in the second portions 1260B. Like the bistable compliant device 1112, the bottom side of the arm 1240 includes a slight square-shaped recess 1261 at the slot 1260, as shown in FIG. 42. The larger head 1262B is the same size as or slightly smaller than the first portion 1260A and can enter the slot 1260 at the first portion 1260A from the top side of the first arm 1240 and nests in the recess 1261 when the stem 1262A is received in the second portion 1260B of the slot 1260 and engaged with the first arm 1240.

[0192]FIG. 43 is a perspective view of another bistable compliant device 1312 for an article of footwear and is also shown in FIGS. 44-46. The bistable compliant device 1312 includes first and second arms 1340, 1342 with respective anterior portions 1340A, 1342A with respective anchor ends 1341 and 1343 that are integral with the base 1013 previously described, with the posterior portions 1340B, 1342B of the first and second arms 1340, 1342 shown prior to connection to one another at complementary connecting features 1360, 1362.

[0193]The arms 1340, 1342 include respective intermediate portions 1340C, 1342C at which the bistable compliant device 1312 flexes under a first applied external force F1 of at least the threshold magnitude to move from a first stable resting state to a second stable resting state, and flexes at the intermediate portions 1340C and 1342C under a second applied external force F2 of at least the threshold magnitude to move from the second stable resting state to the first stable resting state as described with respect to the arms 40, 42. Specifically, the arms 1340, 1342 may have inner and outer walls configured like those of the arms 40, 42 or the arms 840, 842, and connecting the posterior portions 1340B and 1342B by complementary connecting features at the respective distal ends 1351 and 1352 resiliently deforms the arms 1340 and 1342, storing force that urges the posterior portions 1340B and 1342B in an outward direction. The stored force, in combination with the geometry of the arms 1340 and 1342 creates the bistable nature of the bistable compliant device 1312 (e.g., the first and second stable resting states which the bistable compliant device 1312 will adopt and remain in upon application of the force F1 or F2 as discussed herein).

[0194]The longitudinal axes of the posterior portions 1340B, 1342B extend inward toward one another in the disconnected state, each at an angle A4 shown as 36 degrees relative to a longitudinal axis extending along a length of the anterior portion 1340A, 1342A of the respective arm as shown in FIG. 43. In other examples, the angle A4 could be an angle from about 10 degrees to about 80 degrees.

[0195]The complementary connecting features include a slot 1360 extending through the first arm 1340 and a peg 1362 extending from the second arm 1342 and configured to extend through the slot 1360 engage with the first arm 1340 at the slot 1360. The slot 1360 has a first portion 1360A and a smaller second portion 1360B extending from the first portion 1360A as best shown in FIG. 46. The second portion 1360B is disposed closer to the first distal end 1351 of the first arm 1340 than the first portion 1360A. The slot 1360 has an arced perimeter 1360C at the second portion 1360B. The peg 1362 has a stem 1362A with a cylindrical outer perimeter. The cylindrical outer perimeter of the stem 1362A fits in the second portion 1360B. The peg 1362 has a head 1362B that includes a larger portion 1362B1 with a shape that is a portion of a circle and is configured to fit through the second portion 1360B of the slot 1360, and a smaller portion 1362B2 that has a shape that is a portion of a top of the stem 1362A. Once the pegs 1362 are inserted through the first portions 1360A, the arms 1340, 1342 can be slid relative to one another so that the pegs 1362 move into and are secured in the second portions 1360B by an interference fit with the first arm 1340. The outward biasing force of the arms 1340, 1342 (the bias urging them outward toward the disconnected state) will also tend to pull the pegs 1362 away from the first portions 1360A to remain in the second portions 1360B. The bottom side of the first arm 1340 includes a slight circular recess 1361 at the slot 1360, as shown in FIG. 46. The larger head 1362B is the same size as or slightly smaller than the first portion 1360A and can enter the slot 1360 at the first portion 1360A from the top side of the first arm 1340 and nests in the recess 1361 when the stem 1362A is received in the second portion 1360B of the slot 1360 and engages with the second arm 1342 with the cylindrical outer perimeter of the stem 1362A fit in the second portion 1360B against the arced perimeter 1360C.

[0196]FIGS. 47-49 show another bistable compliant device 1412 for an article of footwear. The bistable compliant device 1412 includes first and second arms 1440, 1442, respectively, secured to the same base 1013 previously described (e.g., such that the bistable compliant device 12 is a one-piece, monolithic structure). The arms 1440, 1442 have respective anterior portions 1440A, 1442A secured to and integral with the base 1013, respective intermediate portions 1440C, 1442C, and respective posterior portions 1440B, 1442B shown prior to connection with one another at their distal ends 1451, 1452. The bistable compliant device 1412 flexes at the intermediate portions 1440C and 1442C under a first applied external force of at least the threshold magnitude to move from a first stable resting state to a second stable resting state, and flexes at the intermediate portions 1440C and 1442C under a second applied external force of at least the threshold magnitude to move from the second stable resting state to the first stable resting state as described with respect to the arms 40, 42. Specifically, the arms 1440, 1442 may have inner and outer walls configured like those of the arms 40, 42 or the arms 840, 842, and connecting the posterior portions 1440B and 1442B by complementary connecting features 1460, 1462 at the respective distal ends 1451 and 1452 resiliently deforms the arms 1440 and 1442, storing force that urges the posterior portions 1440B and 1442B in an outward direction. The stored force, in combination with the geometry of the arms 1440 and 1442 creates the bistable nature of the bistable compliant device 1412 (e.g., the first and second stable resting states which the bistable compliant device 1412 will adopt and remain in upon application of the force F1 or F2 as discussed herein).

[0197]Like the bistable compliant device 1012, the posterior portions 1440B, 1442B each extend parallel with one another when in a disconnected state as shown, prior to connection of the posterior portions 1440B, 1442B at the complementary connecting features 1460, 1462.

[0198]The complementary connecting features include a slot 1460 extending through the first arm 1440 and a peg 1462 extending from the second arm 1442 and configured to extend through the slot 1460 and engage with the first arm 1440. In the example shown, the first arm 1440 has two slots 1460 and the second arm 1442 has two pairs of pegs 1462 spaced apart from one another and from the first distal end 1452 of the second arm 1442 such that the pegs 1462 are configured to engage with the first arm 1440 at the slots 1460, a pair of pegs 1462 extending through each of the slots 1460.

[0199]As best shown in FIG. 50, each peg 1462 is a configured as a hooked prong. Stated differently, each pair of pegs 1462 includes a first hooked prong 1462A with a stem 1462C and a hook 1462D extending from the stem 1462C toward the distal end 1452 and a second hooked prong 1462B spaced from the first hooked prong 1462A and with a stem 1462C and a hook 1462D like the hook of the first hooked prong 1462A but extending from the stem 1462C in the opposite direction (away from the distal end 1452).

[0200]Each slot 1460 has a simple rectangular shape. The first arm 1440 has a thickness T1 at the slots 1460 that is not less than and in some examples equal to a height T2 of each of the stems 1462C. Each pair of pegs 1462 are spaced apart by a distance such that the ramped leading ends of the hooks 1462D interface with the first arm at the opposite edges of the slot 1460 through which the hooks 1462D pass, and are partly compressed toward one another as the hooks 1462D pass through the slot 1460, and then spring back outward away from one another after passing through the slot 1460 so that the hooks 1462D rest on the opposite surface of the first arm 1440 at opposite ends of the slot 1460. Stated differently, the first hooked prong 1462A and the second hooked prong 1462B engage the first arm 1440 through which the slot 1460 extends at opposite ends of the slot 1460. The outward biasing force of the arms 1440, 1442 (the bias urging them outward toward the disconnected state) will also tend to pull the hooks 1462D against the surface of the first arm 1440 helping to ensure that the first and second arms 1440, 1442 remain connected by the complementary connecting features 1460, 1462.

[0201]FIG. 52 is a fragmentary perspective view of an alternative arm 1540 for use with the alternative second arm 1542 shown in FIG. 53 in any of the bistable compliant devices disclosed herein. Respective posterior portions 1540B, 1542B are shown having respective complementary connecting features 1560, 1562. Specifically, the complementary connecting feature 1560 is a hole in the posterior portion 1540B, and the complementary connecting feature 1562 is a peg extending from the posterior portion 1542B. Alternatively, the peg 1562 could extend from the posterior portion 1540B and the hole 1560 could be in the posterior portion 1542B. The peg 1562 has a slightly tapered stem 1562A which tapers in width toward a head 1562B. The head 1562B is wider than the stem 1562A where the stem 1562A meets the head 1562B. Moreover, the side surface of the head 1562B is rounded, and is wider at a middle of the head 1562B than at the distal end of the head 1562B. This creates an easier entry of the head 1562B into the hole 1560, gradually requiring more pressure to insert the head 1562B into the hole 1560 past the wide part of the head 1562B, which is wider than the hole 1560. The material of the peg 1562 and/or the arm 1540 at the hole 1560 may be somewhat compliant to enable the peg 1562 to be inserted into the hole 1560 such that the hole 1560 is around the stem 1562A and the head 1562B extends out of the hole 1560 past the arm 1540 when the arms 1540, 1542 are fully connected. Depending upon the tightness of the fit of the stem 1562A to the posterior portion 1540B at the hole 1560, the connecting features 1560, 1562 may allow the posterior portions 1540B, 1542B to rotate relative to one another about an axis extending along the length of the peg 1562 and through a center of the hole 1560, similar to the rotation of the posterior portions 840B, 842B of the arms 840, 842 about the axis PA as described with respect to the bistable compliant device 812.

[0202]FIG. 54 is a fragmentary perspective view of an alternative arm 1640 for use with an alternative second arm 1642 shown in FIG. 55 in any of the bistable compliant devices disclosed herein. Respective posterior portions 1640B, 1642B are shown having respective pairs of complementary connecting features 1560, 1562. Specifically, the posterior portion 1640B has two of the complementary connecting features 1560 (holes) described with respect to FIG. 52, and the posterior portion 1642B has two of the complementary connecting features 1562 described with respect to FIG. 53 (pegs). The holes 1560 are spaced apart from one another at the same spacing as the pegs 1562 so that the pegs 1562 may be received in the respective holes 1560 to secure the posterior portions 1640B, 1642B to one another. Alternatively, the pegs 1562 could extend from the posterior portion 1640B and the holes 1560 could be in the posterior portion 1642B.

[0203]FIGS. 56 and 57 are perspective views of another bistable compliant device 1712 for an article of footwear. The bistable compliant device includes a first arm 1740 and a second arm 1742, with respective anterior portions 1740A, 1742A with respective anchor ends 1741 and 1743 that are integral with the base 1013 previously described (e.g., such that the bistable compliant device 1712 is a one-piece, monolithic structure). The arms 1740, 1742 have respective posterior portions 1740B, 1742B shown prior to connection to one another at respective complementary connecting features 1760, 1762.

[0204]The arms 1740, 1742 include respective intermediate portions 1740C, 1742C at which the bistable compliant device 1712 flexes under a first applied external force of at least the threshold magnitude to move from a first stable resting state (shown in FIG. 61 with the arms connected to one another at the connecting features 1760, 1762) to a second stable resting state in which the posterior portions 1740B, 1742B are closer to the sole structure 814. The arms 1740, 1742 flex at the intermediate portions 1740C and 1742C under a second applied external force of at least the threshold magnitude to move from the second stable resting state to the first stable resting state as described with respect to the arms 40, 42. Specifically, the arms 1740, 1742 may have inner and outer walls configured like those of the arms 40, 42 or the arms 840, 842, and connecting the posterior portions 1740B and 1742B by complementary connecting features at the respective distal ends 1751 and 1752 resiliently deforms the arms 1740 and 1742, storing force that urges the posterior portions 1740B and 1742B in an outward direction. The stored force, in combination with the geometry of the arms 1740 and 1742 creates the bistable nature of the bistable compliant device 1712 (e.g., the first and second stable resting states which the bistable compliant device 1712 will automatically adopt and stay in upon application of the force F1 or F2 as discussed herein).

[0205]The longitudinal axes of the posterior portions 1740B, 1742B extend inward toward one another but each at an angle A4 (described with respect to FIG. 43) relative to a longitudinal axis extending along a length of the anterior portion 1740A, 1742A of the respective arm 1740, 1742 when the posterior portions 1740B, 1742B are disconnected as shown in FIG. 57.

[0206]The complementary connecting features include a slot 1760 extending through the first arm 1740 and a peg 1762 extending from the second arm 1742 and configured to extend through the slot 1760 and engage with the first arm 1740 at the slot 1760. As best shown in FIG. 58, the slot 1760 has a first portion 1760A, a smaller second portion 1760B extending from the first portion 1360A, the second portion 1760B having an enlarged end 1760C. The second portion 1760B is disposed closer to the distal end 1751 of the first arm 1740 than the first portion 1760A. The slot 1760 is elongated in the second portion 1760B and has an arced perimeter 1760D at the enlarged end 1760C of the second portion 1760B.

[0207]The peg 1762 has a stem 1762A with a cylindrical outer perimeter and a head 1762B with a circular perimeter at the end of the stem 1762A as best shown in FIG. 57. The stem 1762A is shown only with hidden lines in FIG. 56 but is configured the same as the stem 1362A shown in FIG. 45, for example. The head 1762B fits through the first portion 1760A of the slot and is larger than the second portion 1760B including the enlarged end 1760C. The stem 1762A may have a width approximately the same as the width of the elongated section of the second portion 1760B to enable the peg 1762 to be moved to the enlarged end 1760C of the second portion 1760B after the head 1762B is inserted through the slot 1760 at the first portion 1760A. Once the head 1762B is inserted through the first portion 1760A, the arms 1740, 1742 can be slid relative to one another so that the head 1762B moves into the enlarged end 1760C. The cylindrical outer perimeter of the stem 1762A may be less than the diameter of the enlarged end 1760C so that the posterior portion 1740B and the posterior portion 1742B may rotate relative to one another about an axis through the peg 1762 and the center of the enlarged end 1760C when the bistable compliant device 1712 moves from the first stable resting state to the second stable resting state, similar to as described with respect to the pivot axis PA of FIG. 21. The outward biasing force of the arms 1740, 1742 (the bias urging them outward toward the disconnected state) will also tend to pull the peg 1762 away from the first portion 1760A to remain in the enlarged end 1760C of the second portion 1760B.

[0208]FIG. 59 is a closeup fragmentary view of an alternative arm 1840 that could be used with the second arm 1742. The alternative arm 1840 is the same as and functions identically to the arm 1740 except a connecting feature 1860 is included in a posterior end 1840B instead of connecting feature 1760. The connecting feature 1860 is a slot having a relatively large first portion 1860A and a second portion 1860B extending from the first portion 1860A toward a distal end 1851 except that the second portion 1860B has an end 1860C with a circular perimeter 1860D of a width that is the same as the width of the remainder of the second portion 1860B such that the second portion 1860B does not have an enlarged end. Accordingly, when the head 1762B is inserted through the first portion 1860A and the stem 1762A is moved to the end 1860C of the second portion 1860B, the stem 1762A will be held in the second portion 1860B by an interference fit with the alternative arm 1840 at the end 1860C.

[0209]FIG. 60 is a plan view of the sole structure 814 described with respect to FIG. 18 with the base 1013 of the bistable compliant device 1712 secured to the side wall 814B at the rim 814A with the posterior portions 1740B, 1742B of the first and second arms 1740, 1742 shown prior to connection to one another. FIG. 61 is a fragmentary lateral side view of the heel region 22 of the sole structure 814 of FIG. 60 and showing the bistable compliant device 1712 with the arms 1740, 1742 connected at the complementary connecting features 1760, 1762 and in a first stable resting state.

[0210]FIG. 62 is a perspective view of an alternative base 1813 of a bistable compliant device 1812 shown in FIGS. 65-66. The base 1813 has many of the same features as the base 813 described herein, and these are indicated with like reference numbers.

[0211]The base 1813 has a first projection 1819A with a first ramped surface 1821A inclining in a rearward direction at the lateral side 28 of the base 1813 and a second projection 1819B with a second ramped surface 1821B inclining in the rearward direction at the medial side 30 of the base 1813. The ramped surfaces 1821A, 1821B are slightly recessed such that the projections 1819A, 1819B have raised lips 1822A, 1822B, respectively except at the rear of the raised surfaces 1821A, 1821B.

[0212]The projections 1819A, 1819B have locating features 1817 that may be small projections or holes, such as threaded holes. The first and second arms 840, 842 described with respect to FIG. 20 may be secured to the projections 1819A, 1819B at the ramped surfaces 1821A, 1821B, respectively, by sliding the anchor ends 841, 843 over the respective ramped surfaces 1821A, 1821B until the anchor ends 841, 843 meet the respective front lips 1822A, 1822B. The anterior portions 840A, 842A may have spaced openings (through holes) that correspond with the locating features 1817. Fasteners 1827 shown in FIG. 65 may then extend through the spaced openings and into the locating features 1817 to secure the arms 840, 842 to the base 1813 at the projections 1819A, 1819B. The first arm 840 and the second arm 842 then extend rearwardly from the first ramped surface 1821A and from the second ramped surface 1821B, respectively, as shown in FIG. 65, in which the bistable compliant device 1812 is in a first stable resting state, and in FIG. 66, in which the bistable compliant device 1812 is in a second stable resting state.

[0213]FIG. 67 shows a first cover 1680A for the projection 1819A of the base 1813 of FIGS. 62-66. Specifically, the first cover 1680A is engageable with the first projection 1819A to cover the first anchor end 841 and the first ramped surface 1821A as shown in FIG. 68. An identical second cover 1680B is engageable with the second projection 1819B to cover the second anchor end 843 and the second ramped surface 1821B as shown in FIG. 68.

[0214]The first cover 1680A is configured as an inverted channel 1681 and has downwardly-projecting legs 1682A, 1682B each having an inner surface 1683 with a groove 1684. The second cover 1680B shown in FIG. 68 has the same features as the first cover 1680A. The projections 1819A, 1819B have rails 1685 projecting outward from both sides of each of the projections 1819A, 1819B as shown in FIG. 62. One of the rails 1685 is shown in FIG. 63. The rails 1685 are configured to interfit with the grooves 1684 of the covers 1680A, 1680B. Specifically, the first cover 1680A may be slid onto the projection 1819A after aligning the rails 1685 of the projection 1819A with the grooves 1684 of the first cover 1680A. The second cover 1680B may be similarly slid onto the projection 1819B. Adhesive may also be added over the arms 840, 842 where they are secured to the ramped surfaces 1821A, 1821B to further secure the covers 1680A, 1680B to the projections 1819A, 1819B. Accordingly, the covers 1680A, 1680B are held to the base 1813 by the interfitting of the rails 1685 and the grooves 1684. In an alternative example, the covers 1680A, 1680B could have the projecting rails instead of grooves, and the sides of the projections 1819A, 1819B could have the grooves that interfit with the rails of the covers.

[0215]FIG. 69 is a medial side view of an article of footwear 1910 including a sole structure 1914 and a footwear upper 1916. The medial side 30 is shown as the article of footwear 1910 is configured for a left foot. FIG. 70 is a fragmentary perspective view of the article of footwear of FIG. 69. The footwear upper 1916 includes a collar 1946 extending at least partially around the ankle opening 20 at the foot-receiving cavity 18.

[0216]A base 1913 is configured like bases 813 and 1813 and has like reference numbers. The bistable compliant device 1812 FIGS. 65-66 and 68 is secured to the base 1913, and includes the first and second arms 840, 842 and rivet 863 as described. The bistable compliant device 1812 is shown in the first stable resting state in FIG. 69. The anchor ends 841, 843 of the bistable compliant device 1812 are secured to the base 1913 with the first and second distal ends 851, 852 of the posterior portions 840B, 842B of the first and second arms 840, 842 connected to one another via the rivet 863 and a collar mount 1870, as best shown in FIG. 70. The collar mount 1870 is secured to the collar 1946. The bistable compliant device 1812 also has a second stable resting state in which the posterior portions 840B, 842B are closer to the sole structure 1914, as described with respect to the bistable compliant devices 12 and 812. The bistable compliant device 1812 flexes at intermediate portions 840C and 842C of the arms 840 and 842 between the first and second stable resting states.

[0217]The collar mount 1870 extends around a rear 20A of the ankle opening 20 from the medial side 30 to the lateral side 28 and is secured to the collar 1946 such as with adhesive at an inner side 1875 of mounting flanges 1871, best shown in FIGS. 71 and 72. Alternatively or in addition, the mounting flanges 1871 may be stitched or otherwise secured to the collar 1946 at apertures 1871A.

[0218]The collar mount 1870 has a hemispherical portion 1872 protruding rearward at an exterior of the collar mount 1870, as shown in FIG. 71. More particularly, and outer surface 1873 of the hemispherical portion 1872 is a hemispherical surface. At least one of the first distal end 851 and the second distal end 852 of the arms 840, 842 interface with the hemispherical portion 1872. In FIG. 70, the rivet 863 couples the first and second posterior portions 840B, 842B to one another in the connected state by extending through the aligned holes 860, 862 (shown in FIG. 20) at the distal ends 851, 852 and into the hemispherical portion 1872. As the arms 840, 842 pivot about the axis PA through the rivet 863 (also shown in FIG. 23), one or both may interface with the hemispherical portion 1872. By configuring the portion as hemispherical, the surface area of the interface of the collar mount 1870 with the arms 840, 842 is minimized thus reducing any resistance to movement between the two stable resting states that may be attributed to the collar mount 1870.

[0219]As best shown in FIGS. 72 and 73, the hemispherical portion 1872 defines a hollow space 1874 at an inner side 1875 of the collar mount 1870 (e.g., at an inner surface 1876 thereof). The rivet 863 or other fastener extends into the hollow space 1874 and terminates outward of the collar 1946. The rivet 863 is shown in phantom in FIG. 73. The outer surface of the collar 1946 is also represented in phantom. In this manner, the rivet 863 does not extend to the wearer's foot.

[0220]Additionally, the collar mount 1870 has a ledge 1878 with a surface 1880 the declines forwardly and downwardly toward the foot-receiving cavity 18, providing a foot entry ramp. The surface 1880 is nonlinear in that it has a slope that becomes progressively steeper toward the inner surface of the collar mount 1870, as best shown in FIG. 73. The ledge 1878 may be depressed by a foot to provide the force needed to move the bistable compliant device from the first stable resting state to the second stable resting state, for example, while also serving as a ramp for the foot to slide into the foot-receiving cavity 18.

[0221]FIG. 74 is a medial side view of the sole structure 1914 and the bistable compliant device 1812 of FIG. 69 with a different collar mount 1970 and showing the bistable compliant device 1812 in the second stable resting state. FIG. 75 is a perspective view of the collar mount 1970. Like the collar mount 1870, the collar mount 1970 is configured to extend around a rear of an ankle opening from the medial side to the lateral side of an upper and to be secured to a collar of the upper such as with adhesive at an inner side 1975 of mounting flanges 1971.

[0222]The collar mount 1970 has a hemispherical portion 1972 protruding rearward at an exterior of the collar mount 1970, as indicated in FIG. 75. More particularly, and outer surface 1973 of the hemispherical portion 1972 is a hemispherical surface and at least one of the first distal end 851 and the second distal end 852 of the arms 840, 842 interface with the hemispherical portion 1972 as the rivet 863 couples the arms 840, 842 to one another and extends into the hemispherical portion 1972 and the arms 840, 842 pivot about the axis PA. As best shown in FIG. 75, the hemispherical portion 1972 defines a hollow space 1974 at an inner side 1975 of the collar mount 1970 (e.g., at an inner surface 1976 thereof). The rivet 863 or other fastener extends into the hollow space 1974 and terminates outward of a collar of an upper to which the collar mount 1970 is secured. Like collar mount 1870, the collar mount 1970 has a ledge 1978 with a surface 1980 the declines forwardly and downwardly toward a foot-receiving cavity when the collar mount 1970 is secured to a footwear upper, providing a foot entry ramp. The surface 1980 is nonlinear in that it has a slope that becomes progressively steeper toward the inner surface of the collar mount 1970.

[0223]FIG. 76 is a lateral side view of an article of footwear 2010 including a footwear upper 2016 secured to the sole structure 814 and the bistable compliant device 812 of FIG. 65 in a first stable resting state. The footwear upper 2016 has a tab 2090 extending at a rear 2016A of the footwear upper 2016. The tab 2090 is shown forming a loop, such as by sewing the tab 2090 into a loop. The tab 2090 is shown extending from a collar 2046 at the rear 2016A of the footwear upper 2016. The posterior portions of the first and second arms (only second arm 842 with posterior portion 842B shown) are secured to the tab 2090. More specifically, the tab 2090 extends around the posterior portions where they are connected by the rivet 863 (discussed with respect to FIG. 65) so that the tab 2090 will cause the rear 2016A of the footwear upper 2016 (and most specifically, the collar 2046) to move with the bistable compliant device 812 between the first and second stable resting states. For example, FIG. 77 shows the bistable compliant device 812 in the second stable resting state with the collar 2046 moved with the bistable compliant device 812 via the tab 2090, and the rear 2016A of the footwear upper 2016 having been deformed in order to move downward. By providing a relatively flexible footwear upper 2016 at the rear 2016A without a rigid heel counter, for example, the footwear upper 2016 moves with the bistable compliant device 812 and does not interfere with the ability of the bistable compliant device 812 to adopt the first and second stable resting states.

[0224]FIG. 78 is a perspective view of an article of footwear 2110 configured as a clog for a right foot. The article of footwear 2110 has a footwear upper 2116, a sole structure 2114, and a bistable compliant device 2112 having first and second arms 2140, 2142, respectively, all as a one-piece, unitary and monolithic component. Stated differently, the footwear upper 2116, the sole structure 2114, and the bistable compliant device 2112 (including the first arm 2140, and the second arm 2142) are a one-piece, unitary and monolithic component. In an example, the footwear upper 2116, the sole structure 2114, the first arm 2140, and the second arm 2142 may be molded together and may be of a foam material. For example, the footwear upper 2116, the sole structure 2114, the first arm 2140, and the second arm 2142 may be molded together in a mold, such as by injection molding. The dimensions and angles of the arms 2140 and 2142 as well as a tilt from an inner edge to an outer edge in the stable resting states, may be as described with respect to the bistable compliant device 12, for example.

[0225]In FIG. 78, posterior portions 2140B, 2142B of the respective arms prior 2140, 2142 are shown prior to connection to one another with complementary connecting features. Any of the complementary connecting features shown and discussed herein may be used. As shown, three spaced pegs 1562 on the second arm 2142 secure to the first arm 2140 at three spaced holes 1560, with the pegs 1562 and holes 1560 functioning as described with respect to FIGS. 52-55.

[0226]The footwear upper 2116 and sole structure 2114 together define an ankle opening 2120 and a foot-receiving cavity 2118 over the sole structure 2114. A first anchor end 2141 of the first arm 2140 is integral with and secured at the lateral side 28 of the sole structure 2114 (i.e., is integral and unitary with the sole structure 2114 as part of the one-piece, monolithic component as discussed). The first posterior portion 2140B is remote from the sole structure 2114 and further rearward than the first anchor end 2141. A second anchor end 2143 of the second arm 2142 is integral with and secured at the medial side 30 of the sole structure 2114 (i.e., is integral and unitary with the sole structure 2114 as part of the one-piece, monolithic component as discussed). The second posterior portion 2142B is remote from the sole structure 2114 and further rearward than the second anchor end 2143.

[0227]The first posterior portion and the second posterior portion are connected with one another by the complementary connecting features 1560, 1562 (shown in phantom in connected states) such that the bistable compliant device 2112 extends around a rear of the foot-receiving cavity 2118 and has a first stable resting state 2112A with the first and second posterior portions 2140B, 2142B in a first position and a second stable resting state 2112B with the first and second posterior portions 2140B, 2142B in a second position closer to the sole structure 2114 than in the first position. The posterior portions 2140B and 2142B are not directly connected to the rear of an upper as, in a clog configuration, the upper 2216 does not extend very far upward around the rear of the heel. Instead, the bistable compliant device 2112 itself wraps around the rear of a wearer's foot, serving as a strap to contain a wearer's heel when in the first position 2112A (the first stable resting state) and moving out of the way to ease foot entry and exit in the second position (the second stable resting state 2112B).

[0228]FIG. 79 is a perspective view of an article of footwear 2210 configured as a clog having the footwear upper 2116 as described and a sole structure 2114A, and having a bistable compliant device 2212 having a single arm 2240. The footwear upper 2116, the sole structure 2114A, and the bistable compliant device 2212 (e.g., the single arm 2240) are all a one-piece, unitary and monolithic component. For example, the footwear upper 2116, the sole structure 2114, and the single arm 2240, may be molded together as one piece from a foam material. The single arm 2240 is integrally formed with and is unitary with the sole structure 2114A as an anchor end 2243. An anchor end 2241 of the arm 2240 is shown prior to connection to the sole structure 2114A at a complementary connecting feature, which in the embodiment shown is a slot 2117. Specifically, the sole structure 2114A is like sole structure 2114 except that it includes a projection 2119 with a ramped surface 2121 inclining in a rearward direction of the article of footwear 2210. The slot 2117 is in a rear face of the projection 2119. The anchor end 2241 of the single arm 2240 secures to the projection 2119 at the slot 2117. In other words, the anchor end 2241 fits into the slot 2117, and may have an interference fit with the projection 2119 at the slot 2117 or may be secured to the projection 2119 at the slot 2117 with adhesive, for example. The single arm 2240 extends rearwardly from the ramped surface 2121. The anchor end 2243 that is integral with the sole structure 2114A may be integral at a projection 2119A like projection 2119 except not having a slot as the end 2243 is integral therewith. The first and second stable resting states 2212A and 2212B are shown in phantom in FIG. 79.

[0229]As shown in FIG. 79, the single arm 2240 has a first posterior portion 2240B and a second posterior portion 2242B that are integral and that define an obtuse angle 2213 when the first anchor end 2241 is disconnected from the sole structure 2114A. The posterior portions 2240B, 2242B are furthest rearward when the anchor end 2241 is in the slot 2117, with anterior portions 2240A and 2242A nearest the ends 2241 and 2243, and intermediate portions 2240C and 2242C between the anterior portion 2240A and the posterior portion 2240B and between the anterior portion 2242A and the posterior portion 2240B, respectively. When the first anchor end 2241 is connected to the sole structure 2114A at the slot 2117 as discussed, the angle between the posterior portions 2240B and 2242B becomes smaller, as indicated by angle 2213A in the first and second stable resting states 2212A, 2212B, shown in phantom. The dimensions and angles of the portions of the single arm 2240 as well as a tilt from an inner edge to an outer edge in the stable resting states, may be as described with respect to the bistable compliant device 12, for example. The posterior portions 2240B and 2242B are not directly connected to the rear of an upper as, in a clog configuration, the upper 2216 does not extend very far upward around the rear of the heel. Instead, the bistable compliant device 2212 itself wraps around the rear of a wearer's foot, serving as a strap to contain a wearer's heel when in the first position 2212A (the first stable resting state) and moving out of the way to ease foot entry and exit in the second position (the second stable resting state 2212B).

[0230]FIG. 80 is a perspective view of an article of footwear 2210A configured like the article of footwear 2210 of FIG. 79 except a bistable compliant device 2212AA is used that is an arm 2240AA that is not unitary, one-piece, and monolithic with the footwear upper 2116 and the sole structure 2114A. Stated differently, the footwear upper 2116 and the sole structure 2114A are configured as a one-piece, unitary and monolithic component and may be molded together as one piece from a foam material, for example. The article of footwear 2210A also includes the bistable compliant device 2212AA, a one-piece arm 2240AA that is separate from the upper 2116 and the sole structure 2114A until connected to the sole structure 2114A at first and second anchor ends 2241 and 2243 of the arm 2240AA. The sole structure 2114A includes the projection 2119 with the slot 2117 on the lateral side 28 as described with respect to FIG. 79, and also includes a like projection 2119 and slot 2117 on the medial side 30. The slots 2117 and the anchor ends 2241 and 2243 are thus complementary connecting features by which the arm 2240AA is secured to the sole structure 2114A, as shown in FIG. 81. Stated differently, both of the first anchor end 2241 and the second anchor end 2243 have connecting features at which the first anchor end 2241 and the second anchor end 2243 are secured to the sole structure 2114A at the slots 2117. The complementary connecting features of the anchor ends 2241 and 2243 are the shapes of the anchor ends 2241 and 2243 and the slots 2117, with which they have an interference fit and/or may be secured to the projections 2119 in the slots 2117 with adhesive.

[0231]The arm 2240AA is otherwise configured like arm 2240, including with the obtuse angle 2213 when disconnected from the sole structure 2114A. The dimensions and angles of the portions of the single arm 2240AA as well as a tilt from an inner edge to an outer edge in the stable resting states, may be as described with respect to the bistable compliant device 12, for example. In FIG. 81, the bistable compliant device 2212AA is shown in a first stable resting state, with a second stable resting state shown in phantom as 2212BB. The bistable compliant device 2212AA is not directly connected to the rear of an upper as, in a clog configuration, the upper 2216 does not extend very far upward around the rear of the heel. Instead, the bistable compliant device 2212AA itself wraps around the rear of a wearer's foot, serving as a strap to contain a wearer's heel when in the first position (the first stable resting state) and moving out of the way to ease foot entry and exit in the second position (the second stable resting state 2212BB).

[0232]FIG. 82 is a perspective view of an article of footwear 2310 configured as a clog having a footwear upper 2316, a sole structure 2314, and a bistable compliant device 2312 having first and second arms 2340 and 2342 all as a one-piece, unitary and monolithic component. Posterior portions 2340B and 2342B of the respective arms 2340 and 2342 are shown prior to connection to one another. Stated differently, similar to the article of footwear 2110, the footwear upper 2316, the sole structure 2314, the first arm 2340, and the second arm 2342 are a one-piece, unitary, and monolithic component. For example, the footwear upper 2316, the sole structure 2314, the first arm 2340, and the second arm 2342 may be molded together as one piece from a foam material. The first and second arms 2340 and 2342 are thus integral and unitary with the one-piece footwear upper 2316 and sole structure 2314 at respective first and second anchor ends 2341, 2343 near respective anterior portions 2340A and 2342A of the arms 2340, 2342.

[0233]FIG. 83 shows a connecting sleeve 2390 configured to fit over the posterior portions 2340B and 2342B of the first and second arms 2340 and 2342 to connect the first and second arms 2340 and 2342 to one another to establish the first and second stable resting states like those of the article of footwear 2110. The sleeve 2390 has slots 2317A and 2317B in which the distal ends 2351 and 2353 of the arms 2340 and 2342 respectively fit. The fit may be an interference fit and/or adhesive may be used in the slots 2317A, 2317B. As such, the slots 2317A, 2317B and the distal ends 2351, 2353 are complementary connecting features. When connected, the bistable compliant device 2312 flexes at intermediate portions 2340C and 2342C between the first and second stable resting states, similar to intermediate portions 2140C and 2142C of FIG. 78. The dimensions and angles of the arms 2340 and 2342 as well as a tilt from an inner edge to an outer edge in the stable resting states, may be as described with respect to the bistable compliant device 12, for example.

[0234]The following Clauses provide example configurations of an article of footwear and footwear heel structure disclosed herein.

[0235]Clause 1. An article of footwear comprising: a footwear upper having a heel region; a sole structure secured to the footwear upper, the footwear upper defining an ankle opening and a foot-receiving cavity over the sole structure; and a bistable compliant device including: a first arm having a first anchor end secured at a medial side of the article of footwear, and having a first posterior portion remote from the sole structure and further rearward than the first anchor end; and a second arm having a second anchor end secured at a lateral side of the article of footwear, and having a second posterior portion remote from the sole structure and further rearward than the second anchor end; wherein the first posterior portion and the second posterior portion are connected with one another such that the bistable compliant device extends around a rear of the foot-receiving cavity and has a first stable resting state with the first and second posterior portions in a first position and a second stable resting state with the first and second posterior portions in a second position closer to the sole structure than in the first position; and wherein the footwear upper is secured to the bistable compliant device at the rear of the heel region.

[0236]Clause 2. The article of footwear of clause 1, wherein the bistable compliant device is configured to: remain in the first stable resting state in the absence of an applied external force of at least a threshold magnitude, and move to the second stable resting state upon application of the applied external force with the footwear upper moving with the bistable compliant device at the rear of the heel region and lowering a rear of the ankle opening; and remain in the second stable resting state in the absence of an applied external force of at least the threshold magnitude in a different direction than the applied external force used to move to the second stable resting state, and move to the first stable resting state upon application of the applied external force in the different direction with the footwear upper moving with the bistable compliant device at the rear of the heel region and raising the rear of the ankle opening.

[0237]Clause 3. The article of footwear of any of the preceding clauses, wherein the bistable compliant device provides a tactile and/or an audible signal when moving from the first stable resting state to the second stable resting state and when moving from the second stable resting state to the first stable resting state.

[0238]Clause 4. The article of footwear of any of the preceding clauses, wherein: each of the first arm and the second arm has an anterior portion at the respective first or second anchor end and an intermediate portion between the anterior portion and the respective first or second posterior portion; and the bistable compliant device flexes at the intermediate portion of each of the first arm and the second arm under a first applied external force of at least a threshold magnitude to move from the first stable resting state to the second stable resting state, and flexes at the intermediate portion of each of the first arm and the second arm under a second applied external force of at least the threshold magnitude in a different direction than the applied external force used to move to the second stable resting state to move from the second stable resting state to the first stable resting state.

[0239]Clause 5. The article of footwear of any of the preceding clauses, wherein a width of the intermediate portion is greater than a thickness of the intermediate portion.

[0240]Clause 6. The article of footwear of any of the preceding clauses, wherein each of the first arm and the second arm tilts inward and downward toward the foot-receiving cavity from an outer extent of the intermediate portion to an inner extent of the intermediate portion when the bistable compliant device is in the first stable resting state.

[0241]Clause 7. The article of footwear of any of the preceding clauses, wherein the intermediate portion of each of the first arm and the second arm has an inner wall that tilts inward toward the foot-receiving cavity from a bottom edge of the inner wall to a top edge of the inner wall when the bistable compliant device is in the first stable resting state.

[0242]Clause 8. The article of footwear of any of the preceding clauses, wherein the intermediate portion of each of the first arm and the second arm has an outer wall that tilts inward toward the foot-receiving cavity from a bottom edge of the outer wall to a top edge of the outer wall when the bistable compliant device is in the first stable resting state.

[0243]Clause 9. The article of footwear of any of the preceding clauses, wherein the intermediate portion of each of the first arm and the second arm has a quadrilateral transverse cross-section at the intermediate portion.

[0244]Clause 10. The article of footwear of any of the preceding clauses, wherein: the first posterior portion has a first distal end and the second posterior portion has a second distal end; the first and second posterior portions are coupled to one another in a connected state; and the first and second arms are each internally biased to a disconnected state in which the first and second posterior portions are not connected to one another and the first and second distal ends are further apart from one another than in the connected state.

[0245]Clause 11. The article of footwear of any of the preceding clauses, wherein the first and second arms extend parallel with one another from the first and second anchor ends to the first and second distal ends in the disconnected state.

[0246]Clause 12. The article of footwear of any of the preceding clauses, wherein: the first arm has a first anterior portion nearer to the first anchor end than the first posterior portion; the second arm has a second anterior portion nearer to the second anchor end than the second posterior portion; the first posterior portion is angled inward between 25 and 45 degrees along a longitudinal axis of the first arm relative to the first anterior portion when the first and second arms are in the disconnected state; and the second posterior portion is angled inward between 25 and 45 degrees along a longitudinal axis of the second arm relative to the second anterior portion when the first and second arms are in the disconnected state.

[0247]Clause 13. The article of footwear of any of the preceding clauses, wherein: the first arm has a first anterior portion nearer to the first anchor end than the first posterior portion; the second arm has a second anterior portion nearer to the second anchor end than the second posterior portion; the first posterior portion is angled inward at 36 degrees along a longitudinal axis of the first arm relative to the first anterior portion when the first and second arms are in the disconnected state; and the second posterior portion is angled inward at 36 degrees along a longitudinal axis of the second arm relative to the second anterior portion when the first and second arms are in the disconnected state.

[0248]Clause 14. The article of footwear of any of the preceding clauses, wherein: the first arm has a first anterior portion nearer to the first anchor end than the first posterior portion; the second arm has a second anterior portion nearer to the second anchor end than the second posterior portion; the first posterior portion is angled inward between 10 and 80 degrees along a longitudinal axis of the first arm relative to the first anterior portion when the first and second arms are in the disconnected state; and the second posterior portion is angled inward between 10 and 80 degrees along a longitudinal axis of the second arm relative to the second anterior portion when the first and second arms are in the disconnected state.

[0249]Clause 15. The article of footwear of any of the preceding clauses, wherein the bistable compliant device includes complementary connecting features by which the first distal end and the second distal end are coupled to one another.

[0250]Clause 16. The article of footwear of any of the preceding clauses, wherein the complementary connecting features include: a slot extending through the first arm and a peg extending from the second arm and configured to extend through the slot and engage with the first arm; or a slot extending through the second arm and a peg extending from the first arm and configured to extend through the slot and engage with the second arm.

[0251]Clause 17. The article of footwear of any of the preceding clauses, wherein: the slot has a first portion and a second portion extending from the first portion; and the second portion is smaller than the first portion and is disposed closer to the first distal end of the first arm than the first portion when the slot extends through the first arm or is disposed closer to the second distal end of the second arm than the first portion when the slot extends through the second arm.

[0252]Clause 18. The article of footwear of any of the preceding clauses, wherein: the slot has a perimeter with three sides at the second portion; and the peg has a stem with a square outer perimeter that fits in the second portion against the three sides.

[0253]Clause 19. The article of footwear of any of the preceding clauses, wherein: the slot has an arced perimeter at the second portion; and the peg has a stem with a cylindrical outer perimeter that fits in the second portion against the arced perimeter.

[0254]Clause 20. The article of footwear of any of the preceding clauses, wherein: the peg is configured as a first hooked prong; the bistable compliant device further comprising a second hooked prong spaced from the first hooked prong; and the first hooked prong and the second hooked prong engage the respective first arm or second arm through which the slot extends at opposing ends of the slot.

[0255]Clause 21. The article of footwear of any of the preceding clauses, wherein the peg has an interference fit with the respective first arm or second arm through which the slot extends.

[0256]Clause 22. The article of footwear of any of the preceding clauses, wherein: each of the first arm and the second arm has a width and a thickness at a cross-section extending in a medial-lateral direction of the article of footwear perpendicular to a longitudinal axis of the article of footwear; and the width is greater than the thickness.

[0257]Clause 23. The article of footwear of any of the preceding clauses, wherein the bistable compliant device further includes: a base secured to the sole structure; and wherein the first and second anchor ends are secured to the base.

[0258]Clause 24. The article of footwear of any of the preceding clauses, wherein: the base has a first slot at a medial side of the base and a second slot at a lateral side of the base; the first anchor end of the first arm is configured to engage with the base at the first slot; and the second anchor end of the second arm is configured to engage with the base at the second slot.

[0259]Clause 25. The article of footwear of any of the preceding clauses, wherein: the base defines an inverted channel; the sole structure includes a rim; and the base fits to the sole structure with the rim in the inverted channel.

[0260]Clause 26. The article of footwear of any of the preceding clauses, wherein: the base has a first projection with a first ramped surface inclining in a rearward direction of the article of footwear at a medial side of the base; the base has a second projection with a second ramped surface inclining in a rearward direction of the article of footwear at a lateral side of the base; the first anchor end of the first arm is secured to the first projection; the second anchor end of the second arm is secured to the second projection; and the first arm and the second arm extend rearwardly from the first ramped surface and from the second ramped surface, respectively.

[0261]Clause 27. The article of footwear of any of the preceding clauses, wherein: the bistable compliant device defines a slot in each of the first projection and the second projection; the first anchor end engages the base at the slot in the first projection; and the second anchor end engages the base at the slot in the second projection.

[0262]Clause 28. The article of footwear of any of the preceding clauses, further comprising: a first cover engageable with the first projection to cover the first anchor end and the first ramped surface; and a second cover engageable with the second projection to cover the second anchor end and the second ramped surface.

[0263]Clause 29. The article of footwear of any of the preceding clauses, wherein: the first cover and the second cover are each configured as an inverted channel that has an inner surface with one of a rail or a groove; the first projection and the second projection each have the other of the rail or the groove; and the rail is configured to interfit with the groove.

[0264]Clause 30. The article of footwear of any of the preceding clauses, wherein the bistable compliant device defines a gap between the first and second posterior portions and the base.

[0265]Clause 31. The article of footwear of any of the preceding clauses, wherein the first anchor end and the second anchor end are configured to be disposed at a midfoot region of the article of footwear.

[0266]Clause 32. The article of footwear of any of the preceding clauses, wherein the first anchor end and the second anchor end are configured to be disposed at a forefoot region of the article of footwear.

[0267]Clause 33. The article of footwear of any of the preceding clauses, wherein the bistable compliant device includes a base that is integral with and extends from the first anchor end and from the second anchor end.

[0268]Clause 34. The article of footwear of any of the preceding clauses, wherein at least one of the first arm or the second arm includes an elongated flange extending outward and configured to receive an applied external force to move the bistable compliant device from the first stable resting state to the second stable resting state.

[0269]Clause 35. The article of footwear of any of the preceding clauses, wherein the footwear upper includes: a base layer defining the ankle opening and the foot-receiving cavity; and foxing disposed between the base layer and the sole structure; and wherein at least one of the first arm or the second arm is at least partially disposed between the foxing and the base layer.

[0270]Clause 36. The article of footwear of any of the preceding clauses, further comprising: a shroud secured to the footwear upper and at least partially covering the first and second arms, with the posterior portions extending above the shroud.

[0271]Clause 37. The article of footwear of any of the preceding clauses, wherein: the footwear upper includes a collar extending at least partially around the ankle opening at the foot-receiving cavity; and the bistable compliant device is operatively secured to the collar.

[0272]Clause 38. The article of footwear of any of the preceding clauses, further comprising: a collar mount extending around a rear of the ankle opening from the medial side to the lateral side and secured to the collar; and wherein the bistable compliant device is secured to the collar mount.

[0273]Clause 39. The article of footwear of any of the preceding clauses, wherein: the first posterior portion has a first distal end and the second posterior portion has a second distal end connected to the first distal end; the collar mount has a hemispherical portion protruding rearward at an exterior of the collar mount; and at least one of the first distal end and the second distal end interfaces with the hemispherical portion.

[0274]Clause 40. The article of footwear of any of the preceding clauses, further comprising: a fastener coupling the first and second posterior portions to one another in a connected state; wherein the hemispherical portion defines a hollow space at an inner side of the collar mount; and the fastener extends into the hollow space and terminates outward of the collar.

[0275]Clause 41. The article of footwear of any of the preceding clauses, wherein the collar mount has a ledge with a surface the declines forwardly and downwardly toward the foot-receiving cavity, providing a foot entry ramp.

[0276]Clause 42. An article of footwear of any of the preceding clauses comprising: a one-piece footwear upper and sole structure together defining an ankle opening and a foot-receiving cavity over the sole structure; and a bistable compliant device including at least one arm having a first anchor end secured at a lateral side of the sole structure, a first posterior portion remote from the sole structure and further rearward than the first anchor end, a second anchor end secured at a medial side of the sole structure, and a second posterior portion remote from the sole structure and further rearward than the second anchor end; wherein the first posterior portion and the second posterior portion are connected with one another such that the bistable compliant device extends around a rear of the foot-receiving cavity and has a first stable resting state with the first and second posterior portions in a first position and a second stable resting state with the first and second posterior portions in a second position closer to the sole structure than in the first position.

[0277]Clause 43. The article of footwear of any of the preceding clauses, wherein the at least one arm is a single arm, the first posterior portion and the second posterior portion are integral.

[0278]Clause 44. The article of footwear of any of the preceding clauses, wherein the single arm is integral and unitary with the one-piece footwear upper and sole structure at one of the first anchor end and the second anchor end, and the other of the first anchor end or the second anchor end and the sole structure have complementary connecting features at which the other of the first anchor end or the second anchor end is secured to the sole structure.

[0279]Clause 45. The article of footwear of any of the preceding clauses, wherein the sole structure and both of the first anchor end and the second anchor end have complementary connecting features at which the first anchor end and the second anchor end are secured to the sole structure.

[0280]Clause 46. The article of footwear of any of the preceding clauses, wherein the first posterior portion and the second posterior portion define an obtuse angle when at least one of the first anchor end and the second anchor end is disconnected from the sole structure.

[0281]Clause 47. The article of footwear of any of the preceding clauses, wherein the at least one arm includes a first arm having the first anchor end and the first posterior portion and a second arm having the second anchor end and the second posterior portion.

[0282]Clause 48. The article of footwear of any of the preceding clauses, wherein the sole structure and both of the first anchor end and the second anchor end have complementary connecting features at which the first anchor end and the second anchor end are secured to the sole structure.

[0283]Clause 49. The article of footwear of any of the preceding clauses, wherein the first posterior portion and the second posterior portion have additional complementary connecting features at which the first posterior portion and the second posterior portion are secured to one another.

[0284]Clause 50. The article of footwear of any of the preceding clauses, wherein the first arm is integral and unitary with the one-piece footwear upper and sole structure at the first anchor end and the second arm is integral and unitary with the one-piece footwear upper and sole structure at the second anchor end.

[0285]Clause 51. The article of footwear of any of the preceding clauses, further comprising: a connecting sleeve fit over the first posterior portion and the second posterior portion and securing the first posterior portion to the second posterior portion.

[0286]Clause 52. A footwear heel structure for easing foot entry into and exit out of an article of footwear of any of the preceding clauses, the footwear heel structure comprising: a bistable compliant device having a first stable resting state and a second stable resting state, the bistable compliant device configured to remain in the first stable resting state or in the second stable resting state in the absence of an applied external force of at least a threshold magnitude; wherein the bistable compliant device has a first arm and a second arm, each having an anterior portion, a posterior portion, and an intermediate portion between the anterior portion and the posterior portion; and wherein the posterior portion of the first arm is connected with the posterior portion of the second arm storing force urging the posterior portions in an outward direction and the anterior portion of the first arm and the anterior portion of the second arm are each anchored and spaced apart from one another.

[0287]Clause 53. The footwear heel structure of any of the preceding clauses, wherein the bistable compliant device flexes at the intermediate portion of the first arm and at the intermediate portion of the second arm under a first applied external force of at least the threshold magnitude to move from the first stable resting state to the second stable resting state, and flexes at the intermediate portion of the first arm and at the intermediate portion of the second arm under a second applied external force of at least the threshold magnitude in a different direction than the applied external force used to move to the second stable resting state to move from the second stable resting state to the first stable resting state.

[0288]Clause 54. The footwear heel structure of any of the preceding clauses, wherein the posterior portion of the first arm and the posterior portion of the second arm rotate about a pivot axis extending through a connection between the posterior portion of the first arm and the posterior portion of the second arm when the bistable device moves from the first stable resting state to the second stable resting state and when the bistable device moves from the second stable resting state to the first stable resting state.

[0289]To assist and clarify the description of various embodiments, various terms are defined herein. Unless otherwise indicated, the following definitions apply throughout this specification (including the claims). Additionally, all references referred to are incorporated herein in their entirety.

[0290]An “article of footwear”, a “footwear article of manufacture”, and “footwear” may be considered to be both a machine and a manufacture. Assembled, ready to wear footwear articles (e.g., shoes, sandals, boots, etc.), as well as discrete components of footwear articles (such as a midsole, an outsole, an upper component, etc.) prior to final assembly into ready to wear footwear articles, are considered and alternatively referred to herein in either the singular or plural as “article(s) of footwear”.

[0291]“A”, “an”, “the”, “at least one”, and “one or more” are used interchangeably to indicate that at least one of the items is present. A plurality of such items may be present unless the context clearly indicates otherwise. All numerical values of parameters (e.g., of quantities or conditions) in this specification, unless otherwise indicated expressly or clearly in view of the context, including the appended claims, are to be understood as being modified in all instances by the term “about” whether or not “about” actually appears before the numerical value. “About” indicates that the stated numerical value allows some slight imprecision (with some approach to exactness in the value; approximately or reasonably close to the value; nearly). If the imprecision provided by “about” is not otherwise understood in the art with this ordinary meaning, then “about” as used herein indicates at least variations that may arise from ordinary methods of measuring and using such parameters. In addition, a disclosure of a range is to be understood as specifically disclosing all values and further divided ranges within the range.

[0292]The terms “comprising”, “including”, and “having” are inclusive and therefore specify the presence of stated features, steps, operations, elements, or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, or components. Orders of steps, processes, and operations may be altered when possible, and additional or alternative steps may be employed. As used in this specification, the term “or” includes any one and all combinations of the associated listed items. The term “any of” is understood to include any possible combination of referenced items, including “any one of” the referenced items. The term “any of” is understood to include any possible combination of referenced claims of the appended claims, including “any one of” the referenced claims.

[0293]For consistency and convenience, directional adjectives may be employed throughout this detailed description corresponding to the illustrated embodiments. Those having ordinary skill in the art will recognize that terms such as “above”, “below”, “upward”, “downward”, “top”, “bottom”, etc., may be used descriptively relative to the figures, without representing limitations on the scope of the invention, as defined by the claims.

[0294]The term “longitudinal” particularly refers to a direction extending a length of a component. For example, a longitudinal direction of a shoe extends between a forefoot region and a heel region of the shoe. The term “forward” or “anterior” is used to particularly refer to the general direction from a heel region toward a forefoot region, and the term “rearward” or “posterior” is used to particularly refer to the opposite direction, i.e., the direction from the forefoot region toward the heel region. In some cases, a component may be identified with a longitudinal axis as well as a forward and rearward longitudinal direction along that axis. The longitudinal direction or axis may also be referred to as an anterior-posterior direction or axis.

[0295]The term “transverse” particularly refers to a direction extending a width of a component. For example, a transverse direction of a shoe extends between a lateral side and a medial side of the shoe. The transverse direction or axis may also be referred to as a lateral direction or axis or a mediolateral direction or axis.

[0296]The term “vertical” particularly refers to a direction generally perpendicular to both the lateral and longitudinal directions. For example, in cases where a sole is planted flat on a ground surface, the vertical direction may extend from the ground surface upward. It will be understood that each of these directional adjectives may be applied to individual components of a sole. The term “upward” or “upwards” particularly refers to the vertical direction pointing towards a top of the component, which may include an instep, a fastening region and/or a throat of an upper. The term “downward” or “downwards” particularly refers to the vertical direction pointing opposite the upwards direction, toward the bottom of a component and may generally point towards the bottom of a sole structure of an article of footwear.

[0297]The “interior” of an article of footwear, such as a shoe, particularly refers to portions at the space that is occupied by a wearer's foot when the shoe is worn. The “inner side” of a component particularly refers to the side or surface of the component that is (or will be) oriented toward the interior of the component or article of footwear in an assembled article of footwear. The “outer side” or “exterior” of a component particularly refers to the side or surface of the component that is (or will be) oriented away from the interior of the shoe in an assembled shoe. In some cases, other components may be between the inner side of a component and the interior in the assembled article of footwear. Similarly, other components may be between an outer side of a component and the space external to the assembled article of footwear. Further, the terms “inward” and “inwardly” particularly refer to the direction toward the interior of the component or article of footwear, such as a shoe, and the terms “outward” and “outwardly” particularly refer to the direction toward the exterior of the component or article of footwear, such as the shoe. In addition, the term “proximal” particularly refers to a direction that is nearer a center of a footwear component, or is closer toward a foot when the foot is inserted in the article of footwear as it is worn by a user. Likewise, the term “distal” particularly refers to a relative position that is further away from a center of the footwear component or is further from a foot when the foot is inserted in the article of footwear as it is worn by a user. Thus, the terms proximal and distal may be understood to provide generally opposing terms to describe relative spatial positions.

[0298]While various embodiments have been described, the description is intended to be exemplary, rather than limiting and it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible that are within the scope of the embodiments. Any feature of any embodiment may be used in combination with or substituted for any other feature or element in any other embodiment unless specifically restricted. Accordingly, the embodiments are not to be restricted except in light of the attached claims and their equivalents. Also, various modifications and changes may be made within the scope of the attached claims.

[0299]While several modes for carrying out the many aspects of the present teachings have been described in detail, those familiar with the art to which these teachings relate will recognize various alternative aspects for practicing the present teachings that are within the scope of the appended claims. It is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and exemplary of the entire range of alternative embodiments that an ordinarily skilled artisan would recognize as implied by, structurally and/or functionally equivalent to, or otherwise rendered obvious based upon the included content, and not as limited solely to those explicitly depicted and/or described embodiments.