IMAGE FORMING APPARATUS

CROSS REFERENCE TO RELATED APPLICATIONS

[0001]The present invention claims priority under 35 U.S.C. § 119 to Japanese Application No. 2024-074425 filed on May 1, 2024, the entire contents of which being incorporated herein by reference.

BACKGROUND OF THE INVENTION

Technical Field

[0002]The present invention relates to an image forming apparatus.

Description of Related Art

[0003]Conventionally, to prevent sheets from sticking to each other, an image forming apparatus has been proposed in which a charge adjustment device (static eliminator) capable of applying charges that repel each other is disposed immediately after an image forming section (e.g., see Japanese Unexamined Patent Publication No. 2016-157011).

[0004]Furthermore, a static eliminator has been proposed that includes discharge electrodes disposed in a non-contact manner with respect to a sheet and that is capable of applying an appropriate voltage corresponding to a sheet conveyance speed (see, for example, Japanese Unexamined Patent Publication No. 2021-111527).

SUMMARY OF THE INVENTION

[0005]However, when the sheet is subjected to the charge elimination processing by the apparatus described in Japanese Unexamined Patent Publication No. 2016-157011 or Japanese Unexamined Patent Publication No. 2021-111527, is further passed through a non-sheet stacking device for subjecting the sheet to post-processing and is stacked on a sheet stacking device, the sheet is re-charged by peeling discharge from a roller and friction with a sheet passing guide surface at the time of passing through the non-sheet stacking device. Therefore, the charge amount of the sheet conveyed to the sheet stacking device located on the downstream side in the sheet conveyance direction relative to the non-sheet stacking device becomes high (see FIG. 7A). Furthermore, when the sheet recharged by the non-sheet stacking device is superimposed on the upper surface of the sheets stacked on the sheet stacking tray of the sheet stacking device, the residual charge of the stacked sheets is cumulatively increased, so that stacking unevenness (stacking shift) of the sheets occurs.

[0006]An object of the present invention is to suppress uneven stacking of sheets in a sheet stacking device located on the downstream side of a non-sheet stacking device in the sheet conveyance direction.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]The advantages and features provided by one or more embodiments of the invention will become more fully understood from the detailed description given hereinafter and the appended drawings which are given by way of illustration only, and thus are not intended as a definition of the limits of the present invention, and wherein:

[0016]FIG. 1 is a diagram illustrating an example of an overall configuration of an image forming apparatus in an embodiment of the present invention.

[0017]FIG. 2 is a diagram schematically illustrating an effect of covering the periphery of the discharging device with an insulator cover;

[0018]FIG. 3 is a diagram schematically illustrating an effect of closing the lower side of the sheet path of the discharging device with an insulator guide plate;

[0019]FIG. 4 is a diagram illustrating a state in which the discharging device is attached between two post-processing devices;

[0020]FIG. 5 is a diagram illustrating a state of a connector when the discharging device is mounted between two post-processing devices as viewed from above;

[0021]FIG. 6 is a diagram illustrating a lock mechanism when the discharging device is attached between two post-processing devices;

[0022]FIG. 7A is a graph illustrating a change in the charge amount on a single sheet during sheet passing in a conventional image forming apparatus not including a discharging device;

[0023]FIG. 7B is a graph illustrating a change in a charge amount on a single sheet during sheet passing in an image forming apparatus in which a discharging device is arranged adjacent to a sheet stacking device on an upstream side in a sheet conveyance direction;

[0024]FIG. 7C is a graph illustrating a change in a charge amount on a single sheet during sheet passing in an image forming apparatus in which a discharging device is disposed adjacent to each of two sheet stacking devices on an upstream side in a sheet conveyance direction thereof;

[0025]FIG. 8 is a diagram illustrating a configuration example of the image forming apparatus in which the discharging device is disposed adjacent to each of two sheet stacking devices on the upstream side in the sheet conveyance direction;

[0026]FIG. 9 is a graph illustrating changes in cumulative charge amount when one to one hundred sheets are stacked in the sheet stacking device of each of the image forming apparatuses in which changes in charge amount are illustrated in FIG. 7A to FIG. 7C; and

[0027]FIG. 10 is a diagram schematically illustrating a state in which the discharging device is disposed on each of an upper side and a lower side of a sheet path.

DETAILED DESCRIPTION

[0028]Hereinafter, one or more embodiments of the present invention will be described with reference to the drawings. However, the scope of the invention is not limited to the disclosed embodiments.

[0029]FIG. 1 is a diagram illustrating an example of an overall configuration of an image forming apparatus 100 according to the present embodiment. As illustrated in FIG. 1, the image forming apparatus 100 is configured by arrangement of a sheet feed device 1, an image forming apparatus main body 2, a non-sheet stacking device (non-sheet stacker) 3A, a non-sheet stacking device (non-sheet stacker) 3B, a non-sheet stacking device (non-sheet stacker) 3C, a sheet stacking device (sheet stacker) 3D, and a sheet stacking device (sheet stacker) 3E in this order from upstream in a sheet conveyance direction. That is, the image forming apparatus 100 is configured such that the non-sheet stacking devices 3A to 3C are arranged adjacent to the image forming apparatus main body 2 on the downstream side in the sheet conveyance direction and the plurality of sheet stacking devices 3D and the sheet stacking device 3E are arranged further downstream.

[0030]The non-sheet stacking device 3A, the non-sheet stacking device 3B, the non-sheet stacking device 3C, the sheet stacking device 3D, and the sheet stacking device 3E are post-processing devices that process a sheet on which an image has been formed by the image forming apparatus main body 2. In the present embodiment, the image forming apparatus 100 including three non-sheet stacking devices on the downstream side of the image forming apparatus main body 2 in the sheet conveyance direction and two sheet stacking devices on the further downstream side of the three non-sheet stacking devices will be described as an example, but the numbers of the non-sheet stacking devices and the sheet stacking devices are not particularly limited.

[0031]Note that in the following description, the non-sheet stacking devices 3A to 3C and the sheet stacking devices 3D to 3E are referred to as the post-processing devices 3 when they are not distinguished from each other.

[0032]In addition, in the image forming apparatus 100 of the present embodiment, as illustrated in FIG. 1, a discharging device (discharger) 4 is disposed adjacent to the sheet stacking device 3D or at least one of the sheet stacking devices 3E on the upstream side in the sheet conveyance direction.

[0033]The sheet feed device 1 contains sheets and feeds the sheets to the image forming apparatus main body 2 under the control of the image forming apparatus main body 2. Note that a base material of the sheet used in the image forming apparatus 100 is not particularly limited, and may be a film made of resin, or may be paper such as plain paper containing paper pulp as a main component and high-quality paper.

[0034]The image forming apparatus main body 2 includes a controller, an image forming section, a fixing section, a sheet conveyance section, and the like. The image forming apparatus main body 2 forms an image on the sheet fed from the sheet feed device 1 by an electrophotographic method, and outputs the sheet on which the image has been formed to the non-sheet stacking device 3A. A discharging section 21 is provided on a downstream side of the fixing section in the housing of the image forming apparatus main body 2. The discharging section 21 discharges the image-formed sheet conveyed from the fixing section. The discharging section 21 may discharge the sheet by contacting the sheet or may discharge the sheet in a non-contact state.

[0035]The non-sheet stacking devices 3A to 3C are post-processing devices having a function of performing processing other than stacking of sheets, such as punching, folding, binding, and bookbinding, on the sheets output from the image forming apparatus main body 2.

[0036]The sheet stacking devices 3D to 3E are post-processing devices exclusively for sheet stacking, which stack the sheet that has passed through the non-sheet stacking devices 3A to 3C.

[0037]The discharging device 4 is a non-contact ion type static eliminator (ionizer). The discharging device 4 generates positive and negative ions and sends the ions to the conveyed sheet to discharge the sheet. As a method of generating ions in the non-contact ion type discharging device, there are a corona discharge method, a plasma method, a soft X-ray method, and the like, and the discharging device 4 may generate ions by any method. In addition, in the present embodiment, the voltage application method to the electrode needle of the discharging device 4 is an AC (alternating current) method but may be any of a DC (direct current) method, a pulse AC method, a pulse DC method, and a high-frequency AC method. In addition, in the discharging device 4, as a method of sending the generated ions to the sheet, there are a radiation type, a windless type, an air type, a gun type, and the like, and any of them may be used. In addition, the discharging device 4 is not limited to a non-contact ion type and may be a discharging device that discharges static electricity from a sheet by an electric line of force radiation method.

[0038]Here, as illustrated on the left side of FIG. 2, when the discharging device 4 is discharged, a spark occurs to the exterior metal plate of the adjacent post-processing device 3, and the capability of eliminating static electricity from the sheet is attenuated. Therefore, as shown on the right side of FIG. 2, the periphery of the discharging device 4 is preferably covered with the cover 45 made of an insulator. Thus, attenuation of the discharging capability can be suppressed. Here, a reference sign P in FIG. 2 and FIG. 10 indicates a sheet.

[0039]In addition, as shown on the left side of FIG. 3, in the discharging device 4, when discharge occurs when a sheet does not pass, spark may occur to the grounding surface 47 of the sheet metal. Therefore, as shown in the right side of FIG. 3, it is preferable that the lower side of the sheet path is closed by a guide plate 46 made of an insulator. Thus, a spark to the ground surface 47 can be prevented. Here, a dotted line in FIG. 3 indicates a sheet path.

[0040]The discharging device 4 is unitized and can be inserted between the post-processing devices 3 of the image forming apparatus 100 from the front so as to be easily attached and detached. The term “between the post-processing devices 3” means between non-sheet stacking devices, between a non-sheet stacking device and a sheet stacking device, or between sheet stacking devices. FIG. 4 is a diagram illustrating a state in which the discharging device 4 is mounted between two post-processing devices 3. FIG. 5 is a diagram illustrating a state in which a discharging device 4 is attached between two post-processing devices 3 when viewed from above. FIG. 5 is an enlarged view of a portion indicated by a rectangle 71 in FIG. 4. FIG. 6 is a diagram illustrating a lock mechanism that fixes the discharging device 4 between the two post-processing devices 3. FIG. 6 is an enlarged view of a portion indicated by a rectangle 72 in FIG. 4.

[0041]As illustrated in FIG. 5, pins 31 for connection to another device are provided at two upper and lower positions on a back side of a side surface 33 on a downstream side of each post-processing device 3. On a far side of the side surface 34 on the upstream side of each post-processing device 3, members having pin holes 32 for connection with other apparatuses in two places, upper and lower, are provided. In a state where the two post-processing devices 3 are connected, the pins 31 of the post-processing device 3 on the upstream side and the pin holes 32 of the post-processing device 3 on the downstream side are engaged with each other in two upper and lower places indicated by dotted-line rectangles in FIG. 4 (ST11 in FIG. 5). The pins 31 and the pin holes 32 are connectors for connecting other devices to the post-processing device 3.

[0042]As illustrated in FIG. 6, fixing metal fittings 35 are provided at two positions, upper and lower, on the near side of a side surface 33 on the downstream side of each post-processing device 3. Fixing brackets 36 are provided at two positions, upper and lower, on a near side of a side surface 34 on an upstream side of each post-processing device 3. The fixing bracket 35 is provided with a pin hole 35a, a screw hole 35b, and a screw hole 35c. The fixing bracket 36 is provided with a pin hole 36a, a screw hole 36b, and a screw hole 36c. In a state where the two post-processing devices 3 are connected, the pin hole 35a, the screw hole 35b, and the screw hole 35c of the fixing metal fitting 35 and the pin hole 36a, the screw hole 36b, and the screw hole 36c of the fixing metal fitting 36 are overlapped with each other, and the locking metal fitting 5 is attached (ST21 in FIG. 6).

[0043]Further, as shown in FIG. 5, pin receivers 41 are provided at two upper and lower positions indicated by rectangles of chain lines in FIG. 4 on the inner side of the side surface 43 on the upstream side of the discharging device 4. On the side surface 44 on the downstream side of the discharging device 4, pins 42 are provided at two upper and lower positions indicated by rectangles of chain lines in FIG. 4. The pin receiver 41 and the pin 42 are connecting members connected to a connector of the post-processing device 3.

[0044]When the discharging device 4 is mounted between the two post-processing devices 3, as shown in FIG. 4, the user releases the connection between the two post-processing devices 3, moves the post-processing device 3 on the downstream side by about 50 mm, and inserts and mounts the discharging device 4 into the vacant space from the front side (front surface) in the arrow direction.

[0045]To be specific, first, the user removes the lock fittings 5 attached to the near side of the connecting portion of the two post-processing devices 3 (ST21 to ST22 in FIG. 6). Next, the user releases the engagement between the pin 31 of the post-processing device 3 on the upstream side and the pin receiver 32 of the post-processing device 3 on the downstream side and moves the post-processing device 3 on the downstream side by about 50 mm (step S11 to S12 in FIG. 5 and step S23 in FIG. 6). Next, the user inserts the discharging device 4 between the two post-processing devices 3 (ST13 in FIG. 5), engages the pin 31 of the upstream post-processing device 3 with the pin receiver 41 of the discharging device 4, and engages the pin receiver 32 of the downstream post-processing device 3 with the pin 42 of the discharging device 4 (ST14 in FIG. 5). Next, the user inserts the pin 61a and the pin 62a of the lock fitting 6 into the pin hole 35a of the fixing fitting 35 and the pin hole 36a of the fixing fitting 36, respectively (ST24 in FIG. 6), and screws the lock fitting 6 (step S25).

[0046]After the insertion of the discharging device 4, when a user attaches a front cover, the attachment of the discharging device 4 is completed.

[0047]In the image forming apparatus 100 of the present embodiment, the discharging device 4 is disposed adjacent to at least one sheet stacking device on the upstream side in the sheet conveyance direction. Further, the discharging device 4 is unitized, and is configured to be insertable (connectable) between the post-processing devices 3. Therefore, in the image forming apparatus 100, it is possible to easily replace the discharging device 4 between the post-processing devices 3 according to the needs of the user.

[0048]Hereinafter, effects of the image forming apparatus 100 configured as described above will be described.

[0049]FIG. 7A is a graph illustrating a change in the charge amount on a single sheet during sheet passing in a conventional image forming apparatus not including a discharging device 4. The charge amount (V) is measured at the discharge port of each device constituting the image forming apparatus and is an average value of 30 sheets. Note that the horizontal axis of the graph starts from the right according to the arrangement order when the image forming apparatus is viewed from the front. The same applies to FIG. 7B and FIG. 7C. As illustrated in FIG. 7A, the charge amount on the sheet fed by the sheet feed device 1 increases due to triboelectric charging as the conveyance length increases, but the charge amount on the sheet temporarily decreases due to discharging by the discharging section 21 of the image forming apparatus main body 2. However, thereafter, the charge amount on the sheet increased due to triboelectric charging as the conveyance length increased, and the final charge amount on the sheet in the sheet stacking device 3E became −2251V.

[0050]In the non-sheet stacking devices 3A to 3C, the sheets do not contact each other unlike the sheet stacking device 3D and the sheet stacking device 3E, and thus the electrostatic problem is unlikely to occur. However, in the sheet stacking device 3D and the sheet stacking device 3E, since electric charge is accumulated due to stacking of sheets, an electrostatic problem such as uneven stacking of sheets occurs.

[0051]FIG. 7B is a graph illustrating a change in the charge amount on a single sheet during sheet passing in the image forming apparatus 100 (FIG. 1) in which the discharging device 4 is disposed adjacent to the sheet stacking device 3D on the upstream side in the sheet conveyance direction. The charge amount (V) is measured at the discharge port of each device constituting the image forming apparatus and is an average value of 30 sheets. As illustrated in FIG. 7B, the sheet fed by the sheet feed device 1 has an increased charge amount due to triboelectric charging as the sheet is conveyed farther, but the charge amount on the sheet temporarily decreases due to the discharging by the discharging section 21 of the image forming apparatus main body 2. Thereafter, the charge amount on the sheet increases again as the sheet passes through the non-sheet stacking device 3A to the non-sheet stacking device 3C, but since the discharging device 4 is arranged immediately before the sheet stacking device 3D, the charge amount on the sheet conveyed to the sheet stacking device 3D is almost zero. Thereafter, the charge amount of the sheet increased by passing through the sheet stacking device 3D and the sheet stacking device 3E, but the final charge amount of the sheet in the sheet stacking device 3E became −576V. This is about ¼ of the charge amount in the sheet stacking device 3E of the conventional image forming apparatus illustrated in FIG. 7A.

[0052]FIG. 7C is a graph of changes in the charge amount on a single sheet during sheet passing in the image forming apparatus 100 (FIG. 8) in which discharging device 4 is disposed adjacent to each of the sheet stacking device 3D and the sheet stacking device 3E each on the upstream side in the sheet conveyance direction. The charge amount (V) is measured at the discharge port of each device constituting the image forming apparatus and is an average value of 30 sheets. As illustrated in FIG. 7C, the sheet fed by the sheet feed device 1 has an increased charge amount due to triboelectric charging as the sheet is conveyed farther, but the charge amount on the sheet temporarily decreases due to the discharging by the discharging section 21 of the image forming apparatus main body 2. Thereafter, the charge amount on the sheet increases again as the sheet passes through the non-sheet stacking device 3A to the non-sheet stacking device 3C, but the charge amount on the sheet to be conveyed to the sheet stacking device 3D is almost zero because the discharging device 4 is arranged immediately before the sheet stacking device 3D. Thereafter, the charge amount on the sheet increased as the sheet passed through the sheet stacking device 3D, but since the discharging device 4 was also arranged immediately before the sheet stacking device 3E, the charge amount on the sheet conveyed to the sheet stacking device 3E became almost zero, and the final charge amount on the sheet at the sheet stacking device 3E became −152V.

[0053]FIG. 9 is a graph illustrating a change in accumulated charge amount when one to one hundred sheets are stacked in the sheet stacking device 3E of each of the image forming apparatuses whose charge amount changes are illustrated in FIG. 7A to FIG. 7C. The conventional image forming apparatus corresponding to FIG. 7A is defined as pattern 1. The image forming apparatus 100 (FIG. 1) corresponding to FIG. 7B is defined as pattern 2. The image forming apparatus 100 (FIG. 8) corresponding to FIG. 7C is referred to as pattern 3. Note that a measuring device having a measurement range of +20 kV was used for measuring the charge amount. As illustrated in FIG. 9, as the sheets are stacked, the accumulated charges are self-discharged to the sheet stacking tray side, so that the charge amount converges to the charge amount of about 50 sheets. The amount of stacking shift of sheets is within the requirement until the charge amount reaches −10 kV but is outside the requirement when the charge amount exceeds −10 kV. That is, when the charge amount exceeds −10 kV, uneven stacking of sheets occurs.

[0054]As illustrated in FIG. 9, in the conventional image forming apparatus of pattern 1, the accumulated charge amount exceeds-10 kV on and after the third stacked sheet, and the uneven stacking of sheets occurs. On the other hand, in the image forming apparatus 100 of the pattern 2 and the pattern 3, the accumulated charge amount does not exceed −10 kV even on the hundredth sheet, and the occurrence of the stacking unevenness of the sheets is suppressed.

[0055]The charged sheets cause a problem such as sticking due to contact between the stopped sheets and contact with a guide plate. On the other hand, such a problem is unlikely to occur during sheet passing. That is, it is considered that a problem such as the sticking of the sheet is unlikely to occur in the non-sheet stacking devices 3A to 3C, but a problem such as the sticking of the sheet occurs in the sheet stacking devices 3D to 3E. Therefore, it is necessary that the sheets be discharged before the sheet stacking device 3D or 3E where the sheets contact each other. In addition, in the sheet stacking devices 3D and 3E, accumulation of residual charges of the sheets occurs, and therefore, it is preferable that the residual charges are made close to 0 V before the sheet stacking device 3D or 3E. In the image forming apparatus 100 of the present embodiment, the discharging device 4 is disposed adjacent to at least one of the sheet stacking devices 3D or 3E on the upstream side in the sheet conveyance direction. Therefore, as illustrated in FIG. 7B and FIG. 7C, the residual charge can be brought close to 0 V before the sheet stacking device. Thus, as illustrated in FIG. 9, even if the accumulation of residual charges occurs in the sheet stacking device 3D or 3E, the accumulation can be suppressed to a low level, so that the occurrence of uneven stacking of sheets can be suppressed. As described above, in the image forming apparatus 100 of the present embodiment, by arranging the discharging device 4 adjacent to the sheet stacking device 3D or at least one of the sheet stacking devices 3E on the upstream side in the sheet conveyance direction, it is possible to perform efficient discharging in terms of costs and performances.

[0056]In addition, as in the past, in a case of a configuration in which the discharging section is disposed in each device (unit) configuring the image forming apparatus, since an inner configuration is greatly different in each unit, it has been difficult to replace the discharging device. On the other hand, in the image forming apparatus 100 of the present embodiment, the discharging device 4 is configured to be detachable between the two post-processing devices 3. Therefore, a user can easily replace the discharging device 4 with another one anywhere between the post-processing devices 3. In addition, conventionally, the discharging members have been provided everywhere in the image forming apparatus (including the inside of the post-processing device), but in the image forming apparatus 100 of the present embodiment, efficient discharging can be performed, and therefore, there is an advantage that they become unnecessary.

[0057]Note that in a case where the non-sheet stacking device 3A to the non-sheet stacking device 3C are the post-processing devices 3 including a stacker of sheets, for example, in a case of a case binding apparatus, a saddle stitch apparatus, a multi-folding apparatus, or the like, it is preferable to arrange the discharging device 4 adjacent to these apparatuses on the upstream side in the sheet conveyance direction thereof. Thus, it is possible to suppress the occurrence of bundle displacement or the like due to the generation of static electricity when sheets are stacked on the stacker.

[0058]In addition, the sheet printed on both sides in the image forming apparatus main body 2 has a large charge amount on both sides. Therefore, as shown in FIG. 10, it is preferable that the discharging device 4 is arranged on each of the upper side and the lower side of the sheet path. Thus, the charge amount on both sides of the sheet can be suppressed, and the occurrence of uneven stacking of sheets can be more effectively suppressed.

[0059]As described above, the image forming apparatus 100 includes the non-sheet stacking devices 3A to 3C adjacent to the downstream side of the image forming apparatus main body 2 in the sheet conveyance direction to perform post-processing on the sheet output from the image forming apparatus main body 2, and further includes the sheet stacking device 3D and the sheet stacking device 3E on the downstream side of the non-sheet stacking devices 3A to 3C in the sheet conveyance direction. In the image forming apparatus 100, a discharging device 4 is arranged adjacent to at least the sheet stacking device 3D on the upstream side in the sheet conveyance direction.

[0060]Therefore, it is possible to efficiently suppress the occurrence of uneven stacking of sheets in the sheet stacking device located on the downstream side of the non-sheet stacking device in the sheet conveyance direction. In particular, by adopting a configuration in which the discharging device is provided adjacent to each of the plurality of sheet stacking devices on the upstream side in the sheet conveyance direction, it is possible to efficiently suppress the occurrence of uneven stacking of sheets in the sheet stacking devices.

[0061]The above-described embodiment is a preferred example of the present invention and not intended to limit the present invention.

[0062]Although embodiments of the present invention have been described and shown in detail, the disclosed embodiments are made for purposes of illustration and example only and not limitation. The scope of the present invention should be interpreted by terms of the appended claims.

[0063]The entire disclosure of Japanese Patent Application No. 2024-074425, filed on May 1, 2024, including description, claims, drawings and abstract is incorporated herein by reference.