OKUMA CORPORATION

A control device, which is configured to control current of a three-phase alternating current motor by d-q axis control, includes a q-axis current controller configured to receive, as one input, an acceleration torque command value τ f calculated based on a position command value X, and output a controller output voltage Δe q to be added to a q-axis voltage command value v q *. The q-axis current controller calculates, based on the acceleration torque command value τ f , an acceleration q-axis current command value i qf *, which is a current command value corresponding to the acceleration torque command value τ f , and adds, to the controller output voltage Δe q , a value obtained by multiplying the acceleration q-axis current command value i qf * by an IP coefficient K IP indicating a ratio of switching between PI control and I-P control and by a q-axis proportional gain G qp .

A position control apparatus detects currents of processing object phases which flow through the three-phase AC motor, applies offset compensation processing to current detected values of the processing object phases based on offset compensation amounts, and controls the three-phase AC motor based on the current detected values of the processing object phases after the offset compensation processing. Processing of obtaining the offset compensation amounts includes processing of obtaining a Fourier coefficient of a frequency component of a torque ripple based on a torque command value signal, processing of obtaining torque amplitude components of the processing object phases, and processing of obtaining the offset compensation amounts with respect to the processing object phases based on the torque amplitude components of the processing object phases.

In a position control device that controls a rotational speed and a rotational angle of a three-phase synchronous motor by calculating a d-axis current command value and a q-axis current command value based on a position command and causing a inverter to adjust current values of respective phases of the three-phase synchronous motor, a processor calculates a d-axis additional current value to be added to the d-axis current command value. The d-axis additional current value oscillates in such a manner that the polarity changes according to an electrical angle and crosses a zero level with an inclination whose polarity is opposite the polarity of a first q-axis current command value at a zero-cross electrical angle. As a result, positional deviation ripples caused by dead time can be suppressed.

A position control apparatus detects currents of processing object phases which flow through the three-phase AC motor, applies offset compensation processing to current detected values of the processing object phases based on offset compensation amounts, and controls the three-phase AC motor based on the current detected values of the processing object phases after the offset compensation processing. Processing of obtaining the offset compensation amounts includes processing of obtaining a Fourier coefficient of a frequency component of a torque ripple based on a torque command value signal, processing of obtaining torque amplitude components of the processing object phases, and processing of obtaining the offset compensation amounts with respect to the processing object phases based on the torque amplitude components of the processing object phases.

A numeric value control unit outputs a connection diagnostic signal to a target position switching unit to place the three-phase motor in a position at an angle that causes no torque generation upon application of a diagnostic current to the three-phase motor, and thereafter, outputs a connection diagnostic signal to a current instruction switching unit to apply a diagnostic current. Then, in order to apply a diagnostic current to the other two phases, the three-phase motor is placed in a position at an angle that causes no torque generation upon second application of a diagnostic current, and a diagnostic current is thereafter applied. When a diagnostic current is applied twice and in the case where no defect in connection is detected in either application, it is determined that connection is normal. Meanwhile, in the case where connection is detected once or twice, it is determined that connection is defective.

A torque ripple and a position error caused by an offset error of the current sensor affects an electrical angle frequency of a motor. In an apparatus of the present disclosure, a computation device executes a power spectrum computing process when a three-phase alternating current motor is at a constant speed, and a value obtained by subtracting a position command value from a position detected by a position detector is fast Fourier transformed, to compute a power spectrum of a position error signal at the electrical angle frequency. Then, the computation device executes an offset correction computing process, to evaluate the power spectrum and to update an offset correction amount. By repeatedly executing these processes when the three-phase alternating current motor is driven at a constant speed, the torque ripple and position error caused by the offset error are reduced.

A window function calculator applies a Hann window function to Vd (n) to obtain a numeric value Vw (n). For twenty successive numeric values Vw(n) for every twenty numeric values (N=20), each of the Fourier calculators to executes Fourier calculation. Further, the SRSS calculators to calculate square root of sum of squares of SIM and COS components of respective orders of the results of Fourier calculation as numeric values A2, A3, A4, A5. A subtractor calculates a numeric value Ci=A3−A5, while a subtractor calculates a numeric value Si=A4−A2. A Frequency calculator calculates a numeric value Fi=(m+1+2*A TAN 2 (Ci, Si)/π)/(NT), which indicates the frequency identified. An amplitude calculator doubles the square root of the sum of squares of the numeric values Ci and Si, and calculates a numeric value Ai that indicates the amplitude of the frequency identified.

A numeric value control unit outputs a connection diagnostic signal to a target position switching unit to place the three-phase motor in a position at an angle that causes no torque generation upon application of a diagnostic current to the three-phase motor, and thereafter, outputs a connection diagnostic signal to a current instruction switching unit to apply a diagnostic current. Then, in order to apply a diagnostic current to the other two phases, the three-phase motor is placed in a position at an angle that causes no torque generation upon second application of a diagnostic current, and a diagnostic current is thereafter applied. When a diagnostic current is applied twice and in the case where no defect in connection is detected in either application, it is determined that connection is normal. Meanwhile, in the case where connection is detected once or twice, it is determined that connection is defective.