Stepping motor drive device

A stepping motor driver for driving a stepping motor according to a position angle command, the stepping motor driver comprising:

• a current detector that detects a phase current of the stepping motor;
• an inverter that applies a current to a winding of the stepping motor;
• and
• a control unit that controls the inverter;
• wherein a rotational coordinate system, which is rotated according to the position angle command, is defined by a dp-axis and a qp-axis orthogonal to each other;
• wherein the control unit comprises:
• a phase current coordinate transformer that transforms the phase current detected by the current detector into a dp-axis component and a qp-axis component in the rotational coordinate system based on the position angle command to generate a dp-axis detection current and a qp-axis detection current;
• a torque correction command generator that generates a torque correction command according to a torque correction waveform indicating a current waveform to be applied to the stepping motor in order to suppress torque fluctuation of the stepping motor;
• a torque correction command coordinate transformer that transforms the torque correction command generated by the torque correction command generator into a dp-axis component and a qp-axis component in the rotational coordinate system based on the position angle command to generate a dp-axis torque correction component and a qp-axis torque correction component;
• an adder that superposes the dp-axis torque correction component and the qp-axis torque correction component generated by the torque correction command coordinate transformer respectively on a dp-axis fundamental current command and a qp-axis fundamental current command based on the rotational coordinate system to generate a dp-axis current command and a qp-axis current command;
• and
• a control command generator that compares the dp-axis detection current and the qp-axis detection current generated by the phase current coordinate transformer respectively with the dp-axis current command and the qp-axis current command generated by the adder and applies a control command to the inverter according to a result of the comparison;
• wherein the torque correction waveform contains a reluctance torque correction waveform component which suppresses reluctance torque fluctuation;
• wherein the reluctance torque correction waveform component has a waveform profile such that an original waveform having a frequency twice that of a fundamental sinusoidal wave of an electrical angle cycle of the stepping motor and having a phase matched with that of the fundamental sinusoidal wave is full-wave-rectified to the same sign as or a different sign from that of the fundamental sinusoidal wave;
• and
• wherein the reluctance torque correction waveform component has a waveform profile such that the original waveform is full-wave-rectified to the same sign as that of the fundamental sinusoidal wave when an amplitude of an angle-differentiated self-inductance of the stepping motor is greater than an amplitude of an angle-differentiated mutual inductance of the stepping motor, and the reluctance torque correction waveform component has a waveform profile such that the original waveform is full-wave-rectified to the different sign from that of the fundamental sinusoidal wave when the amplitude of the angle-differentiated self-inductance is smaller than the amplitude of the angle-differentiated mutual inductance.