BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a technique of advance angle control of a stepping motor.

Description of the Related Art

Stepping motors used in various fields can easily perform a high-accuracy positioning operation by open loop control, but there is a possibility of step-out due to a high load or high-speed rotation during open loop control. Consequently, there is a method of controlling an advance angle of a driving waveform with respect to a rotational phase using a rotational phase signal of a motor which is obtained from a position sensor provided in a stepping motor. According to this method, it is possible to maximize rotation efficiency by optimal advance angle control and to realize an increase in speed and power saving.

Japanese Patent No. 6278622 discloses a method of matching an advance angle value to a target value by changing a period of a driving waveform in microstep drive of a stepping motor. Japanese Patent No. 6207223 discloses a method of matching an advance angle value to a target value by changing an amplitude of a driving waveform in microstep drive of a stepping motor.

The technique disclosed in Japanese Patent No. 6278622 is superior in a high speed region of a motor rotation speed, but a detection period of a position sensor increases in a low speed region of a motor rotation speed. For this reason, a fluctuation in period increases, and thus there is a possibility that noise will be generated in a motor. In addition, regarding a target advance angle, data of a relationship between an advance angle and a rotation speed obtained experimentally is stored in a memory, and a stored advance angle amount is set as a target advance angle. However, there is an individual difference between the motor and a moving member connected thereto, and the state of a load changes due to changes with time, a change in temperature, a difference in posture, or the like. For this reason, it is not possible to obtain a control state for obtaining an optimal advance angle at all times using only data of a relationship between an advance angle and a rotation speed obtained experimentally.

Japanese Patent No. 6207223 is based on the assumption that maximum efficiency is obtained when a follow-up delay of a motor with respect to a driving waveform is 90 degrees. However, a phase deviation of a driving waveform due to the generation of a counter electromotive force occurs during the rotation of a motor, and thus a follow-up delay amount for obtaining maximum efficiency changes depending on the state of generation of a counter electromotive force. That is, an advance angle amount to be controlled is affected by a counter electromotive force, and thus the advance angle amount cannot be determined uniformly.

SUMMARY OF THE INVENTION

A motor control device according to an embodiment of the present invention includes a detection unit which detects a rotational phase of a rotor of a stepping motor, a generation unit which generates a driving waveform for driving the stepping motor, and a control unit which detects a phase difference between a rotational phase of the rotor and a phase of the driving waveform and controls an amplitude or a period of the driving waveform to control the phase difference, and the control unit determines a target phase difference from a variation of the phase difference with respect to a variation of the amplitude of the driving waveform to control the amplitude of the driving waveform. at least one processor or circuit is configured to perform a function of at least one of the units.

Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.

