Motor control apparatus

A motor control apparatus which is applied to an actuator provided with

• a motor that includes a stator having a plurality of salient poles, wound with three-phase windings, on an inner periphery, and a rotor having a plurality of salient poles on an outer periphery, and
• an encoder that outputs, at a predetermined angle interval, an A-phase signal and a B-phase signal that take either Hi or Lo accompanied by rotation of the rotor,
• the motor control apparatus driving the motor, the motor control apparatus comprising:
• a controller that learns an initial position of the rotor based on the A-phase signal and the B-phase signal acquired from the encoder in a state where two-phases out of three phases have been energized during initial drive after power-on, and also decides an energized phase based on a rotational position of the rotor during normal drive after the initial drive;
• and
• a drive circuit that performs switching operation to energize the energized phase, which is decided by the controller,
• wherein:
• the controller learns that, in learning the initial position,
• the initial position of the rotor is a two-phase facing position in which two adjacent salient poles of the rotor face salient poles of two energized phases of the stator when values of the A-phase signal and the B-phase signal are in a first state of both being Hi or both being Lo,
• the initial position of the rotor is a one-phase facing position in which one salient pole of the rotor faces a salient pole of one non-energized phase of the stator when the values of the A-phase signal and the B-phase signal are in a second state of both being Hi or both being Lo;
• the encoder is configured to include a rotary magnet having an annular shape and a magnetic sensor of a hall IC;
• and
• a magnetizing pitch of the rotary magnet is set to 7.5° between N-pole and S-pole.