Sensorless motor driving apparatus

摘要

Disclosed is an apparatus designed to easily and precisely drive a brushless motor by means of sensorless controlling even in a low-speed range. When the motor (1) at rest is started, phase excitation is performed twice such that two different phases are excited. A commutation reference point is set at a position at which the rotor has stopped after the second-time excitation. A position detector outputs pulses in response to a movement of an object driven by the motor (1). The pulses output from the position detector are monitored and commutation is controlled on the basis of the number of pulse edges as counted starting from the commutation reference point. For example, the number of pulse edges output during a period starting from the commutation reference point and ending at a point of time at which commutation should be performed is measured in advance. When the number of pulse edges with reference to the commutation reference point becomes equal to the above predetermined number, it is determined that commutation timing has reached, and commutation is performed.