Method and apparatus for position control of an electric motor

Abstract

A control process and apparatus for positioning an electric motor provided with a rotation angle detector at a designated position positively at a high speed without being accompanied with hunting notwithstanding variation in the motor current and inertia of a load. The control process activated upon starting of the motor and ending at the stoppage of the motor at the designated position includes a first control region in which acceleration of the motor having been started is detected and subsequently a constant speed operation of the motor is effected at a maximum speed. A deceleration initiating time point is determined in dependence on the acceleration. A second control region is provided in which the motor is decelerated in accordance with a deceleration pattern determined in dependence on a rotation angle extending between a position corresponding to the deceleration initiating time point and the commanded stop position, and motor torque and inertia of load is detected at the deceleration initiating time point. During a third control region the motor is progressively decelerated by reducing correspondingly the gain of voltage (current) applied to the motor when the motor position approaches to the commanded stop position. The control process also includes a fourth control region in which, when the motor stops short of or beyond the commanded position, the duty ratio of voltage applied to the motor is progressively increased to thereby re-start the motor toward the commanded position, and a fifth control region in which the motor is held at the commanded stop position.