Control system for stopping spindle at predetermined rotational position

Abstract

A system employed in a machine tool of the type in which a gear mechanism disposed between the spindle and spindle motor transmits the rotational motion of the motor to the spindle. The system allows the spindle to be brought to a stop at a predetermined rotational position in a shorter period of time when the gear mechanism is set in low gear, that is, while the rotational speed of the motor is being reduced by the gear mechanism as it is being transferred to the spindle. This permits the spindle to be stopped at the predetermined position in the same amount of time which is required when no reduction in speed takes place between the motor and spindle. When the spindle arrives at a region where it is to be controlled in order to stop at the predetermined rotational position, a position deviation signal for guiding the spindle to the position is applied as an input signal to a speed control loop for controlling spindle rotation. The position deviation signal varies in dependence upon the gear ratio of the spindle gear mechanism. Positioning gain, which is obtained by dividing the speed of the spindle motor by an amount of spindle motor rotation that depends upon the position deviation of the spindle; is controlled so that it remains constant regardless of the speed change ratio between the spindle and spindle motor as determined by the gear mechanism.