Return and position control for a dc servo system

Abstract

An apparatus is provided for controllably moving a load in a return mode back to a first or home position by a motor driven shaft, which shaft moves the load toward a second position in a forward mode to track a moving object field. An apertured fan-shaped timing disk or element is secured to the rotating shaft to move therewith. A position feedback sensor senses the angular displacement of the shaft by generating a feedback signal upon optoelectronically sensing an aperture in both the forward and return modes. An optoelectronic sensor detects the passage of the moving object field to provide a return signal after the object field has passed a predetermined position. A motor and its amplifier controllably move the load back to the first position in the return mode in response to the return signal. The inertia of the system causes the shaft to rotate to move the load to the second position in the return mode after responding to the return signal. A return home circuit is responsive to the difference in the number of feedback signals in the forward mode and the up-to-date or current number of feedback signals in the return mode to provide an accelerating bias signal and then a decelerating bias signal to the amplifier to accelerate and decelerate the load respectively as the load moves back towards the first position.