Safety interlock circuit for an error-signal-controlled servo system

摘要

In a servo system for manipulating a displaceble member in response to movement of a control through corresponding changes of position, which operates by comparing an electrical signal representative of the position of the control with an electrical signal representative of the position of the displaceable member to provide error signals which can drive the displaceable member in either of two opposite directions, a safety interlock circuit is provided which detects the presence of an error signal in either direction immediately after the application of operating voltage or immediately after the switching of the machinery into a different mode of operation and locks the displaceable member in position if an error signal initially appears until the error signal is cancelled by bringing the manual control into a position corresponding with that of the displaceable member. Unexpected sudden movements that may endanger personnel are thereby prevented. The invention is illustrated with reference to mobile agricultural machinery.