Method and apparatus for controlling zero-point return of a movable element

An apparatus for controlling the return of a movable element of a machine tool to a predetermined grid point by controlling movable element drive means in accordance with feedback pulses generated by an encoder operatively connected to said movable element, while said drive means is being driven to transport said movable element between grid points, said apparatus comprising:

• a current position counter, operatively connected to said encoder for sensing and storing the current position of said movable element;
• control means, operatively connected to said current position counter, for specifying a position remote from said predetermined grid point by a distance which is less than the spacing between grid points, and for producing a signal indicative of the deviation between said specified position and the current position of the movable element stored in said current position counter;
• a driving circuit, operatively connected to said control means, said encoder, and said drive means, for driving said drive means on the basis of the difference between said signal indicating the deviation and said feedback pulses, and for providing said control means with a reduced speed signal when said difference attains a value of zero;
• and
• an inhibit circuit, operatively connected to said driving circuit and said control means, for inhibiting the delivery of said reduced speed signal to said control means in order to stop said movable element at the first grid point encountered after the generation of said reduced speed signal.