Patent ID: 6925916

Claim:
A method for operating a press, wherein the press includes a frame, a table mounted on the frame for supporting a workpiece, a hydraulic actuator mounted on the frame, an actuator piston sliding within an actuator bore, and an actuator piston rod attached to and projecting from the actuator piston toward the table, wherein the actuator piston rod has an end for transferring force from the actuator piston to the workpiece, said actuator piston defining between itself and an end of the actuator bore an actuator pressure chamber, said actuator having a fluid port in flow communication with the actuator pressure chamber, and said actuator piston moves between a retracted position, at which the piston rod end is retracted from the table, and an extended position, at which the piston rod end is adjacent to the table, the method comprising: a) supplying relatively low pressure fluid to the actuator's fluid port in response to a start signal, wherein the pressure of the low pressure fluid is such that a light obstruction such as a human finger can block movement of the actuator piston; b) sensing the position of the actuator piston rod end, and providing a continue signal in response to the actuator piston rod end achieving a predetermined spacing from the table between the retracted and extended positions of the piston rod end relative to the table, wherein blocking of the actuator piston by the light obstruction before the predetermined spacing is reached will prevent the continue signal from being sent; and c) supplying relatively high pressure fluid to the actuator's fluid port in response to the continue signal, wherein the supplying includes pumping the low pressure fluid with a low-pressure supply piston, and the method includes performing the sensing of the piston rod end by sensing a physical feature of the low-pressure supply piston.