Overload control for mechanical power presses

Abstract

An overload control for a mechanical press wherein excess hydraulic pressure generated by the mechanical overload of the press is applied to a transducer which develops an electrical signal which in turn is applied to a circuit which is responsive to the magnitude of the electrical signal and to the time increment during which the magnitude of the electrical signal is developed and applied to the circuit. The circuit includes a timing and reference portion comprising a voltage divider network and an RC network, and the circuit also includes a differential amplifier responsive to a difference in magnitude between the transducer signal and a signal from the timing and reference portion. As a result, when the instantaneous signal from the transducer increases suddenly due to an actual overload on the press, the circuit responds and operates a relay to cause stoppage of the press. On the other hand, the circuit does not respond to a relatively slower change in the transducer signal resulting from a slow change in pressure during non-overload conditions.