Electrical control system for hydraulic equipment, in particular for hydraulic presses

摘要

754,959. Electric selective control systems. DENISON ENGINEERING CO. April 12, 1954 [April 21, 1953] No 10708/54. Class 40(1) [Also in Group XXIX] A reversible fluid pressure motor is controlled by a directional control valve, the spool of which is displaced proportionally to the current flow in the actuating solenoid therefore, this current flow being regulated by marginally operated relays the supply to which is controlled by variable resistors adjusted by the motor The invention is described as applied to a hydraulic press in which the normally retracted ram 25 is advanced rapidly for the first portion of its stroke and then at a reduced rate, andis automatically retracted from a predetermined position. To initiate an operating cycle of the press a start switch 68 is momentarily closed to energize the start-relay 46 which in turn operates a relay 47. Relay 47 locks and energizes the operating coil 38 over an adjustable resistor 87 to move the spool 30 of the control valve 20 to the right. Fluid pressure is thereby admitted to the top of the cylinder 23 to advance the ram 25 at a rapid rate. The ram, as it moves adjusts through a mechanical linkage 60, potentiometers 53, 54, 55 to vary the current flow in relays 50, 51, 52 which are preset by potentiometers 61-63 so as to operate sequentially as the ram is advanced (downwardly) to predetermined positions. The operation of relay 50 has no effect during forward movement of the ram but when relay 51 operates, relay 47 falls off and the energization of coil 38 is now effected over contacts 97, 88 and a resistor 92, adjusted so as to reduce the current flow in coil 38 and hence to reduce the rate of ram advance. When the ram advance energizes relay 52, a relay 48 is energized. This de-energizes the coil 38 and energizes coil 40 over a resistor 102 to move the spool 30 to the left whereby the ram advance is stopped and its retraction started. The retraction speed is set by the resistor 102 and retraction continues until the relay 50 is de-energized by the ram movement to release relay 48 when the spool centralizes under spring bias to stop the ram. By closing a switch 74 the start relay 46 locks when operated and causes continuous cycling of the system until a stop switch 70 is opened.