GB1110595A - Improvements in or relating to presses suitable for use in performing cutting operations on sheet material - Google Patents

Abstract

1,110,595. Cutting-out presses. BRITISH UNITED SHOE MACHINERY CO. 27 May, 1965 [28 May, 1964], No. 22503/65. Heading B4B. In a cutting press comprising a bed 10, Fig. 1, having an electrically conductive pad 12, supporting a workpiece 14 of sheet material on which a knife 16 is placed, a beam 18 having an electrically conductive striking- plate 20, fluid-pressure control means for moving the beam towards and away from the bed and thereby urging the knife through the workpiece to contact the pad, the control means including an hydraulic piston and cylinder 24 supplied with fluid from a sump 28 by means of a pump P driven by a three-phase electric motor M which also drives a flywheel F, the pump supplying fluid through a solenoid valve having a spool 30 and a winding S energizable to cause the spool, and thereby the beam, to be moved downwardly, the control circuit of the press is arranged so that in response to slowing of the pump to a predetermined speed, the motor M is decelerated thereby de-energising the winding S to terminate the downward movement of the beam and cause the beam to return to its upper position. The control circuit comprises a transformer 60, Fig. 2, having a primary winding 62 and secondary windings 64, 66 and 68. When a handle 40, Fig. 1, on the beam is moved downwardly to move the armature 44 of a switch 42 from a contact 46 to a contact 48, the circuit containing leads 70, 72 is tripped to lock transistors 90, 100 to energize the winding S. The circuit is unlocked by means of a limit switch LS or by applying the voltage across a resistor 182 of a beam contact sensing circuit 150 across a resistor 112 to cut off transistor 100. This permits a bias supply containing secondary winding 66 to apply turn off reverse bias to transistor 90 thus de-energizing winding S. The circuit 150 for bringing about an automatic reversal of the beam on the completion of a cutting operation comprises two stages of amplification, including transistors 160, 180, and one stage, including transistor 190, providing a variable time delay. To indicate the presence of current above predetermined value in one of the leads of the motor M corresponding to slowing of the pump, the primary winding of a transformer 200 is connected with a lead 202 of the motor M, a secondary winding 204 of the transformer being connected in a circuit extending between the base of transistor 100 and lead 72 through a neon tube 206, a diode 208 and the primary winding. The diode is poled so that a negative voltage only is applied to the tube 206 which when it exceeds the breakdown voltage of the tube, is applied to the base of transistor 100 to turn it off. This causes transistor 90 to be turned off thereby deenergizing winding S.