Patent GB-810241-A (GB)
Title: Improvements in or relating to presses suitable for use in performing cutting operations on sheet materials
IPC: B26D7/24
Filed: 1956-09-15
Abstract: 810,241. Cutting-out presses. BRITISH UNITED SHOE MACHINERY CO. Ltd. (United Shoe Machinery Corporation). Sept. 13, 1957 [Sept. 15, 1956], No. 28263/56 Addition to 764,634. Class 31 (1). In a press comprising a bed and a presser member between which sheet material and a cutting die are positioned, power-operated means for bringing about relative movement of approach between the bed and presser member, to causes penetration of the sheet material by a cutting edge of the cutting die and, subsequently, relative movement of separation between the bed and presser member, control means for the power-operated means including an electric circuit arrangement which is so constructed and arranged as automatically to arrest the relative movement of approach between the bed and presser member in the urging of the cutting edge of the cutting die through the sheet material, as a consequence of the engagement of a cutting edge portion of the cutting die with the bed, and operator-actuatable means for initiating the action of the poweroperated means to bring about relative movement of approach between the bed and the presser member, means is provided for automatically rendering the operator-actuatable means ineffective unless the control means is capable of exercizing its control function on the power-operated means. As shown, a beam 18 is movable towards and away from a stationary bed 10, on which sheet material 14 and a cutting die 16 are positioned, by means of a fluidoperated motor comprising a piston 22 movable in a cylinder 24, the supply of fluid to the ends of which is controlled by a spring-biased axially movable valve element 28 which is connected to the armature of a solenoid 40 so that when the latter is energized the piston 22 and therefore the beam 18 are moved downwardly. The bed 10 includes a work-supporting member 12, which may consist of conductive rubber, and the beam 18 includes a metal striking plate 19. Action of the fluid-operated motor is initiated by means of a switch 42 having an operating handle 44. The initiating circuit includes four relays 50, 52, 54 and 56. Operation of the initiating means causes the relay 50 to be energized to bring about delayed energization of the relay 52. Upon energization of the relay 52, a lock-in circuit for the relay 50 is formed extending near the lower end of a supply line 46 through contacts 54a, contacts 52d, to the coil of relay 50 and back to a supply line 48. At the same time, an energizing circuit for the solenoid 40 is completed, the circuit starting from the same point on line 46, and extending through contacts 54b, through contacts 52c, to the solenoid and back to line 48. Control means for automatically modifying the operation of the fluid-operated motor comprises two thyratrons 60, 62 which are connected through a time-delay circuit 80 to be fired in sequence by an appropriate signal (i.e. upon completion of the cut or in case a portion of the operator's body should accidentally come between the beam and the bed during a cutting stroke) at the control grid 64 of the thyratron 60 to energize the relay 54 from a power supply 68 through contacts 52b or 50c to interrupt both the lock-in circuit to the relay 50 and the energizing circuit to the solenoid 40, thus causing the valve element 28 to be moved, by its spring 38, into a position in which the fluid-operated motor returns the beam to its upper position. Should the modifying control means not be capable of performing its control function of opening the contacts 54a, 54b in response to the appropriate signal, the stroke-initiating circuit is disabled by energizing the relay 56 whose contacts 56a are in series with the switch 42. An equivalent disabling means is shown in Fig. 2 where a solenoid 82, when energized, bars movement of a handle 44a. The relays 50, 52 provide means for temporarily transferring the function of the modifying control means to the disabling means. At the same time, the relay 50 through its contacts 50b provides a means for providing a signal to the modifying control means which should cause it to perform its control function and open the contacts 54b. This signal is provided by shunting out all bias voltage by effectively connecting the grid 64 to the cathode 74 by grounding the negative side of the bias voltage supply. If the modifying control means is then able to perform its function, the relay 56 (or the solenoid 82) will be de-energized and the initiating means will be operative to initiate a cutting stroke. The relays 50, 52 then act to return the control function of the modifying control means to the fluid-operated motor by re-connecting the contacts 54b in the energizing circuit to the solenoid 40. At the same time, the bias supply is ungrounded and the modifying control means is returned to its normal operating conditions. In operation, the initial condition of the circuits and control relays is as shown in Fig. 1. When the main switch MS is closed, the disabling circuit comprising the relay 56 (or the solenoid 82) is immediately energized. This condition continues until the thyratrons 60, 62 have fired, at which time the relay 54 will de-energize the disabling circuit and the operator may then use the machine. If at any subsequent time, tube or component failure should render the modifying control means unable to energize the relay 54, the operator will be unable to initiate a cutting stroke. If the disabling circuit is deenergized, each time the operator presses down the handle 44 or 44a, the relay 50 will be energized (through the circuit extending via contacts of switch 42 or 42a) (a) to energize (through the closing of contacts 50a) a delayed energizing circuit for the relay 52, (b) to unground (by the opening of contacts 50b) the input of the modifying control means, (c) to disconnect (by the opening of contacts 50c) the plate voltage supply from the thyratrons to permit them to deionise, and (d) to interrupt (by the opening of contacts 50d) the disabling circuit Shortly thereafter, the relay 52 pulls in to restore (viacontacts 52b) the plate voltage to the thyratrons, to complete the energizing circuit (via contacts 52c) to the solenoid 40, and to com plete a holding circuit (via contacts 52d) for the relay 50, thus re-transferring the control function of the modifying control means to control of the fluid-operated motor. Specification 794,979 is referred to.