Patent GB-1021814-A (GB)
Title: Control circuit for power press
IPC: B30B15/14
Filed: 1963-01-28
Abstract: 1,021,814. Controlling clutch brake combinations. DANLY MACHINE SPECIALTIES Inc. Jan. 28, 1963 [Jan. 29, 1962], No. 3493/63. Heading F2L. [Also in Division H3] A " fail-safe " control circuit for the clutch and brake of a press comprises a transistor which, when energized at its input by an A.C. signal and at its output by a rectified A.C. signal, produces a control signal in an output transformer, the latter having a core which saturates if the transistor becomes shortcircuit so that no output signal is produced. The basic circuit element used is shown in Fig. 7. A first signal derived from the A.C. mains supply may be applied through transformer IT and the first diode 34 of an OR gate to the base of transistor T1A and a second similar signal may be applied through transformer 4T and the second diode 52 of the OR gate. A third signal, also derived from the mains supply, may be applied through transistor 2T and a fullwave rectifier circuit 111, 112 to the collector circuit while a fourth similar signal may be similarly applied through transformer 10T. In the presence of either one of the base circuit signals and either one of the collector circuit signals, pulses of current flow through the transistor producing an A.C. output in the secondary of transformer 3T. If transistor T1A becomes open-circuit no output signal is produced while if it becomes short-circuit the flow of current pulses is such that the output transformer 3T is saturated and a negligible output is produced. If one of the rectifiers 111, 112 becomes short-circuit the secondary of transformer 2T becomes effectively short-circuited so that again no output is produced. If one of these rectifiers becomes open-circuited no output is produced if it is that one which conducts simultaneously with the emitter base circuit, while if it is the other rectifier no substantial reduction in output takes place. Accordingly the circuit fails safe in any of these conditions. Press control system (Fig. 1, not shown).-The slide of the press 10 is driven by a motor 12 through a clutch 13 operated by a control solenoid 15 actuating an air valve. The solenoid is controlled by a circuit 20 comprising a selector switch 21, a " run-inch " switch 22, a " stop at top " switch 23 and an " emergency stop " switch 24, control also being dependent upon the action of a limit switch 11. In the detailed circuit, Figs. 3 and 3a, transformer IT is normally energized and its secondary is connected through rectifier 34 to energize the base circuit of transistor T1A. In addition, the primary of transformer 10T is energized through the normally closed contacts LS2a and LS6a to supply full wave rectified D.C. through rectifiers 111 and 112 to the collector emitter circuit of transistor T1A. Accordingly an output signal is produced in transformer 3T. Secondary TSA of this transformer applies current to the emitter base circuit of a transistor T1B in series with a biasing rectifier 74. The collector circuit of this transistor is connected in series with the collector circuit of a further transistor T1C which is energized from a fullwave rectifier 68 receiving power from transformer winding 5TSA, the primary winding of which is energized through a normally closed contact LS1 of an " anti-repeat " switch. On closing the " run-inch " button, contact 22A is made energizing the primary winding 6TSP of a transformer 6T. Secondary winding 6TSB is connected in series with a full-wave rectifier 72 to supply the collector emitter paths of transistor T1C and T1B in series, the path also including output transformer primary winding 7TP. Thus, when the " run-inch " button is operated current pulses now pass through the primary winding 7TP, the secondary windings 7TSA and 7TSB energizing the base emitter circuits of push-pull output transistors T3A, T3B. The second secondary winding 6TSA of the nowenergized transformer 6T is connected in series with the full-wave rectifier 85, 86 to energize the collector emitter circuits of transistor T3A and T3B. Accordingly, current pulses flow in the primary winding 9TP of the output transformer energizing the solenoid 14 to operate the clutch controlling a press. The second secondary winding 3TSB of the output transformer 3T of transistor T1A energizes through a full wave rectifier circuit, the collector emitter path of a " holding " transistor T2. The base emitter path of this transistor is energized by winding 5TSA of a transformer the primary winding of which is energized through " anti-repeat " switch LS1 from the A.C. supply. The resulting current pulses in the primary of the output transformer 4TP energize secondary winding 4TS connected in the base emitter circuit of transistor T1A to provide a holding circuit for transistor T1A when the " run-inch " button on being depressed opens contact 22B in the energizing circuit of transformer IT so removing the initial energization of T1A. Part of the secondary winding of the output transformer 9T is connected to a full-wave rectifier 105, 106 which is connected in series with the output winding 7TA of the series transistor circuit T1C, T1B and as the base circuit of this transistor is energized through winding 5TSB or 8TS the transistor conducts and provides an alternative energizing circuit for winding 7TP. If now the " run-inch button " is released the energizing circuit through transformer 6T is broken at contact 22a interrupting the solenoid current and stopping the press. Accordingly the press may be " inched onwards " by momentary operation of the button. However, at a point in the cycle a limit switch operates to complete alternative circuits to the " run-inch " button contacts. Thus, for example, contacts LSQ and LS6 energize the primary winding of a transformer 2T so energizing winding 2TSB which through its full wave rectifier circuit provides an alternative source of energization for the output amplifier. Accordingly the press now runs when the button is released. If the single-cycle condition has been selected by the control unit an anti-repeat switch LS opens just prior to the completion of the cycle. Contact LS1 opens the primary winding circuit of transformer 5T releasing the holding transistor and de-energizing transistor T1A. Contacts LS2 and LS6 de-energize the primary winding of transistor 8T, de-energizing the " run " transistor T1D. The solenoid is de-energized and the press stops. Stopping would still be effected even if the " run-inch " button had remained depressed and momentary release and depression must take place to restart the operation. If, however, the selector switch in the control unit had been set for continuous operation, the cycle would have been repeated indefinitely until a " stop at top " button had been depressed. This removes energization earlier in the cycle than the " anti-repeat " limit switch because the machine would be running faster. An " emergency stop " button is also provided and the circuit is arranged so that this cannot be used as an inching control. If it is desired to protect against permanent short-circuiting of the " run-inch " contact 22b, the output of transformer 1TP can be rectified in circuit 124 and applied to the base of transistor T1B in opposition to the output of winding 3TSA so that transistor T1B is de-energized so long as the short-circuit is present. Capacitors and resistors are associated with various windings to improve the wave shape and prevent ringing, while a capacitor 113 is connected in the collector circuit of transistor T1A to maintain conduction of transistor T1A while switching conditions are changing over. The clutch may be associated with a brake. Figs. 4, 5 and 6 (not shown) illustrate the circuit connections under various operating conditions.