Patent GB-1021815-A (GB)
Title: Control circuit for power press
IPC: F16P3/20
Filed: 1963-03-04
Abstract: 1,021,815. Locating magnetic and conducting bodies. DANLY MACHINE SPECIALTIES Inc. March 4, 1963 [Aug. 30, 1962], No. 8583/63. Heading G1N. [Also in Divisions F2, H2 and H3] A control for a power press comprises a discontinuous magnetic member rotatable with the shaft of the press and a transducer positioned to produce an A.C. output upon traversal of the discontinuity or discontinuities, the output being applied to a multi-stage transistor amplifier at least some of the stages of which include an output transformer so that if the transistors are open circuited or short circuited the amplifier output is reduced to zero and the control circuit fails safe. The shaft 15 (Fig. 2) of the press carries a metal disc 20 formed with a gap at 23 (Fig. 1) and having half its periphery provided with teeth 26. Located opposite the gap is a transducer 21 which interrupts an output signal when the gap traverses the transducer and opposite the teeth 26 is a second transducer 22 which produces an A.C. output so long as the toothed portion of the disc is moving passed the transducer. The signal from the latter transducer is used to ensure that the "run" push buttons of the press are maintained operated by the operator while the press slide moves to one extreme position and the signals from transducer 21 are used to ensure that the buttons are released before the machine recycles. The disc 20 is carried by a disc 30 driven directly by the shaft and provided at its periphery with teeth 32 which are engaged by projections 33 on the disc 20. The rotary position of the disc 20 relative to the shaft may be adjusted by sliding the knob 45 to the right (Fig. 2) against the pressure of spring 35, rotating the disc 20 by means of the knob and then allowing the projections 33 to return to a different tooth. The selected position is indicated by 41 (Fig. 1). The position of one transducer relative to the other may be varied by moving transducer 22 along a slot 27. In an alternative arrangement (Fig. 4, not shown) the disc 20 is provided with a slot instead of gap 23. In the control circuit (Fig. 5) the transducer 23 is provided with a primary winding 141 supplied with an A.C. signal and a balanced secondary winding arranged so that an output signal is produced from the secondary when the transducer is not opposite the gap in the disc. The output signal is applied to the base of a transistor amplifier biased by a circuit comprises a stabilizing thermistor 147 and the output from the transistor is applied through a transformer 150 to a full wave rectifier to produce a D.C. output signal at 165, 166. This signal is chopped by a transistor 170 controlled by mains driven transformer 171 so that a square wave output 175 is produced having a desired phase relation to the main supply. This square wave is applied through a stabilizing thermistor circuit 185, 186 to an amplifier stage 181, 182 feeding the output transformer 5TP. Diodes 187 and 188 are provided to prevent leakage current flow at high temperature and to provide bias for transistor 182. If any of the transistors become open circuit the A.C. output ceases and the circuit is designed such that this causes the control system to fail safe. Similarly, if any of the transistors become short circuit the A.C. output ceases, for example as a result of the transformers becoming saturated, and again the circuit fails safe. The transducer 22 may be alternatively of the permanent magnet type so that an A.C. output is produced so long as the teeth are moving passed the transducer. The output from this transducer is converted into a pulse signal having a desired phase relation to the supply voltage by a circuit (Fig. 6, not shown) similar to that shown in Fig. 5 and comprising an amplifier stage 145, a rectifier system, a chopper and an output stage. The control circuit described may be incorporated in the overall control system disclosed in Specification 1,021,814.