Patent GB-1396025-A (GB)
Title: Circuit arrangement in a spark erosion machine
IPC: B23H7/18
Filed: 1972-09-19
Abstract: 1396025 Electro-erosion AEG-ELOTHERM GmbH 19 Sept 1972 [28 Sept 1971] 43408/72 Heading B3V In a spark erosion machine, the erosion pulse intervals are lengthened when the number of detected ineffective erosion pulses exceeds a predetermined fraction of the number of pulses actually generated by a clock pulse generator 2 which controls a generator 1 comprising an electronic switch for pulsing the voltage of a D.C. source, and the pulse intervals shortened when the number of ineffective pulses falls below the same or a smaller fraction of the number of generated pulses. The spark voltage at the erosion gap 4 is applied to a circuit 5 which produces an output voltage 11 if it is greater than a reference voltage 10, e.g. 15 volts, indicative of an effective erosion pulse. The spark current at the gap 4 is measured at 6 and applied to a circuit 8 which produces a current signal 9. The circuits 5, 8 are connected to a gate (17) (Fig. 2a, not shown) of a logic circuit 15, the output of the gate (17) being fed together with a clock pulse signal 14, obtained from the generator 2 via a circuit 13, to a gate (18) which generates a signal 16 when no erosion pulse is formed. The output signal 16 is fed together with the clock pulse signal 14 into a comparator circuit 20 which delivers control signals for regulating the feed rate of the electrode tool when the number of ineffective erosion pulses is too high or too low and control signals via a line 22 to a pulse interval adjuster 24 when the number becomes even higher or lower. In one embodiment Fig. 4, the comparator circuit 20 includes a counter 27 for receiving the clock pulse signal n i  and a second counter 28 for receiving the output signal n 0  of the detector circuit 19. The counter 28 produces an output 33 when the count is 17% of the counting capacity, e.g. 10<SP>4</SP>, of the counter 27 and an output 34 when the count is 22%. The counter 27 produces an output 29 when it overruns its counting capacity to cause, via multivibrators 31, 32, the other counter 28 to be reset to zero, and an output 37 when the count is 10<SP>4</SP>-3. When the number of ineffective pulses is less than 17%, an output signal 37 is first produced by the counter 27 and delivered via an open gate 39 to a flipflop 40 which produces a control signal U S 2 for shortening the pulse intervals of the generator 2. Subsequently, the counter 27 reaches its capacity to reset the circuit for another counting cycle. If the number of ineffective pulses is between 17 and 22%, an output signal 33 produced at the counter 28 is applied to the multivibrator 31 which closes the gate 39 so that the subsequent output signal 37 will be ineffective and no control signal will be transmitted from the circuit. When the number of ineffective pulses is above 22%, an output signal 34 is transmitted from the counter 28, after the production of the signal 33, to the multivibrator 32 which actuates a flip-flop 43 to generate an output signal U S 1 for lengthening the pulse intervals. Alternative comparator circuits 20 are described (Figs. 5 and 6, not shown).