GB1423247A - Electric discharge machining - Google Patents

Abstract

1423247 Automatic control of discharge machining INDUSTRIELLE ELEKTRONIK AGIE LOSONE BEI LOCARNO AG 30 Oct 1973 50456/73 Heading G3R The gap width in electro-erosion apparatus is controlled in accordance with measurements of the peak voltage of an applied voltage pulse and the time between the moment when the voltage first exceeds a first predetermined valve and the moment when the voltage subsequently reaches a second lower predetermined value. As shown, the gap voltage is sensed by a detector 3 containing a plurality of pre-set voltage levels m. As the sensed voltage reaches each level, a signal is supplied to a storage register 4 which therefore stores a count representing the peak voltage reached during the pulse. The register 4 also supplies signals to a gate circuit 6 at the moments if and when the predetermined voltage values are reached, and a counter 7 receives clock pulses from a generator 14 during the appropriate time interval, if any. At the end of the applied voltage pulse, the contents of register 4 are added into counter 7 which therefore now holds a value representative of both the peak voltage and duration measurements. This value is fed into a buffer register 10 and then into a regulator circuit 15 which controls the drive of tool electrode 1. The regulator 15 includes an averaging circuit (17), Fig. 4 (not shown), which receives and averages say, four or five successive signals from the register 10 and feeds the result to an add/ subtract circuit (21) which also receives a reference value input, a signal representing the difference between the current and next preceding average values, and a signal representing the difference between the current and preceding electrode positions. The resulting combined control signal is supplied to a logic circuit (24) which determines the motor drive current in dependence on the magnitude and sign of the signal. If the absolute value of the control signal is less than a predetermined value, no drive current is supplied. The arrangement may be adapted for the control of a multiple electrode machine. In this case, the peak voltage for each gap is measured, but the relevant time duration signal is measured only for the electrode with the lowest peak voltage. A control signal is computed in respect of this electrode and is used to control the drive of all the electrodes simultaneously.