Method and apparatus for the automatic control of an electrical discharge machining operation

The method for the automatic control of an electrical discharge machining operation consists in measuring the electric resistance of the spark gap during additionally produced periodic pauses between the pulse groups of the generator. The size of the electric resistance is determined from the voltage drop at the spark gap, which linearly depends upon the resistance to be measured of this spark gap. This voltage drop is produced at the spark gap mentioned only for the duration of the spark-gap resistance measurement. The apparatus intended for carrying out this method contains a current source (1), which is connected via a diode (2) to the electrodes (3, 4) which form the spark gap (5), as well as a timing pulse generator (6) which is electrically connected to a pulse generator (7) and a measuring device (9) for the electric resistance. In addition, the pulse generator (7) and the resistance-measuring device (9) are attached to the electrodes (3, 4). The current source (1) contains a transistor (10) and two voltage sources (11, 12). The outputs of one voltage source (11) are connected to the electrodes (3 or 4) via the diode (2) and the base/collector transition of the transistor (10). The outputs of the other voltage source (12) are applied to the base and the emitter of the transistor (10), and its input is electrically connected to the timing pulse generator (6).