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Abstract

A control system for elecctronic discharge machine includes an automatic relay control and a current cutoff control of particular interest. The automatic relay control controls the energy level of machining pulses as a step function of machining cycle period by cutting in or out resistors in a power circuit through the machining gap. Higher frequency pulses are held to a lower current level to avoid power transistor overload. The relay control circuit includes multivibrators, energized at progressively higher values of pulse period by the counters, and an output circuit for each multivibrator which controls one of the relays which vary the gap circuit resistance. The relay control circuit also includes a threshold responsive circuit which senses any change in the several relay controlling output signals and acts to interrupt machining pulses briefly to allow time for relay operation. The current cutoff control circuit detects abnormally low voltage across the machining gap and reduces gap discharge energy level. Pulses referred to as 'probe pulses' replace the normal master pulses to control gap discharge time duration and time spacing. A logic circuit controls probe pulse duration relative to master pulse duration. It provides for further lowering probe pulse energy by squelching probe pulses periodically if the master pulse period is below a certain time.

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