Abstract: Servo control circuits particularly suited for electric discharge machining apparatus to provide the input to the servomechanism which actuates the tool feed during machining.These circuits respond to a setting of desired gap emf and an input of actual gap emf to control tool movement so as to equalize these inputs. They respond to abnormally low gap emf during the machining "on" pulse to retract the tool to allow the gap to clear of debris.The gap emf during the "on" period of the pulse cycle is stored in a small capacitor coupled to a high-impedance input to power circuits of the servo control, which capacitor normally retains most of its charge during the "off" time of the cycle. Logic circuits responding to the pulse generator and the gap emf discharge this capacitor when abnormally low gap emf occurs during cycle "on" time.

Abstract: A control system for electronic discharge machining 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.

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.