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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. The transistorized circuit directly supplying the servo valve operating coil (or other transducer controlling electrode feed) provides for control by inexpensive low power elements of small size and low energy dissipation.

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First Claim