| 摘要 |
PURPOSE:To make both a large area machining and a finish machining possible by applying a voltage during a pause period through a current restricting resistor for a dc power source for machining, detecting an impedance between electrodes, and controlling to change an internal impedance of the power source. CONSTITUTION:Applying a voltage lower than an arc voltage between electrodes 1 and 2 during a pause period from a machining power source 3 through a current restricting resistor array 5, and detecting the voltage or current between the electrodes by means of a detecting means 10, an impedance between the electrodes is calculated with an operation means 11. Obtaining internal impedances Rx and Ry of the machining power source 3 so as to respectively supply a no load voltage higher than a spark generating voltage during a time of no load and to supply a required machining current after a detector 9 detects the spark generation, a series of actions of switching the current restricting resistor array 5 through a power transistor array 4 are repeated and controlled after the pause period. In this way, the optimum no load current and the required machining current are obtained to make machinings in areas of both a large area machining and a finish machining possible.
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