Electric discharge machining apparatus

摘要

An electric discharge machining apparatus capable of precisely detecting the electric discharge in a case of performing machining by minute machining energy such as in finish machining. A voltage is applied between a tool electrode (1) and a workpiece (2) by repeating ON/OFF of a switching element to charge a stray capacitance between the electrodes to cause electric discharge between the electrodes by the charged voltage. The electric discharge between the electrodes in the electric discharge machining by the minute machining energy is detected. The current between the electrodes is detected by integrating an output of a sensor coil (3). An offset component superposed in the output of the integrator (4) is extracted by a low-pass filter (5). The extracted offset component is eliminated from the output of the integrator by a differential amplifier (6). An output of the differential amplifier is compared with a reference value to detect the electric discharge.