Patent ID: 7113884

Claim:
A positioning apparatus for controlling a gap between an electrode and a workpiece of a die sinking electrical discharge machine without directly contacting the electrode and the workpiece, the positioning apparatus comprising: a power supply for applying a pulse voltage between the electrode and the workpiece without machining the workpiece as the electrode approaches the workpiece; a discharge detecting means for detecting an occurrence of electrical discharge between the electrode and the workpiece resulting from the pulse voltage applied between the electrode and the workpiece, when the electrode and the workpiece are in a non-contact condition, and generating a pulse detection signal corresponding to a detection of the occurrence of the electrical discharge; a counting means for counting the pulse detection signal generated by said discharge detecting means and generating a counting completion signal when the pulse detection signal has been counted a predetermined number of times; and a means for generating a positioning completion signal on the basis of the counting completion signal from said counting means so that positioning is completed when the pulse detection signal has been counted said predetermined number of times.