Abstract: An apparatus is disclosed for use with an EDM machine for controlling the motion of the tool relative to a workpiece. In one embodiment, during the ON time, low power pulses are applied across the machining gap immediately prior to machining pulses. A gap voltage signal produced in response to the low power pulses is used exclusively as an input to control the tool feed mechanism. In another embodiment, the gap voltage signal produced by a low power pulse is combined with a gap current signal produced by a machining pulse to generate control signals which are used to produce command signals for the tool feed mechanism. Further, these control signals may be used to drive a meter which provides a visual indication of the general condition of the machining gap.

Abstract: In an EDM process, a method and apparatus are disclosed for determining the quality of a machining gap by detecting a voltage signal across the gap in response to a low power pulse applied immediately prior to a machining pulse. Upon detecting a first predetermined number of consecutive inferior gap voltage signals in response to corresponding low power pulses the application of low power pulses and machining pulses is terminated for a predetermined period of time. Thereafter, only the low power pulses are applied to the machining gap; and after detecting a second predetermined number of consecutive good gap voltage signals in response to corresponding low power pulses, the machining pulses are reapplied.