Controller for wire electric discharge machine

Abstract

A controller for a wire electric discharge machine which can achieve stable machining with high surface accuracy without requiring adjustment of a gain or the like in wire-electrode feed control. A discharge gap detection unit detects a voltage between a wire electrode and a workpiece. An amount-of-machining-per-unit-distance change detection unit obtains an average machining voltage, and a voltage drop Ethat is a difference between the obtained average machining voltage and a no-load voltage. A comparative determination unit obtains a ratio E/Ebetween a reference voltage drop Estored in a reference-amount-of-machining-per-unit-distance relative value storage unit and the drop voltage E. A feed pulse arithmetic unit obtains a feed speed that makes the amount of machining per unit time constant, on the basis of the ratio E/Eand a predetermined feed speed, and distributes feed pulses to motors to thereby move the wire electrode relatively to the workpiece. Since the amount of machining per unit time is kept constant, the surface accuracy in finishing is high and stable machining can be performed.