Servosystem for gap electrical machining processes (especially electroerosion)

Abstract

A servosystem for electrical machining processes adapted to regulate a spark-discharge gap in electrodischarge machining and other material-removal, shaping or forming operations in which the energy of an electrical discharge across the gap is exploited. Instead of the usual reference voltage or other electrical value for comparison with a gap parameter whereby the difference or other algebraic comparison controls the electrode drive, a gap detector is provided to feed a substantially continuous (analog) value to a discriminator having a threshold value and producing a digital output in accordance with the comparison. The digital output represents an "advance" or a "retract" condition and is communicated via a suitable switch or amplifier to the respective electromagnetic member of the control system, the latter member being a servomotor mechanically coupled with the movable electrode or a fluid-control valve hydraulically or pneumatically coupled with the movable electrode.

I claim: 
     
       1. In the electric-discharge machining of a conductive workpiece wherein a machining electrode and the workpiece electrode, at least one of which is movable, are spacedly juxtaposed to form a dielectric-filled machining gap therebetween and an electro-erosive discharge is intermittently effected across the gap while the gap spacing of the latter is maintained substantially constant as material is removed from the workpiece, a method of controlling said machining gap comprising the steps of: a. deriving an analog signal as a function of a gap variable representative of the gap spacing;   b. providing at least one threshold level corresponding generally to a preselected gap spacing, and establishing a first digital state upon said analog signal exceeding said threshold level and a second digital state upon said analog dropping below said threshold level;   c. deriving a first steep wavefront pulse signal of one polarity and a second steep wavefront pulse signal of the reverse polarity upon the establishment of said first and second digital states, respectively; and   d. shifting said movable electrode in response to said pulse signals in a direction determined by the presence and polarity of one of said pulse signals, said first and second digital states being disestablished upon said analog signal dropping below said threshold level and upon said analog signal exceeding said threshold level respectively,   said first and second pulse signals each being maintained during the presence of said first and second digital states, respectively, and   said first digital signal being a signal driving said movable electrode upwardly; and intermittently canceling said first digital signal while the electrode is in upward movement.     
     
     
       2. In a servocontrol system for electrical machining wherein a machining electrode and a workpiece electrode, at least one of which is servocontrollable, are spacedly juxtaposed to form a coolant-filled machining gap between them and an electrical machining current is passed through the gap to remove material from the workpiece, the improvement which comprises: motive means for controlling the position of said movable electrode relative to the counterelectrode and provided with a pair of control means individually energizable for generating command signals adapted to drive the movable electrode upwardly and downwardly,   a pair of electronic switches operatively coupled and respectively connected with said control means, said switches being operatively in conjugate relationship with one another with each operable substantially in cut-off and saturation ranges to de-energize the control means associated therewith,   means establishing at least one preset value for the machining gap spacing,   the first of said electronic switches being operable in response to a gap signal and adapted to become saturated, in response to said gap exceeding the preset value, to cut off the second switch, the latter being operative to become saturated upon said first switch being cut off in response to said gap signal dropping below a second threshold value.   
     
     
       3. The improvement as defined in claim 2 further comprising an oscillator operable, in conjunction with said first and second electronic switches, to provide an oscillatory signal adapted to intermittently cancel the electrode upward command while the electrode is being fed upwardly.