Servosystem for gap electrical machining processes (especially electroerosion)

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.