Servosystem for electrical machining processes

Abstract

A servosystem for electrical .[.maching.]. .Iadd.machining .Iaddend.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 .[.(anlog).]. .Iadd.(analog) .Iaddend.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. A servocontrol system for relatively positioning a pair of electrodes spacedly juxtaposed across a current-traversing gap, comprising: gap-monitoring means connected across said electrodes for producing an electrical signal representing the gap width;   a first SCHMITT trigger circuit connected to said gap-monitoring means and having an output element;   motive means including coil means energizable to displace said movable electrode in opposite directions;   a first electronic switch connected in circuit with an electrical power source and said coil means and connected to said element and responding to said first SCHMITT trigger for operating said motive means in one direction;   a second SCHMITT trigger connected to said element of said first SCHMITT trigger; and   a second electronic switch connected to said second SCHMITT trigger and in circuit with said source and said coil means for operating said motive means in the opposite direction upon detection by said second SCHMITT trigger of a condition at said first SCHMITT trigger rendering said first electronic switch ineffective.   
     
     
       2. The system defined in claim 1 wherein said gap-monitoring means includes a voltage divider connected across said electrodes and a diode in series with said voltage divider. 
     
     
       3. The system defined in claim 1 wherein said first SCHMITT trigger is provided with a variable resistor establishing a threshold level for the electrical signal representing the gap width. 
     
     
       4. The system defined in claim 1 wherein said coil means includes a pair of oppositely effective coils, said first electronic switch comprising a transistor having one of said coils connected in series with the collector-emitter network thereof, the second electronic switch constituting a transistor having the other of said coils connected in series with the collector-emitter network thereof. 
     
     
       5. The system defined in claim 4 further comprising a respective variable resistor in series with each of said coils. 
     
     
       6. The system defined in claim 5 wherein said first SCHMITT trigger is provided with an amplifier transistor constituting said element and connected to the base of the transistor constituting said first electronic switch, said second SCHMITT trigger having an input transistor with a base connected to said amplifying transistor. 
     
     
       7. The system defined in claim 1 wherein at least one of said SCHMITT triggers defines an operating threshold, further comprising means for automatically modifying said threshold in response to a parameter of said gap. 
     
     
       8. The system defined in claim 1 wherein said gap-monitoring means includes an integrating network between said electrodes and said first SCHMITT trigger. 
     
     
       9. The system defined in claim 1 wherein said movable electrode is a tool electrode and the other electrode is a workpiece electrode, said apparatus further comprising means for circulating a liquid coolant through said gap.