| 摘要 |
900,686. Automatic control systems for spark machining apparatus. GENERAL MOTORS CORPORATION. July 21, 1960 [Aug. 7, 1959], No. 25429/60. Class 38 (4). [Also in Group XXIX] Spark machining apparatus is controlled in such a manner that the width of the gap between the electrode and workpiece is maintained at a predetermined value and that the speed at which the electrode is retracted from the workpiece is greater than the speed at which the electrode is fed towards the workpiece. A workpiece 12 is immersed in a tank filled with a dielectric liquid so as to be a predetermined distance from an electrode 10, the electrode position being altered by a fluid-pressure actuated system 16 and the power supply 14 to the electrode and workpiece being of the capacitor charge/discharge type giving intermittent sparking. The position of the electrode 10 is controlled according to the output of a circuit 96 into which are fed four signals:-a reference signal 100 which is representative of the required electrode position; a dither signal 104 which overcomes static friction in the fluidpressure system; a signal 108 which is representative of the actual position of the electrode 10 and lastly a signal from an electromagnetic device 122 which varies in polarity according to which the electrode 10 is moving towards or away from the workpiece 12. The resultant of these signals is fed to an amplifier 94 which energizes one or other of relays 78, 80 to move a reed 64 whereby the fluid-pressure device is caused to move the electrode 10 until the gap width attains the value set by the signal 100. The signal from the device 122 is associated with a circuit which includes a diode 134 so that the effect of the signal when the electrode 10 is being retracted is limited thereby causing rapid retraction of the electrode. When the electrode is being moved towards the workpiece the signal is not limited by the diode 134; thus the forward movement of the electrode is slower than that of retraction.
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