Abstract: A control system, for a machine tool of the kind in which electrical energy passes across a gap between a tool electrode and a workpiece to erode the workpiece, comprises means for forming signals representative of the rate of erosion of the workpiece and the rate of undesirable erosion or "wear" of the tool electrode, and a computer means which receives the signals and combines them with a signal received from a data input device, which signal represents a desired optimum relationship between the two rates of erosion, and forms an appropriate output signal for controlling the machine tool. The data input device is usable, in rough machining operations where the tool electrode may be relatively cheaper than machine time, to ensure that machining is done in the shortest time by allowing a relatively high rate of tool wear and, in fine machining where the tool electrode is expensive, to ensure minimal tool wear at the cost of machine time.

Abstract: Two condition index variables are used for controlling operation in such a manner that one of the variables is kept as close as possible to a minimum value, while the other is held within an assigned range. Both condition index variables depend on the rate of flow of the flushing liquid through the working gap, on the interval between discharges in the gap or on the duty cycle or repetition frequency and amplitude of the discharge pulses. The condition index variable held to a minimum may be the integral of the square of the error signal from the regulating circuit of the electrode advancing drive, the integral of the square of the acceleration of electrode movement or the quotient obtained by dividing the square of the error signal by the square of the gap current. The regulating value to be held within an assigned range is a calculated breakdown potential defined by the relation of the variation of the error signal to the variation of the electrode spacing.

Abstract: The peak voltage of each discharge pulse is measured and, if the voltage of the pulse exceeds a high threshold value, there is also measured the time between the passing of that value and the moment the pulse voltage thereafter drops below a second lower threshold value. The two measurements are expressed in pulses that are combined, preferably by addition, to provide a regulating value, whose deviation ("error") from a standard value is predicted for a coming period, taking account of recent electrode position change as well as regulating value trend. The sign of the predicted error determines in which direction the electrode drive motor will be energized, but if the predicted error is less than a threshold value no motor energization occurs until the next error prediction.