Electric heating – Metal heating – Cutting or disintegrating
Patent
1989-07-03
1991-04-09
Evans, Geoffrey S.
Electric heating
Metal heating
Cutting or disintegrating
219 6913, B23H 102, B23H 714
Patent
active
050066935
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a gap voltage detector for use in a wire-cut electric discharge machine, which is capable of accurately detecting a gap voltage between a wire electrode and a workpiece.
In a wire-cut electric discharge machine, it is known to effect appropriate control of electric discharge machining on the basis of a detected value of a gap voltage between a wire electrode (hereinafter referred to as wire) and a workpiece. Conventionally, a voltage between the workpiece and a conductor disposed above or below the workpiece for connecting a machining power source with the wire, is detected as the gap voltage. However, the thus detected voltage includes voltage drop components attributable to a wire resistance between the conductor and the workpiece and an inductance therebetween. As a position at which electric discharge occurs between the wire and the workpiece varies, a variation occurs also in these voltage drop components. In particular, a large variation in these components is found when the workpiece has a large thickness. As explained above, the detected voltage includes variable components attributable to a variation in the electric discharge position, and hence cannot indicate an accurate gap voltage.
Further, it is also known to subtract a correction value representative of a voltage drop component attributable to an inductance between the conductor and the workpiece from the detected voltage, so as to correct the detected voltage, as disclosed in Japenese Provisional Patent Publication No. 61-180719. However, even in this case, the detected voltage thus corrected cannot indicate an accurate gap voltage because the just mentioned correction value does not reflect a variation of the voltage drop component. Also, the gap voltage cannot be detected accurately, in the case of effecting correction for voltage drop component associated with the wire resistance.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a gap voltage detector for use in a wire-cut electric discharge machine which is capable of eliminating an adverse effect due to a variation in an electric discharge position, thereby permitting an accurate detection of a gap voltage between a wire electrode and a workpiece.
In order to achieve the aforementioned object, a gap voltage detector in a wire-cut electric discharge machine according to the present invention, comprises: means for detecting a first voltage between a first conductor and a workpiece; means for detecting a second voltage between the workpiece and a second conductor which is disposed in a facing relation with the first conductor; and means for detecting a gap voltage on the basis of the sum of the thus detected first and second voltages.
Preferably, the gap voltage detector includes means for detecting an electric discharge current, and means for detecting a differential value of the electric discharge current, and is operable to detect a first voltage drop component, attributable to a wire resistance between the first and second conductors, and a second voltage drop component, attributable to an inductance between these conductors, on the basis of the detected electric discharge current and its differential value. The device is further operable to correct the sum of the first and second voltages by the use of the detected first and second voltage drop components, to thereby detect the gap voltage.
As explained above, according to the present invention, since the gap voltage is detected on the basis of the sum of the voltages between the first conductor and the workpiece and between the second conductor and the workpiece, and preferably, the sum is corrected by the voltage drop components attributable to the wire resistance and the inductance between these conductors, an accurate gap voltage can be detected free from an adverse effect due to a variation in electric discharge position.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view showing an essential part of a wire-cut electric discha
Izumiya Syunzo
Obara Haruki
Evans Geoffrey S.
Fanuc Ltd
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