Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Patent
1994-02-04
1996-01-23
Wieder, Kenneth A.
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
324551, 219 6913, 219 6919, B23H 102
Patent
active
054867657
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a wire-cut electrical discharge machine, more particularly, to an insulating condition detecting apparatus for detecting the recovery of insulation between a wire electrode and a workpiece.
BACKGROUND ART
In a wire-cut electrical discharge machine, machining is effected by applying voltage between a wire electrode and a workpiece, thereby causing electrical discharge between the wire electrode and the workpiece. An insulating machining fluid is supplied between the wire electrode and the workpiece, so that insulation between the wire electrode and the workpiece is recovered with a termination of every cycle of electrical discharge. After the insulation is recovered, voltage is applied again between the wire electrode and the workpiece, thereby causing an dielectric breakdown and resulting electrical discharge. If another electrical discharge is started without recovering the insulation between the wire electrode and the workpiece after the preceding electrical discharge, the electrical discharges occur in one and the same place (concentrated electrical discharge), thereby adversely affecting the accuracy and quality of the machined surface. If such concentrated electrical discharge has occurred, the machining will have to be suspended.
Conventionally, in order to check whether or not the insulation is recovered, a voltage from another power source, separate from the power source for electrical discharge machining, is applied between the wire electrode and the work piece during the off-time in which no voltage for machining is applied between the wire electrode and the workpiece, and the voltage between them are detected.
If a special power source separate from the power source for machining is used, as in the conventional method, in order to detect the recovery of the insulation between the wire electrode and the workpiece, it needs to provide such power source and its control circuit which render the wire-cut electrical discharge machine costly.
SUMMARY OF THE INVENTION
The present invention provides an insulating condition detecting apparatus capable of detecting insulation between a wire electrode and a workpiece by utilizing a power source for electrical discharge machining without the use of any special power source for detection.
An insulating condition detecting apparatus according to the present invention comprises a capacitor for storing a charging voltage applied between a wire electrode and a workpiece, a switching element for charging the capacitor, a switching element for electrical discharge formed of a semiconductor to apply the charging voltage of the capacitor between the wire electrode and the workpiece, voltage detector, to operate for a period during which the switching element for electrical discharge is turned off and including a period during which the switching element for charging is turned on, to detect the voltage between the wire electrode and the workpiece, and discriminator for comparing the voltage detected by the voltage detector and a set reference value in order to discriminate an dielectric breakdown when the detected voltage is lower than the reference value. The voltage detector may be composed of a peak hold circuit which includes a switching unit and a capacitor.
When the discharging switching element is composed 10 of a semiconductor, a certain voltage is produced between the wire electrode and the workpiece while the capacitor is being charged by turning on the charging switching element with the discharging switching element kept turned off. Presumably, this is attributable to the influence of a leakage current from the discharging switching element which is formed of the semiconductor. The presence of this voltage is confirmed by an experiment. According to the present invention, the voltage between the wire electrode and the workpiece is detected by the voltage detector, utilizing the aforementioned phenomenon, during the so-called off-time period through which the discharging switching element is kept turne
REFERENCES:
patent: 3969602 (1976-07-01), Matulaitis
patent: 3997753 (1976-12-01), Inoue
patent: 4329558 (1982-05-01), Martin
patent: 4602142 (1986-07-01), Itoh
patent: 4710603 (1987-12-01), Obara
patent: 4833289 (1989-05-01), Obara
Patent Abstracts of Japan, vol. 9, No. 316, 12 Dec. 1985 & JP-A-60 150 912, 8 Aug. 1985.
Izumiya Shunzo
Kawahara Akiyoshi
Sakurai Akihiro
Fanuc Ltd.
Tobin Christopher M.
Wieder Kenneth A.
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