Electric heating – Metal heating – Cutting or disintegrating
Patent
1985-02-08
1986-05-20
Paschall, M. H.
Electric heating
Metal heating
Cutting or disintegrating
219 69P, 219 69S, B23P 108
Patent
active
045903530
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to an electric discharge machining power source for an electric discharge machine for machining a workpiece by using a capacitor discharge.
A conventional discharge circuit of an electric discharge machining power source for performing capacitor discharge is illustrated in FIG. 1. A pulse is supplied to a base q2 of a transistor Q2 as a switching element to repeat the ON/OFF operation of the transistor Q2, and a capacitor C0 is charged by a DC high-voltage source through a resistor R0. A charge voltage is applied between an electrode P and a workpiece W, and the discharge current from the capacitor C0 is generated as a spark between the electrode P and the workpiece W, thereby performing electric discharge machining. In this case, in order to stop discharge between the electrode and the workpiece and perform stable discharge, a transistor Q1 as a switching element is inserted in the discharge circuit, as shown in FIG. 1. When the capacitor C0 is completely charged, the transistor Q2 is turned off, and the transistor Q1 is turned on, thereby starting discharge. In this case, when the switching transistor Q1 is turned off during discharge, the switching transistor Q1 can be damaged by a surge voltage generated by an inductance inherent in the electric discharge machine. The switching transistor Q1 must be turned off after the discharge is completed. However, in the electric discharge machine, the capacitance of the capacitor C0 must vary in order to change a discharge time. The discharge time also changes in accordance with the inductance inherent in the electric discharge machine. For this reason, in order to protect the switching transistor Q1 from damage, it must be turned off within a maximum discharge time in view of the above conditions. However, machining efficiency is degraded by such a method of operation.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an electric discharge machining power source having a capacitor discharge circuit with a switching element, wherein the conventional drawbacks are prevented, and the switching element is not damaged.
It is another object of the present invention to provide an electric discharge machining power source, wherein a discharge current from the capacitor is detected, and the OFF time of the switching element in the discharge circuit is controlled to protect the switching element from damage caused by a stray inductance.
In order to achieve the above objects of the present invention, there is provided an electric discharge machining power source used for machining a workpiece by capacitor discharge, the electric discharge machining power source having a discharge circuit with a switching element, comprising a charge voltage detecting circuit for detecting a charge voltage of the capacitor and generating an output when the charge voltage exceeds a reference voltage and a discharge current detecting circuit made of a Logoski coil for detecting a discharge current of the capacitor, wherein charging of the capacitor is stopped by an output from the charge voltage detecting circuit, the switching element is turned on, and thereafter the switching element is turned off when discharge is started and the capacitor is completely discharged, and the capacitor is recharged after a predetermined period of time.
When the predetermined period of time has elapsed after the discharge from the capacitor is completed and the switching element is turned off, and when the charge voltage has reached the reference voltage, charging of the capacitor is stopped. The switching element is then turned on, and the discharge current detecting circuit detects the end of discharge. In this state, the switching element is turned off. As a result, the switching element during the electric discharge will not be damaged by the surge voltage. Even if the capacitance of the discharge capacitor changes, or the discharge time changes in accordance with a change in machine inductance, the switching element i
REFERENCES:
patent: 4350863 (1982-09-01), Inoue
patent: 4387285 (1983-06-01), Obara
Izumiya Shunzo
Obara Haruki
Okuyama Yuji
Sakurai Akihiro
Fanuc Ltd
Paschall M. H.
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