Electric lamp and discharge devices: systems – Periodic switch in the supply circuit – Periodic switch cut-out
Patent
1999-04-12
2000-10-10
Wong, Don
Electric lamp and discharge devices: systems
Periodic switch in the supply circuit
Periodic switch cut-out
219 6913, 219 6916, 219 6918, 323282, H05B 3702
Patent
active
061305103
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an electric discharge machining power source unit for an electric discharge machine.
BACKGROUND ART
The narrower the current pulse width of discharge current, and the larger the peak value of the discharge current, the more the speed of electric discharge machining can be improved. Referring to FIGS. 7A and 7B, there will be described a prior art example of an electric discharge machining power source unit that can give a high peak current value with such a narrow pulse width.
The positive terminal of a DC power source 10 and a workpiece W are connected through a first switching element T11, while the negative terminal of the DC power source 10 and a machining electrode P are connected through a second switching element T12. Further, the negative terminal of the DC power source 10 and the workpiece W are connected through a reversely-connected first diode D11, while the positive terminal of the DC power source 10 and the machining electrode P are connected through a reversely-connected second diode D12.
The first and second switching elements T11 and T12 are each formed of a FET. As shown in FIG. 7B, their respective gates G11 and G12 are controlled by means of a first switching element driver circuit 11 and a second switching element driver circuit 12, respectively. The first and second switching element driver circuits 11 and 12 are driven by means of pulses with a given pulse width delivered from a pulse signal generator circuit 13 for current peak value setting.
When conditions for electric discharge between the workpiece W and the electrode P are fulfilled, the pulses with the set width are delivered from the pulse signal generator circuit 13 for current peak value setting. These pulses are applied to the respective FET gates G11 and G12 of the first and second switching elements T11 and T12 through the first and second switching element driver circuits 11 and 12, thereby turning on both these switching elements T11 and T12.
Thereupon, a discharge current J0 from the DC power source flows through the first switching element T11, workpiece W, machining electrode P, and second switching element T12 to the DC power source 10. When the pulses with the set width from the pulse signal generator circuit 13 for current peak value setting then die out, both the switching elements T11 and T12 are turned off.
After both the switching elements T11 and T12 are turned off, a current J1 (=J0) produced by induced energy that is accumulated by inductance in this electric discharge circuit is fed back to the DC power source 10 through the first diode D11, workpiece W, machining electrode P, and second diode D12.
The workpiece W is subjected to electric discharge machining using the current J0 (machining current) that flows between the workpiece W and the machining electrode P in this manner.
Referring now to FIGS. 8 and 9, there will be described discharge currents (machining currents) that are obtained when the power source unit shown in FIGS. 7A and 7B is operated in the aforesaid manner. FIG. 8 shows current waveforms for the case where the voltage of the DC power source is raised, and FIG. 9 for the case where the voltage of the DC power source 10 is lowered.
When both the first and second switching elements T11 and T12 are turned on by means of pulse signals (with a pulse width t1) from the pulse signal generator circuit 13 for current peak value setting (see (a) and (b) of FIG. 8 and (a) and (b) of FIG. 9), the voltage of the DC power source 10 is applied between the workpiece W and the machining electrode P. Thereupon, the current J0 that flows between the workpiece W and the machining electrode P is caused to increase with time by inductance in the circuit of FIG. 7A. If the voltage of the DC power source 10 is high, in this case, the current J0 rises sharply (see (c) of FIG. 8). If the voltage is low, on the other hand, the current J0 rises gently (see (c) of FIG. 9).
When both the first and second switching elements T11 and T12 are turned off, the feedback
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Kawahara Akiyoshi
Kurihara Masaki
Murai Masao
Sakurai Akihiro
Fanuc Ltd.
Trn Thuy Vinh
Wong Don
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