Electricity: power supply or regulation systems – Output level responsive – Using a three or more terminal semiconductive device as the...
Patent
1991-08-05
1995-12-12
Wong, Peter S.
Electricity: power supply or regulation systems
Output level responsive
Using a three or more terminal semiconductive device as the...
219 6913, G05F 140, B23H 102
Patent
active
054752973
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates generally to a power supply circuit for an electric discharge machine. More particularly, the present invention relates to a power supply circuit for an EDM machine which reduces machining current cutoff without degrading the machining current waveform.
BACKGROUND OF THE INVENTION
An electric discharge machine ("EDM"), such as that described in Japanese Patent No. 58-40225, has a transistor switch placed between the gap and the power source. The transistor switch is periodically turned on and off for short predetermined periods which defines a machining cycle. Within the "on" time of a machining cycle, the transistor may be intermittently triggered on and off. The intermittent turning on and off of the switching transistor maintains a generally continuous machining current.
When conditions are such that the machining current should be lowered during the predetermined "on" time, the current is cutoff. Therefore, the actual "on" time during a machining cycle is less than the predetermined value of "on" time. This premature cutting-off of the machining current results in reduced machining speed and in faster wear down of the electrodes.
Japanese Patent No. 62-5733, discloses a circuit where the machining current cutoff can be eliminated by the insertion of an inductor in series with the gap. Although this inductor reduces the machining current cutoff, it also increases the time constant of the circuit. The increased time constant causes the rise time of the machining current to increase. This in turn causes a drastic reduction in the machining speed, which is the exact opposite of the desired effect.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a power supply circuit for an EDM machine which reduces machining current cutoff without increasing the rise time of the machining current.
It is a further object of the present invention to provide an EDM power supply circuit which minimizes machining current cutoff without causing an undesirable increase in machining current rise time due to an inductance.
These and other objects of the present invention are accomplished by the present invention which generally relates to a power supply circuit for an electric discharge machine that periodically turns on a switching element connected between the gap and the power source. An inductor, placed in series with the gap and the power source, is shorted out of the power supply circuit during the rise time of the machining current. After the machining current rise time period is over, the inductor is switched into the circuit to reduce machining current cutoff.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompany drawings, which are incorporated in and form a part of the specification, illustrate an embodiment of the present invention and, together with the description, serve to explain the principles of the invention. In the drawings:
FIG. 1 is a circuit diagram showing one embodiment of the invention; and
FIG. 2 illustrates signal wave forms at principal points in FIG. 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Reference will now be made in detail to the present preferred embodiment of the invention, an example of which is illustrated in the accompany drawings.
As shown in FIG. 1, a transistor TR1 which serves as a first switching element, is connected between the power source B and gap G. A resistor R1, connected between the transistor TR1 and gap G is used for measuring the current flowing through the gap G. An inductor L is also connected in series with the gap G. A transistor TR2, which serve
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Berhane Adolf
Sodick Co. Ltd.
Wong Peter S.
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