Electric heating – Metal heating – Cutting or disintegrating
Reexamination Certificate
2000-10-30
2004-03-23
Evans, Geoffrey S. (Department: 1725)
Electric heating
Metal heating
Cutting or disintegrating
Reexamination Certificate
active
06710279
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the power supply apparatus of the electric spark (discharge) machine. More particularly, the present invention relates to an improved control circuit for a switching circuit of the power supply apparatus, which is applied for any type of intermittent energy-generating block of the electric spark machine.
DESCRIPTION OF THE PRIOR ART
Most of the prior power supply for the electric spark machine were systems transforming the commercial AC power supply by a low frequency transformer, rectifying through the rectifier, restricting the output current by a resistor and supplying to the electrode gap. Recently, the technology for the power supply that it could provide a requested voltage and current by the pulse width control using switching circuit through direct rectification of the commercial AC source and converting it to high frequency pulse was developed. By this technology, the whole of the power supply apparatus becomes smaller and lighter toward the output capacity because it can be applied in the lightweight and the high efficiency high frequency transformer.
Also, technology was developed that reduces the allowable current value of the restricting resistor or it has no resistor, by restricting the output current.
There are Japanese Non-examined Patent Publication No.54-2595, No.57-138526 and No.5-208316 and Japanese Examined Patent Publication No.57-4452 and so on as the typical examples of such prior art. The technology of an intermittent energy-generating block itself for the electric discharge includes a switching element, and applied the restriction of electric discharge current is described in Japanese Examined Patent Publication No.57-4452. However, the relationship corresponding to the output current and the output voltage between the load-less voltage and the electric discharge start voltage is not controlled intentionally in this prior art.
In Japanese Non-examined Patent Publication No.54-2595 and No.57-138526, the intermittent energy-generating block itself for the electric discharge includes a switching element, and the restriction of the electric discharge current is carried out.
In Japanese Non-examined Patent Publication No.5-208316, the switching element is used for two steps, in the first step, it is used for the DC supply, and in the second step, it is used as the intermittent energy-generating block for the electric discharge and the discharge current is restricted. Also a capacitor is used as the intermittent energy-generating block for the electric discharge, and the power is supplied at its previous step by switching element in Japanese Non-examined Patent Publication No.S54-164086.
Moreover, there is the following disadvantage in the method by setting only a current restriction on the usual fixed voltage switching power supply for the electric discharge processing. A certain higher load-less voltage is necessary so that it causes easily a dielectric destruction at the electrode gap, i.e. the electric discharge starts, and it provides to maintain the stable servo control which is so-called stable electric discharge. Therefore, when a usual switching power supply is applied, it is required to provide this high load-less voltage. This had to be designed that all of the power supply elements have larger maximum consumption electric power capability. It obstructs to miniaturize and to lighten the power supply apparatus including the transformer.
There are Japanese Non-examined Patent Publication No.54-62595, No.56-163830, and No.5-285730 and Japanese Examined Patent Publication No.57-4452, and so on as a prior art, which solves these problems. However, all of these prior arts are consist of the combination of low voltage and high voltage power supply block, and then, it obstructs to miniaturize and to lighten the power supply because it is required two different type of the power supply circuits.
Though considerable miniaturization or weight decreasing or higher efficiency of the power supply for the electric spark machine have been developed by the above prior arts, it is important to provide further miniature and light weight power supply. Even in the country or the area where a higher commercial electric voltage is available higher for obtaining a load-less high voltage easily, it is important to control the discharge current and voltage, and to save the electric power consumption.
The object of the present invention is to provide the smaller size, the lighter weight and the more efficient power supply for the electric spark machine. Further object is to find a control circuit which has the characteristics to generate the high voltage so that it controls easily the steady electric discharge by only one switching power supply based on low voltage and large current.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a smaller size and a lighter weight power supply apparatus for the electric spark machine than that of the prior arts. More particularly, the object is to provide a control circuit for a fly-back switching power supply, which has the characteristics to generate the high voltage to start the electric discharge easily by using only one switching power supply for low voltage and large current capacity. Another object is to provide an efficient power supply for the electric spark machine.
According to one of the preferable embodiment of the present invention, above objects are achieved by a control circuit having the feature which comprises controlling an output voltage for an intermittent energy-generation block so that the output voltage varies as the relation of a negative linear proportion against an output current in the range of the output voltage between the load-less voltage and the electric discharge start voltage plus minus 25V.
This control circuit has a feedback function which maintains the difference to be a constant by comparing the voltage of the summation of the output voltage and the voltage converted from the output current value with the predetermined standard voltage.
According to another preferable embodiment of the present invention, above objects are also achieved by a control circuit having the feature which comprises controlling an output voltage for an intermittent energy-generation block so that the output voltage varies as the relation of an inverse proportion against an output current in the range of the output voltage between the load-less voltage and the electric discharge start voltage plus minus 25V. This control circuit has a function that maintains the difference which obtained by comparing the voltage of the product (multiplication) of the output voltage and the voltage converted from the output current value with the predetermined standard voltage to a certain value.
These control circuits result in a reduction of the overall weight and size of the power supply.
A power supply for the electric spark machine of the 250VA output capacity is provided with about 1000 cubic cm in volume and about 1 Kg in weight by the present invention. By the prior technology of the combination with the low frequency transformer and the restriction resistor, it is about 4000 cubic cm in volume and about 10 Kg in weight. By the prior technology of the combination with two switching power supplies of high voltage and low voltage is about 2000 cubic cm in volume and about 2 Kg in weight.
Further, although it requires that each circuit component have 900VA capability by the combination of prior transformer and the restricting resistor in the case of manufacturing a power supply which has the load-less voltage of 180V and the output current capacity of 5A, in the case of the negative proportional relation of the present invention, since the maximum consumption of the power is about 311VA, all circuit components may be allowed to have only 311VA capability, also in the case of the inverse proportional relations of the present invention, since the maximum output voltage which corresponds the maximum output current 5A is about 50V, all circuit components may b
Evans Geoffrey S.
Higashi EDM Co., Ltd.
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