Electric heating – Metal heating – Cutting or disintegrating
Patent
1985-10-28
1987-12-01
Leung, Philip H.
Electric heating
Metal heating
Cutting or disintegrating
219 69P, 323287, B23H 102, G05F 144
Patent
active
047106034
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a power source for an electric discharge machine such as a die sinking type electric discharge machine or a wire type electric discharge machine for machining a metal or the like by using discharge energy from a capacitor.
A conventional power source circuit for an electric discharge machining power source for performing machining by discharge of the capacitor, is illustrated in FIG. 1. Referring to FIG. 1, reference symbol E denotes a power source; R1, a current limiting resistor; C1, a charging/discharging capacitor; P, an electrode; W, a workpiece; Q1, a transistor as a switching element for charging the capacitor C1; G1, a base of the transistor Q1; Q2, a transistor as a switching element for discharging the capacitor C1; and G2, a base of the transistor Q2. Reference symbols L1 and L2 respectively denote stray inductances present in the power source circuit. In the circuit having the arrangement described above, a pulse is supplied to the base G1 of the transistor Q1 which is then turned on, so that the capacitor C1 is charged. Then, the transistor Q2 is turned on after the transistor Q1 is turned off, and a voltage charged by the capacitor C1 is applied between the electrode P and the workpiece W. A discharge current from the capacitor C1 flows as a discharge spark between the electrode P and the workpiece W, thereby performing electric discharge machining. When a resistance of the current limiting resistor R1 is decreased to charge the capacitor C1 at a high speed, the resistor R1 generates heat, result in large energy loss. Further, when the transistor Q1 is turned off, energy stored by the stray inductance L1 in the power source circuit is applied as a large surge voltage in an emitter-collector path of the transistor Q1 to damage the transistor Q1, resulting in inconvenience. As a result, the current cannot be increased and high-speed charging of the capacitor C1 cannot be performed.
SUMMARY OF THE INVENTION
It is a first object of the present invention to eliminate the conventional drawback and to provide an electric discharge machining power source which can charge a capacitor discharge circuit at a high speed, which eliminates heat dissipation and which provides high power source efficiency.
It is a second object of the present invention to prevent a charging switching element from a capacitor in the capacitor discharge circuit from being damaged by a surge voltage.
It is a third object of the present invention to decrease a stray inductance present in a power source circuit and to minimize energy loss.
It is a fourth object of the present invention to provide an electric discharge machining power source for easily controlling a charging voltage of the capacitor in the capacitor discharge circuit.
In order to achieve the above objects of the present invention, there is provided an electric discharge machining power source for a capacitor discharge circuit with a charging switching element and a discharging switching element, wherein a charging current limiting resistor is omitted to eliminate energy loss caused by the resistor; a diode is connected in parallel with a charging/discharging capacitor, and the diode, the charging switching element and a power source smoothing capacitor are arranged on a printed circuit board to minimize a stray inductance, so that a surge voltage applied to the charging element is decreased to prevent the charging switching element from being damaged, even when the charging switching element through which a large current flows is turned off, thereby achieving high-speed charging.
Energy stored between a circuit portion consisting of the printed circuit board and the charging/discharging capacitor is accumulated in the charging/discharging capacitor through the diode, thereby decreasing energy loss. As described above, since no current limiting resistor is present, energy loss caused by heat dissipation of the resistor can be prevented. In addition, the surge voltage applied to the switching element i
REFERENCES:
patent: 3305767 (1967-02-01), Biehl et al.
patent: 3959714 (1976-05-01), Mihelich
patent: 4382168 (1983-05-01), Inoue
patent: 4580090 (1986-04-01), Bailey et al.
patent: 4592763 (1986-06-01), Dietz et al.
Evans Geoffrey S.
Fanuc Ltd.
Leung Philip H.
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