JPS61182721A - Electric discharge circuit of electric discharge machine - Google Patents

Abstract

PURPOSE:To obtain an electric discharge circuit capable of intermitting power supply with a pulse width ranging broadly by connecting a DC power supply between electrodes forming a circuit with a couple of switching elements connected in series or the several couples connected in parallel arranged to make a common-frequency symmetrical square-wave by making it possible to vary the phase difference of the drive pulse of each element. CONSTITUTION:A DC power supply E is connected between electrodes 1 and 3 forming a circuit with a couple of transistors Tr1 and Tr2 connected in series or the several couples connected in parallel arranged through a current limiting resistor R. By shifting the phases of the symmetrical form pulses impressed to the bases of a couple of transistors Tr1 and Tr2 or the several couples connected in parallel between each of transistors and between each of the couples, a discharge circuit having a switching function capable of intermitting the DC power supply connected between the electrodes 1 and 3 with pulse width ranging broadly can be obtained. And by controlling a pulse width controller to control the output from a pulse generator by connecting a machining condition judging unit 17 between the electrodes 1 and 3, an efficient electric discharge machining can be performed.

Description

DETAILED DESCRIPTION OF THE INVENTION a. Field of Industrial Application This invention relates to a discharge circuit used in a discharge machining apparatus.

b. Prior Art A transistor discharge circuit or a capacitor discharge circuit with transistor control uses a transistor as a switching element, and a multivibrator is generally used as an oscillator for a drive pulse of this transistor. In electric discharge machining, the machining pulse width of the discharge current and the pause width duty ratio (DUTY F) are determined according to the machining conditions.
It is necessary to change the time ratio during which the discharge current is flowing during one cycle of ACTOR2 discharge and rest (hereinafter represented by the symbol). This change is generally made by changing the waveform of the drive pulse by switching the capacitor or resistor of the pulse oscillator, and the waveform is generally an asymmetrical waveform with different widths at the top and bottom.

C1 @ Point of Interest that the Invention Attempts to Solve As mentioned above, since the pulse waveform of the drive pulse oscillator is changed by switching capacitors and resistors, there is a limit to the range of change, and it has not been possible to arbitrarily make wide-ranging adjustments. Also,
Drive pulses generally have an asymmetric waveform, so if an AC coupling (transformer) is used between the pulse oscillator and the transistor, the pulse output changes greatly, making it difficult to drive the transistor over a wide range of duty ratios. child .

In addition, in finishing machining in electrical discharge machining, it is necessary to shorten the pulse width of the discharge current in order to reduce surface roughness, so the pulse width of the pulse oscillator is shortened by changing the capacitor and resistor as described above. ing. In general, transistors have a turn-on mode that slows down the rise and fall of pulses.
There is a turn-off time, and if the pulse width is too short,
The pulse began to fall before it rose sufficiently, and the pulse output to drive the processing switching element could not be obtained.

On the other hand, the turn-off time is generally longer than the turn-on time, which increases the overall pulse width. To shorten the turn-on time, it is necessary to increase the base current at rise, and to shorten the turn-off time, it is necessary to decrease the base current after rise, but it is difficult to do this with a single transistor. Since a multivibrator uses two transistors, it is possible to generate a square pulse with a fast rise, but in a conventional discharge circuit using one transistor, even if the drive pulse is a square wave, it is possible to generate a discharge with a short pulse width. Obtaining current is difficult.

The purpose of this invention is to improve the above-mentioned problems and provide a discharge circuit equipped with a switching function capable of intermittent DC power supply connected between the poles of an electric discharge machine with a wide range of pulse widths. It is something that can be done.

Means for Solving the d9 Problem In order to achieve the above object, the present invention connects 0 sets of two switching elements connected in series (n is an integer of 1 or more) in parallel, and through this, A DC power source is connected between the poles, and the drive pulses of each switching element are symmetrical square waves with the same period and variable phase difference.

01 Effect In this way, the drive pulse that drives the switching element is a square wave with a constant period whose pulse width is always equal on both the upper and lower sides, so even if an AC coupling (transformer) is used between the pulse oscillator and the switching element, the drive state remains constant. It does not change. Furthermore, since the phase difference between the drive pulses is changed by a delay circuit or the like, the duty ratio of the discharge circuit can stably change over a wide range. In addition, since two switching elements are connected in series, the turn-on time of the switching elements can be shortened by increasing the base current of one switching element, and the turn-off time can be shortened by increasing the base current of one switching element.゛The flow can be made smaller and shorter. Therefore, a machining pulse with a short pulse width can be output between the machining electrodes.

f. Example Next, an example of the present invention will be described based on the drawings. FIG. 1 is a circuit diagram showing one embodiment of this invention.
The electrode 1 and the workpiece 3 face each other across the machining gap 5, and a DC power source E is connected between the electrodes (meaning between the electrode 1 and the workpiece 3).
Two transistors Tγ1 and Tγ2 connected in series
and are connected through a current limiting resistor R. Drive circuits 7 and 9 are connected to the transistors Tγ1 and Tγ2, respectively, and the drive circuit 7 is connected to the pulse oscillator 11.
The drive circuit 9 is also connected to a pulse oscillator 11 via a delay circuit 13. A pulse width IIjIll circuit 15 is connected to the delay circuit 13 to control the pulse widths of the two transistors. Further, a machining state determining device 17 is connected between the machining holes, and its output is applied to the pulse oscillator 11 and the pulse width controller 15.

Next, the operation of this device will be explained with reference to FIG.

Figure a is a simplified circuit diagram of Figure 1, and drives 1 and 2 are drive pulses applied to transistors Tγ1 and Tγ2. Figure b shows the case where the phases of the symmetrical rectangular drive pulses 1.2 applied to transistors Tγ1 and Tγ2 match, and the conduction time between A and B is as shown by the shaded area, and is equal to 1/2 of the period T of the drive pulse. Become.

In Figure 0, the phase of drive pulse 2 lags the phase of drive pulse 1 by T/4, and the conduction time between AB is T/4 as shown by the diagonal line. In figure d, the phase of drive pulse 2 lags the phase of drive pulse 1 by T/2,
The conduction time between AS becomes 0. In this way, by controlling the phase of the symmetrical square pulse applied to the bases of transistors Tγ1 and Tγ2, the common conduction time of the two transistors can be varied from 0 to 1/2 of the period of the drive pulse.
can be changed freely. The range of the duty ratio of this discharge circuit is 0 to 50%.

FIG. 3 is a diagram showing another embodiment. As shown in figure a, a set of transistors Tγ1 and Tγ2 connected in series and a set of transistors Tγ3 and Tγ4 connected in the same way are connected in parallel, and the phase of the drive pulse of each transistor is set for each set and each coarse interval. It is made variable. In other words, as shown in figure b, if the phases of drive pulses 1 and 2 are the same and the phases of drive pulses 3 and 4 are delayed by T/2, conduction will always occur between AB and the duty ratio will be 100%. . Also, as shown in Figure 0, each drive pulse is 1°2.3.
If the phase of 4 is sequentially delayed by T/4, conduction will occur between A and 8 for T/4 time every T/4, and the duty ratio will be 50%.

Also, as shown in figure d, if a phase difference of T/2 is given between drive pulses 1 and 2 and between drive pulses 3 and 4, AB
There is always no conduction between them, and the duty ratio is 0%.

In this example, two sets of transistors are connected in parallel, but if two sets of transistors are connected in three sets in series, and the maximum conduction time of each set is T/3. It works even more stably.

As shown in Fig. 1, between the poles of this discharge circuit, a machining state discriminator is connected, and the pulse width controller is controlled by the signal, and the output of the pulse oscillator is controlled, thereby achieving efficient discharge machining. can be done.

Ω1 Effects of the Invention As understood from the above explanation, the present invention has the structure set forth in the claims, so that the DC power supply connected between the poles of the electrical discharge machining device can be switched on and off over a wide range of pulse widths. It is possible to provide a discharge circuit with a switching function that can perform the following functions.

[Brief explanation of the drawing]

FIG. 1 is a discharge circuit diagram showing one embodiment of the present invention, FIG. 2 is an explanatory diagram of the operation of FIG. 1, and FIG. 3 is a discharge circuit and an operation explanatory diagram of another embodiment. (Explanation of symbols representing main parts of the drawing) 1... Electrode 3... Workpiece 5... Machining gap
7.9 Drive circuit 11...Pulse oscillator
13...Delay circuit 15...Pulse width controller 17...Machining state discrimination device Fig. 2 Fig. 3

Claims (3)

[Claims] (1) n sets of two switching elements connected in series (n is an integer of 1 or more) are connected in parallel, and a DC power supply is connected between the poles through this, and the drive pulses of each switching element are , a discharge circuit for an electrical discharge machining device, characterized in that a symmetrical square wave having the same period and a mutually variable phase difference is formed. (2) A DC power supply is connected between the poles through two switching elements connected in series and a current limiting resistor, and a pulse oscillator is provided to output a symmetrical square wave to drive each switching element. 2. The electric discharge circuit for an electric discharge machining apparatus according to claim 1, wherein a delay circuit for generating a phase difference in the supplied drive pulses is provided between the pulse oscillator and one drive circuit. (3) The electric discharge circuit of the electric discharge machining apparatus according to item 1 or 2, wherein a machining state determination device is provided between the machining holes, and the phase difference between the dove pulses of each switching element is controlled by this detection signal.