JPH05329710A - Electric discharge machining device - Google Patents

Abstract

PURPOSE:To economically provide an electric discharge machining device which executes control so as to make the whole voltage mean value of machining voltage occurring at a machining clearance approximate to zero for machining a workpiece. CONSTITUTION:An electric discharge machining device has a positive voltage mean value detecting circuit 14 to detect the mean value of the positive voltage of machining voltage generated at a machining clearance, and a control means to control the product of the constant of the negative voltage pulse-duration modulating reference triangular wave of a negative voltage pulse-duration modulating circuit 15 and the negative voltage of a negative power source 1c so as to be equal to a machining cycle for making the whole voltage mean value of the machining voltage approximate to zero.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric discharge machining apparatus, and more particularly to machining that occurs in a machining gap during electric discharge machining by connecting a positive power source and a negative power source in parallel to the machining gap and applying positive voltage and negative voltage alternately. The present invention relates to an electric discharge machine that performs machining by controlling the average value of all voltages to approach zero.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram showing a conventional electric discharge machine. In the figure, 1a is a positive power source, 1b is a negative power source, 2 is an electrode connected to the positive electrode of the positive power source 1a and the negative electrode of the negative power source 1b,
Reference numeral 3 denotes a workpiece to be processed by the electrode 2, which constitutes a processing gap together with the electrode 2. 4a is a switch for controlling the output of the positive power supply 1a on / off (OFF), 4b is a switch for controlling the output of the negative power supply 1b on / off, 5a
And 5b are resistors for limiting the current peak value in the machining gap, 6a and 6b are backflow blocking diodes for preventing the current in the machining gap from flowing backward, and 7a and 7b are currents in the machining gap after the switches 4a and 4b are turned off. A positive power supply processing circuit and a negative power supply processing circuit are configured with a flywheel diode that reduces Reference numeral 8 is a dummy resistor connected to the machining gap, and 9 is an oscillation circuit for outputting a machining pulse signal.
A machining voltage detector 10 detects and amplifies the voltage in the machining gap. The total voltage average value detection circuit 11 detects the total average value of the output voltages of the processing voltage detector 10. The negative voltage pulse width modulation circuit 12 that modulates the pulse width of the negative voltage based on the output voltage of the total voltage average value detection circuit 11 is the switch 4 of the negative power source 1b.
ON / OFF control of b.

Next, the operation of the conventional electric discharge machine will be described with reference to FIGS. 3 and 4. The machining voltage generated in the machining gap of the machining circuit is detected and amplified by the machining voltage detector 10. The output voltage of the processing voltage detector 10 detects the total average value in the total voltage average value detection circuit 11 and outputs the total voltage average value V _GA . The total voltage average value V _GA is used as a signal for pulse width modulation in the negative voltage pulse width modulation circuit 12, and turns ON / OFF the switch 4b of the negative power source 1b.
A pulse width modulated negative voltage pulse signal is created for control. The pulse width T _N of the negative voltage pulse signal is converted by the equation 1 using the total voltage average value V _GA as a signal by the constant K of the reference triangular wave for negative voltage pulse width modulation created inside the negative voltage pulse width modulation circuit 12. T _R is the rest time. T _N = K · V _GA (T _N <T _R ) ... (Equation 1) FIG. 4 is a machining voltage in which the negative voltage V _N of the negative power source 1b applied to the machining gap during the down time is pulse width modulated. In the waveform example,
Since the no-load time T _L is longer in FIG. 4A than in FIG. 4B, the negative voltage pulse width T _N is modulated longer. The negative voltage average value V _NA is the processing period T ₀ , the negative voltage pulse width T _N, and the negative voltage V _{N in} Equation 2, and the total voltage average value V _GA that is the total average value of the processing voltage is the positive voltage average value V _PA . The negative voltage average value V _NA is expressed by Equation 3, respectively. The positive voltage average value V _PA is calculated by Equation 4
It is a waveform average represented by. V _M is the positive voltage of the positive power supply 1a, V _D is the discharge voltage, and T _P is the pulse width. V _NA = V _N · T _N / T ₀ (Equation 2) V _GA = V _PA −V _NA ··· (Equation 3) V _PA = (V _M · T _L + V _D · T _P ) / T ₀ (Equation 4) Further, the total voltage average value V _GA is represented by Equation 5 from Equation 1, Equation 2 and Equation 3. V _GA = V _PA / (1 + K · _VN / T ₀ ) ... (Equation 5) As described above, the constant K of the reference triangular wave for negative voltage pulse width modulation or the negative voltage V _N is set to a sufficiently large value. As a result, the total voltage average value V _GA is controlled so as to approach zero.

[0004]

Since the conventional electric discharge machining apparatus is constructed as described above, the negative voltage V _N or the negative voltage pulse width must be controlled in order to bring the average value V _{GA of} all voltages close to zero. The constant K of the reference triangular wave for modulation must be set to a sufficiently large value. Therefore, the negative voltage V _{N of the} negative power source 1b
Becomes a high voltage and the apparatus becomes large and expensive, or the constant K of the reference triangular wave for negative voltage pulse width modulation of the negative voltage pulse width modulation circuit 12 becomes very large and the negative voltage pulse width T _N
In a short region of, there is a problem that the processing becomes unstable due to a malfunction of pulse width modulation or a delayed response.

The present invention has been made in order to solve the above problems, and is for negative voltage pulse width modulation in order to perform machining in which the average value V _GA of all voltages of the machining voltage generated in the machining gap is close to zero. An object of the present invention is to provide an electric discharge machining apparatus that controls machining so that the product of a constant K of a triangular wave and a negative voltage becomes equal to the machining pulse period.

[0006]

An electric discharge machine according to the present invention moves an electrode and a workpiece so as to face each other and a positive power source and a negative power source in a machining gap formed by the electrode and the workpiece. In an electric discharge machining apparatus for connecting machining pieces in parallel and applying a machining pulse to supply a pulse current to discharge a workpiece, a machining voltage detector for detecting a machining voltage in a machining gap,
A positive voltage average value detection circuit that detects the positive average value of the processing voltage, and a negative voltage pulse width modulation circuit that pulse-width modulates the negative voltage application time of the negative power supply using the output voltage of this positive voltage average value detection circuit as a signal. , The product of the constant of the reference triangular wave for the negative voltage pulse width modulation of the negative voltage pulse width modulation circuit and the negative voltage of the negative power supply is processed in order to perform the processing in which the average value of all the machining voltages generated in the machining gap is close to zero. And a control means for controlling the pulse period to be equal to the pulse period.

Further, the control means changes the negative voltage of the negative power source with the constant of the reference triangular wave for negative voltage pulse width modulation of the negative voltage pulse width modulation circuit being a fixed value.

Further, the control means sets the negative voltage of the negative power source to a fixed value and changes the constant of the reference triangular wave for negative voltage pulse width modulation of the negative voltage pulse width modulation circuit.

[0009]

In the present invention, the positive voltage average value detection circuit detects the positive average value of the machining voltage, and the negative voltage pulse width modulation circuit uses the output voltage of the positive voltage average value detection circuit as a signal to obtain the negative voltage of the negative power supply. The constant of the reference triangular wave for the negative voltage pulse width modulation of the negative voltage pulse width modulation circuit for performing the pulse width modulation of the applied time, and the control means performing the machining in which the average value of all the voltages of the machining voltage generated in the machining gap approaches zero. Since it is controlled so that the product of the negative voltage and the negative voltage of the negative power source becomes equal to the machining pulse period, it is not necessary to set the constant of the reference triangular wave for negative voltage pulse width modulation or the negative voltage to an excessive value.

Further, since the control means changes the negative voltage of the negative power source by setting the constant of the negative voltage pulse width modulation reference triangular wave of the negative voltage pulse width modulation circuit to a fixed value, the negative voltage is increased as the machining pulse period becomes longer. It becomes high and it becomes easy to discharge. As a result, it works in the direction of shortening the cycle.

Further, since the control means changes the constant of the reference triangular wave for negative voltage pulse width modulation of the negative voltage pulse width modulation circuit with the negative voltage of the negative power source fixed, the negative voltage pulse width becomes longer as the machining pulse period becomes longer. The modulation gain of becomes higher, and the response that brings the average value of all voltages closer to zero becomes faster.

[0012]

【Example】

Example 1. FIG. 1 is a block diagram showing an embodiment of an electric discharge machine according to the present invention. In the figure, 1a is a positive power source, 1c is a negative power source, 2 is an electrode connected to the positive electrode of the positive power source 1a and the negative electrode of the negative power source 1c, 3 is a workpiece to be processed by the electrode 2, and constitutes a processing gap together with the electrode 2. .. 4a is a switch for ON / OF controlling the output of the positive power supply 1a, 4b is a negative power supply 1c
Switches 5a and 5 for controlling ON / OFF of the output of
b is a resistor for limiting the current peak value in the machining gap, 6a and 6b are reverse current blocking diodes for preventing the current in the machining gap from flowing backward, and 7a and 7b are currents in the machining gap after the switches 4a and 4b are turned off. The flywheel diode to be reduced constitutes a positive power processing circuit and a negative power processing circuit. 8 is a dummy resistor connected to the machining gap,
An oscillating circuit 13 outputs a processing pulse signal, a negative voltage pulse width modulation gain signal and a negative voltage signal. A machining voltage detector 10 detects and amplifies the machining voltage generated in the machining gap. The negative voltage pulse width modulation circuit 15 that modulates the pulse width of the negative voltage based on the output voltage of the positive voltage average value detection circuit 14 that detects the average value of only the positive voltage of the output voltage of the processing voltage detector 10 is negative. Turn ON / O switch 4b of power supply 1c
FF control.

Next, the operation will be described with reference to FIGS. 1 and 2. The machining voltage generated in the machining gap of the machining circuit is detected and amplified by the machining voltage detector 10. The output voltage of the processing voltage detector 10 rectifies only the positive voltage in the positive voltage average value detection circuit 14 and then detects the average value of the positive voltage and outputs the positive voltage average value V _PA . Positive voltage average value V
_{The PA} is used as a signal for pulse width modulation in the negative voltage pulse width modulation circuit 15, and the switch 4b of the negative power source 1c is turned on.
A pulse width modulated negative voltage pulse signal is generated for N / OFF control. The pulse width T _N of the negative voltage pulse signal is a positive voltage average value V by the constant K of the reference triangular wave for negative voltage pulse width modulation created inside the negative voltage pulse width modulation circuit 15.
It is converted by Equation 6 using _PA as a signal. T _N = K · V _PA (T _N <T _R ) ... (Equation 6) FIG. 2 shows an example of pulse width modulation of the negative voltage application time of the negative power source 1c during the rest time. Inside view of machining voltage 2
The positive voltage average value signal obtained by averaging only the positive voltage in FIG. 2B and the reference triangular wave for pulse width modulation are compared as shown in FIG. 2C, and the pulse width signal of the negative voltage V _N is shown in FIG. Making (d). The total voltage average value V _GA is expressed by Equation 6, Equation 2 and Equation 3.
Is expressed by Equation 7. V _GA = (1−K · V _N / T ₀ ) · V _PA (Equation 7) The condition that the total voltage average value V _GA becomes zero is expressed by Equation 8 derived from Equation 7. K · V _N / T ₀ = 1 (Equation 8) As described above, the product of the constant K of the reference triangular wave for negative voltage pulse width modulation and the negative voltage V _N should be equal to the machining cycle T _0. By controlling, it is possible to perform processing in which the average value V _GA of all voltages is brought close to zero. Therefore, it is not necessary to set the constant K of the reference triangular wave for negative voltage pulse width modulation or the negative voltage V _N to an excessive value.

Example 2. The condition for bringing the average value V _{GA of} all voltages close to zero is expressed by Equation 8. Among them, the constant K of the reference triangular wave for negative voltage pulse width modulation is fixed to a constant value, and the negative voltage V _N is supplied from the oscillation circuit 13. All average voltage V _GA by controlling the value of the expression 9 derived from equation 8 by a negative voltage signal
Can be brought close to zero. V _N = T ₀ / K (Equation 9) V _N is a machining voltage, which is applied between the electrodes during the no-load time before discharge, and therefore has the effect of changing the ease with which discharge occurs. .. As T ₀ becomes longer, V _N becomes higher and discharge becomes easier, and as a result, T ₀ is shortened to stabilize the machining.

Example 3. Further, the negative voltage V _N in the equation 8 is fixed to a constant value, and the constant K of the reference triangular wave for negative voltage pulse width modulation is derived from the equation 8 by the negative voltage pulse width modulation gain signal from the oscillation circuit 13. By controlling the value to 10, the total voltage average value V _GA can be brought close to zero. _{K = T 0 / V N .........} ( Equation 10) K is the modulation constant, changing the modulation gain of the negative voltage pulse width. As T ₀ becomes longer, the modulation gain of the negative voltage pulse width becomes higher, and the response for bringing the average value of all voltages closer to zero becomes faster.
Therefore, there is an effect of compensating for the response delay when the discharge frequency is lowered.

In the first to third embodiments, the oscillator circuit 13
Is provided with a computer such as a microcomputer and has a function as a control circuit. The function of controlling the negative voltage by the negative voltage signal or the constant K by the modulation gain signal so that K · V _N / T ₀ = 1 expressed by the equation 8 is previously stored in the memory. Achieved by the program stored in. 20
Is a signal line for reading the period T ₀ of the internal machining voltage of the inter-electrode voltage. In addition, in FIG. 1, a portion indicated by a chain line is not a so-called electric wire, but is connected by control. The circuit indicated by 21 resets an integrator that produces a triangular wave for pulse width modulation of the negative voltage pulse width. The integrator is reset while the machining pulse signal (positive voltage) is output, and integration is performed so that a negative voltage is applied during the rest time, and a triangular wave is output. That is, as a result, the square wave whose signal is during the rest time is integrated.

[0017]

As described above, according to the present invention, a positive voltage average value detection circuit for detecting the average value of the positive voltage of the machining voltage generated in the machining gap and a negative voltage average value for making the total voltage average value of the machining voltage close to zero. Since the control means for controlling the product of the voltage and the constant of the negative voltage pulse width modulation reference triangular wave to be equal to the machining pulse period is provided, there is an effect that inexpensive and fast response machining can be stably performed.

Further, since the control means changes the negative voltage of the negative power source by setting the constant of the reference triangle wave for negative voltage pulse width modulation of the negative voltage pulse width modulation circuit to a fixed value, the negative voltage is increased as the machining pulse period becomes longer. It becomes high and it becomes easy to discharge. As a result, it has the effect of working in the direction of shortening the cycle and stabilizing the processing.

Further, since the control means changes the constant of the reference triangular wave for negative voltage pulse width modulation of the negative voltage pulse width modulation circuit by setting the negative voltage of the negative power source to a fixed value, the negative voltage pulse width becomes longer as the machining pulse period becomes longer. The modulation gain of becomes high. Therefore, the response that brings the average value of all voltages close to zero becomes faster, and there is an effect of compensating for the response delay when the discharge frequency decreases.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of an electric discharge machine according to the present invention.

FIG. 2 is a waveform diagram showing an example of negative voltage pulse width modulation.

FIG. 3 is a configuration diagram showing a conventional electric discharge machine.

FIG. 4 is a waveform diagram showing an example of a processing voltage waveform to which a negative voltage is applied.

[Explanation of symbols]

1a Positive power supply 1b, 1c Negative power supply 2 Electrode 3 Work piece 9, 13 Oscillation circuit 10 Processing voltage detector 11 Total voltage average value detection circuit 12, 15 Negative voltage pulse width modulation circuit 14 Positive voltage average value detection circuit T ₀ Processing period T _L unloading time T _P pulse width T _R downtime T _N negative voltage pulse width V _M positive voltage V _D discharge voltage V _N negative voltage

Claims (3)

[Claims] 1. A pulse current in which a positive power source and a negative power source are connected in parallel to a machining gap formed by the electrode and the workpiece while the electrode and the workpiece are moved to face each other and a machining pulse is applied. In an electric discharge machining apparatus for electrifying the workpiece by electric discharge machining, a machining voltage detector for detecting a machining voltage of the machining gap, a positive voltage average value detection circuit for detecting a positive average value of the machining voltage, A negative voltage pulse width modulation circuit that pulse width modulates the negative voltage application time of the negative power source using the output voltage of the positive voltage average value detection circuit as a signal, and the total voltage average value of the machining voltage generated in the machining gap is brought close to zero. And a control means for controlling the product of the constant of the reference triangular wave for negative voltage pulse width modulation of the negative voltage pulse width modulation circuit and the negative voltage of the negative power source to be equal to the machining pulse period. Was it Electric discharge machining apparatus according to claim. 2. The electric discharge machining according to claim 1, wherein the control means sets the constant of the reference triangular wave for negative voltage pulse width modulation of the negative voltage pulse width modulation circuit to a fixed value and changes the negative voltage of the negative power source. apparatus. 3. The electric discharge machining according to claim 1, wherein the control means sets the negative voltage of the negative power supply to a fixed value and changes the constant of the reference triangular wave for negative voltage pulse width modulation of the negative voltage pulse width modulation circuit. apparatus.