JP3343025B2 - Power supply device for electric discharge machine and control method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device for an electric discharge machine and a control method thereof, and more particularly, to a discharge device for controlling a value of a current flowing between the poles when the gap between the poles is sharply reduced during the electric discharge machining process. The present invention relates to a power supply device for a processing machine and a control method thereof.

[0002]

2. Description of the Related Art FIGS. 7 and 8 show a circuit configuration of a conventional power supply device for an electric discharge machine, and particularly prevent the occurrence of electrolysis, electrolytic corrosion and the like on a workpiece during machining. Therefore, this is an example of a power supply device for an electric discharge machine in which a bipolar voltage is applied between a machining electrode and a workpiece.

In FIG. 7, reference numeral 1 denotes a processing electrode; 2, a workpiece to be disposed facing the processing electrode 1; 3, a first DC power supply capable of changing a voltage value; 4, a second DC power supply; A power supply 5 is a third DC power supply that applies a reverse voltage between the electrode 1 and the workpiece 2, that is, a pole, and a first DC power supply 6 controls opening and closing of a voltage between the DC power supply 3. A switching element 7 is a second switching element that controls the application of a voltage between the poles of the DC power supply 4, and a reference numeral 8 is a third switching element that controls the opening and closing of a voltage between the poles of the DC power supply 5.

Reference numerals 9 and 10 denote current limiting resistors for limiting the currents supplied from the first and third DC power supplies 3 and 5, respectively, 11 an oscillation circuit for opening and closing the switching element 6, and 12 a switching element. 7 is a one-shot multivibrator for controlling the opening and closing of 7, 7 is a logical product gate for controlling the opening and closing of the switching element 8, 14 is a logical product gate for controlling a trigger input to the one-shot multivibrator 12, and 15, 16, 17 and 18 are respectively Voltage divider resistor, 1
9 is a capacitor for voltage smoothing, 20 and 21 are differential amplifiers for amplifying the voltage generated across the voltage dividing resistors 16 and 18,
22 is a discharge detection circuit, 23 is a comparator, 24, 25
Is a diode for preventing backflow to each of the DC power supplies 3 and 4.

FIG. 8 is a circuit diagram showing the inside of an oscillation circuit 11 for controlling the opening and closing of the first switching element 6 shown in FIG. In the figure, reference numeral 26 denotes a machining start pulse generator which outputs "1" when machining is on and outputs "0" when machining is off. 27 is an initial set value storage unit, 28 is an up / down counter, 29 is a clock pulse generator, 30 is an oscillation circuit 1
An off-time setting device for setting an off-time, which is a time when the output 11T1 of the “1” becomes “0”;
2 and 33 are AND gates, respectively.

Next, the operation of the conventional power supply device for an electric discharge machine will be described. The discharge detection circuit 22
It is configured to determine whether or not a discharge has occurred between the electrodes based on a change in the voltage between the electrodes, and to output the determination result.
Generally, when a voltage is applied between the electrodes, the voltage between the electrodes maintains the applied voltage when no discharge occurs between the electrodes, but the voltage between the electrodes drops to about 20 V when the discharge occurs.

The discharge detection circuit 22 has a reference voltage Et for comparing the input voltage Ei. The output 22T becomes "1" when Ei <Et, and conversely, the output 22T when Et <Ei. Becomes “0”. That is, the discharge detection circuit 22 is configured so that the output becomes “0” when no discharge occurs between the poles, and the output becomes “1” when the discharge occurs between the poles.

The comparator 23 determines whether or not the average machining voltage between the poles is equal to or higher than OV based on the output of the differential amplifier 21. If the average machining voltage between the poles is equal to or higher than 0V, the comparator 23 determines "1" and 0V or lower. If it is, "0" is output. Further, the average machining voltage between the poles is smoothed by a capacitor 19 and then input to a differential amplifier 21 as a discriminating device.

The oscillation circuit 11 has 11T1, 11T2
Has two outputs. 11T1 becomes “0” after a certain delay time Toff2 when both 11T2 and the output 22T of the discharge detection circuit 22 become “1” after the state becomes “1”, and the set off time Is a pulse signal that maintains the “0” state during the first switching element 6.
Drive. On the other hand, 11T2 is a one-shot signal which becomes "0" for a fixed time Toff1 triggered by 11T1 becoming "1".

Also, a one-shot multivibrator 1
The trigger 2 is input when the output 14T of the AND gate 14 becomes "1". The output becomes "1" for a predetermined time Ton2, and the second switching element 7 is turned on. Further, the AND gate 13 outputs the third signal only when the output 11T1 of the oscillation circuit 11 is “0” and when the output 12T of the one-shot multivibrator 12 is “0”.
Is set to the ON state.

Next, the operation of the circuits shown in FIGS.
This will be described with reference to the timing chart shown in FIG. In FIG. 9, the current waveform and the voltage waveform between the electrodes are I
g, Eg, and the voltage value E ₄ in the voltage waveform Eg.
Is a gap voltage value corresponding to the reference voltage Et of the discharge detection circuit 22.

[0012] First, become output 11T1 "1" of the oscillation circuit 11, the voltage of the voltage value E ₁ from the DC power supply 3 to the machining gap is applied by turning on the switching element 6. A fixed delay time Toff after the output 11T1 becomes "1"
After one elapse, the output 22T of the discharge detection circuit 22 sets the second switching element 7 to either ON or OFF.

That is, when the output 22T of the discharge detection circuit 22 becomes "1" after the delay time Toff1 has elapsed since the output 11T1 of the oscillation circuit 11 became "1", that is,
Or inter-electrode voltage Eg is discharged induced by application between the electrode of the DC power source 3 is Eg <E _4, after the delay time Toff1 elapsed from when the output 11T1 is "1", already output of the discharge detection circuit 22 If 22T is "1", in other words, a discharge has already occurred between the electrodes and the voltage between the electrodes Eg <Eg <
If it turned E _4, output 12T "1" of the one-shot multivibrator 12, and the switching element 7
Is turned on, and the DC power supply 4 having the second high voltage is applied between the poles almost without passing through the limiting resistor, so that the discharge induced by the application of the DC power supply 3 between the poles has a large energy. The discharge is carried over by the DC power supply 4, and the discharge is applied to the output 12 of the one-shot multivibrator 12.
It is inherited and maintained only during the output duration Ton2 of T.

Further, since the discharge by the DC power supply 4 occupies most of the machining energy of the wire electric discharge machine, the DC power supply 4 supplies power for machining energy or the power supply for inducing the discharge of the DC power supply 3. It can also be expressed as

Next, when the output 12T becomes "0", since the output 11T1 has already become "0", the output 13T of the AND gate 13 becomes "1", and the switching element 8 is turned on, and , A reverse polarity voltage determined by the third DC power supply 5 is applied. Further, after the output 11T1 is in the “0” state during the set off time TOFF,
When it becomes "1" again, 13T becomes "0", and the switching element 8 is turned off, and at the same time, the switching element 6 is turned on.

Further, a method of controlling the off time TOFF at which the output 11T1 becomes "0" will be described. Comparator 2
The output 23T of No. 3 is “1” when the average machining voltage between the electrodes is 0 V or more, and is “0” when the average machining voltage is 0 V or less. Next,
Output 23T and output 29 from clock pulse generator 29
The output of the AND gate 32 of T is the up / down counter 2
8 is input to the up-clock U. In addition, output 23T
The output of the AND gate 33 of the output after passing through the inverter 31 and the output 29T is input to the down clock D of the up / down counter 28.

In the up / down counter 28, when the output 26T of the processing start pulse generator 26 is "0", the output values M1, M2, M3... After the output of the command unit becomes "1", the counter value is counted up by the input signal of the up clock, and is counted down by the input signal of the down clock. That is, if the average machining voltage between the poles is 0 V or more, the output 23T is "1", so that the counter value of the up / down counter 28 is counted up in synchronization with the up edge of the output 29T, and conversely, If the average machining voltage is 0 V or less, the output 23T is "0", and the counter value of the up / down counter 28 is counted down in synchronization with the up edge of the output 29T.

The output values Q1, Q2, Q3... Qn of the up / down counter 28 are
And the off time TOFF of the oscillation circuit 11 is set. By the above operation, when the average machining voltage is 0 V or more, the off-time is increased, and when the average machining voltage is 0 V or less, the off-time is reduced.

As described above, the third switching element 8 is turned on during the off time when the discharge pulse from the first and second switching elements 6 and 7 is completed, a reverse voltage is applied to the machining gap, and the average machining is performed. So that the voltage is zero
By controlling the off time of the switching element 6, the application time of the reverse voltage is controlled.

Since the conventional power supply device for an electric discharge machine is configured as described above, a large amount of current flows between the poles when the distance between the poles is sharply reduced, and the power supply device for the electric discharge machine has a problem. In addition, there have been problems such as disconnection of a wire serving as an electrode and generation of streaks on a processed surface of a workpiece.

In FIG. 7, the application time of the reverse voltage to the gap, in other words, the output 11T1
Is automatically controlled using the average voltage between the electrodes. Here, since the input to the differential amplifier 21 for detecting the average voltage between the electrodes is integrated by the capacitor 19, the input is smoothed with a time constant. Furthermore, the off time of the output 11T1 of the oscillation circuit 11 has no lower limit, and there is no means for controlling the ON time of the switching element 7 during the processing.

For example, FIG. 10 shows the signals between the gaps and the respective parts of the electric discharge machine shown in FIG. 7 when the gaps are sharply narrowed. 10, the same reference numerals as those in FIG. 9 denote the same or corresponding parts.

As shown in the figure, the average voltage between the poles is zero.
If the gap is sharply narrowed below V and a short circuit occurs,
Since the output 21T of the differential amplifier 21 has a value of 0 V or less for a while even after the gap between the poles, the application time of the reverse voltage to the gap continues to be shortened, and a large amount of current is supplied by the DC power supply 4 having a high voltage. It will be supplied between the poles.

In order to reduce such a problem, Japanese Unexamined Patent Application Publication No. 7-9256 discloses a technique for setting a lower limit value for the off time of the oscillation circuit 11 and limiting the on time of the switching element 7. It has been disclosed.

Each of FIGS. 11 to 15 is disclosed in
1 shows a conventional electric discharge machine disclosed in Japanese Patent No. 9256.

First, as a conventional example, a prior art in which a lower limit value is applied to the application time of the voltage of the opposite polarity to limit the current flowing between the electrodes will be described with reference to FIGS.
FIG. 11 shows the inside of the oscillation circuit 11 shown in FIG.
FIG. 3 shows a portion for controlling the time when the switching element 6 is turned off. In FIGS. 11 and 12, FIGS.
The same reference numerals denote the same or corresponding parts.

FIG. 11 shows the means for setting the off time of the switching time from the processing start pulse generator 26 to the AND gate 33 in the same manner as in FIG. 34 stores the voltage value of the DC power source 3 in FIG. 1, E ₁ voltage value storing unit for outputting digital data corresponding to the voltage value, 35 is E ₁
An off-time lower limit value setter that outputs digital data programmed based on the digital data from the voltage value storage unit 34, a digital data input from the off-time lower limit value setter 35, and an up-down counter 28 This is a coincidence comparison circuit that compares input digital data and outputs an output value 36T of “0” when the data coincides with each other. Control.

Next, the operation will be described. Voltage value E ₃
Operation of the switching element 7 to control the application between the electrode of the DC power supply 4, and a switching element 8 for controlling the application between the DC power source 4 having a voltage value E ₂ of the opposite polarity poles
Is controlled by the logical product output 13T of the logical product gate 13 of the output 11T1 of the oscillation circuit 11 and the output 12T of the one-shot multivibrator 12, as in the above-described technique. The control method will be mainly described.

In FIG. 11, similarly to the above-described technique, the logical product output of the output 23T of the comparator 23 as the discriminating device and the output 29T of the clock pulse generator 29 via the logical product gate 32 is obtained by the up-clock of the up-down counter 28. Input to U. Further, the output of the inverter 31 of the output 23T of the comparator 23, the output 29T from the clock pulse generator 29, and the output 36T from the coincidence comparison circuit 36 are input to the AND gate 33, and the AND output is up-down. Down clock D of counter 28
Is input to

In the up / down counter 28, when the output 26T of the machining start pulse generator 26 is "0", "0"
.. Mn are loaded into the up / down counter 28 and the processing start pulse generator 26 is output. When the output becomes "1", the counter value is counted up by the upclock input signal and is counted down by the downclock input signal.

Then, the counter output values Q1, Q2, Q3
.. Qn are sent to the off-time setting device 30, and the off-time TOFF of the oscillation circuit 11 is set. On the other hand, as described above, the E ₁ voltage value storage unit 34 stores the digital data corresponding to the voltage value of the DC power supply 3 in FIG. 7 at the time when the output of the machining start pulse generator 26 becomes “1”. Output to the lower limit value setting unit 35. At the same time, the off-time lower limit value setting unit 35 outputs digital data programmed based on the digital data from the E ₁ voltage value storage unit 34 to the coincidence comparison circuit 36.

[0032] Here, the larger the value of the voltage value E _1, the lower limit of the off-time increases, the binary number increases in proportion to the value of the voltage _{E 1 (M1, M2, M3} ···
A value obtained by multiplying Mn) by a certain coefficient or a value obtained by adding a certain constant to the value is output from the off-time lower limit value setting unit 35 as a binary number. A programmable IC or the like is used as the off-time lower limit value setting device 35. The match comparison circuit 36 compares the digital data input from the off-time lower limit value setting unit 35 with the digital data input from the up / down counter 28, and sets the output value 36T to "0" when the data match. While 36T is "0", the output of the AND gate 33 is always "0", and the up / down counter 28 does not count down.

By the above operation, the off-time is controlled so as to increase when the average machining voltage is 0 V or more and to decrease when the average machining voltage is 0 V or less.
It does not become smaller than the lower limit set in.

Next, the state when the gap is sharply reduced will be described with reference to FIG. In the figure, Eg, I
g is a voltage waveform and a current waveform between the electrodes, respectively. The signals indicated by other symbols are the same as those indicated by the same symbols in FIGS. 7 and 11. It is assumed that the state between the gaps is the same as that shown in FIG. 10 used for the description of the above-mentioned conventional technology. That is, the signals from the voltage waveform Eg between the electrodes in FIG. 12 to the output 29T of the clock pulse generator 29 are the same as those in FIG. It is assumed that the lower limit value of the off time is a value indicated by OFFmin in FIG.

As can be seen from FIG. 12, even if the poles are short-circuited and the average voltage 21T1 between the poles is 0 V or less, the time during which the output 11T1 of the oscillation circuit 11 is turned off does not become OFFmin or less. The time when the output 13T of the AND gate 13 is turned on is OFFmin.
It does not fall below.

The current limiting resistor 10 on the reverse voltage side is
Since the discharge on the reverse voltage side promotes the consumption of the electrodes, a resistor having a larger value is generally used as compared with the current limiting resistor 9 on the positive voltage side. In such an electric discharge machine, the longer the time for applying the reverse voltage is, the more the current flowing between the electrodes is limited. In other words, when the gap between the electrodes suddenly narrows, by setting a lower limit value for the application time on the reverse voltage side, and when the power supply voltage value on the side that induces the discharge on the positive voltage side increases, the lower limit value is set. Increasing the size limits the current flowing between the poles.

Next, a method of limiting the time for applying the positive voltage and limiting the current flowing between the electrodes will be described with reference to FIGS.

FIG. 13 is obtained by adding a gap voltage detecting circuit 37 and an AND gate 47 to the device shown in FIG. The inside of the oscillation circuit 11 related to the signal for turning off the switching element 6 is the same as that shown in FIG. 13, the same reference numerals as those in FIG. 7 denote the same or corresponding parts.

FIG. 14 shows an example of the gap voltage detecting circuit 37 shown in FIG. In the drawing, reference numeral 38 denotes a capacitor for smoothing the voltage between contacts divided by the voltage dividing resistors 17 and 18, and 39 to 42 denote capacitors 3 respectively.
A diode for full-wave rectification of the voltage between contacts smoothed by 8; 43 to 44 are resistors; 46 is a resistor 44;
A reference voltage E ₅ set by 45 compares the full-wave rectified value of the machining gap voltage determined by the resistor 43,
This is a comparator that outputs “0” or “1”.

Next, the operation will be described. Voltage value E ₁
A switching element 6 for controlling the application of the DC power supply 3 between the electrodes, and a DC power supply 5 having a voltage value E ₂ of the opposite polarity.
Since control of the switching element 8 for controlling the application between the poles similar to the conventional art, the DC power supply 4 of the voltage value E ₃
A method of controlling the output 12T of the one-shot multivibrator 12 for controlling the switching element 7 for controlling the application to the gap will be mainly described.

The inter-electrode voltage detection circuit 37 shown in FIG.
Determines the change in the electrical state of the machining gap between the machining electrode 1 and the workpiece 2 based on the voltage appearing at both ends of the voltage-dividing resistor 18, and determines the digital value of "0" or "1". It is configured to output an output, "1" when the gap is in a normal discharge state, and "0" when the gap is abnormally narrow.
Is output. The capacitor 38 for smoothing the gap voltage smoothes the gap voltage for off-time control. For example,
As compared with the capacitor 19 shown in FIG. 4, the capacitance is smaller and the smoothing time constant is set smaller.

Therefore, in the comparator 46, the voltage between the electrodes is smoothed with a small time constant and then subjected to full-wave rectification.
_6, a positive reference voltage E ₅ are compared. The comparator 46 outputs “1” if E5 <E6 is satisfied in a normal discharge state between the electrodes, and if the distance between the electrodes is abnormally narrow and the voltage between the electrodes is reduced, as a result, if E5> E6 is satisfied. positive reference voltage E ₅ is configured to output a "0".

In FIG. 13, the output 12T of the one-shot multivibrator 12 is the output 11T of the oscillation circuit 11.
It is controlled by the logical product of T2, the output 22T of the discharge detection circuit 22, and the output 37T of the gap voltage detection circuit 37.

Therefore, the output 11T1 of the oscillation circuit 11
Is turned on, the output 11T2 of the oscillation circuit 11 is kept on after a lapse of time Toff1, and
When the output of the gap voltage detection circuit 37 is "1" in a normal discharge state between the gaps, the gap voltage Eg changes from Eg> E4 to E
Only when the state changes to g <E4, that is, when the output 22T of the discharge detection circuit 22 changes from “0” to “1”, the one-shot multivibrator 12 is triggered, and the switching element 7 is turned on. State. Therefore, when the gap becomes abnormally narrow, the switching element 7 is not turned on.

Next, the state when the gap is sharply reduced will be described with reference to FIG. In the figure, Eg, I
g is a voltage waveform and a current waveform between the electrodes, respectively. The signals indicated by other symbols are the signals of the same symbols shown in FIGS. It is assumed that the state between the gaps is the same as that shown in FIG. 10 used for the description of the above-described conventional technique.

That is, the signals from the voltage waveform Eg between the electrodes to the output 22T of the discharge detection circuit 22 in FIG.
It is the same as that shown in FIG. From FIG. 15, when the gap between the poles is short-circuited and the average voltage 21T1 between the poles is still 0 V or less, the off time of the output 11T1 of the oscillation circuit 11 continues to decrease, but the gap voltage detection circuit 37 has a small time constant. A short circuit between the electrodes is detected, and an interlock is applied so that the switching element 7 is not turned on. That is,
When the gap between the poles is sharply reduced, the application of the DC power supply 4 is completely stopped to limit the current flowing between the poles.

[0047]

Since the conventional power supply device for electric discharge machining is configured as described above, if the distance between the poles is sharply reduced and the current limit between the poles is insufficient, In the case of wire electric discharge machines, there are problems such as disconnection of the wire which is an electrode and generation of streaks on the machined surface of the workpiece, and excessive current limitation between the poles was performed. In such a case, there is a problem that a short circuit between the poles is not easily solved and the processing speed is reduced.

This is because, when the distance between the electrodes is sharply reduced, a lower limit value is set for the application time on the reverse voltage side, and the voltage value of the DC power supply 3 on the side that induces the discharge on the positive voltage side is increased. If the lower limit value is increased, the current flowing between the poles is limited, for example, in a device in which the application time of the DC voltage source 4 on the positive voltage side occupying most of the discharge energy is long. Nevertheless, when the voltage value of the DC power supply 3 is small, the lower limit value becomes smaller in the application time on the reverse voltage side, so that the current flowing between the poles when the gap between the poles narrows sharply is not sufficient. In some cases, the wire electric discharge machine may break the wire.

Conversely, in the same apparatus, when the voltage value of the DC power supply 3 is large, despite the short application time of the DC power supply 4 on the positive voltage side, which occupies most of the discharge energy, the reverse voltage side Since the lower limit of the application time increases, the current flowing through the gap when the gap sharply narrows is more than necessary, and the processing speed is reduced.

Further, in a device for limiting the current flowing between the poles by completely stopping the application of the DC power supply 4 occupying most of the discharge energy when the gap between the poles is sharply reduced, In a wire electric discharge machine, when machining chips and the like are generated between the poles, that is, when a short circuit occurs, the application of the DC power supply 4 blows the machining chips with high energy to restore insulation between the poles. However, in the present apparatus, when the gap between the poles is sharply reduced, the application of the DC power supply 4 is completely stopped, so that it takes time to recover the insulation between the poles, a loss occurs in the processing speed, and the processing efficiency is poor. There was a problem.

The present invention has been made in order to solve the above-described problems, and it is intended to prevent the occurrence of electrolysis, electrolytic corrosion, and the like on a workpiece during processing, and to reduce the gap between the electrodes. An object of the present invention is to provide a power supply device for an electric discharge machine and a control method thereof, which reduce damage due to current concentration on an electrode or a workpiece, enable high-speed machining, and improve machining efficiency.

[0052]

[0053]

[0054]

SUMMARY OF THE INVENTION A power supply device for an electric discharge machine according to the present invention is a power supply device formed between an electrode and a workpiece.
DC voltage to induce discharge between poles as gap
, The output voltage value of which is variable
A DC power supply, and a second DC for applying a DC voltage between the poles.
A power supply, and between the poles, the first and second DC power supplies;
A third DC voltage for applying a DC voltage having a polarity opposite to that of the
And the first, second and third DC power supplies
First and second for turning on / off the voltage application between the electrodes, respectively.
A and third switching means, applied to said machining gap
Mean and machining voltage detecting means to detect an average machining voltage that, prior to
Set the lower limit of off-time of the first switching means
Off-time lower limit value setting device, and the off-time lower limit value
Within the range of the lower limit of the off time set on the setting device
The average processing output from the average processing voltage detection means
The first switching means is controlled so that the voltage becomes zero.
The off-time is variably controlled, and the variably controlled
Turns off the first switching means based on the off time.
A first switching control circuit for turning on and off the first switching control circuit;
At a predetermined delay from the time when the switching means is turned on
The second switch for a predetermined on-time after the time has elapsed.
The second switch to turn on the switching means.
A second switching control circuit for turning on and off the switching means;
In the off time of the first switching means, the third
So that the third switch is turned on.
A third switching system for controlling on / off of the switching means
Control circuit and intermittently generate electric discharge to
In a power supply unit for an electric discharge machine to be machined,
Voltage, and compares the detected voltage with a predetermined voltage.
Detects a short circuit condition where the gap is abnormally narrow
Voltage detection circuit and the detection of this voltage detection circuit
Signal from the first switching control circuit.
Characterized in that it comprises a in-<br/> interlock hand stage subjecting the interlock control to shorten the Futaimu.

[0055] The method of the following according to the invention for an electrical discharge machine power supply, electrodes and the workpiece by generating an intermittent discharge in the machining gap (inter-electrode) which is formed between the workpiece EDM machine electricity supplies power to electric discharge machine for machining a
In the power supply device, the voltage between the poles is detected, and
The gap between the electrodes is abnormal by comparing the detected voltage with the specified voltage
Short-circuit condition, which becomes narrower, is detected.
To reduce the off-time due to the first switching control circuit.
The interlock is applied to the control to be performed .

[0056]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) Embodiments of a power supply device for an electric discharge machine and a control method thereof according to the present invention will be described below in detail with reference to the drawings. First, as an embodiment of the present invention, a method of changing the lower limit value of the application time of the reverse polarity voltage in accordance with the application time of the voltage on the positive polarity side will be described.

FIG. 1 is a circuit diagram showing a configuration of a power supply device for an electric discharge machine according to the first embodiment. FIG. 2 is a circuit diagram showing a switching element 6 inside an oscillation circuit 11 shown in FIG.
FIG. 3 is a circuit diagram showing a part for controlling a time when the switch is turned off. 1 and 2, the same reference numerals as those in FIGS. 7 and 11 showing the related art indicate the same or corresponding parts.

FIG. 1 has substantially the same structure as that shown in FIG. 7, but the application time To of the DC power supply 4
Digital data indicating n2 is supplied from the one-shot multivibrator 12 to the oscillation circuit 11 by the bus 12BUS.
It is transmitted to. Even if it is in FIG.
Although the structure is almost the same as that shown in FIG. 1, reference numeral 47 in the figure denotes an application time storage unit for storing digital data corresponding to the application time between the poles of the DC power supply 4 in FIG.

Next, the operation of the first embodiment will be described. The outline of the operation is basically that a conventional DC power supply 3 is provided by setting a lower limit value for the application time on the reverse voltage side when the gap between the electrodes is sharply narrowed, and by inducing a discharge on the positive voltage side. When the voltage value increases, it is the same as limiting the current flowing between the poles by increasing the lower limit value. Therefore, a method of setting the lower limit value of the off-time different from the prior art will be mainly described.

In FIG. 2, the output 23T of the comparator 23 and the output 29T of the clock pulse generator 29 as a discriminating device are similar to the conventional devices shown in FIGS.
And the logical product output through the logical product gate 32 is input to the up clock U of the up / down counter 28. Further, the output of the inverter 31 of the output 23T of the comparator 23 and the output 29T of the clock pulse generator 29 are output.
And the output 36T from the coincidence comparison circuit 36 are input to the AND gate 33, and the AND output is input to the down clock D of the up / down counter 28.

In the up / down counter 28, when the output 26T of the machining start pulse generator 26 is "0", "0"
.. Mn are loaded into the up / down counter 28 and the processing start pulse generator 26 is output. After the output of “1” becomes “1”, the counter value is counted up by the upclock input signal.
It is counted down by the down clock input signal.
The counter output values Q1, Q2, Q3,..., Qn are sent to the off-time setting unit 30, and the output 1 of the oscillation circuit 11 is output.
An off time TOFF of 1T1 is set.

On the other hand, in the first embodiment, the application time storage unit 47 stores the digital data corresponding to the application time Ton2 between the DC power supply 4 shown in FIG. 35.

Here, as the time during which the switching element 7 is turned on and the current is supplied between the poles by the DC power supply 4 becomes longer, the current flowing between the poles when the gap is short-circuited becomes larger. As a program incorporated in the setting unit 35, a program that increases the off-time lower limit as the application time of the DC power supply 4 to the gap between electrodes increases.

For example, since the lower limit value of the off time increases as the voltage value of the DC power supply 4 increases, the binary number (M1, M2) increases in proportion to the voltage value of the DC power supply 4.
2, M3... Mn) is a value obtained by multiplying the value by a certain coefficient, or a value obtained by adding a certain constant to the value.
What is necessary is just to make it output from the off-time lower limit value setting device 35 as a base number. Further, the off-time lower limit value setting device 35
Outputs the digital data programmed based on the digital data from the application time storage unit 47 to the coincidence comparison circuit 36.

The match comparison circuit 36 compares the digital data input from the off-time lower limit value setting device 35 with the digital data input from the up / down counter 28, and when the data matches, sets the output value 36T to "0". To While the output value 36T from the coincidence comparison circuit 36 is "0", the output of the AND gate 33 is always "0", and the up / down counter 28 does not count down.

By the above operation, the average processing voltage is 0 during the time when the state of the output 11T1 of the oscillation circuit 11 is "0".
When the voltage is equal to or higher than V, the voltage is controlled to increase, and when the voltage is equal to or lower than 0 V, the voltage is controlled to decrease, but does not become smaller than the lower limit set by the off-time lower limit setting unit 35.

Next, the state when the gap is sharply reduced will be described with reference to FIG. In the figure, Eg, Ig
Represents a voltage waveform and a current waveform between the electrodes, respectively. Signals indicated by other symbols are signals of the same symbols shown in FIGS. 1 and 2.

In the state of the gap, a lower limit value is set for the application time on the reverse voltage side, and the lower limit value is increased as the voltage value of the DC power supply 3 on the side that induces the discharge on the positive voltage side increases. compared to FIG. 12 which is used in the description of the prior art, the voltage value E ₁ of the side of the DC power source 3 to induce the discharge of the positive voltage side is the same, the DC positive voltage side of the majority of the discharge energy Since the application time of the power supply 4 is long, OFFmin, which is the lower limit of the application time of the reverse voltage, is also long.

FIG. 3 shows that even if the gap between the electrodes is short-circuited and the average voltage 21T1 between the poles is 0 V or less, the time during which the output 11T1 of the oscillation circuit 11 is turned off does not become OFFmin or less. Time, that is, the time when the output 13T of the AND gate 13 is turned on does not become OFFmin or less.

Further, even if the application time of the DC power supply 4 on the positive voltage side, which occupies most of the discharge energy, becomes longer, OFFmin which is the lower limit value of the application time of the reverse voltage becomes longer. Even if it becomes narrower, the length of OFFmin is longer and the current flowing between the poles is restricted with higher efficiency as compared with the conventional technology, so that the wire is not broken due to the concentration of current.

This is because the current limiting resistor 10 on the reverse voltage side
In general, since the discharge on the reverse voltage side promotes the consumption of the electrode, a large value is generally used as compared with the current limiting resistor 9 on the positive voltage side. In an applied electric discharge machine, the longer the time for applying the reverse voltage, the more the current flowing between the electrodes is limited.

Further, the DC power supply 3 on the side that induces the discharge on the positive voltage side may be applied between the poles via the limiting resistor 9, and its discharge energy is compared with the discharge energy by the DC power supply 4. Is very small, so that the lower limit of the application time of the reverse voltage is determined by the application time between the poles of the DC power supply 4 as compared with the conventional technique in which the lower limit of the application time of the reverse voltage is controlled by the voltage value of the DC power supply 3. Is more precise control.

Here, as the time during which the switching element 7 is turned on and the current is supplied between the poles by the DC power supply 4 becomes longer, the current flowing between the poles when the gap is short-circuited becomes larger. As a program incorporated in the setting unit 35, a program that increases the off-time lower limit as the application time of the DC power supply 4 to the gap between electrodes increases.

For example, since the lower limit value of the off-time increases as the voltage value of the DC power supply 4 increases, the binary numbers (M1, M1) which increase in proportion to the voltage value of the DC power supply 4
2, M3... Mn) is a value obtained by multiplying the value by a certain coefficient, or a value obtained by adding a certain constant to the value.
What is necessary is just to make it output from the off-time lower limit value setting device 35 as a base number.

(Embodiment 2) Next, as Embodiment 2 of the present invention, a circuit for setting the lower limit of the voltage application time of the opposite polarity and a detection circuit for detecting the voltage of at least one polarity between the poles A method for controlling the lower limit value according to the output value of the detection circuit will be described.

FIG. 4 is a schematic diagram of a power supply device for electric discharge machining which realizes the present invention, which is obtained by adding a gap voltage detecting circuit 37I to FIG. 7 showing the prior art. One signal line is connected from the inter-electrode voltage detection circuit 37I to the oscillation circuit 11 related to the signal for turning off the switching element 6.
4, the same reference numerals as those in FIG. 7 showing the prior art indicate the same or corresponding parts.

FIG. 5 is a circuit diagram showing the voltage detecting circuit 3 shown in FIG.
7I shows an example. In the figure, 48 is a capacitor for smoothing the inter-electrode voltage divided by the voltage dividing resistors 17 and 18, 49 is a diode for half-wave rectifying the inter-electrode voltage smoothed by the capacitor 48, 50 to 52 are resistors, A comparator 53 compares the reference voltage E ₆ set by the resistors 51 and 52 with the half-wave rectified value of the voltage between contacts determined by the resistor 50, and outputs “0” or “1”. .

In FIG. 5, portions other than the gap voltage detection circuit 37I surrounded by a broken line are substantially the same as those in FIG. 8 showing the internal circuit of the conventional oscillation circuit 11 shown in FIG.
The input AND gate 33 becomes a three-input AND gate 33I, and an output 37IT from the gap voltage detection circuit 37I is input to the input.
Has been added.

Next, the operation will be described. As in the prior art shown in FIG. 7, the switching element 6 that controls the application of the DC power supply 3 to the gap is provided with the output 11 of the oscillation circuit 11.
The switching element 7 for controlling the application of the DC power supply 4 between the poles by T1 is a one-shot multivibrator 1
The switching element 8 that controls the application of the DC power supply 5 having the opposite polarity to the gap by the output 12T of the second circuit 2 outputs the output 11T1 of the oscillation circuit 11 and the output 12T of the one-shot multivibrator 12 through the AND gate 13. Each is controlled by the logical product output 13T.

The one-shot multivibrator 1
2 and the output 13T of the AND gate 13 are controlled in the same manner as in the prior art shown in FIG. 7, so that the control method of the output 11T1 of the oscillation circuit 11 and the operation of the discharge detection circuit 37I will be mainly described. explain.

The voltage detection circuit 37I shown in FIG.
Is configured to determine a state change between the poles based on a voltage appearing across the voltage dividing resistor 18 and output a digital output of “0” or “1”. If a proper gap is maintained in the discharge state, "1" is output, and if the gap is abnormally small and a short circuit appears, "0" is output.
The voltage smoothing capacitor 48 smoothes the voltage between the electrodes divided by the voltage-dividing resistor 18, and detects the voltage between the electrodes at a higher speed. In comparison with the capacitor 19 shown in FIG. The capacitance is small and the smooth time constant is small.

The diode 49 is for half-wave rectification and detection of only the positive polarity side of the bipolar voltage. The reason is that the power supply device for the electric discharge machine applies a voltage between the poles, which is bipolar and has an average of 0 V, so if the voltage between the poles is detected without rectification, the It is very difficult to detect a state as a voltage.

Generally, if a proper gap is maintained in a normal discharge state between the electrodes, the application time of the DC power supply 3 is several tens of microseconds, and the voltage between the electrodes is smoothed with a small time constant after the voltage division. Thereafter, the + input 53I of the comparator 53, which has been half-wave rectified, becomes large. If the gap between the poles becomes abnormally short and becomes short-circuited, 53I becomes small. Therefore, the comparator 53 compares 53I with the positive reference voltage E ₆ , outputs “1” if E ₆ <53I in a normal discharge state, and abnormally narrows the gap. The voltage drops and E ₆ >
53I, the positive reference voltage E is output so as to output "0".
₆ is set.

In FIG. 5, similarly to the prior art shown in FIGS. 7 and 8, the output from the AND gate 32 of the output 23T of the comparator 23 and the output 29T from the clock pulse generator 29 is determined by the up-down counter 28. Input to clock U. Also, the output 23T of the comparator 23
, The output 29T from the clock pulse generator 29, and the output 37IT of the inter-electrode voltage detection circuit 37I in the present invention are input to the AND gate 33I. The logical product output is input to the down clock D of the up / down counter 28.

In the up / down counter 28, as in the prior art shown in FIGS.
When the output 26T of No. 6 is "0", "0" indicates that the workpiece is not being machined,
Although "1" means that machining is in progress, the output values M1, M2, M3... Mn of the initial setting value storage unit 27 are loaded into the counter, and the output of the machining start pulse generator 26 is "1".
After that, the counter value is counted up by the upclock input signal, and is counted down by the downclock input signal.

Then, the counter output values Q1, Q2, Q3
.. Qn are sent to the off-time setting device 30, and the off-time TOFF of the output 11T1 of the oscillation circuit 11 is set. On the other hand, as already described in the present embodiment, the gap voltage detection circuit 37I outputs “0” when the gap is abnormally small and the gap tends to be short-circuited. Output 37 of the gap voltage detection circuit 37I
While IT is "0", the output of the AND gate 33I is always "0", and the up / down counter 28 does not count down.

According to the above operation, while the state of the output 11T1 of the oscillation circuit 11 is "0", the average processing voltage remains at 0.
The voltage is controlled so as to increase when the voltage is equal to or more than V, and to decrease when the voltage is equal to or less than 0 V.
There is no further reduction.

Next, a state when the gap is sharply reduced will be described with reference to FIG. In the figure, Eg, Ig
Represents a voltage waveform and a current waveform between the electrodes, respectively. Signals indicated by other symbols are signals of the same symbols shown in FIGS. 4 and 5.

The state between the gaps occupies most of the voltage value E ₁ of the DC power supply 3 on the side that induces the discharge on the positive voltage side and the discharge energy shown in FIG. 3 used in the description of the first embodiment. It is assumed that the application time of the DC power supply 4 on the positive voltage side is the same.

FIG. 6 shows that even if the gap between the poles is short-circuited and the average voltage 21T1 between the poles is 0 V or less, the gap voltage detection circuit 37I
When the output 37IT of the oscillation circuit 11 becomes "0", the decrease of the time for turning off the output 11T1 of the oscillation circuit 11 stops, and the time for applying the reverse voltage, that is, the time for turning on the output 13T of the AND gate 13 is OFFlimit or less. It turns out that it does not become.

As described above, the current limiting resistor 10 on the reverse voltage side
In general, since the discharge on the reverse voltage side promotes the consumption of the electrode, a large value is generally used as compared with the current limiting resistor 9 on the positive voltage side. In an electric discharge machine to which the constant voltage is always applied, the longer the time for applying the reverse voltage, the more the current flowing between the gaps is limited. Therefore, when the gap between the poles narrows sharply, the average voltage on the positive polarity side between the poles is detected to decrease, and the reduction of the application time on the reverse voltage side is stopped to reduce the current flowing between the poles. Restrictions are added.

In this embodiment, the circuit for setting the lower limit of the application time of the reverse voltage is not required, and the apparatus is simple. Furthermore, in the present embodiment, as shown in FIGS. 13 to 15, the application of the DC power supply 4 is completely stopped when the gap between the poles is sharply reduced, thereby limiting the current flowing between the poles. When processing dusts between the poles of the apparatus are short-circuited, the processing wastes are blown off by high energy due to the application of the DC power supply 4 and the insulation between the poles cannot be restored. , And the problem that the processing speed is lost is also solved.

Further, in the present embodiment, a half-wave rectifier circuit is used as the gap voltage detecting circuit 37, but the same effect can be obtained by using a full-wave rectifier circuit shown in FIG.

[0094]

[0095]

[0096]

As described above, according to the present invention,
According to the power supply device for the electric discharge machine, the voltage between the electrodes is detected.
And compare this detection voltage with a predetermined voltage.
Inter-pole voltage to detect a short-circuit condition where the gap is abnormally narrow
Detection circuit and the detection signal of this voltage detection circuit
Shortening the off-time by the first switching control circuit
Interlock means to interlock control
Because it is equipped with, while preventing the occurrence of electrolysis and electrolytic corrosion on the workpiece during processing, and reduces the damage due to current concentration on the electrode and the workpiece when the gap between the electrodes is narrowed,
In addition, high-speed processing can be performed, and processing efficiency can be improved.

According to the control method of the power supply device for the electric discharge machine according to the next invention, the voltage between the gaps is detected, and this detection is performed.
By comparing the output voltage with the specified voltage,
Detects a short-circuit condition that is narrowing, and uses this detection signal to
Shortening the off-time by the first switching control circuit
Control is interlocked,
Prevents the occurrence of electrolysis and electrolytic corrosion on the workpiece during processing, reduces damage due to current concentration on the electrodes and workpiece when the gap between the electrodes becomes narrow, and enables high-speed processing,
Processing efficiency can be improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a power supply device for an electric discharge machine according to a first embodiment.

FIG. 2 is a block diagram showing an internal configuration of the oscillation circuit shown in FIG.

FIG. 3 is a timing chart showing a gap state and a state of a power supply device during machining processing of the electric discharge machine shown in FIGS. 1 and 2;

FIG. 4 is a circuit diagram showing a configuration of a power supply device for an electric discharge machine according to a second embodiment.

FIG. 5 is a circuit diagram showing an internal configuration of a gap voltage detection circuit shown in FIG. 4;

6 is a timing chart showing a gap state and a state of a power supply device during machining processing of the electric discharge machine shown in FIGS. 4 and 5. FIG.

FIG. 7 is a circuit diagram showing a configuration of a conventional power supply device for an electric discharge machine.

FIG. 8 is a block diagram showing an internal configuration of the oscillation circuit shown in FIG.

FIG. 9 is a timing chart showing a gap state and a state of a power supply device during machining processing of the electric discharge machine shown in FIGS. 7 and 8;

FIG. 10 is a sectional view of the electric discharge machine shown in FIGS. 7 and 8;
It is a timing chart which shows a gap condition and a state of a power supply device when a processing gap suddenly narrows during processing.

FIG. 11 is a block diagram showing a configuration of a conventional off-time setting unit.

FIG. 12 is a timing chart showing a state of a gap and a state of a power supply device when a machining gap suddenly narrows during machining in the electric discharge machine shown in FIGS. 7 and 11;

FIG. 13 is a circuit diagram showing a configuration of a conventional power supply device for an electric discharge machine.

FIG. 14 is a circuit diagram showing a configuration of a gap voltage detection circuit shown in FIG.

FIG. 15 is a timing chart showing the state of the gap and the state of the power supply device when the machining gap suddenly narrows during machining in the electric discharge machine shown in FIGS. 13 and 14.

[Explanation of symbols]

1 working electrode, 2 workpiece, 3 DC power supply with variable voltage, 4 DC power supply, 5 DC power supply for applying reverse polarity voltage,
Reference Signs List 11 oscillation circuit, 12 one-shot multivibrator, 13 AND gate, 22 discharge detection circuit, 23
Comparator, 28 up / down counter, 30 off-time setting device, 35 off-time lower limit value setting device, 36
Match comparison circuit, 47 application time storage

Claims (2)

(57) [Claims] 1. A process formed between an electrode and a workpiece.
DC voltage for inducing discharge between the poles as a gap
A first direct current that can vary the output voltage value to be applied.
And a second DC power supply for applying a DC voltage between the poles , and a voltage between the first and second DC power supplies between the poles.
A third DC power supply for applying a DC voltage having a polarity opposite to that of the first DC power supply and the first, second, and third DC power supplies to the gap between the electrodes.
First, second, and third, respectively, for turning on / off the voltage application of
Setting the third switching means, and the average machining voltage detecting means to detect an average machining voltage applied to the machining gap, the lower limit of the off-time of the first switching means
And an off-time lower limit value setting device to be set.
Within the range not less than the lower limit, from the average machining voltage detection means
The first processing is performed so that the output average processing voltage becomes 0.
Variable control of the off time of the switching means
The first control is performed based on the variably controlled off-time.
First switching system for turning on / off switching means
From the time when the first switching means is turned on.
Before the specified delay time elapses and before the specified ON time
The second switching means is turned on so that the second switching means is turned on.
Second switching system for turning on / off switching means
Control circuit and the off-time of the first switching means.
So that the third switch is turned on.
A third switching system for controlling on / off of the switching means
And a control circuit for processing the workpiece by intermittently generating discharge.
In the power supply device for the electric discharge machine, the voltage between the electrodes is detected, and the detected voltage is set to a predetermined value.
Short circuit due to abnormally narrow gap between poles compared to voltage
An inter-electrode voltage detection circuit for detecting a taste state, and the first switch based on a detection signal of the inter-electrode voltage detection circuit.
For control to shorten off-time by the switching control circuit
Power supply device for an electrical discharge machine, characterized in that it comprises, interlock hand stage applying interlock. 2. A process formed between an electrode and a workpiece.
DC voltage for inducing discharge between the poles as a gap
A first direct current that can vary the output voltage value to be applied.
And a second DC power supply for applying a DC voltage between the poles , and a voltage between the first and second DC power supplies between the poles.
A third DC power supply for applying a DC voltage having a polarity opposite to that of the first DC power supply and the first, second, and third DC power supplies to the gap between the electrodes.
First, second, and third, respectively, for turning on / off the voltage application of
Setting the third switching means, and the average machining voltage detecting means to detect an average machining voltage applied to the machining gap, the lower limit of the off-time of the first switching means
And an off-time lower limit value setting device to be set.
Within the range not less than the lower limit, from the average machining voltage detection means
The first processing is performed so that the output average processing voltage becomes 0.
Variable control of the off time of the switching means
The first control is performed based on the variably controlled off-time.
First switching system for turning on / off switching means
From the time when the first switching means is turned on.
Before the specified delay time elapses and before the specified ON time
The second switching means is turned on so that the second switching means is turned on.
Second switching system for turning on / off switching means
Control circuit and the off-time of the first switching means.
So that the third switch is turned on.
A third switching system for controlling on / off of the switching means
And a control circuit for processing the workpiece by intermittently generating discharge.
In the power supply device for the electric discharge machine, the voltage between the electrodes is detected, and the detected voltage is set to a predetermined value.
Short circuit due to abnormally narrow gap between poles compared to voltage
The taste state is detected, and the first switch is detected by the detection signal.
Control to reduce the off-time by the switching control circuit.
A control method of a power supply device for an electric discharge machine, wherein an interlock is applied .