JPH09123024A - Power unit for electric discharge machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilely obtain a rectangular current waveform suitable for reducing electrode consumption without complicating a circuit composition. SOLUTION: This power unit includes a processing current supply means 5, which has a DC power system 3 connected to an electrode 1 and a workpiece 2 through a switching element 4, and a current damping means 6 which includes a DC power system 7 connected parallel to the processing current supply means 5 and damps the discharge current. A processing current bypass means 9, which includes a switching element 11 connected in parallel to the processing current supply means 5, is provided and the switching element 11 of the processing current bypass means 9 is turned on for a specific duration by a current control means 20 when the switching element 4 of the processing current supply means 5 is turned off.

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 which supplies machining power between an electrode and a workpiece.

[0002]

2. Description of the Related Art A power supply device for an electric discharge machine supplies a controlled pulse-shaped current waveform having a desired current peak value to a gap between an electrode and a workpiece according to a preset on / off time. It is supplied to generate an electric discharge, and thereby the workpiece is processed into a desired shape.

When the workpiece to be electro-discharge machined is a super hard material, a machining current waveform having a high machining current peak value and a short pulse width is suitable, and in view of this, it is conventionally shown in FIG. Such a processing power supply device is used.

As shown in FIG. 7, the circuit configuration of a conventional power supply device for an electric discharge machine is a DC power supply 3 connected to an electrode 1 and a workpiece 2 via a switching element 4 to supply a machining current. The switching element 4 is composed of a means 5 and a processing current attenuating means 6 including a DC power source 7 and a diode 8 connected in parallel with the processing current supply means 5, and the switching element 4 is a gate signal (driving signal) output from the current control means 20. Turn on / off by.

8 (a) to 8 (c) show the on / off timing of the switching element 4, the inter-electrode voltage waveform, and the inter-electrode current waveform in the above-described power supply device for an electric discharge machine. FIG. 8A shows a voltage waveform between the electrodes when a voltage is applied between the electrodes by an external auxiliary power supply or the DC power supply 3 not shown at the timing indicated by reference numeral T1, and FIG. 8C shows the waveform of the current between electrodes, and FIG. 8C shows the drive signal of the switching element 4. In FIG. 8C, A is the drive signal ON timing of the switching element 4 when a voltage is applied between the electrodes by an external auxiliary power source, and B is a DC voltage when the voltage is applied between the electrodes by the DC power supply 3. The drive signal ON timing of the switching element 4 is shown respectively.

When a voltage is applied at the timing indicated by T1, discharge starts at the timing indicated by T2 when the insulation between the electrodes is destroyed after a no-load time (T1 → T2) in which no discharge occurs. To do. A current starts to flow between the electrodes from the start of discharge, and the current continues to flow for a desired time according to the processing content, so that at the timing of T3 when the desired peak value Ip is reached, the drive signal of the switching element 4 is reached. Turn off.

From the timing of T3, the current between the poles tries to keep the current flowing between the poles by the energy stored in the wiring inductance L1 of the wiring and the power supply line to the pole. The direct current power supply 7 rapidly attenuates the current value.

As described above, the conventional power supply device for an electric discharge machine has a characteristic that a triangular current waveform having a short pulse width and a high peak value can be easily obtained with a simple circuit configuration.

[0009]

However, the triangular current waveform shows excellent characteristics in terms of processing speed particularly when the work piece is a superhard material, but the shape of the electrode is transferred to the work piece. In the case of a die-sinker EDM machine, the consumption of the electrodes may be too large to be ignored. Considering the consumption of the electrodes, it is preferable that the current waveform has a rectangular wave shape with a shorter pulse width and a higher peak value than the triangular shape, but a simple circuit makes it easy to obtain such a current waveform. It was difficult to get to.

As described above, since the conventional power supply device for an electric discharge machine has the above-mentioned current waveform generating characteristics, in order to reduce the electrode wear, a rectangular shape having a high peak value and a short pulse width is used. In order to obtain the wave current, there are problems that the circuit becomes complicated and the circuit configuration becomes expensive.

Further, in the conventional power supply device for an electric discharge machine,
The switching element for applying the processing current is driven for a certain on-time to determine the peak current.Therefore, the processing current depends on the voltage fluctuation of the current power supply, the variation of the arc potential between the poles, the size of the machine tool, the stroke, etc. Due to external factors such as variations in the inductance of the power supply line and wiring, the delay time from the start of discharge until the machining current between the poles reaches the peak value fluctuates, so the peak value of the triangular wave current becomes the desired peak value. However, there were problems such as fluctuations in the total machining accuracy and roughness of the machined surface.

The present invention has been made to solve the above-mentioned problems, and a rectangular current waveform suitable for reducing electrode wear can be easily obtained without complicating the circuit structure. At the same time, it is an object of the present invention to provide an inexpensive and highly reliable power supply device for an electric discharge machine.

[0013]

In order to achieve the above-mentioned object, a power supply device for an electric discharge machine according to the present invention is a first power supply device connected to an electrode and a workpiece in series via a first switching element. Machining current supply means composed of the DC power supply and the first switching element, and a second DC power supply, and is connected in parallel to the machining current supply means for the electrode and the workpiece, and discharge current is supplied. A power supply device for an electric discharge machine, comprising: a current damping means for attenuating; a machining current bypass means having a second switching element, connected in parallel with the machining current supply means; and a turn-off of the first switching element. And a current control means for turning on the second switching element for a predetermined time.

According to the power supply device for the electric discharge machine of the present invention, the machining current supply means has the switching element in the ON state, and the machining gap current is supplied by the DC power supply. When the switching element is turned off, the machining voltage bypass means is switched. By turning on the element, the machining gap bypass means is used to gradually attenuate the machining gap current by the energy stored in the inductance of the power supply line and the wiring, and then the machining voltage bypass means. The switching element is turned off, and the energy stored in the inductance is canceled by the DC power supply of the current attenuating means to rapidly lower the inter-electrode current. As a result, a substantially trapezoidal current waveform close to a rectangular wave is obtained.

A power supply device for an electric discharge machine according to the next invention is a machining device comprising a first DC power supply connected in series to an electrode and a workpiece through a first switching element, and the first switching element. A power supply device for an electric discharge machine having a current supply means and a second direct current power supply, which is connected in parallel to the machining current supply means with respect to the electrode and the workpiece and which attenuates the discharge current. In the above, the current maintaining means having a second switching element and a third DC power source for maintaining current and connected in parallel with the machining current supplying means, and the first switching element are turned off for a predetermined time. And a current control means for turning on the second switching element.

According to the power supply device for an electric discharge machine of the present invention, the inter-electrode current is caused to flow by the DC power supply while the switching element of the machining current supply means is in the ON state, and when the switching element is turned off, the switching element of the current maintaining means. By turning on the power supply, the energy stored in the inductance of the power supply line and the wiring and the DC power source of the current maintaining means maintain the peak value of the inter-electrode current for a predetermined time, and then the current maintaining means. The switching element is turned off, and the energy stored in the inductance is canceled by the DC power supply of the current attenuating means to rapidly lower the inter-electrode current. As a result, a current waveform close to a perfect rectangular wave can be obtained.

In the power supply device for an electric discharge machine according to the next invention, the second DC power supply is a variable voltage type DC power supply, and the peak value is reached from the time when the discharge is started until the machining current between the electrodes reaches the peak value. It has a voltage command section for variably setting the voltage value of the second DC power supply according to the delay time.

According to the power supply device for an electric discharge machine of the present invention, the voltage value of the DC power source of the current attenuating means is variably set according to the peak value arrival delay time, so that the inter-electrode current is raised by the current attenuating means. The descending slope (attenuation rate) is variably set, and a current waveform having a uniform pulse width is repeatedly obtained regardless of fluctuations in the peak value arrival delay time.

In a power supply device for an electric discharge machine according to the next invention, a signal from a current value detection means for detecting a peak value of a discharge current and a discharge start signal output means for detecting a discharge start time and outputting a discharge start signal. And a peak value delay time measuring means for calculating the peak value arrival delay time.

According to the power supply device for an electric discharge machine of the present invention, the peak value of the discharge current is detected by the current value detecting means, the discharge start time point is detected by the discharge start signal output means, and the peak value arrival delay time measuring means. Calculates the delay time for reaching the peak value from this detection time difference.

[0021]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In the embodiments of the present invention described below, the same components as those of the above-described conventional example are denoted by the same reference numerals as those of the above-described conventional example, and description thereof will be omitted.

(Embodiment 1) FIG. 1 shows Embodiment 1 of a power supply device for an electric discharge machine according to the present invention. In this power supply device for an electric discharge machine, a DC power supply 3 is connected to the electrode 1 and the workpiece 2 via a switching element 4, and a DC power supply connected in parallel with the machining current supply means 5. Processing current attenuation means 6 by 7 and diode 8
In addition, it includes a machining current bypass means 9 connected in parallel with the machining current attenuation means 6. The machining current bypass means 9 is composed of a series connection circuit of a diode 10 and a switching element 11, and the switching element 11 is turned on / off by a drive signal output from the current control means 20.

The switching element 11 of the machining current bypass means 9 is turned on by the drive signal output from the current control means 20 after the start of discharge but before the off timing of the switching element 4 and is predetermined from the off timing of the switching element 4. It is turned on over time.

Although MOSFETs will be described as examples of the switching elements 4 and 11 in the figure, these switching elements 4 and 11 are used in other semiconductor switches such as IGBTs, transistors, SITs, and electrical switches such as GTOs. Can be considered similarly.

2 (a) to 2 (d) are switching elements 4 in the power supply device for an electric discharge machine having the above-described circuit configuration.
The on / off timing of the switching element 11, the voltage waveform between contacts, and the current waveform between contacts are shown. FIG. 2A shows a voltage waveform between the electrodes when a voltage is applied between the electrodes by an external auxiliary power supply or a DC power supply 3 not shown at the timing indicated by reference symbol T1, and FIG. 2 (c) and 2 (d) show driving signals for the switching elements 4 and 11, respectively. Note that FIG.
Also in (c), A is the drive signal ON timing of the switching element 4 when a voltage is applied between the electrodes by an external auxiliary power supply, and B is the switching element 4 when a voltage is applied between the electrodes by the DC power supply 3. The respective drive signal ON timings are shown.

When a voltage is applied at the timing indicated by T1, the discharge starts at the timing indicated by T2 when the insulation between the electrodes is destroyed after a no-load time (T1 → T2) in which no discharge occurs. To do. A current starts to flow between the electrodes from the start of discharge, and the current continues to flow for a desired time according to the processing content, so that the desired peak value Ip is reached T3.
At the timing of, the drive signal of the switching element 4 is turned off.

Switching element 11 of bypass means 9
Is already turned on at the timing of T3 (energization stop timing) because it is turned on at the timing of T2, and the current between the poles from the timing of T3 is the wiring inductance of the wiring and the feeding line to the pole. With the energy stored in L1, the machining current bypass means 9 tries to keep the current flowing between the poles. At this time, the decay state of the inter-electrode current is gradually attenuated with a slope a determined by the inter-electrode discharge voltage value, the ON voltage of the semiconductor element forming the bypass means 9, and the impedance of the circuit.

The current control means 20 turns off the drive signal of the switching element 11 of the machining current bypass means 9 at the timing of T4 when a predetermined time t has passed since the drive signal of the switching element 4 was turned off. At the timing of T4 when the switching element 11 is cut off, the DC power supply 7 of the current attenuating means 6 cancels the energy stored in the inductance, and the current is rapidly attenuated.

As described above, since the machining current bypass means 9 causes the machining current to flow, the decay of the machining current is delayed over a predetermined time t, and is close to a rectangular wave as shown in FIG. 2B. A trapezoidal current waveform can be easily obtained,
The consumption of the electrodes can be reduced.

(Second Embodiment) FIG. 3 shows a second embodiment of the power supply device for an electric discharge machine according to the present invention. In this power supply device for an electric discharge machine, a DC power supply 3 is connected to the electrode 1 and the workpiece 2 via a switching element 4, and a DC power supply connected in parallel with the machining current supply means 5. Processing current attenuation means 6 by 7 and diode 8
In addition, it includes a current maintaining means 12 connected in parallel with the machining current attenuating means 6. The current maintaining means 12 is the diode 1 of the machining current bypass means 9 in the first embodiment.
0 and switching element 11 and a DC power supply 13 in series connection circuit.
Is turned on / off by a drive signal output from the current control means 20.

Switching element 11 of current maintaining means 12
Is the same as that in the first embodiment.
With the drive signal output from 0, the switching element 4 is turned on after the discharge is started and before the off timing of the switching element 4, and is turned on for a predetermined time after the off timing of the switching element 4.

The voltage value V3 of the DC power supply 13 is selected to be a voltage value close to the sum of the discharge voltage value between the electrodes and the on-voltage value of the semiconductor elements forming the circuit of the current maintaining means 12, and is usually about 30V to 35V. The value of is chosen.

FIGS. 4 (a) to 4 (d) show switching elements 4 in the power supply device for an electric discharge machine having the above-mentioned circuit configuration.
The on / off timing of the switching element 11, the voltage waveform between contacts, and the current waveform between contacts are shown.

Also in this embodiment, since the switching element 11 of the current maintaining means 12 maintains the ON state at the timing T3 when the switching element 4 is turned off, the current between the electrodes is changed from the timing of T3 to the wiring, The energy stored in the wiring inductance L1 of the power supply line between the electrodes tries to keep the current flowing between the electrodes through the current maintaining means 14.

The decay state of the inter-electrode current at this time is because the inter-electrode discharge voltage value and the on-voltage of the semiconductor element forming the current maintaining means 14 and the DC power supply 13 of the current maintaining means 14 are in equilibrium. The current peak value Ip is not attenuated over a predetermined time t and maintains the peak current value.

The current control means 20 turns off the drive signal of the switching element 11 of the machining current bypass means 9 at the timing of T4 when a predetermined time t has passed since the drive signal of the switching element 4 was turned off. At the timing of T4 when the switching element 11 is cut off, the DC power supply 7 of the current attenuating means 6 cancels the energy stored in the inductance, and the current is rapidly attenuated.

As described above, the machining current flows through the current maintaining means 14, so that the peak current value is maintained.
It becomes possible to easily obtain a current waveform close to a perfect rectangular wave as shown in (3) and reduce the consumption of the electrodes.

(Third Embodiment) FIG. 5 shows a third embodiment of the power supply device for an electric discharge machine according to the present invention. The third embodiment is a modification of the first embodiment, and is different from the first embodiment in that the machining current attenuating means 6 is connected to the DC power supply 7.
Instead, a variable voltage source 14 that can change the voltage according to a voltage command signal from the outside is provided.

The variable voltage source 14 is a variable voltage type DC power source 7, and the voltage value thereof is determined by the voltage command section 21. The voltage command section 21 has a built-in peak value arrival delay time measuring section, and a signal from the current value detection means 15 for detecting the peak value of the discharge current and a discharge start signal for detecting the discharge start time and outputting a discharge start signal. From the discharge start signal from the output means 16, the delay time for reaching the peak value with respect to the discharge start time is also calculated by the detection time difference, and the voltage value of the variable voltage source 14 is determined according to this delay time. This variable voltage source 1
The voltage value of 4 may be set proportionally with a delay time and a proportional coefficient.

Here, the current control means 20 for controlling ON / OFF of the switching elements 4 and 11 and the voltage command section 21.
Are collectively referred to as current waveform control means 22.

FIGS. 6 (a) to 6 (f) show switching elements 4 in the power supply device for an electric discharge machine having the above-mentioned circuit configuration.
The ON / OFF timing of the switching element 11, the inter-electrode voltage waveform and the inter-electrode current waveform, the peak value arrival delay time, and the variable voltage source voltage command signal are shown.

Also in this embodiment, when the voltage is applied at the timing indicated by T1, when the insulation between the electrodes is destroyed after a no-load time during which no discharge occurs, the discharge is performed at the timing indicated by T2. Will start. A current begins to flow between the electrodes from the start of discharge, and then the desired peak value Ip
At the timing of T3 when the temperature reaches T3, the current value detecting means 1
Based on the output signal of 5, the current control means 20 turns off the switching element 4. The current control unit 20 maintains the turn-on of the switching element 11 and turns off the switching element 11 at the timing of T4 when the predetermined time t has elapsed at the timing of T3. At the timing of T4 when the switching element 11 is cut off, the variable voltage source 14 of the current attenuating means 6 cancels the energy stored in the inductance, and the current is rapidly attenuated.

FIG. 6 (e) shows the peak value arrival delay time which is the time from the discharge start time shown by T2 to the time T3 when the machining gap current reaches the peak value Ip, and FIG. 6 (f) shows the peak value. The variable voltage source voltage command signal obtained by converting the arrival delay time into an analog signal is shown. The variable voltage source voltage command signal output by the voltage command unit 21 increases proportionally with a predetermined proportional coefficient according to the peak value arrival delay time. That is, this voltage level increases as the peak value arrival delay time increases, and decreases as the peak value arrival delay time decreases.

The voltage level of the variable voltage source 14 of the current attenuator 6 is determined by the voltage level of the output signal of the voltage command unit 23. As a result, if the peak value arrival delay time is small, the voltage value of the variable voltage source 14 of the current attenuating means 6 is set small, and the slope of the current attenuation (falling slope) is accordingly reduced. On the other hand, if the peak value arrival delay time is large, the voltage value of the variable voltage source 14 of the current attenuator 6 is set to be large, and the slope of the current attenuation is large.

In FIG. 6 (e), when the peak value arrival delay time is large as indicated by dt1, the voltage of the variable voltage source 14 is set to a relatively large Vdt1, and the slope of the current attenuation (attenuation rate). b becomes large (steep), and when the peak value arrival delay time is small as indicated by dt2, the voltage of the variable voltage source 14 becomes relatively small Vdt.
It is set to 2, and the slope b of the current attenuation becomes small (slow).

As a result, the voltage fluctuation of the applied voltage, the difference in the inductance of the feeder line due to the difference in the stroke of the machine,
Despite the variation in the peak value arrival delay time caused by the difference in arc voltage due to the machining state between the poles, etc., from the rise of the machining gap current (T2) until the machining gap current becomes zero after decay. The time (pulse width) can be matched with a predetermined set value, and a current waveform with a uniform pulse width and pulse peak value can be realized.

As a result, a substantially rectangular current waveform suitable for low electrode consumption machining is repeatedly and stably obtained.

The third embodiment can be equally applied to the second embodiment using the current maintaining means 14, and in this case, the same operation and effect can be obtained.

[0049]

As is apparent from the above description, according to the power supply device for an electric discharge machine of the present invention, the inter-electrode current is made to flow by the DC power supply while the switching element of the machining current supply means is in the ON state, and this switching is performed. When the element is turned off, the switching element of the machining voltage bypass means is turned on, so that the energy stored in the inductance of the power supply line and the wiring causes the machining gap bypass means to generate the machining gap current for a predetermined time. It is gradually attenuated, then the switching element of the machining voltage bypass means is turned off, the energy stored in the inductance is canceled by the DC power source of the current attenuation means, and the inter-electrode current is sharply reduced to a rectangular wave. Since a nearly trapezoidal current waveform is obtained, a current waveform close to a rectangular current waveform suitable for low electrode consumption machining is Easily without complicating the road construction, inexpensive, so obtained reliable.

According to the power supply device for an electric discharge machine in the next invention, the inter-electrode current is made to flow by the DC power supply while the switching element of the machining current supply means is in the ON state, and the current maintaining means is switched when the switching element is turned off. By turning on the element, the peak value of the inter-electrode current is maintained for a predetermined time between the energy stored in the inductance of the power supply line and the wiring and the DC power supply of the current maintaining means, and then the current is maintained. By turning off the switching element of the means and canceling the energy stored in the inductance by the direct current power supply of the current attenuating means and rapidly lowering the inter-electrode current, a current waveform close to a perfect rectangular wave can be obtained. A current waveform close to a perfect rectangular wave suitable for low electrode consumption machining is easy, inexpensive and easy without complicating the circuit configuration. -Reliability becomes obtained as to high.

According to the power supply device for electric discharge machine in the next invention, the voltage value of the DC power source of the current attenuating means is variably set according to the peak value arrival delay time, so that the inter-electrode current by the current attenuating means is changed. The falling slope (attenuation rate) is variably set, and the current waveform with a uniform pulse width can be repeatedly obtained regardless of the fluctuation of the peak value arrival delay time, so it is suitable for low consumption machining of electrodes with a uniform current peak value and current width. The rectangular current waveform can be obtained easily, inexpensively and with high reliability without complicating the circuit configuration.

According to the power supply device for electric discharge machine in the next invention, the peak value of the discharge current is detected by the current value detection means, the discharge start time point is detected by the discharge start signal output means, and the peak value arrival delay time is measured. Since the means calculates the delay time for reaching the peak value from this detection time difference, the peak value arrival delay time is accurately measured by the two detectors.

[Brief description of the drawings]

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

FIG. 2 is a waveform diagram and a time chart for explaining the operation of the power supply device for an electric discharge machine according to the first embodiment of the present invention.

FIG. 3 is a circuit diagram showing a second embodiment of a power supply device for an electric discharge machine according to the present invention.

FIG. 4 is a waveform diagram and a time chart for explaining the operation of the power supply device for an electric discharge machine according to the second embodiment of the present invention.

FIG. 5 is a circuit diagram showing a third embodiment of a power supply device for an electric discharge machine according to the present invention.

FIG. 6 is a waveform diagram and a time chart for explaining the operation of the power supply device for an electric discharge machine according to the third embodiment of the present invention.

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

FIG. 8 is a waveform chart and a time chart for explaining the operation of the embodiment of the conventional power supply device for an electric discharge machine.

[Explanation of symbols]

1 electrode, 2 workpiece, 3 DC power supply, 4 switching element, 5 machining current supply means, 6 machining current attenuating means, 7 DC power supply, 8 diode, 9 machining current bypass means, 10 diode, 11 switching element, 12 current Maintaining means, 13 DC power source, 14 variable voltage source, 15 current value detecting means, 16 discharge start signal output means, 20 current control means, 21 voltage command section, 22
Current waveform control means

Claims (4)

[Claims] 1. A first DC power supply connected in series to an electrode and a workpiece via a first switching element, and the first DC power supply.
Machining current supply means including a switching element, and a current attenuating means that has a second DC power supply and that is connected in parallel to the machining current supply means for the electrode and the workpiece and that attenuates the discharge current. In a power supply device for an electric discharge machine having the above, a machining current bypass unit having a second switching element and connected in parallel to the machining current supply unit, and the second unit for a predetermined time when the first switching element is turned off. And a current control means for turning on the switching element of 1. 2. A first direct-current power supply connected in series to an electrode and a workpiece via a first switching element, and the first direct-current power supply.
Machining current supply means including a switching element, and a current attenuating means that has a second DC power supply and that is connected in parallel to the machining current supply means for the electrode and the workpiece and that attenuates the discharge current. In a power supply device for an electric discharge machine having the above, a second switching element and a third DC power source for maintaining a current, a current maintaining means connected in parallel with the machining current supplying means, and the first switching element. And a current control means for turning on the second switching element for a predetermined time at turn-off of the power supply device for an electric discharge machine. 3. The second DC power source is a variable voltage type DC power source, and the second DC power source is responsive to a peak value arrival delay time from the start of discharge until the machining current between the electrodes reaches a peak value. The power supply device for an electric discharge machine according to claim 1 or 2, further comprising a voltage command unit that variably sets a voltage value of the power supply. 4. The peak value using a signal from a current value detection means for detecting a peak value of a discharge current and a signal from a discharge start signal output means for detecting a discharge start time point and outputting a discharge start signal. The power supply device for an electric discharge machine according to claim 3, further comprising peak value delay time measuring means for calculating the arrival delay time.