JP2610899B2 - Power supply circuit for electric discharge machining - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to a power supply circuit for electric discharge machining that supplies a voltage applied between an electrode and a workpiece in electric discharge machining.

[Prior art]

FIG. 5 shows a conventional power supply circuit for electric discharge machining. In FIG. 5, 1 is a DC power supply, 2 is a resistor, 3 is a transistor which is a main switch means for supplying a voltage to a discharge gap, and 4 is a discharge gap and a line leading to the discharge gap on the output side of the main switch means. A transistor which is a switch means of a bypass circuit connected in parallel to a series circuit with
5 is an electrode, 6 is workpiece, the pulse input terminal 7, 8, 9 buffer, 10 are resistors, 11 denotes a diode, C ₀ is the stray capacitance, L ₀ is the lead inductance, C _G is the discharge gap between the capacitance, C ₄ is a gate-to-source capacitance of the transistor 4. (A) Operation when the input pulse is ON When applying a voltage between the electrode 5 and the workpiece 6, an ON input pulse is input from the pulse input terminal 7. Then, a positive signal is input to the gate of the transistor 3 via the buffer 8, the transistor 3 is turned on, and the DC power supply 1
5, DC voltage is applied between the workpieces 6. The input pulse is also applied to the gate of the transistor 4 via the buffer 9 and the diode 11. However, while the transistor 3 is on, the voltage from the DC power supply 1 is applied as a reverse voltage between the drain and source of the transistor 4, so that the transistor 4 is non-conductive. The magnitude of the reverse voltage applied to the transistor 4 is substantially the voltage of the DC power supply 1 until the discharge between the electrode 5 and the workpiece 6 is started, and when the discharge is started, the voltage drops to the voltage of the discharge gap. While the transistor 4 is off, the gate of the transistor 4
Source capacitance C ₄ is charged by a given gate voltage. (B) Operation when input pulse is off When it is desired to stop applying voltage between the electrode 5 and the workpiece 6, the force pulse from the pulse input terminal 7 is turned off. This signal is applied to the gate of the transistor 3 via the buffer 8, the transistor 3 is turned off, and the supply of the voltage of the DC power supply 1 is stopped. Since the output side of the potential of the input pulse is turned off buffer 9 is lowered, the electric charge charged in the gate-source capacitance C ₄ begins to discharge through the resistor 10.
By properly selecting the value of the resistor 10, the gate voltage of the transistor 4 can be kept at a value that allows the transistor 4 to conduct for a while. The transistor 4, the period in which the transistor 3 is turned on but it takes a reverse voltage, is released therefrom is turned off, the forward voltage is applied by the energy stored in the lead inductance L ₀ instead . Therefore, the transistor 4 becomes conductive, current I ₂ flows. Conductivity of the transistor 4 is lower due to the charging voltage of the gate-source capacitance C ₄ is gradually lowered by discharge. That is, the internal resistance of the transistor 4 increases. This becomes possible to attenuate the current I ₂ quickly, will prevent surges liable to occur the energy after off of the transistor 3. Transistor 4
Is provided to prevent this surge.

[Problems to be solved by the invention]

(Problems) However, the above-described conventional power supply circuit for electric discharge machining has the following problems when performing electric discharge machining with a pulse having a short voltage application time. The first problem is discharge with high energy density, that is,
There is a problem that the discharge is not performed with a sufficient ionization time (time from the application of the voltage to the start of the discharge). The second problem is that the discharge current is cut before the rising of the pulse due to the short pulse, and the current is not uniform. Therefore, the processing speed is not increased and the processed surface is not uniform. Is a point. (Explanation of Problem) The first problem will be described. A discharge that takes a sufficient time for ionization while maintaining a long discharge gap and then is performed at a stretch is a discharge having a high energy density (a discharge that consumes a large amount of energy per unit area). Such electric discharge is desired for electric discharge machining. This is because the energy density is high and the cutting efficiency is good, and the discharge gap is long, and the inflow and outflow of the machining fluid can be performed smoothly, so that the machining speed is increased. However, in the conventional discharge machining power supply circuit, when releasing the application of the power supply voltage, energy was in the lead inductance L ₀ and stray capacitance C ₀ is stored in the discharge gap. This energy is released over time, but if a voltage pulse is applied at short pulse intervals, the next pulse will be applied before it is released, and the gap voltage will become zero. Absent. FIG. 6 shows the applied voltage V (FIG. 6A) and the gap voltage V _G1.
Shows the relationship between the (sixth Zuro), the gap voltage when the applied voltage V and the off becomes as shown in V _G1 of Figure 6 (b), the gap voltage is not zero. The electric field due to this voltage restricts the movement of ions (generated by the electrolysis of the machining fluid) and machining chips, and prevents them from being discharged from the discharge gap. If a large amount of ions or machining chips are present in the discharge gap, the discharge will be started without requiring much ionization time (a short circuit may occur). The discharge that occurs in this way has a low energy density. Therefore, it is not suitable for electric discharge machining. The second problem will be described. Since the width of the applied voltage pulse is short, it may become zero when the discharge current starts rising, and the magnitude of the current becomes uneven. As a result, efficient processing is not performed, the processing speed is not increased, and the processed surface is not uniform. An object of the present invention is to solve the above problems.

[Means for solving the problems]

In order to solve the above problem, in the present invention, even in the case of electric discharge machining with a short pulse, the gap voltage is reduced by preventing energy from being stored in the discharge gap during a period in which the applied voltage is off, and a long discharge is performed. The following measures were taken to keep the discharge started after a sufficient ionization time in the gap for a predetermined time. That is, in the power supply circuit for electric discharge machining of the present invention, when the gap voltage decreases within a predetermined short discharge detection time (T ₁ ) after the application of the power supply voltage, the discharge period (T _ON ) for a shorter time than the above, then stop the application only for a predetermined gap energy consumption pause period (T ₃ ), and within a predetermined voltage application set time (T ₀ ) and a short discharge detection time (T ₁ ) If the gap voltage decreases after the elapse, a predetermined discharge period (T _ON ) starts from the time when the gap voltage decreases.
Only applied, and then stops for a predetermined discharge quiescent time (T _OFF), when the gap voltage is not reduced even after the lapse of the voltage application setting time (T ₀₎ is then gap energy consumption for resting period (T ₃ ) The application was stopped only.

[Action]

After off of the main switching means, first and second switching means is caused to turn on, the lead inductance L ₀ that store energy, stray capacitance C _0, the discharge gap between the capacitance C _G, the respective first , And the second bypass circuit and an appropriate circuit. Electric current by each energy flows in those closed circuits,
Energy is consumed in the form of Joule heat generated at that time. Thus, it is possible to prevent energy from being stored in the discharge gap when the main switch is turned off, and to reduce the gap voltage. If the gap voltage decreases within the predetermined voltage application set time (T ₀ ) and after the elapse of the short discharge detection time (T ₁ ), a predetermined discharge period (T _ON ) starts from the time when the gap voltage decreases. By applying only this, it is possible to prevent the magnitudes of the currents from becoming uneven.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a main circuit of a power supply circuit for electric discharge machining according to an embodiment of the present invention. FIG. 2 is a control signal circuit for generating a pulse to be applied to the pulse input terminal of FIG. 1 based on the voltage detected between the discharge gaps in FIG. First, the main circuit of FIG. 1 will be described, then the control signal circuit of FIG. 2 will be described, and finally, the operation flow of FIG. 4 will be described. (Regarding the main circuit ... FIG. 1) In FIG. 1, the same reference numerals as those in FIG. 5 correspond to those in FIG. The configuration differs from the conventional circuit of FIG. 5 in that (1) In addition to the conventional bypass circuit (first bypass circuit) using the transistor 4 as a switch, a resistor 12 and a transistor 13 as a switch are used. Second series circuit
(2) a buffer 14, a photocoupler 15, a resistor 16, and a buffer 17 to provide a circuit for supplying a gate signal to the transistor 13; (3) a transistor 13 in that an input pulse waveform shaping section 18 is provided because a gate signal is also supplied to 13. In addition,
18-1 in the input pulse waveform shaping section 18 is a monostable multivibrator, and 18-2 is a flip-flop. The operation of the circuit shown in FIG. 1 will be described separately when the input pulse from the pulse input terminal 7 is on and off. (A) Operation when input pulse is on At this time, the transistor 3 as the main switch for supplying the voltage of the DC power supply 1 to the discharge gap and the transistor 4 forming the first bypass circuit are shown in FIG. Operates in the same manner as in the conventional example. On the other hand, the transistor 13 forming the switching means of the second bypass circuit is not supplied with the ON gate signal at this time and remains OFF. This is because, when an input pulse is input to the photocoupler 15 via the buffer 14, the output resistance of the photocoupler 15 becomes small, and current flows through the resistor 16. Therefore, the potential of the input terminal of the buffer 17 decreases, and the potential of the output terminal also decreases. Therefore, no ON signal is supplied to the gate of the transistor 13. Therefore, it remains off. (B) Operation when the input pulse is off The transistor 3 is turned off to stop supplying the discharge voltage. Therefore, the reverse voltage applied between the source and the drain of the transistor 4 disappears, and the energy stored in the discharge circuit (mainly, the lead wire inductance)
L ₀ to The stored which was energy) by such a forward voltage. The transistor 4 conducts and suppresses the surge as in the conventional case. When the input pulse is turned off, the output of the buffer 14 becomes zero, no current flows on the input side of the photocoupler 15,
The output resistance becomes large. As a result, the voltage applied to the input terminal of the buffer 17 via the resistor 16 increases, and the output voltage increases. Between the source and the drain of the transistor 13, although it takes a forward voltage due to energy stored in the lead inductance L ₀ and stray capacitance C ₀ and the discharge gap between the capacitance C _G, the output of the buffer 17 to the gate Since a voltage is applied, the transistor 13 quickly conducts, and actively draws current from each location as shown by the dashed line in FIG. Each energy stored in the discharge circuit is consumed in the form of Joule heat current I ₃ through the transistor 13 is generated when flowing through the resistor 12 and the line or the like. Therefore, the discharge gap between the capacitance C _G, thereby preventing that a large energy is accumulated. (Regarding the control signal circuit ... FIG. 2) In FIG. 2, 30 is an inverter, 31 and 32 are D-type flip-flops, 33 is a delay circuit, 34 is an AND circuit, 35 is an OR circuit, and 36 is a voltage application time setting. Timer circuit, 37 is a short discharge detection time timer circuit, 38 to 41 are OR circuits, 42 is a timer circuit, 43 is a gap energy consumption pause period timer circuit, 44 and 45 are D-type flip-flops, 46 is an inverter, 47 is an AND circuit, 48 is a timer circuit, 49 is a discharge period timer circuit, 50 is a discharge period end signal generation circuit, 51 is a discharge pause period (T _OFF ) timer circuit, 52 is a timer circuit, and 53 is a terminal. The CR circuit (36-1) attached to each timer circuit
Etc.) are for determining the time width. The voltage of the discharge gap between the electrode 5 and the workpiece 6 in FIG. 1 is detected and input to the inverter 30. When the discharge gap is open (when the gap voltage is large), the input of “high (high,“ 1 ”) is input, and when the discharge gap is short-circuited (when the gap voltage is small),“ The input of low (low, "0") is entered. The output signal of the control signal circuit of FIG. The signal coming out of this is input to the pulse input terminal 7 in FIG. FIG. 3 is a waveform diagram of each part of the circuit of FIG. The waveforms indicated by the circles in FIG. 3 are the waveforms indicated by the numbers surrounded by the circles in FIG. A new discharge is generated by applying a new power supply voltage after the end of the discharge pause _TOFF of the previous discharge. The power supply voltage is set by the timer circuit 36 for setting the voltage application time.
Is applied for the time set by. First, the operation when the discharge suspension period T _OFF ends is described. When the discharge pause period T _OFF ends, a signal is input from the terminal Q of the discharge pause period (T _OFF ) timer circuit 51 to a terminal A of the timer circuit 52 which outputs a pulse indicating that the discharge pause period has ended, and the CR circuit 52− Pulse (waveform) of width determined by 2
From the terminal -Q. This pulse is applied during the discharge pause (T
_OFF ) The D-type flip-flop 45 for starting the timer circuit 51 is cleared, and the signal enters the terminal A of the OR circuit 41. The signal input to the terminal A of the OR circuit 41 starts the voltage application time setting timer circuit 36 via the OR circuit 40, and the short discharge detection time timer circuit 37 via the OR circuit 35.
To start the (Note that the "short discharge", will be referred to or to or, or short circuit discharge is initiated in a predetermined short time T ₁ from a voltage is applied). That is,
Short discharge detection time T ₁ is started and the voltage application set time T _0. When a voltage is applied the set time T ₀ start, out "1" from the terminal Q of the voltage application time setting timer circuit 36 (waveform), Figure 1 so as to turn on the transistor 3 which is the main switching means of the main circuit And to the terminal A of the AND circuit 34. When the short discharge detection time T ₁ starts, “1” is output from the terminal Q of the short discharge detection time timer circuit 37 and D
"1" is input to the D terminal of the type flip-flop 31. The above is the operation at the end of the discharge suspension period T _OFF , and thereafter, the method of discharging when a voltage is applied to the discharge gap is divided into the following four methods. (1) from the start to discharge (or short) (2) short-discharge detection time T begins to discharge into the ₁ (3) voltage application setting time after a short discharge detection time T ₁ has elapsed T ₀
(4) No discharge even after the voltage application set time T _0. The operation of FIG. 2 in each of the above discharges will be described below. (1) When discharging (or short-circuiting) from the beginning ... Waveform 5-
3. At this time, the gap voltage is applied from the beginning of the application of the power supply voltage.
V _G is small, and the its waveform is as shown in waveform 5-3 of Figure 3. As soon as the power supply voltage is applied, the output of the inverter 30 becomes "1". This output is input to the clock terminal CK of the D-type flip-flop 31, the D terminal of the D-type flip-flop 32, and the clock terminal CK of the D-type flip-flop 44. D-type flip-flop 31 is used to monitor whether the discharge in the short discharge detection time T ₁ is the start.
The D-type flip-flop 32 is for outputting a pulse for terminating the short discharge. D-type flip-flop 44
Is intended to discharge after a short discharge detection time T ₁ elapses monitors whether occurred. Now, when 1 is input to the terminal CK of the D-type flip-flop 31, if 1 is input quickly to the D terminal (when the short discharge detection time T1 starts, ₁ is input to this D terminal. 0) is output from the terminal -Q, and the short discharge detection time timer circuit 37 is restarted via the OR circuit 35. if,
One moment later, if the D terminal is still 0, 1 is output from the terminal -Q and the above restart is not performed. However, since the short-discharge detection time T ₁ has just started now, it is the same thing as whether or not any re-start. When the short discharge detection time T ₁ has elapsed, “1” is output from the terminal −Q of the short discharge detection time timer circuit 37 and enters the clock terminal CK of the D flip-flop 32. "0" is output from the terminal -Q of the D-type flip-flop 32, and the D-type flip-flop 32 itself is cleared after passing through the delay circuit 33. Delay circuit
Reference numeral 33 designates the width of the short discharge end pulse (waveform) outputted from the terminal -Q of the D-type flip-flop 32. The output of the delay circuit 33 clears the D-type flip-flop 31 and clears the voltage application time setting timer circuit 36 via the OR circuits 39 and 38. Thus, the application of the voltage is stopped. With this clear, a timer circuit for setting the voltage application time
36 is "1" from the terminal -Q to start the gap energy consumption for the rest period (T ₃₎ the timer circuit 43 out of. Time T ₃ is determined by the CR circuit 43-1. This time T _3, to flow the current into the bypass circuit consisting of a first view of the transistor 13 or the like, I'll consume energy to be Tamaro the discharge gap. When the time T ₃ is completed, the pulse exits from the terminal -Q of the timer circuit 42 to notify it. Then, the discharge suspension period T
Unless in _OFF, through the AND circuit 47, OR circuit 41, following a short discharge detection time ₁ to start the voltage application set time T _0. (2) ... at the start of discharge in the middle of a short discharge detection time T ₁
Waveform 5-4 The D terminal of the D-type flip-flop 31 has a short discharge detection time T _1.
Since in a 1, the discharge at time t ₁₂ 1 enters the started the clock terminal CK, exits 0 from the terminal -Q. This 0 is
Through the OR circuit 35 enters the timer circuit 37 for short discharge detection time to restart the short discharge detection time T ₁ (waveform 4-4
Of time T ₁ from t ₁₂ to t _13). When the short-discharge detection time was re-start T ₁ has elapsed (t
₁₃ ), 1 comes out from the terminal -Q of the short discharge detection time timer circuit 37 and enters the clock terminal CK of the D-type flip-flop 32. Since the gap is being discharged and 1 is coming to the D terminal, 0 comes out from the terminal -Q. When the output is activated, the voltage application time setting timer circuit 36 is allowed to be in a voltage applied terminated cleared as described above (part of the time t ₁₃ of waveform 3-4), the discharge stops. After this, the gap energy consumption for quiescent period T ₃ is caused to start is the same as the case of (1). (3) a short discharge detection time T ₁ has elapsed after starting the discharge voltage application set time T in ₀ ...... when (such a discharge is desired) the
Although waveform 5-2 1 exits from the short discharge detection time for the timer circuit 37 terminal -Q when short discharge detection time T ₁ is elapsed (t _4), D-type flip-flop 32 for this case has not yet discharged Is 0, the terminal -Q is 1. Also, 1 is input to the terminal B of the AND circuit 34. Meanwhile, the terminal A of the AND circuit 34 1 is being come (during which because power supply voltage is applied, the voltage application set time T ₀ in other words because it is in progress). Therefore, an output is output from the AND circuit 34, and the D terminal of the D-type flip-flop 44 is set to 1. As a result, the D-type flip-flop 44 is set in the discharge period T _ON
You're ready to start your watch. When such discharge at time t ₅ after the state is or start, 1 enters the terminal CK of the D-type flip-flop 44, 1 from the terminal Q, exits 0 from the terminal -Q. The 1 output from the terminal Q enters the discharge period timer circuit 49 to start the discharge period T _ON and also enters the D terminal of the D-type flip-flop 45 (in preparation for starting T _OFF after the end of T _ON ). ). 0 emitted from the terminal -Q enters the voltage application time setting timer circuit 36 via the OR circuit 40, (from t ₅₎ to restart the voltage application set time T _0. When a pulse indicating that the discharge period T _ON has ended is output from the terminal -Q of the discharge period end signal generation circuit 50 (t ₇ ), the voltage application time setting timer circuit 36 is cleared via the OR circuit 38 to apply the voltage application. Terminate. At the same time, the signal enters the D-type flip-flop 45 via the inverter 46 and outputs 1 from its terminal Q (waveform) to start the discharge pause _TOFF . As described above, the voltage application set time T ₀ originally set at the time t ₆ ends, and the discharge period may be shortened. However, in the present invention, the discharge start time (t ₅ ) Since the voltage application setting time T ₀ is restarted from before to prevent the application of the power supply voltage from being stopped, and the application is stopped after the predetermined period T _ON has elapsed, the discharge is performed at the predetermined time. Make sure time continues. As a result, the pulse width of the discharge current becomes constant, and the surface roughness of the machined surface becomes uniform. The 0 output from the terminal -Q of the D-type flip-flop 45 enters the timer circuit 48, outputs a pulse having a width determined by the CR circuit 48-1 from the terminal -Q, and clears the D-type flip-flop 44. This is to prepare for instructing the start of the next discharge period T _ON . (4) When discharge did not occur even after the voltage application set time T ₀ ...
When ... the time T ₀ in waveform 5-1 time t ₂ elapses, the output terminal Q of the voltage application time setting timer circuit 36 becomes 0 (hence, the application of voltage is stopped) terminal -Q 1 with become. This 1 is a pause period timer circuit 43 for gap energy consumption.
To the terminal B. Time T ₃ from the time this starts (waveform). The length of T ₃ is determined by the CR circuit 43-1. And time T ₃ is completed (t _3), a pulse indicative of the completion of the terminal -Q of the timer circuit 42 (waveform) exits. CR
The circuit 42-1 determines the pulse width. This pulse is AND
The signal is sent to the terminal B of the circuit 48, and is ANDed with the negative signal of the discharge pause period T _OFF . That is, an output is output from the AND circuit 47 unless the discharge pause period _TOFF is being performed. As can be seen from FIG. 3, the output is output from the AND circuit 47 and the voltage application set time T ₀ and the short discharge detection time T ₁ are output from the AND circuit 47 because the time t ₃ is not the discharge pause period T _OFF. It is started (waveforms 3-2 and 4-2). The operation of the four possible discharge modes has been described above. FIG. 4 shows an operation flow of the circuit of FIG. (Regarding Operation Flow: FIG. 4) Next, an operation flow will be described based on FIG. Item numbers a to r in the following description correspond to the processes a to r in FIG. (A) It is checked whether or not the discharge suspension period T _OFF (the period from the end of discharge to the next application of the power supply voltage) has ended. Until the processing is completed, the processing does not proceed to the processing (b). (B) The voltage application time setting timer circuit 36 for determining the time for applying the power supply voltage is started. Kimeraru set time T ₀ by a voltage application time setting timer circuit 36 is usually set to be the length of the extent that induces discharge if the this position applied. (C) The short discharge detection time timer circuit 37 is started. (D) Check whether the gap voltage is large.
If it is large, it is determined that the gap is open, and if it is small, it is determined that discharge or short circuit has occurred. This check is performed by the D-type flip-flop 31. A signal corresponding to the gap voltage (see the waveform in FIG. 3) is input to the clock terminal CK of the D-type flip-flop 31 via the inverter 30. Gap voltage advances to the process if a small (o), and waits until time T ₁ set by the timer circuit 37 for short discharge detection time elapses. If the gap voltage is large, the process proceeds to processing (e). (E) time T ₁ set by the timer circuit 37 for short discharge detection time is checked whether or not elapsed. Regardless of whether or not it has passed, the next processing (f), (m)
Then, it is checked whether the gap voltage has become small (that is, whether the discharge has started). However, when the discharge starts, the time when the time T ₁ has elapsed and when it has not
Take different actions. If it has elapsed, the discharge period timer circuit 49 is started to continue the discharge for the regular discharge period T _ON for processing the workpiece 6 (process (g)). If it has not elapsed, the short discharge detection time timer circuit 37 is restarted (process (n)). (F) after the time T ₁ of the timer circuit 37 has passed for a short discharge detection time, checks whether the discharge was started. (G) The fact that the gap voltage becomes small in time T ₁ after, nothing but the fact that the discharged after a above T ₁ ionizing time. Since it has not been possible to wait for such a state to arrive, at this time, the electric discharge is continued for a predetermined T _ON period for electric discharge machining. Therefore, the discharge period timer circuit 4 that determines T _ON
Start 9 The length of the discharge period T _ON depends on the processing conditions of the CR circuit 49−.
The length can be changed to various lengths by switching the resistance of one. To describe in Figure 3, first, the waveform 3-2 of the voltage application time setting timer circuit 36 after from the beginning time T ₀ continued time t _3, starts scheduled ending at time t _6. But,
When the time T ₁ is to start discharge between the times t ₆ and time t ₄ when elapses (when the waveform 5-2 plunged), discharge period T _ON as waveform 10-1 is started. (H) Restart the voltage application time setting timer circuit 36. This is because when the discharge is started after a sufficient ionization time has elapsed, the discharge is continued for a predetermined time (T _ON ). (I) When the time T _ON is restarted and the discharge is continued, wait until the period T _ON set as the discharge time elapses. (J) When the discharge period T _ON ends, the voltage application time setting timer circuit 36 is reset, and the application of the voltage is stopped. (K) At the same time, the discharge period (T _ON ) end signal starts the discharge pause period (T _OFF ) timer circuit 51 via the inverter 46 and the D-type flip-flop 45. (R) Check whether the EDM work has been completed. If not over, the process returns to the first process (a) and the same process is repeated. (M) where, before the time T ₁ which is defined by the timer circuit 37 for short discharge detection time has elapsed, monitors whether the gap voltage is small (discharge or short). An example of a gap voltage becomes small at time T _1, the third
There are cases like waveforms 5-3 and 5-4 in the figure. Waveform 5-3
In the case of, the short circuit has occurred from the beginning.
Case 4 is a case where the discharge is started after a very short ionization time. In such a case, the discharge is not generated after a sufficient ionization time, and is not suitable for electric discharge machining. Then, as described in the next (n), the discharge is performed for a shorter time than the normal discharge period, and the discharge is terminated. This monitoring is performed by the D-type flip-flop 31.
It is. When the discharge is started, the D flip-flop 31
Output from the terminal -Q. (N) as in the case of waveform 5-4, the discharge during the time t ₁₂ the time T ₁ is started, as shown by the waveform 4-4, the short discharge detection time for the timer again from the time t ₁₂ Circuit 37
There are to start operating, newly time T ₁ clock is started. Then, when it has elapsed, stops clock time T ₀ of the voltage application time setting timer circuit 36. That is, to stop the application of the supply voltage (waveform 3-4, drops to zero at time t _13). Since the discharge started without taking enough ionization time (T ₁ or more) is an unfavorable discharge in EDM,
Although it is possible to stop immediately, in such a case, there is a chip or the like that causes the discharge to be started early, forever, between the gaps, and the discharge is started immediately when the next voltage is applied. In order to prevent this, it is necessary to blow away chips and the like to clean the gap. Although This requires energy, and of giving the gap by continuing the energy required time (shorter than the discharge period T _ON of the discharge for discharge machining time) Deke discharge. In the case of this embodiment, the time is also the time of the short discharge detection timer.
T ₁ is the same as, but may be different. For example,
If you start a discharge in a short discharge detection time T ₁ has elapsed before the time t ₁₂ as shown in FIG. 3 waveform 5-4, for continuing the discharge is up to a short discharge detection time T ₁ is passed, where voltage The application may be stopped to terminate the discharge. In short, it is only necessary to continue the discharge long enough to blow enough energy to clean the gap between the discharge gaps by blowing off the chips and the like. (O) the time T ₁ it is checked whether or not elapsed. While the time has not elapsed, it is monitored whether or not the discharge is completed while going around the process (d). In the waveform diagram, the operation of during a period from the time t ₁₂ of the waveform 5-4 to t _13. If (p) time T ₁ is elapsed, resets the voltage application time setting timer circuit 36, to stop the application of the power supply voltage (time t _13). (Q) to start the gap energy consumption for the rest period T _3. Energy such as the lead inductance L ₀ of the discharge circuit and the stray capacitance CS ₀ tends to accumulate in the gap when the discharge is stopped. I'll drain and consume. T ₃ is a pause time taken for that.

【The invention's effect】

As described above, according to the present invention, the following effects can be obtained. (1) Since no large energy is stored in the discharge gap when the application of the power supply voltage is released, the gap voltage is reduced, and the discharge of machining chips and ions from the discharge gap becomes easy. (2) The discharge is continued for a predetermined period (T _ON ) as a discharge period for machining only when the ionization time is longer than a certain level (T ₁ ). The electric discharge machining is performed by the electric discharge. Therefore, the inflow and outflow of the machining fluid between the discharge gaps became easy, and the machining speed could be increased. (3) Since the pulse width of the electric discharge machining current is fixed (T _ON ), stable machining such as uniform surface roughness can be performed. (4) After the discharge period (T _ON ) ends, the discharge pause period T
_{Since the OFF} is started, sufficient time for eliminating ions and the like floating in the gap is secured. As a result, a discharge having a high energy density can be performed as the next discharge.

[Brief description of the drawings]

FIG. 1 is a main circuit of a power supply circuit for electric discharge machining according to an embodiment of the present invention. FIG. 2 is a control signal circuit for the main circuit of FIG. 1. FIG. 3 is a waveform diagram of each part in the control signal circuit of FIG. FIG. 4 is a flowchart for explaining the operation of the present invention. FIG. 5 is a diagram showing a relationship between an applied voltage and a gap voltage in a conventional power supply circuit for electric discharge machining. FIG. DC power supply, 2 is a resistor, 3 and 4 are transistors, 5 is an electrode, 6 is a workpiece, 7 is a pulse input terminal, 8,
9 is a buffer, 10 is a resistor, 11 is a diode, 12 is a resistor, 1
3 is a transistor, 14 is a buffer, 15 is a photocoupler, 16 is a resistor, 17 is a buffer, 18 is an input pulse waveform shaping circuit, 30 is an inverter, 31, 32 are D-type flip-flops, 33 is a delay circuit, and 34 is AND. Circuit, 35 is an OR circuit, 36 is a voltage application time setting timer circuit, 37 is a short discharge detection time timer circuit, 38 to 41 are OR circuits, 42 is a timer circuit, 43 is a gap energy consumption pause period timer circuit, 44 and 45 are D-type flip-flops, 46 is an inverter, 4
7 is an AND circuit, 48 is a timer circuit, 49 is a discharge period timer circuit, 50 is a discharge period end signal generation circuit, 51 is a discharge pause period (T _OFF ) timer circuit, 52 is a timer circuit, 53 is a terminal, and C ₀ is stray capacitance, L ₀ is the lead inductance, C _G is the discharge gap between the capacitance, C ₄ is the gate-source capacitance of the transistor.

Claims (1)

(57) [Claims] 1. A main switch means (3) for turning on / off a power supply voltage applied between an electrode and a workpiece arranged with a gap therebetween, and a first auxiliary switch means (4); A first bypass circuit connected in parallel to a series circuit of the gap and a line leading to the gap at an output side of the switch means, to prevent a surge generated when the main switch means is turned off; 1. A power supply circuit for electric discharge machining comprising a control signal circuit for controlling on / off of a bypass circuit according to (1), wherein a series circuit of a resistor (12) and a second auxiliary switch means (13) connected in parallel to the gap. The second auxiliary switch means (13) is turned on when the main switch means is turned off, so that the second bypass consumes energy stored in the discharge circuit. Together comprise the road, the control signal circuit, when the gap voltage to the predetermined short discharge detection time from the power supply voltage is applied to the gap (T ₁₎ in drops, given from reduced time Apply for a time shorter than the discharge period (T _ON ), then stop applying for a predetermined gap energy consumption pause period (T ₃ ), and detect a short discharge within the predetermined voltage application set time (T ₀ ) If the gap voltage decreases after the lapse of the time (T ₁ ), the application is performed only for a predetermined discharge period (T _ON ) from the time of the reduction, and then the application is stopped for a predetermined discharge pause period (T _OFF ). If the gap voltage does not decrease even after the voltage application set time (T ₀ ) has elapsed, the gap energy consumption pause period (T ₃ ) unless a predetermined discharge pause period (T _OFF ) is started thereafter. Stop applying only A power supply circuit for electric discharge machining, characterized in that it is a control signal circuit that also performs such control.