JPS63312018A - Power source for electric discharge machine - Google Patents

Abstract

PURPOSE:To detect the restoration of insulation accurately in the state where no gap voltage is fluctuated by constituting a small current supply circuit to be a circuit increasing a supply power source gradually, which restores gap insulation with small current supplied after a switching element has been off. CONSTITUTION:Electric current is gradually increased by operating A class actuation of a transistor Tr2 by means of a small current supply circuit consisting of a chopping wave generating circuit after the switching transistor Tr1 of a main power source circuit has been off. Then, the transistor Tr1 is kept on for a set time interval for introducing into discharge between electrodes after voltage between the electrode 1 and a work 2 has exceeded the set comparison voltage and the restoration of insulation has been detected. After the elapse of the set time interval, the transistor Tr2 is operated so as to ascertain the restoration of insulation between the electrode 1 and the work 2 with current increased gradually for allowing the operation as described above to be started again. This constitution thereby enables gap voltage to be fluctuated less, and enables voltage in a specified level indicating the restoration of insulation to be accurately detected even when the gap is excessively contaminated.

Description

[Detailed description of the invention] Industrial applications The present invention relates to an electric discharge machining power supply for an electric discharge machining apparatus.

Conventional technology: A voltage source with a small current that does not maintain discharge is connected between the electrode and the workpiece, and a main discharge circuit that performs on/off switching is connected in parallel with this voltage source to the gap between the electrode and the workpiece. , E2 After the main discharge circuit causes a discharge between the electrode and the workpiece, during the period when the main discharge circuit is off,
A small current is supplied between the electrode and the workpiece from the small current voltage source, and the gap voltage between the electrode and the workpiece increases due to this small current supply, thereby determining the insulation recovery of the gap, and after this insulation recovery, the main discharge circuit A method for turning on the switch is already known from Japanese Patent Publication No. 46-24677.

The outline of this system is an electric discharge machining power supply as shown in FIG. 7, and the operation is as shown in FIG. 8.

That is, in the gap between the electrode 1 and the workpiece 2, a small current supply circuit is constructed that supplies a small current through a resistor RIO having a higher resistance value than the power supply 10, and a switching element Tr5 and a small current supply circuit are arranged in parallel with the resistor R10. A series circuit of a resistor R11 with a resistance value is connected, and while the switching element 1°r5 is off, a small current is supplied between the electrode 1 and the workpiece 2 via the resistor R10, as shown in Fig. 8 (a). As shown, electrode 1 and work 2
rl! When the gap voltage VG of 1 reaches a predetermined level or higher and it is detected that the insulation of the gap has been recovered, the switching element Tr5 is turned on to apply a high voltage to the gap, as shown in FIG. 8(C). This causes a discharge, and a discharge current 2 flows as shown in FIG. supply,
As described above, the insulation recovery between the electrode 1 and the workpiece 2 is detected.

Problems to be Solved by the Invention However, in the above-mentioned method, there is a problem in how to determine the Ti current in the small current supply circuit for detecting the gap state or the resistance value of the resistor R10.For example, when rough machining In this case, the gap is extremely dirty, and if processing is not carried out in that dirty state, carbon from the decomposed oil will adhere to the electrode and the function of preventing electrode wear cannot be maintained. Unless the current in the circuit is increased, the voltage waveform during insulation recovery will fluctuate, making proper control difficult.

On the other hand, in finishing machining, if the gap is not machined in a clean state, machining debris will cause concentrated electrical discharge, so machining should be performed in a manner that minimizes contamination.

The small machining m is also a reason why the gap is relatively clean during finishing machining. During such finishing machining, insulation recovery is faster than during rough machining. However, if the small current circuit for insulation detection used for rough machining is used as is, the current from the small current circuit will impede insulation recovery. In other words, insulation recovery is a phenomenon in which the ■ and ○ ions generated in the gap disappear; the ○ ions move and generate new ■ and ○ ions. Of course, since the current is such that the discharge cannot be maintained, the annihilated ions are larger and the ions will eventually disappear, but in any case, the insulation recovery will be interrupted by this small current.

Generally, the on/off ratio during rough machining and finishing machining is approximately as follows.

ON OFF Rough machining 1m5200μs Finishing machining 2μs 2μs In this way, since the OFF time is long in rough machining, even if the detection current is increased a little, the degree of delay in insulation recovery is not a problem, considering that voltage fluctuations due to dirt are canceled out. However, in finishing machining, processing efficiency is generally a problem, so delays in insulation recovery become a major problem. Therefore, during finishing, the current in the small current circuit for insulation detection must be kept low, and even if it is kept low, the dirt will not be too bad and the voltage will not fluctuate significantly. Therefore, conventionally, it was necessary to change the resistor R10 or the small current power supply for rough machining and finishing machining.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an electrical discharge machining power source that can stably perform both rough machining and finishing machining without changing the resistance or the small current power source.

Means for Solving the Problems The present invention applies a voltage to the gap between the electrode and the workpiece via a switching element that turns on and off to generate a discharge. A small current supply circuit that supplies a small current that does not cause discharge is connected, and when the switching element is off, the small current supplied from the small current supply circuit causes the gap voltage to bounce once, thereby recovering the gear insulation. In the electrical discharge machining power supply that turns on the switching element after detecting the above, the small current supply circuit starts supplying current after the switching element turns off and gradually increases the supplied current. , the above problems were solved.

The current from the small current supply circuit increases with time, so during finishing, insulation recovery of the gap occurs early when the current value from the small current supply circuit is small, and the current value from the small current supply circuit increases as time passes, and the insulation recovery of the gap occurs at an early stage when the current value from the small current supply circuit is small. Since no current is supplied, insulation recovery can be reliably detected. On the other hand, during rough machining, a relatively long time has elapsed since the switching element was turned off, and the current supply increases, so that insulation recovery can be reliably detected in a state where there is no fluctuation in the gap voltage.

Embodiment FIGS. 1 and 2 are circuit block diagrams of an embodiment of the present invention. FIG. 1 shows the basic circuit of the electric discharge machining power supply in this embodiment, and the control circuit shown in FIG. Transistors Tri and Tr2 as switching elements in the basic circuit
This constitutes an electrical discharge machining power supply that controls electrical discharge.

In FIG. 1, 1 is an electrode, 2 is a workpiece, 3 is a DC power supply, Trl is a transistor as a switching element, and T
R2 is operated in the Δ class operation, that is, in the active region of the transistor.
The transistor R1 and R2 are resistors, and the series circuit of the transistor Tr1 and resistor R1 and the transistor T
The series circuit of r2 and resistor R2 connects electrode 1 and DC power supply 3 in parallel.
are connected in parallel between them. The resistor R1 has a smaller resistance value than the resistor R2 and forms a main discharge circuit together with the transistor Tri which operates as a switching element.
Transistor Tr of the main discharge circuit after discharging ffll
1 is off, the gear I between electrode 1 and workpiece 2 is
? It was established to judge the insulation recovery of the horn.

These transistors Tr1. Tr2 is controlled by the leap control circuit shown in FIG. 2, which defines the on-time and off-time of the transistor Tr1, and is a one-shot multivibrator 7 whose output pulse width can be arbitrarily set. .8, the above electrode 1 and work 21
A comparator 4 which divides the gap voltage VG of Il by resistors R3 and R4 and compares the divided voltage with a comparison voltage Vt.
5. A one-shot multivibrator that is triggered at the end of the off-time of the transistor Tr1 and outputs a pulse. When a pulse is output from this one-shot multivibrator 5, it has a triangular wave generation circuit 6 that gradually increases the output voltage, and a one-shot multivibrator 7 that determines the on-time is provided at the base of the transistor Tri.
The output S7 of the above triangular wave generating circuit 6 is input to the base of the transistor Tr2.

Note that ■1 to ■7 are inverters, 01 to G3 are Nant gates, r1 to r4 are resistors, and 01 to C4 are capacitors, and the combinations of each resistor and capacitor are rl-01 and R2-0.
2, R3-03, and R4-04 each constitute a delay circuit.

Next, the operation of this embodiment will be explained with reference to the timing chart of FIG. Before the machining signal S1 of the machining start command is input, the one-shot multivibrator 5.7.8 is not operating, and its output 83.87.
88 is at L level.

Therefore, the transistor Tr1 is in an off state, the triangular wave generating circuit 6 is not operating, and its output S4 is not output, so the transistor Tr2 is also in an off state. As a result, the gap voltage VG is also not applied, and the output S5 of the comparator 4 is at the level. Therefore, since the inputs of the Nant gate G1 are the one-shot multivibrator 7.8 and the outputs 87, 88, and 85 of the comparator 4 through the inverters 14, 16, and 11, these inputs are at H level. However, since only the machining signal S1 is at the L level, the output S2 of the Nant gate G1 is at the H level. Also, the input of the nant gate G2 is a one-shot multivibrator 5.8
The outputs 33.88 of be. Similarly, the output S9 of the Nant gate G3 is also at H level.

In such a state, when the machining signal S1 of the machining start command is input, the inputs of NAND G-1 to G1 are all at the H level, so the output S2 is switched to the L level as shown in Figure 3. Then, the one-shot multivibrator 5 is triggered.

On the other hand, the machining signal S1 is also input to the Nandt gate G2゜G3, but since it is input delayed by the delay circuits r3 and C3, the output S of the one-shot multivibrator 5 is inputted via the inverter I2.17.
Since the input into which 3 is inverted becomes the L level first, its output S6°G9 does not change. The one-shot multivibrator 5 is triggered as described above and the pulse S3 is generated.
, the triangular wave generator 6 outputs a signal S4 whose voltage gradually increases as shown in FIG. and apply current. Therefore, Fig. 3 (e
), the gap voltage VG between work 2 and electrode 1 is
(increases gradually during rough machining, etc., but increases rapidly during finishing machining), this gap? [i
When the divided voltage of i-f V G exceeds the comparison voltage VL of the comparator 4, the output S5 of the comparator 4 switches to H level as shown in FIG. 3(f), and the inverter ■1
Since the L level signal is input to the Nantes gate G1 through the gate, the output S2 of the Nantes gate G1 switches to the H level and the output S3 of the one-shot multivibrator 5 is stopped (Fig. 3(b), ( c). When the output S3 of the one-shot multivibrator 5 stops, the operation of the triangular wave generation circuit 6 also stops, and its output S4 stops.
The operation of transistor Tr2 is stopped. On the other hand, output S3
becomes L level, all inputs of Nant gate G2 become H level, output S6 of Nant gate G2 switches to L level, and one-shot multivibrator 7
(Figure 3(g)).

(see (h)). Note that the output S3 of the one-shot multivibrator 5 becomes L level and a H level signal is input to the Nant gate G3 via the inverter 17, but this signal is delayed by the delay circuit r1 and C1. Before this signal inputs the H level signal to the Nando gate G3, the one-shot multivibrator 7 is triggered, and its output $7 goes through the inverter I5 and the L level signal is first sent to the Punto gate G3. Therefore, the output S9 of the Nandt gate G3 does not change.

In this way, when the output S7 with the set pulse width is output from the one-shot multivibrator 7, the transistor Tri is turned on, and the power supply voltage is applied to the gap between the electrode 1 and the workpiece 2 via the main discharge circuit (the third Figure (e)
reference). When a discharge occurs, the discharge current I flows as shown in FIG. 3(j) and the gap voltage VG decreases, so the output S5 of the comparator 4 goes to the L level as shown in FIG. 3(f). Switch. Then, when a pulse with a set width is output and the output S7 of the one-shot multivibrator 7 becomes L level (see FIG. 3(h)), the transistor Tr1 is turned off, and the voltage is applied between the workpiece 2 and the electrode 1. stops.

When the output S7 of the one-shot multivibrator 7 becomes L level, an H level signal is input to the Nant gate G3 via the inverter I5, so all inputs of the Nant gate Q3 become H level, and the output of the Nant gate G3. S9 switches to the L level as shown in FIG. 3(h), triggers the one-shot multivibrator 8 that defines the applied voltage off period, and the one-shot multivibrator 8 generates an H level of the set width. Pulse output S
Outputs 8. Note that when the output S7 of the one-shot multivibrator 7 stops and becomes L level, an H level signal is input to the Nant gate G1 via the inverter 4, but this signal is input to the delay circuit r4. C4
Since the output signal G8 of the one-shot multivibrator 8 is delayed by does not fall and does not trigger the one-shot multivibrator 5.

Thus, the output S of the one-sided multivibrator 8
8 becomes H level, an L level signal is input to the Nant gate G2 via the inverter I3, so the output S2 of the Nant gate G2 is switched to the H level. and,
When the one-shot multivibrator 8 completes the pulse output S8 of the set width, all the inputs of the Nant gate Q1 become H level, so the output S of the Nant gate G1
2 is switched to the L level, the one-shot multivibrator 5 is triggered, and the above-described operation is repeated.

Note that when the output S8 of the one-shot multivibrator 8 is stopped and switched to the H level, it is switched to the H level via the inverter 3 of the output S8, but it is delayed by the delay circuit r3 and G3 and the Nant gate Since the signal is input to the Nant gate G2, the one-sided multivibrator 5 operates first, and the L level signal obtained by inverting its output S3 with the inverter I2 is input to the Nant gate G2. Output S6 never falls,
The one-shot multivibrator 7 is not triggered.

As described above, the transistor Tr2 was operated in class A mode, the current was gradually increased, and the voltage between the electrode 1 and the workpiece 2 became equal to or higher than the set comparison voltage, and the insulation between the electrode 1 and the workpiece 2 was recovered. After detecting i!, transistor Tr1 is turned on for a set time width, and i! Shun applied a power supply voltage to the electrode 1tt41 and the workpiece 21 to cause a discharge, and when the on-time of the set width of the transistor Tr1 ended, the voltage application to the electrode 1 and the workpiece 21il was stopped for the set time width.
Activating the transistor Tr2 and gradually increasing the current, confirming the insulation recovery between the electrode 1 and the workpiece 2,
Start the above operation again. Therefore, in cases such as finishing machining, insulation recovery is detected when only a small amount of current is flowing, and in rough machining, the current gradually increases, so insulation recovery is detected in this case as well. be able to.

In the above operation, this is a normal operation in which discharge occurs while the one-sided multivibrator 7 is outputting the output pulse S7, but if discharge does not occur during this output pulse 87 period, this output After the end of the pulse S7, the transistor Tri is turned off, and the electrode 1 and the workpiece 211 are
Since no voltage is applied to the inverter 1, the output S5 of the comparator 4 becomes L level and the output of the inverter 1 becomes H level. Therefore, the output pulse S8 of the one-sided multivibrator 8 ends, and the output of the inverter 6 goes high.
level, the output S2 of the Nant gate G1 switches to the L level, so the one-shot multivibrator 5
will be triggered and the above-mentioned operation will be repeated.

In the above embodiment, the on time of the main discharge circuit Tr1,
That is, the width of the output pulse S7 of the one-shot multivibrator 7 is constant, but when using a so-called isopulse method in which the width of the discharge current pulse after the start of discharge is made constant, the one-shot multivibrator 7 can be retriggered. The device may be configured with a one-shot multivibrator, and the configuration for triggering this one-shot multivibrator may be as shown in FIG.

In Fig. 4, 7' is a retriggerable one-simultaneous vibrator used in place of 7 in Fig. 2;
is the Nandt gate G2.4° in FIG. 2; 11 is the comparator 4.4 in FIG. Inverter ■1. The output of the inverter 11 is connected to the resistor r5. The output of the differentiating circuit is input to the OR gate G5, and the output of the Nant gate G2 is also input to the OR gate G5.
The output of No. 2 is input to the operation inhibit input terminal CLR of the one-shot multivibrator 7'.

As mentioned above, when the output S6 of the Nant gate G2 switches from the H level to the [, level, the one-shot multivibrator 7' is disabled and the one-shot multivibrator 7' is triggered. 1
The cut multipipeter tuff' outputs an output pulse S7 (see FIG. 5 and FIG. 3). Electrode 1 and work 2
When a voltage is applied between them, the output S5 of the comparator 4 becomes H level, and then discharge occurs and the output S5 of the comparator 4 switches to L level, the output of the inverter 1 which inverts the output horn S5 of the comparator 4. S10 switches from L level to H level, and differential circuit r5/C5
A positive differential pulse S11 is outputted from (see FIG. 5), and this differential pulse S11 retrigger the one-shot multivibrator 7' via an OR gate G5.

As a result, the one-shot multivibrator 7' outputs a pulse with a predetermined width T after the start of discharge, making the discharge pulse current width constant.

(Also, the configuration of the triangular wave generating circuit 6 is as shown in FIG. 6, for example, to obtain a triangular wave.

That is, the output of the one-shot multivibrator 5 shown in FIG. 2 is inverted by the inverter I8 and inputted to the analog switch SW. Therefore, when the output S3 is output from the one-shot multivibrator 5, the analog switch S
W is turned off and capacitor C10 starts charging. This charging thunderbolt is input to one terminal of the differential amplifier 10,
In addition, the output of a differential amplifier 11 that amplifies the difference between the voltages obtained by dividing the potential across the resistor R2 connected in series with the transistor Tr2 by the resistors R and R is input to the other terminal. The difference between the output of the differential amplifier 11 and the charging voltage of the capacitor C10 is applied to the voltage of the transistor Tr2.

Therefore, charging of capacitor C10? When l1fEE is determined by the values of resistor R10 and capacitor C10, it becomes a constant step response, but it is converted by the differential amplifier 10 as a voltage that increases linearly, and
will be applied to the base of

Further, in the above embodiment, after the on-time of the transistor Tr1 (the output pulse width of the one-shot multivibrator 7) ends, the one-shot multivibrator 5 is immediately activated, and the transistor Tr2 is activated, without causing a minute current to flow. The reason for providing the one-shot multivibrator 8 that turns off the applied voltage is that a minimum insulation recovery time is required immediately after the end of discharge, and within this time, the voltage is increased through the transistor Tr2! It is harmful to flow the i-stream, and 1 in a large area! Compared to processing with elm,
When machining a small area, it is generally necessary to increase the time to stop voltage application, but since the area is small, insulation recovery is quick, and if the transistor Tr1 is turned on earlier, the next discharge will be faster. Since insulation recovery is poor or arcing is likely to occur, a one-shot multivibrator 8 that stops voltage application is installed so that the voltage application stop time can be adjusted.

Further, in the above embodiment, the output pulse S3 of the one-shot multivibrator 5 is stopped by the output of the comparator, which is issued when the gap voltage VG reaches a predetermined level and the insulation recovery of the gigameter is detected. , the operation of the transistor Tr2 is stopped, but it is not necessarily necessary to stop the operation of the transistor Tr2 immediately after insulation recovery is detected. One shot multi vibrator 7
It is sufficient to stop the output pulse until the output pulse ends. For example, when the output S7 of the one-shot multivibrator falls, the output of the one-shot multivibrator 5 may be stopped, and the operation of the transistor Tr2 may be stopped.

Furthermore, in the above embodiment, the one-shot multivibrators 5, 7.8 may be replaced with digital counters, and when each trigger is manually operated, the output may be outputted up to a set value. Roughly speaking, the one-shot multivibrator 5 may be replaced with a flip 70 tube that is reversed at the rising and falling edges of the Nant gate G1.

Effects of the Invention As described above, the present invention has the advantage that since the current of the small current supply circuit for detecting insulation recovery increases with time,
In the case of finishing machining, the gap voltage rises to the voltage level at which insulation recovery is detected while the supply current is small, so there is no delay in insulation recovery due to the current from this small current supply circuit; At times,
Since the voltage application stop time between the electrode and the workpiece increases, the current supplied from this small current supply circuit increases during that time and becomes a relatively large current, so even if the gap is heavily contaminated, fluctuations in the gap voltage will be reduced. Therefore, it is possible to reliably detect a voltage at a predetermined level indicating insulation recovery.

[Brief explanation of the drawing]

Fig. 1 is a basic circuit diagram of an electrical discharge machining power supply according to an embodiment of the present invention, Fig. 2 is a control circuit diagram for controlling the basic circuit in the embodiment, and Fig. 3 is an operation timing chart of the embodiment. , FIG. 4 is a block diagram of the main parts when changing to the isopulse method in the same embodiment, FIG. 5 is a timing chart of the main parts when the isopulse method is adopted, and FIG.
This figure is a block diagram of a triangular wave generating circuit, FIG. 7 is a schematic diagram of a conventional example, and FIG. 8 is an operation timing chart of a conventional example. 1...electrode, 2...work, 3...ram. Trl, Tr2...Transistor, 4...Comparator, 5.7.8...One-shot multivibrator, 6...Triangular wave generation circuit. Figure 1 Figure 1 Figure 4 Figure 5

Claims (3)

[Claims] (1) A voltage is applied to the gap between the electrode and the workpiece via a switching element that turns on and off, and a small current that does not cause discharge between the electrode and the workpiece is supplied in parallel with the main discharge circuit that causes discharge. Connect a small current supply circuit to
In the electric discharge machining power supply, the small current supply circuit turns on the switching element after detecting gap insulation recovery by increasing the gap voltage due to a small current supplied from the small current supply circuit while the switching element is off. The electric discharge machining power source is characterized in that it is constituted by a circuit that starts supplying current after the switching element is turned off and gradually increases the supplied current. (2) The electrical discharge machining power supply according to claim 1, wherein the small current supply circuit starts supplying current after a set time has elapsed after the switching element is turned off. (3) The electrical discharge machining power source according to claim 1, wherein the small current supply circuit stops operating when the gap voltage reaches a predetermined level or higher.