JPH0450124B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention provides a pulse power source for wire electric discharge machining that machining a workpiece by generating intermittent discharge in a machining gap formed between a wire electrode and a workpiece. It is related to the device.

[Background of the invention]

The machining speed of wire electric discharge machines has been rapidly improved in recent years, but the improvement in machining speed is largely dependent on improvements in the pulse power source. The present invention relates to a pulse control circuit.

FIG. 1 shows the overall configuration of a conventional pulse power supply device of this type, and FIG. 2 is a waveform diagram illustrating the circuit operation of FIG. 1. As shown in FIG. 1, a machining gap 3 formed between a workpiece 1 and a wire electrode 2 is filled with machining fluid, and a voltage is applied to the wire electrode 2 via a current-carrying terminal 4. .

Further, the anodes of the main DC power supply 13 and the auxiliary DC power supply 5 are connected to the workpiece 1, and the respective power supplies 13,
The current supply from 5 is performed by forming a power supply closed circuit by turning on the switching elements 12 and 6. 11 is a pulse control circuit that controls switching elements 6 and 12 to turn on and off according to the detected current; 7 is a capacitor; 8 is a resistor; 9 is a diode; 10 is a current detector; 14 is an inductance;
15 is a diode, 17 is a third DC power supply connected in series with the main DC power supply 13, and a resistor 16 is connected in parallel.

The operation of the circuit shown in FIG. 1 will be explained as follows.

First, the first switching element 6 is turned on from the auxiliary DC power supply 5 having a low current capacity as shown in FIG. 2c, and the discharging capacitor 7 is charged via the resistor 8. The voltage in the machining gap 3 at that time is shown in Figure 2a.
become that way. From this state, the discharge capacitor 7
When the charging voltage increases and discharge starts during machining interval 3, the current output from the discharge capacitor 7 becomes
The current flows through the machining gap 3, the current detector 10, and the diode 9 with a small arcuate waveform before the triangular wave in FIG. The start of this discharge is detected by the current detector 10, and when it is input to the pulse control circuit 11, the first switching element 6 is turned off as shown in FIG. 2c, and the second switching element 12 is turned off as shown in FIG. A control signal is output from the pulse control circuit 11 so as to turn on the current detector 10 as shown in FIG.
(There is a slight delay from the time when the start of discharge is detected until the switching elements 6, 12 are actually turned off and on.) Then, a large current (main discharge current) is supplied from the main DC power supply 13 with large current capacity to the machining gap 3.
is output as shown in Fig. 2b, and when the second switching element 12 is turned off after ₁ hour t, the electromagnetic energy accumulated in the inductance 14 of the current-carrying system passes through the diode 15 and the resistor 16 and becomes (T) in Fig. 2b. ₁
−t ₁ ) released in time. However, due to fluctuations in the inductance 14 of the current-carrying system, the inductance in the processing section, or the resistance between the wire electrode 2 and the current-carrying terminal 4, the processing current fluctuates as shown by the broken line in Figure 2b, and as a result, each The problem remains that the discharge energy for each discharge pulse fluctuates, which not only makes the machining state unstable, but also makes the machined surface uneven.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a pulse power supply device for wire electrical discharge machining that can eliminate the problems of the prior art described above and equalize the discharge energy of each discharge pulse.

[Summary of the invention]

A feature of the present invention is that a DC power source for machining is connected between the wire electrode and the workpiece forming the machining gap via a switching element, and the switching element is controlled to turn on and off. In a pulse power supply device for wire electrical discharge machining, which applies a machining DC power supply in pulses to generate intermittent electric discharge to machine the workpiece, the machining interval 〓
a current detector that detects a discharge current flowing through the current detector; and a pulse control circuit that controls the switching element to turn on and off according to a detection signal from the current detector, and the pulse control circuit a discharge start detection circuit that detects the discharge start point based on a detection signal from the discharge detector, and a discharge current value or current change rate detected by the discharge start detection circuit a predetermined time after the discharge start point detected by the discharge start detection circuit, and a discharge current value or current change rate detected by the current detector. A current value detection circuit after the start of discharge that is detected by a signal, and a pulse width setting that is selected in advance according to the current value or current change rate detected by this current value detection circuit and that allows the discharge energy of each discharge pulse to be constant. a memory that outputs a value according to the current value or current change rate; and an on-state of the switching element whose oscillation pulse off point is controlled so that the discharge pulse width is in accordance with the pulse width setting value output from the memory. , and a pulse oscillation circuit for off control.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described in detail with reference to FIGS. 3 and 4. FIG. 3 shows a specific circuit configuration thereof, and to simplify the explanation, only a portion of the pulse control circuit 11 shown in FIG. 1 is shown. Further, only the circuit portion of the pulse control circuit 11 that processes the detection current (discharge current detection signal) of the current detector 10 and outputs a control signal for the second switching element 12 is shown here. S ₁ , S ₂ in Figure 3
is the output terminal of the current detector 10 in FIG. 1, and S ₃
serves as a control signal terminal for the second switching element.

In FIG. 3, 18 is a differential amplifier, with terminals S ₁ ,
It compares and amplifies the detected current input from _S2 . 19a, 19b, 19c...19n are comparators having one input as the output of the differential amplifier 18 and the other inputs as reference voltages _E1 , _E2 , _E3 ...En, respectively. 20 is a timing pulse generation circuit, and 21a, 21b, 21c, . The output of the comparator is inverted via inverter circuits 25a and 25b, and the output is input. 22 is a memory that is selected in advance according to the output level state of each gate circuit 21 and outputs a pulse width setting value that can make the discharge energy of each discharge pulse constant according to the output level state; 23 is a memory that outputs a pulse width setting value that can make the discharge energy of each discharge pulse constant; A discharge start detection circuit 24 detects the discharge start point based on a detection signal from the detector 10 (output signal of the differential amplifier 18), and a discharge pulse width 24 is configured to have a discharge pulse width according to the pulse width setting value outputted from the memory 22. This is a pulse oscillation circuit for controlling the on/off of the switching element, in which the oscillation pulse off point is controlled, and is connected as shown in the figure. The timing pulse generation circuit 20, the comparator 19, and the gate circuit 21 operate for a predetermined period of time from the discharge start point detected by the discharge start detection circuit 23.
A post-discharge current value detection circuit is configured to detect the discharge current value after t _C using the detection signal from the current detector 10 (output signal of the differential amplifier 18).

Next, the circuit operation of FIG. 3 will be explained together with the waveform diagram of FIG. 4. First, the detection signal from the current detector 10 of FIG. 1 described above is input to the differential amplifier 18, and its output is input to the discharge start detection circuit 23 and the comparators 19a, 19b, 19c, . . . , 19n. The discharge start detection circuit 23 detects the discharge start point by detecting the discharge current from the discharge capacitor 7 shown in FIG. 1 using the detection signal from the current detector 10 (output signal of the differential amplifier 18). , gives its output signal to the pulse oscillation circuit 24. This causes the pulse oscillation circuit 24 to generate a control signal for the second switching element 12, in this case an ON signal.
Output S ₃ . Further, _S3 is input to the timing pulse generation circuit 20, and as shown in c of FIG.
A timing pulse is output after a predetermined time _tc delay from the discharge start point detected by the discharge start detection circuit 23, and the pulse is transmitted to the gate circuits 21a, 21b,
..., is input to 21m. Comparator 19a,
Reference voltages E ₁ , E ₂ ,
E ₃ ,...En are applied, and are compared with a signal e _i proportional to the main discharge current, and the results are input to gate circuits 21a, 21b,..., 21n via inverter circuits 25a, 25b,..., 25n. do.

In this way, the main discharge by the main DC power supply 13 starts (strictly speaking, as mentioned above, the start of discharge by the discharge capacitor 7 is detected by the discharge start detection circuit 23 based on the detection signal from the current detector 10). (Here, however, this is regarded as the start of the main discharge.) Then, determine which of the comparator reference voltages E ₁ , E _{2 ,} E ₃ , ..., En the value after time t _c reaches. To detect. Since the reference voltage is between E ₁ and E ₂ when the waveform is e _i1 in FIG. 4a, only the output of the first gate circuit 21a in FIG. The output becomes "L" level.

The output of each gate circuit 21 is input to the memory 22. The memory 22 uses the output level state of each gate circuit 21 as an address, and outputs a prestored pulse width setting value according to the address (the output level state). For example, in the case of waveform ei ₁ in Fig. 4a (the output signal of the differential amplifier 18 (detection signal from the current detector 10) ei is the reference voltage
between E ₁ and E ₂ , and only the output of the gate circuit 21a is at "H" level), the pulse width is t ₁
(See Figure 4b), and the pulse width for ei ₂ is
The pulse setting value is stored in the memory 22 so that t' ₁ (see FIG. 4d), and each gate circuit 2
The corresponding pulse width setting value is output according to the output level state of 1. At this time, the pulse width setting value is selected to be a value that can keep the discharge energy of each discharge pulse constant regardless of the difference in the output level state of each gate circuit 21.

The pulse oscillation circuit 24 is one in which the oscillation pulse off point is controlled so that the discharge pulse width is in accordance with the pulse width setting value outputted from the memory 22.
Since the pulse-on point is constant based on the discharge start point detected by the discharge start detection circuit 23,
In the end, the output signal of the differential amplifier 18 (current detector 1
The pulse width is controlled according to the magnitude of the detection signal (detection signal from 0) ei, and the discharge energy of each discharge pulse becomes constant.

In the above embodiment, the pulse width is controlled according to the magnitude of the output signal ei of the differential amplifier 18 (detection signal from the current detector 10), but the rate of change of the signal ei (rate of current change) ) may be used to control the pulse width. In this case, the differential value of ei may be input to the comparator 19.

Further, in the above-described embodiment, the case where the present invention is applied to a device having the auxiliary DC power source 5 has been described, but the present invention can also be applied to a device not having the auxiliary DC power source 5.

〔Effect of the invention〕

As is clear from the above-mentioned embodiments, according to the present invention, the discharge energy of each discharge pulse can be made uniform, so that not only can electric discharge machining be stabilized, but also a high-quality machined surface can be obtained. be.

[Brief explanation of the drawing]

Fig. 1 is a circuit configuration diagram of a conventional pulse power supply device for wire electrical discharge machining, Fig. 2 is a waveform diagram explaining the circuit operation of Fig. 1, and Fig. 3 is a main circuit configuration showing an embodiment of the present invention. 4 are waveform diagrams illustrating the operation of the circuit shown in FIG. 3. 1... Workpiece, 2... Wire electrode, 5, 13,
17... DC power supply, 6... First switching element, 11... Pulse control circuit, 12... Second switching element, 18... Differential amplifier, 19a,
19b, 19c to 19n...Comparator, 20
...timing pulse generation circuit, 21a, 21b
~21n...Gate circuit, 22...Memory, 23
... discharge start detection circuit, 24 ... pulse oscillation circuit, 25a, 25b ... inverter circuit.

Claims (1)

[Claims] 1. A DC power source for machining is connected between the wire electrode and the workpiece forming the machining gap via a switching element, and the DC power source for machining is connected to the machining gap by controlling on/off of the switching element. A pulse power supply device for wire electrical discharge machining that processes the workpiece by generating intermittent electrical discharge in a pulsed manner includes a current detector that detects the electrical discharge current that flows during the processing, and a detection signal from the current detector. turning on the switching element according to the signal;
and a pulse control circuit that performs off control, and the pulse control circuit includes a discharge start detection circuit that detects a discharge start point based on a detection signal from the current detector, and a discharge start detection circuit that detects a discharge start point detected by the discharge start detection circuit. A post-discharge current value detection circuit that detects the discharge current value or current change rate after a predetermined time from the point in time using a detection signal from the current detector; and a current value or current change rate detected by the current value detection circuit. a memory that outputs a pulse width setting value selected in advance according to the current value and capable of keeping the discharge energy of each discharge pulse constant according to the current value or current change rate; 1. A pulse power supply device for wire electrical discharge machining, comprising: a pulse oscillation circuit for controlling on/off of the switching element, wherein the oscillation pulse off point is controlled so as to have a discharge pulse width of 1.