JPS61297014A - Power source for electric discharge machine - Google Patents

Abstract

PURPOSE:To suppress the coarseness on the machining face while to lower the machining speed by providing second charging circuit for charging the stray capacity at the inter-electrode gap while blocking counterflow of current to a capacitor connected in parallel with said gap and increasing the voltage when compared with first charging circuit. CONSTITUTION:Upon turning on of a switching element 4, a capacitor 8 is charged through first current limiting resistor 5. On the other hand, the stray capacity 10 at the inter-electrode gap is charged through second current limiting resistor 20 and it will rise quickly because of low level. Consequently, the disabling time for detecting discharge can be set to low level. While since second current limiting resistor 20 and the stray capacity 10 are never influenced by the machining conditions, the disabling time is not required to be modified. Furthermore, the machining face is never roughed because there is no discharge current having long pulse width nor failure of detection of discharge, while since the oscillator is self-excited, the machining is never stopped thus to prevent droppage of machining speed.

Description

[Detailed Description of the Invention] [Industrial Use Minute Hand] This invention ij is an electrical discharge machining device in which a capacitor is connected to the gap between electrodes and a workpiece, and the entire electrical discharge machining is performed using the energy stored in this capacitor. The present invention relates to the improvement of power supplies for machining.

[Prior Art] Fig. 4 is a circuit diagram showing a machining power source of a conventional electrical discharge machining device, and in Fig. 5, (1) is an electrode, (2) is a workpiece,
(3) is a processing voltage source, and (4) is a switching element.

(5) is a current limiting resistor, (6) and (7) are diodes,
(8) is a capacitor, which includes a processing voltage source (3), a switching element (4), a resistor (5), and a diode (6) (
7) and the inter-electrode gap formed by the electrode (1) and the workpiece (2) are connected to the IK row, and the capacitor (8) is connected in parallel to the above-mentioned inter-electrode gap.
(to) 9 o'clock is a voltage dividing resistor, and α force is a comparator, the input terminal of which is connected to a reference voltage (divided voltage of direction and electrode gap voltage).

In addition, (10 is the stray capacitance existing in the circuit. Figure 5 is a configuration diagram of the interpolar gap tracking device, and in the figure b,
(100) is the processing power supply shown in Fig. 4, (101
3 is a slider that sprays electricity 1i (1), (1 (1
2) is a fixed head, (10B) is a slider (101
), (H14) (105) divides the gap voltage between the poles using a voltage dividing resistor and generates an operational amplifier (107).
) plus 1. A (106) is a servo reference voltage, which is added to the arithmetic amplification width 11 (107). (108)
is a servo amplifier, which is driven by the motor (10B)' according to the output of the operational amplifier (107). Note that the servo reference voltage (106) is usually variable.

Next, the operation will be explained. See Figure 6.

(f) is the voltage waveform in the gap between the electrodes, (6) is the current waveform flowing in the I-1r gap, and (a) is the output waveform of the +s comparator (1η.) When the soching element (4) is turned on, the current limiting resistor (5), capacitor (8) and stray capacitance t (1G
The voltage across the electrode gap rises with a time constant determined by . Then, adjust the voltage of the processing power supply (3) and remove it. When discharge occurs in the J'1 gap, the capacitor (
A current (b) with a narrow pulse width and a high peak value flows from 8), and electrical discharge machining is performed. On the other hand, the voltage across the electrode gap is
The comparator aη compares it with the reference voltage (to) and outputs (
Q)' is obtained. The rise of the waveform indicated by (0) has a delay time from the timing when the switching element (4) turns ON #, and this delay time varies depending on the resistor (5), capacitor (8), stray capacitance QQ, etc. Take the time. Discharge is detected at the falling edge of the gap voltage, that is, the falling edge of the output (0) of comparator 0, but the discharge occurs before the gap voltage reaches the discharge detection level. Then, the output (al) of the comparator αη cannot be determined. Therefore, ¥Jr, the signal shown in FIG. 6(d), ie, f.

A signal that remains at a high level for a predetermined time T from the timing when the switching element (4) is turned 5ON' is outputted by an oscillator (not shown), and is logically summed with the output (0) of the comparator Q7), as shown in FIG. Obtain the signal (e). This signal (
The drop in V in e) is used as the timing for generating discharge. Here, the time T[ of the signal (d) becomes a so-called discharge detection prohibition time. As soon as a discharge is detected, or after a predetermined time, the switching element (4) is switched to '01'i'F.
# is set to pause for a predetermined time, and the switching element (4)? Set it to 'ON'. In Figure 6.

Immediately after detecting a discharge, switch the switching element (4) to %QQ.
Normally, there is a delay in cutting off the machining current due to the delay of the switching element (4) and the inductance in the circuit. Here, the diode (7) allows current to flow in the positive half wave direction of the capacitor (8)17. This prevents current from flowing in the reverse half-wave direction, but can it be omitted? There is f.

Further, as the tll\ machining progresses, the interpolar gap follower vr, x #) shown in FIG. 5 and the electrode (1) are sent.

In Fig. 5, the 5wl open gap voltage is the resistance (1 (14) (
The voltage is divided by the operational amplifier (1 (17)) and compared with the reference voltage (106), and the difference voltage at this time is input to the servo amplifier (108).
The motor (10B) is driven according to the voltage difference between the two voltages.

ζ so that the average voltage of the gap between the poles becomes -T,
IFfM (1) advances and recedes, and the interpolar gap length becomes approximately -U.

[Problems to be Solved by the Invention] Since the machining power source of the conventional electric discharge machining apparatus is configured as described above, the problem is the selection of the time T during which discharge detection is prohibited. This discharge detection inhibition time T is selected according to the time constant determined by the resistor (5), capacitor (8), and stray capacitance o1, but these values are determined by the machining conditions depending on the purpose of machining, so they are not uniform. 0 When the discharge detection prohibition time T becomes longer, the current waveform becomes N (as shown in FIG. When shortens, discharge detection fails and the output of the first oscillator becomes an output similar to a self-excited state.This phenomenon will be explained with reference to FIG.

In the figure, (a) I (Q) 1 mouth), (e
) is (to) I (0) @), (e) in Figure 6
and correspond to each other. When the interelectrode gap voltage reaches the discharge detection level after the discharge detection prohibition time of output m, (el appears in Figure 1), discharge detection is performed, and the switching element (4) shifts to OFF #. Therefore, since the gap voltage between the electrodes remains low, a discharge occurs. 4
) becomes 1ON', the same phenomenon occurs again.

On the other hand, the electrode gap tracking device t detects that the error voltage is zero when the signal (to), that is, the divided voltage value of the average voltage of the electrode gap voltage is equal to the reference voltage (106) shown in FIG. To become
The slider (101) does not move up and down and is in a state of balance, resulting in a significant decrease in machining speed, such as machining sometimes not progressing.

As described above, by selecting the discharge detection prohibition time T.

Problems such as roughening of the machined surface and significant reduction in machining speed occur. Furthermore, the optimum value of the discharge detection inhibition time T varies depending on the machining conditions, making it difficult to select one.

In addition, when machining carbide, etc., the leakage current between the machining electrodes increases due to machining powder, which causes the no-load voltage to decrease, and the problems caused by the failure of discharge detection described above can occur even if the discharge detection prohibition time is extended. There is.

This is particularly likely to occur when the processing area becomes large and it is difficult to remove processed powder. Also, is this phenomenon caused by a small difference between the discharge detection level and the servo reference voltage?

This tends to occur when the servo reference voltage is lower.

There were some problems.

This invention was made to solve the above-mentioned problems, and it simplifies the selection of the discharge detection prohibition time, and
For machining with electrical discharge machining equipment that eliminates the need to change depending on machining conditions, and prevents discharge detection failure even when leakage current due to machining powder increases, thereby preventing roughness of the machined surface and reduction in machining speed. It is used for the purpose of obtaining power.

[Means for solving problems]

The machining power source of the electric discharge machining apparatus according to the present invention is as follows.

i! flows to the second charging circuit that charges the floating container in the gap between the electrodes and the workpiece. R style.

The above-mentioned I! The charging W voltage t by the second charging circuit, and the charging i! by the first photoelectric circuit that charges the capacitor. It is thicker than pressure.

[For production]

The second charging circuit of the present invention easily sets the discharge detection prohibition time using a time constant determined by the resistance of this circuit and the stray capacitance of the gap between the electrodes, and also allows leakage current due to machining powder during machining. To reliably detect discharge even when the amount of water increases.

[Examples of invention]

Hereinafter, one embodiment of the present invention will be described. 1st
In the figure, the same symbols as in Figure 4 indicate the same parts, (5
) is the first current limiting resistor, (6) is the first diode,
(7) fl second diode, (a) a second current limiting resistor, and (c) a variable voltage source. and.

The switching element (4), the first current limiting resistor (5) and the first diode (6) are connected in series in parallel to the gap formed between the electrode (1) and the workpiece (2). A capacitor (8) connected to the total light ν constitutes the first charging circuit, a switching hexagon (1), a variable resistor 0
9 and the second current limiting resistor (1) constitute a second charging circuit that fully charges the stray capacitance in the gap between the electrodes.

Note that the second diode (7) is a switching element (
4) when the full voltage is applied to the gap between the electrodes at SQN#L.

The current flowing in the charging circuit of 1JII2 is the capacitor (8)
It is connected in series with the first charging circuit.

FIG. 2 shows the operation of the die casting example in FIG. 1. In FIG. 1) Is the discharge detection inhibition time Tt? The signal shown, (e) is the comparator (
17) output ((1) and discharge detection level time (('l)
With the logical sum of the signals.

The timing of falling is the timing of discharge detection. When the switching element (4) in FIG. 1 becomes 1ON', the capacitor (
8) Try charging. On the other hand, the stray capacitance OI in the inter-electrode gap is charged through the second current limiting resistor, but since the chain of stray capacitance is relatively small, the rise in the inter-electrode gap is relatively quick. Therefore, the discharge detection inhibition time T shown in FIG. 2 (6) can be set to a short t[Vc stage. Moreover, depending on the processing conditions, the second current limiting resistance and stray capacitance aQ
Therefore, the discharge detection prohibition time T depends on the machining conditions.
It is not necessary to change lH due to the discharge current with long pulse width.

Since no discharge detection failure occurs, the machining surface will not be roughened, and one oscillator will be in the automatic state and machining will not stop, thereby preventing a decrease in machining speed.

In addition, since the conventional power supply fully adjusts the servo reference voltage (106), that is, the reference voltage, to determine the duty factor, when the servo base #1 voltage (106) is set below the discharge detection level, the voltage as shown in FIG. However, it is easy to enter an automatic state due to failure of discharge detection.

In this invention, by adjusting and setting the servo reference voltage (106) k to a level higher than the discharge detection level using the variable voltage source e (g) provided in the second charging circuit, the duty factor is equal to or even higher than that of a conventional power supply. Moreover, the self-excitation state caused by failure of discharge detection can be completely avoided.

In addition, in the above embodiment, the switching element of the second channel II? Although this is shared with the switch and y switching element (4) of the first charging circuit, it is also possible to provide a switching element @2 for the charging circuit as shown in FIG.

〔Effect of the invention〕

As described above, according to the present invention, the second charging circuit charges the stray capacitance in the gap between the electrodes. Provided, and.

The charging circuit is configured so that the current flowing through the charging circuit does not flow back to the capacitor connected in parallel to the gap between the electrodes, and the charging voltage by the second charging circuit is controlled.

Since the charging voltage is set higher than the charging voltage of the first charging circuit that charges the capacitor, the discharge detection prohibition time can be shortened, and malfunction of discharge detection can be prevented, which suppresses the roughness of the workpiece machined surface and increases the machining speed. This has the effect of providing a machining power source for the electrical discharge machining device that prevents deterioration.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing a machining power source of an electric discharge machining apparatus according to an embodiment of the present invention, Fig. 2 is a schematic diagram showing the same operation, and Fig. 8 is a machining circuit diagram of an electric discharge machining apparatus according to another embodiment of the present invention. 4 is a circuit diagram showing the machining power source of a conventional electric discharge machining device, FIG. 5 is the same configuration diagram, and FIGS. 6 and 7 are
The figure is an explanatory diagram of the direction movement. In the figure, (1) is the electrode, (2) is the workpiece, and (4) @
(5) is the first current limiting resistor, (
6) is the first diode, (7) is the second diode,
(8) is a capacitor, QO is a stray capacitance, C is a second current limiting resistor, and (C) is a variable voltage source. In addition, in FIG. 1, the same reference numerals indicate the same or equivalent parts.

Claims (3)

[Claims] (1) a first charging circuit that charges a capacitor connected in parallel to the gap formed between the electrode and the work;
a second charging circuit that charges the stray capacitance in the gap between the electrodes, configured to prevent the current flowing through the second charging circuit from flowing back to the capacitor, and the voltage charged by the first charging circuit. A machining power source for an electric discharge machining device, characterized in that a charging voltage by a second charging circuit is higher than that of a second charging circuit. (2) A machining power source for an electric discharge machining apparatus according to claim 1, wherein the second charging circuit comprises a switching element, a current limiting resistor, and a rectifying semiconductor element. (3) A machining power source for an electric discharge machining apparatus according to claim 2, wherein the rectifying semiconductor element is a diode.