JPH0240457B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to an improvement in an electric discharge machine that uses a servo feed method to control the relative feed speed between a workpiece and an electrode so that the average machining voltage is approximately constant. More specifically, the present invention relates to an electric discharge machine capable of preventing a backward phenomenon occurring at the start of machining.

Prior Art and Problems In a wire cut electric discharge machine that moves the workpiece and a wire electrode relatively and processes the workpiece into an arbitrary shape by electric discharge, the workpiece and wire electrode are moved so that the average machining response voltage is approximately constant. Many machines are now using the servo feed method, which controls the feed relative to the wire electrode and makes it possible to keep the machining groove width almost constant even when the thickness of the workpiece changes. I'm getting used to it.

Figure 1 is a block diagram of a conventional wire-cut electrical discharge machine that uses the servo feed method, where P is the wire electrode, W is the workpiece, ES is the machining power supply, OA is the operational amplifier, VF is the voltage frequency converter, and COM is a voltage comparator, AND1 is an AND gate, NC is a numerical controller, SX and SY are X and Y axis servo units, MX and MY are X and Y units that control the relative movement between the workpiece W and the wire electrode P. Axis motor, R1~
R4 is a resistor, and C1 is a capacitor. Note that a smoothing circuit HK1 is constituted by an operational amplifier OA, resistors R3 and R4, and a capacitor C1. Also,
2A to 2D are explanatory diagrams of the operation of FIG. 1.

At the start of machining (time t ₁ ), the numerical controller NC is
As shown in FIG. A, the output signal a is set to "1". As a result, the machining power supply ES is turned on,
A machining voltage is applied between the wire electrode P and the workpiece W. Figure B shows the voltage V _W obtained by dividing the voltage between the wire electrode P and the workpiece W by resistors R1 and R2, and as shown in the figure, the voltage V _W suddenly rises at the rise of the signal a. Rising smoothing circuit HK1
is for smoothing and amplifying the difference between the divided voltage V _W and the reference voltage V _L and outputting the same, and the output signal b is affected by the capacitor C1, so that the difference between the divided voltage V W and the reference voltage V L is smoothed and output.
The voltage frequency converter gradually increases as shown in
Added to VF and voltage comparator COM. The voltage frequency converter VF outputs a pulse signal with a frequency corresponding to the voltage as signal b, and the output signal is sent to the numerical control device via the AND gate AND1.
Added to NC. In addition, the voltage comparator COM compares the level of signal b and the ground level (0V), and while the level of signal b is lower (time _t1 to _t2 ), its output is Set signal c to “1”,
This is in addition to the numerical control device NC.

When the signal c is “0”, the numerical controller NC
Based on the command program that indicates the machining path, the pulse signal from the voltage frequency converter VF is distributed to the servo units SX and SY, and the workpiece W and wire electrode P are
When the signal c is "1", a signal is applied to the servo units SX and SY to retract the relative feed between the workpiece W and the wire electrode P. Operate the motors MX and MY so that they are separated from the wire electrode P. Therefore, in this case, the workpiece W and the wire electrode P are fed in the direction in which they are separated from each other between times t ₁ and _{t 2} .

As described above, in the conventional wire-cut electric discharge machine, since the smoothing circuit HK1 has a response delay, a backward phenomenon occurs at the start of electric discharge machining, and during this period (time t ₁ to _{t 2} ), the workpiece W - Since the discharge between the wire electrodes P (mainly occurring between the side surface of the wire electrode P and the workpiece W) occurs normally [see figure B], the width of the machining groove at the start of machining is The drawback was that it was wider than other parts.

OBJECT OF THE INVENTION The present invention improves the above-mentioned drawbacks, and its purpose is to prevent the regression phenomenon that occurs during electrical discharge machining. Examples will be described in detail below.

Embodiment of the Invention FIG. 3 is a block diagram of an embodiment of the present invention, in which the present invention is applied to a wire-cut electrical discharge machine. In the same figure, HK
2 is a smoothing circuit, which differs from the smoothing circuit HK1 shown in Figure 1 in that it has a resistor R5 and an AND gate.
This is because a series circuit consisting of a switch SW which is turned on when the output signal e of AND2 is "1" is connected in parallel to the resistor R3. Further, M is a multivibrator which sets its output signal d to "1" for a certain period of time at the rising edge of signal a, and the same reference numerals as in other parts of FIG. 1 represent the same parts. 4A to 4F are explanatory diagrams of the operation of FIG. 3.

At the start of electrical discharge machining (time t ₁ ), the numerical control device NC sets its output signal a to "1" as shown in FIG. 4A, as described above. This allows machining power
ES turns on and the workpiece W-wire electrode P
The voltage obtained by dividing the voltage between them by resistors R1 and R2
V _W rises rapidly as shown in Figure B, and
The multivibrator M outputs its output signal d as shown in the figure c.
It is set to "1" for a certain period of time as shown in . Furthermore, at the start of electrical discharge machining (time t ₁ ), the level of the output signal b of the smoothing circuit HK2 is lower than the ground level as shown in FIG. As shown in Figure E, the output signal d of the multivibrator M becomes "1", and the output signal d of the multivibrator M becomes "1" as shown in Figure E.
As shown in , it is “1”, so the AND gate
The output signal e of AND2 becomes "1" as shown in FIG. F, turning on the switch SW.

By the way, the amplification factor of the smoothing circuit HK2 is different when the switch SW is on and off, and the amplification factor A _ON when the switch SW is on and the amplification factor A _{OFF when the switch SW is off} . are respectively the following formulas
(1) and (2).

A _ON = R4・(R3+R5)/R3・R5…(1) A _OFF =R4/R3…(2) That is, as can be seen from equations (1) and (2), the switch SW
The amplification factor A _ON when the switch SW is on is larger than the amplification factor A _OFF when the switch SW is off.

Therefore, at the start of electrical discharge machining (time t ₁ ) when the switch SW is turned on, the amplification factor of the smoothing circuit HK2 is large, so the output signal b of the smoothing circuit HK2 is as shown in D in the figure. As shown by the solid line, it rises rapidly and reaches the ground level at time _t3 . In addition, in the same figure D, the dotted line shows the output signal b of the conventional smoothing circuit HK1. Then, at time _t3 , when the output signal b of the smoothing circuit HK2 reaches the ground level, the voltage comparator
The output signal c of COM is “0” as shown in E of the same figure.
And along with this, the AND gate AND2
The output signal e also becomes "0" as shown in FIG.

In this way, in this embodiment, at the start of electrical discharge machining, the amplification factor of the smoothing circuit HK2 is increased, and the output signal b
Since the output signal c of the voltage comparator COM is set to rise rapidly to the ground level, the period (time t ₁ to t ₃ ) during which the output signal c of the voltage comparator COM is “1” is extremely short, and therefore, the discharge Compared to the conventional example in which the output signal c of the voltage comparator COM was "1" for a considerable period of time from the start of machining (time t ₁ to t ₂ ), the period during which the regression phenomenon occurs can be made much shorter. can. Therefore, according to this embodiment, it is possible to make the machining groove width at the machining start portion equal to the machining groove width at other portions.

Note that although the present invention is applied to a wire-cut electrical discharge machine in the embodiment, it goes without saying that the present invention may also be applied to a die-sinking electrical discharge machine.

Effects of the Invention As explained above, the present invention uses an electrical discharge machining start signal (signal a in the embodiment) to adjust the output voltage of the smoothing circuit to a level at which the relative feed direction between the workpiece and the electrode advances. (in the example, a multivibrator M,
Voltage comparator COM, AND gate AND2, resistor R
5. Since the present invention is equipped with a switch SW), it is possible to prevent the regression phenomenon that occurs at the start of electrical discharge machining. Therefore, if the present invention is applied to a wire cut electrical discharge machine, the It has the advantage that the width of the machining groove can be made equal to the width of the machining groove of other parts, and the machining speed can be improved (because it is possible to eliminate wasteful regression phenomenon at the start of machining), and it is also possible to make the machining groove width equal to the width of the machining groove in other parts. Hunting is less likely to occur even when applied to a machine, so there is an advantage that processing speed can be improved.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the conventional example, Fig. 2 A to D
1 is an explanatory diagram of the operation of FIG. 1, FIG. 3 is a block diagram of an embodiment of the present invention, and FIGS. 4A to 4F are explanatory diagrams of the operation of FIG. P is the wire electrode, W is the workpiece, OA is the operational amplifier, VF is the voltage frequency converter, COM is the voltage comparator, NC is the numerical controller, SX, SY are the servo units, MX, MY are the motors, and M is the multivibrator. , ES is the processing power supply, HK2 is the smoothing circuit, SW
is a switch, AND1 and AND2 are and gates,
R1 to R5 are resistors, and C1 is a capacitor.

Claims (1)

[Claims] 1. A smoothing circuit that smoothes the voltage between the workpiece and the electrode is provided, and the relative feed between the workpiece and the electrode is controlled depending on whether the output voltage of the smoothing circuit exceeds a reference level. In an electric discharge machine to which a servo feed method is applied, an electric discharge machining start signal forcibly increases the output voltage of the smoothing circuit to at least a level at which the relative feed direction between the workpiece and the electrode is advanced. An electric discharge machine characterized by being equipped with means.