JPH0579443B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a servo feed system in a wire cut electrical discharge machine.

BACKGROUND OF THE INVENTION A servo feed method has conventionally been adopted as a method for controlling the relative feed speed between a workpiece and a wire electrode in a wire-cut electric discharge machine.

This servo feed method subtracts the set voltage from the partial pressure value of the average machining voltage applied between the workpiece and the wire electrode, and outputs a feed pulse proportional to the subtracted value, and the weight per pulse is always constant. They sent the table.

Problems to be Solved by the Invention With the conventional servo feeding method described above, during machining such as finishing machining where the discharge energy is low per run, the reason is not clear, but the shift from straight machining to corner machining, etc. When the amount of machining increases, the workpiece and wire electrode may shoot due to fast feeding, causing hunting. Furthermore, when the amount of machining to be processed becomes small, the feed becomes too slow, which increases the amount of machining and causes a drop in machining accuracy.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a servo feed system for electric discharge machining that can obtain stable electric discharge and a uniform machined surface by adjusting the servo gain of servo feed.

Means for Solving the Problems The present invention compares the partial pressure value of the average machining voltage between the workpiece and the wire electrode with a reference voltage, converts the difference voltage into a pulse train using a voltage frequency converter, and outputs the output pulse train. In electrical discharge machining servo feeding that moves each axis relative to the workpiece and wire electrode, the output pulses of the voltage frequency converter are counted at regular intervals, and the difference between the counted value and the set value is calculated. The above-mentioned problem was solved by calculating the deviation gain by , and adding the deviation gain to the servo gain of the set servo feed system and outputting the result as the servo gain for the next cycle.

Effect The number of output pulses within a certain period from the voltage frequency converter above is Pi, and the set value for the set feed rate is P.
Assuming that the deviation gain is ΔGi, the set servo gain is G, and the servo gain in the next cycle is Gi+1, the deviation gain ΔGi has a value shown in the first equation.

ΔGi=K(Pi-P)...(1) Note that K is a constant. Then, by adding this deviation gain to the set gain G, the next period's servo gain Gi+1 is obtained as shown in the following second equation.

Gi + 1 = G + ΔGi ... (2) On the other hand, since the number of pulses Pi from the voltage frequency converter output within one cycle is proportional to the difference between the average applied voltage and the reference voltage, the above pulse The number Pi indicates the average machining voltage between the workpiece and the wire electrode, and as the amount of machining increases at corners etc., the average machining voltage decreases, and the number of pulses in one cycle output from the voltage frequency converter Pi decreases and becomes smaller than the set value P, the deviation gain ΔGi from the first equation
is negative, and from the second equation, the servo gain of the next cycle is
Gi+1 will decrease. Servo gain Gi
When +1 decreases, the relative feed speed between the workpiece and the wire electrode decreases, and as a result, the gap between the workpiece and the wire electrode increases, the average machining voltage increases, the number of pulses in one cycle increases, and the deviation increases. A negative value of the gain ΔGi becomes smaller, increases the servo gain Gi+1, and works to lower the average machining voltage; if it is lowered too much, the servo gain decreases as described above, and works to increase the average machining voltage, eventually reducing the average machining voltage. acts so that it remains constant. Also, when the amount of machining decreases and the average machining voltage increases, and the output pulse Pi from the voltage frequency converter within one cycle increases, the value of the deviation gain ΔGi increases, and from the second equation, the servo gain Gi + 1 of the next cycle increases the relative feed speed between the workpiece and the wire electrode, as a result, the gap between the workpiece and the wire electrode becomes smaller, the average machining voltage decreases, and the number of output pulses from the voltage frequency converter within one cycle decreases. Pi decreases, the deviation gain ΔGi is lowered, and the average machining voltage is automatically controlled to be constant as described above.

Embodiment FIG. 1 is a block diagram of an embodiment of the present invention, in which 1 is a wire electrode, 2 is a workpiece, R and R are resistors that divide the voltage between the wire electrode 1 and the workpiece 2, and 3 is a resistor. An integrator 4 smoothes the voltage between the wire electrode 1 and the workpiece 2 divided by R and _R to obtain an average machining voltage. A differential amplifier that amplifies the difference; 5 is a voltage frequency converter that converts the output voltage of the differential amplifier 4 into the frequency of the pulse train; 6 is a numerical control device that divides the frequency of the pulse train from the voltage frequency converter 5; 7. Adjust the frequency division ratio of the frequency dividing means 7 as a servo gain, and calculate the amount of movement of the incremental value of each axis of the wire electric discharge machine (only the X axis and Y axis are shown) using the machining program. an arithmetic processing unit 8 consisting of a microprocessor that outputs the pulses to the pulse distributors of each axis;
A memory unit 9 for temporary storage of control programs and data, a counter 10 that counts the output of the voltage frequency converter 5 every cycle, a tape reader 11 that reads programs from a tape 12 that stores NC machining programs, and various commands and A manual data input device 13 for inputting data, and a servo circuit 16, 17 for each axis using a pulse train as a speed command output from the frequency dividing means 7 to calculate the amount of movement for each axis output from the arithmetic processing unit 8. It has pulse distributors 14 and 15 that output to. 16 is an X-axis servo circuit, 17 is a Y-axis servo circuit, 18 is a servo motor that drives the X-axis, and 19 is a servo motor that drives the Y-axis.

Next, the operation of this embodiment will be explained.

First, the manual data input device 13 is used to set the relative set feed speed P between the workpiece 2 and the wire electrode 1 during servo feeding, and the servo gain G corresponding to the frequency division ratio of the frequency dividing means ( The periodicity is λ
Then, there is a relationship of λ=1/G). and,
When the NC machining program is read from the tape reader 11 and machining is started, the voltage applied between the wire electrode 1 and the workpiece 2 is divided by resistors R and R, and this divided voltage is smoothed by the integrator 3 to obtain the average machining voltage. The signal is input to the differential amplifier 4 as a signal. The differential amplifier 4 compares it with a reference voltage V ₀ , and the difference is amplified and output, and the voltage-frequency converter 5 converts it to a pulse frequency. The output of the voltage frequency converter 5 is input to a counter 10, and the output pulses are counted, and the frequency is divided by a frequency dividing means 7, and input as a feed rate command to the X-axis and Y-axis pulse distributors 14 and 15. Ru. The pulse distributors 14 and 15 are connected to registers in which incremental movement commands ΔX and ΔY output from the arithmetic processing unit 8 to each axis according to the NC machining program are set, an accumulator, and pulses from the frequency dividing means 7. It has an adder that adds the incremental values ΔX and ΔY set in the register to the contents of the accumulator each time the register is generated. In the pulse distributors 14 and 15, overflow pulses generated from each accumulator are applied as distribution pulses to the servo circuits 16 and 17 for each axis at the next stage to drive the servo motors for the X and Y axes, respectively. The wire electrode is moved along the commanded machining path relative to the workpiece.

On the other hand, the microprocessor of the arithmetic processing unit 8 performs the processing shown in FIG. 2 at regular intervals.
The value Pi of the counter 10 is read, and then the counter 10 is reset (step S1). Next, the calculation shown in the first equation, that is, the read value Pi of counter 10
Then, the deviation gain ΔG is obtained by subtracting the set value P as the feed speed command and multiplying by the constant K (step S2). Next, the obtained deviation gain ΔG is added to the set servo gain G, and the next cycle servo gain is calculated.
Gi+1 is determined, and this servo gain Gi+1 is output to the frequency dividing means 7 to change the frequency division ratio. Immediately, the second equation is calculated to obtain a new servo gain, and the frequency dividing means 7
(step S3,
S4).

The arithmetic processing section performs this process at regular intervals, and now assume that the amount of machining has increased and the average machining voltage has decreased. The output from the differential amplifier 4 becomes smaller, the frequency output from the voltage frequency converter 5 decreases, and the value Pi of the counter 10 read in step S1 becomes smaller. Therefore, the deviation gain ΔG obtained in step S2 becomes a negative value (assuming that the amount of machining has been constant and the servo gain G has been constant in the state of ΔG=0).

As a result, the servo gain Gi+1 for the next cycle determined in step S3 decreases, and since the pulse train output from the frequency dividing means 7 is Pi.G, the number of output pulses decreases and the X-axis and Y-axis pulses are distributed. The speed of the distribution pulse output from the device decreases, and the
Reduce the rotation speed of the Y-axis servo motor, and
The relative feed speed of the wire electrode 1 and the wire electrode 1 decreases, and the gap between the workpiece 2 and the wire electrode 1 increases, so the average machining voltage increases, the output voltage from the differential amplifier 4 increases, and the voltage frequency converter 5 The output increases, and the number of pulses Pi counted in one cycle by the counter 10 also increases, increasing the deviation gain ΔG and increasing the servo gain Gi+1. The relative feed speed between the workpiece 2 and the wire electrode 1 will increase, and this operation will be performed in sequence, and the average machining voltage will be automatically adjusted to be constant.

In addition, even when the amount of machining suddenly decreases, the servo gain G is adjusted so that the average machining voltage quickly becomes constant. There is no longer any loss in accuracy.

Note that as a method of adjusting the servo gain, there is also a method of finely adjusting the reference voltage of the differential amplifier 4, in addition to the method of changing the frequency division ratio of the frequency dividing means 7. That is,
When the servo gain G obtained in steps S1 to S4 becomes large, the D/A converter lowers the reference voltage _V0 to increase the servo gain, and then steps
When the servo gain obtained in S1 to S4 becomes small, the reference voltage may be finely adjusted by increasing the reference voltage _V0 and reducing the servo gain.

Effects of the Invention The present invention counts the pulses output from the voltage frequency converter at regular intervals, and uses the counted value to calculate the difference between the average machining voltage between the workpiece and the wire electrode and the set reference voltage to the above-mentioned constant value. Since the servo gain is determined for each cycle and changed according to this difference, the servo gain is automatically adjusted at every fixed cycle according to the difference between the average machining voltage and the reference voltage. Therefore, when machining a corner, etc., the amount of machining increases, the average machining voltage decreases, and the count value for each constant cycle decreases, the servo gain automatically decreases and the relative feed speed of the workpiece and wire electrode decreases. decreases, increasing the gap between the workpiece and the wire electrode, and preventing the workpiece and the wire electrode from being shot.

In addition, when the amount of machining decreases and the difference between the average machining voltage and the reference voltage increases and the above count value increases, the servo gain automatically increases to increase the feed rate and reduce the gap between the workpiece and the wire electrode. This results in a decrease in the amount of processing and an increase in the amount of processing.

In this way, the servo gain is adjusted at regular intervals according to the difference between the average machining voltage and the reference voltage, and the larger the difference, the more the servo gain is increased to increase the feed rate and improve tracking. This quickly reduces the gap between the workpiece and the wire electrode, reducing the average machining voltage. on the other hand,
In order to reduce the above difference, reduce the servo gain, reduce the feed speed, increase the gap between the workpiece and the wire electrode, and increase the average machining voltage.
The servo gain is controlled so that the average machining voltage is constant, that is, the machining amount is constant, with good responsiveness and stability. Moreover, since the servo gain is adjusted based on the difference between the above-mentioned average machining voltage and the reference voltage detected at regular intervals, the servo gain does not fluctuate suddenly but changes continuously, resulting in stable control. becomes possible. As a result, during finishing machining, hunting does not occur, the amount of machining per time is always constant, the machined surface is uniform, and the accuracy of the finished surface can be significantly improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a flowchart of servo gain adjustment processing. DESCRIPTION OF SYMBOLS 1... Wire electrode, 2... Work, 3... Integrator, 4... Differential amplifier, 5... Voltage frequency converter, 6... Numerical control device, 7... Frequency dividing means, 8...
...Arithmetic processing unit, 10...Counter.

Claims (1)

[Claims] 1. Compare the partial pressure value of the average machining voltage between the workpiece and the wire electrode with a reference voltage, convert the difference voltage by a pulse train using a voltage frequency converter, and use the output pulse train to control each axis. In the electric discharge machining servo feeding method that moves the workpiece and the wire electrode relatively, the output pulses of the voltage frequency converter are counted at regular intervals, and a predetermined proportionality constant is applied to the difference between the counted value and the set value. An electric discharge machining servo feed method that multiplies the deviation gain to find the deviation gain and adds the deviation gain to the set servo gain of the servo feed system to use as the servo gain for the next cycle. 2 The output pulse of the voltage frequency converter is divided by a frequency dividing means, each axis is sent by the output of the frequency dividing means, and the servo gain is adjusted by changing the frequency division ratio of the frequency dividing means. The electrical discharge machining feeding method according to claim 1, which changes the electrical discharge machining feeding method.