JPS637227A - Servo feed system for electric discharge machining - Google Patents

Abstract

PURPOSE:To obtain stable electric discharge and a uniform machined surface as a servo gain for a succeeding cycle by counting an output pulse from a voltage-frequency converter for every predetermined cycle, obtaining a deviation gain between a counted value and a set value, and adding the deviation value to a servo gain outputted in the concerned cycle for a servo feed system. CONSTITUTION:When means machining voltage has given a drop with an increase in machining quantity, there is a drop in frequency from a voltage- frequency converter 5. In this case, a deviation gain between an output pulse read by a counter 10 and a pulse so far applied for machining turns into a negative value in an arithmetic processing part 8 and a servo gain for the next cycle drops. This drop causes reduction in relative feed rate between a workpiece 2 and an electrode 1 via a dividing means 7, pulse distributions 14 and 15, and servo motors 18 and 19. As a result, a gap between the workpiece 2 and the electrode 1 increases, the mean machining voltage gives a rise and operation contrary to the aforementioned operation is carried out, thereby making constant the mean machining voltage automatically. According to the aforesaid constitution, a constant machining quantity per hour is obtained and a remarkably improved finish surface becomes available.

Description

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

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 electrical discharge machine.

This servo feeding method subtracts the set voltage from the partial pressure of the average machining voltage applied between the workpiece and the wire electrode (1 cycle), and outputs a feed pulse proportional to the subtracted 1 cycle, and the weight per pulse is Always sent the table as constant.

Problems to be Solved by the Invention With the above-mentioned conventional servo feeding method, during machining such as finishing machining where the discharge energy per run is small,
Although the reason is not clear, when moving from straight line machining to corner machining, etc., and the machining wander increases, the fast feed may cause a short circuit between the workpiece and the wire electrode, causing hunting. Furthermore, when the number of machining bases decreases, the feed rate becomes too slow, which increases the amount of machining and reduces machining accuracy.

SUMMARY OF THE INVENTION Therefore, 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 converts the output pulse train into a pulse train. In electrical discharge machining servo feeding, in which each axis is fed and the workpiece and wire electrode are moved relative to each other, the output pulses of the voltage frequency converter are counted at regular intervals, and the deviation due to the difference between the counted value and the set value is calculated. The above problem was solved by calculating the gain, adding the deviation gain to the servo gain of the servo feed system output in the relevant cycle, and outputting the result to adjust the servo gain in the next cycle.

Function The number of output pulses from the voltage frequency converter within a certain period is Pi, the setting value for the set feed rate is P, the deviation gain is Gi, and the servo gain in the period is G.
If the servo gain in the i-1st period is Qi-ml, the deviation gain ΔQi will be the value shown in the first equation.

△Oi = K (Pi - P) ... (1)
Note that K is a constant. Then, this deviation gain is added to the gain Gi of the current cycle to obtain the servo gain G of the next cycle.
1+1 is expressed as the following second equation.

Gi +1 = Gi + △Qi ... (2) -
On the other hand, the number of pulses P1 from the voltage frequency converter output within a - period is proportional to the difference between the average machining voltage and the reference voltage, so the number of pulses Pi is the number of pulses between the workpiece and the wire electrode. This indicates the average machining voltage, and as the amount of machining increases at corners etc., the average machining voltage decreases, and the number of pulses P1 in one cycle output from the voltage frequency converter decreases, becoming smaller than the set value P. Then, according to the first formula, the deviation gain ΔGi becomes negative, and according to the second formula, the servo gain G of the next cycle is
i+1 will decrease. When the servo gain Qi+1 decreases, the relative feed speed between the workpiece and the wire 14f decreases, and as a result, the gap between the workpiece and the wire electrode increases, the average machining voltage increases, and the number of pulses Pi within one cycle increases. , becomes equal to the set value P, the deviation gain △Gi becomes 0 according to the first formula, and the servo gain Qi+1 of the next cycle becomes the same value as the previous cycle according to the second formula, and the pulse number P
As long as 1 is equal to the set IP, the servo gain does not change and is held constant. In addition, the amount of machining decreases, the average machining voltage increases, and the output pulse P within one round from the voltage frequency converter increases.
When i exceeds the set value, the deviation gain ΔQi becomes a positive value, and according to the second equation, the servo gain Gi +1 of the next cycle is increased, and the relative feed speed of the workpiece and the wire electrode is increased.
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 Pi from the voltage frequency converter within a period decreases. Then, when the number of pulses Pi becomes equal to the setting fifiP, the servo gain does not vary and is held constant as described above.

In other words, the servo gain is changed so that the average machining voltage is constant (so that the output pulse Pi within one cycle from the voltage frequency converter is equal to the set value P), and the relative feed speed between the workpiece and the wire electrode is quickly adjusted. It will change.

Embodiment FIG. 7 is a block diagram of an embodiment of the present invention.
1 is a wire electrode, 2 is a workpiece, R and R are resistors that divide the voltage between wire electrode 1 and workpiece 2, and 3 is a voltage that smoothes the divided voltage between wire electrode 1 and workpiece 2 by resistors R and R. An integrator that takes out the average machining voltage; 4 a differential amplifier that amplifies the difference between the average machining voltage output from the integrator 3 and a reference voltage Vo; 5 converts the output voltage of the differential amplifier 4 into the frequency of a pulse train. A voltage frequency converter 6 is a numerical control device, and frequency dividing means 7 divides the frequency of the pulse train from the voltage frequency converter 5. While adjusting the frequency division ratio of the frequency dividing means 7 as a servo gain, 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) is calculated by using the Ni program. Arithmetic processing section 8 consisting of a microprocessor that outputs to the pulse distributor of each axis.
Memory section 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 a program from a tape 12 that stores an NC program. Manual data input device 13 for inputting various commands and data. Furthermore, a pulse distributor 14 outputs the movement amount for each axis output from the arithmetic processing unit 8 to the servo circuits 16 and 17 of each axis by a pulse train as a speed command output from the frequency dividing means 7.
It has an angle of 15°. 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, from the manual data input device 13, the relative set feed speed P of the workpiece 2 and the wire electrode 1 during servo feeding is determined.
The initial value Go of the servo gain corresponding to the frequency division ratio of the frequency dividing means
(If the frequency division ratio of the frequency dividing means is λ and the servo gain is G, then there is a relationship of λ=1/G). When the tape reader 11 reads the NG program and starts machining, the voltage applied between the wire electrode 1 and the workpiece 2 is divided by the resistors R and R, and this divided voltage is smoothed by the integrator 3 and averaged. It is input to the differential amplifier 4 as a processing voltage.

The differential amplifier 4 compares it with the reference voltage Vo, 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, the output pulses are counted, and the frequency is divided by a frequency dividing means 7 to be sent as a feed rate command to the X axis, Y@
is input to the pulse distributor 14.15. The pulse distributors 14 and 15 receive incremental movement commands △
, △Y are set, an accumulator, and an adder that adds the incremental values △X, △Y set in the register to the contents of the accumulator every time a pulse is generated from the frequency dividing means 7. There is. and,
In such a pulse distributor 14.15, the overflow pulse generated from each accumulator becomes a distribution pulse and is applied to each axis servo circuit 16.17 at the next stage.
The servo motors for the axis and Y axis are respectively driven to move the wire electrode along the commanded machining path relative to the workpiece.

On the other hand, the microprocessor of the arithmetic processing unit 8 performs the process shown in FIG. 2 at regular intervals, first reading the value Pi of the counter 10, and then resetting the counter 10 (step S1). Next, the calculation shown in the first equation is carried out, that is, from the read value Pi of the counter 10, the set value P as the feed speed command is subtracted and multiplied by the constant K to obtain the ViM difference gain ΔG.
(Step 32). Next, the obtained deviation gain ΔG is added to the servo gain G (initially 1111 set value Go) of the cycle stored in the memory 9, and the stored contents of the address of the memory 9 where the servo gain is stored are added to this value. The servo gain is rewritten to a new servo gain, and this new servo gain is output to the frequency dividing means 7 to change the frequency division ratio. That is, a new servo gain is obtained by performing the second expression, and the frequency division ratio of the frequency dividing means 7 is changed (step 83.34).

The arithmetic processing section performs this process at regular intervals, and it is now assumed 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 P1 of the counter 10 read in step S1 becomes smaller. Therefore, the deviation gain ΔG obtained in step S2 becomes a negative one (assuming that the amount of processing has been constant and the servo gain G has been constant in the state of ΔG=O).

As a result, the new servo gain G determined in step S3 decreases, and the pulse train output from the frequency dividing means 7 becomes
Since Pl ・G, the number of output pulses decreases and xl
The speed of the distribution pulse output from the NI and Y-axis pulse distributor decreases, the rotational speed of the X@ and Y-axis servo motors is reduced, and the relative feeding speed between the workpiece 2 and the wire electrode 1 decreases. 2 and the wire electrode 1 increases, the average processing voltage increases, the output voltage from the differential amplifier 4 increases, and the output of the voltage frequency converter 5 increases, within one period counted by the counter 10. The pulse vlPi also increases, increasing the deviation gain ΔG and increasing the servo gain G. Then, when the number of pulses Pi within the - period exceeds the set value P, the deviation gain ΔG becomes a positive value and the servo gain G
As a result, the relative feeding speed between the workpiece 2 and the wire electrode 1 increases. This operation is performed sequentially, and the servo gain G is quickly adjusted so that the deviation gain ΔG becomes O.

Similarly, when the machining amount suddenly decreases, the deviation gain Δ
Since the servo gain G is adjusted so that G quickly reaches O, there is no longer any problem of hunting or excessive machining that degrades machining accuracy, as was the case in the past.

Note that as a method of adjusting the servo gain, the frequency dividing means 7
In addition to the method of changing the matching ratio, there is also a method of finely adjusting the reference voltage of the differential amplifier 4. That is, when the servo gain G obtained in steps 81 to S4 becomes large, the D/A
When the converter lowers the reference voltage Vo and increases the servo gain, and the servo gain obtained in steps 81 to S4 becomes small, the reference voltage Vo is increased to decrease the servo gain to finely adjust the reference voltage. You may do so by doing so.

Effects of the Invention As mentioned above, when the amount of machining increases when machining corners etc., the servo gain is quickly lowered to reduce the relative feed speed between the workpiece and the wire electrode, and when the amount of machining decreases, the servo gain is quickly increased. Since the feed rate is increased by increasing the feed rate, the relative feed rate between the workpiece and the wire electrode changes automatically and quickly in accordance with the increase or decrease in machining ω of the workpiece, and operates to keep the average machining voltage constant. Therefore, during finishing machining, hunting does not occur, the amount of machining per time is always constant, the machined surface is uniform, and the finishing quality is significantly improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG.
The figure 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. Figure 2

Claims (2)

[Claims] (1) Compare the partial pressure value of the average machining voltage between the workpiece and the wire electrode with the reference voltage, convert the difference voltage by a pulse train using a voltage frequency converter, and use the output pulse train to feed each axis to the workpiece. In electrical discharge machining servo feed that moves the wire electrode relatively, the output pulses of the voltage frequency converter are counted at regular intervals, the deviation gain is determined by the difference between the counted value and the set value, and the output pulse is output at the relevant cycle. This is an electric discharge machining servo feed method in which the deviation gain is added to the servo gain of the servo feed system to obtain the servo gain for the next cycle. (2) The output pulse of the voltage frequency converter is divided by the frequency dividing means, each axis is sent by the output of the frequency dividing means, and the frequency division ratio of the frequency dividing means is changed to control the servo control. The electric discharge machining feeding method according to claim 1, which changes the gain.