JPH068053A - Electric discharge machining method - Google Patents

Abstract

PURPOSE:To hold electric discharge gap length always optimum by setting position deviation between a moving command to first drive mechanism and the actual displacement as the moving command value to second drive mechanism. CONSTITUTION:Even when a moving command is inputted into first drive mechanism 6 in order to adjust a gap between a machining tool electrode 1 and a workpiece 2, the correction of the gap is delayed unless the first drive mechanism 6 has sufficient responsiveness; however, second drive mechanism 3 has good responsiveness. Accordingly, if position deviation between the moving command value to the first drive mechanism 6 and the actual displacement of the first drive mechanism 6 is given as the moving command to the second drive mechanism 3, the second drive mechanism 3 corrects the delay of the first drive mechanism 6. As a result, the gap length is adjusted with good responsiveness on the whole.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric discharge machining method,
In particular, it relates to an electric discharge machining method suitable for a die-sinking electric discharge machine.

[0002]

2. Description of the Related Art In an electric discharge machine, a machining tool electrode and a work piece are opposed to each other with a minute gap therebetween, a machining liquid is filled in the gap, and a voltage is applied between the two to generate an electric discharge, thereby performing machining. This is for processing the work piece by partially removing the work piece and sequentially changing the discharge position, and performing the work while maintaining the gap between the working tool electrode and the work piece at a predetermined value. Is. The control of the discharge gap is generally performed by moving the machining tool electrode by a servo motor or the like to maintain the discharge gap at a predetermined value by controlling the position and speed of the servo motor. Furthermore, a method of controlling the discharge gap length by two driving devices, a driving device having a large drivable moving amount and a driving device having a small drivable moving amount but good responsiveness, has been developed.

FIG. 4 shows a discharge gap length control mechanism having a first drive mechanism having a large movable distance, a movable distance smaller than that of the first drive mechanism, and a speed higher than that of the first drive mechanism. It is a control block diagram of one control system of an electric discharge machine provided with the 2nd drive mechanism which has movement speed or response time. In FIG. 4, 101 is a discharge gap length setting device, and the discharge gap length zs set by the discharge gap length setting device 101 and the discharge gap length zr detected by the discharge gap detection device 111 from the actual electric discharge machining process 110. And the displacement command obtained by multiplying the error ε by the distribution ratios α, β to the first drive mechanism and the second drive mechanism by the elements 102 and 103, and the detectors 108 and 109. Positional deviation is obtained by subtracting the displacement amount of the first and second drive mechanisms to be detected,
The position control gain kp of the first drive mechanism is added to each position deviation.
The position control gain kp2 of the first and second drive mechanisms is multiplied respectively to drive the first and second actuators 106 and 107, and the state of the electric discharge machining process 110 is changed. That is, the actuators 106 and 107 drive the machining tool electrode or the workpiece to control the discharge gap to match the discharge gap length set by the discharge gap length setting device 101. The amount of movement of the machining tool electrode or the work piece is the sum of the amounts of movement of the actuators 106 and 107 of the first and second drive mechanisms.

In the electric discharge machining process 110, the electric discharge gap length including the removal of the workpiece by the electric discharge machining and the consumption of the tool machining electrode is detected by the electric discharge gap detecting device 111 and fed back to perform the above-mentioned feedback control.

The block diagram shown in FIG. 5 also has a first drive mechanism having a large movable distance and a movable distance smaller than that of the first drive mechanism, and a movement speed or response time faster than that of the first drive mechanism. FIG. 6 is a control block diagram of a control system of an electric discharge machine including a discharge gap length control mechanism including a second drive mechanism having the above. In the example shown in FIG. 5, the error gap ε is obtained by subtracting the discharge gap length zr detected by the discharge gap detection device 208 from the discharge gap length zs set by the discharge gap length setter 201, and the error ε is detected. The position deviation is obtained by subtracting the sum of the movement amounts of the actuators 204 and 205 of the first and second drive mechanisms detected by the detector 206, and the position control gains Kp1 and Kp2 of the first and second drive mechanisms are added to the position deviation. The first and second actuators 204 and 205 are driven by a value obtained by multiplying by. Actuator 20 of the first and second drive mechanisms
The sum of the movement amounts of 4,205 becomes the movement amount of the machining tool electrode or the workpiece, and the state of the electric discharge machining process 207 changes. Then, the discharge gap detection device 208 detects the discharge gap of the electric discharge machining process 207 and feeds it back as described above to control the discharge gap to the set value Zs.

[0006]

In the control system shown in FIG. 4, the error between the set discharge gap length zs and the actually detected discharge gap length zr is corrected by a certain distribution ratio α. With β, the first and second drive mechanisms are simultaneously instructed. The second drive mechanism has a small maximum movement amount and a high response speed. Therefore, even if the movement of the second drive mechanism ends, the movement of the first drive mechanism does not end, and as a whole,
The time required to change the commanded discharge gap length is determined by the response time of the first drive mechanism having a slow response and becomes slow. As a result, the characteristic of the second drive mechanism having high responsiveness cannot be effectively utilized.

In the system shown in FIG. 5, the error ε, which is the difference between the set discharge gap length zs and the actually detected discharge gap length zr, is commanded as a correction command, and the first and second drive mechanisms are driven. Since the actuators 204 and 205 of the first and second drive mechanisms are commanded with a value proportional to the position deviation by comparing with the sum of the movement amounts of the actuators 204 and 205. Since the actuator 205 of the second drive mechanism moves first to reduce the deviation, the displacement command to the first drive mechanism becomes small, and as a result, only the commanded correction amount of the discharge gap length is obtained. It took a long time to displace.

Further, in the system shown in FIGS. 4 and 5,
When the discharge gap correction command exceeds the displacement limit of the second drive device having a short movable distance, the second drive mechanism is displaced to its maximum position and fixed, and the discharge gap length correction command is issued. However, there is a drawback in that the responsiveness to this will be limited by the response speed of the first drive mechanism. Therefore, an object of the present invention is to provide a control mechanism for the discharge gap length with a first drive mechanism having a large movable distance, a movable distance smaller than the first drive mechanism, and a movement at a higher speed than the first drive mechanism. It is an object of the present invention to provide an electric discharge machining method capable of controlling the electric discharge gap length with good responsiveness in an electric discharge machine having a second drive mechanism having a speed or response time.

[0009]

According to the present invention, there is provided a mechanism for controlling a discharge gap length by moving either one or both of a machining tool electrode and a workpiece, a first driving mechanism having a large movable distance, It is configured by a combination of a second drive mechanism having a movable distance smaller than that of the first drive mechanism and a high response speed, and a movement command value to the first drive mechanism and an actual displacement of the first drive mechanism. Is used as a movement command for the second drive mechanism to drive the first and second drive mechanisms to control the gap. Further, the movement command value to the first drive mechanism is defined as an error between the target gap length and the actual gap length. In particular, the second drive mechanism is constituted by means for expanding and contracting in proportion to the amount of applied electric power, and the like, and the movement command value to the first drive mechanism and the first command given to the second drive mechanism The drive mechanism is displaced in proportion to the amount of positional deviation from the actual displacement.

[0010]

In order to adjust the gap between the machining tool electrode and the workpiece, even if a movement command is input to the first drive mechanism, the first drive mechanism is not sufficiently responsive. Gap correction will be delayed. However, since the second drive mechanism has good responsiveness, the position deviation between the movement command value to the first drive mechanism and the actual displacement of the first drive mechanism is used as the movement command to the second drive mechanism. If given as a value, the second drive mechanism corrects the delay of the first drive mechanism, and the gap length is adjusted with good response as a whole.

Particularly, since the first drive mechanism is controlled so as to follow the movement command, the position deviation amount between the movement command value and the actual displacement in the first drive mechanism is It does not exceed a certain limit determined by the maximum speed of the movement command and the responsiveness of the first drive mechanism. Therefore, if the movable distance of the second drive mechanism having a small movable distance but good responsiveness is designed based on the limit of the deviation amount of the first drive mechanism, the movable distance may be insufficient during driving. Instead, you will always be able to utilize the highly responsive exercise. Further, since the position deviation of the first drive mechanism is used as the movement command value of the second drive mechanism having good responsiveness, the follow-up deviation of the entire mechanism is determined by the response characteristic of the second drive mechanism having good responsiveness.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram of essential parts of an embodiment for carrying out the present invention. In the present embodiment, a mechanism composed of a servo motor is used as the first drive mechanism having a large movable distance, has a movable distance smaller than that of the first drive mechanism, and is faster than the first drive mechanism. A second drive mechanism having a motion speed or a response time is a mechanism including a piezoelectric element.

In FIG. 1, the tool machining electrode 1 faces the workpiece 2 with a minute gap, and although not shown, the gap is filled with a machining liquid. The machining tool electrode 1 is fixed to the piezoelectric element 3 via a coupling means 5. Further, the piezoelectric element 3 is detachably fixed to a frame 4, and the frame 4 is fixed to an output shaft of a transmission mechanism 7 which is driven by a servomotor 6 and which converts a rotational movement into a linear movement. The piezoelectric element 3 is formed by laminating a large number of piezoelectric materials, deforms when a voltage is applied to the piezoelectric element 3, and the amount of deformation changes according to the magnitude of the voltage. 1 is to be moved. A position sensor 10 such as a linear scale that detects the amount of movement of the frame 4 that is moved by the servo motor 6, and a position sensor 9 such as a linear scale that detects the amount of movement of the machining tool electrode 1 that is moved by the piezoelectric element 3. Are provided respectively.

The discharge gap control device 11 detects the voltage of the discharge gap between the machining tool electrode 1 and the work piece 2, finds the discharge gap length zr from the average voltage, and determines the discharge gap length setter 12.
From the discharge gap length zs set by
The error is calculated by subtracting r, and this error is sent to the tool electrode drive controller 13 as a correction command. As will be described later, the tool electrode drive control device 13 receives signals from the position sensors 9 and 10 and the correction command, and receives the servo motor drive device 1
4 and the piezoelectric element driving device 15 are feedback-controlled and driven.

FIG. 2 is a control block diagram of the discharge gap control of this embodiment. From the discharge gap length zs set by the discharge gap length setting device 12, the discharge gap length z detected by the discharge gap detection means 24 provided in the discharge gap control device 11
The error ε is obtained by subtracting r, and this error is used as a correction command and used as a movement command to the servo motor 6 of the first drive mechanism. The movement amount z detected by the position sensor 10 from the correction command ε
The position deviation x1 is obtained by subtracting 1 and this position deviation x1 is multiplied by the position control gain Kp1 of the element 20 to obtain a movement command (torque command) to the servo motor 6, and the servo motor 6 is operated via the servo motor drive device 14. To drive. When the servo motor 6 is driven, the frame 4 moves via the transmission mechanism 7, and the machining tool electrode 1 via the piezoelectric element 3 and the coupling means 5.
Moves. When the frame 4 moves, the amount of movement is detected by the position sensor 10 and fed back.

On the other hand, the positional deviation x1 between the correction command ε and the movement amount z1 detected by the position sensor 10 is also used as a movement command for the second drive mechanism composed of the piezoelectric element 4. This second
The movement command to the piezoelectric element 4 of the drive mechanism is the position deviation x1 of the first drive mechanism, which is the difference between the correction command ε and the movement amount z1 detected by the position sensor 10, and further the error ε. The value obtained by multiplying the value obtained by multiplying the feedforward coefficient Kf is set (this feedforward coefficient Kf may be "0"), and the error obtained by subtracting this value from the movement amount detected by the position sensor 9 Control gain Kp2
Is multiplied and is used as a movement command to the piezoelectric element 3. A voltage corresponding to this command is output from the piezoelectric element driving device 15,
The piezoelectric element 3 is displaced. When the piezoelectric element 3 is displaced, the machining tool electrode 1 moves via the coupling member 5, and this movement is detected by the position sensor 9 and fed back. In this way, the machining tool electrode 1 moves, the state of the electric discharge machining process changes, and the electric discharge machining electrode 1 moves based on the movement of the servo motor 6 and the movement by the piezoelectric element 3, and the movement causes the discharge gap to change. The discharge gap changes and is detected by the discharge gap detecting means 24, and the detected discharge gap is controlled so as to match the set discharge gap zs.

As described above, this embodiment operates, but when this operation is examined in more detail, the error ε between the command discharge gap length zs and the detected discharge gap length zr is constituted by the servomotor as a correction command. The servomotor 6 is input to the first drive mechanism, and moves until the position deviation x1 of the difference between the correction command ε and the movement amount z1 detected by the position sensor 10 becomes “0”. On the other hand, since the positional deviation x1 drives the piezoelectric element 3 as a movement command to the piezoelectric element 3 of the second drive device, the piezoelectric element 3 is simultaneously driven together with the servomotor 6, and the machining tool electrode 1 moves. Become. When the machining tool electrode 1 moves, both the error (correction command) ε and the position deviation x1 approach “0”, but when the correction command ε and the position deviation x1 approach “0”, a command to the piezoelectric element 3 ( x1 + Kf · ε) also becomes small, and the value of the position deviation x2 of the difference between this command and the movement amount z2 detected by the position sensor 9 becomes a small value or a negative value.
As a result, the command voltage to the piezoelectric element 3 is proportional to Kp2 · x2, so this command voltage has a small value or a negative value. Therefore, the movement of the machining tool electrode 1 by the piezoelectric element 3 moves in the opposite direction as the command (x1 + Kf.ε) becomes smaller. A bias voltage is applied to the piezoelectric element 3, and when the positional deviation x2 is "0", the piezoelectric element 3 is
When the movement command voltage is not input to, the length corresponding to the bias voltage is held, and the position deviation x2 expands and contracts from the position according to the positive / negative of the position deviation x2, and the amount thereof is the absolute value of the position deviation x2. Proportional to size.

Finally, the machining tool electrode 1 moves to a position where the set discharge gap length zs is held, and the position deviation (correction command) ε becomes "0".
Since the position deviation x1 in the servo motor 6 of the drive mechanism is asymptotically approached to "0", the input to the piezoelectric element 3 becomes "0", and finally the machining tool electrode 1 by the piezoelectric element 3 The movement becomes “0”, and the discharge gap length is held at the set length by the positioning by the servo motor 6. This means that when the correction command ε is issued, both the servo motor 6 and the piezoelectric element 3 are driven at the same time, and the machining tool electrode 1 is moved at a high response speed by the piezoelectric element 3 having a fast response, and then the servo motor 6 is driven. When the position sensor 10 detects the movement of the servo motor 6, the machining tool electrode 1 moves in an overlapping manner, and the error x1 becomes small. Therefore, the command value to the piezoelectric element 3 becomes small and the machining tool electrode by the piezoelectric element 3 becomes small. The moving speed of 1 will decrease or move in the opposite direction. That is, the movement of the machining tool electrode 1 by the piezoelectric element 3 serves to correct the response delay of the movement by the servo motor, and, as a whole, the response of the movement of the machining tool electrode to the correction command ε is eventually seen as a whole. Is achieved quickly.

Since the servomotor of the first drive mechanism is controlled so as to follow the correction command ε with respect to the correction command ε, the position deviation x1 which is a delay in tracking the correction command and the servomotor 6 Does not exceed a certain limit determined by the maximum speed of the correction command and the responsiveness of the first drive mechanism. Therefore, if the maximum movable distance of the piezoelectric element 3 which is the second drive mechanism having high responsiveness is designed based on the limit of the positional deviation x1, it is possible to avoid shortage of the movable distance during driving, Highly responsive exercise is always available.

FIG. 3 is a flowchart of the machining tool electrode control process executed by the processor of the tool electrode drive control device 13 every predetermined period T. First, the processor reads the correction command (error) ε transmitted from the discharge gap control device 11, and also reads the movement amounts z1 and z2 in the section T of the previous cycle from the position sensors 10 and 9 (steps S2 and S).
3). Then, the displacement z1 in the previous cycle read from the sensor 10 is subtracted from the correction command ε to obtain the position deviation x1 (step S4), and the position deviation x1 is multiplied by the position control gain Kp1 set to the servo drive device 14. Output (step S5). Furthermore, the correction command ε has a setting coefficient Kf.
The position deviation x1 is added to the value obtained by multiplying by, and the movement amount z2 found in step S3 is further subtracted to find the position deviation x2 with respect to the piezoelectric element 3 (step S6).
The position control gain Kp2 set to 2 is multiplied and output to the piezoelectric element driving device 15. Thereafter, the processor of the tool electrode drive control device 13 executes the processing of steps S1 to S7 at every predetermined cycle T, and the discharge gap between the machining tool electrode 1 and the workpiece 2 is controlled so as to match the set value zs. It will be.

In the above embodiment, the piezoelectric element 3 is used as the second drive mechanism having a short movable distance but a high response speed. Instead of this piezoelectric element, a magnetostrictive element which deforms and expands and contracts when a magnetic field is applied. May be used.

[0022]

According to the present invention, as a mechanism for controlling the discharge gap length, a first driving mechanism having a large movable distance and a second driving mechanism having a small movable distance and a high response speed than the first driving mechanism. Since the position deviation, which is the difference between the movement command in the first drive mechanism and the actual displacement, is used as the movement command in the second drive mechanism, the response of the entire mechanism for controlling the discharge gap length is configured. Is determined by the response characteristic of the second drive mechanism. Therefore, a discharge gap control method with good responsiveness can be obtained. In particular, even if the follow-up characteristic of the first drive mechanism is slightly inferior, or if there is some vibration in the movement of the first drive mechanism, the second drive mechanism causes poor follow-up of the first drive mechanism. Therefore, the discharge gap length is always kept optimal because it operates to correct the vibration and the vibration.

Further, since the feedback control of the first drive mechanism is performed with the low frequency characteristic and the low gain, even if the feedback control with the high frequency characteristic and the high gain is performed in the control of the second drive mechanism, the low response characteristic is obtained. It does not destabilize the control of the first drive mechanism.

Further, according to the present invention, the command for correcting the discharge gap length is commanded to the first drive mechanism having a large movable distance, and the command position and the actual position caused by the lack of responsiveness of the first drive mechanism are set. Since the deviation of 1 is used as the movement command of the second drive mechanism having high responsiveness, the movement command given to the first drive mechanism is the same as when the second drive mechanism is not added. Therefore, even when the electric discharge machine does not include the second drive mechanism and has only the first drive mechanism,
Even if the drive mechanism is provided, the command method for feeding the machining tool electrode or the workpiece for adjusting the discharge gap can be the same. Further, even in the electric discharge machining apparatus in which the second drive mechanism having high responsiveness according to the size and mass of the machining tool electrode and the work piece is temporarily detached and used, the first drive mechanism can be used. Is the second command method
It is not necessary to change over according to the attachment and detachment of the drive mechanism of.

[Brief description of drawings]

FIG. 1 is a block diagram of a main part of an electric discharge machine for carrying out an embodiment of the present invention.

FIG. 2 is an operation block diagram of discharge gap length control in the embodiment.

FIG. 3 is a flowchart of a discharge gap control process executed by a processor of the tool electrode drive control device in the embodiment.

FIG. 4 shows a first drive mechanism having a large movable distance and a movable distance smaller than that of the first drive mechanism, and
FIG. 6 is a control block diagram of a conventional control method of an electric discharge machine including a control mechanism of a discharge gap length, which is a combination of a second drive mechanism having a higher motion speed or response time than the drive mechanism of FIG.

FIG. 5 is a control block diagram of another control method in the conventional example.

[Explanation of symbols]

 1 Processing Tool Electrode 2 Workpiece 3 Piezoelectric Element 4 Frame 5 Coupling Member 6 Servo Motor 7 Transmission Mechanism 9, 10 Position Sensor

Claims (5)

[Claims] 1. An electric discharge machining in which a machining tool electrode and a workpiece are opposed to each other with a minute gap filled with a machining liquid therebetween, a voltage is applied between the two to generate an electric discharge, and the workpiece is removed. In the method, a mechanism for controlling the gap length by moving either one or both of the machining tool electrode and the workpiece is a first drive mechanism having a large movable distance and a movable distance smaller than that of the first drive mechanism. Second with high response speed
And a position deviation between the movement command value to the first drive mechanism and the actual displacement of the first drive mechanism as the movement command of the second drive mechanism.
An electric discharge machining method for controlling a gap by driving a second drive mechanism. 2. The electric discharge machining method according to claim 1, wherein the movement command value to the first drive mechanism is an error between the target gap length and the actual gap length. 3. A movement command to the second drive mechanism,
3. The electric discharge machining method according to claim 2, wherein the position deviation of the first drive mechanism is added with a value obtained by multiplying the error by a constant. 4. The mechanism according to claim 1, wherein the second drive mechanism is a mechanism that is displaced in proportion to a positional deviation amount between the movement command value to the second drive mechanism and an actual displacement. The electric discharge machining method according to claim 3. 5. The electric discharge machining method according to claim 4, wherein the second drive mechanism is constituted by means that expands and contracts in proportion to the amount of electricity applied.