JPH1043946A - Control device of electric discharge machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain a clearance such as expected discharge can be obtained even at machining time under a condition where work liquid reaction is large. SOLUTION: When a relative moving distance obtained by a relative moving distance calculating part 11 moves in the direction for narrowing a clearance by exceeding an excessive approach quantity determined by an excessive approach quantity determing part 12, and when it is judged as nondischarge by a discharge condition judging part 10, a moving speed factor is reduced by a moving distance operation processing part 6, and an operation is performed on a moving vector quantity. A driving apparatus 8 is driven at crawling speed through a driving apparatus control part 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an electric discharge machine, and more particularly to a control for maintaining a proper gap between electrodes and a workpiece in order to generate a stable electric discharge.

[0002]

2. Description of the Related Art In electric discharge machining, an electric discharge is successively generated between an electrode immersed in a machining fluid and a workpiece, that is, between electrodes.
Processing is performed by the melting and removing action of the workpiece accompanying this. In order to generate discharges sequentially, the distance between the poles, that is, the gap must be properly maintained. Since the workpiece is gradually removed when the discharge is sequentially generated, an automatic control system called gap control is configured so that the gap is appropriately maintained according to the removal of the workpiece.

FIG. 5 shows an example of the configuration of a gap control section of a control device of a conventional electric discharge machine. The electrode 1 and the workpiece 2 face each other via the working fluid 3, and a discharge power supply 4 is connected. The electrode 1 is moved toward or away from the workpiece 2 by the driving device 8. With such a configuration, the average voltage V1 is generated by the average voltage generator 5 via a filter or the like based on the voltage appearing between the electrode 1 and the workpiece 2. The moving amount calculation processing unit 6 calculates the driving direction and speed from the difference between the inter-electrode average voltage V1 and the reference voltage V2, and drives the driving device 8 via the driving device control unit 7.
Then, as a result of the feedback control, the gap between the electrode 1 and the workpiece 2 maintains an appropriate gap for performing discharge.

[0004] With the action of melting and removing the workpiece by the electric discharge, machining chips are generated between the poles. Since excessive machining detriment hinders normal discharge, the moving amount calculation processing unit 6 executes a so-called “jump operation” in which the electrode is separated by a predetermined amount at regular time intervals and returned to the original position again, and the machining debris is extremely reduced. They are discharged outside.

[0005]

The gap for performing proper discharge is several tens μm to several hundreds μm, and the working fluid 3 is filled in this slight gap. For this reason, when the electrode 1 is moved, a reaction force acts in a direction opposite to the moving direction, and attempts to suppress the movement of the electrode 1. This reaction force generally becomes maximum when the electrode approaches after the jump operation. Since the reaction force causes physical distortion between the driving device 8 and the electrode 1, the followability of the electrode position, which is the object of indirect control in the gap control system, deteriorates.
An appropriate gap for discharging can not be maintained. As a result, the discharge does not occur successively, so that not only the machining efficiency is reduced, but also the short-circuit is increased to cause a localized concentrated discharge, thereby deteriorating the electrode surface and the workpiece surface.

[0006] The above-mentioned phenomenon becomes remarkable especially in finishing processing in which the electrode area is large and the distance between the electrodes is small. FIG. 6 (A)
FIG. 6B shows a state of processing under a condition of a small reaction force, and FIG. 6B shows a state of processing at a condition of a large reaction force. The horizontal axis is the time axis, p1 is the position in the drive unit, p2 is the electrode position, and v1 is the average voltage between the electrodes. Note that the average voltage between contacts v
When 1 is the maximum value, non-discharge is dominant in the gap state, and when the average gap voltage is 0, short-circuit is dominant in the gap state. When the inter-electrode average voltage v1 matches the reference voltage v2, an expected discharge appears between the interelectrodes.

In FIG. 6A, since the reaction force is small, the electrode position p2 moves following the drive device section position p1.
The inter-electrode average voltage v1 fluctuates with the electrode position p2 and converges to the reference voltage v2. As a result, a discharge expected between the inter-electrodes is stably generated. On the other hand, in FIG. 6B, when the electrode position p2 moves in the approaching direction, the driving device unit position p1 is moved by the reaction force.
Is distorted. The driving device is driven so that the gap voltage v1 converges to the reference voltage v2 by the gap control. However, the driving device portion position p1 and the electrode position p2 enter an oscillating state due to the deterioration of the electrode position following capability, and the gap average is changed. The voltage v1 also does not converge. In other words, under conditions where the reaction force is large,
In the gap state, non-discharge or short circuit is dominant,
There is a problem that machining is performed in a state where the expected discharge is hardly generated.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem, and is an electric discharge machine capable of maintaining a gap so as to generate an expected electric discharge even when machining under conditions of a large reaction force. The purpose is to supply a control device.

[0009]

SUMMARY OF THE INVENTION The present invention relates to a control device for an electric discharge machine which performs machining by successively generating electric discharge between an electrode and a workpiece.
Average voltage generation means for detecting a voltage between the electrode and the workpiece to generate an average voltage, discharge state determination means for determining a discharge state based on the average voltage, and a discharge stable state where the discharge is continued Relative movement amount calculating means for obtaining a relative movement vector amount of the driving device that moves the electrode from the time point when it is determined that the electrode is moved, and approaching the workpiece from the position of the driving device at the time point when the discharge stable state is determined. An over-approaching amount determining unit that determines an over-approaching amount indicating a vector amount to a possible position of the driving device; and a moving amount calculating unit that obtains a driving speed of the driving device. This is achieved by reducing the driving speed of the driving device when the relative movement vector amount is located in a direction in which the distance becomes smaller. Further, the over-approaching amount is determined based on a machining condition, the over-approaching amount is changed after a jump operation, and the discharge state determination means calculates a cumulative value of time during discharge. The biting state is determined on the basis of the following. In the case of the biting state, the driving speed of the driving device is not changed, thereby achieving each of them more effectively.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A control device for an electric discharge machine according to the present invention comprises means for judging from a mean gap voltage V1 whether a gap state is non-discharge or discharge, and a gap state in which discharge is continued. Means for storing the relative movement amount of the driving device from the point in time when it is determined that the driving device is in use, and determining whether or not the driving device is at a position excessively close to the workpiece using the relative movement amount. If it is located in an excessively close position, and if the gap state is non-discharge, it is determined that distortion has occurred between the electrode and the driving device, and means for reducing the driving speed of the driving device are provided. I have. If the driving speed of the driving device is reduced when the reaction force causes distortion, the reaction force between the electrodes is attenuated, and the electrode gradually approaches the workpiece, so that the discharge can be stably maintained. In this method, particularly in the finishing process with a large reaction force, the amount of workpiece removal per unit time is extremely small, and the change in the electrode position for maintaining or restarting the discharge is
It takes advantage of the phenomenon that it is very slow in the approach direction.

In general, the above-mentioned phenomenon does not apply immediately after the jump operation and immediately after the start of machining called "biting". Immediately after the jump operation, machining dust between the poles is reduced. Therefore, it is desirable that the gap appropriate for successively generating the normal discharge be slightly narrower than the gap maintained for the previous discharge. In addition, in the biting, the position of the electrode to be discharged frequently changes, so that the next time the discharge is not always performed at the previously discharged electrode position, and when the driving speed of the driving device is reduced by the above-described means, the processing efficiency is reduced. There is. In view of these two cases, the present invention has the following control means.

In the first control means, only after the jump operation, a predetermined over-approaching distance Dj is determined from the position of the previously discharged electrode.
A distortion judgment is performed at a position that is a minute closer. When the moving speed of the driving device is reduced after the jump operation, the position of the driving device is already at a position close to the workpiece by the over-proximity distance Dj. Move to a position closer by minutes. As a result, after the jump operation, the discharge is restarted in a state where the gap is narrow by the over-approaching distance Dj, and the discharge is likely to occur sequentially. Note that it is desirable that the over-approaching distance Dj be smaller as the processing condition has a smaller surface roughness, and thus the over-approaching distance Dj is determined based on, for example, the peak current value of the processing condition.

Further, the second control means determines that biting has occurred until the cumulative time when it is determined that electric discharge has appeared in the gap from the start of machining until a cumulative time exceeds a predetermined time. By not performing the above-described distortion determination and the accompanying reduction in the driving speed, a reduction in machining efficiency is suppressed.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing an example of a control device for an electric discharge machine according to the present invention in correspondence with FIG.

The discharge state determination unit 10 determines the state of the gap from the average gap voltage V1 generated by the average voltage generator 5. An operation example of the discharge state determination unit 10 will be described with reference to the flowchart of FIG. When the inter-electrode average voltage V1 is equal to or lower than the non-discharge judgment voltage and equal to or higher than the short-circuit judgment voltage (steps S1 and S2), the discharge cumulative time and the discharge duration time are counted up (steps S3 and S4). Resets the discharge duration (step S
5). Subsequently, the cumulative discharge time is compared with the biting determination time. If the cumulative discharge time is shorter than the biting determination time (step S6), it is determined that the biting state is present (step S7). On the other hand, when the discharge continuation time is longer than the continuation determination time (step S8), it is determined that the discharge is stable (step S9). Further, when it is not in the biting state and in the stable discharge state, and when the average voltage V1 between the electrodes is equal to or higher than the non-discharge determination voltage (step S10), it is determined that the battery is in the non-discharge state (step S11).

The relative movement amount calculation unit 11 generates a relative movement vector amount Di of the driving device 8 from the time when the discharge state is determined to be stable. While the movement command vector amount output from the movement amount calculation processing unit 6 is sequentially integrated, the relative movement vector amount Di is set to 0 when the discharge state determination unit 10 determines that the discharge is stable. In this embodiment, when the driving device 8 moves in the direction approaching the workpiece 2, the relative movement vector amount Di is a positive value, and when the driving device 8 moves in the direction separating from the workpiece 2, the relative movement vector amount Di is relatively large. The movement vector amount Di is a negative value.

The over-approaching amount determining section 12 determines the workpiece 2 after the jump with respect to the distance between the poles that has been stably discharged in the past.
Is determined, that is, the over-approaching amount Dj. The over-approaching amount determining unit 12 has a determination table indicating the amount of over-approaching in advance corresponding to the peak current value and the current value. Based on the currently selected peak current, the corresponding peak current value from the determination table is used. And employs the corresponding over-approach amount. The determination table may be determined using a function other than using the determination table as a means for determining the over-approaching amount. An example of the function is shown in Equation 1.

[0018]

## EQU1 ## Over-approach amount Dj = 2 × √ (peak current value)

The moving amount calculating section 6 calculates a moving vector amount of the driving device 8. An example of the operation of the movement amount calculation processing unit 6 will be described with reference to the flowchart of FIG. If it is a jump timing (step S20), the over-approaching amount Dj determined by the over-approaching amount determining unit 12 is obtained (step S21), and a moving vector amount for the jump operation is generated (step S22). When it is not the jump timing, the relative movement vector amount Di and the over-approach amount Dj are compared, and when the relative movement vector amount Di is large, that is, the over-approaching amount D
j and approaching the workpiece (step S2
3) While setting the over-approach amount Dj to 0 (step S2)
4), it is determined whether or not the gap state determined by the discharge determination unit 10 is non-discharge (step S25). When the gap state is non-discharged, that is, when distortion occurs, and when the gap average voltage V1 is larger than the reference voltage V2, that is, when the gap should be moved in the approaching direction (step S26), the movement speed coefficient Is reduced (step S27). On the other hand, step S
In 23, when the position of the driving device is not approaching the workpiece exceeding the over-approaching amount Dj, or when there is no distortion in step S25, or when it should be moved in the separating direction in step S26, A standard value is adopted as the speed coefficient (step S28). Finally, the difference between the inter-electrode average voltage V1 and the reference voltage V2 is multiplied by a moving speed coefficient to calculate a moving vector amount (step S29).

The driving device control unit 7 includes a moving amount calculation processing unit 6
The driving device 8 is driven based on the movement vector amount generated in. Since the electric discharge machine generally has a plurality of orthogonal driving devices, the driving device control unit 7 distributes the movement vector amount to each driving device along a machining locus specified by a program or the like. Then, they are driven in synchronization with each other.

With the above-described structure, the discharge can be stably maintained even when machining is performed under the condition where the reaction force by the machining fluid is large, and it is expected that a decrease in machining efficiency and a decrease in machining surface quality can be suppressed. What is more characteristic is that the drive speed reduction processing according to the present invention is ineffective when the reaction force of the machining fluid is small. When the frequency fluctuates frequently, the driving speed does not decrease, and the electrodes move at a high frequency to obtain a good discharge. FIG. 4 shows a state of processing using the gap control according to the present invention. In FIG. 4, although a distortion is generated between the position of the driving device and the position of the electrode, the average voltage v1 between the electrodes eventually coincides with the reference voltage V2 by reducing the driving speed of the driving device, and the expected discharge is stabilized. And appear in the gap.

In the above embodiment, the operation of the main part according to the present invention has been described with reference to the flowchart. However, even if all or a part of the operation is realized by using software or hardware, there is no problem in terms of function. Absent. Also,
Although an electric discharge machine configured to move an electrode by a driving device has been described as an example, the present invention can be applied to an electric discharge machine configured to move a workpiece instead of an electrode.

[0023]

As described above, according to the control apparatus for an electric discharge machine of the present invention, the electric discharge can be stably maintained even in the finishing work having a large electrode area and a large reaction force, which has been conventionally difficult. In addition, it is possible to suppress the deterioration of the processing speed and the processing quality.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an example of a control device of an electric discharge machine according to the present invention.

FIG. 2 is a flowchart illustrating an operation example of a discharge state determination unit of the device of the present invention.

FIG. 3 is a flowchart illustrating an operation example of a movement amount calculation processing unit of the apparatus of the present invention.

FIG. 4 is a view showing a state of processing when a reaction force is large in the apparatus of the present invention.

FIG. 5 is a block diagram showing an example of a control device of a conventional electric discharge machine.

FIG. 6 is a diagram showing a state of processing in a conventional apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electrode 2 Workpiece 3 Machining fluid 4 Discharge power supply 5 Average voltage generator 6 Movement amount calculation processing unit 7 Driving device control unit 8 Driving device 10 Discharge state determination unit 11 Relative movement amount calculation unit 12 Over approach amount determination unit

Claims (4)

[Claims] 1. A control device for an electric discharge machine which performs machining by successively generating electric discharge between an electrode and a workpiece, comprising: an average for detecting a voltage between the electrode and the workpiece to generate an average voltage. A voltage generation unit, a discharge state determination unit that determines a discharge state based on the average voltage, and a relative movement vector amount of a driving device that moves the electrode from a time point when the discharge is determined to be continued and the discharge is stable. A relative movement amount calculating means for obtaining an over-approaching amount indicating a vector amount from a position of the driving device at the time when the discharge stable state is determined to a position of the driving device accessible to the workpiece. An approach amount determining means, and a movement amount calculating means for obtaining a drive speed of the drive device, wherein the drive of the drive device is performed when the relative movement vector amount is located in a direction in which the gap is narrowed beyond the over approach amount. speed Electric discharge machine control apparatus being characterized in that so as to decrease. 2. The control apparatus for an electric discharge machine according to claim 1, wherein the over-approaching amount is determined based on machining conditions. 3. The control apparatus for an electric discharge machine according to claim 1, wherein the over-approaching amount is changed after a jump operation. 4. The discharging state determining means determines a biting state based on a cumulative value of time during discharging, and does not change a driving speed of the driving device in the biting state. The control device for an electric discharge machine according to claim 1, 2, or 3.