JPH0525616B2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention detects a change in the machining voltage applied between an electrode and a workpiece, and determines the direction and speed of movement of the electrode in accordance with the change. The present invention relates to a method and device for controlling electrode retraction of an electrical discharge machine.

(Prior Art) FIG. 1 is a schematic explanatory diagram of an electric discharge machine. The conventional technology will be explained based on this figure. The electrode EP, which has the same shape as the punch, is supported by a spindle SP, and a processing feed is applied in the direction of the arrow by a servo motor (not shown). Further, a rectangular waveform machining voltage is applied from a power source PS in the machining liquid between the workpiece WK, which will become a die, and the electrode EP. Therefore, if the electrode is processed and fed while forming a minute gap between the workpiece WK and the electrode EP, the electrode EP is transferred to the workpiece WK and processed by spark discharge. In order to generate a good discharge between the electrode EP and the workpiece WK, the electrode
It is necessary to always maintain a constant value between EP and workpiece WK. For this reason, conventionally, a synchronous feeding method has been used in which the forward speed and backward speed of the electrode EP are controlled in accordance with changes in the interpolation detection voltage. In other words, the machining power supply side compares the machining voltage with a predetermined voltage, and if the machining voltage is higher than the predetermined voltage, a positive pulse is generated from the machining voltage detection circuit, and if it is lower, a negative pulse is generated. and sends it to the NC side.
On the NC side, the pulses are counted by a reversible counter, read and reset at regular intervals, and the direction of movement is determined by the sign of the read pulses. That is, if it is positive, the electrode advances in the forward direction, and if it is negative, it advances the electrode in the reverse direction. This point will be explained in more detail. FIG. 2 is an explanatory diagram of the synchronous feeding method,
The case of reverse control is shown. Electrode EP and work
When WK approaches the predetermined interval, the detection voltage
Vd decreases from voltage Va in normal state, limiting voltage
When it falls below Vb, it will start moving backwards. Electrode at this time
The moving speed v of the EP is proportional to the detected voltage Vd.
This retreat of the electrode EP widens the distance between the electrode EP and the workpiece WK, and the interval detection voltage Vd rises. When the interval detection voltage Vd returns to the limit voltage Vb, the electrode EP
will stop moving backwards and start moving forward again. The re-advance speed v at this time is proportional to the inter-detection voltage Vd.
When the forward speed deceleration point is reached, the forward speed v is decelerated and returns to the backward start point. By the way, in such a conventional electrode retraction control method of an electric discharge machine, the control of the retraction and re-advancement speeds is in accordance with the interval detection voltage Vd, so that prompt retraction and re-advancement cannot be performed. Therefore, the retraction and re-advance speed of the electrode is firstly determined by multiplying the speed determined from the detected voltage by a certain multiplier, and secondly, the speed during that time is
During that time, a method was devised in which the speed is maintained at a predetermined speed based on the lowest detected voltage. This point will be explained in detail with reference to FIGS. 3 and 4. FIG. 3 is an explanatory diagram of the backward control method in the synchronous feeding method. First, the detection voltage Vd
When V decreases, the electrode moving speed v also decreases. In this case, a constant magnification a is applied to the speed determined from the detection voltage.
Since the detection voltage Vd is multiplied by
When Vc, a backward speed v ₂ is set which is a times the conventional speed v ₂ '. When the electrode EP retreats in this manner, the detection voltage Vd increases. but,
The electrode retraction speed v is maintained at the retraction speed value _v2 set by the lowest voltage value Vc of the detection voltage Vd. Accordingly, from the viewpoint of the backward speed v, the detection voltage Vd is clamped to the lowest voltage value Vc. In this way, the electrode rapidly retreats.

Therefore, the inter-detection voltage Vd increases rapidly, and when the inter-detection voltage Vd reaches the limit voltage value Vb at time _t1 , the electrode EP stops retreating and moves forward again. At this time, the re-advancing speed is different from the conventional one which is proportional to the detection voltage Vd, and is the same value _v3 as the retracting speed _v2 . This causes the electrode EP to rapidly advance again.
FIG. 4 is a block diagram for the synchronous feeding system, in which the same parts as in FIG. 1 are indicated by the same symbols. In the figure, 101 is a hole with NC command information for numerically controlling (NC) the electrical discharge machine.
It is NC tape. 102 is a processing section, which includes a paper tape reader 102a, a memory 102b for storing NC command information, etc., a microcomputer-configured processing circuit 102c for performing processing such as position control and backward control of the electric discharge machine, and a distribution pulse generator to be described later. It has a current position counter 102d that performs reversible counting according to the direction of movement. The processing circuit 102c decodes the input information and sends it to the machine via a power board (not shown) if it is an M, S, T function command, etc., or sends it to the machine side if it is a movement command Zc, and then sends it to the machine side if it is a movement command Zc. output to the device. 103 is a pulse distributor, which executes a known pulse distribution calculation based on the movement command Zc and distributes pulses with a frequency according to the command speed.
Generate Ps. 104 linearly accelerates the pulse speed of the distribution pulse train Ps when the pulse train is generated;
Also, there is a known acceleration/deceleration circuit that linearly decelerates at the end of the pulse train to generate the pulse train Pi, 105 is a DC motor that processes and feeds the electrode EP, and 106 is a feeder that is connected to a feed every time the DC motor rotates by a predetermined amount. The pulse coder 107 that generates the back pulse FP is an error calculation storage unit, for example, constituted by a reversible counter, and is configured to calculate the difference Er between the number of input pulses Pi generated from the acceleration/deceleration circuit 104 and the feedback pulse FP.
remember. That is, assuming that the DC motor 105 is rotating in the forward direction, the error calculation storage unit 107 counts up the input pulse Pi every time the input pulse Pi occurs, and counts up the input pulse Pi every time the feedback pulse FP occurs. The contents are counted down and the difference Er between the input pulse and the number of feedback pulses is stored in the error register 107b. 108 is a DA converter that generates an analog voltage proportional to the contents of the error register 107b, and 109 is a speed control circuit. 110a is a voltage detection circuit between the electrodes
From the applied voltage between EP and workpiece WK to the detected voltage
110b is a counter; 110b is a counter; During 110a, the pulse SIP is counted.

Next, the operation of the synchronous feed system configured in FIG. 4 will be explained with reference to the processing flow diagram in FIG. here,
It is assumed that electrode EP has already been fed for machining and electrical discharge machining is performed between electrode EP and workpiece WK.

Since a voltage is applied between the electrode EP and the workpiece WK from the power source PS, the voltage detection circuit 110a outputs a pulse SIP at a frequency corresponding to the detected value, and the reversible counter 110b counts this. do. The processing circuit 102c is a reversible counter 110
The value of b is read periodically, and the reversible counter 110b is reset each time it is read. This counter 110
The value SS of b is zero when the detected voltage Vd is equal to the limit value Vb, positive when Vd>Vb, and negative when Vd<Vb.

(1) The processing unit 102 reads the value of the reversible counter 110b, that is, the synchronous feed input pulse.

(2) Next, the number of pulses corresponding to the moving speed v of the electrode EP is calculated based on the count value SS. This number of pulses P is equal to the synchronous feed input pulse SS and the synchronous feed pulse multiply (parameter
SFMLT). In addition, during the above-mentioned relationship between the detection voltage Vd and the limit value Vb, if Vd>Vb then P>0, and if Vd<Vb then P<
It becomes 0.

(3) The processing unit 102 checks the current control status. Current control status CS is memory 10
2b, the processing unit 102
Read and identify the control status CS from memory 102b. Since the backward alarm that occurs when a predetermined backward distance is exceeded during backward control is not set in the control status CS during the aforementioned machining feed (forward), the processing unit 102 determines that the control status CS is not a backward alarm. to decide.

(4) Next, the processing unit 102 determines whether the control status CS stored in the memory 102b is in retreat.

(5) If processing is currently in progress, the control status
Since the CS is not moving backward, the processing unit 102 determines whether the control status CS is moving forward again.

(6) Since processing is in progress and the control status is not in progress again, the processing unit 102 executes step (1).
The number of pulses P calculated in is set in the memory 102b as the command speed Pc.

(7) Next, the processing unit 102 determines whether the command speed Pc is positive or negative. If Pc is positive, that is, the detected voltage is greater than or equal to the limit value Vb, it is in a normal state, so as described later, the command speed Pc is sent to the pulse distributor 103 to move the electrode EP forward (processing feed).
let

(8) Furthermore, the processing unit 102 includes a pulse distributor 103
Current position counter 10 that counts the distributed pulses of
2d and updates the current position GP in the memory 102b.

On the other hand, when the distance between the electrode EP and the workpiece WK becomes smaller and the distance detection voltage Vd becomes equal to or less than the limit voltage value Vb, the following backward control is performed.

(9) When the detection voltage Vd becomes less than the limit voltage value Vb, the number of pulses P, that is, the command speed Pc becomes negative,
In step (7) above, the backward control process is commanded, and the processing unit 102 stores the control status in the memory 102b.
Set CS to backwards.

(10) Next, the processing unit 102 calculates a deceleration start point DSP at the time of re-advancement, which will be described later, from the current position GP in the memory 102b, and stores it in the memory 102b.

(11) Next, the processing unit 102 calculates the command speed v (Pc') and stores it in the memory 102b. That is, a command speed a times the command speed Pc for machining feed is set and sent to the pulse distributor 103 to feed the electrode EP backward.

(12) Next, the processing unit 102 calculates the current position counter 1.
Current position in memory 102b from the contents of 02d
Update GP and retreat distance l.

(13) Next, the processing unit 102 compares the retreat distance l in the memory 102b with the possible retreat distance ld stored in the memory 102b in advance. Retreat distance l
If the distance is within the retractable distance ld, step again.
Return to (1). After this, P is negative because the vehicle is moving backward.

(14) In step (4) above, the control status
Since the CS is in retreat, the processing unit 102
determines whether the number of pulses P is positive or negative. If the number of pulses P is negative, then backward control is in progress, so it is compared with the speed Pc stored in the memory 102b.
Since the vehicle is moving backward, both the speed Pc and the number of pulses P are negative. Therefore, when Pc>P, the absolute value is |P|>|Pc|. If P is large as an absolute value, the storage speed Pc of the memory 102b is updated to the number of pulses P. If Pc<P, that is, |P|
If <|Pc|, the storage speed Pc of the memory 102b is used for subsequent backward control. That is, the maximum speed when reversing is used for reverse control.

(15) Next, the processing unit 102 performs the step (11) described above.
Execute (12) and (13).

In this way, steps (1), (2), (3), (4), (14), (15)
When the electrode EP is moved back at the maximum speed, the detection voltage Vd becomes equal to or higher than the limit voltage value Vb (i.e.,
is correct). As a result, the following re-advance control is performed.

(16) If P becomes positive during retreat, the above step (14)
In this case, the processing unit 102 determines that it is correct, and sets the control status CS of the memory 102b to "re-advancing".

(17) Next, the processing unit 102 calculates the command speed Pc' in step (11) above from the maximum speed |Pc| during retraction stored in the memory 102b, sends it to the pulse distributor 103, and sends it to the pulse distributor 103. advance again.

(18) Next, the processing unit 102 calculates the current position counter 1.
From the contents of 02d, the current position of memory 102b
Update GP.

(19) The processing unit 102 compares the deceleration start point DSP set in the memory 102b in step (10) with the current position GP in the memory 102b, and if the deceleration start point DSP has not been reached, step (1) is executed. Return to

In this way, steps (1), (2), (3), (4),
Re-advance control is performed by (14), (16), (17), (18), and (19). When it is determined that the deceleration start point DSP has been reached in step (19) by this re-advance control, the processing section 102 sets the control status CS in the memory 102b to normal forward movement. As a result, the processing section 102 executes steps (1) to (8) and returns to normal processing feed.

(20) Furthermore, in step (13) during the above-mentioned backward control, if the backward distance l exceeds the possible backward distance ld, that is, even if the possible backward distance ld is reached, the detected voltage Vd becomes the control voltage value. If Vb is not exceeded, the control status CS in the memory 102b is set to a backward alarm.

(21) As a result, as long as the number of pulses P is negative, a backward alarm signal is generated and the electrode EP is not controlled. That is, if the detected voltage Vd does not rise even after the vehicle has moved backward sufficiently, this indicates some kind of failure, so the control is stopped and an alarm is issued if necessary.

(22) On the other hand, if P becomes positive even during the backward alarm, the alarm signal will be turned off and the control status CS in the memory 102b will be set to the state that the vehicle is moving forward again.
Thereafter, the re-advance control in steps (17) to (19) is executed.

(Problems to be Solved by the Invention) As stated on page 4 of this specification, when the voltage between electrodes becomes lower than a predetermined voltage, it is necessary to retreat as soon as possible to prevent arc discharge. .
When the voltage between electrodes suddenly drops, the feedback pulse FP from the pulse coder 106 is
Until then, the pulse in the positive direction is detected by the error calculation storage unit 10
7 is entered. Therefore, even though a negative direction pulse is input, the value read by the error register 107b still has a positive value, so the acceleration/deceleration circuit 104 outputs the next pulse distribution. There is a situation where even if the output Pi becomes negative, it does not become negative immediately. In other words, since the pulse SIP is input during the negative direction, there is a state where the read value is not negative even though the negative direction pulse is input.
In other words, there are situations in which a negative direction pulse is output but is not recognized as backward movement. For this reason, there is a disadvantage that the recognition of retreat is delayed by several cycles, causing arc discharge, or in the worst case, collision between the electrode and the workpiece, which deteriorates the precision of the machined surface of the workpiece. Further, there was also a drawback that the backward control took time and the machining speed was correspondingly slow. In particular, there was a problem in the responsiveness when the electrode suddenly changed from a forward state to a state in which it should be moved backward.

An object of the present invention is to provide a sufficiently large negative value of the retraction speed immediately after the retraction signal from the counter is turned on when the electrode suddenly changes from a forward state to a state where the electrode should be retracted. An electrode retraction control method for an electrical discharge machine, which can accurately and quickly control the electrode retraction by commanding the same, prevent arc discharge and collision between the electrode and the workpiece, and improve machining speed; The objective is to obtain a control device for this purpose.

(Means for Solving the Problems) In order to solve the above-mentioned problems, according to the present invention, electric discharge machining is performed by applying a machining voltage between an electrode and a workpiece, and the electrode and the workpiece are During this period, the difference between the detected voltage and a predetermined voltage is converted into a feed speed pulse so that the detected voltage remains constant, and the acceleration/deceleration circuit is controlled by the numerical control device according to a speed proportional to this speed pulse. In an electrode retraction control method for an electrical discharge machine in which the electrode is advanced or retracted by distributing pulses through a There is provided an electrode retraction control method for an electrical discharge machine, which includes the step of transmitting a retraction command signal to a numerical control device separately from the feed rate pulse, and sending the electrode at a separately determined high speed for retraction and re-advancement.

Further, according to the present invention, electric discharge machining is performed by applying a machining voltage between the electrode and the workpiece, and the detection voltage is maintained constant between the electrode and the workpiece. Electrical discharge machining in which the difference between the voltage and the specified voltage is converted into a feed speed pulse, and the pulse is distributed from a numerical control device via an acceleration/deceleration circuit according to a speed proportional to this speed pulse to move the electrode forward or backward. The machine converts the difference between the gap detection voltage and a predetermined voltage into a feed speed pulse, and separately from the circuit that sends it to the numerical control device, detects when the gap detection voltage becomes less than the predetermined voltage, and sends the detection signal. an amplifying circuit for outputting an output; a switch operating circuit for operating a switch using the output signal of the circuit; a switch for opening/closing the transmission of a detection signal obtained when the voltage falls below the predetermined voltage; An electrode retraction control device for an electric discharge machine is provided which includes an amplifier for obtaining a retraction signal and a bypass circuit for connecting the retraction signal to a numerical control device.

(Example) FIG. 6 is an explanatory diagram of a method for retracting electrodes using a synchronous feeding method according to the present invention.
By detecting that it has become lower than Vb,
We know that the electrode has suddenly changed from its forward state. Thereafter, in response to this detection signal, a retraction signal is immediately sent to the numerical control device separately from the count value SS that determines the feeding speed, and the electrode is controlled to be retracted immediately. Note that the retraction speed in this case can be set arbitrarily. Further, the dotted line is an explanatory diagram of a conventional synchronous feeding electrode retraction control method (see FIG. 3). As is clear from this figure, according to the retraction control method according to the present invention, the retraction control of the electrode can be made responsive and the machining time can be shortened.

FIG. 7 is a block diagram for explaining the electrode retraction control device according to the present invention. In the figure, the same parts as in FIG. do. To explain the characteristic configuration of the present invention, in addition to the counter 110b that counts the interval pulse SIP, there is provided an amplifier 111 that is operated by a negative detection voltage from the interval voltage detection circuit 110a, and its output is activated by a switch. The signal is supplied to the circuit 112. A switch 113 is provided which is closed by the operation of this circuit 112.
The negative detection voltage (detection signal) detected by 10a is amplified by amplifier 114 to obtain an electrode retraction signal,
The configuration is such that this signal is sent to the processing unit 102. It goes without saying that the switch 113 may be constructed as a non-contact switch.

Next, the operation of the system of the present invention shown in FIG. 7 is clear from the processing flow diagram of FIG. 8. In addition, the conventional processing flow diagram (see Fig. 5 processing flow and its explanation)
Differences between the two are marked with dotted lines in the block diagram.

In short, when the gap between the electrode EP and the workpiece WK becomes smaller and the gap detection voltage Vd becomes equal to or less than the limit voltage value Vd, the following backward control is performed.

(a) When the detected voltage Vd becomes equal to or less than the limit voltage value Vb, the 1 reverse signal shown in FIG. 8 (Part 1) is turned on, and a reverse control process is commanded. That is, apart from the explanation of the flowchart, the detection voltage circuit 11
The negative voltage detected at 0a is transferred to amplifier 11
1 and activates the switch activation circuit 112. Activation of this circuit 112 closes the switch, and the negative voltage is amplified by an amplifier 114 to obtain an electrode retraction signal. This reverse signal is NC
side, the servo motor 105 is immediately reversed to control the electrode backward.

(b) The speed when reversing should be much larger than the speed P mentioned above. Note that this backward speed can be set arbitrarily.

FIG. 9 is a block diagram of another embodiment for explaining the reverse control method according to the present invention in an easy-to-understand manner. As is clear from this figure, when the detected voltage falls below a predetermined voltage and a retraction signal is generated, the circuit consisting of the V/P converter and counter is bypassed and the signal is sent directly to the arithmetic unit. Control can be made responsive. In this case, since negative pulses are not involved in the counter, there is no need to provide an expensive reversible counter as in the prior art.

(Effects of the Invention) As explained above, according to the electrode retraction control method for an electric discharge machine of the present invention, even if the voltage between the electrodes suddenly decreases, the value read by the error register will still be a positive value. Even if the output Pi from the acceleration/deceleration circuit that remains and is output in the next pulse distribution becomes a negative value,
The state where I was told that it would not become negative soon disappeared,
Improves responsiveness. Further, according to the electrode retraction control device for an electrical discharge machine of the present invention, when it is detected that the inter-current detection voltage has become lower than the limit voltage value, the retraction command signal is immediately sent separately from the inter-interval pulse SIP.
By transmitting it to the NC side, the error register can be made negative despite the presence of the acceleration/deceleration circuit during the next pulse distribution, and rapid retraction control of the electrode can be performed. In particular, it is possible to reliably prevent arc discharge and collision between the electrode and the workpiece, and
Processing time can be shortened. Therefore,
It is possible to have the effects of increasing machining efficiency and improving machining accuracy.

Although the present invention has been described with reference to one embodiment, various modifications can be made within the scope of the present invention, and these are not excluded from the scope of the present invention.

[Brief explanation of the drawing]

Fig. 1 is a schematic explanatory diagram of an electrical discharge machine, Figs. 2 and 3 are explanatory diagrams of a conventional retraction control system, Fig. 4 is a block diagram of an example of a conventional retraction control system, and Fig. 5 (Part 1) ) (Part 2) is a process flow diagram of an embodiment of a conventional reverse control method, FIG. 6 is an explanatory diagram of the reverse control method of the present invention, and FIG. Embodiment Block Diagrams FIG. 8 (Part 1) (Part 2) is a processing flow diagram of an embodiment of the reverse control method according to the present invention, and FIG. 9 is a block diagram of another embodiment of the apparatus of the method according to the present invention. It is a diagram. In the figure, EP...electrode, WK...work, 110
Between a...Voltage detection circuit, 102b'...Counter, 111...Amplifier, 112...Switch operation circuit, 113...Switch, 114...Amplifier.

Claims (1)

[Claims] 1. Electric discharge machining is performed by applying a machining voltage between the electrode and the workpiece, and the detection voltage is maintained constant between the electrode and the workpiece so that the detection voltage is constant. An electric discharge machine that converts the difference from a predetermined voltage into a feed speed pulse, and distributes the pulse from a numerical control device via an acceleration/deceleration circuit according to a speed proportional to this speed pulse to move the electrode forward or backward. In the electrode retraction control method, the step of detecting that the detected voltage has become lower than the limit voltage value during the above period, immediately transmitting a retraction command signal to the numerical control device in accordance with the detection signal separately from the feed rate pulse; An electrode retraction control method for an electrical discharge machine, comprising the step of feeding the electrode at a separately determined high speed for retraction and re-advancement. 2. Electric discharge machining is performed by applying a machining voltage between the electrode and the workpiece, and between the electrode and the workpiece, the detection voltage is kept constant. In an electrical discharge machine that converts the difference into a feed speed pulse and distributes the pulse from a numerical controller through an acceleration/deceleration circuit according to a speed proportional to this speed pulse to move the electrode forward or backward, the detection voltage Separately from the circuit that converts the difference between the detection voltage and the predetermined voltage into a feed speed pulse and sends it to the numerical control device, there is a circuit that detects when the detected voltage is below the predetermined voltage and sends it to the numerical control device.
Regarding the retraction and re-advancement of the electrode, there is an amplifier circuit that outputs a detection signal for sending the electrode at high speed, a switch operating circuit that operates a switch based on the output signal of the circuit, and a switch that is obtained when the voltage falls below the predetermined voltage. An electrical discharge machine comprising: a switch for opening and closing transmission of a detection signal; an amplifier for amplifying the detection signal to obtain an electrode retraction signal; and a bypass circuit for connecting the retraction signal to a numerical control device. Electrode retraction control device.