JPH0457620A - Electric discharge machining control circuit and method therefor - Google Patents

Abstract

PURPOSE:To quickly avoid the occurrence of abnormal continuous shortcircuit liable to cause the break of a wire electrode by monitoring a continuous shortcircuit condition at the time of shortcircuit discharge state in machining, and lowering the feed rate of the wire electrode or a workpiece to a level different from the case of normal machining, upon appearance of the abnormal condition where the aforesaid shortcircuit state continues or concentrates. CONSTITUTION:When an across-electrode abnormal signal is inputted to a rate control section 23 from a shortcircuit monitor section 24, selection is made from a normal feed curve A to a curve B governed by F-1' of the abnormal F-DATA of F-DATA. Then, the original normal curve A is selected in the predetermined time (reset time). Data governing the reset time is also included in F-1' of the abnormal F-DATA.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to electrical discharge machining control circuits and methods.

[Conventional technology]

Conventionally, this type of electric discharge machining gap control technology involves counting a predetermined number of intermittent voltage pulses applied to the machining gap in order to maintain a stable discharge in the electric discharge machining gap consisting of a wire electrode and the workpiece. In addition, a short circuit signal between electrodes indicating that the discharge machining gap is extremely narrow is detected, the applied voltage pulses are counted, and the short circuit rate is calculated from the two counted values.
The relative moving speed between the wire electrode and the workpiece is reduced only for a predetermined period of time after the short circuit rate exceeds a predetermined value.

Figure 4 shows an example of the change in short circuit rate over time during processing.Due to various factors, the short circuit rate begins to increase at t''Tt.
After that, the short-circuit rate continues to increase, and finally shows a disconnection at the 0 point.

[Problem to be solved by the invention]

In general, when short circuit pulses occur concentratedly in a short period of time, that is, in a short circuit state, the gap between the electrodes is extremely narrow, and if this state continues for a long time, machining time becomes longer and wire electrode breakage occurs. This means that the

The conventional electrical discharge machining control circuit described above counts the number of voltage pulse application cycles and the number of short circuit pulses that occur during the predetermined number of cycles, and defines the ratio of the number of short circuit pulses to the number of voltage pulse application cycles as the short circuit rate. Therefore, if short circuits occur continuously, even if the electrical discharge machining gap is in an extremely poor condition, short circuits will occur on average during the application cycle of the same number of short circuit pulses and a predetermined number of voltage pulses. The disadvantage is that the short circuit rate is the same as when the short circuit is closed, making it difficult to detect successive short circuit states, and also making it difficult to recover from the short circuit state.

[Means to solve the problem]

The electric discharge machining control circuit of the present invention includes a detection means for detecting a discharge starting voltage by applying intermittent voltage pulses to an electric discharge machining gap between a machining electrode and a workpiece, and a discharge start detected by the detection means. a conversion means for converting the voltage into digital electric discharge machining gap length data; and a short circuit in the electric discharge machining gap is detected from the discharge starting voltage detected by the detection means, and the number of voltage pulses applied within a preset time. and a first means for counting the number of short-circuited pulses to calculate the short l1lI rate; a second means for outputting a position movement command corresponding to the machining gap length data; and a position movement speed that is reduced only for a predetermined period of time from when the value of the short circuit rate calculated by the first means exceeds a predetermined value; and a third means for changing the speed command data according to the invention, a third means for counting consecutive discharge gap short circuits within the preset time and storing a maximum value of the continuous short circuit count. and a fifth means for obtaining the maximum short circuit rate based on the short circuit rate obtained by the first means and the maximum value of continuous short circuits obtained by the fourth means.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention.

The positive electrode sides of the DC power supplies 8 and 9 are connected to the workpiece through transistors 10.11, which are switching elements, and resistors 12.13, which limit the machining current, respectively. Further, the negative electrode sides of the DC power supplies 8 and 9 are connected to the wire electrode 15. Therefore, the gate signal Vs□t of transistor 10.11
By turning Vs□ on and off, voltage pulses can be applied intermittently to the discharge machining gap. Simulated pole-to-pole signal V. L is the electrode voltage V
, , is obtained by dividing the voltage by resistor 18.17.

The comparator 5 and the differential circuit 6 are circuits that detect the start of discharge after applying a voltage pulse to the machining gap, and generate a simulated machining gap signal V. A discharge start signal is obtained through a differentiating circuit 6 which compares L with a predetermined threshold voltage VD by a comparator 5 and differentiates only when the output changes from logic "1" to "O".

Further, the comparator 4 compares a predetermined threshold voltage Vs with a simulated machining gap signal VOL for determining whether or not a voltage pulse is applied to the machining gap when the machining gap is extremely narrow, that is, in a short-circuited state. I am getting a short circuit signal.

The inter-electrode short circuit signal and the discharge start signal are fed back to the pulse generating circuit 1.

P-DATA, which is the input data of the pulse generation circuit 1, is
The machining current pulse width, pause time, etc. are given by the upper central processing unit according to various machining purposes. The outputs Vscm and VSO4 of the pulse generation circuit are pulse source signals that turn on and off the transistors 10 and 11, and the preamplifiers 2 and
3 and input to transistors 10 and 11.

The pulse generating circuit 1 first applies a first voltage pulse to VS for the purpose of determining whether the machining gap is short-circuited or not.
(!1 is turned ON. The current caused by this first voltage pulse is generally small. After that, when a normal discharge, that is, a discharge that is not in a short-circuit state occurs in the machining gap, the discharge start signal is activated. , a second voltage pulse having a predetermined pulse width is applied.

When the second voltage pulse turns "OFF", the first voltage pulse also turns "OFF". 1st. “O” of the second voltage pulse
The FF" state lasts for a predetermined pause time in order to deionize the machining gap. Thereafter, the first voltage pulse is applied and the workpiece is machined while repeating the above operation.

However, in a short circuit state, even if the first voltage pulse is applied, the machining gap voltage does not rise to the desired voltage. ) and the AND gate 7 to generate an inter-electrode short circuit signal. The short circuit detection pulse is outputted from the pulse generation circuit 1 after a predetermined delay time after the first voltage pulse turns "ON".

Furthermore, it is well known that when a relatively large current is passed in a short-circuited state, there is a high probability that the wire electrode will break.

Therefore, the pulse generating circuit 1 is configured to reduce the pulse width of the second voltage pulse to a predetermined value when the inter-electrode short circuit signal is generated.

Thus, as the workpiece is machined, the machining gap expands in places and the frequency of discharge decreases, so the wire electrode is used as a position servo mechanism to control the relative position of the wire electrode and the workpiece. or a motor 25 mechanically coupled to the workpiece. An encoder 26 and a control circuit 27 are provided.

The discharge servo control unit 21 normally receives machining path data (PATH-D) from the upper central processing unit according to the machining shape of the workpiece.
ATA), feed specification data (F-DATA) mainly determined by the workpiece and machining process, and a simulated machining gap signal V. Based on the gap data (G-DATA) obtained from L through the AD comparator 18, a position movement command is generated to the motor control circuit 27 to control the relative position.

The counter 19 counts the number of pulses of the inter-electrode short circuit signal. Further, the counter 20 counts the total discharge pulse (D-P) including both normal discharge and short circuit discharge, and the total discharge pulse is outputted from the pulse generation circuit 1. Both the counter 19 and the counter 20 can count only when the count start signal (C-8T) from the discharge servo control unit 21 is logic "1", and when the count data of the counter 20 reaches a predetermined value, the counter 20 stops counting. At the same time, the counter 19 also outputs a counting stop signal (C-8
Counting is stopped by P).

The outputs of the counters 19 and 20 are short circuit pulse data (S-DATA) and full discharge pulse data (D-DATA) each having a predetermined data width, and are connected to the discharge servo control section 21.

The discharge servo control section 21 mainly operates as a machining path interpolation processing section 2.
2, a speed control unit 23 that controls the feed rate based on gap data (G-DATA) obtained by converting the machining gap voltage by the A/D converter 18, and a short circuit that detects a short circuit state during machining and generates a gap abnormality signal. It is composed of a monitoring section 24. The interpolation processing section 22 outputs an axis distribution command to the motor control circuit based on the determination of the optimum axis distribution direction and the feed speed data from the speed control section 23 for the machining path.

Here, the features of the present invention are surrounded by a dashed line.

The machining gap voltage level detection signal Sd is inverted by the inverter 28, and ANDed with the short circuit detection pulse (S-CP) at the AND gate 29 to obtain the normal discharge occurrence detection signal S.
Generate a.

The normal discharge occurrence detection signal Sa is connected to the comparison enable input of the digital comparator 32 and the flip-flop 30.
The trigger is connected to human power. The counter 31 counts the short circuit detection pulse signal (S-CP) and resets the count by the normal discharge occurrence detection signal Sa.

In other words, the counter 31 counts the short circuit detection pulses that occur continuously, and stops counting when the occurrence of normal discharge is detected.
The count value is reset. Further, the count output 0UT1 is connected to the latch circuit 33 and the digital comparator 32, and when the occurrence of normal discharge is detected, the continuous short circuit data stored and held in the output 0UT2 of the latch circuit 33 until then is connected to the digital comparator 33.
If 0UTI is a larger value than 0UT2, it is latched) IJ gar signal Sc is generated and 0UT
The data of 1 is set to 0UT2.

Furthermore, the latch circuit 33 is reset by a counting start signal (C-8T) output from the short circuit monitoring section 24, and sets the maximum value of the continuous short circuit count value for each counting cycle to its output 0UT2. .

The short circuit monitoring section 24 receives F-DAT from the counters 19 and 20.
A and D-DATA are periodically detected, and the short circuit rate Ps (
S-DATA/D-DATA) is calculated. In addition, with the short circuit rate Ps, it is not possible to distinguish between cases where short circuits occur on average in the counting cycle and cases where short circuits occur continuously, so the maximum continuous short circuit count value that is the output from the latch circuit 33 Maximum short circuit rate P from (OUT2) and short circuit rate Ps
Calculate s-max (Ps* (OUT2)). Then, when the short circuit rate Ps-max exceeds a predetermined value Ps-AL, a gap abnormality signal is sent to the speed control section 23 as an alarm.

When the gap abnormality signal is not generated, the speed control unit 23 outputs predetermined F-DATA and gap data (G-DAT).
The feed speed data determined by A) is sent to the interpolation processing section 22. For example, in Figure 2, the vertical axis is the feed rate (F)
, the horizontal axis is G-DATA, the feed curve A is a curve obtained from F-0 of the basic F-DATA of F-DATA, and the feed speed data is determined as a function of the curve A.

Next, when the above-mentioned gap abnormality signal is input from the short circuit monitoring section, the abnormality F- of F-DATA is determined from the normal feeding curve A.
The feed curve is switched to the feed curve B determined by F-1' of DATA. Then, after a predetermined time (return time), the original "feed curve A" is returned again. Data that determines the return time is also included in F-1 of the abnormal F-DATA.

Figure 3 shows an example of the change in short circuit rate over time during machining, and since the feed speed is reduced, the short circuit rate Ps-m
The value of ax can also be gradually reduced, and as a result, disconnection of the wire electrode is prevented.

〔Effect of the invention〕

As explained above, the present invention monitors the continuous short-circuit state during the short-circuit discharge state during machining, and if the short-circuit state continues or
When a concentrated abnormal condition occurs, by reducing the feed speed of the wire electrode or workpiece to a feed speed that is different from that during normal machining, abnormal continuous short circuits that can easily cause wire electrode breakage can be quickly avoided. It becomes possible to
This has the effect of allowing stable wire electrical discharge machining with less wire electrode breakage.

[Brief Description of the Drawings] Figure 1 is a block diagram showing one embodiment of the present invention, Figures 2 and 3 are time charts and graphs showing the operation of the present invention, and Figure 4 is a conventional example. It is a graph. 1... Pulse generation circuit, 2, 3... Preamplifier, 4
．． 5... Comparator, 6... Differential circuit, 7...
AND gate, 8, 9...DC power supply, 10.11...
・Transistor, 12, 13, 18, 17...Resistor, 14...Workpiece, 15...Wire electrode, 18.
・・AD converter, 19, 20 ・・Counter, 21
...discharge servo control section, 22... interpolation processing section, 23
...Speed control section, 24...Short circuit monitoring section, 25...
Motor, 26... Encoder, 27... Motor control circuit, 28... Inverter, 29... AND gate, 30... Flip or flop, 31... Counter, 32... Digital comparator , 33...Latch.

Claims (1)

[Scope of Claims] 1. A detection means for detecting a discharge starting voltage by applying intermittent voltage pulses to a discharge machining gap between a machining electrode and a workpiece, and a discharge starting voltage detected by the detecting means. converting means for converting into more digital electric discharge machining gap length data; and detecting a short circuit in the electric discharge machining gap from the discharge starting voltage detected by the detection means, and determining the number of voltage pulses applied within a preset time. , a first means for counting the number of short-circuited pulses to calculate a short-circuit rate; and a position servo mechanism for moving the distance of the electric discharge machining gap at a preset movement speed, the electric discharge machining gap obtained by the conversion means. a second means for outputting a position movement command corresponding to the length data; and a second means for outputting a position movement command corresponding to the length data; and a fourth means for counting consecutive discharge gap short circuits within the preset time and storing a maximum value of the continuous short circuit count. and fifth means for obtaining a maximum short circuit rate based on the short circuit rate obtained by the first means and the maximum value of continuous short circuits obtained by the fourth means. circuit. 2. A detection procedure for detecting the discharge starting voltage by applying intermittent voltage pulses to the discharge machining gap between the machining electrode and the workpiece, and a digital discharge machining gap length determined from the discharge starting voltage detected by the detection procedure. A short circuit in the discharge machining gap is detected from the discharge start voltage detected by the conversion procedure for converting into data and the detection procedure, and within a preset time,
A first step of calculating the short circuit rate by counting the number of voltage pulses applied to and the number of short-circuited pulses, and a preset movement speed of the position servo mechanism for moving the distance of the electric discharge machining gap a second means for outputting a position command corresponding to the electric discharge machining gap length data obtained by the conversion procedure; and a second means for outputting a position command corresponding to the electric discharge machining gap length data obtained by the conversion procedure; and a third means for changing the speed command data so as to reduce the position movement speed by time, the discharge control method includes counting consecutive discharge gap short circuits within the preset time, and calculating continuous short circuits. a fourth step of memorizing the maximum value of the numerical value; and a fifth step of obtaining the maximum short circuit rate from the short circuit rate established by the first means and the maximum value of continuous short circuits obtained by the fourth step. An electric discharge machining control method characterized by: