JP2000015524A - Control method and apparatus for electric discharge machine - Google Patents

Abstract

(57) [Summary] [Problem] To accurately calculate an average voltage between contacts even when an analog voltage between contacts is detected. SOLUTION: In a control method of an electric discharge machine for machining while maintaining a constant average voltage between the electrodes 4 and a work 5 while relatively moving an electrode 4 and a work 5 along a predetermined machining path, detecting a discharge frequency f _d and the short frequency f _s at the time of normal discharge, calculate the waiting time based on these frequencies, while the discharge-on when determining the short state of the machining gap, is determined not to be shorted The main voltage MV is applied between the poles only for a time, and when it is determined that the state is the short state, the MV is applied between the poles only for the short on-time.
The voltage MV at the time of discharge of the MV applied between the electrodes during the discharge ON time
1. The average voltage between the electrodes is calculated based on the voltage MV2, the short-on time, and the waiting time of the MV applied between the electrodes during the discharge-on time and the short-on time, so that the average voltage between the electrodes is constant. The position servo control circuit 11 operates.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method and an apparatus for controlling an electric discharge machine, and more particularly, to a method and an apparatus for controlling an electric discharge machine by an average voltage between contacts method.

[0002]

2. Description of the Related Art In general, control methods of an electric discharge machine are roughly classified into two methods, that is, an average voltage between poles control and a waiting time control. In either method, a pulse voltage is intermittently applied between a pole between an electrode and a work according to a preset energizing time and a pause time, and the work is processed by a discharge generated between the poles. Is different in the following points. That is, the inter-electrode average voltage control method applies a pulse voltage between the electrodes so as to maintain the inter-electrode average voltage between the electrode and the work constant, and maintains the gap between the electrode and the work constant. The feed axis for relatively moving the electrode and the work is controlled.

On the other hand, in the waiting time control method, the waiting time from the application of a pulse voltage between the electrode and the work to the start of discharge is obtained by directly counting using, for example, a clock pulse or the like. On the basis of the waiting time, for example, a feed axis for relatively moving the electrode and the workpiece is controlled so as to keep the waiting time constant. In the conventional average voltage control method between the electrodes, the voltage between the electrodes is detected using an analog circuit including, for example, an OP amplifier. The cable length between the gap and the analog circuit usually depends on the model of the electric discharge machine, so especially when the pulse voltage to be applied is at a high frequency, the stray capacitance at the input end of the analog circuit is caused by this cable length. Because of the difference, as shown in FIG. 4, the detection waveform of the voltage between the electrodes changes, and the average voltage between the electrodes cannot be accurately detected. As a result, there arises a problem that the processing accuracy is deteriorated.

Japanese Patent Application Laid-Open No. Hei 7-246518 discloses a control method and apparatus for an electric discharge machine by a waiting time control method. This control method and apparatus accurately detects a waiting time (corresponding to a no-load time in this publication) in consideration of a short circuit during machining even when the discharge frequency fluctuates, and improves machining accuracy. A normal discharge frequency and a short frequency are detected, and a wait time is calculated based on these frequencies, an energizing time and a pause time during a normal discharge, a short determination time, an energizing time and a pause time during a short, and the calculated wait time is calculated. The feed axis that moves the electrode and the workpiece relative to each other is controlled in accordance with, and the machining gap is controlled to be constant.

[0005]

Incidentally, in a wire electric discharge machine, there is a case where it is desired to set a long rest time as a machining condition in order to avoid wire breakage. From the experimental results, it was found that when the pause time was changed, there was a difference in the change of the discharge gap between the gap voltage control method and the waiting time control method.

FIG. 5 is a diagram showing a change in the discharge gap when the pause time is changed. As shown in FIG. 5, in the inter-electrode voltage control method, when the pause time is set to be long, the machining speed, that is, the feed speed is greatly reduced, and the number of discharge pulses is also reduced with the decrease in the feed speed. The discharge gap is going to be narrowed by the decrease of. However, when the feed speed is greatly reduced, the discharge gap tends to be widened, so that these are offset and the change in the discharge gap is small, so that the machining is not adversely affected. On the other hand, in the waiting time control system disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 7-246518, if the pause time is set to be long, the feed speed does not greatly decrease as compared with the inter-electrode average voltage control system. However, the discharge gap is narrowed by the decrease in the number of discharge pulses, which causes a problem of adversely affecting machining.

Therefore, the present invention solves the above-mentioned problem, captures the voltage between the electrodes as a digital signal instead of an analog signal, accurately calculates the average voltage between the electrodes from the digital detection signal, and changes the pause time. Another object of the present invention is to provide a method and an apparatus for controlling an electric discharge machine by an inter-electrode voltage control method with a small change in a discharge gap and a good machining accuracy.

[0008]

A method of controlling an electric discharge machine according to the present invention for solving the above-mentioned problems is directed to a method of controlling an electric discharge machine which discharges a work by applying a voltage pulse between an electrode and a work. It is determined whether the gap between the electrode and the workpiece is in a normal discharge state or a short-circuit state. When the gap is in a normal discharge state, the first energizing time (ON
A), when the gap is in a short state, a voltage is applied between the poles for a preset second energizing time (ONB), and the number of discharges (f _d ) in a normal discharge state in a predetermined time and the short-circuit state in the short state The number of shorts (f _s ) is detected, and the number of discharges (f _d ) and the number of shorts (f _s ) detected, and a preset discharge pause time (O
FF), a discharge waiting time (TW) at the predetermined time is calculated based on the first and second energizing times (ONA, ONB) and the like, the calculated discharge waiting time (TW), and the detected number of discharges (f _d) ) and a short-number (f _s), and quantified by calculating the average gap voltage (V _av) between the electrode and the workpiece based on preset search voltage (SV) and the like,
The relative feed between the electrode and the work is controlled so that the calculated inter-electrode average voltage (V _av ) becomes a constant value.

A control apparatus for an electric discharge machine according to the present invention for solving the above-mentioned problems is a control apparatus for an electric discharge machine which applies a voltage pulse between a pole between an electrode and a work to perform electric discharge machining on the work. A gap state determining means for determining whether the gap between the electrodes is in a normal discharge state or a short state, and a first energization time (O
NA), a pulse generation circuit for applying a voltage between the electrodes for a preset second energizing time (ONB) when the electrodes are in a short-circuit state, and the number of discharges (f _d ) in a normal discharge state during a predetermined time. Detecting means for detecting the number of short circuits (f _s ) in the short state, and the first energizing time (ONA) and the second energizing time (ONB), and the discharge pause time (OFF), search voltage (SV), etc. Storage means for storing preset machining conditions; and the number of discharges (f _d ) and the number of shorts (f
_s ) and the processing condition stored in the storage means, and calculates a discharge waiting time (TW) at the predetermined time, and based on the calculated discharge waiting time (TW) and the processing condition, a gap average voltage (V _av). ), And a servo control means for controlling the relative feed between the electrode and the work so that the calculated inter-electrode average voltage (V _av ) becomes a constant value. It is characterized by the following.

According to the control method and apparatus for an electric discharge machine of the present invention, with the above configuration, the voltage between the electrodes is captured as a digital signal instead of an analog signal, and the average voltage between the electrodes is accurately calculated from the digital detection signal. Even if the pause time is changed, the change in the discharge gap is small, and the machining accuracy is improved.

[0011]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a block diagram showing an embodiment of a control device for a die sinking electric discharge machine according to the present invention. In FIG. 1, a positive output of a main power supply 1 for electric discharge machining is switched by a transistor 2, connected to a relief electrode 4 through a current limiting resistor 3, and a negative output of the main power supply 1 is connected to a work 5. The normal discharge detection circuit 6 and the short detection circuit 7
A voltage applied between the die sinking electrode 4 and the work 5 is detected, and when a normal discharge is performed, a normal discharge detection circuit 6
Outputs a normal discharge pulse. When a normal discharge is not performed and a short circuit occurs, the short detection circuit 7 outputs a short pulse.

F_dCounter 8 and f_sThe counter 9
Normal discharge pulse and short pulse
Count the normal discharge frequency f_d(Hz), short
Frequency f_s(Hz), and the CPU 10 processes
F_dData and f_sConvert to CPU1
Output to 0. In the embodiment shown in FIG. _d
Counter 8 and f_sNormal discharge frequency by counter 9
Number f_d(Hz), short frequency f_s(Hz)
However, in the present invention, the counter only performs counting,
0 means that the count value of the counter is sampled
Read in every cycle, read count value and sampling cycle
Based on the normal discharge frequency f_d(Hz), short circuit
Wave number f_s(Hz) may be calculated separately.
No.

The CPU 10 includes a plurality of CPUs and a ROM.
And a control circuit comprising a memory of the RAM, as will be described later, f _d data, perform various arithmetic based on f _s data and other data, control the gap length of the die sinking electrode 4 and the workpiece 5 Is output to a position servo control circuit 11 such as a numerical controller. The pulse train generating circuit 12 outputs a switching control signal to the transistor 2 based on a command from the CPU 10 so that a main voltage MV or a search voltage SV, which will be described later, is applied between the engraved electrode 4 and the work 5. The output of the position servo control circuit 11 is connected to a motor 13, which is mechanically connected to the engraved electrode 4, and drives the motor 13 to relatively move the engraved electrode 4 and the workpiece 5.

FIG. 2 is a diagram showing waveforms of a voltage applied between the electrodes and a voltage between the electrodes during a normal discharge and a short circuit. In FIG. 2, the horizontal axis represents time, and the vertical axis represents the applied voltage Vap in the upper part and the gap voltage Vg in the lower part. At time t0, when the search pulse voltage SV as a sub power supply is applied from the power supply 1 to the gap between the engraved electrode 4 and the work 5, a discharge is induced in the gap between the engraved electrode 4 and the work 5, and the waiting time At time t1 after the lapse of TW, a main pulse voltage MV as a main power supply is applied, and discharge starts between the poles. During the discharge ON time ONA from time t1 to t2 when the main pulse voltage MV is applied, a discharge current flows and the work 5 is processed. Next, the pause time OF
At time t10 after the lapse of F, the search pulse voltage SV is applied again, and thereafter, times t11 and t12 and times t20, t21, and t
22, the same pulse voltage is supplied.

By the way, after the search pulse voltage SV is applied between the poles, there is a case where the die sinking electrode 4 and the work 5 are short-circuited. In order to detect whether or not the gap is in a short-circuit state, the above-described normal discharge detection circuit 6 and short-circuit detection circuit 7 perform the following processing. That is, the voltage applied between the electrodes during the short-circuit determination time TS is detected, and the detected voltage is compared with a predetermined threshold value indicated by a broken line in the lower part of FIG. 2 to make the determination. That is, when the detected gap voltage is larger than a predetermined threshold, it is determined that the gap is not in a short state, and when the detected gap voltage is equal to or smaller than a predetermined threshold, the gap is in a short state. Is determined. The detected value of the voltage applied between the electrodes reads a stable voltage that is not affected by the stray capacitance at the input terminal of the analog circuit, and compares the read value with a threshold value.

When it is determined from the above determination result that the gap is not in the short-circuit state, the discharge on-time ONA (t1 to t1) which is set in advance according to the processing conditions and stored in the RAM memory.
The main pulse voltage MV is applied between the electrodes only for t2, t11 to t12). On the other hand, when it is determined from the above determination result that the gap is in the short state, the short on-time ONB set in advance according to the processing conditions and stored in the RAM memory is determined.
The main pulse voltage MV is applied between the electrodes only for (t21 to t22).

The first output voltage MV1 during the discharge of the main voltage MV applied between the discharge ON time ONA and the second output voltage MV2 during the short circuit of the main voltage MV applied between the discharge ON time ONB are: It is determined based on experimental data, is stored in the RAM memory in advance, and is used when calculating the inter-electrode average voltage V _av . FIG. 3 is a flowchart of a routine for calculating the average voltage between contacts. This routine is executed at a predetermined cycle, for example, every 100 ms. First, in step 301, reads the discharge pulse frequency f _d and the short pulse frequency f _s. In step 302,
The discharge ON time ONA, the short ON time ONB, the pause time OFF, and the short determination time TS are read.

In step 303, steps 301 and 3
Using the data read in step 02, the discharge waiting time TW at a predetermined time is calculated from the following equation. _{TW = {1-f s ×} (TS + ONB + OFF) / f d} - (ON
A + OFF) In step 304, as described above, the first output voltage MV1, the second output voltage MV2, and the search voltage SV previously stored in the RAM are read.

In step 305, steps 301 and 3
Each data read in steps 02 and 304 and step 3
03, using the discharge waiting time TW calculated in
Pressure V _avIs calculated from the following equation. V_av= F_d× (ONA × MV1 + TW × SV) + f_s× ONB ×
MV2 This calculated average voltage between contacts V_aVTo maintain a constant value
The position servo control circuit 11 controls the motor 13.

In the embodiment described above, a die sinking electric discharge machine has been described as an example. However, the present invention is not limited to this, and can be applied to a wire electric discharge machine.

[0021]

As described above, according to the control method and apparatus of the electric discharge machine of the present invention, first, the discharge frequency and the short frequency, the energizing time and the pause time during the normal discharge, the short determination time and the short time The waiting time is calculated based on the energizing time and the pause time, and then the voltage between the electrodes is detected as an analog signal.By comparing the voltage when this detection signal is stabilized with a threshold value, An analog signal is captured as a digital signal to determine a short-circuit state between the poles. When it is determined that the gap is not a short-circuit state according to the result of the determination, the main voltage is applied between the poles for a preset discharge ON time. However, when it is determined that the gap is in a short state, the main voltage is applied to the gap for a preset short on-time, and finally the main voltage is applied. Since the inter-electrode average voltage is accurately calculated from the first output voltage at the time of discharging, the discharge on time, the second output voltage at the time when the main voltage is shorted, the short on time, and the calculated waiting time, the pause time is changed. Even if it does, the change of the discharge gap is small, and the machining accuracy can be improved. Further, the problem of the variation in the average voltage between the electrodes due to the change in the detection waveform of the voltage between the electrodes shown in FIG.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a control device for a die sinking electric discharge machine according to the present invention.

FIG. 2 is a diagram showing waveforms of a voltage applied between gaps and a gap voltage during normal discharge and short circuit.

FIG. 3 is a flowchart of a routine for calculating a gap average voltage.

FIG. 4 is a diagram showing a detection waveform of an inter-electrode voltage based on an analog signal.

FIG. 5 is a diagram showing a change in a discharge gap when a pause time is changed.

[Description of Reference Numerals] 1 ... main power 2 ... transistor 3 ... current limiting resistor 4 ... electrode 5 ... workpiece 6 ... normal discharge detection circuit 7 ... short-circuit detecting circuit 8 ... f _d counter 9 ... f _s counter 10 ... CPU 11 ... position Servo control 12 ... Pulse train generation circuit 13 ... Motor

Claims (2)

[Claims] 1. A control method for an electric discharge machine which discharges a workpiece by applying a voltage pulse between the electrode and the pole of the workpiece, wherein it is determined whether the gap between the electrode and the workpiece is a normal discharge state or a short state. When the gap is in a normal discharge state, a voltage is applied between the poles for a preset first energization time (ONA) when the gap is in a short state, and when a gap is in a short state, the voltage is applied for a preset second energization time (ONB). The number of times of discharge (f _d ) in a normal discharge state and the number of short circuits (f _s ) in a short state during a predetermined time are detected, respectively, and the detected number of discharges (f _d ) and number of short circuits (f _s ) are set in advance. Discharge pause time (OF
F), a discharge waiting time (TW) at the predetermined time is calculated based on the first and second energizing times (ONA, ONB) and the like, the calculated discharge waiting time (TW), and the detected number of discharges (f _d ), The number of short circuits ( _fs ), and a predetermined search voltage (SV) based on the average voltage (V _av ) between the electrode and the work and calculated into a numerical value. A method for controlling an electric discharge machine, characterized by controlling relative feeding between the electrode and the work so that V _av ) becomes a constant value. 2. A control device for an electric discharge machine which discharges a workpiece by applying a voltage pulse between the electrode and the workpiece, wherein it is determined whether the gap between the electrode and the workpiece is a normal discharge state or a short state. An inter-electrode state determining means, the inter-electrode gap being a predetermined first energization time (ONA) when the inter-electrode is in a normal discharge state, and the pre-set second energization time (ONB) when the inter-electrode is in a short-circuit state; A pulse generating circuit for applying a voltage to the first power supply; a detecting means for detecting the number of times of discharge (f _d ) in a normal discharge state and the number of short circuits (f _s ) in a short state during a predetermined time; And the second energizing time (ON
B), the discharge pause time (OFF), the search voltage (S
V) and the like, and a predetermined time based on the number of discharges (f _d ) and the number of short circuits (f _s ) detected by the detection means and the processing conditions stored in the storage means. Calculating means for calculating a discharge waiting time (TW) in the above and calculating a numerical value by calculating a gap average voltage (V _av ) based on the calculated discharge waiting time (TW) and the machining conditions; A control device for an electric discharge machine, comprising: servo control means for controlling a relative feed between the electrode and the work so that an average voltage (V _av ) becomes a constant value.