JPH02298425A - Electric discharge machine - Google Patents

Abstract

PURPOSE:To easily control stable feed velocity by providing a command feed velocity operating means for operating a new command feed velocity based on the increased or decreased feed velocity operated by an increased/decreased feed velocity operating means, and on a reference feed velocity operated by a reference feed velocity operating means. CONSTITUTION:Based on first and second detection results by a detecting means 20, no-load period of time from the starting of the voltage application to the starting of discharge is measured by a measuring means 22. Per a preliminarily determined sampling cycle, the measured value is summed by the no-load time summing means 22, with a reference value being preliminarily set to the summed value, based on the difference between the summed value and the reference value, increased or decreased feed velocity is determined by an increased/decreased feed velocity operating means of a CPU 23. According to a previous actual value of a command feed velocity so as to relatively move a discharge electrode and a work, a feed velocity that works as a reference is calculated by a reference feed velocity operating means of the CPU 23. Based on the increased/decreased feed velocity as well as on the reference feed velocity, a new command feed velocity is determined by a command feed velocity operating means of the CPU 23.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a discharge machine for machining a workpiece by generating an electric discharge in a machining gap between a discharge electrode and a workpiece.

[Conventional technology]

A wire-cut electric discharge machine winds up a thin wire made of brass or the like and uses it as an electrode to feed the desired contour shape through numerical control.The wire-cut electric discharge machine uses a scroll saw to cut the contour into a workpiece separated by a predetermined machining gap. This is an electric discharge machine that hollows out and processes.

This wire-cut electric discharge machine detects the machining condition during electric discharge machining in order to stabilize the machining condition, which changes due to changes in workpiece thickness, machining shape, disturbances, etc., and to keep the machining gap constant. The feed rate of the machine is controlled.

Conventionally, in such a feed rate control device, a reference feed rate is input into the device in advance according to processing conditions, and control is performed based on the value. Additionally, trial machining was performed in advance, the average speed at that time was stored as data, and control was performed based on this data.

[Problem to be solved by the invention]

By the way, in order to input reference feed rate data according to machining conditions in a conventional feed rate control device, it has been necessary to input the data manually or automatically, for example. Therefore, each time the machining conditions change, it is necessary to reset the standard feed rate data according to the change, so it is necessary to prepare a large amount of data. In addition, there were other problems such as the need to obtain data through preliminary trial machining, which required time and effort for trial machining.

The present invention has been made to solve the above-mentioned problems, and when machining conditions change or fluctuate, it is possible to "re-input", "re-read", or "Determine the data by trial processing"
It is an object of the present invention to provide an electric discharge machine that can stably control the feed rate without such complicated operations.

[Means to solve the problem]

In order to achieve this objective, the discharge application machine of the present invention moves the discharge electrode and the workpiece relatively at a predetermined feed rate, and applies a voltage to the gap between the discharge electrode and the workpiece. In an electrical discharge machine that processes a workpiece by generating an electric discharge and machining a workpiece using the discharge energy, the electric discharge machine includes a first detecting means for detecting the start of application of the voltage, and a first detecting means for detecting the start of the electric discharge in the gap. a detecting means; a measuring means for measuring the no-load time from the start of voltage application to the start of discharge based on the detection results of the first detecting means and the second detecting means; and a measurement made by the measuring means. A no-load time totaling means that totals the values at each predetermined sampling period, and a reference value is set in advance for the total value summed by the no-load time totaling means, and the difference between the total value and this reference value is set in advance. a feed rate increase/decrease calculation means for calculating an increase/decrease in the feed rate based on the above, and a reference feed rate according to the past actual value of the command feed rate for relatively moving the discharge electrode and the workpiece. Calculate a new command feedrate based on the reference feedrate calculation means to calculate, the feedrate increase/decrease calculated by the feedrate increase/decrease calculation means, and the reference feedrate calculated by the reference feedrate calculation means. The present invention is characterized in that it includes a command feed rate calculation means.

[Effect]

A "difference" between the sample value for each sampling period summed by the no-load time summation means, a preset reference value, and -4'- is calculated. This "difference" is substituted into a predetermined formula to calculate "feed rate increase/decrease".

On the other hand, a "reference feed rate" is calculated according to the past actual value of the command feed rate, and a "new command feed rate" is calculated based on this "reference feed rate" and the "feed speed increase/decrease".

Therefore, since the "new commanded feed rate" is determined based on the "past track record feed rate," stable feed control can be achieved.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of the present invention, and FIG. 2 is a block diagram of an embodiment of the present invention.

As shown in FIGS. 1 and 2, the workpiece 1 is movable in a horizontal plane by means of a feed motor 11.1-2. The wire electrode 2 is stretched approximately vertically by means of wire guides 13, 14 and faces the crop 1 via the processing gap G. The workpiece 1 is directly connected to the positive electrode of a machining power source 5, and is also grounded. The wire electrode 2 is connected to the negative electrode of a double source 15 via a switching element (transistor) 16 and a feeder 17 . A discharge detection circuit (first and second detection means) 20 that detects the start of application of a discharge voltage and the start of discharge is connected to the electric wire 18 connecting the switching element 16 and the power supply T-17, and its output signal is input to the no-load time counting circuit (measuring means, no-load time totaling means) 22 of the control device 21. The control device 2] is a CPU (feed speed increase/decrease calculation means, reference feed speed calculation means).

Command feed rate calculation means)23. Memory 24. It is equipped with a keyboard 25, etc. The feed motor]1.12 is controlled by the CPU 23 via a motor drive circuit 26, and the switching element 16 is controlled via a drive circuit (not shown).

FIG. 3 is a circuit diagram showing detailed configurations of the discharge detection circuit 20 and the no-load time count circuit 22.

The discharge detection circuit 20 includes a buffer amplifier 31 that receives the voltage 2a of the wire electrode 2, and a comparator 32 that compares its output voltage with a predetermined threshold voltage (2). The no-load time counting circuit 22 includes an AND circuit 34 to which the output signal 32a from the comparator 32 and the clock signal from the clock circuit 33 are input, and a counter 35 which counts the number of times the output signal 34a is input. , the output signal 35a of the counter 35 is input to the CPU 23 and read there. Here, the no-load time is the time from when voltage 2a is applied to when discharge actually starts.

FIG. 4 is a waveform diagram illustrating the operation of each of the circuits 20 and 22. Voltage of wire electrode 2, that is, voltage 2 of machining gap G
As for a, when the switching element [6] is turned on, a positive voltage of the machining power supply 15 appears, and when the switching element 16 is turned off and the discharge ends, the waveform repeats, returning to zero. In the discharge detection circuit 20, a predetermined threshold voltage V is used to discriminate a state where a voltage is applied before the start of discharge, and the output signal 32a of the comparator 32 becomes a pulse-like signal.

The pulse width of this pulse-like signal 32a is
This corresponds to the no-load time 1, 12, 13, etc. from when voltage is applied to the start of discharge until the start of discharge, and the start of discharge can be detected by the fall of this -7= signal 32a. In the no-load time counting circuit 22, the AND circuit 34 is open only while the pulse signal 32a from the comparator 32 is being output. While this is open, the clock circuit 33
A clock signal of about I MHz is input to the counter 35, and the number of clocks is counted. Therefore, the output signal 34a of the AND circuit 34 and the count value 35a of the counter 35 are accumulated over time as shown. The CPU 23 reads the accumulated count value 35a at every predetermined sampling period and calculates the difference from the previous count value, thereby calculating the total for each predetermined sampling period.

Next, FIG. 5 shows a flowchart of the first embodiment.

This first embodiment is based on the premise that internal and external human information, mathematical formulas, etc., which will be described below, are used. That is, as "internal input information", a value that is the sum of the counts of no-load time during a certain period of time (usually 501 isec) [sample value: maximum force I/number of times (50,000 times) is used. Then, the voltage between electrodes (V ) within a certain period of time (5011 sec)
is calculated and determined by the following formula.

V = V
This is the count value of the MHz clock.

Further, as the "external input information" in the first embodiment, "target voltage" as a reference value for feed control and "gap control gain (GAIN) J" for preventing control oscillation are input manually.

In the first embodiment, by inputting the above-mentioned "internal input information" and "external input information", the feed speed is calculated and commanded, and the voltage between the electrodes is controlled so as to match the target voltage. . In addition, as an "output signal", a table feed speed command corresponding to electrode feed is output, and the command cycle is 5.
Every 0 m5ec.

Next, a flowchart of the first embodiment shown in FIG. 5 will be explained. First, the target voltage (V
) and the calculated interelectrode voltage (V ) g is calculated (step Sl).

The feed rate increase/decrease (F u
d) is calculated (step S2). Here, the feed rate increase/decrease (F ud) is calculated by the difference ΔN (dv) and the gain (G
AIN), the proportional calculation is performed for each sampling period according to the following equation.

F udNk X dv X GA I Nwhere, k
is a proportional coefficient such as a speed conversion coefficient.

After step S2, step S3 calculates the average value of the past 10 actual values of commanded feedrates including the current value as a reference feedrate for maintaining the feedrate for one second.
), a new commanded feed rate is calculated by adding this reference feed rate and the calculated feed rate increase/decrease (F ud) (step S4). Then, when the command feed speed calculation is completed and the operator has given a command to perform speed control (step s5), after commanding the drive system the calculated command feed speed, 50 m5e
c. Determine whether or not the product has been flushed, and after that, repeat each of the above steps again.

Note that in the first embodiment, the average value of the past 10 commanded feedrates is calculated as the reference feedrate, and that value is held for 1 second, but the changes in the past commanded feedrates It is also possible to use it as data by giving it weight or applying a filter depending on it, or to use it as a reference feed rate.

Further, by continuing to hold this value for a long time (1 second or more), it is possible to perform control more suitable for processing.

Next, a second embodiment will be described based on the flowchart shown in FIG.

First, the difference g ΔN1 (dvl) between the target voltage (V 2 ) and the calculated interelectrode voltage (V 2 ) is calculated for each predetermined sampling (step 511).

Compare this "currently" calculated value ΔN1 with the value of 8 No. calculated by the "previous" sampling (step 512), and if the values are "same sign", calculate the feed rate increase/decrease (step 512). 813), and in the case of "opposite sign", the value of the feed speed increase/decrease is set to 0 (step 514). In other words, in the case of "different signs", it means that the "target voltage" was crossed between the "previous time" and "this time", and since the electrical discharge machining is being performed near the "target voltage", the feed rate remains the same. Just leave it there. Conversely, in the case of "same sign", the "target voltage" has not yet been reached, so it is necessary to further calculate the increase/decrease in the feed speed.

Next, the average value of the past 10 actual values of commanded feedrates including the current value is calculated as a reference feedrate that holds that value for 1 second (step 515), and the calculated feedrate increase/decrement and this average value are calculated. A new commanded feed rate is calculated by adding (step 516). and,
When the command feed speed calculation is completed and the operator has issued a command to perform speed control (step 51
7) After commanding the calculated command feed rate to the drive system,
It is determined whether 50 m5ec has elapsed or not, and after that elapse, the above-mentioned steps are repeated again.

)・3. In this second embodiment, the difference (ΔN1−
The increment/decrement of the feed speed was calculated when the sign of 8 NO) is the same as the sign of 1 previous time (i.e., the same sign), but the increase/decrease in feed rate is calculated according to ``previous previous time'' or even ``past change'' (i.e. , based on a large number of actual values), it is also possible to perform more stable control.

Furthermore, the aforementioned discharge detection circuit 20 (see FIG. 3) may be of the type that detects "current" instead of "voltage". FIG. 7 is a circuit diagram showing a "current detection type" discharge detection circuit 2OA. A current transformer (CT) 40 is attached to the electric wire 18 leading to the feeder 17, and its output is insulated by a photocoupler 41 and connected to the logic circuit 4.
2 is set to be input. This logic circuit 42 outputs an output signal 42a from when the discharge permission signal is input manually until a current is detected by the current transformer 40 and the output of the photocoupler 4 is input. The output signal 4.2a of this logic circuit 42 corresponds to the output signal 32a of the comparator 32, and is a pulse-like signal that is at a high level from the time the voltage is applied to the machining gap G until the discharge starts. It becomes a signal. The pulse width corresponds to the no-load time. As described above, the no-load time counting circuit 22 counts the pulse width of its output signal.

Note that the above-mentioned "gap control gain" will be explained in detail. This is the target voltage (
The increase/decrease in speed (F u
This is to adjust the value of d). When the "gain" is large, the increase/decrease in speed becomes large, and the target voltage (V) is quickly set.
However, oscillation is more likely to occur. vice versa"
When the "gain" is small, the speed at which the voltage approaches the target voltage (V) is slow.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an electrical discharge machine according to the present invention, FIG. 2 is a block diagram showing an embodiment of the electrical discharge machine according to the present invention, and FIG. 3 is an electric discharge machine showing the main circuit of the embodiment. 4 is a waveform diagram showing the operation of the electric circuit diagram, FIG. 5 is a flowchart showing the processing of the first embodiment, and FIG. 6 is a flowchart showing the processing of the second embodiment.
, FIG. 7 is an electrical circuit diagram showing a current detection type discharge detection circuit. DESCRIPTION OF SYMBOLS 1... Workpiece, 2... Wire electrode, 20... Discharge detection circuit (1st and 2nd detection means), 22... No-load time argument circuit (measuring means, no-load time counting circuit) , 23・
...CPU (feed speed increase/decrease calculation means, reference feed speed calculation means, command feed speed calculation means), G/machining gap. Applicant's agent Yasuo Ishikawa = 16 - Figure 5 Figure 6 Figure 7

Claims (1)

[Claims] The discharge electrode and the workpiece are moved relative to each other at a predetermined feed rate, and a voltage is applied to the gap between the discharge electrode and the workpiece to cause a discharge, and the discharge energy moves the workpiece. In an electric discharge machine for machining, a first detection means for detecting the start of application of the voltage, a second detection means for detecting the start of electric discharge in the gap, the first detection means and the second detection means a measuring means for measuring the no-load time from the start of voltage application to the start of discharge based on the detection result of the measurement means; and a no-load time totaling means for summing the measured values measured by the measuring means at each predetermined sampling period. A reference value is set in advance for the total value summed by the no-load time totaling means, and a feed rate increase/decrement calculation means calculates an increase/decrease in the feed rate based on the difference between the total value and the reference value. , a reference feed speed calculation means for calculating a reference feed speed according to past actual values of a command feed speed for relatively moving the discharge electrode and the workpiece; and a calculation means for calculating a feed speed increase/decrease amount. An electric discharge machine comprising: a command feedrate calculation means for calculating a new command feedrate based on the increase/decrease in the feedrate calculated by the reference feedrate calculation means and the reference feedrate calculated by the reference feedrate calculation means. .