JP2003165028A - Electric discharge machining device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric discharge machining device provided with both high machining accuracy and speed particularly suitable for fine machining. <P>SOLUTION: In the electric discharge machining device, a work piece is machined by applying voltage from a power source for machining to an interval formed by an electrode and the work piece, generating electric discharge and relatively moving the electrode and the work piece. It is characterized by that it is provided with a current detecting means of detecting a current fed from the power source for machining and converting it into an analog voltage, a comparator means of comparing a voltage proportional to the detected current with a reference voltage and outputting a logic signal, a pulse width stretching means of storing a logic value for a certain time by using either one of rising or falling of the logic signal as a trigger, an OR means of determining a logical sum of an input and output of the pulse width stretching means, and a discharge state detecting means comprising a smoothing means of smoothing a logic signal output of the OR means and converting it into an analog voltage. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric discharge machining apparatus for machining a work piece by electric discharge machining, and in particular, electric discharge machining for machining a fine axis of 50 micrometers or less by wire machining with high machining accuracy in a short time. Regarding the device.

[0002]

2. Description of the Related Art Electric discharge machining has many features such as high precision and easy machining of fine shapes using an electric discharge phenomenon as a medium, and is a non-contact machining. For this reason, it is necessary to always maintain the distance between the electrode and the workpiece at a distance suitable for generating an electric discharge. In die-sinking EDM, it is necessary to constantly push the gap between electrodes by the amount by which the electrode and the work piece are removed as the machining progresses.However, machining scraps between the electrodes, gas generation, changes in the shape of the discharge surface, etc. Correspondingly, it is necessary to maintain the discharge electrode spacing.

Further, in wire electric discharge grinding as disclosed in Japanese Patent Laid-Open No. 1-103234, an outer edge of a wire slowly traveling on a wire guide is used for a portion corresponding to a grindstone for ordinary grinding, and a rotating workpiece is machined. It is a method of machining an object like cylindrical grinding, but when making a notch, it is necessary to always push in the polar interval by the amount that the electrode and the workpiece are removed as the machining progresses Similarly to the above, it is necessary to maintain the discharge electrode interval.
In wire electric discharge machining, the discharge area also changes when the plate thickness of the work piece changes, so the amount of electric discharge also changes, and the groove width changes significantly when feeding at constant electrical conditions and constant speed. However, the processing accuracy is significantly reduced. That is, since the discharge electrode interval changes with the change in the processing area, it is necessary to maintain the discharge electrode interval corresponding to the change in the plate thickness.

In order to solve such a problem, generally, there is a method of comparing the inter-electrode average voltage of the discharge interval with a certain reference voltage and changing the feed rate so that the inter-electrode average voltage becomes constant. It is taken. Furthermore, there is also a method that outputs not only the feed rate but also the optimum electrical conditions using a computer (Precision Engineering Society New Edition Precision Machinery Handbook, Corona P46).
5, P494 <1992>). A short circuit between the electrode and the workpiece can be detected by detecting the average voltage between the electrodes. Japanese Patent Laid-Open No. 59-75
In No. 23, in addition to the method of controlling the feed rate so that the average voltage between electrodes is constant, the average machining current is further detected, and the relative speed between the workpiece and the wire electrode and the desired machining groove width are determined. We provide wire-cut electric discharge machines that detect plate thickness and switch electrical processing conditions.

In Japanese Patent Laid-Open No. 10-235521, the number of electric discharges per unit time is counted in the wire electric discharge grinding, and the counted value is compared with a predetermined value to determine the feed rate and the distance between the electrode and the workpiece. Provided is an electric discharge machining apparatus that controls electric discharge machining conditions. This utilizes the property that the number of discharges increases as the spacing between the discharge electrodes becomes narrower. For example, if the workpiece has undulations, the amount of electrical discharge machining to be removed increases at the ridges, so the number of electrical discharges increases, so it is possible to supply the desired amount of electrical discharge machining by slowing the feed rate. A short circuit can be prevented and the discharge interval can be made constant. On the contrary, since the electric discharge machining amount to be removed is small in the valley portion, the number of electric discharges is reduced, and the machining speed can be increased by increasing the feeding speed.

[0006]

However, in such a conventional electric discharge machine, a method of controlling the electric discharge machining conditions by detecting the average voltage between the electrodes and the average machining current is a constant cycle and a constant width. It is very effective for a circuit that uses a switching element that supplies a pulse voltage between the electrodes, but the voltage supply between the electrodes is irregular, and the discharge energy supply period is ignored compared to the non-supply period. In a circuit that uses the charging and discharging of a capacitor and a resistor that supply a pulse that is as steep as possible, there is almost no difference between the average voltage between contacts and the average machining current when there is no discharge, so there is the problem that control is difficult. .

Further, since the inter-electrode average voltage and inter-electrode average current are the result of the combination of the discharge energy and the discharge frequency and are output, when the discharge energy is changed between rough machining and finishing machining, the peak value or Since the parameters such as pulse width have to be taken into consideration, there is a problem that the reference point cannot be determined by a simple calculation such as a proportional formula. In this respect,
In Japanese Unexamined Patent Publication No. 10-235521, the value of the number of discharges is used for control, so that it is also effective in a circuit using charging and discharging of a resistor and a capacitor.

However, at least a certain time is required for counting, which is disadvantageous in terms of responsiveness, and a short circuit detecting means is additionally required, so that the number of parts is increased and there is a problem in cost. Furthermore, when fine processing such as processing a fine shaft of 50 micrometers or less is required, the discharge interval becomes short and the insulating liquid that has the function of suppressing discharge does not easily enter, so that the discharge pulse attenuation characteristics are reduced. Since the number of discharge pulses is deteriorated and the discharge pulse is counted several times in one discharge, there is a possibility that the number of discharge times more than twice the actual number of discharge is erroneously counted.

The present invention is intended to solve the above problems, and an object of the present invention is to provide an electric discharge machining apparatus having both high machining accuracy and high speed, which is particularly suitable for fine machining.

[0010]

In order to achieve the above object, the invention according to claim 1 applies a voltage from a machining power source to a gap formed by an electrode and a workpiece. In an electric discharge machining apparatus that generates electric discharge and moves the electrode and the workpiece relative to each other to machine the workpiece, current detection that detects a current supplied from the machining power source and converts the current into an analog voltage. Means, comparator means for comparing a voltage proportional to the detected current with a reference voltage and outputting a logic signal, and a pulse for holding a logic value for a certain period of time triggered by either one of rising or falling of the logic signal. The width extending means, the logical sum means for obtaining the logical sum of the input and output of the pulse width expanding means, and the logical signal output of the logical sum means are smoothed and converted into an analog voltage. Characterized by comprising a discharge state detection means comprising a smoothing means for. According to the invention,
The discharge frequency, which changes according to the discharge electrode interval, can be converted into an analog voltage with a fast response without miscounting, and short-circuit detection can also be provided. Further, it is easy to recognize the difference in discharge frequency even when using a processing power source that uses charging and discharging of a resistor and a capacitor. Furthermore, since only the discharge frequency is detected, it is easy to obtain a reference point for control, and thus it is possible to detect the pole interval for realizing highly accurate machining.

According to a second aspect of the present invention, the analog voltage data output from the discharge state detection means and the set value data of the machining power source recorded in the storage means are used.
A discharge electrode interval calculation means for calculating an estimated discharge electrode distance between the electrode and the work piece, and a relative result of the electrode and the work piece recorded in the storage means from a calculation result of the discharge electrode distance calculation means. It is characterized by further comprising an axial movement control means for correcting the movement condition and an axial movement driving means for realizing the correction of the relative movement condition of the electrode and the workpiece according to the correction condition. According to the present invention, the discharge electrode interval can be estimated from the output of the discharge state detecting means, and mechanical control can be performed to keep the discharge electrode interval constant, and high-precision machining can be performed in a short time.

According to a third aspect of the present invention, there is provided a machining power supply control means for correcting the electrical condition of the machining power supply recorded in the storage means from the calculation result of the discharge electrode interval calculation means. Characterize. According to the present invention, it is possible to estimate the discharge electrode interval from the output of the discharge state detection means and perform electrical control so as to keep the discharge electrode interval constant, thereby enabling highly accurate machining.

According to a fourth aspect of the present invention, the machining power source control means is configured to control the PW according to the voltage applied to the machining power source.
One of the M control signal and the analog signal is output to change the reference voltage of the comparator means. According to the present invention, even when the peak value of the current pulse detected by changing the setting of the electrical processing condition set by the processing power source changes significantly, the threshold value of the comparator is changed to prevent false detection of discharge. Can be prevented.

According to a fifth aspect of the present invention, in the electric discharge machining device wherein the electrode is a wire electrode and the workpiece is a fine shaft rotated by a rotating means, the wire electrode and the shaft of the fine shaft are provided. It is characterized by having a wire guide for traveling in a direction orthogonal to the direction. According to the present invention, it is possible to process a fine axis of 50 micrometers or less with high accuracy.

According to a sixth aspect of the present invention, the electrode is a tool electrode pre-machined into a desired three-dimensional shape, and the three-dimensional shape of the tool electrode is transferred to the workpiece. To do. According to the present invention, high-precision machining is possible even in a die-sinking electric discharge machine.

According to a seventh aspect of the present invention, in an electric discharge machining device in which the electrode is a wire electrode and the workpiece is a plate-shaped conductor, the wire electrode and the plane direction of the plate-shaped conductor are different from each other. At least 2 for changing the relative positions of the wire electrode and the plate-shaped conductor while making them orthogonal to each other.
It is characterized in that it is provided with an axis moving means which is larger than the axis. According to the present invention, it is possible to perform highly accurate machining even in a wire cut electric discharge machine.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows a first configuration example of an electric discharge machine according to the present invention. The processing power supply 1 includes a DC power supply 2, a resistor 3, and a capacitor 4. DC power supply 2
Of the DC power source 2 is connected to the electrode 6. The space between the workpiece 5 and the electrode 6 is filled with water, discharge oil or the like. Further, the workpiece 5 is connected to an axial movement drive unit 7 that moves vertically and horizontally.

When the DC power supply 2 applies a DC voltage, the capacitor 4 is charged with electric charge, and the voltage across the terminals of the capacitor 4 gradually rises. When the voltage between the terminals of the capacitor 4 exceeds the discharge start voltage in the interval between the work piece 5 and the electrode 6, a discharge is generated between the work piece 6 and the electrode 6. The change in current in this process is detected by the current detecting means 8. Regarding the current detection means 8, there are a method of measuring the voltage across the shunt resistance, a method of measuring using the magnetism generated around the electric wire, and the like. The position of the current detection means 8 is
Examples include a path between the capacitor 4 and the workpiece 5, a path between the capacitor 4 and the electrode 6, and a path between the DC power supply 2 and the resistor 3.

The detected value of the current detecting means 8 is inputted to the discharge state detecting means 9 composed of the comparator means 10, the pulse width extending means 11, the logical sum means 12 and the smoothing means 13, and is inputted to the discharge electrode interval calculating device 14. It outputs an analog signal proportional to the discharge frequency. The discharge electrode interval calculation device 14 estimates the discharge electrode interval, and based on the estimated value, issues a speed change command or a temporary reverse operation command of the feed operation to the axis movement control means 15 to move the axis. The drive means is operated so that the discharge electrode interval is constant.

FIG. 2 shows the waveform of each part of the discharge detection circuit according to the present invention. The waveform 18 of the output 18 from the current detecting means 8 is as shown in FIG. 23. When discharge is generated at the polar interval between the workpiece 5 and the electrode 6, a pulse current flows through the circuit and is attenuated. The attenuation of the electric current is terminated early because the electric discharge is suppressed by the entry of water or discharge oil into the space between the workpiece 5 and the electrode 6. The detected current value is converted by the comparator means 10 into a discharge-time comparator section output waveform 24 which is a digital signal waveform. That is, if the current value is greater than or equal to the reference value, it becomes HIGH, and if it is less than the reference value, it becomes LOW.
In addition, when the discharge electrode gap between the work piece 5 and the electrode 6 is narrow and water or discharge oil is difficult to enter due to finish processing, the current may be slowed down at a slow rate. It is possible that a single pulse will be generated in the comparator output waveform 24 during discharge. The discharging comparator section output 19 is branched into two, one of which is input to the pulse width extending means 11 and the other of which is input to the logical sum means 12.

Incidentally, it is desirable to insert a delay circuit for adjusting the timing in the latter path which does not pass through the pulse width expansion means 11. The pulse width expansion means 11 uses, for example, a monostable multivibrator, outputs a pulse having an arbitrarily set time width by using an input pulse as a trigger, and ignores the rising edge of the pulse input within the time width. As a result, even if a plurality of pulses are generated in one discharge in the discharge comparator output waveform 24, one pulse and a pulse width expansion means output at discharge that outputs a pulse with a constant time width It becomes a waveform 25.

Further, since the discharge cycle is random and the current pulse width output from the current detection section 8 is very short with respect to the discharge cycle, even if the output of the current detection section 8 is directly smoothed, the discharge frequency will vary. Although the change width of the smooth signal due to the change is small, the change width of the smooth signal depending on the discharge frequency can be increased by increasing the pulse width of one discharge by the pulse width expansion means 11. That is,
Although the pulse width due to the discharge is constant, the smoothing signal changes greatly depending on the discharge frequency because the discharge cycle is random. The discharge pulse width expansion means output 20 is input to the logical sum means 12 and logically summed with one of the signals branched by the comparator means output 19. When discharged,
The waveform of the pulse width extending means output waveform 25 becomes the logical sum means output waveform 26 as it is, is input to the smoothing means 13, and becomes the analog signal waveform 27 that changes according to the discharge frequency.

The above is the case where the electric discharge is normally generated between the workpiece 5 and the electrode 6, but when the short circuit accident occurs, the smoothing means output 22 becomes constant at the maximum voltage and the short circuit can be detected.

FIG. 3 shows the waveform of each part of the discharge detection circuit when a short circuit according to the present invention is detected. When a short circuit occurs, a current having a value obtained by dividing the applied voltage of the DC power supply 2 by the resistance value of the resistor 3 is detected by the current detection means 8. By setting the output to be HIGH according to the current value at the time of short circuit based on the reference of the comparator unit 10, the output 19 of the comparator unit 10 due to the short circuit continues to be in the HIGH state from the time of occurrence of the short circuit as shown by the waveform 29. Will be done. At this time, the pulse width extending means 11 outputs a pulse having a constant width when a short circuit occurs, and then outputs LO until the short circuit is resolved.
It remains W.

On the other hand, since the output 19 of the comparator means 10 continues to be in the HIGH state after the short circuit, the logical sum means 12
The output 21 of the signal continues to be in the HIGH state after the short circuit as shown by the waveform 31. Therefore, the output 22 of the smoothing means 22 is the waveform 32.
As described above, the maximum voltage becomes constant, and a short circuit can be detected by monitoring this. Further, as shown in FIG. 3, the smoothing means output waveform 27 at the time of discharge becomes analog data of a higher value as the discharge frequency increases, and as a result of the discharge frequency becoming too high, a short circuit occurs and the maximum voltage is reached. The logic of is also consistent and easy to control.

FIG. 4 shows a second configuration example of the electric discharge machine according to the present invention. On the basis of the estimated discharge electrode interval, the inter-discharge electrode calculation means 14 compares the set value of the processing power supply 1 recorded in the storage means 16, and the processing power supply control means 17 controls the processing power supply. , The applied voltage change command, etc., are operated so that the discharge electrode interval becomes constant.

FIG. 5 is an explanatory diagram of the comparator means having the variable reference voltage according to the embodiment of the present invention. Any CPU
It is possible to transmit a PWM control signal waveform 37 which is controlled by a constant cycle and variable pulse width from 33, converts it into an analog signal waveform 38 by the PWM pulse smoothing means 34, and changes the reference voltage of the comparator means 10. As a result, it becomes possible to correct the reference voltage of the comparator means 10 according to the change in the electrical processing conditions of the processing power source 1 recorded in the storage means 16. It should be noted that the signal from the CPU 33 is directly converted into a D / A converted analog signal without passing through the PWM pulse smoothing means 34, and the comparator means 1 is directly operated.
You may input into the reference voltage input terminal of 0.

In the above embodiment, the wire electric discharge grinding is mainly described as an example, but the present invention may be applied to die-sinking electric discharge machining or wire cut electric discharge machining.

[Brief description of drawings]

FIG. 1 is a diagram showing a first configuration example of an electric discharge machine according to an embodiment of the present invention.

FIG. 2 is a diagram showing a waveform of each part of the discharge detection circuit according to the embodiment of the present invention.

FIG. 3 is a diagram showing a waveform of each part of the discharge detection circuit when a short circuit according to an embodiment of the present invention is detected.

FIG. 4 is a diagram showing a second configuration example of an electric discharge machine according to the present invention.

FIG. 5 is an explanatory diagram of comparator means having a variable reference voltage according to an embodiment of the present invention.

[Explanation of symbols]

1 ... Machining power supply, 2 ... DC power supply, 3 ... Resistance, 4 ... Capacitor, 5 ... Workpiece, 6 ... Electrode, 7 ... Shaft movement drive means,
8 ... Current detecting means, 9 ... Discharge state detecting means, 10 ... Comparator means, 11 ... Pulse width expanding means, 12 ... Logical sum means, 13 ... Smoothing means, 14 ... Discharge electrode calculation section, 15 ...
Axis movement control unit, 16 ... Storage unit, 17 ... Machining power supply control unit, 18 ... Output of current detection unit, 19 ... Output of comparator unit, 20 ... Output of pulse width expansion unit, 21 ... Output of OR unit, 22 ... Smoothing unit Output, 23 ... Output waveform of current detection means during discharge, 24 ... Output waveform of comparator section during discharge, 25 ...
Discharge pulse width expansion means output waveform, 26 ... Discharge logical sum means output waveform, 27 ... Discharge smoothing means output waveform 28 ... Short circuit current detection means output waveform, 29 ... Short circuit comparator output waveform, 30 ... Short circuit Pulse width expansion means output waveform,
31 ... OR-means output waveform at short circuit, 32 ... Smoothing means output waveform at short circuit, 33 ... CPU, 34 ... PWM pulse smoothing means, 35 ... Current value input terminal, 36 ... Reference voltage input terminal,
37 ... PWM pulse signal waveform, 38 ... Comparator means output waveform

Claims (7)

[Claims] 1. A voltage is applied from a machining power source to generate a discharge in a space formed by an electrode and a work piece, and the electrode and the work piece are relatively moved to process the work piece. In an electric discharge machining device for performing, a current detection means for detecting a current supplied from the machining power source and converting it into an analog voltage, and a comparator means for comparing a voltage proportional to the detected current with a reference voltage and outputting a logic signal. A pulse width extending means for holding a logical value for a certain period of time by using either one of the rising edge and the falling edge of the logic signal as a trigger, and a logical sum means for taking a logical sum of an input and an output of the pulse width extending means, An electric discharge machine comprising: a discharge state detecting means comprising a smoothing means for smoothing a logical signal output of the logical sum means and converting it into an analog voltage. 2. An estimated discharge electrode distance between the electrode and the workpiece is calculated from analog voltage data output from the discharge state detection means and setting value data of the processing power source recorded in the storage means. A discharge electrode interval calculation means for calculating, an axial movement control means for correcting the relative movement condition of the electrode and the workpiece recorded in the storage means from the calculation result of the discharge electrode distance calculation means, and the correction condition. The electric discharge machining apparatus according to claim 1, further comprising: an axial movement driving unit that corrects a relative movement condition between the electrode and the workpiece. 3. A machining power supply control means for correcting the electrical condition of the machining power supply recorded in the storage means from the calculation result of the discharge electrode interval calculation means. The electric discharge machine described. 4. The processing power supply control means outputs either a PWM control signal or an analog signal in accordance with a voltage applied to the processing power supply to change the reference voltage of the comparator means. Claims 1 to 3 characterized
The electric discharge machine described. 5. In the electric discharge machining apparatus, wherein the electrode is a wire electrode and the workpiece is a fine shaft rotated by a rotating means, the wire electrode and the fine shaft run in a direction orthogonal to each other. An electric discharge machine according to any one of claims 1 to 4, further comprising: 6. The method according to claim 1, wherein the electrode is a tool electrode pre-machined into a desired three-dimensional shape, and the three-dimensional shape of the tool electrode is transferred to the workpiece. The electric discharge machine according to item 4. 7. In an electric discharge machine in which the electrode is a wire electrode and the workpiece is a plate-shaped conductor, the wire electrode and the plate-shaped conductor are orthogonal to each other, and the wire electrode is 5. The electric discharge machine according to claim 1, further comprising at least two or more axis moving means for changing the relative position of the plate-shaped conductor.