JPS6034221A - Electric discharge machine - Google Patents

Abstract

PURPOSE:To improve the working efficiency by increasing the servo gain upon deterioration of inter-pole state between an electrode and a work thereby increasing the opening/closing speed of gap thus achieving proper speed. CONSTITUTION:Multiplier type D/A converter 100 is comprised of an element for outputting in such form as multiplied by analog signal Vr-Vs in accordance to the output from a counter 67 to serve as a volume for the input signal. In other word, the level of said volume is varied by the output from an abnormal state detection/decision circuit. The servo gain is increased by said converter 100 as the inter-pole state deteriorates then provided through an amplifier 24 comprised of resistors 102, 103 and an operational amplifier 104 to the control coil of a servo valve 26 to increase the speed of servo actuator. Here, the servo gain is increased linearly in proportion to the deterioration of inter-pole state to achieve high working efficiency when the setting speed is 5-10mm./min.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electric discharge machining apparatus, in particular, an electrode and a workpiece (1) are faced to each other with an insulating machining liquid interposed therebetween, and an electric discharge is generated in the gap between the electrodes to machine the workpiece. This invention relates to electrical discharge machining equipment for machining objects.

FIG. 1 shows a schematic configuration diagram of a conventional electric discharge machining apparatus. In FIG. 1, the electric current 8iiio faces a workpiece 14 placed in a processing tank 12 with an insulating processing liquid 16 interposed therebetween. A processing power source 18 is connected between the electrode 10 and the workpiece 14.
is connected. This processing power supply 18 is a DC type 1lti
18a, a switching element 18b for on/off of the machining current, a current limiting resistor 18c, and an oscillator 18d for controlling the on/off of the switching element 18b. It is supplied to the gap 20 between the poles and the workpiece 14.

The above-mentioned machining current l is expressed by the following formula: ■=Wataru (E is the voltage value of the DC type source 18a, R is the resistance value of the current limiting resistor 18c, and vg is the voltage between electrodes). The voltage between electrodes v9 is 20 to 30v during arc discharge, Ov during short circuit, and E during no discharge.
V, and O when switching element IBb is off.
It becomes v.

(2) Therefore, if this inter-electrode voltage value vg is detected and averaged by the smoothing circuit 22, the inter-electrode gap can be controlled using this value. That is, when the inter-electrode gap 20 is wide, discharge is difficult to occur and the average voltage value Vs is high. When the inter-electrode gap 20 is narrow, short circuits or discharges occur easily, resulting in a decrease in the average voltage value Vs. Therefore, if this average voltage value Vs is compared with the reference voltage value Vt and this difference is amplified by the amplification N24 and inputted to the hydraulic servo coil 26, the hydraulic servo coil composed of the hydraulic pressure generation pump 28 and the hydraulic cylinder 30 Depending on the mechanism, the distance between poles l
The electrode 10 can be controlled so that I20 is approximately constant.

When determining whether the machining state is good or bad with a conventional electric discharge machining device, the most common method is the average voltage value V of the above machining voltage value v9.
sele! It is to measure. That is, the average voltage value V
When s is low, the impedance between poles is low,
Short circuits and continuous arc discharge may occur, and machining powder and sludge may remain in the gap 20 between the poles. However, the most dangerous abnormal arc discharge in electric discharge machining is that once it occurs, carbon is generated due to thermal decomposition of the machining fluid (3), resulting in an electric discharge between the carbon and the workpiece, and the impedance between the electrodes increases. It becomes a state. Therefore, there was a drawback that it was impossible to detect deterioration of the inter-electrode gap condition due to abnormal arc discharge at the average voltage value Vs of 111n.

The present invention has been made in view of the above-mentioned conventional problems, and its purpose is to analyze the frequency spectrum of the discharge voltage waveform of the gap between electrodes when a discharge occurs, to distinguish between normal discharge and abnormal discharge, and to determine the state of the gap between electrodes. By controlling the servo gain of the servo mechanism for the pole gap servo so that the
It is an object of the present invention to provide an electric discharge machining apparatus which can obtain appropriate machining distance and approach speed.

In order to achieve the above object, the present invention provides an electric discharge machining apparatus that machines the workpiece by arranging an electrode and a workpiece to face each other with an insulating machining liquid interposed therebetween, and generating electric discharge in the opposing gap. , an abnormal discharge detection means that analyzes the frequency spectrum of the discharge voltage waveform between the electrode and the workpiece and identifies whether it is an abnormal discharge state or a normal discharge state; an interpolation state determining means for outputting a signal;
The present invention is characterized by comprising a control means for controlling the servo gain of the pole gap servo based on the output of the discrimination means.

Hereinafter, preferred embodiments of the present invention will be described based on the drawings. Figure 2 shows a discharge voltage waveform and its frequency spectrum to explain the detection principle in the present invention. It can be expressed relatively easily, and the spectrum when the amplitude is E2, the period is T, and the pulse intensity is τ can be expressed as follows. (However, in the case of a discharge waveform, it is at random and is difficult to formulate.) The spectrum diagram in FIG. 2 is described using the case of T=2τ as an example. The following items can be learned from this spectral distribution and discharge state.

(1) No matter which state the spectrum is in, the period T(
5) It shows high output at the frequency f, which is the reciprocal of . However, in the case of normal discharge, the peak value is low compared to others.

(2) In the case of a discharge related to 1-ri, the high frequency f1
．． 1 (approximately 2 MH2 or more) hardly exists, and in the case of normal discharge, high frequency components are generated up to around 200 MH2 without attenuation.

If the output at +31 f is low and the output at fH is sufficient, it can be considered that normal discharge is occurring.

From the above results, it can be seen that if it can be determined that the state described in item (3) is present, abnormality in the discharge state can be identified.

FIG. 3 is a schematic diagram showing this embodiment, which basically has the same configuration as that of frequency spectrum analysis.

The voltage signal F(t) in the gap between the poles is mixed with the output signal f(t) of the FM modulation M51 by a mixing circuit, and by heterodyne detection, an intermediate frequency j is determined from the frequency of the sum of F(t) and f(t). (Only the frequency of tl is extracted and a difference is also produced, but this is amplified by an intermediate frequency amplifier 53 that is removed by a filter, and the amplitude component is detected by a detection (6) wave 54 and amplified by a low frequency amplifier 55. F.The above-mentioned FM modulation l#51 is frequency-modulated by the analog voltage AV, so by changing this analog voltage ^ν in proportion to time, the relationship between time and frequency becomes linear, and the F(tl
The amplitude of the frequency spectrum can be extracted as the output of the low frequency amplifier 55 by an amount corresponding to the frequency of j (t). Therefore, the analog voltage ^ν is the above fo, f
The time at which the voltage corresponds to H can be determined by an accurate oscillator 56 and a counter 57 that counts this output. 58 is a discriminator for fo, and 59 is a discriminator for fI+. The contents of the counter 57 become the analog voltage AV by the D/A change I/i4 sound, and the content of the counter 57 becomes the analog voltage AV by the D/A change
Modulate 1. The level comparison N61 responds to the timing signal from the f discriminator or the fi1 discriminator and determines whether the amplitude amplified at a lower frequency, that is, the frequency spectrum, is larger or smaller than a predetermined reference value at that timing,
Based on this result, an output 84 is output when abnormal discharge occurs. For example, let f be 3KH2 and fH be SM& (7). Also, if the intermediate frequency is 10.7M)i, then f (t
) is 10.693MHz, fo is 5.700M
When H, each spectrum of f can be detected. FM modulation 5
1 is a broadband one, and when the input voltage is Ov, it is 5MHz.
, IOV is 10 MHz, and if the D/A conversion is 16bj type, it will be a spectrum analyzer with a resolution of about ±80H2. Also ■. Since the parameters are always changed every time the machining conditions are selected, it is necessary to perform arithmetic control for one machine (however, the period T is the sum of the on-time and off-time).

Now, regarding the above output S^, level comparator 6 in Figure 4
This will be explained in more detail using detailed explanatory diagram No. 1. The output of the low frequency amplifier 55 is output by an analog switch 82.63.
Compare each other than the timing of f, discrimination and f1 discrimination @64
．． 65 so that it is not connected. And '9
At the determination timing, if the spectrum amplitude vo is larger than vl, the output of the comparator 64 is determined to be "1", and AN
Counter 67 is counted up via D gate 66. In addition, at the f,1 determination timing, if the above ■ is 111 larger than v2, the output of the comparison 965 becomes "1", and the AND
Since the counter 67 is reset via the gate 68,
This counter 67 increases when the spectrum amplitude is large at f0 timing, and immediately becomes zero when vo is large at fH timing. Therefore, if there is a high frequency component, it will be 0%; if the acid component is large, it will increase. It is possible to determine whether the gap condition is good or bad. That is, vo
If it is large, it means that abnormal discharge is approaching.For example, sludge may have accumulated in the gap between the electrodes due to the retention of machining powder, or carbon may be generated due to thermal decomposition of the machining fluid 16 due to an abnormal arc. Problems such as a part of the electrode being damaged and a piece of it existing in the interpolar gap 20 can be easily detected.

However, in a very short period of time, the state of the gap between the poles is constantly changing, and even if the above-mentioned V exists for a short time, the gap between the poles does not always change.
It cannot be determined that the I-gap condition is bad. Therefore, it is necessary to detect whether the output value of the digital-to-analog conversion N40 exceeds a predetermined (9)57 value and continues for a certain period of time to judge whether the state of the gap between the poles is good or not.

A voltage comparison 914B in FIG. 5 determines whether the output voltage of the digital-to-analog conversion @40 is larger or smaller than a predetermined value v11. When V(1>V, , voltage comparison @l!
The output of 148 becomes negative, turning off switching transistor 152 via base resistor 150. Therefore, the time measuring capacitor 154 is charged via the resistor 156, and the voltage V31 across the capacitor 154 is expressed as follows. Voltage across the capacitor 1543. is compared with reference voltage -1 by voltage comparison 1Il1158. Since the output of the voltage comparator 158 does not become negative during this period, the light emitting diode 16o does not light up. Mote v.

(10) When the state of 〉vll continues for a predetermined period of time and becomes η/〉”21, the output of the voltage comparison wr158 becomes negative, and the light emitting diode 160 is turned on via the resistor 162 to prevent abnormal occurrence of the gap between the electrodes. It is to be displayed.

The switch 164 is a switch for switching whether to judge the interpole gap state only as a function of time or as a function of the product of the magnitude of the output V of the digital analog/4G converter 1972 and time. In other words, in machining where it is difficult to determine abnormalities in the gap between the poles by simply detecting time, for example, in the machining of cemented carbide, where cracking due to one-hole or tungsten chipping occurs instantaneously, the difference can be detected. The occurrence of an abnormality can be quickly detected as a function of the product of voltage and time. That is, if the difference is large even for a short time, the charging current of the capacitor C will increase, and the capacitor voltage will immediately reach v2.

Furthermore, by directly observing the voltage difference with a voltmeter, it is possible to directly observe the difference between the optimum value and the current value, and it is clear that this can be used as a monitor for the state of the gap between the poles.

(11) Now, by changing the servo gain of the inter-pole servo based on the output obtained by the detection circuit, the short circuit, open state, or arc precursor state can be recovered. In other words, in the case of a bad gap condition like the one mentioned above, by increasing the servo gain and increasing the speed of opening and closing the gap, it is possible to quickly avoid the bad mechanical condition and improve the condition. It is possible to recover the temporary state. An embodiment for realizing this will be explained in detail using FIG. 6. Reference numeral 100 designates a multiplication type digital-to-analog converter, which is an element capable of outputting the result of multiplying the input analog signal Vr-Vs according to the output of the counter 67, and AD7520 manufactured by Analog Devices, Inc. in the United States is a well-known device. In other words, it can be thought of as having a volume function on the input signal. The value of the volume changes depending on the output (digital value) of the detection circuit. Therefore, according to this example, the servo gain is increased by the multiplier type D/A converter as the gap condition worsens, and the servo gain is increased by the multiplier type D/A converter, and the servo gain is increased by the servo valve 26 through the amplifier Sho 24 constituted by the resistors 102 and 103 and the operational amplifier (12) amplifier 104. control coil, and the speed of the servo's actuator increases. In this embodiment, the servo gain is increased almost linearly in proportion to the poorness of the inter-electrode condition, but it does not necessarily have to be changed linearly, and may be changed in a quadratic function or in a polygonal manner. The above detection signal S
It is easier to implement the present invention by performing two-stage control using A, and the present invention can be implemented at a lower cost.

According to experiments, when the interpolar condition worsens, at least 2
It has been found that if the speed is not higher than 0-min, a speed of about 200++/min is required when arc discharge occurs and a large amount of machining powder stays between the poles. In addition, for stable machining, in finishing machining with a surface roughness of 1.5μRmax or less,
It has also been confirmed that the machining efficiency is high at a speed of 5 to 10 .mu./min, and it is considered that the speed should generally be set in these ranges.

As described above, according to the present invention, an abnormality in discharge is determined by the above-described detection method, and based on the detection result, the servo gain is changed to recover the servo actuator. The purpose of the present invention is to provide an unprecedented electric discharge machining apparatus that controls the speed of the gap between the poles and quickly opens and closes the gap between the poles.

[Brief explanation of drawings]

Fig. 1 is a principle diagram showing a conventional electrical discharge machining device, Fig. 2 is an explanatory diagram of the principle according to the present invention, Fig. 3 is an explanatory diagram of a frequency spectrum analysis circuit, and Fig. 4 is an abnormal state detection/discrimination circuit diagram. FIG. 5 is a display circuit diagram thereof, and FIG. 6 is a detailed explanatory diagram of the present invention. In the figure, 10 is an electrode, 14 is a workpiece, 18 is a processing power source, and 67 is an abnormality detection counter. Note that the same reference numerals in the figures indicate the same or equivalent parts. Agent Masuo Ohatsu (14)

Claims (1)

[Claims] An electric discharge machining device that processes the workpiece by making an electrode and a workpiece face each other with an insulating machining liquid interposed therebetween, and generating an electric discharge within the gap between the electrodes, and controlling the gap length between the electrodes. In an apparatus equipped with a servo mechanism, a detection means for detecting the distribution of frequency components in an electric signal in the gap between the electrodes and the workpiece when electric discharge occurs in the gap between the electrodes and the workpiece, and a frequency component detected by the detection means. a comparison means for comparing distributions of frequency components whose distributions are set in advance; an interpole gap state determining means for determining a state of the interpolar gap based on an output signal of the comparing means and outputting a signal; and this determining means An electric discharge machining apparatus comprising: a control means for controlling a servo gain of the servo mechanism based on the output of the servo mechanism.