JPH0319011B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electric discharge machining apparatus, in particular, an electric discharge machining apparatus, in which an electrode and a workpiece are opposed to each other with an insulating machining liquid interposed therebetween, and a pulse voltage is applied to the gap between the electrodes to process the workpiece. This invention relates to electrical discharge machining equipment.

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

The machining current I is expressed by the formula: I=E-V _g /R (E is the voltage value of the DC power supply 18a, R is the resistance value of the current limiting resistor 18c, and V _g is the voltage between electrodes). The interelectrode voltage value V _g is 20 to 30 V during arc discharge, 0 V during short circuit, EV during no discharge, and 0 V when switching element 18b is in the off state.

Therefore, if this inter-electrode voltage value V _g 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 V _s is high.
When the inter-electrode gap 20 is narrow, short circuits or discharges occur easily, and the average voltage value V _s decreases. Therefore, this average voltage value V _s is compared with the reference voltage value V _t and this difference is amplified by the amplifier 24 and the hydraulic servo coil 2
6, a hydraulic servo mechanism consisting of a hydraulic pressure generating pump 28 and a hydraulic cylinder 30 will control the electrode 1 so that the inter-electrode gap 20 is approximately constant.
0 can be controlled.

When determining whether the machining state is good or bad using a conventional electric discharge machining apparatus, the most common method is to observe the average voltage value V _s of the machining voltage value V _g . In other words, when the average voltage value V _s is low, the electrode impedance is low, resulting in short circuit and continuous arc discharge.
Processing powder, sludge, etc. 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, resulting in an electric discharge between the carbon and the workpiece, resulting in a state where the impedance between the electrodes becomes high. become. For this reason, observation of the average voltage value V _s has the disadvantage that it is impossible to detect deterioration of the inter-electrode gap condition due to abnormal arc discharge.

The present invention has been made in view of the above-mentioned conventional problems, and its purpose is to reduce the low frequency component corresponding to the frequency of the pulse voltage applied to the gap between the electrodes and the predetermined high frequency component of the voltage between the electrodes when a discharge occurs. The frequency component is detected to distinguish between normal discharge and abnormal discharge, and the applied value of the pulse voltage applied to the gap between the electrode and the workpiece is controlled so that the gap between the electrodes and the workpiece becomes normal. The object of the present invention is to provide an electrical discharge machining device that has the following features.

In order to achieve the above object, the present invention makes an electrode and a workpiece face each other with an insulating working fluid interposed therebetween,
In an electrical discharge machining device that processes the workpiece by applying a pulse voltage to the opposing gap, the frequency of the pulse voltage applied to the gap is determined by the voltage between the electrodes and the workpiece. Abnormal discharge detection means detects corresponding low frequency components and predetermined high frequency components and identifies whether it is an abnormal discharge state or a normal discharge state, and outputs a signal according to the inter-electrode gap state based on this analysis. The present invention is characterized in that it comprises a gap state determining means and a control means for controlling the applied value of the pulse voltage based on the output of the determining means.

Hereinafter, preferred embodiments of the present invention will be described based on the drawings.

Figure 2 shows the discharge voltage waveform and its frequency spectrum to explain the detection principle in the present invention. This can be expressed relatively easily, and the spectrum when the amplitude is E, the period is T, and the pulse width is τ can be expressed as follows. (However, the discharge waveform is atrandom and difficult to formulate.) f _(t) = τ/TE+∞ 〓 ⁿ⁼¹ 2τ/TE×sinnωr/2/nωr/2・cosnωt However, ω=2π/T The spectrum diagram in FIG. 2 is illustrated using the case of T=2τ as an example. The following items can be understood from this spectral distribution and discharge state.

(1) Regardless of the state of the spectrum, a high output is shown at the frequency f ₀ which is the reciprocal of the period T.
However, in the case of normal discharge, the peak value is low compared to others.

(2) In the case of discharges such as those associated with arcs, high frequency
f _H (approximately 2 MHz or more) hardly exists, and in normal discharge, high frequency components occur up to around 200 MHz without attenuation.

(3) If the output at f ₀ is low and the output at f _H is sufficient, it can be considered normal discharging. From the above results, if it can be determined that the state is as described in (3), then it is discharged. It can be seen that it is possible to identify abnormalities. Further, since it is possible to detect that the process is just before arc discharge occurs, it is possible to prevent failures in electric discharge machining.

FIG. 3 is a schematic diagram showing this embodiment,
Basically, it has the same configuration as a frequency spectrum analyzer.

The oscillator 56 outputs a pulse signal of a predetermined frequency. The counter 57 counts the number of pulses of this pulse signal and outputs the counted value to the D/A converter 60. The D/A converter 60 converts the count value of the counter 57 into an analog voltage _AV . Furthermore, the FM modulator 51 generates a signal f(t) corresponding to the analog voltage A _V
is output to the mixer 52. Next, the mixer 52 mixes the voltage signal F _(t) of the gap between the poles and the output signal f _(t) of the FM modulator 51, and generates a signal j _(t) at the frequency of the difference.
Output. An intermediate frequency amplifier 53 amplifies the signal j _(t) , a detector 54 outputs a voltage corresponding to the amplitude of the signal j _(t) , and a low frequency amplifier 55 amplifies this.

The FM modulator 51 converts the analog voltage A _V into a frequency and outputs it, so by changing the analog voltage A _V in proportion to time, the relationship between time and frequency becomes linear, and the gap between the poles is reduced. Voltage signal F _(t)
The time when the voltage becomes the voltage corresponding to the frequencies f ₀ and f _H can be determined by the oscillator 56 and the counter 57 that counts the output of the oscillator 56 . 58 is a discriminator for f ₀ , and 59 is a discriminator for f _H . counter 5
The content of 7 becomes an analog voltage A _V by the D/A converter 60, and modulates the FM modulator 51. The level comparator 61 responds to the timing signal from the f ₀ discriminator or the f _H discriminator, and outputs an amplitude amplified at a lower frequency than a predetermined reference value at that timing.
That is, it is determined whether the frequency spectrum is large or small, and based on this result, an output V ₃ corresponding to the processing state is output. For example, f ₀ is 3KHz, f _H is 5MHz,
If the intermediate frequency is 10.7MHz, f _(t) is 10.703MHz
When f ₀ and f _(t) are 15.7MHz, f _H can be detected. If the FM modulator 51 is wideband, 5 MHz when the input voltage is 0 V, and 10 MHz when the input voltage is 10 V, and the D/A conversion is 16 bit type, the spectrum analyzer has a resolution of about ±80 Hz.
Furthermore, since f ₀ is always changed every time machining conditions are selected, it is necessary to perform calculation control of f ₀ =1/T (however, period T is the sum of on-time and off-time).

Now, the output _V3 will be explained in more detail using the detailed explanatory diagram of the level comparator 61 in FIG. The output of the low frequency amplifier 55 is configured by analog switches 62 and 63 so that it is not connected to the comparators 64 and 65 except at the timing of f ₀ determination and f _H determination, respectively. Then, at the f ₀ determination timing, if the spectral amplitude V ₀ is larger than the set low frequency component V ₁ , the output of the comparator 64 becomes "1",
Counter 67 is counted up via AND gate 66. Also, at the _fH determination timing, if V ₀ is larger than the set high frequency component V ₂ ,
The output of the comparator 65 becomes "1" and the counter 67 is reset via the AND gate 68, so the content of this counter 67 increases when the spectrum amplitude is large at the f ₀ timing, and the content of the counter _{67 increases when the spectral amplitude is large at the f 0 timing} . When is large, the counter contents immediately become zero. Therefore, if there is a high frequency component, the value becomes zero, and if the _f0 component is large, the value increases. Therefore, by observing the analog voltage _V0 using the D/A converter 40, the contents of this counter can be expressed as follows: It is possible to determine whether the inter-electrode gap condition is good or bad. In other words, if V ₀ is large, it means that abnormal discharge is approaching, and it can be determined that, for example, sludge is accumulating in the gap between the poles due to the retention of machining powder, or that abnormal arc discharge is occurring. . A continuous arc, which can also be called a discharge accident, is when the discharge is concentrated in one point.
In order to prevent the concentration of discharge and disperse it, the best means is to make the discharge slow.

The embodiment shown in FIG. 5 is an example in which the voltage applied to the gap between the electrodes is changed based on the output signal V ₃ , and if the discharge starting voltage is lowered, the discharge becomes harder.
Concentration of discharge in the same discharge gap can be prevented. Furthermore, when there is no discharge concentration, by increasing the voltage applied to the gap between the electrodes, it is possible to increase the ease of discharge in the same discharge gap.

Reference numeral ₄₁ in FIG.
This is an amplifier for amplifying the signal and applying it to the oscillator 100 that controls the signal. Now, the voltage V _g applied to the gap between the electrodes is expressed as follows.

V _g = I _c R ₁ ...(1) Also, I _c is almost equal to the current flowing through the emitter follower load R ₂ of the transistor 51 (about 99%)
This I _c is expressed as I _c =V _E /R ₂ ≒V _B /R ₂ (2). Therefore, V _g becomes V _g = R ₁ /R ₂ V _B (3) from equations (1) and (2). Here R ₁ = 30KΩ, R ₂ = 1KΩ, E =
Assuming 300V, V _B changes from 0 to 10V due to a change of 0 to 10V.
Makes a change of 300V. As a result, when the content of the counter 67 increases due to concentration of discharge, the D/A
The output V ₃ of the converter 40 increases and the pole gap voltage V _g
decreases, and the concentration of discharge disappears.

In the above embodiment, the voltage applied to the gap between the electrodes is continuously changed according to the contents of the abnormal discharge detection counter 67, but the counter contents and the voltage do not necessarily have to have a proportional relationship, but have an exponential relationship. It has also been confirmed through experiments that changing the temperature to 1 is more effective in preventing arc discharge transfer.

As described above, according to the present invention, an abnormality in discharge is determined based on the frequency spectrum of the discharge waveform, and in addition, in order to normalize the discharge state, the applied value of the pulse voltage applied to the gap between the electrodes is controlled. An electrical discharge machining device is realized.

[Brief explanation of the drawing]

Fig. 1 is a principle diagram showing a conventional electric 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, Fig. 4 is an abnormal state detection and discrimination circuit diagram, FIG. 5 is a circuit diagram for controlling the voltage applied to the gap between the electrodes. 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.

Claims (1)

[Claims] 1. By placing an electrode and a workpiece facing each other with an insulating working fluid interposed therebetween, and applying a pulse voltage of a predetermined frequency to the gap formed by the electrode and the workpiece, In an electric discharge machining device that processes the workpiece by generating an electric discharge between the machining parts, the machining voltage can be determined by detecting the machining voltage when a discharge is generated between the machining parts at a predetermined timing. Among them, a detection means for detecting at least a low frequency component and a predetermined high frequency component corresponding to the frequency of the pulse voltage, and a set low frequency component and a set high frequency component that preset the low frequency component and the high frequency component. If the comparison result of the comparing means and the comparing means is that the low frequency component is smaller than the set low frequency component and the high frequency component is larger than the set high frequency component, the discharge is determined to be normal and the distance between the electrodes is determined as normal discharge. Between poles to judge the state of
An electric discharge machining apparatus comprising: a state determining means; and a control means for controlling the applied value of the pulse voltage based on the state of the inter-electrode gap.