JP2552143B2 - EDM control device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an electric discharge machining control device for always maintaining an appropriate electric discharge machining state in electric discharge machining to improve electric discharge machining efficiency.

[Prior Art] FIG. 4 shows a conventional electric discharge machining control apparatus shown in, for example, mechanical technology (June 1980, Vol. 28, No. 7, pages 25 to 27, published by Nikkan Kogyo Shimbun). It is a block diagram. In the figure, 1 is a machining electrode, 2 is a workpiece, 3 is a machining tank, 4 is a machining liquid, 5 is an electrode driving device for vertically moving the machining electrode 1 for controlling a machining gap, and 6 is an electrode driving device 5. An electrode controller that issues a control signal, 7 is a setter for a reference value that is preset in order to optimally maintain the electric discharge machining state, 8 is an electric discharge state detector for detecting a state quantity that can evaluate the electric discharge machining state, Reference numeral 9 is a filter, and 10 is a processing power source.

 Next, the operation will be described.

In order to realize stable electric discharge machining, it is necessary to always adjust the gap between the work piece 2 and the machining electrode 1 in order to keep the electric discharge state optimum. Therefore, in FIG. 4, the state quantity capable of evaluating the electric discharge machining state is detected by the electric discharge state detector 8 as the inter-electrode voltage, and the detected value is passed through the filter 9 and averaged to obtain the inter-electrode voltage value. , The reference value preset by the command value setter 7 is compared, and the machining electrode 1 is moved downward or upward by the electrode driving device 5 via the electrode controller 6 so that the deviation becomes zero. The position of the machining electrode 1 is controlled.

Fig. 5 shows a typical inter-electrode voltage waveform observed at this time. The time td from the application of voltage to the machining gap until the start of discharge, that is, the no-load time 11, is the machining that floats in the machining gap. It fluctuates irregularly under the influence of the amount of waste and minute unevenness of discharge marks generated on the machined surface.

Fig. 3 shows the probability density function of no-load time observed within a certain period of time. In the figure, 12 is when the above reference value is set large and 13 is when the reference value is set small. Is shown. The mean values 12a and 13a of these probability density functions 12 and 13 are controlled by the reference value, and the respective variances are due to the aforementioned irregular fluctuation. Therefore, it is considered that the conventional control technique for keeping the electric discharge machining state optimal is to optimally control the average value of the no-load time.

In addition, here, the no-load time observed at the time of machining was described, but as the evaluation value of the electric discharge machining state, the average voltage of the machining interval, that is, the average inter-electrode voltage, and the impedance of the machining gap immediately after the start of the discharge are included. The same applies to these.

[Problems to be Solved by the Invention] Since the conventional electric discharge machining control apparatus is configured as described above, as long as the no-load time of each electric discharge fluctuates irregularly, for example, its fluctuation range, that is, dispersion. Considering the value, the reference value must be set within the range where the frequency of short-circuit discharge does not increase, and as a result, the no-load time, in other words, the time during which machining is not performed, increases, and sufficient machining efficiency is obtained. Had a problem.

The present invention has been made in order to solve the above problems, in the electric discharge machining in which there is an irregular disturbance due to the amount of machining scraps and electric discharge marks, of the detected value of the state quantity that can evaluate the electric discharge machining state. It is an object of the present invention to obtain an electric discharge machining control device capable of setting a smaller reference value as compared with the related art by controlling the dispersion value to be small and improving machining efficiency.

[Means for Solving Problems] The electric discharge machining control device according to the present invention detects the state quantity by which the electric discharge machining state can be evaluated by the electric discharge state detector as in the conventional case. In addition to controlling, the irregular fluctuation component included in the detected value is regarded as the output time series of the machining disturbance model, the machining disturbance model is further estimated by the machining disturbance model estimator, and the estimation result is used as the basis. In addition, the variable processing power source is controlled so that the dispersion value of the detection value becomes small by configuring the dispersion controller of the detection value. That is, the electric discharge machining control device of the present invention includes a discharge state detector that detects any one of the following state quantities capable of evaluating a discharge state, and an irregular electric transformation included in a detection value of the discharge state detector. A machining disturbance model estimator that estimates the machining disturbance model when the component is regarded as the output time series of the machining disturbance model, and is configured to control the variance of the detected value based on the estimation result of the estimator. And a variable machining power source controlled by the variance value controller, wherein the variance value controller varies the superimposed voltage value or the slope of the superimposed voltage that is superimposed in synchronization with the main power source for machining. It is characterized in that it is configured to.

No-load time of discharge waveform Average voltage of discharge gap, that is, average gap voltage Impedance of machining gap immediately after the start of discharge Here, the introduced machining disturbance model is equivalent to the generally known forming filter. It is assumed that white noise is assumed to be the input of the above, and an output time series having the same dynamic characteristic as the irregular fluctuation component included in the above-mentioned detected value is created.

[Operation] In the electric discharge machining control device according to the present invention, the machining disturbance model estimator estimates the dynamic characteristics of the irregular fluctuation component included in the detection value of the electric discharge state detector, and the variance is estimated based on the estimation result. Since the value controller is configured, the dispersion value controller issues a command to the variable processing power source so as to compensate the above-mentioned fluctuation component, so that the dispersion value of the detected value can be controlled to be small.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention. In the figure, 1 to 9 are the same as those of FIG. 4 showing a conventional example. 15 is a machining disturbance model estimator that estimates the machining disturbance model based on the detection value of the discharge state detector 8, 16 is a variance value controller configured based on the estimation result by the machining disturbance model estimator 15, 17 Is a variable processing power source for controlling the dispersion value of the detection value in the discharge state detector 8 according to the instruction of the dispersion value controller 16.

As mentioned above, the no-load time observed within a certain period of time fluctuates irregularly due to the influence of the amount of scraps and electrical discharge marks,
It has the characteristics shown in FIG. Therefore, consider the electrical discharge machining process model 18 shown in FIG. In the figure, Gv
(Z) is the dynamic characteristic of the machining disturbance model, Gs (Z) is the dynamic characteristic of the no-load time control system by the variable machining power source, r (t) is the target command value of the no-load time, and td ^* (t) is the variable machining. It is a definite value controlled by the power supply 17. Therefore, in the no-load time td (t) observed at the sample time t, the irregular disturbance component w (t) and the deterministic component td ^* (t) described above are algebraic sums.

Assuming that the machining disturbance model Gv (Z) is an AR model and the input is white noise λv (t), the irregular disturbance component w (t) is w (t) = − a ₁ w (t− _{1) -a 2 w (t-} 2) - ... ... -a n w (t-n) + b o v (t) b o = λ or a, w (Z) = Gv ( Z) · v (Z) It can be described as b _o = λ.

However, here, for the sake of simplicity, the sampling period is set as a unit time, and w (Z) and v (Z) are w (t) and v (t), respectively.
Is Z-transformed.

The machining disturbance model estimator 15 uses the N detection values {td (t) | t = 1,2, ... N} obtained from the discharge state detector 8 and uses the above-mentioned AR model parameter θ = [a ₁ , a ₂ , ... a _n ,
b _o ] ^T is determined by least-squares estimation or maximum-length estimation.

Further, the order n of the AR model is determined so that the information amount reference AIC defined by the following equation is minimized.

AIC = N · log _e σ _n ² + 2 · n where n is the order, N is the number of data, and σ _n ² is the variance of the estimation error.

Based on the above estimation results, the variance value controller 16 is configured according to, for example, the minimum variance control theory.

The variable machining power source 17 reduces the no-load time according to the command value of the dispersion value controller 16, for example, by increasing the superimposed applied voltage value, and conversely increases the no-load time by reducing the superimposed applied voltage value. Then, the detection value is operated so that the variance value becomes smaller.

In electrical discharge machining, machining power supply conditions vary depending on the types of rough, medium, and finish machining, and the machining depth changes as the machining progresses.
Since the machining area changes, the dynamic characteristics of the machining disturbance model are not always constant. Therefore, in the configuration of the variance value controller 16, the machining disturbance model is estimated in advance for various machining conditions, and the variance value controller corresponding to each condition is obtained, or The estimation of the machining disturbance model and the calibration of the variance value controller may be appropriately performed for each cycle.

According to the electric discharge machining control device configured as described above,
As shown in FIG. 3 in comparison with the conventional case, the probability density function 14 in the no-load time of the present invention can control the variance value to be smaller than the conventional probability density functions 12 and 13, and the frequency of occurrence of short circuit discharge. It is shown that the average value 14a can be set to be small without increasing, and therefore, improvement of the possible efficiency can be realized.

Although the AR model is assumed as the machining disturbance model in the above embodiment, an ARMA model as in the following equation may be assumed.

_{w (t) = - a 1} w (t-1) -a 2 w (t-2) - ... ... -a n w (t-n) + b o v (t) + b 1 v (t-1) + _{... + b m v (t-} m) or a, w (Z) = Gv ( Z) · v (Z) Further, in the above embodiment, the case where the discharge state is detected by the no-load time has been described, but it may be the state quantity of the above-mentioned average inter-electrode voltage or the impedance of the machining gap immediately after the start of the discharge. Has the same effect.

Further, also with respect to the variable processing power source, the slope of the superimposed applied voltage may be variable instead of the case where the superimposed applied voltage value is variable, and the same effect as that of the above-described embodiment is obtained.

[Effects of the Invention] As described above, according to the present invention, the state quantity capable of evaluating the electric discharge machining state is detected, the irregular fluctuation component included in the detected value is supplemented by the machining disturbance model, and the dispersion of the detected value is detected. Since the electric discharge machining control device was configured to control the value small,
It becomes possible to set a smaller reference value than before,
The electric discharge machining efficiency can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a block diagram of an electric discharge machining process assumed in the present invention, and FIG. 3 is observed within a certain time in a conventional example and an embodiment of the present invention. FIG. 4 is a diagram comparing probability density functions of no-load time, FIG. 4 is a block diagram of a conventional example, and FIG. 5 is a diagram showing a typical inter-electrode voltage waveform in electric discharge machining. 8 ... Discharge state detector 15 ... Machining disturbance model estimator 16 ... Variance value controller 17 ... Variable machining power source In the figures, the same symbols indicate the same or corresponding parts.

Claims (1)

(57) [Claims] 1. A discharge state detector for detecting any one of the following state quantities capable of evaluating a discharge state, and an irregular fluctuation component included in a detection value of the discharge state detector for a machining disturbance model: A machining disturbance model estimator that estimates the machining disturbance model when considered as an output time series, and a variance value controller configured to control the variance value of the detected values based on the estimation result of the estimator A variable machining power source controlled by the variance value controller, wherein the variance value controller is configured to vary the superimposed voltage value or the slope of the superimposed voltage that is superimposed in synchronization with the main power source for machining. An electric discharge machining control device characterized in that No-load time of discharge waveform Average voltage of discharge gap, that is, average gap voltage Impedance of machining gap immediately after the start of discharge