KR950002091B1 - Arc preventing method by the classification of monitering pulse - Google Patents

Abstract

The method classifies electric voltage or current wave shapes generated from EDM (electric discharge machinning) process, and prevents the electric arc by use of the wave shape classification result. The method comprises a step of obtaining signals of more than set values corresponding to electric arcs by comparing the voltage/current wave with the predefined values; a step of using an electric discharge clock and a logic combination signal as a gate signal of an electric discharge current control semiconductor. The method prevents damages resulting from the arc or disconnection, and improves working efficiency.

Description

Arc prevention method by classification of discharge processing waveform

1 shows a schematic discharge waveform. The upper half of the figure shows a discharge current waveform, and the lower half shows pulses of an EDM clock (see text).

2 shows the temporal position of the sampling pulse for the discharge clock (EDM clock). It is always located at the beginning of the ON period. The upper half of the figure shows an EDM clock, and the lower half shows a monitoring pulse.

3-1 shows a logic table illustrating the principles of the present invention.

FIG. 3-2 is the same as FIG. 3-1.

4-1 show the results of one embodiment. The upper half of the figure shows the discharge current, and the lower half shows the arc generation signal by the monitoring pulse.

4-2 show some of the effects of the present invention, the upper half of the figure shows a discharge current and the lower half shows an EDM clock.

The present invention relates to a method of classifying a waveform of a voltage or current wave generated during electro discharge machining (EDM) and a method of preventing the generation of arc by using the result.

In the past, a number of methods designed for monitoring the occurrence of harmful arcs have been proposed. The application of arc is determined by the voltage drop between the discharge electrodes or the increase in the average current, and appropriate measures are taken to prevent arc. For example, the effect was increased by increasing the OFF TIME.

The fundamental difference between the present invention and the conventional method is characterized by the following two points. That is, firstly, it is determined whether or not arcing is performed in pulse units every discharge pulse, and the following is different from the conventional method in that appropriate measures are taken before the pulse unit ends. In other words, the measurement, classification, and adjustment are performed at the same time every pulse unit.

Hereinafter, the present invention will be described.

It is mainly used as a method for monitoring the state of the discharge machining, such as analyzing the radio frequency generated during the discharge spark, measuring the electrical resistance between the electrode wave processing object, or analyzing the discharge waveform There are methods to do this, and it can be said that the waveform analysis method is preferred. To date, a summary of the research on the discharge processing waveform analysis method is as follows. S. Snoeys, CIRP vol 24, 1974, S. Bhattacharyya, ASME J. of Eng. Ind., 1980, M. Otto, ISEM 7, 1983, A. Endel , ISEM7, 1983), P. Dand (S. Pandit, ASME J. of Eng. Ind., 1984), D. Dauw, CIRP vol 35, 1986), P. Dand (S. Pandit, ASME J. of Eng. Ind , 1987), and Cogun (C. Cogun, ASME PED vol 31, 1988) have performed waveform analysis and related studies.

A significant difference between the gist of the present invention and the results of the above published studies is that the method of using the waveform classification results for arc prevention has been devised. In order to facilitate understanding of the advantages, briefly described published facts about discharge waveforms during discharge processing will be described.

In general, there are four types of voltage or current waveforms (voltage = current X resistance) that occur during Transistorized pulsed discharge machining (hereinafter referred to as "discharge machining"). Randomly), that is, normal or effective discharge or spark, arc, short, and open waves (see FIG. 1). Among them, the pygo-open wave, which is effective only in standing waves, is not preferable because it lowers the processing efficiency, and short-circuits and arcs are not preferable because they can damage the workpiece as well as the processing machine if they last for a long time. Therefore, if the above four waveforms can be classified as fast as possible, they can greatly contribute to monitoring the discharge machining status.

According to the present invention, when the arc generation signal or the short circuit generation signal is generated by classifying the above waveform, the discharge power supply is immediately supplied (Note: the arc generation signal is always located at the leading edge of every cycle. One unique method of blocking only a few percent of or during the due cycle, and its use.

Hereinafter, the present invention will be described in more detail.

In the present invention, a current waveform is used, and a waveform classification and a method of preventing side effects due to arc or short circuit using the same are described (voltage waveform description is the same).

First, when the discharge waveform is generated, processing by discharge means applying a constant DC pulse voltage between the workpiece and the electrode separated at a suitable distance with a dielectric (mainly used for hydrocarbons such as diesel). Spark is generated by the condition. This energy causes part of the workpiece to melt and evaporate, and part of it is scattered by the explosive evaporation pressure of the surrounding dielectric. As a result, a few discharge craters are formed in the workpiece, and processing is performed by their average accumulation. At this time, the waveform of voltage or current can be sampled. However, depending on the conditions, there is no guarantee that only a flame discharge will occur each time. For example, when the gap is large enough, an open wave is generated and practical processing is not performed at all. If the distance is too close, a short wave is generated and machining is not performed again. In addition, due to excessive turbidity of the dielectric or other reasons, the local electrical resistance is smaller than that of other parts, and the discharge may be concentrated in one spot, which is called arc. Generally, the electric discharge machine is designed and manufactured so that only stationary or semi-normal waves can be generated, but realistically, several to tens of percent of invalid and harmful waves are generated.

For the purpose of the next discharge waveform classification, the main purpose of the classification is to monitor the discharge machining state to distinguish between good and bad condition. In addition, this information can be used for self-control. In the present invention, by blocking the power supply in the event of arcing or short circuit occurs to protect the workpiece and the discharger at the same time.

In the following rough classification method, a discharge waveform is received within a predetermined sampling period and compared with a variable voltage (Variable) adjusted to an appropriate voltage range and a set voltage (Reference) of a predetermined size by a preconfigured circuit. In the present invention, the set voltage is set to a high level and a low level. The potential setting range is 95 to 99 percent of the peak of the current wave at the top and 25 to 90 percent at the bottom.

Regarding the determination of the next sampling time, the discharge waveform is a waveform in which a cycle consisting of an on time and an off time is composed and repeated regardless of the type. In the present invention, the above variable voltage (Variable) is sampled only at the start of the circuit opening (see FIG. 2). In addition, even when the monitoring pulse (Sampling pulse) for sampling is changed by the computer's own main clock and the ON-OFF signal length for discharge is changed randomly, it is ON time without any problem. To always occur in the same location.

With respect to the following logic chart, the logic diagram shows the logic of the present invention, which logic structure detects arc waves in the discharge waveform, and once the arc waves are detected, the logic power blocks the discharge power immediately. To explain. Two methods for discharging power are presented. In other words, the blocking period is described as being invariant and variable.

W shown in FIGS. 3-1 and 3-2 represents a discharge current waveform (Variable, hereinafter referred to as an input signal), H is a preset reference high potential, 95 to 99 percent of the maximum input signal value, and L is Similarly, the low level is displayed and is set at 25 to 95 percent of the maximum input signal. The current waveforms show only five representative waveforms for ease of explanation. Also, parts not directly related to the present invention are omitted.

From the left side of the figure, it is normal waveform, open waveform, arc waveform, short waveform, and semi-normal waveform. The dotted line in the figure is the original input signal waveform, and the solid line indicates the modified part because the power is cut off according to the present invention. That is, when arcs and short circuits occur, it can be seen that according to the present invention, the arcs and short circuits are blocked as a result of the modification.

It should be noted that the voltage waveform is the opposite of the current waveform.

It should be noted that the normal and seminormal waveforms are very similar. It is also worth noting that the actual machining in these waveforms is only part of the normal waveform, the seminormal waveform, and the arc.

Here, in the case of invariant blocking, signal (2) in the figure shows the logic signal when the input signal is higher than the low level.

Reference numeral 14 denotes a signal of an EDM clock, and the on-off size may change freely depending on the operation state of the discharger.

(6) shows the sampling pulse which occurs continuously in the sampling circuit and is always located at the beginning of the above (14). (Tsuly, Timing IC 8254 is often used.)

(9) shows the AND logic signal of (2) and (6), which is a signal which proves arc generation.

(17) is an inversed Q or Q bar inputted to D-flipflop D with the above signal (2) and (6) as the clock.

(15) shows an AND logic signal of (14) and (17), indicating that all parts of the on time become low level at the time of arcing. That is, if the discharge power is controlled using the signal 15, it can be seen that the discharge power is automatically stopped at the time of arcing.

In the case of cutoff variable, signal (2) in the figure shows the logic signal when the input signal is higher than the low level.

Reference numeral 14 denotes a signal of an EDM clock, and the on-off size may change freely depending on the operation state of the discharger.

(6) shows sampling pulses that occur continuously in the sampling circuit and is always located at the beginning of the top 14 (often a Timing IC 8254 is often used).

<9> represents an AND logic signal of <2> and <6>, and is a signal for verifying arc generation.

<23> represents the main clock of the computer.

<17> represents a signal outputted by connecting signal <9> to a gate of a down-counter (down IC, for example, IC 8254) which uses signal <23> as a clock. The down count size is set by the computer program.

<15> is an AND logic signal of <14> and <17>, and indicates that the entire portion of the on time becomes low during arcing. In other words, it can be seen that the discharge power is automatically stopped when the discharge power is controlled using the signal <15>.

Characteristic here is that as described above, the input signal is sampled at the beginning of every cycle ON using the signal &lt; 6 &gt;, and the signal &lt; 15 &gt;

Examples of the present invention are as follows.

EXAMPLE

Discharge current signal of the electric discharge machine driven by a square wave with one cycle of 50 microseconds and an ON time of 30 microseconds is transmitted to a device having a waveform analysis function. signal). At this time, to confirm whether the discharge current waveform is an output (Off state), the above two signals were recorded at the same time with an oscilloscope. 4-1 shows the result. As shown in FIG. 4-1, it is apparent that a part of the discharge current is not supplied in the period in which the arc monitoring signal is present. The reason why the interruption period is not constant is because of the break down delay caused by the dielectric.

As described above, the effect of the present invention was smoothly performed even under adverse conditions in which arc was continuously generated as shown in FIG. 4-2.

It can be seen that the desired purpose can be achieved by inputting the signal 15 to the gate of power transistor (Gate of power transistor). In other words, if the arc or short signal sent by the discharge waveform analyzer is modified by AND logic combination as the signal 15 by the logic circuit as described above, the arc or short circuit always occurs when an arc or short circuit occurs. Discharging becomes impossible. The conclusion is that an electric discharge machine can be constructed that does not cause damage due to arcs and short circuits. Therefore, it is possible to make an electric discharge machine having the following advantages. In other words, there is no damage by arc, and the processing time can be improved by reducing the OFF time extremely.

Claims (2)

The voltage or current waveform generated during pulsed discharge machining is set at 25 to 95 percent of the peak value of the dynamic current wave at the high level of the sampling pulse that occurs early in the circuit ON time. After acquiring a one-to-one correspondence to arc as a signal that is above the setpoint value compared to the pre-potential potential, the watchdog wave is clocked, flip-floped, and the EDM clock and (AND). A method for preventing arcing by classifying an electric discharge processing waveform, comprising a logic circuit characterized in that arc current flow can be prevented by using a logic-coupled signal as a gate signal of a discharge current control semiconductor. ＂ In pulse type discharge processing, a signal that is higher than or equal to the set value compared with the set level set at 25 to 95 percent of the peak of the same current wave at the high level of the supervisory wave generated at the beginning of the circuit ON time. After a one-to-one correspondence with arc, the trigger triggers the gate of the pre-set down counter as the signal, and combines the output of the counter with the EDM clock and the logic of AND. A method for preventing arcing by classifying an electric discharge processing waveform, characterized by comprising a logic circuit characterized in that arcing or short-circuit current flow can be prevented by using a signal as a gate signal of a discharge current control semiconductor.