JPS594250B2 - Device for determining the quality of electrical discharge pulses in electrical discharge machining - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention examines the quality of each discharge in electrical discharge machining, that is, normal or abnormal discharge, and the presence or absence of high-frequency components contained or weighed in the discharge voltage of the machining gap, the discharge current, or the gap impedance during discharge. Alternatively, the present invention relates to an improvement of a device for determining the quality of discharge pulses in electrical discharge machining, which detects and discriminates based on the content level.

It has been known that the discharge voltage, discharge current, or gap impedance during normal discharge includes a high frequency component of about 10 MH2. To explain this with a diagram, Figure 1 shows an enlarged voltage waveform diagram of the discharge that occurs when a pulse voltage is intermittently applied to the machining gap between the electrode and 10 workpieces with a rest period. D is the time when pulse voltage application starts, which occurs relatively often during normal discharge. Period 1 until the discharge start point tl
The no-load voltage portion A of 5 is a discharge voltage waveform of normal discharge and continues from the discharge start point to a more desired set discharge duration, that is, the pulse end point 2. B is a discharge voltage waveform of defective or abnormal discharge such as arc discharge, and in this case, the no-load voltage 20 portion D often does not appear. Further, C is a voltage waveform at the time of a gap short circuit, and in this case, the above-mentioned no-load voltage portion usually does not appear. However, in the case of a normal discharge, the discharge voltage waveform (in the case of a discharge current, the discharge current waveform) during the discharge has a waveform of 25% as shown in waveform A in Figure 1.
Usually, high frequency components of about 10 MH2 or so, which constantly change and have an undefined frequency, appear in a superimposed manner. That is, the discharge voltage waveform constantly oscillates at the above-mentioned high frequency, and the discharge voltage constantly changes at high frequency.

On the other hand, in the case of abnormal discharge such as arc discharge, the first
As shown in waveform B in the figure, perhaps because the discharge column is in a safe state of arc discharge, there is no superimposition of high frequency components as in the case of normal discharge, in other words, there is no high frequency vibration in the discharge voltage waveform, and the discharge voltage waveform is almost constant linear. It becomes a waveform. Therefore, whether or not the above-mentioned high frequency components are included or appear in the discharge voltage or discharge voltage waveform during the discharge 95 of each pulse discharge, whether the magnitude (level) is large or small, or whether it is above or below the desired level is determined. By detecting and determining whether the discharge belongs to the above, it is possible to know whether the discharge is a desired normal discharge or an arc or other abnormal discharge. In this way, a capacitor or an appropriate filter is used to detect and determine the presence or absence of a high frequency component in the discharge voltage and its content level. The relatively low frequency voltage change component is cut off to detect the high frequency voltage component, and if necessary, it is rectified and taken out from the resistor terminal, or if necessary, it is integrated and taken out. Some signals are appropriately amplified and used as control signals for various control systems used in electrical discharge machining.

Most commonly, a method is adopted in which high-frequency waves are detected from the voltage in the machining gap at all times during machining. The force is extremely large compared to the force of the high frequency component generated during the discharge after the start of the discharge, and the high frequency generated at the start of the discharge is a pulse voltage even if the discharge due to each machining pulse is a defective discharge such as an abnormality. After the rest time, a voltage pulse is applied, and as the voltage is applied, an abnormal discharge such as an arc starts, so even though the power of the high frequency component generated at the start of the discharge is weak,
The above-mentioned high frequency components are generated to some extent and die, so that not only is it impossible to accurately determine whether a discharge pulse is good or bad without noise, but also a control signal suitable for performing desired control cannot be obtained. In addition, although the above-mentioned method of detecting high-frequency components by cutting off a capacitor, etc., has a relatively simple circuit configuration, it requires constant detection and discrimination operation, not to mention during the pulse voltage application period including during discharge as described above. Since it continues, it is not possible to detect or even prevent noise input, and it is difficult to distinguish pulsed discharges that transition to abnormal discharges in the latter half after the middle of discharge, so accurate detection and discrimination is expected. I couldn't do it. In addition, when detecting the high frequency component superimposed on the discharge voltage etc. to determine the quality of each discharge as described above, discharge is started to prevent noise from being mixed in due to instability of discharge at the time of discharge start. It is necessary to output a check pulse that defines a predetermined detection period after a certain time delay when the discharge state is stabilized, and to perform detection and discrimination only during the period of the check pulse, but the configuration is complicated and the machining pulse width is limited. Under conditions where the distance is not very wide, a sufficient delay time after the start of discharge cannot be taken, and it is also not possible to change the delay period etc. depending on the machining conditions, making accurate detection impossible.

Furthermore, with such conventional detection methods, it is not possible to detect a transition to a defective discharge in the middle of a discharge, such as after the end of the check pulse described above, and as a result, the control operation may be delayed or the application of the next machining voltage pulse may be delayed. Alternatively, there are disadvantages in that the deterioration of the gap condition is only known after detection and discrimination based on the discharge caused by the pulse. Taking these points into consideration, the present invention includes a DC power source for machining, a switching element that supplies machining pulses to the machining gap by an on/off switch connected in series to the power source, and a switching element that controls on/off operation. In a discharge pulse quality determination device of an electrical discharge machining machine equipped with a time device that supplies a pulse signal, the discharge pulse voltage in the machining gap is actuated by an on end signal or an off start signal of a switching element outputted from the time device. , discharge current,
Alternatively, a device is provided that detects and determines the presence or absence of a high frequency component superimposed on the impedance.

However, detection discrimination based on the presence or absence of high frequency components as described above does not require switching the detection level, amplification degree, etc. depending on the processing conditions as much as, for example, voltage level detection discrimination, or there is no need to switch between normal discharge and high frequency components. This method is effective because it can accurately and reliably distinguish it from almost zero arc discharge. The apparatus of the present invention will be explained below with reference to the block diagram of one embodiment shown in FIG.

First, VG is a signal input terminal to which a voltage signal of the discharge gap is input, and the signal is input to both terminals of the operational amplifier 0P via a resistor R1. The voltage signal detected at the input terminal VG is input as is in the same phase to the + side input terminal, but since the resistor R1 and capacitor C1 are provided at the one side input terminal, a delayed signal corresponding to the capacitance of the capacitor C1 is input. input. Also, one side input terminal and output terminal A1
A resistor R2 is provided between the output terminal A1 of the operational amplifier 0P, and a signal in phase with the input detection signal from the terminal VG, and a delayed signal having a delayed phase difference. The sum (in this case, subtraction) of is created and output.

If the discharge based on the application of a pulse voltage is a normal discharge and the discharge voltage contains a high frequency component, a signal is output to the output terminal A1 of the operational amplifier 0P, but if it is an abnormal discharge such as an arc discharge, a signal is output. No signal is output during discharge other than at this point.

Figures 3A and 3b show VG, Al, A2, BO, BIyB2F, which are shown in Figure 2 to explain the operation of the circuit in Figure 2.
B3FM29Ml9O2E01 These are waveform diagrams showing the voltage signals of each terminal in the same time phase, where FIG. 3a shows the case of normal discharge and FIG. 3b shows the case of abnormal discharge such as arc discharge.

As mentioned earlier, in the present invention, discrimination is made by detecting whether or not a high frequency component is included at a predetermined level or higher, so the detection and discrimination time point may be before or after the time of application of the pulse voltage, or before or after the time of applying the pulse voltage. It is at least not preferable to select a time before or after the time when discharge starts after the application of the pulse voltage. In addition, the point at which the discharge starts is undesirable in this sense because a high frequency component is generated due to the start of the discharge, regardless of whether the start of the discharge is simultaneous with the point of application of the pulse voltage or delayed. A desired period is selected from the period from the time when the discharge starts in the gap until the end of the discharge after a certain period of time.

However, in this type of apparatus, electrical discharge machining is performed by intermittent discharge by applying a pulse voltage having a constant or undefined pulse duration to the machining gap after a desired rest time by turning on and off an electronic switch element such as a transistor. In such a device, even after the on-gate signal to the switch element is turned off, the switch element remains open for several μ8.
Although it is a very short period of time as described below, there is a slight period in which the discharge continues even after the gate-on signal ends, such as continuing to be on for a short period of time following the period in which the gate-on signal was applied, and then turning off.

In other words, this is due to the turn-off time due to storage time in semiconductor switching elements such as transistors and silicon-controlled rectifier elements, and the operating rated voltage and current used for machining pulse shaping in electrical discharge machining are on the order of tens of thousands. In normal semiconductor switching devices of several amps or more, the above turn-off time is around several μs, and these trends and characteristics are almost the same in other switching devices such as electron tubes. be. The present invention focuses on this point, and the detection period of the presence or absence of high frequency components contained in the discharge voltage etc. or the level of the contained components is determined such that the discharge ends after the gate on signal of the switching element ends or the gate off signal starts. or a predetermined short period from the time of the on-end signal (or the off-start signal) to the end of the discharge in the gap, thereby detecting the on-end signal or the off-start signal of the switching element. It can be used as it is as a signal to start the operation or detection period, so there is no need to change or switch even if the processing conditions such as pulse width are changed, and there is no need to change or switch abnormal discharge during the period from the middle to the end of the discharge. It has become possible to obtain advantages such as being able to reliably detect and discriminate even pulsed discharges that have shifted to . In FIG. 2, the output of the operational amplifier 0P outputs the signal shown in FIG. 3 AOAl to the output terminal A1 in the case of normal discharge.
The output is applied to one input terminal of the AND circuit AND, and the other input terminal of the AND circuit AND is connected to the terminal B1.
A signal is input from the on-gate signal when the on-gate signal is turned off.

In this case, terminal B. is an input terminal for the on-gate signal, and the on-gate signal is input to the timer T1.
1 is configured to output a signal to the output terminal B1 when the on-gate signal becomes O. Also, S provided before the AND circuit AND is a sense amplifier for amplification and waveform shaping. Dual trigger circuit and IC. Channel. sense. Amblyfire etc. are used. In this way, if the discharge in the gap is normal, when the on-gate signal disappears, the output terminal A2 of the AND circuit M1 will release the
A signal is output with a pulse width before and after, and the output signal is
Enter 4. The signal at the other terminal B1 is also input to the timer T2, and a signal for operating the timer T2 and operating the timer T3 and the timer T4 is input from the terminal B2 to, for example, 0.
．． It is output as a pulse signal of about 6 μs. Timer T4
is operated by signal input from terminals A2 and B2, and inputs output signals from two output terminals M1 and M2 having mutually opposite phases to one terminal of NAND circuits NAND and NAND2. Each of the NAND circuits NANDl,NA
A pulse with a minute pulse width, for example, a check pulse with a pulse width of 0.2 μs is inputted from the timer T3 to the other terminal of the ND2 from the terminal B3 at the time when the operation of the timer T2 ends;
A logic circuit composed of two opposite phase output terminals M1 and M2 of timer T4 and two NAND circuits NANDl and NAND2 is used to detect high frequency components in the analog quantity signal of the gap during discharging, such as the discharging voltage. A pulse signal, that is, a pulse signal indicating a normal discharge, is output from the output terminal 02 of the NAND circuit NAND2, and if the high frequency component is not included due to an abnormal discharge such as an arc discharge, the other pulse signal is output as shown in Fig. 3b. Terminal 01 of NAND circuit NANDl
A pulse signal, that is, a pulse signal indicating abnormal discharge is output. Therefore, the second method for achieving the above object of the present invention is as follows.
Specific examples of each active element in the block diagram are as follows. The operational amplifier 0P is a so-called linear IC, and is manufactured by Teledyne Corporation 1322, Sense. Similarly, the amplifier fire S and the AND circuit AND are also called 1.
The timer Tl, , T2, T3, and T4 are all digital ICs manufactured by Texas Corporation (<7) SN74l2l, and the NAND circuit NANDl,2 using a part is manufactured by Texas Corporation. SN74O
It is O.

The switching element that forms the machining voltage pulse is a transistor 2SC558 (maximum rating VCE: 100V, I
c: 5A, electrical characteristics TOffMAX: 4.0μs) are used in parallel, and the machining pulse conditions are, for example, no-load voltage: 80V1 discharge current pulse width: 4001ts voltage pulse rest width: 50μs, discharge current amplitude, 80A It is processed as FIG. 2A shows details of one design example of the input/output portion of the operational amplifier 0P, and a specific example of circuit element constants is as follows.

Resistor R1: 5KΩ R2: 200KΩ R3: 1KΩ R4: 10KΩ R5: 2KΩ R6: 50Ω Capacitor C: 0.001 μf An amplifier is inserted between the output of resistor R5 and the subsequent stage, if necessary.

Further, the CR time constants of the timers T1, T2, T3, and T4 are appropriately set according to the pulse width of each timer output described above, such as R=1.8KΩ and C=1000PF in the timer T4. Since the repetition of discharge in the discharge gap is usually at a high frequency of 1 KHz or more, the output terminal 0
, and 02 to obtain a control signal by displaying or determining whether the discharge state of the gap is normal, good, or abnormal, for example, from each output terminal 01.
02 and 02, and compare the counts of both counters at predetermined time intervals, or set the counter provided corresponding to terminal 01 to output a signal based on 4 counts. On the other hand, the counter provided corresponding to terminal 02 is set to output a signal by counting 8 pieces, and before the latter counts 8 pieces, the former one counts 4 pieces.
Alternatively, the terminal B may be configured to output a control signal to a control system that indicates that the machining condition is bad or eliminates the defective machining condition by counting the number of pieces. , Bl, B2, and B3, the on-gate signal of the pulse voltage is counted by a counter, and the count number of the on-gate counter and the count number of at least one of the counters provided at the output terminals 01 and 02 are calculated. By adding the signal output according to the comparison or each set count number to the logic operation circuit, it can be used as desired, such as for detecting or determining the discharge state that occurs during the application period of two or more pulse voltages, or for controlling based on the determination. can. According to the present invention, as described above, normal discharge and abnormal discharge such as arc can be reliably detected and distinguished for each discharge, and even when changing the type or combination of electrode workpieces or machining condition settings, etc. There is no need to change the detection level settings as in the case of discrimination by detecting the discharge voltage value, but for example, even if a short circuit discharge can be detected and determined, a short circuit requires immediate elimination, so short circuit detection is performed separately. There is nothing that precludes the provision of a separate detection and control device for discharge gap conditions that are different from the detection and discrimination of the present invention, such as attaching a device and separately outputting a control signal for protection against short circuits to perform necessary control. isn't it. The above embodiment detects the analog quantity as a means for detecting the weight or high frequency component contained in the analog quantity during discharge of the machining gap, such as discharge voltage, discharge current, or discharge gap impedance,
A signal having a phase difference with the analog quantity signal is created by delaying (or leading) the detected analog quantity signal, and then a difference (or sum) between the analog quantity signal and the signal having the phase difference is created. The present invention is configured to determine the presence or absence of the high frequency component based on the presence or absence of the difference (or sum) signal, but conventionally known capacitor cut methods and methods using high-frequency pass filters are also applicable. can.

Furthermore, it is of course possible to make various design changes without departing from the spirit of the present invention, such as sampling and detecting the machining pulses to be detected, for example every three pulses, in carrying out the present invention. .

As described above, the present invention uses the signal as a trigger to determine whether or not there is a high frequency component contained in the discharge voltage, etc., to determine the condition or quality of the discharge in the machining gap after the signal that terminates the discharge in the gap is obtained. It is designed to discriminate based on the level, and as mentioned above, it is a new and useful detection/discrimination method.

[Brief explanation of the drawing]

Fig. 1 is a discharge waveform diagram based on pulse voltage application during electric discharge machining, Fig. 2 is an example block diagram of the apparatus of the present invention,
Figure 2A is a detailed circuit diagram of one design example, Figures 3A and b are the second design example.
FIG. 2 is a waveform diagram for explaining the operation of the device. 0P is operational amplifier, S is sense, amplifier fire, T
l, T2, T3, T4 are timers, AND is an AND circuit,
NANDl and NAND2 are NAND circuits.

Claims (1)

[Claims] 1 DC power supply for processing and a power supply connected in series to the power supply and turned on.
In an apparatus for determining whether a discharge pulse is good or bad in electric discharge machining, the device includes a switching element that supplies a voltage pulse to a machining gap by off-switching, and a time device that supplies a control signal for on/off operation to the switching element. a detection device that outputs a detection signal by determining the presence or absence of a high frequency component included in the discharge voltage, discharge current, or gap impedance during discharge generated by the voltage pulse application; and a control signal output from the time device. A device that generates a pulse signal in synchronization with an on end signal or an off start signal of a switching element, and a logic circuit to which the generated pulse signal of the pulse signal generator and the output detection signal of the detection device are input, An apparatus for determining whether a discharge pulse is good or bad in electrical discharge machining, comprising a determining circuit that outputs a signal indicating whether the discharge pulse is good or bad depending on the presence or absence of the detection signal.