JPH04289022A - Discriminating method for short circuit state between electrodes of wire electric discharge machine and device thereof - Google Patents

Abstract

PURPOSE:To quickly discriminate a short circuit state between electrodes of a wire electric discharge machine. CONSTITUTION:Interelectrode short circuit state is discriminated by detecting interelectrode voltage of a condenser electric discharge machining circuit. For detection of interelectrode voltage, at every discharge, interelectrode voltage directly before applying succeeding machining pulse is detected, and the device is constituted out of a potential dividing circuit to divide potential, a low-pass wave filter circuit to remove high frequency component from the waveform of output of the potential dividing circuit, a discriminating circuit to compare the voltage of output waveform of the low-pass wave filter circuit with the reference voltage following to a prescribed timing output from a timing circuit and judge to be short circuit state if it is under the reference voltage, and a detection timing pulse generating circuit to set the detection timing of interelectrode voltage directly before generation of the succeeding machining pulse.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for determining the discharge state of an electric discharge machine.

0002

[Prior Art] In conventional wire electric discharge machines, the voltage waveform between the electrodes is used to determine the discharge state between the electrodes. The waveform is classified as a short-circuited discharge waveform, and the generation of machining pulses and the feeding of the workpiece are controlled based on the discharge state.

[0003] Conventional methods and devices for determining the discharge state for performing such control are disclosed in, for example, Japanese Patent Publication No. 58-19408 or Japanese Patent Publication No. 62-10.
There is 7916. All of these mainly detect and control the no-load discharge waveform. In order to accurately detect a no-load discharge condition, it is necessary to measure that no no-load voltage appears for a relatively long period of time, equivalent to several cycles of the duration of the electrical discharge machining pulse, and to detect the short-circuit discharge condition. Similarly, detection is also carried out by making measurements over a relatively long period of time. That is, in the conventional technology, a method of integrating the discharge waveform between the electrodes and comparing it with a reference voltage has been used to detect a short-circuit discharge state.

0004

[Problems to be Solved by the Invention] However, different from determining a no-load discharge state, determining a short-circuit state does not necessarily require long-term measurement. Furthermore, if the short-circuit condition is left unattended, the discharge voltage will not rise and discharge machining will not be successful. Therefore, the longer it takes to detect a short-circuit condition, the longer the avoidance of the short-circuit condition will be delayed, and the machining time will increase. Therefore,
The present invention aims to determine whether the discharge waveform between electrodes is a short-circuit waveform for each machining discharge, quickly avoid a short-circuit state, reduce machining interruption time, and increase machining efficiency.

[0005]

[Means for Solving the Problems] In order to solve the above-mentioned problems, the method of the present invention provides a method for determining the inter-electrode state of a capacitor electric discharge machining circuit having a switching control section.
Immediately before applying a processing pulse to the switching control section, a timing pulse is generated, and while the timing pulse is being output, the voltage level between the electrodes is detected, and the voltage level between the electrodes is compared with a reference voltage. It consists of a method for determining the short-circuit condition between.

[0006] In order to solve the above problems, the device of the present invention has the following features:
An interelectrode determination device that determines the interelectrode state of a capacitor discharge machining circuit that has a switching control section includes a voltage divider circuit that divides the discharge voltage between the electrodes, and a low-pass filter that removes high frequency components from the output of the voltage divider circuit. circuit, a discrimination circuit that compares the output voltage of the low-pass filter circuit with a reference voltage and generates a short circuit signal if the voltage is below the reference voltage, and a processing command signal from the control unit installed in the electrical discharge machine. It consists of a machining pulse generation circuit that generates machining pulses and applies the pulses to a machining power supply circuit, and a detection timing generation circuit that generates a detection timing pulse for the discrimination circuit immediately before the rise of the machining pulse.

[0007]

[Operation] The operation of the present invention utilizes the following phenomena and facts. In a wire electrical discharge machine that has a capacitor discharge circuit with switching control, when the electrodes are short-circuited, the voltage level between the electrodes after a predetermined period of time after discharge is either effective discharge or no discharge. The voltage level is lower than that under load. Further, in a capacitor discharge circuit with switching control, charging and discharging of the capacitor is performed at regular intervals.

[0008] Based on the above reasons, the method of the present invention sets the detection timing immediately before applying the next processing pulse after a predetermined time has elapsed after applying the processing pulse to the gate of the switching control section. Generates a pulse, uses this detection timing pulse to activate the gate of the circuit that detects the voltage after discharge between the wire electrode and the electrode of the workpiece, and compares the detected voltage with a predetermined reference voltage. and determines whether there is a short circuit between the electrodes.

The device of the invention operates as follows. The voltage between the wire electrode and the workpiece is detected by a voltage divider circuit, the voltage is divided, and then the divided voltage waveform is input to a low-pass filter circuit, and the output waveform from the low-pass filter circuit is Input to the discrimination circuit. A discrimination circuit compares the measured voltage waveform with a reference voltage, and when a short circuit condition is detected, a short circuit signal is applied to the control section. The control unit avoids the short circuit condition based on this short circuit signal,
When effective electrical discharge machining can be performed, a machining command signal is applied to the machining pulse generation circuit. The machining pulse generation circuit generates machining pulses based on the machining command signal,
It is input to the processing power supply circuit and a detection permission signal is applied to the detection timing generation circuit. The detection timing generation circuit generates a detection pulse based on the detection permission signal and applies it to the gate circuit of the discrimination circuit to enable discrimination.

0010

[Embodiment] An embodiment of the present invention will be described with reference to the drawings. The circuit shown in FIG. 2 is an example of an electric discharge machining circuit and a power supply circuit to which the present invention is implemented. The discharge circuit 1 has a configuration in which a wire electrode 3, a workpiece 5, and a charging/discharging capacitor 7 are connected in series. This discharge circuit 1 includes a stray capacitance 9 due to the lead wire of the wire electrode and a minute inductance 11.
exists. A DC power supply 13, a switching section 15, and a protective resistor 17 are connected in series to the discharge circuit 1 as a charging circuit. The switching section 15 can be composed of one or more transistors or FETs connected in parallel. Continuity of the switch section 15,
Non-conduction is controlled by the machining pulse generation circuit 19.

When the discharge waveform of the discharge circuit 1 is an effective discharge,
FIG. 1 shows the cases of short-circuit discharge and no-load discharge. In order to explain the discharge waveform of FIG. 1, an equivalent circuit 21 of the discharge circuit 1 is shown in FIG. 3(a), and the discharge waveform of this equivalent circuit 21 will be explained.

In the equivalent circuit 21, the resistor r and the switch S are an equivalent circuit between electrodes, the inductance L is a minute inductance included in the wire electrode, and the capacitor C includes stray capacitance. After charging the conductor C with a constant voltage, when the switch S is closed, the interelectrode voltage e
p and the discharge current ip form damped oscillation waveforms (solid line waveforms) shown in FIGS. 3(b) and 3(c). However, when an effective discharge is actually occurring, the insulation between the two electrodes is restored after one or two discharges, and no discharge occurs thereafter, and ep becomes a constant voltage and ip becomes 0.

The actual waveforms of the interelectrode voltage ep and the discharge current ip are more complicated than the response waveforms of the equivalent circuit 21 described above, and are as shown in FIG.

FIG. 1 shows that the switch unit 1
5 shows a discharge waveform when a machining pulse eb having a pulse width tn is added to No. 5. Figure 1(a) shows the case where an effective discharge state continues, ep increases due to charging, drops rapidly when discharge occurs, and after insulation recovery, the interelectrode voltage ep
becomes constant. Figure 1(b) shows a case in which the bulges of the melted parts caused by discharge contact or weld together to form a bridge, resulting in a short-circuited state continuing, resulting in incomplete charging and insulation recovery. Since a portion of the battery is still short-circuited, the interelectrode voltage ep does not rise much even during charging, and gradually becomes 0 because current is constantly flowing. Figure 1(c)
is a case where sufficient discharge is not performed, and the interelectrode voltage ep maintains a high voltage. Note that the actual discharge waveform is a waveform in which a high frequency component due to ringing or the like is included in the discharge waveform described above.

From the above consideration of the discharge waveform, a short circuit state can be determined as follows.

(a) After insulation recovery or after a certain period of time has passed, measure the voltage between the electrodes before charging.

(b) Remove high frequency components from the measured voltage between electrodes.

(c) The measured voltage is compared with a predetermined reference voltage, and if it is less than the reference voltage, it is determined that there is a short circuit.

FIG. 4 shows an apparatus for determining a short-circuit condition. In FIG. 4, the electrode-to-electrode voltage ep of the discharge electrode 23 is detected by the waveform voltage dividing circuit 25, divided, and then passed to the low-pass filter circuit 25.
7. The output of the low-pass filter circuit is applied to the discrimination circuit 29, where it is compared with a separately set reference voltage to determine the state. The determination circuit 29 sends a short circuit signal to the control unit 31 when determining a short circuit state. The control unit 31 issues a processing command signal after avoiding the short circuit state. When the machining pulse generation circuit 33 receives the machining command signal, it generates a machining pulse, applies it to the machining power supply circuit 37, and also applies a detection permission signal to the detection timing generation circuit 35, which generates a detection pulse of a constant width. is the discrimination circuit 29
is applied to FIG. 5 shows the timing relationship between processing pulses and detection pulses. That is, the detection pulse falls just before the processing pulse rises. FIG. 6 shows a specific circuit example.

In FIG. 6, a power supply circuit 39 is for charging a charging/discharging capacitor 39b, and a protective resistor 3
9a, a switch 39c, and a gate circuit 39d. The discharge voltage of the discharge electrode 41 is divided by a voltage dividing circuit 43. The voltage dividing circuit 43 includes voltage dividing resistors 43a and 43b and a buffer 43c. The voltage is divided and the discharge voltage is determined by the low-pass filter circuit 4.
5 removes high frequency components such as noise and ringing. The low-pass filter circuit 45 includes a resistor 45a and a capacitor 45b having appropriate values, and has a limiter circuit 45c. The signal from which the high frequency components have been removed is compared with a reference voltage VREF by a comparator 47a in a discrimination circuit 47. The signal from the comparator 47a is input to the gate 47b, and only when a detection pulse is output from the detection timing circuit 55, a short-circuit state signal is input to the control section 49. The control unit 49 performs control to avoid a predetermined short circuit state,
When the processing becomes possible, a processing command signal is issued, and at the same time, the counter 53a of the processing pulse generation circuit 53 is reset. A clock signal from a clock generator (not shown) is applied to the gate 51, and the gate 51 outputs the clock signal only when there is a processing pulse. The clock signal is applied to a processing pulse generation circuit 53 and a detection generation timing circuit 55. The processing pulse generation circuit 53 calculates a clock signal using a counter 53a, and generates a clock pulse every period T. This crop pulse is connected to a monostable multivibrator 53.
b, generates a machining pulse of a predetermined width, and outputs it to voltage circuit 3.
The voltage is applied to the gate 39d of No.9. The counter 5 of the timing generation circuit 55 is activated by the detection permission signal of the counter 53a.
Reset 5a. The counter 55a is appropriately determined to generate a pulse after a predetermined time t seconds after being reset (T/2<t<T). The output pulse of the counter 55a is inputted to a monostable multivibrator 55b to form a pulse of a predetermined width, and the pulse is applied to the gate 47b of the discrimination circuit 47. FIG. 7 shows the time relationship of each signal of the short-circuit state detection circuit. Figure 7
(a) is a clock pulse signal, and FIG. 7(b) is a control unit 4.
7, which is the output signal of the gate 51 in FIG. 7(c). FIG. 7(d) shows the output signal of the counter 53a, and FIG. 7(e) shows the processing pulse signal, which is generated every period T and has a pulse width of a predetermined charging time tN. Figure 7(f)
is the output signal of the counter 55a, and FIG. 7(g) is the timing pulse. The timing pulse is generated a predetermined time s ahead of the processing pulse, and has a pulse width of sN.

[0021]

Effects of the Invention As can be understood from the embodiments, the present invention determines the short-circuit state between electrodes for each discharge waveform, so the short-circuit state can be quickly determined. It has the effect of being evasive. Furthermore, in the method and apparatus of the present invention, since the voltage between the electrodes is determined immediately before the application of the next machining pulse, the short-circuit state can be reliably determined.

[Brief explanation of the drawing]

[Fig. 1] (a) shows the inter-electrode voltage and current waveforms when an effective discharge is occurring, and (b) shows the short-circuited state.
(c) shows the waveform in a no-load state.

FIG. 2 is a diagram showing an example of a capacitor discharge circuit with switching control.

FIG. 3 is a diagram showing an equivalent circuit of a discharge circuit, its voltage waveform, and current waveform.

FIG. 4 is a block diagram showing one embodiment of an implementation device of the present invention.

FIG. 5 is a diagram showing the temporal relationship between machining pulses and discharge pulses.

FIG. 6 is a diagram showing a specific circuit related to an embodiment of the device of the present invention.

FIG. 7 is a diagram showing a comparison of waveforms of main parts of a specific circuit of this example.

[Explanation of symbols]

1 Discharge circuit 3 Wire electrode 5 Workpiece 7 Charge/discharge capacitor 13 DC power supply 15 Switch part 17 Protective resistance 19 Processing pulse generator 21 Discharge equivalent circuit 23 Discharge electrode 25 Waveform voltage divider circuit 27 Low-pass filter circuit 29 Discrimination circuit 31 Control section 33 Pulse generation circuit 35 Detection timing generation circuit 37 Processing power supply

Claims (2)

[Claims] 1. A method for determining a state between electrodes of a capacitor electric discharge machining circuit having a switching control section, wherein a timing pulse is generated immediately before applying a machining pulse to the switching control section, and the timing pulse is output. 1. A method for determining a short-circuit condition between electrodes of an electric discharge machine, comprising: detecting a voltage level between the electrodes while the electric discharge machine is in operation, and comparing the inter-electrode voltage with a reference voltage to determine a short-circuit condition between the electrodes. 2. An interelectrode state determination device for determining the state between electrodes of a capacitor discharge machining circuit having a switching control section, comprising: a voltage divider circuit that detects and divides the discharge voltage between the electrodes; and an output of the voltage divider circuit. a low-pass filter circuit that removes high-frequency components from the low-pass filter; a discrimination circuit that compares the output voltage of the low-pass filter circuit with a reference voltage and generates a short circuit signal when the output voltage is lower than the reference voltage; a machining pulse generation circuit that generates a machining pulse based on a machining command signal from a control section and applies the pulse to a machining power supply circuit; and a machining pulse generation circuit that generates a detection timing pulse for the discrimination circuit immediately before the rising edge of the machining pulse. 1. An apparatus for determining a short-circuit state between electrodes of a wire electric discharge machine, comprising a detection timing generation circuit.