JP2545802B2 - Discharge gap detection circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a discharge gap detection circuit that detects a discharge gap in electric discharge machining and maintains a normal discharge.

[Prior Art] In this type of electric discharge machining, an output voltage of a machining DC power source is turned on / off by a switching element and applied as an intermittent voltage pulse to a machining gap composed of a machining electrode and a workpiece. It is supposed to do. In this case, the electric discharge machining gap signal for adjusting the electric discharge gap includes the first means for applying the voltage pulse to the machining gap to detect the electric discharge start voltage, and the machining gap from the start of the application of the applied pulse. Second means for detecting the time until the discharge is started. That is, the machining gap signal obtained by the first means and the discharge waiting time signal obtained by the second means are added, and the added value is used as the discharge gap signal.

[Problems to be Solved] In the above-mentioned configuration, when the machining waste generated by the electric discharge machining accumulates in the machining gap, the insulating property in the machining gap becomes low, and when a leakage current occurs in the machining gap, The discharge starting voltage obtained in the machining gap has a lower value than the discharge starting voltage when no leakage current is generated.

In this case, the time from the application of the machining pulse voltage to the start of the discharge is the same as when the leakage current does not occur at the same machining gap distance.

In the above-described conventional technique, the discharge detection signal is obtained by adding the machining gap signal and the discharge waiting time signal, but since the same control method is used regardless of the occurrence of leakage current in the machining gap, Since no special action such as removing accumulated processing waste is performed, processing waste is accumulated,
There is a drawback that the insulating property in the processing gap is lost and abnormal discharge such as arc discharge is caused.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a discharge gap detection circuit capable of preventing abnormal discharge due to accumulation of machining chips.

[Means for Solving the Problems] In order to achieve the above object, the present invention applies an intermittent voltage pulse to an electric discharge machining gap composed of a machining electrode and a workpiece to determine the original electric discharge machining gap voltage until the start of electric discharge. Detecting means for detecting, and the primitive electric discharge machining gap voltage detected by this detecting means is stored until a predetermined time before the next application start timing, and the stored primitive electric discharge machining gap voltage data is stored in the voltage pulse. Means for obtaining a first machining gap signal related to the electric discharge machining gap voltage by correcting with machining data defined by the applied voltage and machining conditions of the electric discharge, and the discharge from the start of the application of the voltage pulse to the start of the electric discharge. The waiting time signal and the threshold signal that is output only when the applied gap voltage is equal to or higher than the threshold voltage when the voltage pulse is applied to the electric discharge machining gap are input to determine the discharge waiting time effective signal. Second means for detecting and storing a flip-flop and a binary counter, and a discharge waiting time signal obtained by the discharge waiting time valid signal stored by the second means and the machining data defined by the machining conditions. 3 means and by correcting the first machining gap signal relating to the electric discharge machining gap voltage obtained by the first means with the discharge waiting time signal obtained by the third means, the electrode and the workpiece And a fourth means for obtaining a second machining gap signal for controlling the machining gap.

Example Next, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of a discharge gap detection circuit according to an embodiment of the present invention.

In FIG. 1, the "+" side output voltage V _P from the processing DC power supply PS is connected to the collector of the switching transistor TR1, and the "-" side is grounded.

An on / off gate signal V _G is connected to the base of the transistor TR1 from the outside of the figure. Intermittent voltage pulse is applied to the working electrode H through a control resistor R ₅ from the emitter of the transistor TR1, the workpiece W is grounded. This voltage pulse is used as the original machining gap signal V _H and the machining gap voltage detection resistors R ₁ , R ₂
A machining gap signal B, which is grounded via a resistor and is divided from the connection point of the resistors R ₁ and R ₂ , is connected to the base of the transistor TR ₂ .

From the outside, the voltage V _C is connected to the collector of the transistor TR ₂ . The emitter of the transistor TR ₂ is grounded via the analog switch AS 1, and is also connected to one terminal of the capacitor C and the AD converter AD 1 via the resistor R ₆ .

The signal S _c output immediately before the start of pulse application is input to the analog switch AS1, and the other terminal of the capacitor C is grounded. The analog signal is converted from the AD converter AD1 and the digital signal is connected to the function memory circuit ROM1.

Output voltage V _P of the processing DC power supply PS is resistor R _3, is via the R ₄ grounding, resistor R _3, the divided voltage from the connection point of R ₄ is A
AD converter AD2 connected to -D converter AD2
The analog signal is converted from and the digital signal is connected to the function memory circuit ROM1. The processed data S _d is also input to the function storage circuit ROM1 from outside the drawing.

Resistors R _1, primitive machining gap signal B from the connection point of the R ₂ is connected to one input of the comparator OP1, the other input of the voltage V _C from outside the figure resistors R _7, R ₈ binary pressurized by the comparator OP1 Connected to.

Here, the features of the present invention are a threshold value determination portion and a discharge waiting time effective determination portion surrounded by a broken line in FIG. That is, the resistance R _1, the primitive machining gap signal from the connection point of R ₂ B is connected to one input of the comparator OP2, and the voltage V _C is divided resistors R _9, R ₁₀ bisection from outside FIG comparator OP2
Connected to the other input of. The discharge waiting time signal T _W from the comparator OP1 and the threshold judgment signal T _W from the comparator OP2
_TH is connected to flip-flop FF,
FF output discharge wait time valid signal T _WON is a binary counter
Connected to CT.

The clock signal S _d and the reset signal S _b are input to the binary counter CT from outside the figure. Binary signals from the binary counter CT is connected to the function storage circuit ROM 2, the function storage circuit ROM 2, also processed data S _d is inputted. The discharge waiting time signal OUT2 from the function memory circuit ROM2 and the machining gap signal OUT1 from the function memory circuit ROM1 are respectively connected to the full adder FA, and the machining gap signal is output from the full adder FA.
OUT3 is connected to a circuit (not shown) for controlling the machining gap between the electrode H and the workpiece W.

Next, the operation of the discharge gap detection circuit configured as described above will be described. In FIG. 1, in the machining gap between the machining electrode H and the workpiece W, the transistor TR1 and the control resistor R1 to which the output voltage V _P of the machining DC power supply PS is applied with a predetermined ON / OFF gate signal V _{G. After 5} , the voltage is applied as an intermittent voltage pulse, and on the basis of this, electric discharge occurs and machining is performed.

Since the original machining gap signal V _H is generally a high voltage,
The original machining gap signal B is obtained by being divided by the machining gap voltage detection resistors R ₁ and R ₂ . Furthermore, with the transistor TR2,
The maximum voltage of the machining gap signal B is stored in the capacitor C. For each pulse of the intermittent voltage pulse, the signal S _c which is output to the pulse start printing immediately before is input to the analog switches AS1, the voltage stored in the capacitor C, is reset via an analog switch AS1.

Therefore, at the output of the capacitor C, a voltage proportional to the maximum voltage of the machining gap signal B is obtained for each pulse of the intermittent voltage pulse. Further, the output of the capacitor C is input to the AD converter AD1, and a digital signal proportional to the maximum voltage of the machining gap signal B is obtained at its output. In addition, the output voltage V _P of the processing DC power supply PS specified by the processing conditions is divided by the resistors R ₃ and R ₄ to detect
Analog-to-digital conversion is performed by the D converter AD2, and the digital value of the detection signal of the output voltage V _P is output.

The predetermined machining data S _d defined by the machining conditions such as the machining electrode H, the workpiece W, and the material of the machining liquid are generally supplied from a computer or the like. From the function memory circuit ROM1,
The output data of the A-D converter AD1 and AD2, the machining gap signal OUT1 is outputted as a function of the data of the processed data S _d. The machining gap signal OUT1 is used as the discharge gap signal in the past, and is the discharge machining gap voltage detected by applying the voltage set by the machining conditions.
A− obtained from the original machining gap signal V _H in EDM
The output of the D converter AD1 is corrected by the output voltage V _P of the DC power supply PS and the processing data S _d .

Further, the voltage V _C is divided by the resistors R ₇ and R ₈ , the preset discharge start reference voltage and the original machining gap signal B are compared by the comparator OP1, and after applying the voltage pulse to the machining gap, The discharge wait time signal T _W of logic “1” is output from the comparator OP1 until the discharge starts. Similarly, the voltage V _C is divided by the resistors R ₉ and R ₁₀ , and the preset threshold voltage and the original machining gap signal B are compared with each other by the comparator OP2.
When a voltage pulse is applied to the machining gap,
Only when the machining gap voltage is equal to or higher than the threshold voltage V _TH , the threshold signal T _TH of logic “1” is output from the comparator OP2.

When the discharge wait time signal T _W and the threshold signal T _TH are input to the flip-flop FF and the threshold signal T _TH changes from logic “0” to logic “1”, the discharge wait time signal T _W becomes logic “1”.
The discharge waiting time valid signal T _WON which becomes logic “0” when the logic changes from logic “1” to logic “0” is output from the flip-flop FF.

Clock S _a and the discharge waiting time effective signal T _WON generated at a predetermined period is counted binary signal only during the logic "1" (2 ⁰ -2 ¹¹⁾ is output from the binary counter CT.
The reset signal S _b of the binary counter CT is designed to be generated immediately before the next voltage pulse is applied.
From the function storage circuit ROM 2, the discharge waiting time signal OUT2 to the processed data S _d which is defined by the output data and the processing conditions of the binary counter CT and function is output. The discharge waiting time signal OUT2 is obtained by correcting the output of the binary counter CT, which is a machining gap signal obtained from the discharge waiting time effective signal T _WON , with the machining data S _d . Further, the machining gap signal OUT1 and the discharge waiting time signal OUT2 are input to the full adder FA, the machining gap signal OUT3 of the addition result is generated, and is input to the circuit for controlling the machining gap between the electrode H and the workpiece W. To be done.

FIG. 2 is a voltage waveform diagram of each signal of the discharge gap detection circuit of this embodiment. In FIG. 2, (I) shows a case of one discharge gap example, and (II) shows a case where the leakage current occurs in the machining gap in the same machining gap as (I), which will be described. ON / OFF gate signal V _{G in} Fig. 2 (1)
Indicates a control signal applied to the gate of the transistor TR1 in FIG. 1, and the original machining gap signal V _H indicates the discharge voltage of the electric discharge machining gap based on the on / off gate signal V _G.
The voltages V _OUT1 , V _OUT2 and V _OUT3 are the machining gap signal OUT1, the discharge waiting time signal OUT2 and the machining gap signal OUT3 in FIG.
3 shows voltage waveforms when each output signal of 1 is converted to analog.

If the leakage current does not occur in the machining gap,
As in the case of (I) shown in FIG. 2 (2), at the same time as the voltage pulse is applied, the machining gap voltage becomes the predetermined threshold voltage V _TH.
Rises up to the machining gap voltage V _P set by the machining data, and discharge is started after the discharge waiting time T ₁ determined by the discharge waiting time end voltage V _D. At this time, the electric discharge machining gap is the machining gap signal shown in (I) of FIG. 2 (3).
When the value of V _{OUT1 and} the value of discharge waiting time T ₁ are used as the waiting time signal T _W , the voltage V _OUT2 shown in (I) of FIG. 2 (4)
_Is detected by the voltage V _OUT3 shown in FIG. 2 (5).

On the other hand, if the leakage current occurs in the machining gap,
As shown in (II) of Fig. 2 (2), the machining gap voltage does not rise to the threshold voltage V _TH even if a voltage pulse is applied,
Discharge is started at a lower voltage than in the case of (I) in FIG. Here, from (II) of Fig. 2 (2), the discharge wait time
Since T ₁ is not counted because the machining gap voltage has not risen to the threshold voltage V _TH , the second value _obtained by adding the voltage V _OUT1 and the voltage V _OUT2 shown in (II) of FIGS. 2 (2) and (3) The voltage V _OUT3 shown in FIG. (5) has the same value as V _OUT1, and the electric discharge machining gap is detected as a value smaller than that when the leakage current does not occur.

[Effects of the Invention] As described above, according to the present invention, in the electric discharge machining gap detection circuit for controlling the relative position between the machining electrode and the workpiece, the voltage pulse defined by the machining conditions is applied to the machining gap. After that, by generating a machining gap signal that counts the time from when the machining gap voltage exceeds a predetermined voltage to when the discharge starts, the discharge machining gap is generated when abnormal machining waste accumulation occurs in the machining gap. Since the signal can be made smaller than the predetermined target value, there is an effect that the relative position between the machining electrode and the workpiece can be rapidly expanded in order to avoid abnormal discharge such as arc discharge.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the discharge gap detection circuit of the present invention, and FIG. 2 is a voltage waveform diagram of each portion of FIG. AD1, AD2: A-D converter AS: Analog switch B: Processing gap signal, C: Capacitor CT: Binary counter, FA: Full adder FF: Flip-flop, H: Processing electrode OP1 :, OP2: Comparator OUT1, OUT3: Machining gap signal OUT2: Discharge wait time signal PS: DC power supply for machining, R _{1 to} R ₁₀ : Resistor ROM1, ROM2: Function memory circuit TR1, TR2: Transistor T _W : Discharge wait time signal T _WON : Discharge wait time effective signal T _TH : Threshold judgment signal, V _C : External power supply voltage V _G : On-off gate signal V _H : Primitive machining gap signal V _P : Output voltage of machining DC power supply W: Workpiece, S _a : Clock S _b : Reset Signal S _c : Signal output immediately before pulse application starts S _d : Processing data, V _TH : Threshold voltage V _D : Discharge wait time end voltage

Claims (1)

(57) [Claims] 1. A detecting means for detecting a primitive electric discharge machining gap voltage up to the start of electric discharge by applying an intermittent voltage pulse to the electric discharge machining gap consisting of a machining electrode and a workpiece, and detecting by this detecting means. The primitive electric discharge machining gap voltage is stored until a predetermined time before the next application start timing, and the stored primitive electric discharge machining gap voltage data is processed data defined by the applied voltage of the voltage pulse and machining conditions. A first means for obtaining a first machining gap signal relating to the electric discharge machining gap voltage by correction, a discharge waiting time signal from the start of application of the voltage pulse to the start of discharge, and a voltage pulse to the electric discharge machining gap. A flip-flop and a bias that detect and store a discharge wait time valid signal by inputting a threshold signal that is output only when the machining gap voltage is higher than the threshold voltage when applied. A second means comprising a recounter; a third means for obtaining a discharge waiting time signal from the discharge waiting time valid signal stored by the second means and the machining data defined by the machining conditions; For controlling the machining gap between the electrode and the workpiece by correcting the first machining gap signal relating to the electric discharge machining gap voltage obtained by the means described above with the discharge waiting time signal obtained by the third means. And a fourth means for obtaining a second machining gap signal from the discharge gap detection circuit.