JP2002144153A - Electric discharge machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric discharge machine capable of surely preventing a short-circuit and open-circuit during machining by sufficiently controlling the distance of a machining clearance even if machining conditions such as discharge delay time, voltage application stop time, and discharge frequency are varied. SOLUTION: In this electric discharge machine, a machining electrode 1001 and a machined object 1002 are opposed to each other through a minute machining clearance, and a pulse voltage is applied to the machining clearance to generate electric discharge for machining the machined object 1002. The discharge machine comprises an inter-pole average voltage detection circuit 511 for detecting the average voltage of the pulse voltage, a frequency detection circuit 10 for detecting a discharge frequency from the pulse voltage and outputting a signal corresponding to the detected discharge frequency, and a division circuit 20 for dividing the average voltage detected by the inter-pole average voltage detection circuit 511 by the signal corresponding to the discharge frequency outputted from the frequency detection circuit 10. The distance of the machining clearance is controlled based on the output signal of the division circuit 20 and a specified set value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method in which a workpiece (workpiece) and a machining electrode are opposed to each other via a minute machining gap, and a pulse voltage is applied to the gap between the workpiece and the machining electrode. More particularly, the present invention relates to a technique for optimally controlling a machining gap to prevent a short circuit phenomenon and an open phenomenon during electric discharge machining.

[0002]

2. Description of the Related Art There are various types of electric discharge machines, such as die-sinking electric discharge machining and wire electric discharge machining. In die-sinking electrical discharge machining, an electric discharge is generated between an electrode and an object to be processed by using an electrode of a specific shape, and the electric discharge is used to perform machining into a predetermined shape. In wire electric discharge machining, a conductive wire is used as an electrode, and the wire is wound and moved while supplying power to the wire to generate an electric discharge between the wire and a workpiece, and the electric discharge is used for machining.

[0003] Fig. 7 shows "Electric discharge machining technology" [Saito, Mori,
Takawashi, Furuya: Nikkan Kogyo Shimbun (1997)] p. 117
1 shows a configuration of a conventional general wire electric discharge machine shown in FIG. In the figure, 1001 is a wire as a processing electrode, 1002 is a processing target (workpiece), 10
03 is a processing power supply, 1004a and 1004b are power supply cables, 1005 is a power supply terminal, 1006 is a supply reel, 1007 is a take-up reel, 1008 is a brake, 1
009 is a take-up roller, 1010 is a cross table, 1
011 is an X-axis motor, 1012 is a Y-axis motor, 1013
a and 1013b are motor control cables, 1011, respectively.
4 is a control device, 1015 is a servo circuit, 1016 is a working fluid tank, 1017 is a pump, 1018a, 1018b.
Are working fluid supply pipes.

Next, the operation will be described. Processing power supply 10
From 03, a voltage is applied between a wire (that is, a processing electrode) 1001 and a processing object 1002 through power supply cables 1004a and 1004b and a power supply terminal 1005. Here, when the potential difference between the wire 1001 and the workpiece 1002 exceeds the discharge starting voltage, a discharge occurs between the wire 1001 and the workpiece 1002, and this discharge removes a part of the workpiece 1002. Processing is performed. In this case, the surface of the wire 1001 is also removed by the discharge. For this reason, usually, while winding the wire 1001 in order to prevent the wire 1001 from breaking, the machining is performed so that electric discharge occurs at different positions on the surface of the wire 1001.

The wire 1001 is supplied from a supply reel 1006 through a brake 1008 and a guide 1019. A winding roller 100 is provided below the workpiece 1002.
9. Take-up reel 1007, used wire 1
Wind up 001. As the wire 1001, for example, a copper wire or a brass wire having a diameter of 0.3 mm to 0.03 mm is used.

The object to be processed 1002 is a cross table 1
010 is fixed. The cross table 1010 is provided with an X-axis motor 1011 and a Y-axis motor 1012. Further, an X-axis motor 1011 and a Y-axis motor 1012
Are motor control cables 1013a and 1013, respectively.
b is connected, the control circuit 1014, the servo circuit 1015
Is supplied. With this configuration, the cross table 1010 includes the control circuit 1014 and the servo circuit 1
015 according to the instruction of the NC device consisting of
Move position 2. As a result, the processing target can be processed into a shape as instructed by the NC device.

Reference numeral 1016 denotes a working fluid tank. For the working fluid tank 1016, for example, deionized water is used. The working fluid is supplied to the discharge field through the working fluid supply pipe 1018 by the action of the pump 1017. Here, the processing gap (that is, the wire 1001 and the workpiece 10
02, which is also referred to as a gap), if the voltage is too wide, no discharge occurs even if a voltage is applied, and if it is too narrow, a short circuit occurs when the voltage is applied.

Therefore, in order to obtain optimum machining conditions, the average voltage of the machining gap is detected to control the machining gap (inter-electrode) distance. FIG. 8 is a diagram showing a configuration of a conventional electric discharge machining apparatus that controls the machining gap distance by detecting an average voltage of the machining gap (between poles). In FIG. 8, reference numeral 1020 denotes a gap average voltage detection circuit that detects a substantially average voltage of a machining gap (between poles); 1021a and 1021b denote cables connecting the gap average voltage detection circuit 1020 with the object 1002 and the wire 1001; Is a cable connecting the inter-pole average voltage detection circuit 1020 and the control circuit 1014.

Since the average voltage of the machining gap includes information on the machining gap distance, the average gap voltage detection circuit 1020
Is input to the control circuit 1014 and the control circuit 1014
If it is determined that the machining gap is wider than the set value, the servo circuit 1015 is used to narrow the machining gap. If it is determined that the machining gap is smaller than the set value, the servo circuit 1
015 is used to widen the processing gap. Although not shown, the inter-electrode average voltage detection circuit 1020 and the control circuit 10
14, a voltage comparator circuit that includes a voltage comparator that compares the output from the inter-electrode average voltage detection circuit 1020 with a predetermined set value and a gain adjustment circuit that adjusts the output level is provided. I have.

FIG. 9 is a block diagram showing a configuration of a main part of a conventional electric discharge machining apparatus disclosed in Japanese Patent Application Laid-Open No. 8-108320 as an example of controlling the distance of a machining gap. FIG.
, 1001 is a wire as a processing electrode, 1001
2 is an object to be processed, 510 is an average gap voltage detection circuit, 52
0 is a voltage comparison circuit. Inter-pole average voltage detection circuit 510
Is composed of a voltage smoothing circuit 530 and an A / D conversion circuit 540. The voltage between the electrodes (that is, the voltage applied to the machining gap, which is the gap between the wire 1001 and the workpiece 1002) is input to the voltage smoothing circuit 530, and this voltage is smoothed to average the voltage applied to the machining gap. Vave is detected.

The output of voltage smoothing circuit 530 is converted to a digital signal by A / D conversion circuit 540 and input to voltage comparison circuit 520. The voltage comparison circuit 520 includes a voltage comparator 545 and a gain adjustment circuit 550. The input signal from the average gap voltage detection circuit 510 to the voltage comparison circuit 520 is compared by the voltage comparison circuit 545 with a predetermined set value (a predetermined value determined according to the set value of the gap distance during processing) Vset. The difference is calculated by the gain adjustment circuit 55.
By 0, the output is multiplied by a constant according to the input level of the control circuit 1014 (Vcotrol). Using this value (ie, Vcotrol, which is the output of the gain adjustment circuit 550), the control circuit 1014 and the servo circuit 1015 control the machining gap distance.

FIG. 10 shows the above-mentioned Japanese Patent Application Laid-Open No. 8-108320.
FIG. 1 shows an example of a pulse-like voltage waveform applied to a machining gap in a conventional electric discharge machining apparatus disclosed in Japanese Patent Application Laid-Open Publication No. H11-209,036. Time a ₁ is a time until the discharge is generated from application of voltage to the machining gap, it referred to as a discharge delay time. The time b ₁ is the time during which the discharge is continued (that is, the processing time), and the time c ₁ is the voltage application stop time until the next voltage pulse is applied after the end of the discharge.

[0013] Also, see "Electric Discharge Machining Technology" [Saito, Mori, Takashi, Furuya: Published by Nikkan Kogyo Shimbun (1997)], p. 247
~ P. 248 shows a system in which the polarity of the voltage applied to the machining gap is switched between positive polarity and reverse polarity and applied.
By switching the polarity of the voltage applied to the machining gap and applying the voltage, an effect of preventing electrolytic corrosion can be obtained. FIG. 11 shows an example of a system in which the polarity of the voltage applied to the machining gap is switched and applied. In FIG. 11, t ₁ is a time (period) during which the voltage V ₀₁ is applied to the machining gap. After the voltage is applied, the generated discharge starts at time t ₁ ′. Time t ₁
Corresponds to the discharge delay time a ₁ shown in FIG. 10. Here, in the case of FIG. 11, the discharge generated between the time t ₁ ′ and the time t ₁ is used exclusively for forming a discharge path in the machining gap.
The main current of processing a workpiece 1001 is generated by applying a machining voltage from the main power supply at time t _1.

The period (machining time) during which the machining current flows and the workpiece is machined is t ₂ . The time in t ₂ at the processing current is 0, rest period after (dwell time) t _3,
To apply a reverse polarity voltage -V ₀₂ for preventing electrolytic corrosion. To prevent electrolytic corrosion, first discharge period (e.g., the discharge period T ₁ or the discharge period T ₂₎ the sum of the average voltage in the so that 0V, the value of the reverse polarity voltage application time t ₄ is set. afterwards,
After the voltage application stop period (time) t _5, the next discharge pulse is applied. Here, the discharge delay time t ₁ is a value determined by the conditions of the discharge field, and includes information on the machining gap distance. That is, when the machining gap distance is large, the discharge delay time t ₁ is long, and when the machining gap distance is small, the discharge delay time t ₁ is short. T ₂ ~t ₅ other than it is a value that can be determined and set by the operator.

With respect to the voltage waveform shown in FIG. 11, an example of a circuit for detecting the average voltage of the pulsed voltage applied to the machining gap during the discharge delay time t ₁ (ie, an average voltage detection circuit between the electrodes) is shown. As shown in FIG. 12, reference numeral 511 denotes a gap average voltage detection circuit. The gap average voltage detection circuit 511 includes a voltage dividing circuit 560, a rectifier circuit 570, a voltage smoothing circuit 530, and an operational amplifier 580. The voltage of the processing gap (that is, the gap between the processing electrode 1001 and the processing object 1002) is divided by the voltage dividing circuit 560 and input to the rectifying circuit 570. Here, since the distance information between the machining gaps is included in the discharge delay time t ₁ , the rectifier circuit 570
Portion positive voltage is applied in the machining gap voltage (i.e., the discharge delay time portion of the t ₁₎ with extract only information.

The output of rectifier circuit 570 is applied to voltage smoothing circuit 53
0 average voltage Vave of the discharge delay time t ₁ is obtained by smoothing by. That is, the average voltage Vave detected by this circuit, which corresponds to the average voltage between first discharge period of the pulsed voltage applied to the machining gap in the discharge delay time t ₁ in order to generate a discharge in the machining gap is there. This value is converted by the operational amplifier 580 to a level that can be easily controlled by the control circuit 1014 at the subsequent stage, converted into a digital signal by the A / D converter 540, and output to the control circuit 1014.

[0017]

When the machining gap distance is long, the discharge delay time t ₁ is large, and when the machining gap distance is short, the discharge delay time t ₁ is small. Therefore, the average voltage of the pulsed voltage applied to the machining gap during the discharge delay time t ₁ tends to be high when the machining gap distance is long, and to be low when the machining gap distance is short. In the conventional apparatus, utilizing this, the machining gap distance is controlled by estimating the machining gap distance from the level of the average voltage of the pulsed voltage applied to the machining gap. Here, in controlling the machining gap distance, if the machining gap distance and the discharge delay time, and the discharge delay time and the machining gap average voltage have a linear relationship, it is easy to control. For example, if the relationship between the discharge delay time and the average voltage of the machining gap is linear as shown in FIG. 13, information on the machining gap distance can be obtained based on the detected average voltage of the machining gap. The processing gap distance can be processed at a constant gain in the system.

However, in practice, the relationship between the discharge delay time and the average voltage of the machining gap does not become as shown in FIG. 13, but as shown in FIG. The characteristic shows that the average voltage is saturated. For this reason, conventionally, in FIG. 14, complicated processing such as switching the processing gain of the control system between a steep part and a gentle part of the characteristic line is required, and the processing is performed by approximating the inclination of the characteristic line. There was a problem that sufficient accuracy could not be obtained. Also,
For example, varying the voltage application stop time t ₅ in FIG. 11, the average voltage characteristic of the machining gap with respect to the discharge delay time t ₁ is the phenomenon which changes were observed. FIG. 14 also shows this state. A voltage application stop time t ₅ short when (i.e., t ₅ is small), the average voltage of the machining gap is increased.

Therefore, in the control system, the voltage application stop time t
_{When 5} is short, it was erroneously determined that the machining gap distance was widened, and control was performed to shorten the machining gap distance. Therefore, when the voltage application stop time t ₅ short, actual machining gap distance is too shrinks as compared with the ideal value, the short circuit phenomenon is likely to occur. As described above, in the conventional apparatus, since the relationship between the discharge delay time and the average voltage of the machining gap changes depending on machining conditions, there has been a problem that the machining gap distance cannot be sufficiently controlled and abnormal phenomena such as short-circuiting and wire breakage occur.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and sufficiently controls the machining gap distance even when machining conditions such as a discharge delay time, a voltage application stop time, and a discharge frequency change. It is an object of the present invention to provide an electric discharge machine which can perform a machining and can surely prevent a short circuit phenomenon and an open phenomenon during machining.

[0021]

In the electric discharge machining apparatus according to the present invention, a machining electrode and a workpiece are opposed to each other with a small machining gap, and a pulse-like voltage is applied to the machining gap to generate electric discharge. An electric discharge machining apparatus for machining an object to be machined, comprising: a gap average voltage detection circuit for detecting an average voltage of the pulsed voltage applied to a machining gap; and detecting a discharge frequency from the pulsed voltage. A frequency detection circuit that outputs a signal corresponding to the detected discharge frequency, and a division that divides an average voltage detected by the inter-electrode average voltage detection circuit by a signal corresponding to the discharge frequency output from the frequency detection circuit. And a circuit configured to control a distance of the machining gap based on an output signal of the division circuit and a predetermined set value.

Further, the frequency detecting circuit of the electric discharge machine according to the present invention comprises a first low-pass filter for removing a discharge noise component, a differentiating circuit for differentiating the output of the first low-pass filter, It comprises a monostable multivibrator to which an output waveform is input, and a second low-pass filter for smoothing the output waveform of the monostable multivibrator.

In the electric discharge machining apparatus according to the present invention, the machining electrode and the object to be machined are opposed to each other with a small machining gap, and a pulse-like voltage is applied to the machining gap to generate an electric discharge. An electric discharge machining apparatus for machining an object, comprising: a gap average voltage detection circuit for detecting an average voltage of the pulsed voltage applied to a machining gap; and an average voltage detected by the gap average voltage detection circuit and a predetermined voltage. And an arithmetic circuit for calculating a discharge delay time from the machining condition command value, and the distance of the machining gap is controlled based on an output signal of the arithmetic circuit and a predetermined set value.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the average voltage applied between the electrodes (that is, the machining gap between the wire 1001 as the machining electrode and the workpiece 1002) with respect to the discharge delay time is as follows. The reason why the characteristics become saturated as shown in FIG. 14 and the reason why the relationship between the discharge delay time and the machining gap average voltage changes depending on the machining conditions were investigated. In the conventional electric discharge machine, the machining gap (that is, the wire 100
As shown in FIG. 9 or FIG. 12, the average voltage in one discharge cycle of (the gap between 1 and the processing object 1002) is obtained by smoothing the average voltage in the processing gap by the voltage smoothing circuit 530.

In this case, the average voltage Vave obtained is
It is represented by the following equation (1). _{Vave = V 0 × (duty)} = V 0 × (t 1 / T) ···· (1) where, V ₀ is applied to the machining gap in the discharge starting voltage applied (i.e., the discharge delay time t ₁ a value of the pulsed voltage. corresponding to V ₀₁ in FIG. 11), t ₁ is discharge delay time, T is a discharging period. For example, the discharge cycle T consists of only the discharge delay time t ₁ and the voltage application stop time t ₅ ,
When the discharge period T is constant average voltage Vave is proportional to the discharge delay time t _1. However, for example,
In the case of the voltage application sequence as shown in FIG. In the case of the waveform shown in FIG. 11, the discharge cycle T is represented by the following equation (2). T = t ₁ + t ₂ + t ₃ + t ₄ + t ₅ (2)

Accordingly, the average voltage Vave is expressed by the following equation (3). _{Vave = V 0 × {t 1} / (t 1 + t 2 + t 3 + t 4 + t 5)} ··· (3) where, t ₁ is discharge delay time, t ₂ is the processing time, t ₃ is downtime, t ₄ is the reverse polarity voltage application time for preventing electrolytic corrosion, t ₅ is the voltage application stop time. FIG. 15 shows the relationship between the discharge delay time t ₁ expressed by the equation (3) and the average voltage between the electrodes (machining gap).
Shown in Note that the average voltage on the vertical axis is obtained by applying Vave to the applied voltage V _0.
Are shown as values (au) normalized by. Discharge cycle T
When = t ₁ + t ₂ + t ₃ + t ₄ + t ₅ is constant, the discharge delay time and the average voltage are in a proportional relationship, so that control is easy.

However, in this case, even when the distance between the electrodes is small and the discharge delay time t ₁ is small, it is necessary to increase the voltage application stop time t _{5 and the} like in order to keep the discharge cycle T constant. Therefore, even when the distance between the electrodes is small and the discharge delay time t ₁ is small, the discharge frequency cannot be increased, and the machining speed cannot be increased. On the other hand, when the discharge cycle T = t ₁ + t ₂ + t ₃ + t ₄ + t ₅ changes with the discharge delay time t ₁ , the average voltage of the machining gap is saturated with respect to the discharge delay time t ₁ as shown in FIG. It shows the characteristics of For this reason, the slope of the characteristic line changes depending on the magnitude of the discharge delay time, and the characteristic is difficult to control.

FIG. 15 also shows the characteristics when the voltage application stop time t ₅ is changed (when t ₅ = 0 μs, t ₅ = 2 μs, and t ₅ = 4 μs). As shown, the machining gap (machining gap) average voltage varies with the voltage application stop time t ₅ is changed. This not only when changing the _{t 5, t 2, t 3} , t 4 is sometimes changed likewise characteristic line changes. Since the relationship between the discharge delay time and the average voltage changes as the processing conditions change, it is very difficult to control. For example, FIG.
As shown in FIG. 5, when the operation was performed with t ₅ = 4 μs as the standard condition, the average voltage Vave was Vave = 0.53 V when the discharge delay time t ₁ = 20 μs (A in FIG. 15).
point). The control system sets the target value Vset of the average voltage to Vset = 0.
When operated at 53 V, the average voltage of the machining gap is 0.
The discharge delay time t ₁ is set to t ₁ = 2.
The processing proceeds while maintaining the processing gap distance to be 0 μs.

Here, when processing is performed with a voltage waveform such that t ₅ = 0 μs by changing the processing conditions, the characteristic line is shown in FIG.
Therefore, when the target value Vset is Vset = 0.53 V, t ₁ = 1 when the target value Vset is Vset = 0.53 V, although it is desired to perform the processing while maintaining the processing gap distance such that t ₁ = 20 μs.
It becomes 1 μs. That is, in FIG. 15, the operating point is point B despite the fact that it is desired to perform machining at point C. Therefore, the processing gap distance is t ₁ = 20 μs
As compared with the case of the above, the state is shortened and a short circuit is likely to occur.

The above phenomenon will be described with reference to FIG. 16 as the relationship between the average voltage of the machining gap and the machining gap distance (inter-electrode distance).
FIG. 16 shows the relationship between the average voltage and the machining gap distance obtained assuming that there is a proportional relationship between the machining gap distance and the discharge delay time. We are asking each for the case of _{t 5 = 4μs, t 5 =} 0μs. Thus when the voltage application stop time t ₅ short, the machining gap distance when the same average voltage is obtained is shortened. Thus when the voltage application stop time t ₅ short, the machining gap distance when operated at the same average voltage set value is shortened. The above is a description unlucky when a voltage application stop time t _{5 changes, t 2, t 3, t} 4 is the same as the machining gap distance may have changed varies.

[0031] In the conventional electric discharge machining apparatus, the output of the average voltage detector circuit using the voltage smoothing circuit is changed by processing conditions, equation (2) to the average voltage in the discharge delay time t ₁ the other as seen This is because the term has an effect. Therefore, since the information of the machining gap distance is included in the discharge delay time t _1, it is considered a method of obtaining a discharge delay time t ₁ from the average voltage of the pulsed voltage applied to the machining gap in order to generate a discharge . One of them is a method using a discharge frequency. From Expression (3), the discharge delay time t ₁ can be expressed as in Expression (4). t ₁ = (Vave / V ₀ ) × T = (Vave / V ₀ ) × (1 / f) (4) From this, the average voltage Vave obtained by the smoothing circuit (ie, the discharge delay time t ₁₎ A value Vave obtained by dividing an average voltage of the pulse voltage applied to the machining gap in one discharge cycle by a discharge frequency (that is, the number of times the pulse voltage having the voltage value V ₀ is applied to the machining gap per unit time) f. / F is as shown in equation (5). Vave / f = V ₀ × t ₁ (5)

That is, the value Vave / f obtained by dividing the average voltage Vave between the electrodes by the discharge frequency f is proportional to the discharge delay time t ₁ . By using this, it is possible to obtain a value having a linear relationship with the discharge delay time t ₁ as shown by a straight line in FIG.
The problem that is difficult to control, which has conventionally been a problem, is solved. In this case, never characteristic line is changed by processing conditions such as the applied voltage downtime t _5. The present invention has been made based on such knowledge, and specific embodiments of the present invention will be described below.

An embodiment of the present invention will be described with reference to the drawings. The same reference numerals as those in the related art indicate that they are the same as or equivalent to those in the related art. Embodiment 1 FIG. FIG. 1 is a block diagram showing a configuration of a main part of an electric discharge machine according to a first embodiment of the present invention. In the figure, 1001 is a wire as a processing electrode, 1002
Is a workpiece (workpiece) as an electrode to be processed, 500
520 is a gap voltage processing circuit characterized by the present embodiment;
Denotes a voltage comparison circuit, 1014 denotes a control circuit, and 1015 denotes a servo circuit.

As shown in FIG.
Is a voltage dividing circuit 560 for dividing the voltage of the machining gap, a rectifying circuit 570 for rectifying the output voltage of the voltage dividing circuit 560, a voltage smoothing circuit 530 for smoothing the output voltage of the rectifying circuit 570, and an output voltage of the voltage smoothing circuit 530. A gap average voltage detection circuit 511 composed of an operational amplifier 580 that outputs a signal X after converting the signal to a predetermined number of times and a frequency of an output signal from the rectifier circuit 570 are detected, and correspond to the detected frequency ( A frequency detection circuit 10 which outputs a signal Y proportional to
A division circuit 20 to which an output signal Y of the frequency detection circuit 10 and an output signal Y of the operational amplifier 580 (that is, an output signal of the inter-electrode average voltage detection circuit 511) are input, and calculate and output X / Y; It comprises an operational amplifier 30 for converting the output of the operational amplifier 20 to a predetermined level, and an A / D converter 540 for converting the output value of the operational amplifier 30 to a digital signal. The voltage comparison circuit 520 includes a voltage comparator 545 for comparing the output from the inter-electrode voltage processing circuit 500 with a predetermined set value Vset, and a gain adjustment circuit 550.

Next, the operation will be described. In FIG. 1, the voltage between contacts (that is, the wire 1001 and the workpiece 10
02 is input to the average voltage detecting circuit 511 in the voltage processing circuit 500, and the voltage dividing circuit 560
And input to the rectifier circuit 570. The rectifier circuit 570 extracts only the pulsed voltage waveform (see FIG. 11) corresponding to the discharge delay time t ₁ , and averages it in the voltage smoothing circuit 530. Accordingly, the average of the voltage divided by the voltage dividing circuit 560 of the pulse voltage applied to the machining gap until the discharge occurs after the voltage is applied to the machining gap, that is, during the discharge delay time t _1. The value is obtained as an output of the voltage smoothing circuit 530. In addition, as shown in the circuit block of the inter-electrode voltage processing circuit 500 in FIG. 1, the output of the rectifier circuit 570 is also input to the frequency detection circuit 10.

In the frequency detecting circuit 10, the rectifying circuit 570
The waveform of the portion of the discharge delay time t ₁ output from the controller is input, and the discharge frequency f (ie, the number of pulse-like voltages applied to the machining gap in order to generate a discharge in a unit time)
And outputs a signal Y corresponding (proportional) to the detected discharge frequency f. Signal Y output from frequency detection circuit 10 (that is, a signal corresponding to discharge frequency f)
And the signal value X (ie, Vave) obtained by multiplying the output value of the voltage smoothing circuit 530 by a constant by the operational amplifier 580 is input to the division circuit 20. The division circuit 20 calculates X / Y (that is, Vave / f) from both input signals and outputs the result.

After the result is converted by the operational amplifier 30 into a voltage level which can be easily processed by the control system, the A / D converter 54
0, the signal is changed to a digital signal, and a voltage comparison circuit 52
Enter 0. The voltage comparison circuit 520 includes a voltage comparator 545
And a gain adjustment circuit 550. An input signal from the gap voltage processing circuit 500 to the voltage comparison circuit 520 is
The voltage is compared with a predetermined set value Vset by a voltage comparator 545, and the difference is compared by a gain adjustment circuit 550 in the control circuit 10.
The output is multiplied by a constant according to the input level of No. 14.

Here, the predetermined set value Vset is a value determined corresponding to the set value of the gap distance at the time of machining. For example, when the operator wants to perform machining with the gap distance dg of dg = 30 μm, the magnitude of the set value Vset is determined according to this distance. The set value Vset is large when the gap distance dg is large, and small when the gap distance dg is small.
In this case, if the actual distance between the poles is longer than the distance set by the operator, the voltage processing circuit 50
The output of 0 becomes larger than the set value Vset, and the voltage comparison value 5
This is determined at 45. The processing gap distance is controlled by the control circuit 1014 and the servo circuit 1015 using this value.

FIG. 2 is a diagram for explaining the effect of the gap voltage processing circuit 500 in the electric discharge machine according to the present embodiment. 2, white circles, using conventional machining gap average voltage detecting circuit 510 shown in FIG. 12, in the case of changing the t ₅ the voltage application stop time average gap voltage detection circuit 51
0 shows an output voltage characteristic. Further, black circle, with the inter-electrode voltage processing circuit 500 according to the present embodiment shown in FIG. 1, shows the output voltage characteristic of the inter-electrode voltage processing circuit 500 in the case of changing the t ₅ the voltage application stop time ing. FIG.
Open circles and as seen in the data shown in the, in the case of using the conventional average gap voltage circuit 510 shown in FIG. 12, the detection output voltage when changing the t ₅ the voltage application stop time constant without voltage detection signal is reduced in case of increasing the t ₅ the voltage application stop time. This is shown in FIGS.
This is the same phenomenon as described using.

On the other hand, in the case of using the inter-electrode voltage processing circuit 500 according to the present invention shown by black circles in FIG. 2, a constant detection signal output regardless of the voltage application stop time t ₅ were obtained. This is because Vave / f is proportional to the discharge delay time t ₁ as shown in equation (5), and the machining gap distance is controlled using this value, so that the machining gap distance is kept constant during machining. It is shown that. In the above description, the voltage application stop time t
_Although the example in which ₅ has changed has been described, the processing time t ₂ ,
Even when the pause time t ₃ and the reverse voltage application time t ₄ for preventing electrolytic corrosion change, the characteristics are the same as those when the voltage application stop time t ₅ changes, as shown in Expression (3).

For example, in FIGS. 15 and 16, when the machining time t ₂ , the pause time t ₃ , and the reverse voltage application time t ₄ for preventing electrolytic corrosion change, the voltage application stop time t ₅ also changes. Similarly, the average voltage characteristic changes. Further, by using the inter-electrode voltage processing circuit 500 according to the present embodiment, even when the processing time t ₂ , the pause time t ₃ , and the reverse voltage application time t ₄ for preventing electrolytic corrosion change, the voltage application in FIG. constant detection signal output as if the stop time t ₅ has changed is obtained. As described above, if the configuration according to the present embodiment is used, the processing time t ₂ , the pause time t ₃ , the reverse voltage application time t ₄ for preventing electrolytic corrosion, the voltage application stop time t _{5, and the} like change the processing conditions. However, a value proportional to the discharge delay time t ₁ can be obtained from the gap voltage processing circuit 500.

FIG. 3 shows the relationship between the output of the gap voltage processing circuit 500 according to the present embodiment and the gap distance (ie, the distance between the wire 1001 and the workpiece 1002). As shown in FIG. 3, the output of the gap voltage processing circuit 500 corresponds in one-to-one correspondence with the machining gap distance (inter-gap distance), and is very easy to control, thereby improving the control accuracy of the machining gap. Can be. Further, since this relationship does not change depending on the processing conditions, it is possible to prevent a phenomenon that when the processing conditions are changed, the processing gap distance for the same setting changes and the short circuit or the open state is likely to occur. In the above-described embodiment, a method has been described in which the average voltage detection signal of the machining gap (ie, signal X) is divided by the signal corresponding to the detected discharge frequency (ie, signal Y) using the division circuit 20. However, a method of multiplying the average voltage detection signal X of the machining gap by the period of the machining discharge pulse using a multiplication circuit may be used.

Embodiment 2 FIG. 4 is a block diagram showing a configuration example of the frequency detection circuit 10 in the inter-electrode voltage processing circuit 500 shown in FIG. In the figure, Vin is an input signal from the rectifier circuit 570 in the inter-electrode average voltage detection circuit 511, 60 is a first low-pass filter, 40 is a differentiator,
50 is a monostable multivibrator, 61 is a second low-pass filter, and Vout is the output of the second low-pass filter 61 (that is, the output of the frequency detection circuit 10).

Next, the operation will be described. A commercially available general-purpose frequency counter may be used as the frequency detection circuit 10 shown in FIG. 1, but in this case, the device becomes large. There is also a problem that a malfunction due to discharge noise occurs. The frequency detection circuit 10 shown in FIG. 4 is provided to solve such a problem, and is disposed on the input side and removes a noise component of the input signal Vin.
, A differentiating circuit 40 for differentiating the output waveform of the first low-pass filter 60, a monostable multivibrator 50 for outputting a pulse having a constant width in response to a positive differential pulse, and an output of the monostable multivibrator 50. And a second low-pass filter 61 for smoothing.

FIG. 5 shows the frequency detection circuit 10 shown in FIG.
It is a figure for explaining operation of. Frequency detection circuit 10
The, dividing the voltage of the machining gap at the voltage dividing circuit 560 in the inter-electrode voltage processing circuit 511 is a signal taken out of the discharge delay time t ₁ through the rectifier circuit 570 signals Vi
n is the first low-pass filter 6 of the frequency detection circuit 10
Input to 0. As shown in FIG. 5, the discharge delay time t
_{Since 1} (that is, the width of the pulse-like voltage applied to generate a discharge in the machining gap) varies for each discharge cycle, the pulse width of the input signal Vin changes for each discharge cycle. That is, as shown in FIG.
Discharge delay time t ₁ of the next discharge pulse of the discharge period T ₂ following discharge delay time t ₁ of the discharge pulse ₁ and to this are different.

Since the first low-pass filter 60 removes only high-frequency noise components of the input signal Vin, the differentiating circuit 40 generates a differential pulse at the rising and falling portions of the input signal Vin. That is, the discharge delay time t ₁
A differentiated pulse is generated at the start point and end point of. This differentiated pulse waveform is input to the monostable multivibrator 50.
The monostable multivibrator 50 is designed to respond only to positive polarity pulses among the input differential pulse waveforms, and outputs a pulse waveform having a constant width every time a positive polarity pulse is input. FIG. 5A shows an output waveform of the large low-pass filter 60 (that is, a signal from which the noise component of the input signal Vin has been removed), and FIG. 5B shows an output waveform of the differentiating circuit 40 (differential pulse waveform). FIG. 5C shows the output waveform of the monostable multivibrator 50, and FIG. 5D shows the output waveform of the second low-pass filter 61.

Although the discharge delay time t ₁ of the input signal Vin changes every discharge cycle, the pulse width of the output waveform of the monostable multivibrator 50 is set by the monostable multivibrator 50 to a pulse waveform having the same pulse width. I do. In the second low-pass filter 61, the output waveform of the monostable multivibrator 50 is smoothed. As described above, the monostable multivibrator 50 outputs a pulse waveform having the same pulse width every discharge cycle in response to the pulse-like voltage applied to the machining gap to generate a discharge. The output value of the waveform is proportional to the number of pulses of the pulse voltage applied to the machining gap per unit time.
Therefore, the output of the second low-pass filter 61 (that is, the output of the frequency detection circuit 10) has a value proportional to the discharge frequency.

As described above, in the electric discharge machining apparatus according to the present embodiment, the frequency detecting circuit 10 which outputs a value proportional to the electric discharge frequency includes the differentiating circuit, the monostable multivibrator, the first and second two low-pass circuits. Since the filter is used, this part can be realized by a very small and inexpensive circuit. In addition, when a discharge frequency is detected by a general-purpose frequency counter in an electric discharge machine, the frequency counter often malfunctions due to discharge noise generated between machining gaps. However, in the frequency detection circuit 10 according to the present embodiment, the first low-pass filter 60
And several tens of kHz to several hundreds of Hz during electric discharge machining.
Since the discharge noise component higher than the discharge frequency is removed, the discharge frequency can be reliably detected.

Embodiment 3 FIG. 6 is a block diagram showing a configuration of a main part of the electric discharge machine according to the third embodiment.
In the figure, reference numeral 1001 denotes a wire as a processing electrode;
02 is an object to be processed as an electrode to be processed, 501 is an inter-electrode voltage processing circuit, 520 is a voltage comparison circuit, 1014 is a control circuit, and 1015 is a servo circuit.

Inter-pole voltage processing circuit 50 according to the present embodiment
Reference numeral 1 denotes a voltage dividing circuit 560 that divides a voltage between the wire 1001 and the workpiece 1002 (that is, a voltage between the electrodes), a rectifying circuit 570 that rectifies an output voltage of the voltage dividing circuit 560, and smoothes an output voltage of the rectifying circuit 570. Average voltage detection circuit 5 comprising an operational amplifier 580 for converting the output voltage of the voltage smoothing circuit 530 to a predetermined multiple of the level.
11, the average voltage output from the inter-electrode average voltage detection circuit 511, and the processing condition command value (that is, the processing time t ₂ ,
A timing command value such as a pause time t ₃ , a reverse polarity voltage application time t ₄ , and a voltage application stop time t ₅ ), and a calculation circuit 70 that calculates a discharge delay time t ₁ based on the following equation (6). Have been. Also, the voltage comparison circuit 520
Is composed of a voltage comparator 545 for comparing the output from the inter-electrode voltage processing circuit 501 (that is, the output of the arithmetic circuit 70) with a predetermined set value Vset, and a gain adjustment circuit 550. Note that the predetermined set value Vset is a value determined according to the set value of the gap distance during machining, as described in the first embodiment.

Next, the operation will be described. When the discharge cycle T is represented by the equation (2), the discharge delay time t ₁ is represented by the following equation (6) from the equation (3). t ₁ = {Vave / (V ₀ −Vave)} × (t ₂ + t ₃ + t ₄ + t ₅ ) (6) Here, in equation (6), the applied voltage V ₀ (that is, the discharge delay time) a voltage value of the pulsed voltage applied to the machining gap in t _1, V corresponding to ₀₁₎ and processing the waveform condition t ₂ ~t ₅ in FIG. 11 is a machining condition command value, the operator It is a value that can be set and determined. Therefore, the discharge delay time t ₁ may be calculated from the average voltage obtained by the smoothing circuit using the equation (6).

In FIG. 6, the voltage in the machining gap is divided by a voltage dividing circuit 560 and input to a rectifying circuit 570. The waveform of only the portion of the discharge delay time t ₁ shown in FIG. 11 is Desa taken by the rectifier circuit 570, the voltage smoothing circuit 5
Averaged at 30. The output of the voltage smoothing circuit 530 is gain-multiplied by an operational amplifier 580 for easy processing, and is input to the arithmetic circuit 70. On the other hand, the arithmetic circuit 70 supplies the applied voltage V ₀ from the processing device control system and the processing waveform conditions t _{2 to} t _5.
(Processing condition command value) is input. Arithmetic circuit 70
Then, an operation is performed from these inputs in accordance with equation (6),
Determine the discharge delay time t _1. Obtained discharge delay time t
₁ is digitized in the arithmetic circuit 70 and input to the voltage comparison circuit 520. The voltage comparison circuit 520 includes a voltage comparator 545 and a gain adjustment circuit 550.

The input signal from the inter-electrode voltage processing circuit 501 to the voltage comparison circuit 520 is compared with a predetermined set value Vset by the voltage comparator 545, and the difference is used as the gain adjustment circuit 55.
At 0, the value is multiplied by a constant according to the input level of the control circuit 1014 and output. Using this value, the control circuit 1014 and the servo circuit 1015 use the processing gap (that is, wire 1).
The distance between the 001 and the workpiece 1002) is controlled. As described above, in the present embodiment, by using the inter-electrode voltage processing circuit 501 having a simpler configuration than in the case of Embodiment 1 as shown in FIG.
Also it is possible to obtain the discharge delay time t ₁ corresponding to the machining gap distance in case of changing the processing conditions, it is possible to control the machining gap distance constant.

In the above embodiment, the processing voltage waveform shown in FIG. 11 has been described as an example. However, the present invention is not limited to this processing voltage waveform, and the present invention can be applied to a processing voltage waveform different from that shown in FIG. As determined equation (1) to in accordance with concepts described in (6) determining the discharge delay time t ₁ from the period of the discharge pulse relationship if may be carrying out the calculation by the calculation circuit 70.

[0055]

According to the electric discharge machining apparatus of the present invention, a machining electrode and a workpiece are opposed to each other with a small machining gap, and a pulse-like voltage is applied to the machining gap to generate a discharge. An electrical discharge machining apparatus for performing the machining of, the gap average voltage detection circuit that detects the average voltage of the pulse voltage applied to the machining gap, and the discharge frequency is detected from the pulse voltage, the detected discharge frequency A frequency detection circuit that outputs a corresponding signal, and a division circuit that divides the average voltage detected by the inter-electrode average voltage detection circuit by a signal corresponding to the discharge frequency output from the frequency detection circuit. Since the distance of the machining gap is controlled based on the output signal and a predetermined set value, it is possible to obtain an average voltage that has a linear relationship with the discharge delay time regardless of machining conditions. Machining gap distance control can be sufficiently performed in the electric discharge machining apparatus can be realized which can avoid a short circuit phenomenon and open phenomenon by.

The frequency detection circuit of the electric discharge machine according to the present invention comprises a first low-pass filter for removing a discharge noise component, a differentiation circuit for differentiating the output of the first low-pass filter, and an output waveform of the differentiation circuit. Since it is composed of the input monostable multivibrator and the second low-pass filter for smoothing the output waveform of the monostable multivibrator, the frequency detection circuit is not only compact and inexpensive, but also has a low A highly reliable and highly reliable electric discharge machine can be realized.

Further, in the electric discharge machining apparatus according to the present invention, the machining electrode and the object to be machined are opposed to each other with a minute machining gap, and a pulse-like voltage is applied to the machining gap to generate an electric discharge. An electric discharge machining apparatus for performing machining of a workpiece, comprising: a gap average voltage detection circuit that detects an average voltage of a pulsed voltage applied to a machining gap; and an average voltage detected by the gap average voltage detection circuit and a predetermined machining. An arithmetic circuit for calculating the discharge delay time from the condition command value, and configured to control the distance of the machining gap based on an output signal of the arithmetic circuit and a predetermined set value. It is possible to obtain an average voltage that is linearly related to time with a simpler circuit configuration, thereby sufficiently controlling the processing gap distance and avoiding a short circuit phenomenon and an open phenomenon. The electric discharge machining apparatus can be realized that.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a main part of an electric discharge machine according to a first embodiment.

FIG. 2 is a diagram for explaining an effect of a gap voltage processing circuit in the electric discharge machine according to the first embodiment.

FIG. 3 is a diagram showing a relationship between an output of a gap voltage processing circuit of the electrical discharge machine according to the first embodiment and a gap distance;

FIG. 4 is a block diagram showing a configuration of a frequency detection circuit of an electric discharge machine according to a second embodiment.

FIG. 5 is a diagram for explaining an operation of the frequency detection circuit according to the second embodiment.

FIG. 6 is a block diagram showing a configuration of a main part of an electric discharge machine according to a third embodiment.

FIG. 7 is a diagram showing a configuration of a conventional general electric discharge machine.

FIG. 8 is a diagram showing a configuration of a conventional electric discharge machining apparatus that controls an inter-machining distance by detecting an average voltage of a machining gap.

FIG. 9 is a block diagram showing a configuration of a main part of a conventional electric discharge machine.

FIG. 10 is a diagram showing a machining gap voltage waveform of a conventional electric discharge machining apparatus.

FIG. 11 is a diagram showing a machining gap voltage waveform of a conventional electric discharge machine.

FIG. 12 is a block diagram showing a configuration of a gap average voltage detection circuit of a conventional electric discharge machine.

FIG. 13 is a diagram showing an ideal relationship between a discharge delay time and an average voltage of a machining gap.

FIG. 14 is a diagram showing a relationship between a discharge delay time and an average voltage of a machining gap in a conventional electric discharge machining apparatus.

FIG. 15 is a view showing a relationship between a discharge delay time and an average voltage of a machining gap in a conventional electric discharge machining apparatus.

FIG. 16 is a diagram showing a relationship between a gap-to-pole (machining gap) average voltage and a machining gap distance in a conventional electric discharge machining apparatus.

[Explanation of symbols]

Reference Signs List 10 frequency number detecting circuit 20 dividing circuit 30 operational amplifier 40 differentiating circuit 50 monostable multivibrator 60 first low-pass filter 61 second low-pass filter 70 arithmetic circuit 500 inter-electrode voltage processing circuit 501 inter-electrode voltage processing circuit 511 inter-electrode average voltage Detection circuit 520 Voltage comparison circuit 530 Voltage smoothing circuit 540 A
/ D converter 550 Gain adjustment circuit 560 Voltage divider circuit 570 Rectifier circuit 580 Operational amplifier 1001 Wire (working electrode) 1002
Processing object 1003 Processing power supply 1014
Control circuit 1015 Servo circuit

Continued on the front page (72) Inventor Akihiko Iwata 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Electric Corporation (72) Inventor Taichiro Minda 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Electric Co., Ltd. Within the company (72) Inventor Jun Taneda 2-3-2 Marunouchi, Chiyoda-ku, Tokyo F-term (reference) 3C059 AA01 AB01 AB03 CA01 CB06 CC01 CD04 CE08 CF01 CH01

Claims (3)

[Claims] 1. An electric discharge machining method in which a machining electrode and a workpiece are opposed to each other with a small machining gap, and a pulsed voltage is applied to the machining gap to generate a discharge, thereby machining the workpiece. An apparatus, comprising: a gap average voltage detection circuit that detects an average voltage of the pulsed voltage applied to a machining gap; a discharge frequency detected from the pulsed voltage; and a signal corresponding to the detected discharge frequency. A frequency detection circuit for outputting, and a division circuit for dividing an average voltage detected by the inter-electrode average voltage detection circuit by a signal corresponding to the discharge frequency output from the frequency detection circuit. An electric discharge machining apparatus for controlling a distance of a machining gap based on an output signal and a predetermined set value. 2. A frequency detection circuit comprising: a first low-pass filter for removing a discharge noise component; a differentiation circuit for differentiating an output of the first low-pass filter; and a monostable to which an output waveform of the differentiation circuit is input. The electric discharge machining apparatus according to claim 1, further comprising a multivibrator, and a second low-pass filter for smoothing an output waveform of the monostable multivibrator. 3. An electric discharge machining method in which a machining electrode and a processing object are opposed to each other with a small processing gap, and a pulse-like voltage is applied to the processing gap to generate a discharge, thereby processing the processing object. An apparatus, comprising: a gap average voltage detection circuit that detects an average voltage of the pulsed voltage applied to a machining gap; and an average voltage detected by the gap average voltage detection circuit and a predetermined machining condition command value. An electric discharge machining apparatus comprising: an arithmetic circuit for calculating a discharge delay time; and controlling a distance of a machining gap based on an output signal of the arithmetic circuit and a predetermined set value.