JPH0716819B2 - EDM distance control device - Google Patents

Description

TECHNICAL FIELD The present invention relates to an inter-electrode distance control device for electric discharge machining, and more particularly to a device for controlling the inter-electrode distance so as to be optimum for sustaining an electric discharge.

A known electric discharge machining apparatus is one that melts a material such as a conductive metal using high temperature energy generated during electric discharge.

In this electric discharge machine, a pulsed electric current is usually used as electric energy, but in order to maintain the electric discharge by the pulsed electric current, it is necessary to maintain the distance between the tool electrode and the workpiece, that is, the distance between the electrodes. is important. In particular, since the work piece is melted and removed as the working progresses, when the electrode and the work piece are fixed, the distance between the electrodes is expanded and the state in which discharge is unlikely to occur occurs, Eventually, the electric discharge is expanded to a distance that cannot be sustained, and electric discharge machining stops there.

In order to prevent this and maintain a constant discharge state, usually, as the machining progresses, the electrode is brought closer to the workpiece and control is performed to maintain the inter-electrode distance.

By the way, during machining, sludge generated by machining is generated between the gaps, which is usually washed away by a working fluid or the like. However, when the machining fluid cannot be sufficiently supplied to the discharge position or when the distance between the electrodes is small, sludge discharge is delayed, so that the sludge often bridges the electrodes and is electrically short-circuited. In this case, a sufficient voltage to generate an electric discharge between the electrodes is not generated, the electric discharge is stopped, or an excessive current is concentrated to damage the work piece. In such a case, the distance between the electrodes is increased, the bridging or short-circuited portion is cut off, or the flow path of the working liquid is secured.

That is, in electrical discharge machining, under the control of reducing or expanding the gap distance, machining progresses while maintaining a constant gap distance on average. Control is a fundamental performance that has a large impact on processing capacity.

As described above, controlling and maintaining the distance between the electrodes is a fundamental and important performance in electric discharge machining, but it is not easy and practically impossible to measure the distance between the electrodes during electric discharge. Therefore, normally, by detecting the state quantity that can be regarded as equivalent to the inter-electrode distance, the inter-electrode distance is determined,
Control is performed by comparing the magnitude of the inter-electrode distance that is optimal for sustaining the discharge.

[Prior Art] FIG. 3 is a block diagram showing a conventional inter-electrode distance control device for electric discharge machining, FIG. 4 (a) is a waveform diagram of an inter-electrode voltage, and FIG. 4 (b) is a waveform diagram of a deviation signal. Is. In the figure, (1)
Is a power supply for electric discharge machining of an electric discharge machine, (2) is a resistance for setting a machining current, (3) is a switching element, (4) is a workpiece, (5) is a machining electrode, and (6) is an electrode drive. Actuator, (7) an inter-electrode voltage detector for detecting the inter-electrode voltage between the machining electrode (5) and the workpiece (4), and (8) an electrode detected by the inter-electrode voltage detector (7). A comparator for comparing the inter-voltage and the reference voltage Vr of the reference voltage setter (9), (10) sends an electrode drive signal to the actuator (6) based on the deviation signal S output from the comparator (8). It is an electrode drive circuit. (11) is the no-load voltage time in the voltage waveform between electrodes of the interelectrode voltage Vg, (12) is the voltage application pause time, and (13) is the discharge duration time.

The conventional inter-electrode distance control device for electric discharge machining is configured as described above, and during electric discharge machining, the inter-electrode voltage detector (7) detects the inter-electrode voltage between the machining electrode (5) and the workpiece (4). is doing. The inter-electrode voltage waveform of the inter-electrode voltage Vg is as shown in FIG. 4 (a). In the comparator (8), the inter-electrode voltage Vg detected by the inter-electrode voltage detector (7) and the reference voltage setting device (9)
Of the reference voltage Vr when the inter-electrode distance is optimal for sustaining the discharge of
Are compared and the deviation signal S is output as shown in FIG. The comparator (8) determines the distance between the electrodes. Normally, when the distance between the electrodes is widened, the discharge is unlikely to occur. Therefore, the time from the application of the voltage between the electrodes to the discharge, that is, no load is applied. The voltage time (11) becomes long, and conversely, when the distance between the electrodes is short, the no-load time (11) becomes short. For example, the no-load voltage time (11a) of the voltage waveform of the pulse output from the voltage detector between electrodes (7) shown in FIG. 4 (a).
Is the no-load voltage time of the reference voltage waveform, the no-load voltage time (11c), (11d) of the voltage waveform for each one pulse is the longer one, and (11b) is the shorter one. In this case, the fourth
The waveform of the deviation signal S shown in FIG. 6B is created corresponding to the voltage between contacts (this means the average voltage between contacts for one pulse including the no-load voltage time, discharge duration and voltage application pause time). Therefore, the waveform of the signal is as shown in FIG.

In the waveform of the deviation signal S shown in FIG. 4 (b), the voltage value between contacts of the voltage waveform for one pulse having the no-load voltage time (11a) is the waveform of the deviation signal S in which the machining electrode (5) is not moved. Becomes Since it uses the condition that a waveform with no-load voltage time (11a) is obtained as the reference for electrode drive,
The deviation signal S obtained from the corresponding one pulse of the no-load voltage time (11a), the discharge duration (13), and the voltage application pause time (12) is the command value for lowering, raising (small), and raising (large), respectively. However, when the deviation signal S is integrated, the deviation signal S has a value that is neither biased up nor biased down. That is, the deviation signal S coincides with the driving reference value and the machining electrode (5) is not moved.

When a no-load voltage time (11b) shorter than the no-load voltage time (11a) is obtained as the voltage waveform between contacts, similarly, the no-load voltage time (11b), discharge duration (13), voltage application pause The deviation signal S corresponding to the time (12) is obtained. However, when the one pulse is integrated, the drive amount is further reduced, so the deviation signal S corresponding to the no-load voltage time (11b) is for machining. The waveform of the deviation signal S that raises the electrode (5) is obtained.

When the no-load voltage time (11c) or the no-load voltage time (11d) shorter than the no-load voltage time (11a) is obtained as the voltage waveform between contacts, the no-load voltage time (11c) or the no-load voltage time (11d), discharge duration (13), voltage application pause time (12) corresponding to the deviation signal S,
When these 1 pulses are integrated, the drive amount increases more. Therefore, the deviation signal S corresponding to the no-load voltage time (11c) or the no-load voltage time (11d) is the deviation that lowers the machining electrode (5). It becomes the waveform of the signal S. Based on the deviation signal S output from the comparator (8), the electrode drive circuit (10) sends an electrode drive signal Ds to the actuator (6) of the electric discharge machining device, and the machining electrode ( The distance between the electrodes 5) and the workpiece (4) is controlled, the distance between the electrodes is kept constant, and the electric discharge machining in the optimum state is maintained.

By the way, according to the above method, it is possible to keep the distance between the electrodes constant during the electric discharge machining. However, in this method, the machining distance for controlling the distance between the electrodes, that is, the voltage application pause time (12) And the effect of discharge duration (13) appears.

The processing conditions are selected according to the size and shape of the workpiece, the type of electrode, the desired processing speed and the state of the processed surface after processing, and there are many different combinations.
On the other hand, the control of the inter-electrode distance is required to always perform the control in the optimum state regardless of the selected processing conditions.

However, in the above-mentioned conventional example, for example, when the pause time (12) is changed, the signal to the electrode drive circuit (10) also changes, so that the gap distance is changed, and the gap distance is also changed at the same time as the pause time. It gives a large change in the processing state.

In order to prevent this, there is a method of controlling the distance between the electrodes from the waveform of the voltage between the electrodes based on the no-load time from the application of the voltage to the discharge.

Fig. 5 shows one of them, and the measurement of the no-load time is divided into three categories. That, t ₁ <provided t ₂ a is t _1, t ₂ by time division, the first segment time unloading time td is _{0 <td <t 1, t} 1 <td < Second is t ₂ Classification time, t ₂ <
It is categorized as td 3rd division time. Then, in the case of a pulse corresponding to the first division time, it is determined that the inter-electrode distance is small and the electrode is raised, and in the case of the second division time, it is determined that the inter-electrode distance is appropriate and the electrode is raised. In the stopped state where the electrode is not lowered and when it corresponds to the third division time, the electrode driving device is driven so as to lower the electrode by determining that the distance between the electrodes is wide. In this case, since the movement amount of the electrode is given for each time segment, there are only three command values. In other words, it cannot handle small changes in the no-load time and is a kind of discrete value control. Therefore, it is not possible to cope with highly accurate control.

FIG. 6 shows another example. In this example, the distribution of the no-load time is detected, and the electrode movement command is determined according to the distribution shape. In this case, since it takes a lot of time to measure the time distribution which is the detection amount, high-speed control cannot be performed, the control response becomes extremely poor, and it is often not suitable for practical use.

When considering the difference in which the no-load time is the control amount, it is the most essential and natural idea to use the electrode movement amount corresponding to the no-load time in each pulse as the command value. However, when the no-load time is used as the control amount of the electrode movement, it is generally difficult to realize in the following points.

That is, in principle, the no-load time is detected only after the discharge is generated, and the measurement and the detection are completed. Therefore, when the discharge is not generated, the electrode movement command cannot be generated. Therefore, if the electrodes retreat significantly due to a short circuit between the electrodes and then the gap between electrodes is released due to the discharge of sludge, etc., the electrode drop command will not be output unless the next discharge occurs. Cannot access the work piece again in the released state, resulting in an uncontrollable state.

In the prior art, in order to avoid this point, the no-load voltage time zone to be measured is limited to three sections as in the above example, or the time distribution is dealt with, but the problem that occurs in this case Is as described above.

[Problems to be Solved by the Invention] In the conventional device for controlling the distance between electrodes in electric discharge machining as described above, when the voltage between the electrodes is used as a controlled variable, high-speed response is possible, but it depends on the machining conditions. There is a problem in that the control state cannot be kept constant because the inter-pole control amount changes.

In addition, when the no-load time of the voltage waveform between contacts is used as the control amount, it is not affected by the processing conditions, but the conventional method cannot achieve high-speed and highly accurate detection, and the original control performance can be achieved. could not.

The present invention has been made in consideration of the above problems, and in order to realize high-speed and high-precision control by using a no-load time that is not affected by processing conditions as a controlled variable, This makes it possible to accurately detect the no-load time.

[Means for Solving the Problem] As described above, the inter-electrode voltage waveform used as the control amount of the inter-electrode distance in the conventional electric discharge machining is replaced with the no-load time, and the no-load time is detected at high speed. In order to detect with high accuracy, it is configured as follows.

That is, a first detector that detects a no-load voltage state between the machining electrode and the electrode of the workpiece, a no-load time measuring device that measures a no-load time in the no-load voltage state, and a predetermined no-load time measuring device. A no-load time upper limit value setting unit that sets a no-load time upper limit value, and a second detector that detects a no-load time of a certain time or more and outputs the no-load time upper limit value of the no-load time upper limit value setter, Hold for holding and outputting the current value of the no-load time of the no-load time measuring device, and for holding and outputting the no-load time upper limit value when the second detector detects the no-load time of a certain time or more And a comparator that outputs a deviation signal by comparing the holding signal output from the holder with a preset no-load time set value signal, and an electrode drive that drives the machining electrode from the deviation signal of the comparator What is configured to include an electrode drive circuit that outputs a signal A.

[Operation] In the present invention, the first detector detects the no-load voltage state from the voltage waveform between the electrodes of the machining electrode and the workpiece during the electric discharge machining, and the first time in the no-load time measuring device. The no-load time in the no-load voltage state detected by the first detector is measured, and the current value of the measured no-load time is held by the holder for each pulse and output. The comparator outputs the deviation signal by comparing the current value of the no-load time output from the cage with the no-load time preset as the control target, and the electrode drive circuit drives the machining electrode from the deviation signal. An electrode driving signal for controlling the distance between the electrodes is controlled. Further, when the inter-electrode distance is so large that no discharge occurs, the no-load time is so large that the current value of the no-load time cannot be held and output for each pulse by the retainer. Therefore, the second
Detector detects the no-load time of a certain time or more, and outputs the no-load time upper limit set by the no-load time upper limit setter to the cage, and the cage holds the no-load time upper limit. Output to the comparator. The comparator compares the no-load time upper limit value with the set no-load time to output a deviation signal, and the electrode drive circuit outputs an electrode drive signal from the deviation signal to control the distance between the dischargeable electrodes. To do.

[Embodiment] FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 (a) is a waveform diagram of an electrode voltage, and FIG. 2 (b) is a waveform diagram of a no-load time signal. FIG. 2C is a waveform diagram of the no-load time upper limit value signal, and FIG. 2D is a waveform diagram of the electrode drive signal. In the figure, the same components as those of the conventional example are designated by the same reference numerals, and the description of the duplicate components is omitted. (20) is the inter-electrode voltage between the machining electrode (5) and the workpiece (4)
A first detector that detects a no-load voltage state from the voltage waveform of Vg between electrodes and outputs a no-load voltage signal Vs, (21) is based on the no-load voltage signal Vs from the first detector (20) No-load time measuring device that measures the no-load time and outputs the no-load time signal Ts, (22) is a no-load time upper limit setter that sets a predetermined no-load time upper limit, and (23) is between electrodes The second detector (24) that detects the no-load time of a certain time or more from the voltage waveform of the voltage Vg and outputs the no-load time upper limit signal Tus of the no-load time upper limit setter (22) is Controlled by the no-load voltage signal Vs and the no-load time upper limit signal Tus, the no-load time signal Ts of the no-load time measuring device (21) or the no-load time upper limit at the time of detection of the second detector (23) Retainer that holds and outputs the signal Tus, (25) is the no-load time set value corresponding to the no-load time as the control target value No load time setter that outputs the No. Trs, (26) is the no load time set value signal Trs of the no load time setter (25) and the no load time signal Ts of the no load time measuring instrument (21) or the second A comparator that compares the no-load time upper limit signal Tus of the detector (23) and outputs a deviation signal S, and (27) drives an actuator (6) based on the deviation signal S output by the comparator (26). It is an electrode drive circuit that outputs an electrode drive signal Ds.

Next, the operation of the above embodiment will be described with reference to FIGS.

During electric discharge machining by the electric discharge machine, an inter-electrode voltage is applied to the electrodes of the machining electrode (5) and the workpiece (4). The waveform of the voltage between contacts of this contact voltage Vg is as shown in FIG. 2 (a). The first detector (20) detects the no-load voltage state from this voltage waveform between contacts and outputs the no-load voltage signal Vs as shown in FIG. 2 (b). The no-load time measuring device (21) which receives the no-load voltage signal Vs measures the no-load time during which the no-load voltage state continues and outputs the no-load time signal Ts corresponding to the no-load time. The retainer (24) that receives this signal Ts and the no-load voltage signal Vs compares the no-load time present value signal Tps, which holds the time for each pulse, until the next no-load time measurement ends (26). Output to. The comparator (26) compares the current no-load time value signal Tps output from the retainer (24) with the no-load time set value signal Trs set by the no-load time setter (25) to obtain no-load. The deviation signal S for controlling the time constant is output.

Here, the no-load time of the no-load time signal Ts ₁ detected by the first detector (20) shown in FIG. 2 (b) is set by the no-load time setter (25). If the same as the no-load time set value of the instrument signal Trs, the no-load time of the no-load time signal Ts ₂ is smaller than the no-load time set value, and the no-load time of the no-load time signal T ₃ is less than the no-load time set value. large. Therefore, the deviation signal S output from the comparator (26)
Is a signal that commands the creation of an electrode drive signal Ds as shown in FIG. 2 (d) that raises the machining electrode (5) when the signal is Ts ₂ , and when the no-load time signal Ts ₃ is the machining electrode ( It becomes a signal for instructing the creation of the electrode drive signal Ds that lowers 5).

By changing the no-load time set by the no-load time setting device (25), it is possible to change the inter-electrode distance to be maintained. In the electrode drive circuit (27) that receives the deviation signal S output from the comparator (26), the electrode (5) for machining is sent to the actuator (6) of the electric discharge machining device, and the electrode drive signal Ds is sent to the actuator (6). The operation controls the distance between the machining electrode (5) and the workpiece (4). The control of the gap distance of this embodiment is not affected by the arbitrarily selected machining conditions, etc., and is because the gap distance is controlled based on the no-load time that can essentially detect the discharge state. Not only is it not affected by changes in processing conditions, but it also controls the optimal distance between the poles so that abnormal conditions such as concentrated discharge and arc discharge do not easily occur.

By the way, for example, when the machining electrode (5) has to be moved a long distance to the vicinity of the workpiece (4) without being accompanied by electric discharge to a distance sufficiently close to electric discharge, or immediately after the start of electric discharge machining or due to a short circuit. If the distance is wide, or if the sludge between the poles is eliminated, the machining electrode is intentionally made larger (5)
If the inter-electrode distance is so large that the discharge does not occur, such as when the voltage is raised, the current value of the no-load time is held and output for each pulse by the retainer (24) only after discharging. Since the comparator (26) and the electrode driving circuit (27) can be controlled to change the inter-electrode distance, the inter-electrode distance cannot be controlled in the state where no discharge occurs.

In this case, when the distance between the electrodes is so large that no discharge occurs, the no-load time becomes very large because the electric power remains applied between the electrodes. Therefore, in this state, as shown in FIG.
When the detector (23) detects the no-load time signal Ts ₄ of a certain time or longer, the no-load time upper limit value set by the no-load time upper limit value setter (22) as shown in FIG. 2 (c). The signal Tus is output to the holder (24). The holder (24) holds the no-load upper limit signal Tus and outputs it to the comparator (26). In the comparator (26), the no-load time upper limit value Tus of the no-load time upper limit signal Tus and the set no-load time signal T
The deviation signal S is output by comparing with the no-load time of rs, and the electrode driving circuit (27) outputs the deviation signal S from the deviation signal S.
Output Ds and control the distance between the electrodes so that discharge is possible. Therefore,
It is possible to properly and optimally control the inter-electrode distance not only when the inter-electrode distance is discharged but also when the inter-electrode distance is so large that no electric discharge occurs.

The no-load time measuring device (21) of this embodiment is configured by an analog charging circuit using a capacitor and a resistor, a digital circuit D / A converter using a reference oscillation clock and a counter circuit, and the like. It may be configured. Further, the no-load time can be fetched as data and processed by software including the electrode drive circuit.

[Effects of the Invention] As described above, the present invention detects the no-load voltage state from the inter-electrode voltage waveform between the electrodes by the first detector, and the no-load time state measuring device detects the no-load voltage state. Is measured and the current value of the no-load time is held and output for each pulse by the holder, or the no-load time of a certain time or more is detected by the detector of FIG. The no-load time upper limit set by the setter is held and output by the retainer, and the comparator outputs the no-load time preset as the control target and the current value or no-load of the no-load time output from the retainer. The deviation signal is output by comparing with the load time upper limit value, and the electrode driving circuit outputs the electrode driving signal for driving the machining electrode from the deviation signal to control the distance between the electrodes. In case of distance between poles Is controlled by the no-load voltage time that can essentially detect the discharge state without being influenced by the arbitrarily selected processing conditions, and abnormal discharge such as concentrated discharge or arc discharge is performed. It is possible to control the optimum inter-electrode distance that is unlikely to occur, improve the control response when the inter-electrode distance is far enough to prevent discharge, and perform normal inter-electrode distance control. There is an effect that machining efficiency during machining is also improved, and high-speed electric discharge machining which is 20% faster than the conventional one can be realized.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 (a) is a waveform diagram of inter-electrode voltage, FIG. 2 (b) is a waveform diagram of no-load time signal, and FIG. 2 (c). Is a waveform diagram of the no-load time upper limit value signal, FIG. 2 (d) is a waveform diagram of the electrode drive signal, and FIG.
FIG. 4 is a block diagram showing a conventional inter-electrode distance control device for electric discharge machining, FIG. 4 (a) is a waveform diagram of an inter-electrode voltage, FIG. 4 (b) is a waveform diagram of a deviation signal, and FIG. In the waveform diagram showing the inter-electrode control method that distinguishes the no-load time of different electric discharge machining into three, t ₁ of (50) and 5 _{2 of} (51) are set time to divide the section, (52) Shows a machining gap control signal set on the basis of the detected no-load time, and FIG. 6 is a waveform showing a machining gap control method for performing electrode movement according to another conventional no-load time distribution of electric discharge machining. In the figure, (53), (54), (55),
(56), (57), (a), (b) and (c) are the distributions of the voltage between contacts and the no-load time in the open state, arc state, narrow pole state, normal state and wide pole state, respectively. Is shown. In the figure, (4) is a workpiece, (5) is a processing electrode,
(20) is the first detector, (21) is the no-load time measuring device,
(22) is a no-load time upper limit setting device, (23) is a second detector, (24) is a holder, (26) is a comparator, and (27) is an electrode drive circuit. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A first detector for detecting a no-load voltage state from application of a voltage between an electrode for machining to be subjected to electric discharge machining and an electrode for a workpiece to a discharge, and a first detector. A no-load time measuring device that measures the no-load time of the detected no-load voltage state, a no-load time upper limit value setter that sets a predetermined no-load time upper limit value, and detects a no-load time of a certain time or more, A second detector for detecting the no-load time upper limit value of the no-load time upper limit value setting device, and a current value of the no-load time measured by the no-load time measuring device being held and output, and a second detection When the container detects a no-load time of a certain time or more, the holder that holds and outputs the no-load time upper limit set by the no-load time upper limit setter, the holding signal output from the holder, and the preset Deviation signal is output by comparing with the no-load time set value signal That comparator and comparator electrode distance control device for electrical discharge machining, characterized by comprising an electrode driving circuit for outputting an electrode driving signal for driving the tool electrode from the deviation signal.