JP4339601B2 - Electric discharge state detection method and electric discharge machine - Google Patents

Description

[0001]
[Technical field to which the invention belongs]
The present invention relates to an electric discharge state detection method and an electric discharge machine, and more particularly to an electric discharge state detection method and an electric discharge machine suitable for application in microwave electric discharge machining.
[0002]
[Prior art]
In general, when machining a workpiece with an electric discharge machine, there is a strong demand for stabilizing the electric discharge during machining. For that purpose, it is important to surely grasp the three states at the time of electric discharge machining, that is, (1) no discharge, (2) electric discharge that contributes to machining, and (3) short-circuit states. It is important to detect information related to the machining speed in the discharge state ▼.
[0003]
Factors affecting the processing speed include a peak current, a pulse time width, and an average current, and a processing speed calculation formula using these as parameters has been published (for example, see Non-Patent Document 1).
[0004]
Conventionally, there is a method of monitoring an average current as a method for detecting information related to the machining speed that is most commonly performed. According to this method, according to the formula described in Non-Patent Document 1, the processing speed can be grasped, and the short-circuit state can be reliably detected.
[0005]
[Non-Patent Document 1]
"Electric Discharge Machining Technology-From Basics to Future Prospects", page 31, co-authored by Nagao Saito and three others, published on September 30, 1997, Nikkan Kogyo Shimbun [0006]
[Problems to be solved by the invention]
However, in the method of monitoring the average current, the time constant of the current detection circuit becomes a problem. That is, the discharge is generated by repeating very fast pulses of tens of thousands to hundreds of thousands per second, while the average time constant of the monitored current is about 0.01 seconds to 1 second. . That is, this method is effective when the short-circuit frequency is low and the discharge continues for a few seconds at a constant intensity, for example, when the machining speed is high, such as rough machining, but the discharge state changes frequently from moment to moment. In the case of a simple target, there is a problem that it cannot immediately follow the change.
[0007]
In addition, there is another method for measuring the time from the pulse application to the start of discharge, that is, the time to discharge for each discharge pulse. However, since this method depends on the length of the discharge gap and the concentration of the processing waste in the discharge gap, it has no relationship with the processing speed, and it can only be distinguished whether it was a discharge or a short circuit.
[0008]
The present invention has been made to solve the above-described conventional problems, and even when discharge and short-circuit are frequently mixed and the discharge state frequently changes, the discharge that contributes to machining is accurately detected, and the discharge It is a first object to provide a discharge state detection method capable of monitoring the strength of the discharge.
[0009]
It is a second object of the present invention to provide an electric discharge machine capable of realizing stable electric discharge machining by applying the electric discharge state detection method.
[0010]
[Means for Solving the Problems]
According to the first aspect of the present invention, in the discharge state detection method, a pulse voltage generated from a pulse power source is applied to a gap formed between a workpiece and an electrode respectively connected to the power source via two lead wires. When the workpiece at the gap position is subjected to electric discharge machining, each of the two lead wires and the loop formed by the workpiece and the electrode has an open end and is electromagnetically coupled. Two loop antennas comprising two annular conductors, a load resistor connected to the open end of each loop antenna, and at least one of the load resistors connected to the two loop antennas, respectively. and sensitive only to the discharge, and adjusted to a value that does not sensitive to short circuit detects the high-frequency voltage generated in the load resistance across the one of the loop antenna, the detection high-frequency voltage By counting the raw frequency, by detecting the discharge state based on the emitting raw frequency is obtained by solving the first problem.
[0011]
That is, in the present invention, since the frequency of the high frequency generated during the electric discharge during the electric discharge machining can be detected, only the electric discharge contributing to the machining is counted, and the count density which is the count number within a predetermined unit time is used. It is possible to monitor the strength of the discharge with the strength of the discharge. Such a monitor value of the discharge intensity has an extremely strong correlation with the machining speed, so that the machining state can be accurately grasped.
[0013]
According to a second aspect of the present invention, in the discharge state detecting method according to the first aspect, a high frequency voltage generated at both ends of a load resistor connected to the loop antenna is detected by a transistor whose base is grounded.
[0014]
According to a third aspect of the present invention, in the discharge state detection method according to the first aspect, a high frequency voltage generated across a load resistor connected to the loop antenna is detected by a bipolar logic IC and converted to a logic level by the IC. It is what I did.
[0015]
According to a fourth aspect of the present invention, in the discharge state detecting method according to the first aspect, a signal detected from both ends of the load resistor connected to the loop antenna is input to a counter that is continuously refreshed at a separately defined frequency, The count value immediately before the refresh by the counter is the frequency of the high-frequency voltage.
[0016]
According to a fifth aspect of the present invention, in the discharge state detecting method according to the fourth aspect , the count value immediately before the refresh of the counter is converted into an analog value by a DA converter, and the discharge occurrence frequency is determined based on the analog voltage after the conversion. It is made to feature.
[0017]
According to a sixth aspect of the present invention, in the electric discharge machine, the discharge state detection method according to any one of the first to fifth aspects is applied, and the work and the electrode are The second problem is solved by providing control means for performing feedback to the drive means for adjusting the discharge gap therebetween.
[0018]
According to a seventh aspect of the present invention, in the electric discharge machine according to the sixth aspect, the position signal output from the work mounting means having a position detecting function, wherein the driving means for adjusting the discharge gap can mount the work. Drive control is performed by the control means based on a control signal obtained by superimposing the analog voltage in Item 5 .
[0019]
According to an eighth aspect of the present invention, in the electric discharge machine according to the seventh aspect , the drive means is a motor that moves the work mounting means in one axial direction.
[0020]
According to a ninth aspect of the present invention, in the electric discharge machine according to the sixth aspect , the drive means for adjusting the discharge gap is an actuator capable of mounting the workpiece and having no position detection function, and the actuator is the fifth aspect. Is driven and controlled by the control means based on the analog voltage.
[0021]
According to a tenth aspect of the present invention, in the electric discharge machine according to the ninth aspect , the actuator is a piezoelectric element attached to a moving table or a fixed base.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0023]
In FIG. 1, the outline | summary of the whole structure of the electric discharge machine of 1st Embodiment which concerns on this invention is shown. The electric discharge machine of the present embodiment includes a DC pulsed power supply (pulse power supply) 10 that can generate a pulse voltage by controlling the time width, a positive pole of the pulse power supply 10, and a workpiece W to be processed. A lead wire 12A for electrically connecting the negative electrode of the pulse power source 10 and a negative lead wire 12B for connecting the machining electrode 14. A pulse voltage is supplied from the pulse power source 10 to the workpiece W and the electrode 14. An electric discharge is generated by applying to the gap formed between the two, and the work W located in the gap is partially melted, so that the electric discharge machining for the work W can be performed.
[0024]
Further, in this electric discharge machine, a double conductor in which an annular conductor is electromagnetically tightly coupled along a loop formed by the + lead wire 12A and the workpiece W, the-lead wire 12B and the electrode 14. A (two-circuit) loop antenna 16 is provided. As schematically shown in an enlarged view in FIG. 2A, the double loop antenna 16 includes loop antennas 16A and 16B each formed of two annular conductors each having an open end. A load resistor composed of a fixed resistor R1 and a variable resistor R2 is connected to the open ends of the antennas 16A and 16B. A detection means 18 for detecting a high-frequency voltage generated during machining is connected to both ends of one fixed-side load resistor R1, and a counter 20 for counting the high-frequency voltage detected by the detection means 18; A DA converter 22 for converting the count signal output from the counter 20 into an analog discharge intensity signal is installed, and the signal output from the converter 22 is a workpiece mounting means 24 for mounting the workpiece W. Is output to the drive control unit of the moving table 24A, and the gap between the workpiece W and the electrode 14 is appropriately controlled.
[0025]
The electric discharge machine will be described in more detail. The double loop antenna 16 is bundled (arranged) along the loop including the + lead wire 12A, the work W, the electrode 14, and the-lead wire 12B. It is possible to detect only a high-frequency component when a discharge occurs between the workpiece W and the electrode 14. As described above, the use of the two loop antennas 16A and 16B can increase the degree of freedom in later signal processing. In addition, since the two loop antennas 16A and 16B need to be electromagnetically tightly coupled to ensure the signal identity, it is effective to use a bifilar winding.
[0026]
Further, in this double loop antenna 16, signals are detected from both ends of the load resistor R1 connected to one (fixed side) loop antenna 16A and used as a detection signal at the time of occurrence of discharge. By adjusting the load resistance R2, it is possible to respond only to electric discharge that contributes to machining and not to short circuit. Needless to say, the load resistance may be adjusted on the detection side or on both sides.
[0027]
Further, the counter 20 to which this detection signal is input is refreshed by a refresh signal which will be described later at a constant time interval, so that the number of discharges generated at this time interval is counted. The count value is converted into an analog voltage through the DA converter 22.
[0028]
The output of the DA converter 22 represents the discharge occurrence frequency. When the occurrence frequency is low, the discharge gap is narrowed. Conversely, when the occurrence frequency is too high, the discharge gap is widened. Control for applying feedback (feedback) for moving the moving table 24A is executed. This control will be described later.
[0029]
In FIG. 2 (B), by the pulsed power supply 10, a case of applying a pulse voltage of the pulse width t _p with period T, is induced in the loop antenna 16 shows the waveform of the detection by the oscillograph. As shown in this figure, it can be seen that the discharge contributing to machining and the other states can be clearly distinguished. That is, as described above, the value of the variable resistor R2 is determined so that the discharge state can be clearly distinguished. In this example, as shown in FIG. 6A, the load resistances R1 and R2 of the loop antennas 16A and 16B are both set to 47Ω, so that a good distinction can be obtained. If these resistance values are increased, the waveform at the time of a short circuit becomes larger and worse, and conversely, if the resistance value is decreased, the waveform of the electric discharge contributing to machining also decreases, so it is important to adjust these resistance values to appropriate values.
[0030]
FIG. 3 shows an example of a specific circuit constituting the detection means 18. Since the pulse width is as narrow as 1 nsec, it cannot be detected well with a general high-speed diode. Therefore, a transistor base grounding circuit is used. As such a base-grounded transistor, a commercially available transistor of about 6 GHz can be used. Further, here, a threshold value Vth is provided to slice the input waveform. The detection output should be connected to the logic IC via a high-speed comparator, but can be connected to the logic IC as it is if the bias conditions are matched.
[0031]
FIG. 4A shows another example of the detection means 18 in which detection is performed using a bipolar logic IC 18A composed of a commercially available JK flip-flop, and the signal is directly converted to a logic level by the same IC. .
[0032]
Since the logic IC 18A includes a circuit very similar to the base ground circuit on the input side, the circuit shown in FIG. 3 is unnecessary. Further, there is an advantage that chattering can be prevented by using the flip-flop in this way.
[0033]
FIG. 4B shows that the frequency of occurrence of discharge is accurately detected as shown in the example of the signal at the time of discharge detected and digitized by the bipolar logic IC 18A.
[0034]
FIG. 5A specifically shows a functional part that converts a high-frequency signal detected by the bipolar logic IC 18A into a count density (discharge occurrence frequency for each refresh time). The output frequency of the flip-flop formed in the logic IC 18A is half the pulse rate generated by the pulse power supply 10 at the maximum even if the discharge is a discharge that contributes to machining. Therefore, a refresh signal is output to the counter 20 from the time interval generator 26 at a frequency approximately 1/100 of the maximum frequency, and the counter 20 is continuously refreshed periodically. Note that if the refresh frequency set here is too low, the response becomes slow. On the other hand, if it is too high and approaches the maximum frequency, the detection resolution of the discharge generation density becomes coarse.
[0035]
As a specific example, the counter 20 has 7 bits, the pulse rate generated by the pulse power supply 10 is 600 kilopulses / second, and the refresh frequency is 2.5 kHz. In this case, the update (refresh) interval is 0.4 msec, and the ratio between the maximum detection value and the minimum detection value of the discharge density is 127.
[0036]
The relationship between the input waveform to the counter 20 and the output waveform from the DA converter 22 obtained by actual detection under such conditions is shown in correspondence with FIG. It can be seen that the generation density of the contributing discharge can be reliably grasped as an analog voltage signal, and the discharge occurrence frequency can be determined based on the magnitude of the converted analog voltage.
[0037]
In FIG. 6, feedback control is performed on a motor (driving means) 28 that moves the uniaxial moving table 24 </ b> A of the work mounting means 24 in the direction of the arrow based on the discharge generation density output from the DA converter 22. An outline of the control means is shown.
[0038]
The workpiece mounting means 24 has a fixed table 24B together with a movable table 24A on which workpieces can be mounted. When the workpiece W is mounted on the movable table 24A and moved, the scale 24C attached to the table 24A is It is read by the position detection head 24D attached to the fixed table 24B, and the amount of movement is detected. Then, the detection signal from the position detection head 24D is output to the superimposer 32 as a table position signal via the amplifier 30.
[0039]
In the superimposer 32, the input position signal and the voltage signal of the discharge generation density input in consideration of the time constant from the DA converter 22 are superimposed, and the result is output to the motor driver 34. Thus, the motor 28 is driven and controlled, and the discharge gap between the electrode 14 and the workpiece W is appropriately adjusted.
[0040]
That is, the superimposer 32 compares the output of the DA converter 22 with a target value (not shown), and adds a signal obtained by adding or subtracting the output of the converter 22 to the position signal input from the amplifier 30 based on the result. By moving the moving table 24A in the direction in which the discharge gap becomes wider when the output of the DA converter 22 rises above the target value, and in the opposite direction, the direction becomes narrower by outputting to the motor driver 34. An appropriate discharge gap can be maintained.
[0041]
The time constant can be set to 0.03 seconds, for example, in accordance with the control performance of the movement table 24A. In this way, by inserting a large time constant after the DA converter 22 and matching the motion performance of the table 24A, the discharge gap can be controlled appropriately. As a result, in the case of microwave electric discharge machining, the current value itself was small and discharge was unstable in the conventional average current method, but the stability could be greatly improved.
[0042]
According to the present embodiment described in detail above, the discharge can be accurately detected even during the electric discharge machining in which the discharge and the short circuit contributing to the machining are frequently mixed. In the conventional average current method, in such a case, it is considered that the discharge current is large.
[0043]
In addition, the reference time for updating the count number has a high degree of freedom in setting and can be determined in consideration of the discharge pulse rate. Specifically, it is arbitrary from 0.000001 seconds to 0.001 seconds, and can be several orders of magnitude faster than the case of the average current method.
[0044]
Therefore, by detecting and monitoring the discharge intensity, the system shown in FIG. 6 and the like that controls the discharge gap by using the monitored value (discharge generation density) is constructed. The discharge intensity can be stabilized since the discharge current can be made extremely fast. In particular, when mirror machining is performed by a micro electric discharge machine, the peak current must be lowered to the limit, which is effective because a short circuit easily occurs.
[0045]
In addition, since the responsiveness can be freely determined, it is possible to cope with a slow gap control system, and it can be mounted on a conventional electric discharge machine as it is.
[0046]
In FIG. 7, the principal part of the electric discharge machine of 2nd Embodiment which concerns on this invention is shown.
[0047]
In the present embodiment, the workpiece W is mounted on the actuator (driving means) 36 attached to the moving table (moving table) 24A as shown in FIG. 6, and the output of the DA converter 22 is sent to the comparator 32A. Input, compared with a target value (not shown), the deviation signal is fed back to the actuator driver 38, the actuator 36 is driven so that the deviation becomes zero, and the work W is moved, so that the discharge gap is adjusted appropriately. It has come to be. The actuator 36 may be attached to a fixed base having no moving function.
[0048]
This embodiment is suitable when it is not necessary to move a table having a large mass as shown in FIG. For example, in the case of micro discharge, a moving distance of 10 μm is sufficient. Therefore, an actuator 36 such as a piezoelectric element is more suitable for displacing such a small distance. In the case of micro discharge, since the work W is small and the mass is small, the response frequency can be swung to the performance limit of the actuator 36.
[0049]
【The invention's effect】
As described above, according to the present invention, the discharge state contributing to the machining can be accurately detected even when the discharge and the short circuit contributing to the machining are frequently mixed and the discharge state frequently changes.
[0050]
Therefore, it is possible to appropriately control the gap between the machining electrode and the workpiece by monitoring the detected discharge state and controlling the drive unit of the electric discharge machine based on the monitored value. The accuracy can be improved.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing an outline of an electric discharge machine according to a first embodiment of the present invention. FIG. 2 is an example of a double loop antenna that detects a high-frequency voltage and a diagram showing its characteristics. FIG. 4 is a circuit diagram showing a grounded base detection circuit constituting a detection means for detecting a voltage. FIG. 4 is a diagram illustrating another example of a detection means for detecting a high-frequency voltage and its characteristics. FIG. FIG. 6 is a block diagram showing a functional unit for converting to a count density and a diagram showing the operation thereof. Block diagram extracting and showing the main part of the drive control system of the electric discharge machine of the second embodiment
10 ... DC pulsed power supply (pulse power supply)
DESCRIPTION OF SYMBOLS 12 ... Lead wire 14 ... Processing electrode 16 ... Double loop antenna 16A, 16B ... Loop antenna 18 ... Detection means 20 ... Counter 22 ... DA converter 24 ... Work mounting means 24A ... Moving table 28 ... Motor 32 ... Superimposer 32A ... Comparator 36 ... Actuator W ... Work R1, R2 ... Load resistance

Claims (10)

A pulse voltage generated from a pulse power supply is applied to a gap formed between a workpiece and an electrode respectively connected to the power supply via two lead wires and discharged to discharge the workpiece at the gap position. When processing
A two-circuit loop antenna comprising two annular conductors each having an open end and electromagnetically coupled is provided along a loop formed by the two lead wires and the workpiece and the electrode. And connecting a load resistor to each open end of each loop antenna,
At least one of the load resistors connected to the two loop antennas is adjusted to a value that is sensitive only to discharge and not sensitive to short circuit,
A discharge state detection method comprising: detecting a high frequency voltage generated at both ends of a load resistance of one loop antenna; counting a frequency of occurrence of the detected high frequency voltage; and detecting a discharge state based on the frequency of occurrence. . In claim 1,
A discharge state detection method, comprising: detecting a high-frequency voltage generated at both ends of a load resistor connected to the loop antenna by a transistor whose base is grounded. In claim 1,
A discharge state detection method comprising: detecting a high-frequency voltage generated at both ends of a load resistor connected to the loop antenna by a bipolar logic IC and converting the detected high-frequency voltage to a logic level by the IC. In claim 1,
The signal detected from both ends of the load resistor connected to the loop antenna is input to a counter that is continuously refreshed at a separately defined frequency, and the count value immediately before the refresh by the counter is set as the frequency of generation of the high-frequency voltage. A discharge state detection method characterized by the above. In claim 4 ,
A discharge state detection method comprising: converting a count value immediately before refreshing the counter into an analog value by a DA converter, and determining a discharge occurrence frequency based on the converted analog voltage. Applying the discharge state detection method according to any one of claims 1 to 5 , feedback is made to a drive means that adjusts a discharge gap between the workpiece and the electrode based on the frequency of occurrence of the counted high-frequency voltage. An electric discharge machine comprising control means for applying. In claim 6 ,
Said drive means for adjusting the discharge gap, can be attached to the workpiece, the position signal output from the workpiece mounting means having a position detecting function, based on a control signal obtained by superimposing the analog voltage at claim 5 The electric discharge machine is controlled by the control means. In claim 7 ,
An electric discharge machine characterized in that the driving means is a motor for moving the work mounting means in one axial direction. In claim 6 ,
The drive means for adjusting a discharge gap is an actuator that can mount the work and does not have a position detection function, and the actuator is driven and controlled by the control means based on the analog voltage in claim 5 . An electric discharge machine characterized by that. In claim 9 ,
An electric discharge machine, wherein the actuator is a piezoelectric element attached to a movable table or a fixed table.

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