JP2005144651A - Penetration detecting device, method and electric discharge machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device and a method for accurately detecting penetration of hole machining, when performing electric discharge hole machining on a hollow-shaped work. <P>SOLUTION: This penetration detecting device in the electric discharge hole machining, is composed of a means for detecting updating of a lowering position when an electrode lowers; a means for providing maximum voltage by sampling, measuring and digitalizing voltage between the electrode and the work; a means for controlling a means for performing sampling and numerical expressing; a means for comparing a first maximum voltage value with a second maximum voltage value, by setting the maximum voltage equivalent to a first predetermined frequency as the first maximum voltage value, and setting the voltage as the second maximum voltage value, when the maximum voltage lower than the first maximum voltage value is provided by the next sampling; and a means for determining that a hole formed by discharge is penetrated, when a phenomenon of enhancing the first maximum voltage value by a predetermined voltage value or more than the second maximum voltage value, is continuously generated by a second predetermined frequency or more, by updating the lowest position when the electrode lowers. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a penetration detection apparatus and method for hole machining by electric discharge, and an electric discharge machine.

  In drilling by electric discharge, especially when the workpiece has a hollow shape and you want to drill only in the upper layer, or when the workpiece already has a horizontal hole and you do not want to drill a vertical hole toward the horizontal hole and pass the horizontal hole, the workpiece has a hollow shape. When a hole is drilled obliquely with respect to the upper layer surface (processed surface) and the lower layer of the workpiece is not required to be processed, it is necessary to accurately detect that the hole processing has been completed (penetrated).

  In addition, even when narrow hole machining is performed as a starting hole in the case of wire cut electric discharge machining, it is necessary to accurately detect that drilling has been completed (penetrated) in order to improve efficiency or automation. .

  Furthermore, the penetration detection can reduce the time such as extra electrode lowering. Therefore, the penetration detection is necessary to increase the machining efficiency in a large number of discharge hole machining operations.

  As methods for detecting penetration in electric discharge hole machining, Japanese Patent Laid-Open Nos. 04-283022, 05-285738, 07-164249, 09-239625, 11-1213616, 2002-292522, etc. There is a description.

  Japanese Laid-Open Patent Publication No. 04-283022 discloses a method for detecting penetration in fine hole electric discharge machining as an electric discharge machining start hole for wire cut electric discharge. This is a technology of a device that electrically detects penetration by contacting a contact under the workpiece after the electrode has penetrated the hole. This technique is difficult to adapt to hollow workpieces.

  Japanese Patent Laid-Open No. 05-285738 discloses a technique of an electric discharge machining apparatus that detects the penetration by detecting that the machining fluid pressure on the penetration outlet side in the discharge hole machining is changed by the penetration. This technology is also difficult to adapt to hollow workpieces.

  Japanese Laid-Open Patent Application No. 07-164249 is not a technique for directly detecting the penetration of electric discharge hole machining, but detects the current value flowing through the electrode and the current-carrying member below the workpiece, Discharge hole data generator, machining state identification unit that determines whether or not electrical discharge machining is abnormal from the position data, and narrow hole electric discharge machining with machining condition control unit that controls machining conditions based on the output from the identification unit The technology of the apparatus is disclosed, and it is considered that this configuration can be applied to the detection of penetration in discharge hole machining. However, there is no description of a specific technology as penetration detection.

  Japanese Laid-Open Patent Application No. 09-239625 discloses a technique of an electrode machining apparatus for electric discharge machining provided with a penetration detection means for detecting penetration by an electrode based on the frequency of occurrence of a short-circuit current flowing between the electrode and the workpiece. . Although this technique seems to be applicable to hollow workpieces, the point of penetration detection is that the frequency of occurrence of short-circuit current flowing between the electrode and the workpiece is reduced.

  In Japanese Patent Laid-Open No. 11-1213616, penetration is detected by a non-contact sensor such as a photo sensor or a magnetic sensor by passing the tip of the electrode out of the hole outlet and energizing the contactor, and the machining liquid is placed near the penetration part. A technique for obtaining a high-precision finish of drilling holes is disclosed. This technique is difficult to adapt to hollow workpieces.

Japanese Patent Laid-Open Publication No. 2002-292522 discloses a technique in which a target is provided in advance in a planned penetration portion, and when the electrode comes into contact with the target, the penetration detection of the electrode is detected by a contact detection means constituted by a resistor, a photocoupler, and the like. Yes. Although this technique can be applied to a workpiece having a limited shape having a horizontal hole, a special jig or the like is required to adapt to a hollow workpiece having various shapes, and it is considered difficult to apply.
JP-A-4-283022 JP 05-285738 JP 07-164249 A JP 09-239625 Japanese Patent Laid-Open No. 11-1213616 JP2002-292522

  Due to the above-mentioned problems of the prior art, the problem to be solved by the present invention is to drill only the upper layer in a hollow workpiece, oblique narrow hole drilling, horizontal hole by a method other than measuring the short-circuit current between the electrode and the workpiece. It is an object of the present invention to provide an apparatus and method for detecting penetration that can be applied to machining of a discharge hole such as drilling of a non-through vertical hole in a workpiece that already has a through hole, and a thin hole electric discharge machine equipped with the penetration detection apparatus.

  As a result of intensive studies, the present inventor has means for detecting that the electrode is descending in the vertical direction and has updated the lowest position; means for sampling and measuring the voltage between the electrode and the workpiece and digitizing the voltage Means for controlling means for sampling and digitizing; obtaining a digitized voltage for a first predetermined number of times and storing the maximum voltage therein as a first maximum voltage value in a first storage device; Means; if a maximum voltage lower than the first maximum voltage value is obtained in the next sampling, means for storing the voltage in the second storage device as a second maximum voltage value; Means for comparing the second maximum voltage value; an event in which the electrode updates its lowest position, and an event in which the first maximum voltage value is higher than the second maximum voltage value by a predetermined voltage value or more If it occurs continuously more than the number of times, the generated hole Have found that the above problems can be solved by a through sensing apparatus comprising a through-the means for determining.

  Further, as specific means of each means and default value of the above-mentioned device, the means for detecting that the electrode is descending and the lowest position is updated is a signal from the encoder linked to the Z-axis moving servo motor. CPU for processing; means for sampling and digital digitization is an A / D converter; sampling period is in the range of 0.01 to 1 millisecond; means for controlling the means for sampling and digital digitization; Means for obtaining a measurement voltage maximum value for a predetermined number of times, first storage device, second storage device, means for storing first and second maximum voltage values, first maximum voltage value and second maximum The means for comparing voltage values and the means for determining penetration are microcomputers (microelectronic computers) having a CPU, I / O, and memory for storage; the first predetermined number of times is in the range of 1 to 100 times. If the found that the above problems can be solved.

  As a means for detecting that the electrode is descending in the vertical direction and the lowest position is updated, the electric discharge machine generally has a servo mechanism that moves the electrode up and down in the Z-axis direction. By attaching an encoder to the servo motor, the Z-axis position information of the head holding the electrode is sent to the CPU of the microcomputer every unit time, and the CPU is in the lowering of the head (that is, the electrode is lowering) and the bottom It is obtained by judging that the position has been updated. As another detection means, a linear scale may be used.

  The means for sampling and measuring the voltage between the electrode and the workpiece and digitizing them, and the means for controlling them are the input unit connected to the electrode and the workpiece, respectively, and the output unit for outputting the measured voltage digital output to the CPU of the microcomputer Is obtained by setting the sampling frequency of the voltage measured from the CPU of the microcomputer, the measurement time, and the like, and taking the digital voltage value into the CPU of the microcomputer.

  The digitized voltage is obtained for the first predetermined number of times, the maximum voltage value is stored in the first storage device, and if a voltage lower than the maximum voltage value is obtained by the next sampling, the voltage value is Means for storing in the second storage device, means for comparing the voltage value stored in the first storage device with the voltage value stored in the second storage device, and the electrode updates its lowest position, If the event that the voltage value stored in the storage device is higher than the voltage value stored in the second storage device in the range of the predetermined voltage value continuously occurs for the second predetermined number of times or more, the generated hole has penetrated. As a means for determination, it is obtained by a microcomputer having a CPU, a memory, and an I / O (input / output unit). Of course, it is also efficient to serve as a CPU for controlling the A / D converter.

  FIG. 5 shows a typical graph in which the voltage between the electrode and the workpiece is measured over time in drilling by electric discharge. When this voltage transition is carefully observed, the voltage changes drastically due to the discharge phenomenon, and sometimes a noise value is also found. It was observed that the maximum voltage gradually decreased with the progress of processing. Further, when observing the descending distance of the Z axis measured simultaneously, that is, the machining depth + the electrode consumption length, the right axis of the graph shows the descending distance, but the descending distance proportional to the square root of time was observed.

  As the machining progressed and finally penetrated, the voltage between the electrode and the workpiece was found to increase by an average of about d volts as shown in the graph of FIG. A slight change was also observed in the descending distance. Actually, the instant of visual penetration was the time indicated by P in the graph.

  At first, we tried to detect penetration by detecting the change in the descending distance of the electrode. However, since the change appears slightly later than the actual penetration when the change is small, the penetration is focused on the change in voltage. We considered to detect.

  First, in order to eliminate the influence of an impulsive abnormal voltage value that occasionally occurs, it is determined that a case where a change in an event considered to be a penetration occurs continuously for a certain number of times is a penetration. Next, an event that is considered to be a penetration was detected as an increase in the discharge voltage that exceeds the reference voltage.

  The sampling period for measuring the voltage is desirably 0.01 to 1 millisecond, the number of detected voltage peak values is desirably 1 to 100, the difference between the through voltage and the reference voltage is desirably 0.1 to 50 V, and the repetition of the event The number of times is preferably 1 or more and 99 or less.

  By many experiments, the reference voltage is defined as the discharge peak voltage over time, and the sampling frequency, the maximum (peak) voltage value detection data number, the difference between the through voltage and the reference voltage, and the number of repetitions of the event are specified as described above. It was found that reliable penetration can be determined.

  According to the present invention, it is possible to accurately detect the end of drilling (penetration) with respect to non-piercing drilling of a workpiece having only a hollow shape workpiece by an electric discharge, oblique hole machining, horizontal hole or oblique hole machining. There are advantages such as improved machining efficiency, improved machining accuracy, reduced defect rate, and adaptation to automation.

  FIG. 1 shows an outline of a desirable electric discharge machine according to the present invention. The electric discharge machine 10 includes a machine body 1, a penetration detection device 20, a power supply unit 2, and a servo control unit 3. The processing machine body 1 includes a motor 7 that rotates the pipe electrode 12, a chuck 9 that holds the pipe electrode 12, a servo motor 6 that moves the pipe electrode in the Z-axis direction, a steady rest 11 that prevents the pipe electrode from shaking, and a workpiece 13, a servo motor 14 that moves the work table in the X-axis direction, a servo motor 15 that moves in the Y-axis direction, and the like.

  An encoder 8 is attached to the servo motor 6 that controls the movement in the Z-axis direction (pipe electrode), and a negative DC voltage is applied to the pipe electrode 12 and a positive DC voltage to the work 13 via a chuck 9 that is insulated from the main body. It is desirable that the movement of the Z axis is controlled by the servo control unit 3 so as to maintain a so-called steady discharge state based on the Z axis position signal supplied from the power supply unit 2 and the voltage between the gaps from the encoder 8.

  In order to detect penetration, the voltage between the pipe electrode 12 and the work 13 (between the gaps) is first taken into the A / D converter 5, and the sampling frequency, the predetermined sampling number N, etc. are set by the program control of the microcomputer 4. Thus, it is preferable to obtain a digital digitized voltage.

  Next, of the obtained voltage data N times, the maximum voltage value is stored in the first memory of the microcomputer 4 as the first maximum voltage value V1.

  Next, if the maximum voltage value obtained by the next sampling generates a maximum voltage value smaller than the previous first maximum voltage value V1, it is set as the second maximum voltage value V2, and the second memory of the microcomputer 4 is used. Remember me.

  By sequentially comparing the first maximum voltage value V1 and the second maximum voltage value V2, events in which the first maximum voltage value V1 is higher than the second maximum voltage value V2 by a predetermined voltage difference M are continuously determined. If the number of times is T or more, it is determined that the electrode has penetrated. These procedures are shown as a process flow diagram in FIG.

  These series of operations and control are all desirably set in advance in the microcomputer 4 as a program. In FIG. 1, the arrangement of the power supply unit 2, servo control unit 3, microcomputer 4 and A / D converter 5 is easily understood. However, specific combinations or all of them may be combined into one device.

  FIG. 2 shows a block diagram of the penetration detection device 20 including the microcomputer 4 and the A / D converter 5 and an external device, and FIG. 3 shows a circuit diagram of the same configuration. The microcomputer 4 also performs electric discharge machining pulse voltage control between the electrode 12 and the workpiece 13 via the switching transistor 16.

  A signal line for measuring the voltage between the gaps is connected to the circuit charged on the electrode side and the workpiece side, and an AD7572JN12 manufactured by Analog Devices is used as an A / D converter. Connected via O and I / F. NEC's 32-bit control microcomputer consists of a 1 GHz clock, 256 MB of RAM as a storage device, 20 GB HDD, I / O, I / F, etc., using Microsoft's OS: Windows NT, and Microsoft's Visual. It is programmable by Basic and the A / D converter can be controlled by a program created by the user.

  Only the upper layer of the SKD11 hollow box-shaped workpiece 13 having an overall thickness of 10 mm and a thickness of 3 mm is discharged with a brass pipe electrode 12 having an outer diameter of 1 mm and a hole having a diameter of 1.05 mm by the electric discharge machine shown in FIG. processed.

  In the pipe electrode 12, a machining liquid mainly composed of water is flowed at a water pressure of 5 Mpa, and the pipe electrode 12 side is negative, the work 13 side is positive, and a DC pulse voltage is charged from the power supply unit 2 at an open voltage of about 120V. The Z axis was lowered to the start of discharge. The discharge start voltage is about 45V, and the so-called steady discharge state in which the Z-axis position data from the CB500LV encoder 8 manufactured by Line Seiki Co., Ltd. attached to the Z-axis servomotor 6 and the discharge current between the gaps is 10 ± 2A. The servo control of the servo control unit 3 lowered the Z axis as the discharge hole machining progressed.

  Corresponding to the process steps shown in FIG. 4, determination of Z-axis bottom update from servo control, discharge voltage measurement command to A / D converter, extraction of maximum (peak) voltage from A / D converter, maximum voltage rise The control microcomputer was operated by creating a program that made the above-mentioned determination and the determination of reaching the specified number of times.

  Note that the program is created by setting the first predetermined number of times, which is the predetermined number of samples, to 10 times, the sampling period to 0.02 milliseconds, that is, the frequency is 50 KHz, the predetermined voltage value is 5 V, and the second predetermined number is 3 times. did.

  The time from the start of discharge to penetration detection was around 75 seconds. When penetration was detected, the output signal could be applied to automated operations such as stopping electrical discharge machining and starting the next process operation. In this embodiment, visual penetration detection is not necessary, contributing to work efficiency and reducing manpower.

  According to the present invention, it is possible to accurately know the completion (penetration) of drilling in electric discharge drilling, in particular, fine hole electric discharge machining. Therefore, the drilling of a hollow workpiece, the drilling of a workpiece that already has a horizontal hole, and the hollow shape It is possible to contribute to the efficiency of electric discharge hole machining work by adapting precision machining technology for slanted hole machining to this workpiece and automating these electric discharge machining.

It is the schematic of the electric discharge machine by this invention. It is the schematic of the penetration detection apparatus by this invention. It is a block circuit diagram of the penetration detection device by the present invention. It is a flowchart of the penetration detection process by this invention. It is the graph which measured the voltage between gaps and the fall (drilling) depth with time.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electric discharge machine main body 2 Power supply 3 Servo control part 4 Microcomputer 5 A / D converter 6 Z-axis servo motor 7 Electrode rotation motor 8 Encoder 9 Electrode attachment chuck 10 Electric discharge machine 11 Electrode shake prevention apparatus 12 Pipe electrode 13 Hollow shape workpiece 14 X-axis servo motor 15 Y-axis servo motor 16 Switching transistor 20 Penetration detector

Claims (11)

  Means for detecting that the electrode is descending vertically and updating the lowest position; means for sampling and measuring the voltage between the electrode and the workpiece and digitizing; and said sampling and digitizing Means for controlling the means; means for obtaining the digitized voltage for a first predetermined number of times, and storing the maximum voltage therein as a first maximum voltage value in a first storage device; Means for storing the voltage in the second storage device as a second maximum voltage value if a maximum voltage lower than the maximum voltage value is obtained in the next sampling; Means for comparing the maximum voltage value; the electrode is being lowered and the lowest position is updated, and the first maximum voltage value stored in the first storage device is stored in the second storage device From the second maximum voltage value If generated increases the value or event is continuously second predetermined number of times or more, through detection device in the discharge hole drilling comprising a means for determining that the generated holes penetrated by discharge.   2. The penetration detection device in discharge hole machining according to claim 1, wherein the means for detecting that the electrode is descending and that the lowest position has been updated is a CPU that processes a signal from an encoder linked to a Z-axis movement servo motor. .   The penetration detecting device in electric discharge hole machining according to claim 1, wherein the means for sampling and digitizing is an A / D converter, and the sampling period is in the range of 0.01 to 1 millisecond.   Means for controlling means for sampling and digitizing; means for obtaining a measured voltage maximum value for a first predetermined number of times; first and second storage devices; first and second storage means; first storage The means for comparing the maximum voltage value stored in the device with the maximum voltage value stored in the second storage device and the means for determining penetration are a microcomputer (micro computer) having a CPU, I / O, and storage memory. The penetration detection device in discharge hole machining according to claim 1.   The penetration detection device in electric discharge hole machining according to claim 1, wherein the first predetermined number of times is any one of 1 to 100 times.   The penetration detection device in discharge hole machining according to claim 1, wherein the predetermined voltage value is a voltage within a range of 0.1 to 50V.   The penetration detection device in electric discharge hole machining according to claim 1, wherein the second predetermined number of times is any one of 1 to 99.   When the electrode is descending in the vertical direction and the lowest position is updated, the signal from the encoder is detected by the CPU, and the voltage between the electrode and the workpiece is sampled and measured by the A / D converter. Digitally digitizing; controlling means for sampling and digitizing by means of a microcomputer (micro computer) having a CPU, I / O, and storage memory; and converting the digitized voltage to a first predetermined number of times And the first voltage value is stored in the first storage device as a first maximum voltage value; if a maximum voltage lower than the maximum voltage value is obtained in the next sampling, the voltage is set to the second maximum voltage value. A value stored in a second storage device; the first maximum voltage value stored in the first storage device is compared with the second maximum voltage value stored in the second storage device; Has updated its lowest position, and if an event in which the first maximum voltage value is higher than the second maximum voltage value by a predetermined voltage value or more continuously occurs for a second predetermined number of times or more, A method for detecting penetration in electric discharge hole machining comprising a step of determining that a generated hole has penetrated.   The sampling period is in the range of 0.01 to 1 millisecond, the first predetermined number of times is in the range of 1 to 100 times, the predetermined voltage value is in the range of 0.1 to 50 V, and the second The method for detecting penetration in electric discharge hole machining according to claim 8, wherein the predetermined number of times is in a range of 1 to 99 times.   Means for detecting that the electrode is descending in the vertical direction and updating the lowest position; an A / D converter that samples and measures the voltage between the electrode and the workpiece and digitizes the voltage; and said sampling and digital Means for controlling means for digitizing; means for obtaining the digitized voltage for a first predetermined number of times and storing the maximum voltage therein as a first maximum voltage value in a first storage device; If a maximum voltage lower than the maximum voltage value is obtained in the next sampling, the means for storing the voltage value in the second storage device as the second maximum voltage value, the first maximum voltage value and the second voltage value Means for comparing the maximum voltage value, wherein the electrode has updated its lowest position, and the voltage value stored in the first storage device is higher than the voltage value stored in the second storage device by a predetermined voltage value or more. The event Penetration detection device having a microcomputer (micro computer) having a CPU, I / O, and storage memory as means for determining that a hole generated by electrical discharge machining has penetrated if it occurs continuously more than the number of times EDM machine equipped with.   The sampling period is in the range of 0.01 to 1 millisecond, the first predetermined number of times is in the range of 1 to 100 times, the predetermined voltage value is in the range of 0.1 to 50 V, and the second The electric discharge machine provided with the penetration detection device according to claim 10, wherein the predetermined number of times is in a range of 1 to 99 times.

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