JPS6165724A - Electric discharge machining device - Google Patents

Abstract

PURPOSE:To make it possible to prevent an electrode, a workpiece or the like from being broken, by taking into a picture the outer contour line part of a working gap with the use of image sensors in synchronism with the generation of electric discharge, and by comparing image signals with the use of a correlator so that the electric discharge machining device is controlled when the signals exceed a predetermined value. CONSTITUTION:Image sensors 8, 10 are scanned in association with instruction pulses, and the thus obtained image signals are once stored in memories 23, 24, are then transferred into memories 25, 26 and are further transferred into memories 27, 28. Next the correlating function F1 between a new image signal X1 stored in the memory 24 and the previous image signal X2 stored in the memory 26 is calculated, and when it exceeds a threshold value, it is delivered to an AND circuit 34. Similarly, a correlator 32 calculates the correlating function F2 between an image signal X3 stored in the memory 26 and the previous image signal X3 stored in the memory 28, and delivers it to the AND circuit 34 when it exceeds the threshold value. Further, when abnormal electric discharge such as, for example, discharge in gas or centralized discharge is started to occur, the value comes to be near to +1 or -1, and therefore the centralized discharge or the like may be at once detected and is delivered to a control circuit to control associated sections for normalization.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to electrical discharge machining equipment.

[Conventional technology]

Unlike normal machining, which performs machining by directly applying mechanical force to the workpiece, electrical discharge machining equipment applies voltage pulses to the gap between the workpiece and the electrode, where the machining fluid is present, and the resulting This is a non-contact machining process that utilizes electrical discharge phenomena.

Therefore, when performing electrical discharge machining, the material of the electrode should be selected taking into account the material of the workpiece, the purpose and conditions of machining, etc., and the machining conditions should be selected to suit the shape of the workpiece and the purpose of the product. In other words, the power supply voltage, the duration of the voltage pulse or the discharge current pulse, the rest time thereof, the amplitude of the discharge current, and the method of supply intervention such as the hydraulic pressure of the machining fluid, the required machined surface roughness, and the electrode Machining is performed by selecting and setting the wear ratio and machining speed.

Therefore, when electrical discharge machining is performed well, the electrical discharge between the electrode and the workpiece is distributed randomly and occurs at a uniform frequency in each part, but when the electrical discharge between the workpiece and the electrode If the relative position is not set correctly or if gas or machining debris is unevenly distributed in the machining fluid in the machining gap, the discharge in the machining gap between the electrode and the workpiece will become irregular. At the same time, the discharge is no longer distributed approximately evenly over the entire machining gap, and the discharge between the electrode and the workpiece is concentrated in one place, and furthermore, this transforms into an abnormal discharge such as an arc. It turns out.

As mentioned above, if electrical discharge is not performed normally, the machining speed will decrease, and machining performance such as electrode wear and machined surface roughness will change, not only will machining not be performed smoothly. In some cases, the expensive electrode or workpiece may be damaged.

Conventionally, the state of discharge or whether it is good or bad has been determined by measuring the discharge voltage or discharge current, etc., but it is difficult to accurately grasp the state of discharge or whether it is good or bad depending on the above-mentioned determination method. Ta.

In particular, when a harmful discharge occurs, a concentrated discharge occurs before it occurs, but it is difficult to detect the occurrence of the precursor concentrated discharge at an early stage.

Moreover, such a situation often occurs immediately after the start of machining, and therefore, it is necessary for a skilled person to set up the machining, and furthermore, it is necessary to continue monitoring for a considerable period of time even after the start of machining.

These concentrated discharges can be easily observed using a video camera that can photograph the machining part, but the machining fluid is usually cloudy and gas is generated, so it is difficult to detect them. It's not easy.

[Problems to be solved by the present invention]

The present invention was made from the viewpoint of ridges, and
The purpose of this is to use an image sensor to photograph the machined part of the workpiece that faces the electrode during electrical discharge machining, and the outer peripheral contour of the machining gap formed by the two, in synchronization with the occurrence of electrical discharge, and to generate the video signal. The occurrence of abnormal discharges such as concentrated discharges is monitored by recording multiple frames of video signals and comparing these video signals with a correlator, and if the correlation coefficient is greater than a predetermined value, the occurrence of concentrated discharges etc. Electrical discharge machining equipment that can immediately control the equipment as if an abnormal discharge has occurred, return it to a normal discharge state, and prevent damage to the electrode or workpiece due to abnormal discharge, etc. This is what we are trying to provide.

[Means to solve the problem]

The above object is to provide a light source in an electric discharge machining apparatus that illuminates a machining part of a workpiece facing the electrode during electric discharge machining, particularly a desired part of the outer peripheral contour of the machining gap formed by the two. an image sensor for photographing a desired outer peripheral contour of the machining part or the machining gap; a circuit for scanning the image sensor in synchronization with the generation of electric discharge and generating a video signal; and a first circuit for storing the video signal. a second stage memory, at least one subsequent stage memory that sequentially stores the video signal stored in the first stage memory before the first stage memory starts storing the next one; Abnormal discharge monitoring device for concentrated discharge, etc., comprising a correlator that calculates the correlation coefficient between the new video signal and the video signal stored in the subsequent memory and generates an output signal when the value exceeds a certain threshold. This is achieved by providing

The first stage memory records the image signal obtained by scanning the image sensor record during the last discharge, and the second stage memory records the image signal obtained by scanning the image sensor record during the last discharge. Records are recorded sequentially.

When a serial number n is given to each element of the image sensor, its image signal value is An, and the corresponding recorded values of the first and second stage memories are Xr (An) and X2 (
An), the correlation coefficient F between the recorded data of the first stage memory and the second stage memory is the covariance Cov CX1 (An), X2 (An) of Xl (80), x2 (static).
)) and the variance σI of Xt(An) and X2(An)
2, and the square root of the product of σ22.

Cov(Xl(An),X2(An))=E
(Xt (An), X2 (An)) E
(Xt (An)) ・E(X2(8n)
) (However, E indicates the average value.) σ12=Var・Xl (An) = E(Xt(An) −E (Xt(An)
) ) 2a22=Var-X2 =E CX2 (An) -E (Xt (An
) ) ) 2.

However, here, it is not necessary to strictly calculate the value of F, and it goes without saying that a known approximate calculation formula or the like may be employed.

[For production]

As described above, the machining part of the workpiece facing the electrode is photographed by an image sensor in synchronization with the generation of electric discharge, and the position of the discharge appearing in the video signal photographed by the image sensor and the position of the electric discharge in the next video signal are A correlator compares the position of the discharge that appears in This prevents the electrode or the workpiece from being damaged by electrical discharge or the like.

〔Example〕

Hereinafter, the details of the present invention will be specifically explained with reference to the drawings.

FIG. 1 is an explanatory diagram showing one embodiment of the electrical discharge machining apparatus according to the present invention, FIG. 2 is an explanatory diagram showing another embodiment of the image sensor portion thereof, and FIG. 3 is a front view thereof. .

In Figures 1, 2, and 3, ■ is the main body of the electrical discharge machining device, 2 is a machining head that is installed on a column set up on the head, etc. so that it can be moved up and down, position the feed, or control the feed. 4 is a processing tank; 4a and 4a are support arms formed on the outer peripheral wall of the processing tank 4; 5 and 6 are thumb screws; 7 and 8 are support arms 4a and 4a, respectively.
A rond is attached to the holder so that the vertical position can be adjusted, and holders 7a and 8a are formed at the tips of the holders 7a and 8a for attaching the COD image sensors 9 and 10, respectively. A light source attached to the tip of each CCD image sensor 9 and IO, 15 a workpiece housed in the processing tank 4, 1
6 and 17 are cross slide tables that move the processing tank 4 in the X-axis and Y-axis directions; 1 is a turntable that is mounted on the cross slide table 16 and gives rotational motion to the processing tank 4; 19 is the above-mentioned turntable; The base on the bed of the electric discharge machine main body 1 on which the cross slide tables 16 and 17 are mounted, 2o, 21 and 22 are the cross slide tables 16, 17 and turntable 18.
The motors that drive the first memory, the first memory, and the second
6 is a second memory, n and 28 are third memories, 29 and 3o are first correlators, 31 and 32 are second correlators,
33 and 34 are AND circuits, 35 is a resistor, 36 is a DC power supply, 37 is a switching transistor, 38 is a switching transistor control circuit that controls the switching transistor 37, 39 is a Schmitt trigger circuit, 4o
is a monostable element, 48.49 is a preset counter, 41 is a CCD image sensor, 42 is a housing,
43 is a glass, 44 is a motor that drives the wiper 45, 4
6 is an O-ring, and 47 is oil.

The operations of the above-mentioned parts are collectively controlled by a control device (not shown) according to a predetermined program.

Thus, the workpiece 15 is attached to the processing tank 4, and the turntable 18 on which the processing tank 4 is mounted is mounted.
Rotary movement and machining feed movement in the X-axis and Y-axis directions are provided by cross slide tables 16 and 17.

Support arms 4a, 4a are formed on the outer peripheral surface of the processing tank 4, and rods 7 and 8 are fixed to the support arms 4a, 4a with thumbscrews 5 and 6, respectively. By loosening the screws 5 and 6, the vertical positions of the lofts 7 and 8 can be adjusted. Further, holders 7a and 8a into which CCD image sensors 9 and 10 are fitted are formed at the tip portions of the rods 7 and 8, and the CCD image sensors 9 and 10 are fitted into the holders 7a and 8a with thumbscrews 11 and 8a. 12 so that the position can be adjusted.

A DC power supply 36 is turned on and off by a switching transistor 37 and is applied as a voltage pulse of a predetermined value between the electrode 3 and the workpiece 15.

A light source 13 is provided on the outer peripheral wall surface of the tip portions of the CCD image sensors 9 and 10 for irradiating infrared light, laser light, halogen light, or the like onto the processing portion of the workpiece 15 and the desired outer peripheral contour portion of the processing gap formed by both. and 14 are attached.

During electrical discharge machining, the desired outer peripheral contour of the machining portion of the workpiece 15 and the machining gap is exposed to the irradiation devices 13 and 14.
At the same time, images are taken by the CCD image sensor 9 and XO every predetermined minute period (or time) consisting of the part, and are displayed on a screen (not shown), and between the electrode 3 and the workpiece 15 When a discharge occurs, the discharge is detected by the resistor 35, the Schmitt trigger circuit 39, and the monostable element 40, and the pulses generated by the monostable element 40 are counted by a predetermined number of times (approximately during a predetermined minute period of imaging by the CCD). Correspondingly, the preset counters 48, 49 each generate a scanning command pulse.

In such a case, the CC, DCCD image sensor 10 is scanned, and the video signal obtained thereby is stored in the first memory 24, and the first memory 24 stores the following: For example, the video signal data stored in the first memories 23 and 24 is transferred to the second memories 25 and 24, starting with the next output pulse of the preset counters 48, '49. Furthermore, when the first memories 23 and 24 start the next storage, the video signals previously stored in the second memories 5 and 26 are transferred to the third memories 27 and 28, and The video signals stored in the memories 23 and 24 are sequentially stored in the second memories 25 and 26.

In the figure, the COD image sensor 10, the first
memory 24, second memory 26, third memory 28,
First correlator 30, second correlator 32 and AND circuit 3
The CCD image sensor 9 shown on the right side is the same as the action of 4.
First memory 23, second memory 25, third memory 2
7. The functions of the first correlator 29, the second correlator 31, and the AND circuit 33 are the same except for the length of the storage target period and the fact that they may have a temporal phase difference, so the following will be explained. The former effect will be explained.

The first correlator 30 calculates a correlation coefficient F1 between the new video signal X1 stored in the first memory 24 and the previous video signal X2 stored in the second memory 26. When a certain threshold value is exceeded, the output is outputted to the AND circuit 34. Similarly, the second correlator 32 is connected to the second memory 26.
A correlation coefficient F2 is calculated between the video signal X2 stored in the third memory 28 and the previous video signal X3 stored in the third memory 28, and when the value exceeds a certain threshold, the output is sent to the AND circuit 34. Output.

The values of Fl and F2 are between +1, and while discharges occur randomly and discretely, the magnitudes of Fl and F2 are close to O, but abnormal discharges such as discharges in gas or concentrated discharges occur. Since the value becomes close to +1 or -1 when it starts, abnormal discharges such as concentrated discharges can be detected immediately.

The AND circuit 34 outputs a pulse signal in which the re-input signal becomes state 1 at the same time to a control circuit (not shown), and the control device controls each part of the device, for example, by temporarily retracting the electrode 3 and discharging it. is configured to return to normal state.

Thus, as described above, the CCD image sensors 9 and 10
During machining, the light sources 13 and 14 attached to the outer peripheral wall surface of the tip of the workpiece 15, the desired outer peripheral contour of the machining gap, and the desired outer peripheral contour of the machining gap are always sufficiently illuminated. Even if the machining fluid is contaminated with machining debris etc., the CCD image sensors 9 and 10 can display the machining portion of the workpiece 15 on a display device (not shown). Electric discharge machining is performed while constantly comparing the discharge situation that appeared in the new video signal stored in the second memories 23 and 24 with the discharge situation that appeared in the previous video signal stored in the second memories 25 and 26. Therefore, if the discharge is not uniformly applied to the workpiece 15 during machining, or if an abnormal discharge such as discharge in gas or arc occurs, this will be immediately detected and the control device will immediately control each part. Since the discharge state is controlled to return to a good discharge state, machining can be performed in a stable discharge state at all times.

The CCD image sensors 9 and 10 are usually oil-resistant ones that are directly fitted into the holders 7a and 8a of the rods 7 and 8, but as shown in FIGS. 2 and 3, at least the CCD image sensors The lens 41 is immersed in oil 47 and hermetically housed in the housing 42, and the glass 43 is wiped away by a wiper 45 while photographing the processed part of the workpiece 15. Also used are those made by With this configuration, a clear image can be displayed on a display device (not shown), making it possible to observe the exact position and state of discharge.

〔Effect of the invention〕

Since the present invention is structured like a ridge, when the present invention is used, a CCD image sensor photographs the machined part of the workpiece facing the electrode during electric discharge machining and the desired outer contour line of the machining gap, and displays the image on the screen. At the same time, the correlation coefficient between the video signal indicating the current discharge position and the video signal indicating the discharge position a certain period of time ago is determined, and if the value is greater than a predetermined value, each part of the device is immediately Since this control is carried out, abnormal discharges such as concentrated discharges or arc discharges can be prevented, and furthermore, expensive electrodes or workpieces can be prevented from being damaged by the abnormal discharges. It is.

Note that the present invention is not limited to the embodiment on ridges. That is, for example, in this embodiment, a CCD image sensor is shown as an image sensor, but this may be another device, such as a video camera. Furthermore, although the light source is provided at the tip y111 of the CCD image sensor, it may be provided separately.Furthermore, the above-mentioned irradiation device is not limited to laser light or halogen light, and can sufficiently irradiate the processing portion of the workpiece. Other known light sources can be used if available.

In addition, the method of mounting the image sensor, the method of controlling each part, etc. can be freely changed in design within the scope of the purpose of the present invention, and the present invention does not cover all of them. be.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing one embodiment of the electric discharge machining apparatus according to the present invention, Fig. 2 is an explanatory diagram showing another embodiment of the image sensor portion thereof, and Fig. 3 is a front view thereof. It is.

Claims (1)

[Scope of Claims] 1) A machining fluid is supplied between the workpiece and the electrode, and a voltage pulse of a predetermined value is applied between the two from a power supply circuit to generate an electric discharge, thereby performing machining. In the machining device, a light source that illuminates the machining part of the workpiece opposite to the electrode during electric discharge machining, or the outer circumferential contour of the machining gap formed by both; an image sensor that photographs the area; a circuit that scans the image sensor in synchronization with the occurrence of electric discharge and generates a video signal; a first stage memory that stores the video signal; and the first stage memory stores the following: at least one rear-stage memory that sequentially stores the video signal stored in the first-stage memory before starting the process, and a new video signal stored in the first-stage memory and the new video signal stored in the second-stage memory. The electric discharge machining apparatus as described above is provided with an abnormal discharge monitoring device for concentrated discharge or the like, which comprises a correlator that calculates a correlation coefficient of a video signal and generates an output signal when the value exceeds a certain threshold. 2) The electric discharge machining apparatus according to claim 1, wherein the image sensor is a CCD image sensor. 3) The electric discharge machining apparatus according to claim 1, wherein the image sensor is a video camera. 4) The electric discharge machining apparatus according to claim 1 or 2, wherein the central monitoring device includes a device for displaying a machined part of the workpiece photographed by an image sensor.