JPH04144028A - Automatic detecting method for mask clogging of color cathode ray tube - Google Patents

Abstract

PURPOSE:To discriminate the defect of a fluorescent screen itself and that due to mask clogging by subtracting the data of the image of a raster, photographed with a high frequency A.C. magnetic field applied, from the data of the image of a raster photographed with an A.C. magnetic field not applied. CONSTITUTION:In a memory device 5, data are memorized which are A/D- converted image signals obtained by photographing a raster displayed on a cathode ray tube 1 without electrifying a coil 3. Also in a memory device 6, digital data are memorized which are of the image of a camera 2 which photographed the condition of a raster displayed on the cathod ray tube 1 with an A.C. flowed in the coil 3. In a memory 7, resuts are memorized which are obtained by subtracting data, memorized in a device, from data, memorized in the device 5, at every each address. By this constitution, only a picture image defect due to shadow mask clogging is displayed on a picture image display 8. A picture image defect, based on the failure of a fluorescent screen itself, can be seen by picture-image-displaying data in the device 6.

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to an automatic color cathode ray tube mask clogging detection method that is capable of separately detecting only image defects caused by clogging of the shadow mask aperture of a color cathode ray tube. [Prior art] Among the image defects of the 1~U mask type color A pole ray tube, due to poor coating of the phosphor that forms the phosphor surface, the phosphor surface does not emit light even when an electron beam scans it. This is because there is a defect in the fluorescent surface itself, and the opening of the shadow mask for the electron beam to pass is clogged with foreign matter such as dust, which prevents the electron beam from reaching the fluorescent surface. This occurs because the fluorescent surface, which should normally emit light, is not excited by the electron beam. For manufacturers of color cathode ray tubes, front pressure image defects must also be eradicated, but since the causes of the two types of defects mentioned above are generally different and the countermeasures are different, it is necessary to distinguish between the two. No. [Problem to be solved by the invention] Inspecting mass-produced products such as color cathode ray tubes by relying on human five senses, such as visual inspection with the naked eye, is difficult due to the personal condition of the inspector and the It has been pointed out for a long time that it is difficult to always obtain normal results due to various factors such as individual differences such as degree of physical or mental fatigue, sexual tendencies, etc. With progress, automatic inspection machines are being put into practical use. When detecting image defects in color cathode ray tubes, as mentioned above, the target is usually quite small, so visual inspection by the inspector's southern limit can accurately detect all defects without missing them, such as when one worker becomes fatigued. It is difficult to expect that this will happen, so it is desirable to introduce an automatic inspection machine. However, conventionally, automatic inspection machines for color cathode ray tubes have been used for quantitative determination.
Although it has been put into practical use, the image defects detected by inspecting the image display condition of color cathode ray tubes are either due to a defect in the phosphor surface itself or due to blockage or clogging of the electron beam aperture in the shadow mask. There was no established automatic inspection machine or automatic discrimination method that could clearly distinguish whether or not it was based on the above. Of course, it is not impossible to research and identify the causes of image defects in a relatively small number of products, rather than conducting a 100% inspection of a large number of mass-produced products. The present invention automatically inspects a large number of mass-produced shadow mask type color cathode ray tubes to detect image defects.
It is an object of the present invention to provide a method for distinguishing between image defects caused by clogging of a shadow mask and defects caused by a defective fluorescent surface. [Means for Solving the Problems] In order to achieve the object 2, the present invention automatically and sequentially causes the color cathode ray tube to display a raster that scans the entire 2 display surfaces; From the digital data of the image taken with the side video camera, the video is then generated in the same raster scanning state as above, while moving the fluorescent surface landing position of the electron beam in the color gland duct at high speed by applying a high frequency alternating magnetic field. We decided to consider the result of subtracting the digital data of the image taken by the camera as data indicating an image defect caused by clogging of the electron beam passage opening in the shadow mask of the color cathode ray tube to be tested. [Operation] In a shadow mask type color cathode ray tube, the electron beam passing through a specific electron beam passage aperture of the shadow mask is
The i-color electron beam must be emitted by striking each specific phosphor forming the phosphor surface on the inner surface of the panel. However, as shown in FIG. 2(a), if the electron beam passing gap 11 of the shadow mask 1b is clogged with foreign matter in the tube, causing a clogging 12, the fluorescent surface 1a is scanned. Since the day beam 1o cannot pass through the clogged hole, a black shadow 13 that does not emit light always appears on the fluorescent surface 1a, that is, an image defect. On the other hand, when an alternating current magnetic field is applied by the coil 3 to the electron beam trajectory in the color cathode ray tube 1 as shown in FIG. As the beam trajectory 13' is bent until it reaches the optical surface, the position of the image defect 13 occurring on the fluorescent surface 1a also moves. If an electromagnetic field due to high frequency alternating current is applied, the position of the image defect 13 will also move at high speed. By appropriately selecting the sensitivity and exposure (shutter opening) time of the video camera 2 that photographs the screen of the cathode ray tube 1, the video camera 2 can record images while applying a magnetic field due to high-frequency alternating current.
In the video, the image defect 13 due to the clogging of the shadow mask 1b no longer appears as a clear black shadow, and even if it does appear, it is thin, vague, and spread over a wide range. Such thin and wide shadows can be completely removed by adjusting the camera sensitivity appropriately or by selecting data with an appropriate threshold somewhere in the video circuit. In other words, image defects due to defects in the fluorescent surface itself will always occur at the same location on the fluorescent surface of the cathode ray tube, no matter what happens to the electron beam trajectory that reaches the fluorescent surface along the way (that is, even when a high-frequency AC magnetic field is applied). On the other hand, image defects due to shadow mask clogging are no longer retained as data in images shot by a video camera when a high-frequency alternating current magnetic field is applied. Therefore, if we subtract the data of the raster image taken C3 while applying a high-frequency AC magnetic field from the data of the raster image taken C3 without applying an AC magnetic field, we can obtain the data of the two types of image data. What is included on the right is data indicating image defects caused by defects in the fluorescent surface itself, so the remainder after subtraction is data about image defects caused by clogging of the shadow mask. [Example] FIG. 1 is a schematic explanatory diagram of an example of the present invention. In the figure, 1 is a color cathode ray tube to be tested, 2 is a video camera, and 3 is a video camera.
is a coil that sends alternating current at a high frequency by -1 minutes, and 4 is A /
D converter, 5 is the cathode IiA tube 1 without energizing the coil 3.
The storage device r, 6 for storing the data converted into 7/゛D by photographing the raster image displayed on the video signal 6 sends the data to the cathode ray tube 1 by passing an alternating current through the coil 3 to swing the electron beam trajectory in the cathode ray tube. The storage device 57 for digital data of the image taken by the video camera 2 that captures the displayed raster state is: 2.
'1115 f,,1'-: Store I=, t:-te 9 or I) Storage device

[31 pieces of stored data are stored in each atto: 1.2 every 19, - a storage device that stores the subtraction result, 8 is an image display of the data in the storage device 7, 9 is a control device, 13 is a screen 1 Image defect due to clogging] 4 is an image defect due to a defect in the fluorescent surface itself. Note that, in reality, several dozen video cameras 2 may be used in order to obtain images with sufficiently high definition. In addition, the storage device 5,
6.7 may of course be a storage area allocated according to the storage contents in a large capacity storage device. Registers may be used in place of the memory devices 5, 6, 7, etc., but the data of the automatic test results for such a large number of products should be saved for a while in the memory device. It is often more convenient. The control device 9 may be an MPU that only controls the series of processes described above, or a CPU that controls a fully automatic inspection system. Image display 8 shows only image defects 13 due to shadow mask clogging. Image defects due to defects in the fluorescent surface itself υ) can be detected by displaying the image of the pig in the storage device 6 and checking the visibility. 1III. The photoelectric conversion element for each pixel of the video camera 2 used in this example was one with a light accumulation time of 1/3 o or ]/60 seconds. Frequency position 5ON 7 or higher tl:f, 1N Images with image defects due to clogging become invisible. The alternating current magnetic field generated by the coil 3 has components (a) and (4) perpendicular to the trajectory of the electron beam in the color cathode ray tube. [Effects of the Invention] As described above, according to the present invention, image defects due to defects in the fluorescent surface itself of a shadow mask type color cathode ray tube and image defects due to shadow mask clogging can be eliminated by visual inspection. This is an oversight that can easily occur. This makes it possible to automatically and reliably separate and detect 2) without causing problems such as power problems, and is extremely effective in improving the manufacturing process of color shadow ray tubes.

[Brief explanation of drawings]

Fig. 1 is a schematic explanatory diagram of an embodiment of the present invention, Fig. 2 (a) is a diagram illustrating the occurrence of an image defect due to a clogged shadow mask, and Part 2 (b) is a diagram illustrating the occurrence of an image defect due to a clogged shadow mask. 1. To prevent defects from appearing by applying an alternating magnetic field. - Figure 7" showing the colored state, 1 Color shaded radiation tube, 1a - Fluorescent surface, ]b Shade mask, 2 Video camera, 3 Coil,
, 4-A/D converter, 5.6 Storage device for image defect video data, 7 Storage device for subtraction results, 8 Image display for subtraction results, 9 Control device, 10-Electron beam, 11-Shadow mask 12-Clogging, 13-Image defect due to shadow mask clogging, Figure 4-'tffDtl if()2%% I=X6alX''
X'S white diagram lb)

Claims (1)

[Claims] 1. Automatically and sequentially display a raster pattern that scans the display surface on the color cathode ray tube, and then convert this display from the digital data of the image taken by the video camera, and then apply an alternating current magnetic field in the same raster scanning state as above. While moving the position where the electron beam of the color cathode ray tube reaches the phosphor screen, the result of subtracting the digital data of the image taken by the video camera is used to detect the blockage of the electron beam passage opening of the shadow mask of the color cathode ray tube under test. An automatic color cathode ray tube mask clogging detection method characterized in that the data is regarded as indicating a defect in an image caused by the clogging.