JP2003185528A - Method and device for inspecting liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and device for inspecting a liquid-crystal display device capable of accurately inspecting even if an inspection device is exchanged, without affected by individual difference among inspection devices. <P>SOLUTION: Above a table 2 on which a liquid-crystal display device 1, which is to be inspected, is placed, an instrument selection means is provided as to face the table 2. The selection means selectively arranges a luminance meter 6 and a CCD camera 7 face the liquid-crystal display device 1. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inspection method and an inspection device in a lighting inspection of a liquid crystal display device.

[0002]

2. Description of the Related Art Various types of automation technology relating to various inspections of the lighting state of a liquid crystal display device (hereinafter referred to as LCD) have been proposed and some have been commercialized. For example, JP-A-3-217817 or JP-A-3-217817.
According to the technique disclosed in Japanese Patent No. 53291, CC
Using a D camera, measure the display image on the liquid crystal display panel,
This is performed by sending the video signal to an image processing device and performing binarization processing or pattern recognition. Of these, the former is a method of finding a lit pixel as a defective pixel in the dark spot inspection similarly to the bright spot inspection, and the latter is a method of finding a horizontal stripe defect that appears when the liquid crystal display panel is lit to an intermediate brightness. It is detecting.

However, in the actual manufacturing site, in many cases, the final inspection depends on human visual inspection. Therefore, further research and development of automation technology is required.

[0004]

In the inspection method based on the above-mentioned automated technique, in the technique disclosed in Japanese Patent Laid-Open No. 3-217817, neither the dark spot inspection nor the bright spot inspection is performed because the non-defective pixel is not lit. , It is possible to inspect defective pixels,
It is not possible to measure their lighting brightness. Further, according to the technique disclosed in Japanese Patent Laid-Open No. 3-53291, the horizontal stripe defect is merely determined based on the absolute brightness of the lighting brightness of each display pixel, and the contrast, color tone, etc. It is not possible to detect display unevenness indicating the degree of subtle change. Therefore, due to these circumstances, the conventional inspection method has been dominated by the visual inspection for display unevenness.

Further, one of the major reasons why automated technology cannot be established in inspection is that human judgment criteria are not defined as numerical values, and that various parameters of the inspection device used during inspection are also common. Since it is often not a numerical value using a unit or a standard, it is difficult to compare it with various parameters of the inspection device.

For example, the brightness of each display element of the LCD is
It is generally evaluated by the pixel value of an image taken by a CCD camera, but the pixel value is only a numerical value obtained by dividing a certain range of brightness with a certain resolution. There is a problem that it depends on individual differences and the inspection environment.

In other words, there is a strong demand for the development of an inspection method capable of performing an inspection by using a reference value common to the inspecting apparatus and being able to perform the inspection without being influenced by the individual difference of the inspecting apparatus or the inspection environment.

The present invention has been made based on these circumstances, and an inspection method and an inspection device for a liquid crystal display device which are not affected by individual differences of the inspection device and can always perform accurate inspection even if the inspection device is replaced. Is intended to provide.

[0009]

According to a first aspect of the present invention, a first area of a display screen of a liquid crystal display device in which a constant density pattern is formed is illuminated with a uniform brightness. 1 lighting process, and from the upper part of the display screen, the first
A first luminance measuring step of measuring the luminance value of the area of No. 1 by a luminance meter, and a step of calculating an average pixel value in the first area by photographing the display screen including the first area with a CCD camera. A pixel calculation step; a second lighting step of lighting a second area of the display screen of the liquid crystal display device at a position different from the first area with uniform brightness; and a second lighting step from above the display screen. Second luminance measurement step of measuring the luminance value of the area of the second area with the luminance meter, and the display screen including the second area of the second luminance measuring step
The second pixel calculation step of calculating an average pixel value in the second area by photographing with a CD camera and the measured brightness value and the calculated pixel value of each of the first and second areas correspond to each other. Then, a conversion function deriving step of deriving a conversion function between the luminance value and the pixel value, a predetermined area of the display screen of the liquid crystal display device to be inspected is imaged by the CCD camera, and the number of pixels in the predetermined area is calculated. A method for inspecting a liquid crystal display device, comprising: a brightness value calculating step of calculating a brightness value using the conversion function; and an inspection step of inspecting the liquid crystal display device based on the calculated brightness value. .

According to the second aspect of the invention,
Each of the steps from the first lighting step to the conversion function deriving step is an inspection method for a liquid crystal display device, which is performed only when the CCD camera is replaced.

According to the means of the invention of claim 3,
A table on which the liquid crystal display device is mounted, a measuring device selecting unit arranged above the table so as to oppose the table so that a luminance meter and a CCD camera are opposed to the liquid crystal display device, the luminance meter and the An inspection device for a liquid crystal display device, comprising: a control means for controlling a CCD camera.

According to the means of the invention of claim 4,
The luminance meter is attached to the measuring device selecting means at least when the CCD camera is exchanged, which is an inspection apparatus for a liquid crystal display device.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

In the inspection of the display screen of the LCD, when each LCD is turned on, it is confirmed whether or not each part of the display screen has a uniform brightness value within a predetermined value. They take a picture of the display screen with a CCD camera that is also a high-resolution luminance meter,
Partially cut out at each measurement point and measure its brightness,
It is inspected whether the brightness is within a predetermined value. However, since the CCD camera may deteriorate and deteriorate with time in terms of accuracy after a certain period of time, a similar inspection is performed by replacing the CCD camera with a new one every predetermined period. In that case, when the CCD camera is replaced, it is necessary to use the same standard for the measured values of the CCD camera before and after the replacement.

FIG. 1 is a correlation graph of the luminance value of the luminance meter and the pixel value of the CCD camera for explaining the basic principle of the present invention. The vertical axis represents the pixel value captured by the CCD camera, and the horizontal axis represents the brightness value measured by the brightness meter.

First, a luminance meter is used in an installed environment to measure a luminance value for each gray scale gradation using a standard gray scale prepared in advance. Next, each CCD camera captures a reference grayscale pattern at least at two locations (for example, a white portion and a black portion), and the pixel value is a luminance value (the luminance values of the white portion and the black portion of the grayscale are: It is measured with a luminance meter). The correspondence between the remaining pixel value and the luminance value between the two measured points is linearly interpolated. As a result, for example, when the relationship between the pixel value and the brightness value is different between the two CCD cameras A and B, one CCD camera A is the A line and the other CCD camera B is the B line. Become. In this case, two CCDs
To make the camera A and the CCD camera B have the same brightness value, for example, when the brightness value is 100 Cd / m ² , one CCD camera A has a pixel value of 80.
In the other CCD camera B, the pixel value may be set to 65. Therefore, the luminance value can be measured by the same standard by reading each corresponding pixel value.

Next, the LCD inspection apparatus of the present invention will be described with reference to the schematic diagram shown in FIG. The LCD 1, which is the object to be measured, is placed on the table 2. A power source and a control unit (not shown) for lighting the LCD 1 are connected to the table 2, and when the LCD 1 is placed at a predetermined position, it is electrically connected by a terminal (not shown). At opposite positions on the table 2, two arms 4 and 5 which are rotatable in the horizontal direction around the support shaft 3 are provided as measuring device selecting means. A luminance meter 6 is attached to the tip of one arm 4 with its measuring surface facing the table 2, and a CCD camera 7 is attached to the tip of the other arm 5 with its measuring surface facing the table 2. ing. The luminance meter 6 and the CCD camera 7 are both connected to a controller 8 that controls them, and the controller 8 is connected to a personal computer 9 that transmits a signal to the contrailer 8. It should be noted that the luminance meter 6 attached to the arm 4 may be attached at least when the CCD camera 7 is replaced, and should be removed when the following calibration of the newly attached CCD camera 7 is completed. You can leave it.

Next, the operation of the LCD inspection device having the configuration shown in FIG. 2 will be described with reference to the flow chart of the operation shown in FIG.

When a new CCD camera 7 is used in the LCD inspection device, first, an arbitrary luminance measurement area (area A) of the display screen of the LCD 1 provided with a reference gray scale placed on the table 2 is set. Illuminates the pixels to a uniform brightness. The area A is, for example, about 40 × 40 pixels. In addition, as shown in FIG. 4, in areas other than the area A, for example, a color different from the area A is displayed so that the area A is displayed.
(S1). The brightness of the illuminated area A is measured by the brightness meter 6 and set as the brightness value A (S2). Next, the arm 5 is rotated to move the CCD camera 7 to the LCD 1
The display screen of the LCD 1 is photographed from above the display screen of the LCD 1 vertically above the display screen of the LCD 1 by the CCD camera 7 (S3). The pixel average value A of the portion where the area A is reflected in the captured image is calculated (S4).

Next, the pixels in an arbitrary brightness measurement area (area B) different from the area A of the display screen of the LCD 1 provided with a reference gray scale are lit to a uniform brightness (S5). . Area B illuminated by rotating arm 4
Is measured by the luminance meter 6 and is set as the luminance value B (S6).
Next, the arm 5 is rotated and the CCD camera 7 is moved to the LCD.
The display screen of the LCD 1 is photographed by the CCD camera 7 at a position facing the display screen of No. 1 (S7). The pixel average value B of the portion where the region B is reflected in the captured image is calculated (S8).

Next, a conversion function of the brightness value and the pixel value is derived from the brightness value A and the brightness value B, and the pixel average value A and the pixel average value B (S9). That is, since two points at which the brightness value and the pixel value correspond are obtained, the conversion function can be obtained by linearly interpolating these two points. This allows
The CCD camera 7 can obtain the correlation by the pixel value with respect to the reference of the brightness value of the brightness meter 6.

After the correlation is obtained, the inspection of the actual display screen of the LCD 1 is started.

That is, the CCD camera 7 is arranged so as to face the display screen of the LCD 1 which is the object to be measured placed on the table 2. The CCD camera 7 captures the display screen of the LCD 1 and captures it in the image. The captured image, as shown in FIG. 5, is subjected to image processing to generate peripheral patterns B, C, D,
Except for E, F, G, H, and I, the image display area is a grid-like area A.
₁ , A ₂ , A ₃ ... A ₁₆ are cut out and each region A ₁ , A ₃ is cut out.
A pixel value is calculated for each of A ₂ , A ₃ ... A ₁₆ . in this case,
Each region _{A 1, A 2, A 3} ... A 16 CCD camera 7 above
It is preferable to match the area with the area when the correlation between the luminance meter 6 and the luminance meter 6 is obtained, but it is needless to say that the area does not need to be matched if the mutual area relationship is specified. If the entire area of the display screen of the LCD 1 does not fit into the area captured by the CCD camera 7 at a time because of the size of the image pickup area of the CCD camera 7 and the size of the display screen of the LCD 1, the table is sequentially stepped to 2. Move, CC
The screens are sequentially captured by the D camera 7 and processed accordingly.

Next, the total value or average value of all pixel values is calculated. This total value or average value is compared with a threshold value calculated in advance, and it is compared whether or not it is within a predetermined range. Thereby, it is possible to perform the inspection determination as to whether or not the display screen is within the range of the predetermined brightness value. After that, when inspecting with the same CCD camera 7, the LCD 1
It is not necessary to calibrate the luminance meter 6 every time
Next, when a new CCD camera 7 is attached, the luminance meter 6 is calibrated, and an inspection may be performed using the result of which the correlation is derived.

By repeating these operations when the CCD camera 7 is replaced, it is possible to make correspondence between the pixel value and the brightness value of the CCD camera 7 for each inspection environment. The difference in measurement due to the individual difference of each is eliminated, and the LCD 1 is always accurate according to the same standard.
Can be inspected.

As a result, even if the inspection environment is different, the inspection having the same criterion is always guaranteed.

Further, by performing the inspection using the luminance value depending on the human visual acuity, it is possible to perform the inspection closer to the human sense.

[0028]

According to the present invention, even if the measuring device is replaced by measuring the display screen of the LCD, it is possible to always carry out a highly accurate measurement without being affected by it.

[Brief description of drawings]

FIG. 1 is a correlation graph between the luminance value of a luminance meter and the pixel value of a CCD camera, which explains the basic principle of the present invention.

FIG. 2 is a schematic diagram of an LCD inspection device of the present invention.

FIG. 3 is a flow chart of the operation of the LCD inspection device of the present invention.

FIG. 4 is an explanatory diagram of a luminance measurement area.

FIG. 5 is an explanatory diagram of a grid-shaped region of a captured image.

[Explanation of symbols]

1 ... Liquid crystal display (LCD), 2 ... Table, 6 ... Luminance meter, 7 ... CCD camera

Claims (4)

[Claims] 1. A first lighting step of lighting a first area of a display screen of a liquid crystal display device, in which a constant density pattern is formed, with uniform brightness; and a first lighting step from above the display screen. A first luminance measuring step of measuring a luminance value of a region with a luminance meter; and a first pixel for calculating an average pixel value in the first region by photographing the display screen including the first region with a CCD camera. A calculating step; a second lighting step of lighting a second area of the display screen of the liquid crystal display device at a position different from the first area with uniform brightness; and a second lighting step from above the display screen. A second luminance measuring step of measuring a luminance value of an area with the luminance meter; a step of calculating an average pixel value in the second area by photographing the display screen including the second area with the CCD camera; 2 pixel calculation step, and each of the first and second regions A conversion function deriving step of deriving a conversion function between the brightness value and the pixel value by associating the measured brightness value with the calculated pixel value, and a predetermined area of the display screen of the liquid crystal display device to be inspected,
A brightness value calculating step of calculating a brightness value from the number of pixels in the predetermined area using the conversion function, and an inspection step of inspecting the liquid crystal display device based on the calculated brightness value. A method for inspecting a liquid crystal display device, comprising: 2. The method for inspecting a liquid crystal display device according to claim 1, wherein the steps from the first lighting step to the conversion function deriving step are performed only when the CCD camera is replaced. 3. A table on which the liquid crystal display device is placed, and a measuring device selecting means which is disposed above the table so as to face the table and allows a luminance meter and a CCD camera to face the liquid crystal display device in a freely selectable manner. The luminance meter and the CC
An inspection apparatus for a liquid crystal display device, comprising: a control means for controlling the D camera. 4. The inspection apparatus for a liquid crystal display device according to claim 3, wherein the luminance meter is attached to the measuring device selecting means at least when the CCD camera is replaced.