Optical detection system

Abstract

The utility model relates to an optical detection system for detecting a polarizing plate. The system comprises a camera, a first filter disc, a second filter disc, a third filter disc and a light source, the first filter disc is arranged below the camera, the second filter disc is arranged below the first filter disc, the third filter disc is arranged below the second filter disc, the light source is arranged below the third filter disc, and an optical film to be detected is placed between the second filter disc and the third filter disc; and the first filter is a phase difference sheet, the second filter is a view compensation sheet, and the third filter is a band-pass filter. By using the optical detection system, the accuracy of a detection result is greatly improved.

Description

Technical Field

[0001] The utility model relates to an optical detection system for detecting polarizing plates. Background Art

[0002] The optical detection system for detecting polarizing plates in the prior art cannot detect the bright spots of the polarizing plates well, thus resulting in insufficient accuracy of the detection results. Utility Model Content

[0003] The purpose of the utility model is to provide an optical detection system for detecting polarizing plate defects. The system adopts relatively advanced detection technology and can achieve more accurate polarizing plate defect detection.

[0004] The utility model discloses an optical detection system, which includes a camera, a first filter, a second filter, a third filter and a light source. The system is configured to extract bright spot characteristic values ​​of an optical film to be tested;

[0005] The first filter is disposed below the camera, the second filter is disposed below the first filter, the third filter is disposed below the second filter, the light source is disposed below the third filter, and the optical film to be measured is placed between the second filter and the third filter; and

[0006] The first filter is a phase difference plate, which forms an orthogonal Nicol prism with the optical film to be tested, and is used to compensate for the birefringence phenomenon in the optical film to be tested. The second filter is a field compensation plate, and the third filter is a bandpass filter.

[0007] Optionally, the optical film to be tested is a polarizing plate.

[0008] Optionally, the distance between the camera and the first filter is 20-70 mm, the distance between the first filter and the second filter is 0-40 mm, the distance between the second filter and the optical film to be tested is 0-40 mm, and the distance between the optical film to be tested and the third filter is 5-30 mm.

[0009] Optionally, the camera is an area array camera.

[0010] Optionally, the resolution of the camera is 3-15 μm / pixel.

[0011] Optionally, the camera is subjected to continuous white balance adjustment so that when the light source output is 255 and the camera exposure time is 300 μs, the grayscale value in the imaging plane is 120-160.

[0012] Optionally, the phase difference plate is selected from a plurality of phase difference plates with different phase differences.

[0013] Optionally, the visual field compensation plate is a multiple phase difference visual field compensation plate.

[0014] Optionally, the number of layers of the multiple phase difference visual field compensation film is 5 to 100.

[0015] Optionally, the number of layers of the multiple phase difference visual field compensation film is 50 to 70.

[0016] Optionally, the main wavelength of the bandpass filter is in the range of 380 to 780 nm.

[0017] Optionally, the main wavelength of the bandpass filter is in the range of 500 to 700 nm.

[0018] Optionally, the system is configured to extract the bright spot characteristic value on the optical film to be measured under the bandpass filter with a main wavelength of 380 to 780 nm.

[0019] Optionally, the system is configured to extract the bright spot characteristic value on the optical film to be tested under different conditions, and the different conditions include:

[0020] Complex light source + bandpass filter matching the wavelength + algorithm matching the channels;

[0021] Monochromatic light source + matching channel algorithm.

[0022] Optionally, the monochromatic light source has a fixed wavelength.

[0023] Compared with the prior art, the main differences and effects of this utility model are:

[0024] The optical detection system for detecting polarizing plates proposed by the utility model greatly improves the accuracy of detection results. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 shows an overall schematic diagram of an optical detection system according to an embodiment of the present utility model;

[0026] Figure 2 A schematic diagram showing the structure of a product to be tested according to an embodiment of the present utility model is shown;

[0027] Figure 3 A schematic diagram showing the field of view of a camera according to an embodiment of the present invention is shown;

[0028] Figure 4 A schematic diagram of a first filter set according to an embodiment of the present invention is shown; DETAILED DESCRIPTION

[0029] To make the purpose and technical solutions of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] The polarizing plate used in liquid crystal display devices or organic EL display devices is usually constructed in a manner that the polarizer is sandwiched between two protective films. In order to attach the polarizing plate to the display device, an adhesive layer is laminated on the protective film on one side, and then a release film (formed by PET resin) is laminated on the adhesive layer. In addition, in most cases, a release film is also attached to the protective film on the other side to protect its surface. The polarizing plate is circulated and transported in a state in which the release film is laminated. When it is attached to the display device during the manufacturing process of the display device, the release film is peeled off.

[0031] However, during the manufacturing stage of the polarizing plate, foreign matter or residual bubbles may be mixed in between the polarizer and the protective film, or, when the protective film functions as a phase difference film, there may be orientation defects inside the protective film (hereinafter, these foreign matter, bubbles, and orientation defects are sometimes collectively referred to as "defects"). When a polarizing plate with defects is attached to a display device, the defective portion may be visually identified as a bright spot (referred to herein as a bright spot), or image distortion may be observed at the defective portion. In particular, defects that are visually identified as bright spots are easily visually recognized when the display device displays black.

[0032] Therefore, before attaching the polarizing plate to a display device (the polarizing plate is provided with a release film), an inspection is performed to detect defects in the polarizing plate. This defect inspection is generally performed by optical inspection using the polarization axis of the polarizing plate.

[0033] An embodiment of the present invention relates to an optical detection system for detecting polarizing plates. An embodiment of the present invention will be described in detail below.

[0034] Now refer to Figure 1 , the optical detection system in this embodiment includes a camera 101, a first filter 102, a second filter 103, a third filter 105 and a light source 106.

[0035] In one embodiment, the first filter is disposed below the camera, the second filter is disposed below the first filter, the third filter is disposed below the second filter, the light source is disposed below the third filter, and the optical film 104 to be tested is placed between the second filter and the third filter; and

[0036] The first filter is a phase difference plate, the second filter is a field of view compensation plate, and the third filter is a bandpass filter (ie, BPF). Since the release film in the optical film to be measured will cause birefringence, the first filter is used to compensate for it. During compensation, the first filter and the optical film to be measured form an orthogonal Nicol prism. In addition, since the deviation of the phase difference of the release film fluctuates greatly, a first filter group consisting of multiple first filters with different in-plane phase differences is required. During measurement, the first filter with the lowest light transmittance under orthogonal Nicol transmission is selected for measurement. In the first filter group, the in-plane phase difference value of the first phase difference plate at a wavelength of 550nm is approximately the same as the in-plane phase difference of the release film at a wavelength of 550nm, and the in-plane phase difference value of the second phase difference plate at a wavelength of 550nm is 50 to 100nm larger than the in-plane phase difference of the release film at a wavelength of 550nm.

[0037] The distance between the camera and the first filter is 20-70 mm, preferably 40 mm, the distance between the first filter and the second filter is 0-40 mm, preferably 5 mm, the distance between the second filter and the optical film to be measured is 0-40 mm, preferably 12 mm, and the distance between the optical film to be measured and the third filter is 5-30 mm, preferably 20 mm.

[0038] In one embodiment, the article to be tested 104 is an optical film, and more specifically, the article to be tested 104 is a polarizing plate. Figure 2 As an example, a polarizing plate has a multilayer structure: a circularly polarizing plate 1 as a main body to be inspected; and a release film 16a laminated on the circularly polarizing plate 1 via an adhesive layer 15. The circularly polarizing plate 1 is formed by laminating protective films 12a and 12b on both sides of a polarizing film 11, and forming a phase difference film 14 on the protective film 12a on the side having the release film 16a via an adhesive layer 13. In addition, another release film 16b is laminated on the surface of the circularly polarizing plate 1 on the side not having the release film 16a. The circularly polarizing plate 1 is generally used in a display device, such as a liquid crystal display device or an organic EL display device. When used, the release film 16a is peeled off and the plate is attached to the display device via an adhesive layer 15.

[0039] It should be noted that, in this specification, "circularly polarizing plate" includes both circularly polarizing plates and elliptically polarizing plates. Also, "circularly polarized light" includes both circularly polarized light and elliptically polarized light.

[0040] In one embodiment, the camera 101 is an area array camera. In contrast, when a line scan camera is used for scanning and capturing images, light leakage may occur in the scanned image due to insufficient light compensation in the oblique direction, which has a certain adverse effect on the accuracy of the detection result.

[0041] In one embodiment, the resolution of the camera 101 is 3-15 μm / pixel, preferably 5.5 μm / pixel, so as to meet the minimum detection requirement of bright spots (about tens of microns), and can be used with a suitable lens.

[0042] In one embodiment, the overall field of view of the camera 101 is 22.5 mm*16.5 mm.

[0043] The camera's field of view is divided into nine-square grid areas, represented by A1 to C3, such as Figure 3 As shown in the figure, after replacing the area array camera with the one in the camera's field of view (A1, A3, C1, and C3), the brightness and darkness in the corners of the camera's field of view (A1, A3, C1, and C3) showed large deviations and poor uniformity. However, the uniformity in the center of the field of view (B2) was good (uniformity refers to the range of the average brightness of each sub-area within a given area; the smaller the range, the better the uniformity). Due to the good uniformity in the B2 area, during the inspection process, the various parts of the product to be tested were moved to the B2 area for imaging. The imaging results met the requirements, so the area array camera was selected as the imaging camera for the inspection system.

[0044] Specifically, the size of the B2 area is 7 mm*6 mm.

[0045] Now refer to Figure 4 The first filter shown in FIG. In this embodiment, the first filter includes 8 phase difference filters a1-a8, but it is worth noting that in other embodiments, the first filter may include more or fewer phase difference filters according to the actual detection requirements. When the light source output value is 179 (i.e., the illuminance value at the center of the light source surface is 138,000 lux) and the exposure time is the same (16,800 in this embodiment), the filter with the lowest average grayscale in the imaging surface is selected for the detection process. The filter selection process is automatically performed by the system without the need for manual selection and switching.

[0046] In one embodiment, a second filter is positioned 5 mm below the first filter. This second filter is a multi-phase retardation field of view compensator, designed to mitigate the narrow field of view caused by the PET release film. The multi-phase retardation field of view compensator can have 5 to 100 layers, preferably 50 to 70 layers.

[0047] The present invention uses the SN ratio to reflect the compensation effect. The SN ratio is an indicator reflecting the distinction between the bright point and the surrounding area. The larger the SN ratio, the higher the distinction. The calculation formula of the SN ratio is as follows:

[0048] SN ratio = (bright spot brightness - average brightness) / (highest brightness other than bright spots - average brightness)

[0049] Experiments have shown that the SN ratio is superior when using multiple-phase retardation compensation films compared to when not using them. Bright spots can be more clearly distinguished from surrounding areas, allowing for more accurate detection of bright spots on polarizing plates. Further experiments were conducted using multiple-phase retardation compensation films with varying numbers of layers (e.g., 40, 45, 50, 55, 60, and 65 layers).

[0050] In the embodiment of the present application, the SN ratio and uniformity in the B2 area of ​​the 70-layer multi-phase difference field of view compensation plate are better.

[0051] Then, after testing, it was found that placing the product to be tested 12 mm below the field of view compensation sheet can meet both equipment design and bright spot detection requirements.

[0052] To reduce interference caused by surface contamination (e.g., foreign matter, markings from previous production processes) on the optical film being inspected, a third filter is attached to the area array light source, located 20 mm below the product being inspected. At specific wavelengths, the image obtained using this third filter allows for better extraction of bright spot feature values ​​using a feature extraction algorithm. The dominant wavelength can be within the 380-780 nm range, preferably 500-700 nm.

[0053] Table 1 shows the maximum grayscale and area of ​​bright spots in the image obtained when filters of different wavelengths can just extract bright spots under corresponding exposure.

[0054]

[0055] As can be seen, the 600nm filter requires the shortest exposure time and has the best detection effect, followed by the 580nm BPF. It is understandable that when obtaining bright spot characteristic parameters, a relevant threshold is used to control the obtained bright spot characteristic parameters, so areas below the threshold are recorded as 0.

[0056] In addition, different combinations were introduced into the system to test the polarization plate. The conditions of the different combinations included a polychromatic light source + a bandpass filter with matching wavelengths + an algorithm for matching channels; and a monochromatic light source with a fixed wavelength + an algorithm for matching channels.

[0057] In the embodiments of this application, four main combinations are used. These four combinations are: ① "polychromatic light source + 540nm BPF + G-channel algorithm", ② "polychromatic light source + 600nm BPF + R-channel algorithm", ③ "592nm monochromatic light source + R-channel algorithm", and ④ "620nm monochromatic light source + R-channel algorithm". The polychromatic light source is synthetic light, and the monochromatic light source is monochromatic light of a fixed wavelength. Those skilled in the art will understand that the selection of these four combination conditions is only for example and is not to be considered as a limitation to the implementation method.

[0058] Now refer to Table 2 to analyze the above four combinations.

[0059]

[0060] It can be seen that the combination of "polychromatic light source + 600nm BPF + G-channel algorithm" produces the bright spot with the largest grayscale and the largest area when detecting bright spots, that is, the bright spot detected is the most obvious, and therefore the effect is the best. Therefore, in this embodiment, the combination of "polychromatic light source + 600nm BPF + G-channel algorithm" is used for bright spot detection. In addition, since the use of a monochromatic light source will cause interference from the marks on the surface, affecting the extraction of bright spot features, and the use of a polychromatic light source will not cause mark interference, the polychromatic light source + BPF combination is preferred. Therefore, although the detection result data of combinations ③ and ④ are better than combination ①, in this embodiment, except for the optimal combination ②, the second best combination is combination ①.

[0061] It is worth noting that the description of the distance between the various components of the system in the above description is not restrictive, but is only given as an example. In other test situations or test requirements, the component spacing can be adjusted arbitrarily according to actual conditions.

[0062] In one embodiment, considering space factors, the size of the area array light source is 60mm*60mm. After testing, the light source illumination of the area array light source at a measurement height of 5mm and a light source output value of 255 is as follows:

[0063] Complex light source illumination: 100,000 to 150,000 lux

[0064] BPF+light source: 30,000 to 40,000 lux. This value is the reference illumination value for testing.

[0065] In addition, if the camera's white balance is inaccurate, readjust the white balance by adjusting the camera and light source. The specific method is as follows:

[0066] If the hue of the image of the same product is different when the PC film height changes, the white balance needs to be re-determined, especially when the camera is in continuous white balance (also known as automatic white balance);

[0067] First, the ambient light is removed, and only the light source 106 provides illumination;

[0068] Adjust the output value of the light source 106 to 255, make sure there is no obstruction between the camera and the light source, and then turn on the camera and the corresponding software program;

[0069] Adjust the camera exposure to 300 μs so that the average grayscale value of the image plane is between 120 and 160. Perform continuous white balance at this time. After determining the white balance, turn off continuous white balance and save the settings.

[0070] In summary, the optical detection system proposed in the present invention can not only realize the basic bright spot detection function by introducing the third filter, but also can well detect the bright spots through the third filter, making the detection result more accurate.

[0071] It should be noted that in the claims and specification of this patent, the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," "outer," and the like, indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended only to facilitate the description of the present invention and simplify the description. They do not indicate or imply that the devices or components referred to must have a specific orientation, be constructed, or operate in a specific orientation, and therefore should not be understood as limiting the present invention. Furthermore, relational terms such as first and second are merely used to distinguish one entity or operation from another, and do not necessarily require or imply any actual relationship or order between these entities or operations. Furthermore, the terms "comprise," "include," or any other variant thereof are intended to encompass non-exclusive inclusion, such that a process, method, article, or apparatus comprising a series of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a" does not exclude the presence of additional identical elements in the process, method, article, or apparatus comprising the element.

[0072] Although the present invention has been illustrated and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

Claims

1. An optical detection system, characterized in that: The system includes a camera, a first filter, a second filter, a third filter, and a light source, and is configured to extract bright spot characteristic values ​​of the optical film to be measured; The first filter is disposed below the camera, the second filter is disposed below the first filter, the third filter is disposed below the second filter, the light source is disposed below the third filter, and the optical film to be measured is placed between the second filter and the third filter; as well as The first filter is a phase difference plate, which forms an orthogonal Nicol prism with the optical film to be tested, and is used to compensate for the birefringence phenomenon in the optical film to be tested. The second filter is a field compensation plate, and the third filter is a bandpass filter.

2. The system according to claim 1, wherein: The optical film to be tested is a polarizing plate.

3. The system according to claim 2, characterized in that The distance between the camera and the first filter is 20-70 mm, the distance between the first filter and the second filter is 0-40 mm, the distance between the second filter and the optical film to be tested is 0-40 mm, and the distance between the optical film to be tested and the third filter is 5-30 mm.

4. The system according to claim 3, characterized in that The camera is an area array camera.

5. The system according to claim 4, characterized in that The resolution of the camera is 3-15 μm / pixel.

6. The system according to claim 5, characterized in that The camera is continuously white-balanced so that when the output value of the light source is 255 and the exposure time of the camera is 300 μs, the grayscale value in the imaging plane is 120-160.

7. The system according to claim 6, characterized in that The phase difference plate is selected from a plurality of phase difference plates having different phase differences.

8. The system according to claim 7, characterized in that The visual field compensation plate is a multiple phase difference visual field compensation plate.

9. The system according to claim 8, characterized in that The number of layers of the multiple phase difference visual field compensation film is 5 to 100.

10. The system according to claim 9, characterized in that The number of layers of the multiple phase difference visual field compensation plate is 50 to 70.

11. The system according to claim 8, wherein: The dominant wavelength of the bandpass filter is within the range of 380 to 780 nm.

12. The system according to claim 11, wherein: The dominant wavelength of the bandpass filter is within the range of 500 to 700 nm.

13. The system according to claim 11, wherein: The system is configured to extract the bright spot characteristic value on the optical film to be measured under the bandpass filter with a main wavelength of 380 to 780 nm.

14. The system according to claim 11, wherein: The system is configured to extract the bright spot characteristic value on the optical film to be tested under different conditions, wherein the different conditions include: The light source is a polychromatic light source and uses a band-matched bandpass filter; and The light source is monochromatic.

15. The system according to claim 14, wherein: The monochromatic light source has a fixed wavelength.

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