WO2009088212A1 - Method for inspecting stain in polarizer due to uneven dyeing and automatic inspection system using the same - Google Patents

Method for inspecting stain in polarizer due to uneven dyeing and automatic inspection system using the same Download PDF

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Publication number
WO2009088212A1
WO2009088212A1 PCT/KR2009/000060 KR2009000060W WO2009088212A1 WO 2009088212 A1 WO2009088212 A1 WO 2009088212A1 KR 2009000060 W KR2009000060 W KR 2009000060W WO 2009088212 A1 WO2009088212 A1 WO 2009088212A1
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Prior art keywords
objective
polarizer
polarizing plate
polarizing
automatic inspection
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PCT/KR2009/000060
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French (fr)
Inventor
Joo-Sung Lee
Kyun-Il Rah
Yong-Sung Choi
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Lg Chem, Ltd.
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Priority to JP2010518132A priority Critical patent/JP5538220B2/en
Priority to CN2009800004921A priority patent/CN101688942B/en
Publication of WO2009088212A1 publication Critical patent/WO2009088212A1/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/21—Polarisation-affecting properties
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/30—Polarising elements
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L1/00—Measuring force or stress, in general
    • G01L1/24—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet

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  • the present invention relates to an automatic inspection system for inspecting stain in a polarizer due to uneven dyeing, and more particularly, to an automatic inspection system for inspecting stain in a polarizer, which is designed to maintain uniform product quality and improve production efficiency by quantifying stains in a polarizing plate so as to provide an objective inspection standard and automatically inspecting stains of the polarizing plate in a production line.
  • a polarizing plate refers to an optical device that is used to generate a polarized light in a certain direction.
  • the polarizer is prepared by swelling, dyeing, cross-linking and stretching a polyvinyl alcohol film. The process of preparing a polarizer is now described in more detail. First, a polyvinyl alcohol film is dipped and dyed in a solution containing an iodine or dichroic dye.
  • the dyed polyvinyl alcohol film is dipped in an aqueous boric acid solution to cross-link the iodine molecule or dichroic dye molecules with the polyvinyl alcohol film, and the cross-linked polyvinyl alcohol film is stretched so that the iodine molecules or dichroic dye molecules can be arranged in a stretched or machine direction, thus to prepare a polarizer.
  • the polarizer is dried, and a protective film such as triacetyl cellulose (TAC) film with an adhesive is attached to both sides of the dried polarizer to prepare a final polarizing plate.
  • TAC triacetyl cellulose
  • the dyeing, cross-linking and stretching process may be sequentially carried out, or carried out at the same time.
  • the brightness of a screen is not uniform and the final products are inferior due to the severe stains in the polarizer. Therefore, a sorting operation is required to pick out inferior products by determining a level of stains in the polarizing plates.
  • the recent inspection of the stains in the polarizing plate is carried out with the naked eye of inspectors.
  • this inspection method has problems in that it is difficult to produce products having uniform product quality since an inferiority degree of the final products is subjectively determined by the inspectors. Also, it has a problem in that the production efficiency is very low since the inspectors should inspect products one by one.
  • the present invention is designed to solve the problems of the prior art, and therefore it is an object of the present invention to provide a standardized automatic inspection system for inspecting stains in a polarizer, which is designed to objectively determine a level of stains in the polarizer, monitor inferior polarizer or inferior polarizing plates in the production line in real time and automatically perform a quality inspection of the polarizing plate after cutting out the polarizing plate, thereby improving the product quality and production efficiency of the polarizing plate.
  • an automatic inspection system for inspecting stains in a polarizer due to uneven dyeing, including a light source; an inspection unit positioned in the front of the light source and including at least two reference polarizing plates whose polarizing axes are arranged in parallel with each other and an objective polarizer or objective polarizing plate positioned between the reference polarizing plates and arranged so that the polarizing axis of the objective polarizer or objective polarizing plate is orthogonal to the polarizing axes of the reference polarizing plates; an imaging unit taking a picture of the inspection unit to collect image data; and an arithmetic operation unit analyzing the image data collected in the imaging unit to determine whether the objective polarizer is inferior.
  • the imaging unit may include a CCD camera.
  • the image analysis in the arithmetic operation unit may be carried out, including: extracting brightness data from the collected image data at constant distances along a transverse direction (TD) of the objective polarizer or objective polarizing plate; quantifying the brightness data into raw data; obtaining a reference curve from the raw data; and calculating the standard deviation of the raw data for the reference curve value.
  • TD transverse direction
  • the automatic inspection system may further include a display unit displaying information on the standard deviation calculated in the arithmetic operation unit, or whether the objective polarizer or objective polarizing plate is inferior.
  • an automatic inspection method for inspecting stains in a polarizing plate includes: irradiating an inspection unit with light, the inspection unit including at least two reference polarizing plates and an objective polarizer or objective polarizing plate positioned between the reference polarizing plates; transmitting image data, which are obtained by taking a picture of the inspection unit, to an arithmetic operation unit; extracting brightness data from the transmitted image data at constant distances along a transverse direction (TD) of the objective polarizer or objective polarizing plate and quantifying the brightness data into raw data; obtaining a reference curve from the raw data; calculating the standard deviation of the raw data for the reference curve value; and determining whether the objective polarizer or objective polarizing plate is inferior by comparing the standard deviation with a predetermined reference value.
  • TD transverse direction
  • the automatic inspection method for inspecting stains in a polarizing plate may useful to maintain uniform product quality since it objectively quantifies the stains in the polarizing plate from the image data and determines whether the final products are inferior, based on the quantified level of the stains.
  • the automatic inspection system for inspecting stains in a polarizer may useful to curtail the manufacturing time and improve production efficiency since the polarizing plates are automatically inspected in the production line without allowing inspectors to inspect the polarizing plates one by one.
  • FIG. 1 is a diagram illustrating an automatic inspection system according to one exemplary embodiment of the present invention.
  • FIG. 1 shows an automatic inspection system according to one exemplary embodiment of the present invention.
  • the automatic inspection system according to one exemplary embodiment of the present invention includes a light source 10, an inspection unit 20, an imaging unit 30 and an arithmetic operation unit 40.
  • the light source 10 functions to visualize stains by irradiating the inspection unit 20 with light, and is positioned in the rear of the inspection unit 20.
  • the light source 10 includes a backlight of a display device, etc.
  • the inspection unit 20 includes reference polarizing plates and an objective polarizer or objective polarizing plate.
  • the reference polarizing plates and the objective polarizer (or objective polarizing plate) are arranged so that they can be orthogonal to each other.
  • the expression orthogonal to each other means that the polarizing axis of the reference polarizing plate is crossed to the polarizing axis of the objective polarizing plate.
  • the inspection unit 20 of the present invention preferably includes at least two reference polarizing plates.
  • the reference polarizing plates are arranged so that their polarizing axes can run parallel with each other, and the objective polarizer or objective polarizing plate is positioned between the reference polarizing plates.
  • the polarizing plate has an advantage in that it may be easily measured in an automation system. Therefore, two reference polarizing plates whose polarizing axes are parallel with each other may be used in the present invention to prevent visualization of the stains in the reference polarizing plates but visualize only stains of the objective polarizer or objective polarizing plate.
  • FIG. 1 shows an automatic inspection system for inspecting stains in a polarizing plate including two reference polarizing plates according to one exemplary embodiment of the present invention.
  • a reference polarizing plate positioned close to a light source is referred to as a first reference polarizing plate
  • the other reference polarizing plate positioned remote from the light source is referred to as a second reference polarizing plate.
  • the inspection unit 20 is irradiated with light from the light source 10. Theoretically, among the irradiated light, only a light polarized along the polarizing axis of the reference polarizing plate is transmitted through the first reference polarizing plate. In this case, since the transmission axes of the reference polarizing plate and the objective polarizer (or, objective polarizing plate) are orthogonal to each other as described above, the light transmitted through the first reference polarizing plate, that is, the light that is polarized along the transmission axis of the reference polarizing plate may not be transmitted through the objective polarizer (or, objective polarizing plate).
  • the light is transmitted through the objective polarizer (or, objective polarizing plate)
  • the light transmitted through the objective polarizer (or, objective polarizing plate) may not be transmitted through a second reference polarizing plate since the polarizing axis of the second reference polarizing plate is also orthogonal to the transmission axis of the objective polarizer. Therefore, the light should not be transmitted through the inspection unit.
  • the stains of the objective polarizing plate are visualized by irradiating the inspection unit 20 with light, a picture is taken of the inspection unit 20 to collect image data in an imaging unit 30 described later, and the collected image data are quantified to determine whether the polarizing plate is inferior.
  • the automatic inspection method according to one exemplary embodiment of the present invention will be described in more detail.
  • the imaging unit 30 functions to take a picture of the inspection unit 20 to collect image data, and may include video processor apparatuses such as a CCD camera, etc.
  • the imaging unit 30 takes a picture of the inspection unit 20 to collect image data and transfer the collected image data to the arithmetic operation unit 40.
  • the image data may include information such as intensity or brightness of light, etc.
  • the arithmetic operation unit 40 functions to determine whether the polarizer (or polarizing plate) is inferior by analyzing the image data collected in the imaging unit 30 to calculate a level of the stains in the objective polarizer or objective polarizing plate.
  • the image analysis in the arithmetic operation unit 40 is preferably carried out following 4 operations.
  • brightness data are extracted from the image data taken with a CCD camera at constant distances along a transverse direction (TD) of the objective polarizer or objective polarizing plate (First operation).
  • the extracted brightness data are quantified into raw data (Second operation).
  • a reference curve is calculated from the raw data (Third operation).
  • the reference curve may be obtained by curve-fitting the raw data, for example, by using the following Equation 1.
  • Equation 1 is merely one exemplary equation to obtain a reference curve, but the present invention is not particularly limited thereto.
  • f i represents a brightness value (or gray value) of an i th pixel in a transverse direction.
  • the difference between corresponding values of the reference curve and the raw data is calculated to determine the standard deviation of the calculated difference values (Fourth operation).
  • the high standard deviation obtained through the four above-mentioned operations means that an actual measured value is far beyond of the range of the reference curve.
  • the stains appear vividly in the polarizing plate due to the high difference in light and shade.
  • the low standard deviation means that an actual measured value is substantially similar to the reference curve.
  • the stains appear dimly since there is no radical difference in light and shade. That is to say, it is revealed that the standard deviation is in proportion to a level of the stains. Therefore, the calculated standard deviation may be used to objectively determine a level of the stains in the polarizing plate.
  • the arithmetic operation unit 40 determines whether the objective polarizer is inferior by comparing the calculated standard deviation with a pre-set reference value.
  • the automatic inspection system for inspecting stains in a polarizing plate may further include a display unit 50 displaying information on the standard deviation calculated in the arithmetic operation unit, or whether the objective polarizer is inferior.
  • the arithmetic operation unit 40 transfers the inspection results, in the form of signals, to the display unit 50 to allow an inspector to check the inspection results.
  • the automatic inspection system for inspecting stains in a polarizing plate according to one exemplary embodiment of the present invention may automatically inspect the stains in the polarizing plate in the polarizing plate production line.
  • the automatic inspection system for inspecting stains in a polarizing plate according to one exemplary embodiment of the present invention may be used to inspect stains of the finished polarizing plate, and also used to inspect a polarizer prior to installing a protection film.
  • the automatic inspection system according to one exemplary embodiment of the present invention is installed in the last operation of the polarizing plate production line, and, in order to inspect the polarizer, the automatic inspection system is installed after an operation of drying the polarizer. Therefore, it is possible to automatically inspect inferiority of the polarizer and the polarizing plate in the production line.
  • the method for inspecting stains in a polarizing plate includes: irradiating an inspection unit with light, the inspection unit including at least two reference polarizing plates and an objective polarizer or objective polarizing plate positioned between the reference polarizing plates; transmitting image data, which are obtained by taking a picture of the inspection unit, to an arithmetic operation unit; extracting brightness data from the transmitted image data at constant distances along a transverse direction (TD) of the objective polarizer or objective polarizing plate and quantifying the brightness data into raw data; calculating a reference curve from the raw data; calculating the difference between values of the reference curve and the raw data corresponding to the reference curve to determine the standard deviation of the calculated difference values; and determining whether the objective polarizer or objective polarizing plate is inferior by comparing the standard deviation with a predetermined reference value.
  • TD transverse direction
  • an objective polarizer or objective polarizing plate is arranged between two reference polarizing plates that are arranged parallel with each other in the inspection unit, so that the objective polarizer or objective polarizing plate can be orthogonal to the reference polarizing plates. Then, stains in the objective polarizer or objective polarizing plate are visualized by irradiating the inspection unit with light from a light source positioned in the rear of the inspection unit.
  • the imaging unit takes a picture of the inspection unit whose stains is visualized, and transfers the resulting image data to the arithmetic operation unit.
  • the arithmetic operation unit extracts brightness data from the image data transferred from the imaging unit at constant distances along a transverse direction (TD) of the objective polarizer or objective polarizing plate, and then quantifies the brightness data into raw data.
  • the quantification of the brightness data may be carried out by numerically expressing a brightness level of the extracted data.
  • a reference curve is obtained by curve-fitting the quantified data.
  • the curve-fitting may be carried out, for example, by the Equation 1.
  • the difference between values on the reference curve and the raw data corresponding to the reference curve namely, an actually measured data value, is calculated to determine the standard deviation of the calculated difference values.
  • the calculated standard deviation is in proportion to a level of the stains, as described above.
  • the polarizing plate When the calculated standard deviation exceeds a pre-set reference value, the polarizing plate is determined to be inferior, and the polarizing plate is determined to be good when the calculated standard deviation is not more than the reference value.
  • the inspection results may be transferred in the form of signals to the display unit to display the inspection results.
  • a non-stretched PVA film was dyed in a dye bath at a temperature of 28°C for a residence time of 139 seconds, and stretched 4.7 times to prepare a polarizer.
  • the polarizer thus prepared had a single transmittance of 42.5%.
  • the prepared polarizer was installed between two reference polarizing plates (single transmittance: 42.0%) that are arranged parallel with each other and positioned on a 42-inch backlight (LG Philips LCD) so that the polarizer can be orthogonal to the reference polarizing plates, and a picture was then taken with an image camera (SONY DSC-V1). Then, the standard deviation was calculated by performing an image analysis using the method of the present invention.
  • a level of the stains of the prepared polarizer was also observed with the naked eye.
  • the level of the stains was divided into three levels: severe, median and slight levels.
  • a polarizer was prepared in the same manner as in Example 1, except that the residence time in the dye bath is changed to 128 seconds. Then, the prepared polarizer was installed between two reference polarizing plates that are arranged parallel with each other and positioned on a backlight, so that the polarizer can be orthogonal to the reference polarizing plates. Then, the standard deviation was calculated by performing an image analysis using the method of the present invention.
  • a level of the stains of the prepared polarizer was also observed with the naked eye.
  • the level of the stains was divided into three levels: severe, median and slight levels.
  • a polarizer was prepared in the same manner as in Example 1, except that the residence time in the dye bath is changed to 150 seconds. Then, the prepared polarizer was installed between two reference polarizing plates that are arranged parallel with each other and positioned on a backlight, so that the polarizer can be orthogonal to the reference polarizing plates. Then, the standard deviation was calculated by performing an image analysis using the method of the present invention.
  • a level of the stains of the prepared polarizer was also observed with the naked eye.
  • the level of the stains was divided into three levels: severe, median and slight levels.
  • a polarizer was prepared in the same manner as in Example 1, except that the temperature in the dye bath is changed to 33°C. Then, the prepared polarizer was installed between two reference polarizing plates that are arranged parallel with each other and positioned on a backlight, so that the polarizer can be orthogonal to the reference polarizing plates. Then, the standard deviation was calculated by performing an image analysis using the method of the present invention.
  • the automatic inspection system according to one exemplary embodiment of the present invention may be useful to objectively determine the inferiority degree of the products, and thus to maintain the uniform product quality, compared to the conventional inspection methods which have been carried out with the naked eye of inspectors. Also, the automatic inspection system according to one exemplary embodiment of the present invention may be useful to reduce the inspection time, curtail unnecessary expenditure and improve the production efficiency by installing the automatic inspection system in the polarizing plate production line to automatically inspect polarizing plates.

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Abstract

There is provided an automatic inspection system for inspecting stains in a polarizing plate due to uneven dyeing, the automatic inspection system including a light source; an inspection unit positioned in the front of the light source and including at least two reference polarizing plates whose polarizing axes are arranged in parallel with each other and an objective polarizer or objective polarizing plate positioned between the reference polarizing plates and arranged so that the polarizing axis of the objective polarizer or objective polarizing plate is orthogonal to the polarizing axes of the reference polarizing plates; an imaging unit taking a picture of the inspection unit to collect image data; and an arithmetic operation unit analyzing the image data collected in the imaging unit to determine whether the objective polarizer or objective polarizing plate is inferior.

Description

METHOD FOR INSPECTING STAIN IN POLARIZER DUE TO UNEVEN DYEING AND AUTOMATIC INSPECTION SYSTEM USING THE SAME
The present invention relates to an automatic inspection system for inspecting stain in a polarizer due to uneven dyeing, and more particularly, to an automatic inspection system for inspecting stain in a polarizer, which is designed to maintain uniform product quality and improve production efficiency by quantifying stains in a polarizing plate so as to provide an objective inspection standard and automatically inspecting stains of the polarizing plate in a production line.
A polarizing plate refers to an optical device that is used to generate a polarized light in a certain direction. In general, the polarizer is prepared by swelling, dyeing, cross-linking and stretching a polyvinyl alcohol film. The process of preparing a polarizer is now described in more detail. First, a polyvinyl alcohol film is dipped and dyed in a solution containing an iodine or dichroic dye. Then, the dyed polyvinyl alcohol film is dipped in an aqueous boric acid solution to cross-link the iodine molecule or dichroic dye molecules with the polyvinyl alcohol film, and the cross-linked polyvinyl alcohol film is stretched so that the iodine molecules or dichroic dye molecules can be arranged in a stretched or machine direction, thus to prepare a polarizer. Subsequently, the polarizer is dried, and a protective film such as triacetyl cellulose (TAC) film with an adhesive is attached to both sides of the dried polarizer to prepare a final polarizing plate. In this case, the dyeing, cross-linking and stretching process may be sequentially carried out, or carried out at the same time.
However, when the polarizing plates are stacked so that their polarizing axes can be orthogonal to each other, put on backlight and observed, stains such as stripes are founded in a stretching direction. Theoretically, since light should not be transmitted through the polarizing plates when the polarizing plates are overlapped in cross with each other, the polarizing plates should be under a complete dark state. Practically speaking, however, no polarizer is perfect and the cross transmittance is not exactly zero. Due to the factors such as the uneven dyeing or poor alignments of a dye and the like, however, light is transmitted through the polarizing plates and stains occur in the polarizing plate since the transmission of the polarizing plates may also be varied according to the position on the polarizer.
The brightness of a screen is not uniform and the final products are inferior due to the severe stains in the polarizer. Therefore, a sorting operation is required to pick out inferior products by determining a level of stains in the polarizing plates. The recent inspection of the stains in the polarizing plate is carried out with the naked eye of inspectors. However, this inspection method has problems in that it is difficult to produce products having uniform product quality since an inferiority degree of the final products is subjectively determined by the inspectors. Also, it has a problem in that the production efficiency is very low since the inspectors should inspect products one by one.
The present invention is designed to solve the problems of the prior art, and therefore it is an object of the present invention to provide a standardized automatic inspection system for inspecting stains in a polarizer, which is designed to objectively determine a level of stains in the polarizer, monitor inferior polarizer or inferior polarizing plates in the production line in real time and automatically perform a quality inspection of the polarizing plate after cutting out the polarizing plate, thereby improving the product quality and production efficiency of the polarizing plate.
According to an aspect of the present invention, there is provided an automatic inspection system for inspecting stains in a polarizer due to uneven dyeing, including a light source; an inspection unit positioned in the front of the light source and including at least two reference polarizing plates whose polarizing axes are arranged in parallel with each other and an objective polarizer or objective polarizing plate positioned between the reference polarizing plates and arranged so that the polarizing axis of the objective polarizer or objective polarizing plate is orthogonal to the polarizing axes of the reference polarizing plates; an imaging unit taking a picture of the inspection unit to collect image data; and an arithmetic operation unit analyzing the image data collected in the imaging unit to determine whether the objective polarizer is inferior.
In this case, the imaging unit may include a CCD camera.
Also, the image analysis in the arithmetic operation unit may be carried out, including: extracting brightness data from the collected image data at constant distances along a transverse direction (TD) of the objective polarizer or objective polarizing plate; quantifying the brightness data into raw data; obtaining a reference curve from the raw data; and calculating the standard deviation of the raw data for the reference curve value.
Additionally, the automatic inspection system according to one exemplary embodiment of the present invention may further include a display unit displaying information on the standard deviation calculated in the arithmetic operation unit, or whether the objective polarizer or objective polarizing plate is inferior.
Also, according to another aspect of the present invention, there is provided an automatic inspection method for inspecting stains in a polarizing plate. Here, the method includes: irradiating an inspection unit with light, the inspection unit including at least two reference polarizing plates and an objective polarizer or objective polarizing plate positioned between the reference polarizing plates; transmitting image data, which are obtained by taking a picture of the inspection unit, to an arithmetic operation unit; extracting brightness data from the transmitted image data at constant distances along a transverse direction (TD) of the objective polarizer or objective polarizing plate and quantifying the brightness data into raw data; obtaining a reference curve from the raw data; calculating the standard deviation of the raw data for the reference curve value; and determining whether the objective polarizer or objective polarizing plate is inferior by comparing the standard deviation with a predetermined reference value.
As described above, the automatic inspection method for inspecting stains in a polarizing plate according to one exemplary embodiment of the present invention may useful to maintain uniform product quality since it objectively quantifies the stains in the polarizing plate from the image data and determines whether the final products are inferior, based on the quantified level of the stains.
Also, the automatic inspection system for inspecting stains in a polarizer according to one exemplary embodiment of the present invention may useful to curtail the manufacturing time and improve production efficiency since the polarizing plates are automatically inspected in the production line without allowing inspectors to inspect the polarizing plates one by one.
FIG. 1 is a diagram illustrating an automatic inspection system according to one exemplary embodiment of the present invention.
Hereinafter, exemplary embodiments of the present invention will be described in more detail.
FIG. 1 shows an automatic inspection system according to one exemplary embodiment of the present invention. As shown in FIG. 1, the automatic inspection system according to one exemplary embodiment of the present invention includes a light source 10, an inspection unit 20, an imaging unit 30 and an arithmetic operation unit 40.
First of all, the light source 10 functions to visualize stains by irradiating the inspection unit 20 with light, and is positioned in the rear of the inspection unit 20. For example, the light source 10 includes a backlight of a display device, etc.
Meanwhile, the inspection unit 20 includes reference polarizing plates and an objective polarizer or objective polarizing plate. In this case, the reference polarizing plates and the objective polarizer (or objective polarizing plate) are arranged so that they can be orthogonal to each other. Here, the expression orthogonal to each other means that the polarizing axis of the reference polarizing plate is crossed to the polarizing axis of the objective polarizing plate.
Also, the inspection unit 20 of the present invention preferably includes at least two reference polarizing plates. In this case, the reference polarizing plates are arranged so that their polarizing axes can run parallel with each other, and the objective polarizer or objective polarizing plate is positioned between the reference polarizing plates. When one reference polarizing plate is used, stains of the objective polarizer or objective polarizing plate may be distorted due to the presence of stripped stains in the reference polarizing plate. Also, since stains in the objective polarizer or the objective polarizing plate are observed clearly in the use of at least two reference polarizing plates that are arranged parallel to each other, the polarizing plate has an advantage in that it may be easily measured in an automation system. Therefore, two reference polarizing plates whose polarizing axes are parallel with each other may be used in the present invention to prevent visualization of the stains in the reference polarizing plates but visualize only stains of the objective polarizer or objective polarizing plate.
FIG. 1 shows an automatic inspection system for inspecting stains in a polarizing plate including two reference polarizing plates according to one exemplary embodiment of the present invention. For convenience sake, a reference polarizing plate positioned close to a light source is referred to as a first reference polarizing plate, and the other reference polarizing plate positioned remote from the light source is referred to as a second reference polarizing plate.
When the objective polarizer or objective polarizing plate is arranged in the inspection unit 20, the inspection unit 20 is irradiated with light from the light source 10. Theoretically, among the irradiated light, only a light polarized along the polarizing axis of the reference polarizing plate is transmitted through the first reference polarizing plate. In this case, since the transmission axes of the reference polarizing plate and the objective polarizer (or, objective polarizing plate) are orthogonal to each other as described above, the light transmitted through the first reference polarizing plate, that is, the light that is polarized along the transmission axis of the reference polarizing plate may not be transmitted through the objective polarizer (or, objective polarizing plate). Although the light is transmitted through the objective polarizer (or, objective polarizing plate), the light transmitted through the objective polarizer (or, objective polarizing plate) may not be transmitted through a second reference polarizing plate since the polarizing axis of the second reference polarizing plate is also orthogonal to the transmission axis of the objective polarizer. Therefore, the light should not be transmitted through the inspection unit.
However, light may be leaked due to the uneven dyeing or the poor alignment of a dye, etc., and stains including light and shade stripes may be observed in an machine direction (MD) of the polarizing plate. Such stains are generated due to the deviation in the transmission of the objective polarizer, and when the stains are severely formed as described above, the brightness of a screen may not be uniform, and an image quality may be deteriorated.
Therefore, in accordance with one exemplary embodiment of the present invention, the stains of the objective polarizing plate are visualized by irradiating the inspection unit 20 with light, a picture is taken of the inspection unit 20 to collect image data in an imaging unit 30 described later, and the collected image data are quantified to determine whether the polarizing plate is inferior. Hereinafter, the automatic inspection method according to one exemplary embodiment of the present invention will be described in more detail.
Next, the imaging unit 30 functions to take a picture of the inspection unit 20 to collect image data, and may include video processor apparatuses such as a CCD camera, etc. When the inspection unit 20 is irradiated with light to visualize stains of the objective polarizer or objective polarizing plate, the imaging unit 30 takes a picture of the inspection unit 20 to collect image data and transfer the collected image data to the arithmetic operation unit 40. In this case, the image data may include information such as intensity or brightness of light, etc.
The arithmetic operation unit 40 functions to determine whether the polarizer (or polarizing plate) is inferior by analyzing the image data collected in the imaging unit 30 to calculate a level of the stains in the objective polarizer or objective polarizing plate.
The image analysis in the arithmetic operation unit 40 according to one exemplary embodiment of the present invention is preferably carried out following 4 operations.
First, brightness data are extracted from the image data taken with a CCD camera at constant distances along a transverse direction (TD) of the objective polarizer or objective polarizing plate (First operation). Next, the extracted brightness data are quantified into raw data (Second operation). Then, a reference curve is calculated from the raw data (Third operation). In this case, the reference curve may be obtained by curve-fitting the raw data, for example, by using the following Equation 1. However, the following Equation 1 is merely one exemplary equation to obtain a reference curve, but the present invention is not particularly limited thereto.
Equation 1
Figure PCTKR2009000060-appb-I000001
wherein fi represents a brightness value (or gray value) of an ith pixel in a transverse direction.
When the reference curve is calculated through the above-mentioned operations, the difference between corresponding values of the reference curve and the raw data is calculated to determine the standard deviation of the calculated difference values (Fourth operation).
The high standard deviation obtained through the four above-mentioned operations means that an actual measured value is far beyond of the range of the reference curve. In this case, the stains appear vividly in the polarizing plate due to the high difference in light and shade. On the contrary, the low standard deviation means that an actual measured value is substantially similar to the reference curve. In this case, the stains appear dimly since there is no radical difference in light and shade. That is to say, it is revealed that the standard deviation is in proportion to a level of the stains. Therefore, the calculated standard deviation may be used to objectively determine a level of the stains in the polarizing plate.
When the standard deviation is calculated through the above-mentioned image analysis, the arithmetic operation unit 40 determines whether the objective polarizer is inferior by comparing the calculated standard deviation with a pre-set reference value.
The automatic inspection system for inspecting stains in a polarizing plate according to one exemplary embodiment of the present invention may further include a display unit 50 displaying information on the standard deviation calculated in the arithmetic operation unit, or whether the objective polarizer is inferior. In this case, when the inspection in the arithmetic operation unit 40 determining whether the objective polarizer is inferior is completed, the arithmetic operation unit 40 transfers the inspection results, in the form of signals, to the display unit 50 to allow an inspector to check the inspection results.
Meanwhile, when the automatic inspection system for inspecting stains in a polarizing plate according to one exemplary embodiment of the present invention is installed in a polarizing plate production line, the automatic inspection system may automatically inspect the stains in the polarizing plate in the polarizing plate production line. The automatic inspection system for inspecting stains in a polarizing plate according to one exemplary embodiment of the present invention may be used to inspect stains of the finished polarizing plate, and also used to inspect a polarizer prior to installing a protection film. In order to inspect the polarizing plate, the automatic inspection system according to one exemplary embodiment of the present invention is installed in the last operation of the polarizing plate production line, and, in order to inspect the polarizer, the automatic inspection system is installed after an operation of drying the polarizer. Therefore, it is possible to automatically inspect inferiority of the polarizer and the polarizing plate in the production line.
Next, the method for inspecting stains in a polarizing plate using the automatic inspection system according to one exemplary embodiment of the present invention is described in more detail.
The method for inspecting stains in a polarizing plate according to one exemplary embodiment of the present invention includes: irradiating an inspection unit with light, the inspection unit including at least two reference polarizing plates and an objective polarizer or objective polarizing plate positioned between the reference polarizing plates; transmitting image data, which are obtained by taking a picture of the inspection unit, to an arithmetic operation unit; extracting brightness data from the transmitted image data at constant distances along a transverse direction (TD) of the objective polarizer or objective polarizing plate and quantifying the brightness data into raw data; calculating a reference curve from the raw data; calculating the difference between values of the reference curve and the raw data corresponding to the reference curve to determine the standard deviation of the calculated difference values; and determining whether the objective polarizer or objective polarizing plate is inferior by comparing the standard deviation with a predetermined reference value.
The operations of the method for inspecting stains in a polarizing plate according to one exemplary embodiment of the present invention are sequentially described in more detail.
First, an objective polarizer or objective polarizing plate is arranged between two reference polarizing plates that are arranged parallel with each other in the inspection unit, so that the objective polarizer or objective polarizing plate can be orthogonal to the reference polarizing plates. Then, stains in the objective polarizer or objective polarizing plate are visualized by irradiating the inspection unit with light from a light source positioned in the rear of the inspection unit.
Next, the imaging unit takes a picture of the inspection unit whose stains is visualized, and transfers the resulting image data to the arithmetic operation unit.
The arithmetic operation unit extracts brightness data from the image data transferred from the imaging unit at constant distances along a transverse direction (TD) of the objective polarizer or objective polarizing plate, and then quantifies the brightness data into raw data. The quantification of the brightness data may be carried out by numerically expressing a brightness level of the extracted data.
Then, a reference curve is obtained by curve-fitting the quantified data. In this case, the curve-fitting may be carried out, for example, by the Equation 1.
Subsequently, the difference between values on the reference curve and the raw data corresponding to the reference curve, namely, an actually measured data value, is calculated to determine the standard deviation of the calculated difference values. In this case, it is revealed that the calculated standard deviation is in proportion to a level of the stains, as described above.
When the calculated standard deviation exceeds a pre-set reference value, the polarizing plate is determined to be inferior, and the polarizing plate is determined to be good when the calculated standard deviation is not more than the reference value.
The inspection results may be transferred in the form of signals to the display unit to display the inspection results.
Hereinafter, exemplary embodiments of the present invention are described in more detail.
Example 1
A non-stretched PVA film was dyed in a dye bath at a temperature of 28℃ for a residence time of 139 seconds, and stretched 4.7 times to prepare a polarizer. The polarizer thus prepared had a single transmittance of 42.5%. The prepared polarizer was installed between two reference polarizing plates (single transmittance: 42.0%) that are arranged parallel with each other and positioned on a 42-inch backlight (LG Philips LCD) so that the polarizer can be orthogonal to the reference polarizing plates, and a picture was then taken with an image camera (SONY DSC-V1). Then, the standard deviation was calculated by performing an image analysis using the method of the present invention.
For the purpose of comparison, a level of the stains of the prepared polarizer was also observed with the naked eye. Here, the level of the stains was divided into three levels: severe, median and slight levels.
The results on the standard deviation and the inspections with the naked eye are listed in the following Table 1.
Example 2
A polarizer was prepared in the same manner as in Example 1, except that the residence time in the dye bath is changed to 128 seconds. Then, the prepared polarizer was installed between two reference polarizing plates that are arranged parallel with each other and positioned on a backlight, so that the polarizer can be orthogonal to the reference polarizing plates. Then, the standard deviation was calculated by performing an image analysis using the method of the present invention.
For the purpose of comparison, a level of the stains of the prepared polarizer was also observed with the naked eye. Here, the level of the stains was divided into three levels: severe, median and slight levels.
The results on the standard deviation and the inspections with the naked eye are listed in the following Table 1.
Example 3
A polarizer was prepared in the same manner as in Example 1, except that the residence time in the dye bath is changed to 150 seconds. Then, the prepared polarizer was installed between two reference polarizing plates that are arranged parallel with each other and positioned on a backlight, so that the polarizer can be orthogonal to the reference polarizing plates. Then, the standard deviation was calculated by performing an image analysis using the method of the present invention.
For the purpose of comparison, a level of the stains of the prepared polarizer was also observed with the naked eye. Here, the level of the stains was divided into three levels: severe, median and slight levels.
The results on the standard deviation and the inspections with the naked eye are listed in the following Table 1.
Example 4
A polarizer was prepared in the same manner as in Example 1, except that the temperature in the dye bath is changed to 33℃. Then, the prepared polarizer was installed between two reference polarizing plates that are arranged parallel with each other and positioned on a backlight, so that the polarizer can be orthogonal to the reference polarizing plates. Then, the standard deviation was calculated by performing an image analysis using the method of the present invention.
For the purpose of comparison, levels of the stains of the polarizers prepared in Example 1 to 4 were also observed with the naked eye. Here, the level of the stains was divided into three levels: severe, median and slight levels.
The results on the standard deviation and the inspections with the naked eye are listed in the following Table 1.
Table 1
Figure PCTKR2009000060-appb-T000001
As listed in Table 1, it was revealed that the standard deviation is increased in proportion to the level of the stains in the polarizer, as measured according to the automatic inspection method for inspecting stains in a polarizing plate according to one exemplary embodiment of the present invention. This indicates that the automatic inspection system according to one exemplary embodiment of the present invention may be used to quantify the level of the stains in the polarizing plate into an objective numerical value.
As described above, the automatic inspection system according to one exemplary embodiment of the present invention may be useful to objectively determine the inferiority degree of the products, and thus to maintain the uniform product quality, compared to the conventional inspection methods which have been carried out with the naked eye of inspectors. Also, the automatic inspection system according to one exemplary embodiment of the present invention may be useful to reduce the inspection time, curtail unnecessary expenditure and improve the production efficiency by installing the automatic inspection system in the polarizing plate production line to automatically inspect polarizing plates.

Claims (6)

  1. An automatic inspection system for inspecting stains in a polarizer due to uneven dyeing, comprising:
    a light source;
    an inspection unit positioned in the front of the light source and including at least two reference polarizing plates whose polarizing axes are arranged in parallel with each other and an objective polarizer or objective polarizing plate positioned between the reference polarizing plates and arranged so that the polarizing axis of the objective polarizer or objective polarizing plate is orthogonal to the polarizing axes of the reference polarizing plates;
    an imaging unit taking a picture of the inspection unit to collect image data; and
    an arithmetic operation unit analyzing the image data collected in the imaging unit to determine whether the objective polarizer or objective polarizing plate is inferior.
  2. The automatic inspection system of claim 1, wherein the imaging unit comprises a CCD camera.
  3. The automatic inspection system of claim 1, wherein the image analysis in the arithmetic operation unit is carried out, comprising:
    extracting a brightness data from the collected image data at constant distances along a transverse direction (TD) of the objective polarizer or objective polarizing plate;
    quantifying the brightness data into raw data;
    obtaining a reference curve from the raw data; and
    calculating the standard deviation of the raw data for the reference curve.
  4. The automatic inspection system of claim 1, further comprising a display unit displaying information on the standard deviation calculated in the arithmetic operation unit, or whether the objective polarizer or objective polarizing plate is inferior.
  5. The automatic inspection system of any one of claims 1 to 4, wherein the automatic inspection system is installed in a polarizing plate production line.
  6. An automatic inspection method for inspecting stains in a polarizer due to uneven dyeing, the method comprising:
    irradiating an inspection unit with light, the inspection unit including at least two reference polarizing plates and an objective polarizer or objective polarizing plate positioned between the reference polarizing plates;
    transmitting image data, which are obtained by taking a picture of the inspection unit, to an arithmetic operation unit;
    extracting a brightness data from the transmitted image data at constant distances along a transverse direction (TD) of the objective polarizer or objective polarizing plate and quantifying the brightness data into raw data;
    obtaining a reference curve from the raw data;
    calculating the standard deviation of the raw data for the reference curve; and
    determining whether the objective polarizer or objective polarizing plate is inferior by comparing the standard deviation with a predetermined reference value.
PCT/KR2009/000060 2008-01-07 2009-01-07 Method for inspecting stain in polarizer due to uneven dyeing and automatic inspection system using the same WO2009088212A1 (en)

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