JPH063637A - Detecting method for polarizing plate - Google Patents

Abstract

PURPOSE:To enable the position of a supplied polarizing plate to be stably detected at a process where the polarizing plate is automatically pasted to a liquid crystal cell. CONSTITUTION:An analyzer 9 for controlling a light quantity transmitted through a polarizing plate 1 to be fed and pasted to a liquid crystal cell 13, is laid between the plate 1 and an optical sensor 6 fitted for the detection thereof. The analyzer 9 has a transmission axis orthogonal with the transmission axis of the plate 1, and a cross-Nicol relationship therewith. The sensor 6 is constituted of a projector 7 for irradiating light toward the plate 1 and a light receiver for receiving light emitted from the plate 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting a polarizing plate attached to a liquid crystal panel. More specifically, it relates to a method of optically detecting the positions of the polarizing plates sequentially supplied when the polarizing plates are attached to a liquid crystal cell using an automatic attaching device.

[0002]

2. Description of the Related Art In order to facilitate understanding of the present invention, first, the function of a polarizing plate will be briefly described with reference to FIG. The polarizing plate 101 used in the liquid crystal display device has a film shape in which a molecular type polarizing film is sandwiched between a pair of transparent plastic films and is mass-produced by Polaroid. Polarizing plate 10
1 has a transmission axis Y and an absorption axis Z which are orthogonal to each other. The light source light that enters the polarizing plate 101 along the optical axis X has various vibrating surfaces. The polarizing plate 101 selectively transmits only a light component having a vibrating surface parallel to the transmission axis Y to obtain linearly polarized light.

Next, a method of using a polarizing plate in a liquid crystal display device will be described with reference to FIG. A pair of polarizing plates A and B are combined in a state where their transmission axes are orthogonal to each other, and a twisted and aligned liquid crystal cell 102 is sandwiched therebetween to form a display device. The TN mode liquid crystal cell 102 has a function of rotating the vibration plane of incident light by 90 °. Therefore, the incident light, which becomes linearly polarized light parallel to the transmission axis of the polarizing plate A, is large because the vibrating surface thereof is rotated by 90 ° while passing through the liquid crystal cell 102 and becomes parallel to the transmission axis of the polarizing plate B on the exit side. The amount of transmitted light can be obtained. On the other hand, when a driving voltage is applied to the electrodes of the liquid crystal cell 102 to make the liquid crystal molecules stand in the direction of the electric field, the rotating function or the optical rotatory power with respect to the vibrating surface is lost and the amount of transmitted light is reduced. In this way, the polarizing plate is used to extract the change in the orientation of the liquid crystal molecules as the change in the amount of transmitted light.

Conventionally, a polarizing plate is attached to a liquid crystal cell manually. However, when foreign matter such as dust adheres between the liquid crystal cell and the polarizing plate, fingerprints of human hands adhere, or bubbles remain, the image quality of the liquid crystal display device is significantly impaired. Therefore, it is necessary to attach the polarizing plate from one side of the liquid crystal cell by pressing the polarizing plate with a roller in a clean environment. Recently, an automated integrated assembling method has been adopted in order to improve the manufacturing efficiency and the quality of liquid crystal display devices, and an automatic sticking device has been introduced in the process of sticking a polarizing plate. For automatic attachment, it is necessary to supply individual polarizing plates at a predetermined conveying pitch, and for this purpose, a transparent transparent tape 103 as shown in FIG. 6 is used. On the surface of the transparent tape 103, the individual polarizing plates 10 are arranged with a predetermined interval.
1 are arranged so that they can be easily peeled off. Polarizing plate 1
The back surface of 01 is pre-coated with an adhesive and the liquid crystal cell 1
02 can be fixed by adhesion.

[0005]

In the automatic polarizing plate attaching apparatus, the polarizing plate is sequentially peeled off from the transparent tape by using the suction head and is transferred to the surface of the liquid crystal cell which is positioned and fixed on the stage. For this reason, it is necessary to detect the position of each polarizing plate supplied by the transparent tape in advance. Conventionally,
An optical detection method is adopted, in which the moving transparent tape is irradiated with light using a fixed light projector, and the light quantity change is detected by a corresponding light receiver.
When the polarizing plate passes through the light irradiation point, the amount of light received changes, so position detection is performed. However, the polarizing plate is semi-transparent and is substantially transparent in appearance. Therefore, there is a problem or a problem that the change of the light amount is relatively small and stable detection of the polarizing plate cannot be performed. Not only is it difficult to adjust the sensitivity of the sensor in order to detect a nearly transparent polarizing plate with high accuracy, but it was also impossible to detect it stably after adjustment due to various fluctuation factors. If erroneous detection of the polarizing plate occurs, it causes a problem of the automatic sticking device itself, and causes a problem that the operation rate is reduced and the production amount is reduced accordingly. When the erroneous detection of the polarizing plate occurs, a suction error of the suction head occurs or a sticking error of the polarizing plate to the liquid crystal cell occurs.

[0006]

SUMMARY OF THE INVENTION In view of the above problems and problems of the prior art, it is an object of the present invention to provide a method capable of performing stable position detection of a polarizing plate. In order to achieve such an object, between a polarizing plate supplied for sticking to a liquid crystal cell and an optical sensor for detecting this polarizing plate, for detecting the amount of light passing through the polarizing plate. The means of arranging a polarizing plate was taken. Preferably, the transmission axis of the detection polarizing plate is arranged so as to be orthogonal to the transmission axis of the polarizing plate supplied for attaching to the liquid crystal cell. The optical sensor is composed of a light projector that projects light toward the polarizing plate and a light receiver that receives the light emitted from the polarizing plate. In the case of a transmissive optical sensor, the light projector and the light receiver are arranged separately from each other via a polarizing plate to be detected. When a reflection type optical sensor is used instead of this, a reflection surface is provided behind the polarizing plate to be detected, and the light projector and the light receiver are integrally arranged.

[0007]

In the present invention, the polarizing plate for detection or the analyzer is interposed between the polarizing plate supplied at a predetermined pitch and the optical sensor. The analyzer and the polarizing plate have a so-called crossed nicols relationship, and the transmission axis of the analyzer and the transmission axis of the polarizing plate are orthogonal to each other. Therefore, the light transmitted through the polarizing plate is dimmed by the analyzer, and the amount of light received by the light receiver is extremely reduced. For this reason, there is a very significant difference in the amount of light received between the presence and absence of the polarizing plate in the light projecting area of the optical sensor, and the position of the polarizing plate can be detected more stably than in the conventional case.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic diagram showing the configuration of an automatic polarizing plate sticking apparatus used for carrying out the polarizing plate detecting method and the polarizing plate sticking method according to the present invention. For this polarizing plate sticking device, each polarizing plate 1 is supplied by a transparent tape 2 serving as a carrier. The transparent tape 2 in which the polarizing plates 1 are arranged at a predetermined pitch is wound around the supply reel 3 in advance. The polarizing plate 1 is made of a film having an adhesive applied on the back surface and is placed on the transparent tape 2 so that it can be easily peeled off. The tip of the transparent tape 2 is attached to the take-up reel 4, and the transparent tape 2 is taken up at a predetermined speed and a predetermined pitch by controlling the rotation speed thereof. A knife edge 5 is in contact with the transparent tape 2 stretched between the take-up reel 4 and the supply reel 3. This knife edge 5 can be driven back and forth along the moving direction of the transparent tape 2.

An optical sensor 6 is fixedly arranged at a predetermined position in the feeding path of the transparent tape 2. The optical sensor 6 is of a reflective type and has a structure in which a pair of a light projector 7 and a light receiver 8 are integrated. The light projector 7 is composed of an LED or the like and projects a certain amount of light. On the other hand, the light receiver 8 is composed of a phototransistor, a photodiode or the like and receives and detects the reflected light. It should be noted that this reflected light is return light from the reflecting surface located immediately below the light projecting area. In this embodiment, the surface of the knife edge 5 also serves as a reflecting surface. Further, an analyzer 9 is interposed between the optical sensor 6 and the transparent tape 2 passage region. The analyzer 9 is composed of a polarizing plate, and is preferably arranged so that its transmission axis is orthogonal to the transmission axis of the polarizing plate 1 conveyed by the transparent tape 2, and has a so-called crossed Nicols relationship.

A suction head 10 facing the knife edge 5 and movable up and down is incorporated. The shape of the lower end surface of the suction head 10 is a frame shape as shown in the drawing, and has vacuum holes 11 on four sides. In addition, the window 1 in the center
Two are provided.

A fixed stage 14 for positioning and holding the liquid crystal cell 13 is provided near the knife edge 5. The individual liquid crystal cells 13 are sequentially supplied to the stage 14 via a transport mechanism (not shown). Further, the suction head 10 described above is controlled so that it can move in parallel between the knife edge 5 and the stage 14 with a predetermined stroke. For example, the suction head 10 is supported by a robot arm (not shown) having a horizontal axis and a vertical axis. Movable parts such as the take-up reel 4, the knife edge 5, the suction head 10, the liquid crystal cell transfer mechanism, and the robot arm described above are all controlled by the CPU or the like based on the detection result of the projector 8, and a consistent polarizing plate is provided. The automatic pasting process is performed.

Continuing to refer to FIG. 1, the method of detecting a polarizing plate and the method of attaching a polarizing plate according to the present invention will be described in detail. When the apparatus shown in FIG. 1 is started up, first, the liquid crystal cell 1
3 is positioned and fixed to the stage 14. The liquid crystal cell 13 is stored in a cassette or a tray in advance,
It is sequentially supplied onto the stage 14 via a transport mechanism (not shown). Next, the take-up reel 4 is rotated at a constant speed in the clockwise direction as indicated by the arrow to feed the transparent tape 2 leftward in the drawing. In the state shown in the drawing, the light projection spot from the light projector 7 directly irradiates the portion of the transparent tape 2 exposed between the pair of adjacent polarizing plates, and the light receiver 8 receives a relatively large amount of reflected light via the analyzer 9. ing. The polarizing plate 1 enters the light projection spot with the passage of time. When the leading edge 15 of the polarizing plate 1 coincides with the projected spot 16, the amount of reflected light is extremely reduced. This is because the returning light that has passed through the polarizing plate 1 is dimmed by the analyzer 9 having a crossed Nicols relationship. In response to this change in the amount of received light, the optical sensor 6 outputs a detection signal. In synchronization with the output of the detection signal, the take-up reel 4 further winds the transparent tape 2 for a predetermined length and then stops rotating. In this state, the polarizing plate 1 is correctly positioned with respect to the suction head 10. That is, the take-up reel 4 is rotated at a constant speed for a time period during which the polarizing plate 1 is correctly and accurately transferred to a position immediately below the suction head 10 from the time when the leading edge 15 is detected.

Then, the suction head 10 descends and comes into contact with the polarizing plate 1 immediately below to suck the same. As shown in the drawing, the vacuum head 11 and the window 12 are provided in the lower end surface of the suction head 10, so that even if the suction head 10 comes into contact with the polarizing plate 1, the surface of the polarizing plate of the effective display portion is not damaged. . In this state, the knife edge 5 is retracted to the right in the drawing. The polarizing plate 1 sucked by the suction head 10 as the knife edge 5 retracts is peeled off from the transparent tape 2. When completely detached from the transparent tape 2, the suction head 10 rises. At the same time, the knife edge 5 moves forward again and tension is applied to the transparent tape 2 between the take-up reel 4 and the supply reel 3 to return to the initial state.

The suction head 10 that has sucked the polarizing plate is horizontally moved by a predetermined distance via a robot arm (not shown), and moves directly above a stage 14 that holds and fixes the liquid crystal cell 13. With the surface of the liquid crystal cell 13 and the lower end surface of the suction head 10 accurately aligned, the suction head 10 descends again and the polarizing plate 1 is attached to the surface of the liquid crystal cell 13. After the suction force of the suction head 10 is released and only the suction head 10 is raised, a roller (not shown) is placed on the attached polarizing plate to remove bubbles and the like. In this way, the liquid crystal cell 13 having the polarizing plate attached to one surface thereof is taken out of the stage 14 by a carrying mechanism (not shown) and transferred to another stage (not shown) in an inverted state. At this stage, another polarizing plate is attached to the back surface side of the liquid crystal cell by the same operation.

Another embodiment of the present invention will be described with reference to FIG. Compared with the embodiment shown in FIG. 1, the arrangement structure of the optical sensor is particularly different, and therefore only the relevant portion is shown.
Also, for ease of understanding, the same elements as those of the components shown in FIG. 1 are designated by the same reference numerals. The optical sensor used in this embodiment is a transmissive type, and the light projector 7 and the light receiver 8 are arranged to face each other via the transparent tape 2 to which the paper is fed. The incident light spot from the projector 7 is the analyzer 9.
The light is received by the light receiver 8 through the transparent tape 2 that moves across the optical axis after passing through. When the polarizing plate 1 supported by the transparent tape 2 crosses the optical axis, the incident light linearly polarized by the analyzer 9 is blocked by the polarizing plate 1 and the amount of received light is extremely reduced, so that the position can be detected.

FIG. 3 shows the wavelength dependence of the transmittance of incident light.
The curve IN represents the amount of light transmission after passing through the analyzer 9 in the arrangement shown in FIG. 2, which is about 50% on average over the entire visible region. On the other hand, the curve OUT shows the light transmittance after passing through the polarizing plate 1, and corresponds to the amount of light received by the light receiver 8. It can be seen that the average is about several percent over the entire visible range, and the light is extremely dimmed.

[0017]

As described above, according to the present invention, it is possible to detect the position of a semitransparent polarizing plate with high sensitivity and stability by interposing an analyzer between the optical sensor and the polarizing plate to be detected. The effect is that it is possible to do. When this detection method is applied to an automatic polarizing plate sticking device for liquid crystal cells,
Since the polarizing plate can be supplied accurately and without malfunction, there is an effect that the operation rate of the device can be improved and the production amount can be greatly increased.

[Brief description of drawings]

FIG. 1 is a schematic view showing an automatic polarizing plate sticking device used for carrying out a polarizing plate detecting method and a polarizing plate sticking method according to the present invention.

FIG. 2 is a schematic diagram showing a modified example of the apparatus of FIG.

FIG. 3 is a graph showing dependency of transmittance on incident light wavelength.

FIG. 4 is a schematic diagram for explaining a polarization function of a polarizing plate.

FIG. 5 is a schematic diagram showing a general configuration of a liquid crystal display device.

FIG. 6 is a plan view showing a transparent tape used for automatically supplying a polarizing plate.

[Explanation of symbols]

 1 Polarizing Plate 2 Transparent Tape 3 Supply Reel 4 Winding Reel 5 Knife Edge 6 Optical Sensor 7 Emitter 8 Light Receiver 9 Analyzer 10 Adsorption Head 11 Vacuum Hole 12 Window 13 Liquid Crystal Cell 14 Stage 15 Leading Edge 16 Spot

Claims (7)

[Claims] 1. A detection polarizing plate for controlling a transmission amount of light passing through the polarizing plate is arranged between a polarizing plate supplied for attaching to a liquid crystal cell and an optical sensor for detecting the polarizing plate. A method for detecting a polarizing plate characterized by the above. 2. The method for detecting a polarizing plate according to claim 1, wherein the detecting polarizing plate is a polarizing plate having a transmission axis orthogonal to the transmission axis of the polarizing plate. 3. The polarizing plate according to claim 1, wherein the optical sensor includes a light projector that projects light toward the polarizing plate and a light receiver that receives light emitted from the polarizing plate. Detection method. 4. The method for detecting a polarizing plate according to claim 3, wherein the light projecting device and the light receiving device detect the polarizing plate with a transmissive optical sensor provided separately from each other through a polarizing plate. 5. The detection of a polarizing plate according to claim 3, wherein a reflecting surface is provided behind the polarizing plate, and the polarizing plate is detected by a reflection type optical sensor in which the light projector and the light receiver are integrated. Method. 6. A detection polarizing plate for controlling the amount of light passing through the polarizing plate is arranged between the polarizing plate supplied for attaching to the liquid crystal cell and an optical sensor for detecting the polarizing plate. And a step of detecting the polarizing plate, and a step of attaching the detected polarizing plate to the outer surface of the liquid crystal cell. 7. A detection polarizing plate for controlling the amount of light passing through the polarizing plate is arranged between the polarizing plate supplied for attaching to the liquid crystal cell and an optical sensor for detecting the polarizing plate. A polarizing plate sticking device comprising: a means for detecting a polarizing plate by means of a polarizing plate; and a means for sticking the detected polarizing plate on the outer surface of the liquid crystal cell.