Computer graphics processing and selective visual display system – Computer graphics processing – Graph generating
Reexamination Certificate
1998-09-10
2001-10-09
Brier, Jeffery (Department: 2672)
Computer graphics processing and selective visual display system
Computer graphics processing
Graph generating
C349S187000
Reexamination Certificate
active
06300954
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to methods and apparatus for detecting parameters of a liquid crystal display for use, for example, in a liquid crystal display unit. More particularly, the present invention relates to methods and apparatus for measuring the thickness of a liquid crystal layer and the twist angle of liquid crystal molecules within the liquid crystal layer.
2. Description of the Related Art
Liquid crystal displays (LCDs) having liquid crystal molecules oriented parallel to the surface of two substrates of the display, wherein the direction of orientation of the liquid crystal molecules are gradually twisted or rotated between the two substrates, are well known. One type of such liquid crystal displays is known as a twisted nematic liquid crystal display (hereinafter referred to as “TN display”), in which the direction of orientation is twisted 90 degrees from the front substrate to the back substrate. Another known twisted nematic liquid crystal display is a super twisted nematic liquid crystal display (hereinafter referred to as “STN display”), in which the direction of orientation of the liquid crystal molecules is twisted between 180 to 270 degrees. These liquid crystal displays are used widely in various liquid crystal display units, such as display units for word processors, personal computers and televisions.
For such liquid crystal display units, the image quality directly relates to the distance between the two substrates, and in particular, to the uniformity of the thickness of the liquid crystal layer. The thickness determines the distribution of the twist angle of the liquid crystal molecules and is directly related to the contrast properties of the LCD. The uniformity of cell thickness and twist angle distribution throughout the entire panel therefore determines the display performance of LCDs. In addition, the anchoring energy (i.e., the orientation restricting force in the azimuth angle direction on each substrate surface of the liquid crystal display), which is another important parameter of liquid crystal displays, can be determined from the thickness of the liquid crystal layer and the twist angle of the liquid crystal molecules between the two substrates. Therefore, the quick and accurate determination of the thickness of the liquid crystal layer and the twist angle of the liquid crystal molecules are long-felt needs for both practical manufacturing processes and fundamental physical studies of liquid crystals.
The following methods have been developed to determine such liquid crystal display parameters: (1) measuring the electrostatic capacity and optical phase difference of a liquid crystal display to determine the thickness of the liquid crystal layer; (2) measuring light interference and electrostatic capacity of an empty display before the liquid crystal molecules are sealed between the substrates, to thereby determine the thickness of the liquid crystal layer; (3) measuring the distance between the two substrates using a three-dimensional shape measuring method, to thereby determine the thickness of the liquid crystal layer; (4) disposing a liquid crystal display between two polarizing plates and adjusting the optical path difference using a photo-elastic modulation element to perform curve fitting of the transmitted light intensity characteristics and determine the twist angle of the liquid crystal molecules; and (5) disposing a liquid crystal display between two polarizing plates and rotating one or both of the liquid crystal display and the polarizing plates to find an angle at which the maximum or minimum transmitted light intensity is transmitted, to thereby determine the thickness of the liquid crystal layer and the twist angle of the liquid crystal molecules in the layer using the Jones Matrix Display. These methods are described, for example, in “J. Appl. Phys.” (Vol. 69, pages 1304-1309, 1991), “Jpn. J. Appl. Phys.” (Vol.33, pages L434-L436, 1994), “Jpn. J. Appl. Phys.” (Vol.33, pages L1242-L1244, 1994), “Jpn. J. Appl. Phys.” (Vol.35, pages 4434-4437, 1996), “Lecture Manuscripts for the 22
nd
Panel Discussion for Liquid Crystal” (pages 139-140).
These methods may be classified into two types: extinction measurement methods and optoelectrical methods. The extinction measurement methods require some complicated rotation operations of the liquid crystal cell and/or polarizers for determine the angles of maximum and minimum transmissions. The optoelectrical measurement methods involve measuring optical transmissions at two different frequencies while rotating the analyzer and fitting the experimental curve using the Jones matrix method. Further, these methods are basically suited to measuring cell thickness and twist angle at only one probing point. In order to map a two-dimensional cell, the LCD must be mechanically moved from point to point. Thus, measurements of the cell thickness and twist angle of an entire display can not be performed quickly and with high accuracy using these methods.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to provide improved methods and apparatus for quickly, accurately and easily detecting parameters of a liquid crystal display, such as the thickness of a liquid crystal layer and the twist angle of liquid crystal molecules within the liquid crystal layer.
Preferably, liquid crystal parameters are determined by methods and apparatus that measure Stokes parameters of the liquid crystal display. For example, light intensity transmitted through a liquid crystal display can be measured and Stokes parameters for a particular of location within the liquid crystal display are determined based upon the measured transmitted light intensity. The thickness of the liquid crystal layer and/or the twist angle of the liquid crystal molecules can then be calculated using the determined Stokes parameters for the liquid crystal display. The methods and apparatus taught according to the present invention enable the simple, rapid and inexpensive determination of important characteristics of a liquid crystal display.
In an additional aspect of the present teachings, the apparatus can be adjusted so that light intensity transmitted through the liquid crystal display can be measured at an extreme value, i.e. a maximum or a minimum value. By calculating the Stokes parameters based upon these measured light intensities, the measuring operation can be further simplified.
Further, the liquid crystal parameters may be simultaneously or substantially simultaneously determined for a plurality of points within the liquid crystal display using an apparatus having a simple configuration. In this aspect of the present teachings, a two-dimensional photodetector may be utilized to measure light intensities. Thus, Stokes parameters, and therefore liquid crystal parameters, can be calculated for a variety of points within the liquid crystal display in a single operation. As a result, this aspect can permit an efficient operation to measure liquid crystal parameters for an entire liquid crystal display.
Other objects, feature and advantages of the present invention will be readily understood after reading the following detailed description together with the accompanying drawings and the claims.
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He Zhan
Sato Susumu
Togashi Yoshihiro
Zhou Ying
Blackman Anthony J.
Brier Jeffery
Meiryo Tekunika Kabushiki Kaisha
Patterson Thuente Skaar & Christensen P.A.
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