Investigating the effect of gravity on the optical performance of large-sized liquid crystal displays

This paper proposes a method to investigate the effect of gravity on optical performance of large-sized liquid crystal displays (LCDs). Combined with the finite element analysis and the LCD optical simulation, the change in optical performance of large-sized LCDs under the influence of gravity is analyzed. Compared with the condition without tilt angle, the Δu'v' is 0.025 in the bottom area of the 100-in LCD with the substrate thickness of 0.3 mm at a tilt angle of 1.5°, leading to a noticeable color shift. With the decrease of tilt angle or the increase of substrate thickness, the change in optical performance becomes unnoticeable and thus avoids the occurrence of visible display defect. Utilizing the proposed method, the assembly precision of large-sized LC panels can be calculated and the display defect caused by gravity can be effectively prevented.     

面向光学薄膜瑕疵检测的二值图像快速Blob分析算法

针对光学薄膜瑕疵检测应用中的高实时性图像处理要求,提出一种基于游程的二值图像快速Blob分析算法。采用步进式动态扫描方式,每个游程仅需扫描一次,且不必与相邻行的所有游程进行比较,算法的搜索空间得到压缩;游程连通性比较的分支少,简化了判断过程,提高了操作效率;所设计的游程及目标对象的数据结构允许由任一游程节点快速访问其所属链表的首部和尾部,不仅为后续的数据访问提供了便利,且提高了标记冲突时链表合并的操作速度,避免了冲突等价表的介入。实验结果表明该算法具有鲁棒、高效的特性,并已在光学薄膜瑕疵检测系统中得到了应用。     

Calculation of contrast in dyed phase-change liquid crystal displays

The properties of dyed phase-changed liquid crystals are presented and their dependences investigated. This information is used to simplify expressions from earlier work describing performance variations in displays which experience changes in cell or LC parameters.     

Progress and prospects of complex liquid crystal displays

After a brief introduction to the relevant electro-optic effects, the problems of matrix addressing complex liquid crystal displays are described. The various possible approaches are outlined and their fundamental advantages and weaknesses discussed. Current state of the art and research activities are reviewed, with emphasis on reflective displays.     

Ripple phenomenon of displays with nematic liquid crystal

Liquid crystal displays will show ripple if the display surface or display bracket is subjected to tactile forces. In this paper, the ripple of liquid crystal displays is investigated by dealing with elastic wave propagation in a liquid crystal layer. The model proposed for a visco‐elastic medium like liquid crystals (LCs) is generalized by combining the properties of a crystalline solid and an anisotropic fluid. The governing equation is derived by using visco‐elastic and wave equations. In the experiments, a linear motor is used to touch the display panel for producing ripple. Displays of three different amounts of LCs are compared. Experimental results also show that each display panel has its own wave propagation velocity that is not changed by different motor touch speeds. In addition, both theoretical analysis and experimental results depict that displays with a larger amount of LCs lead to slower ripple speed.     

Smectic dynamic scattering in laser-addressed liquid crystal projection displays

Two viable methods of producing high-uniformity scattering, suitable for laser-scanned high- resolution light-on-dark contrast liquid crystal projection displays, are reported. The advantages of dynamic scattering over heat-pulse-induced scattering are outlined in terms of power consumption, addressability, uniformity and thermal management.     

Effect of small liquid crystal molecules on the driving voltage of cholesteric liquid crystal displays

In order to achieve a lower driving voltage of a cholesteric liquid crystal display (Ch-LCD) we formulated new nematic liquid crystal mixtures with dopants. The interesting thing is that the driving voltage is decreased more by adding the low molecular weight of liquid crystal materials in the cholesteric mixtures without decreasing its reflectivity. The cholesteric mixture is optimized by adding 20 wt% of CN-007 enough to drive the display, necessary for using a commercial STN driver. Homogeneous alignment layers provide a higher reflective panel because of stabilizing the planar texture of cholesteric liquid crystal, while homeotropic alignment layers provide a higher contrast ratio because of stabilizing focal-conic structure. The rubbing condition depending on the driving scheme also affects the panel properties. The combination of the panel structure and the process condition of cholesteric mixtures make the Ch-LCD high reflectivity and contrast ratio. Two 5.7 in. VGA monochromic cholesteric reflective liquid crystal displays with a high resolution like this folding type are demonstrated using a STN driver.     

Feasibility study of novel fast‐switching liquid crystal displays using electric birefringence effect

Both theoretical and experimental studies were made on electric birefringence effect of nematic liquid crystals in isotropic phase with respect to its applicability to novel LCDs. It was confirmed that response times are <1 ms, and a critical point exists where electro‐optic hysteresis vanishes. Substrate surface treatments were also found to improve the electro‐optic characteristics. The results are promising for both projection and direct view display applications featuring fast switching and high image quality.     

Extended Jones matrix method and its application in the analysis of compensators for liquid crystal displays

We describe an extended Jones matrix method which is a powerful tool to treat the transmission of light through birefringent networks, where the incident angle of light and the optical axis of the birefringent media are arbitrary. The method is generalized to cover all dielectric media including uniaxial and biaxial crystals and gyrotropic materials that exhibit optical rotatory power and Faraday rotation. We then apply this method to investigate various birefringent optical thin films that can be used to improve the viewing angle characteristics and gray scale stability of conventional twisted nematic liquid crystal displays (TN-LCDs). The birefringent phase retardation films include negative uniaxial, positive uniaxial and biaxial films of various orientations. The results are presented and discussed.     

Brightness and contrast of nematic liquid crystal bistable configuration displays

A photometer was used to measure the angular dependence of the brightness and contrast ratio of bistable configuration displays in both reflection and transmission modes. The essential result is that the field of view is not limited by any cut-off in the angular properties of the bistable configurations themselves, but is determined primarily by the conditions of illumination and properties of the reflector. The contrast ratio drops off only slightly for large viewing angles, and hence the acceptable field of view is determined primarily by the angular dependence of the brightness. The latter depends strongly on the nature of the illumination. For normally incident light, the full width at half maximum of the reflective display was 25° with a contrast ratio about 2.4. The transmission display was illuminated through a ground glass scattered by light normally incident on the ground glass. Under these conditions, the full width at half maximum was essentially the same as that of the ground glass alone, about 15dg and a contrast ratio of about 2. The photometer measurements of contrast ratio are in rough agreement with densitometer measurements of the absorption characteristics of the dichroic dye guest in the liquid crystal host in its parallel-aligned state.     

Automatic inspection of the surface defects of cast metals

A method of detecting the surface defects of cast metals is described. The proposed automatic inspection system consists of an industrial television camera (ITVC) and a micro-computer. A picture is taken from the ITVC in 8-bit digital form and stored in the memory of the microcomputer. The computer calculates features from the picture and decides if there is any defect on the surface of the cast metal. Belt pulleys cast in a local foundry are selected as one example of objects for inspection. There are two types of defect which are most likely to appear on the surface of cast metal: fins and notches. In the foundry operation a cast pulley which has a large fin is transferred to the definning process and the fin is broken off by a hammer. A small fin is scraped off by a grinder. Both normal cast and definned metals are then transferred to the next machining process. Basic experiments are carried out using belt pulleys cast in a real foundry. It is concluded that a large percentage of the defective casts can be extracted by the proposed system. It has wide applications in the field of automatic inspection in a foundry.     

A composite model for accurate colorimetric characterization of liquid crystal displays

This paper presents a composite color‐characterization model for Liquid Crystal Displays (LCDs), considering channel dependence and poor chromaticity constancy of primaries. The proposed model consists of two parts, that is, the Piecewise Linear assuming Variation in Chromaticity (PLVC) model and a partition compensation error model. PLVC model can accurately predict CIEXYZ for primaries and calculate the CIEXYZ of any digital input values ( d _r , d _g , d _b ) based on the channel independence assumption. In addition, the prediction error of PLVC model is compensated in RGB subspace using the partition compensation error model. The color difference Δ was used to evaluate the accuracy of the model. The result of this experiment shows that PLVC model performs well for LCDs with channel independence and poor chromaticity constancy of primaries, compared with other characterization models. For channel dependence and poor chromaticity constancy LCDs, our result shows that proposed composite color‐characterization model also has better prediction accuracy than all other tested models. In this study, measurements were conducted in ambient light environment, and the experiment results consist with practical applications.     

Visibility of transmissive liquid crystal displays under dynamic lighting conditions.

Liquid crystal displays maintain superior contrast under bright sunlight conditions compared with cathode-ray tube displays. This attribute, along with reduced weight, volume, and power requirements, make liquid crystal displays especially desirable for use in vehicular applications. The present experiment was designed to determine the luminance requirements for transmissive liquid crystal displays viewed under a wide range of lighting conditions typical of many vehicular environments. Both the ambient illumination incident on the display surface and the forward-field-of-view adaptation luminance were parametrically manipulated. The visual task involved speeded spatial discrimination responses for detection of the gap in a modified Landolt-C acuity target. The results indicate that under the worst lighting conditions tested, a display luminance of approximately 180 cd/m2 yielded asymptotic spatial discrimination performance. The results have been incorporated into a predictive visual performance model for spatial discrimination tasks, which describes the present data well and represents a first step toward a device-independent model of display visibility.     

Floating drive schemes for dual-frequency addressing of complex liquid crystal displays

A circuit configuration for the dual-frequency addressing of complex liquid crystal matrix displays is described. After division of the high and multilevel drive voltages into several digital signal components, they are superposed in digital 15 V CMOS ICs. The signals so produced have an amplitude which exceeds the value of the supply voltage and which involves three or four levels. The technique is suitable for modification of existing display drive systems to reach a higher number of multiplexed lines or to allow better selection.     

Investigating surface crystal growth using an intrinsic exposed core optical fibre sensor

Surface, or heterogeneous crystallisation processes, also known as scale formation, has been monitored directly using an intrinsic, exposed core optical fibre sensor (IECOFS). Optical attenuation was found to be linearly correlated with scale layer height and average crystal contact area and the optical signal was found to be restored following chemical removal of deposited crystals (without physical intervention). The IECOFS was found to be insensitive to bulk-solution (homogenous) crystallisation processes, making it a potentially powerful tool for the study of heterogeneous-only crystallisation processes. Kinetic parameters extracted from the obtained crystallisation measurements showed that the IECOFS is capable of providing a reliable means of monitoring surface crystal growth.     

Instrumented film-insert injection compression molding for lens encapsulation of liquid crystal displays

A film-insert injection compression molding process was introduced to encapsulate cholesteric liquid crystal displays with flexible and rigid lens for full protection of displays to replace the currently used time consuming hand lamination technique. For this purpose, a new interchangeable cavity instrumented hot runner mold was designed and constructed. This complex method was carefully optimized considering challenges arising from an insert multilayer display with +80% liquid crystal content as well as different thermal expansion coefficients between the layers and the lens material as a high potential of delamination and warpage. Concerning the desired physical properties including transparency, low melt viscosity and melting temperature as well as a wide range of hardness grades from soft (flexible) to hard (rigid), three different hardness grades of thermoplastic polyurethanes were found to be the best candidates for this lens application. During proposed lens encapsulation, the pressure changes were evaluated with screw and mold movements using position detection via displacement transducers attached to track the mold closure and screw forward motion. The quality of encapsulation and shrinkage related problems, as well as their elimination, were all discussed. Display substrate material selection criteria for lowered warpage were defined with supporting thermal characterizations. Among the process parameters, tested also by applying the design of experiments with Taguchi method, mold temperature was found to be the most influential parameter on warpage, followed by pin gate opening time, packing pressure, and cooling time.     

Displays for business machines: operation liquid crystal displays of photocopier machines

It is important to remember that liquid crystal display (LCD) technology was common in business machines long before it was adopted by the cellular telephone industry.This chapter details the role of LCD technology in business machines, using the multi-function photo copier as an illustrative example. Additionally, the function sharing capability of hard keys in conjunction with LCD technology is introduced.     

Auto‐calibration of drive condition for cholesteric liquid crystal displays

Dynamic drive scheme (DDS) is known widely as passive matrix addressing that obtains both high‐speed re‐writing and a high contrast ratio in the field of cholesteric liquid crystal displays (LCDs). However, DDS has a serious problem in that the proper drive condition is very narrow and it is largely influenced by individual differences in LCDs that arise during their production. We have developed a new auto‐calibration system that adjusts both the contrast ratio and color balance automatically using capacitances of effective pixels and temperature compensation models that utilize the physical properties of cholesteric LCDs. We have managed to optimize the driving conditions between 5 and 35 °C with this method, and obtained both stable and high‐quality color images where the reflectance is 36%, contrast ratio is 8, and NTSC ratio is 20%. This auto‐calibration system has been able to greatly improve the production yield of cholesteric LCDs and made it possible to make practical use of cholesteric LCDs.