Browsing by Author "Chen, LY"

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Flow effect in the chiral-homeotropic liquid-crystal cell
(1999-11-29)
Chen, SH
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Chen, LY
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光電工程學系
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Department of Photonics
We investigated the dynamics of the chiral-homeotropic liquid-crystal cell and found that the flow of liquid crystal causes an optical bounce after switching on a high applied voltage. We analyzed the behavior of the directors by computer simulation and found that the field-induced backflow effect results in the abnormal twist of the directors near the substrates. The abnormal twist slows down the rising speed of the chiral-homeotropic cell and produces an optical bounce during the rising period. Our results indicate that the backflow effect should be considered on the design of fast chiral-homeotropic liquid-crystal cells. The significant distinctions between this field-induced optical bounce and the well-known optical bounce of the twisted nematic liquid-crystal cell are also described in this letter. (C) 1999 American Institute of Physics. [S0003-6951(99)04148-0].
Homeotropic liquid-crystal device with two metastable states
(1999-06-21)
Chen, LY
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Chen, SH
;
光電工程學系
;
Department of Photonics
We report a homeotropic liquid-crystal device which has two metastable states when an electric field is applied. The behaviors of these two metastable states are similar to the bistable twist nematic device. We control this device electrically in the rising period to switch it from the homeotropic state toward either the twist or homogeneous state. It not only behaves as a conventional homeotropic cell but also provides another twist structure for further applications. The back-flow effect in the rising period plays an important role in the switching mechanism. The experimental results are described in this letter. (C) 1999 American Institute of Physics. [S0003-6951(99)01525-9].
Robust neuro-fuzzy controller design via sliding-mode approach
(2004)
Hsu, CF
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Lee, TT
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Lin, CM
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Chen, LY
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電控工程研究所
The computed torque or inverse dynamics control techniques are based on a good understanding of the system dynamics and even its environment. For the real-time applications, the system dynamics always is difficult to obtain. To tackle this drawback, the goal of this paper is to develop a model-free control method which is referred to as robust neuro-fuzzy sliding-mode control (RNFSMC) system. The proposed RNFSMC system is comprised of a fuzzy controller and a robust controller. The fuzzy controller is utilized to approximate an ideal controller by the developed tuning algorithms, and the robust controller is designed to achieve H-infinity tracking performance index. To investigate the effectiveness of the proposed RNFSMC system, it is applied to control a Chua's chaotic circuit system. Finally, simulation results demonstrate that the effect of the fuzzy approximation error on the tracking error can be attenuated efficiently by the proposed method without any knowledge of the controlled systems.
The optical bounce effect of the chiral-homeotropic cell
(1999)
Chen, LY
;
Chen, SH
;
Hao, CW
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光電工程學系
;
Department of Photonics
We examined the dynamic response of the chiral-homeotropic liquid crystal cell by measuring the optical transmittance. It was found that the well-known optical bounce phenomenon which was originally found in the twist nematic cells, also appears in the chiral-homeotropic cells. The field induced backflow causes this optical bounce and it may influence the dynamic response of the cell. In this paper, we will present the experimental data and use a simple model based on ELF theory to explain the optical bounce phenomenon appearing in the homeotropic to planar state transition.