Browsing by Author "Shih, Kai-Teng"

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A novel low-torque ball re-positioning scheme based on a sliding-mode ball observer for an automatic balancer system
(2008)
Chao, Paul C. -P.
;
Chiu, Chi-Wei
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Shih, Kai-Teng
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電控工程研究所
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Institute of Electrical and Control Engineering
A novel low-torque ball re-positioning scheme based on a sliding-mode ball observer is developed in this study with the aim to precisely reside the rolling ball inside an automatic balancer system (ABS) to its desired position-180 degree opposite to the inherent imbalance of the rotating system which the ABS is attached to. In this way, the ABS is capable of substantially reducing radial vibrations of the rotating system for a decent balancing. For preliminary feasibility, the case of a single ball is considered in this study. The first step is to establish the dynamic model of the system, which is followed by the analysis to ensure stability of the desired ball position. The second step is to forge a sliding-mode observer for estimating on-line position and velocity of the ball. With ball estimation capability, a low-torque speed regulator that essentially generates a series of speed drops to the neighborhood of suspension resonance is proposed to overcome practical ball rolling friction for residing the ball at the desired position. The design characteristic of low-torque required for the regulator is particularly suited to most of commercial spindle motors which can only output limited torques at high speeds. Finally, simulations and experiments are conducted for a benchmark problem of optical disc drives in order to verify the effectiveness of the proposed scheme of the sliding-mode observer and the low-torque speed regulator.
Developing a Quality Assessment Method for Evaluating Focusing Quality of an LC lens used in an Optical Pickup
(2012)
Shih, Kai-Teng
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Chao, Paul C. -P.
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Kao, Yung-Yuan
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電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
The liquid crystal (LC) lens with multi-ring electrodes for cameras in cell phones is designed in this study based on theoretical analysis, simulations and optimization. This study starts with the calculations to show that a substantial size reduction of a lens module can be offered by an insertion of LC lens. As compared to conventional cameras, the lens module in phone cameras particularly requires shorter focal length (around 8cm) and larger aperture (greater than 3 mm). The currently available LC lenses, however, fails to provide both the above capabilities. To remedy the problem, the method to design a large-aperture LC lens with multi-ring electrodes is developed in this study, and a new quality-assessment method is developed to evaluate the designed multi-ring LC lens via point spread function (PSF) and modulation transfer function (MTF). The number and widths of the ring-type electrodes are further optimized to reach certain required levels of PSF and MTF for the LC lens. This is achieved by designating a finite number of ring electrodes first and then assigning the width of each electrode proportional to the slope of the required applied voltage along the radius of the LC lens. Optimization results show that the three-ring LC lens with ring widths particularly designed reached satisfactory MTF of 65% for 5 and 48% for 7 line pairs per millimeter, which are not increased significantly even with the ring number increased to seven.