Positioning control of an underwater robot with tilting thrusters via decomposition of thrust vector

Positioning control of an underwater robot is a challenging problem due to the high disturbances of ocean flow. To overcome the high disturbance, a new underwater robot with tilting thrusters was proposed previously, which can compensate for disturbance by focusing the thrusting force in the direction of the disturbance. However, the tilting motion of the thrusters makes the system nonlinear, and the limited tilting speed sometimes makes the robot unstable. Therefore, an optimized controller is necessary. A new positioning controller is proposed for this robot using a vector decomposition method. Based on the dynamic model, the nonlinear force input term of the tilting thrusters is decomposed in the horizontal and vertical directions. Based on the decomposition, the solution is determined by a pseudo-inverse and null-space solution. Using the characteristics of the decomposed input matrix, the final solution can be found by solving a simple second-order algebraic equation to overcome the limitations of the tilting speed. The positioning was simulated to validate the proposed controller by comparing the results with a switching-based controller. Tracking results are also presented. In future work, a high-level control strategy will be developed to take advantage of the tilting thrusters by focusing the forcing direction toward the disturbance with a limited stability margin.

     

Novel frame buffer pixel circuits for liquid-crystal-on-silicon microdisplays

A 32 /spl times/ 16 liquid-crystal-on-silicon (LCOS) backplane with novel frame buffer pixels is designed and fabricated using the AMI Semiconductor's 0.5-/spl mu/m double-poly triple-metal CMOS process. The three novel pixel circuits described herein increase the brightness of an XGA LCOS microdisplay by at least 36% without sacrificing image contrast ratio. The increase of brightness is attributed to maximizing overall image view time, allowing an image to be displayed at full contrast while the next image is buffered onto the backplane. The new circuits achieve this by removing charge sharing and charge inducement problems shown in previously proposed frame buffer pixel circuits. Voltages on the pixel electrodes measured through rail-to-rail operational amplifiers with negative feedback vary from 0 to 4.25 V (6-V power source). All data voltage levels remain constant over a frame time with less than 1% drop, thus ensuring maximum contrast ratio. Modeling and experimental measurement on the fabricated chip show that these pixel circuits outperform all others to date based on storage time, data storage level, and potential for highest contrast ratio with maximum brightness.     

Optimal design of a micro evaporator with lateral gaps

This paper presents an optimal design of a micro evaporator, to maximize the heat transfer coefficient (HTC) and it forms the starting point in developing miniaturized vapor–compression refrigeration system. The experimental design is adopted to determine the optimal parameters of the evaporator for realizing the inlet–outlet conditions of the refrigerating cycle, and for increasing the HTC. The number of lateral gaps, channel width, and lateral gap size were optimized to maximize HTCs of 2062, 2029, and 1895 W/m²K for heating powers of 40, 60, and 80 W, respectively. The refrigerant and the mass flow rate were fixed as R-123 and 0.72 g/s, respectively. Among the three design parameters, the channel width is the most sensitive parameter influencing the HTC. A periodic change of flow pattern was observed in the evaporator with high HTCs, and a dryout was observed in the evaporator with low HTCs.