Heidar A. Malki, Ph.D., Assistant Professor, Electrical-Electronic Technology, and G. Ron Chen, Ph.D. Associate Professor, Electrical and Computer Engineering, UH
Figure 1. Block diagram and physical setup for the robot arm experiment.
Researchers seek to develop a robust fuzzy proportional-integral-derivative (PID) controller for tracking control of some flexible and uncertain robotic systems in aerospace engineering applications.
Our UH research team has investigated a typical flexible-joint robot arm model shown in Figure 1, a nonlinear dynamical system that generally has six uncertain system parameters in its control process. When the robot arm operates, the effects of nonlinearities, time-varying parameters, and external disturbances (such as unmodeled friction and damping), all together cause the system very significant tracking errors. The situation is even worse when the robot arm has structure flexibility.
The robust fuzzy PID controller designed by UH researchers has demonstrated considerable capability in handling these problems with a high degree of success. Computer simulation results have validated the capabilities of the controller. Figure 2 shows the result of a typical tracking performance of the controller on the uncertain robot arm system. It has demonstrated the controllability for up to ten percent uncertain tolerance in all the six system parameters.
Figure 2. Link positions when trajectory is 10exp(0.1t)-10 with uncertainties.
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John H. Miller, Jr., Ph.D., Associate Professor, Physics, Nilesh Tralshawala, Ph.D., Postdoctoral Research Associate, and James Claycomb, Research Assistant, UH
We have carried out experimental and theoretical investigations of high-Tc SQUID (HTSQUID) gradiometers, which have been developed and tested in unshielded laboratory and clinical environments. Noise due to ambient magnetic fields, including 1/f noise caused by hopping of flux vortices in the earth's field,1 must be reduced to enable operation with a sufficiently wide bandwidth (about 0.3-400 Hz) for clinically useful magnetocardiographic (MCG) applications. We have designed novel localized high-Tc superconducting (HTS) shields,2 which are capable of reducing ambient field noise without affecting the signals of interest (in our case, the current sources in the heart). These shields, made of sintered YBCO and melt-casted BSCCO, are small in size, the largest dimension being 10 cm, and enable acute discrimination between the signals of interest and nearby noise sources. Active noise compensation3 techniques are also employed to further reduce the effects of low frequency noise, such as magnetic noise caused by vibrations of the HTSQUIDs in the earth's field. In addition, digital finite impulse response (FIR) filters are utilized to eliminate noise at power line frequencies (60 Hz and its harmonics).4
We have implemented both planar and axial gradiometers, which have been used to obtain adult MCG signals in a catheterization laboratory at Texas Children's Hospital. Currently, we are limited to 0.3-100 Hz bandwidth, and efforts are under way to push this bandwidth to higher frequencies. These efforts include the design of a novel gantry structure to obtain vibration isolation and reduce the pickup of microphonics. In addition, adaptive noise cancellation techniques5 are being developed to further alleviate the effects of vibrations and to compensate for imperfections in the mechanical and electronic alignment of the individual components of the gradiometers.
References
1Miklich, A. H., D. Koelle, T. J. Shaw, F. Ludwig, D. T. Nemeth, E. Dantsker, J. Clarke,
N. McN. Alford, T. W. Button, and M. S. Colclough. App. Physics Lett. 64 (1994): 3494-96.
2Tralshawala, N., J. H. Miller, Jr., and D. R. Jackson. IEEE Trans. on Applied
Supercon-ductivity 5 (1995): 2354-57.
3Aarnink, W. A. M., P. J. van den Bosch, T.-M. Roelofs, M. Verbiesen, H. J. Holland, H. J.
M. ter Brake, and H. Rogalla. IEEE Trans. on Applied Superconductivity 5 (1995): 2470-73.
4Ying, Q., N. Tralshawala, N. Fan, J. H. Miller, Jr., and D. R. Jackson. The DSPx'95
Technical Program (1995): 520-27.
5Widrow, B., J. R. Glover, Jr., J. M. McCool, J. Kaunitz, C. S. Williams, R. H. Hearn, J.
R. Zeidler, E. Dong Jr., and R. C. Goodlin. Proc. IEEE 63 (1975): 1692-1716.
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Lawrence S. Pinsky, Ph.D., Professor and Chair of Physics, UH
University researchers have undertaken the development of a computer simulation of the radiation environment in spacecraft. The basic idea is to adapt present Monte Carlo calculation codes used in high energy physics to simulate the radiation present in spacecraft during a mission. The initial effort would be directed towards Shuttle missions, but the clear intention would be to develop a program for the accurate prediction of the radiation environment likely to be encountered on future planned endeavors such as the Space Station, possible lunar return mission, or, most importantly, a Mars mission. The longer the mission, especially those which will not have the shielding of the earth's magnetic field, the more critical the radiation threat will be. At the present time, radiation shielding is the major hurdle foreseen in the design of a Mars mission.
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Irving N. Rothman, Ph.D., Professor, English, UH
The editorial staff of the Institute for Space Systems Operations has the task of gathering documentation from principal investigators and reporting their research for widespread dissemination throughout the scientific community. Traditionally, this effort has meant printed publication. This current Annual Report represents two years of research awards and, and in some efforts, it documents the advancement of a project from one stage to another.
However, Internet has offered a new avenue of communication. Under the hand of Debbie Villarreal, senior editorial assistant, the ISSO home page has been established to include (1) the total contents of the 1992-93 Annual Report and (2) current announcements about the new aerospace postdoctoral fellowship program by which UH faculty, in league with NASA researchers, afford aerospace fellows the opportunity to conduct advanced research in the high-tech laboratories of NASA. ISSO editorial services are advancing into the second generation of graphical reproduction by employing portable document format technology (PDF) for the display of publications with designed pages on the Internet.
Contents
ISSO -- Institute for Space Systems Operations
1994-1995 Annual Report
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