Limiting vibration in systems with constant amplitude actuators through command preshaping. M.S Thesis - MIT

The basic concepts of command preshaping were taken and adapted to the framework of systems with constant amplitude (on-off) actuators. In this context, pulse sequences were developed which help to attenuate vibration in flexible systems with high robustness to errors in frequency identification. Sequences containing impulses of different magnitudes were approximated by sequences containing pulses of different durations. The effects of variation in pulse width on this approximation were examined. Sequences capable of minimizing loads induced in flexible systems during execution of commands were also investigated. The usefulness of these techniques in real-world situations was verified by application to a high fidelity simulation of the space shuttle. Results showed that constant amplitude preshaping techniques offer a substantial improvement in vibration reduction over both the standard and upgraded shuttle control methods and may be mission enabling for use of the shuttle with extremely massive payloads. Thesis Supervisor: Warren P. Seering FAGE BLANK MOT FHJMEB PAGE. . INTENTIONALLY BLANK A c k n o w l e d g m e n t May 3, 1994 This thesis was prepared at the Charles Stark Draper Laboratory, Inc., under contract NAS9-18426. Publication of this thesis does not constitute approval by Draper or the sponsoring agency of the findings or conclusions contained herein. It is published for the exchange and stimulation of ideas. I hereby assign my copyright of this thesis to the Charles Stark Draper Laboratory, Inc., Cambridge, Massachusetts. J Permission is hereby granted by the Charles Stark Draper Laboratory, Inc., to the Massachusetts Institute of Technology to reproduce any or all of this thesis . BLANK NOT FILMED 8LANK A c k n o w l e d g m e n t s There are quite a few people who helped me get to this point, and I would like to take this space to thank them. Thanks first to the Charles Stark Draper Laboratory for providing me with the financial and academic support which have allowed me to complete my Masters Degree at MIT. Next, I'd like to thank my supervisor at Draper, Kevin Gift, and my advisor at MIT, Professor Warren Seering. They have both done a great job of keeping me on track and providing with feedback on my work. Thanks also to my officemates at Draper and the AI lab, Mark Jackson and Andy Christian, who were both excellent sources of ideas and humored me when I needed to bounce my own off of someone else. Andy, your experience with preshaping and insight into the issues involved were a great, great help. I'd also like to express my appreciation of all the folks in the (former) Manned Space Flight Group at Draper who were always willing to lend a hand and answer questions about the shuttle. Finally, I'd like to thank my mother and brother for all the love and support that they have given me over the years. Without them, I could not have gotten here. PAGE W-ANK MOT RLMSC PAG£._L—...INTFNTiCMALLY BI/NK