M.S. Thesis Presentation by Erika A. Ooten
Monday, November 13, 2000

(Dr. William E. Singhose, advisor)

"Command Generation for Flexible Systems using Numerator Dynamics and Sliding Mode Control"


Moving a system quickly and accurately can be difficult when the system has flexible dynamics.  However, if the flexible dynamics are known with some accuracy, then their effect can be reduced.  Specifically, it has been shown that a decrease in the overall maneuver time can be realized if the numerator dynamics are taken into account.  For sequential repetitive motions, decreasing the cycle time can result in significant cost savings.  However, there are some particular times when using the numerator dynamics will increase the overall cycle time.  Consequently, a procedure detailing when to utilize the numerator dynamics is presented.

If the flexible dynamics are not well know, the system's trajectory tracking suffers if the controller is not insensitive to parameter uncertainties.  Sliding Mode Control (SMC) can provide systems with known parameter uncertainties with perfect trajectory tracking.  However, SMC is susceptible to high actuator effort and chattering.  If the actuator chatters, any unmodeled high frequency dynamics may be excited; consequently, the performance of the overall system will degrade.  For systems with an unobservable mode, utilizing command generation, specifically input shaping, can enhance the performance of SMC.  The SMC is designed using a system model that does not take the unobservable mode into account, hence it is a reduced-order system model.  The input shaper is designed to counteract the unobservable mode dynamics and together, the overall performance of the Sliding Mode Controller is enhanced.  Using input shaping and SMC produces better tracking performance, requires less actuator effort and would be much easier to implement than using only SMC.