Command generation for flexible systems

For many types of mechanical systems flexibility presents the biggest challenge to the control system. If the mechanical components undergo deflection during the course of operation, it may prove difficult to track a desired trajectory or avoid obstacles. Furthermore, once the system has reached a setpoint, the residual vibration will degrade positioning accuracy and may cause a delay in task completion. Even if the mechanical components are very stiff, a closed-loop controller may introduce flexibility of its own that is detrimental to system performance. The desired motion of a system is fed into a command generator that transforms the desired motion into a reference command. The reference command is then used to either drive an openloop system, or form an error signal for a closed-loop system. Not every control system has a closed-loop controller; however, every control system does have some form of command generator. In many systems the command generator may not be immediately obvious and it may not be programmed into a computer. For example, the command generator for a construction crane is the human operator who attempts to produce an appropriate reference command in real time. This thesis presents methods for designing command generators for flexible systems. Specifically, it is concerned with what shape the reference commands should have. If the commands have an appropriate shape, then they will produce the desired motion, while reducing the detrimental effects of flexibility. In this thesis, the reference command is treated as a design variable (within some bounds) rather than a given parameter. Thesis Committee: Prof. Warren P. Seering, Chairman Prof. Stephen H. Crandall Prof. Jean-Jacques E. Slotine Prof. George C. Verghese Dr. Neil C. Singer

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