Results on the Robust Observer-based Position Controller for Parallel Kinematic Machines |
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Authors: | Margareta Stefanovic Huijuan Zhang |
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Affiliation: | 1.Department of Electrical and Computer Engineering,University of Wyoming,Laramie,USA |
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Abstract: | The problem of state observation and position control by output feedback for a nonlinear three degrees-of-freedom (3-DOF)
parallel kinematic machine (PKM) system is considered, based on the limited signal availability (only the moving platform
displacement measurements are assumed available). Unknown velocity signals are estimated via a nonlinear robust observer that
is designed for the nonlinear system with observable linear dynamics part and bounded nonlinearities and disturbances, and
that guarantees global exponential stability of the observation error. A proportional-derivative (PD) controller is designed
to solve the position control problem, utilizing the estimated velocity, as well as the gravitation compensation, dynamic
friction and external disturbance compensation for the PKM. The closed-loop system is proven to have global asymptotical stability
according to the Lyapunov analysis method and LaSalle’s invariance principle. Performance of the resulting observer and controller
is illustrated in a simulation study of a 3-DOF PKM. Modifications to the nonlinear observer and control law are discussed,
that assure convergence of the position error and state observation error to zero when the upper bounds on the model uncertainties/disturbances
are not known a priori. |
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Keywords: | |
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