Control of sandwich nonlinear systems

An open control problem: control of sandwich nonlinear systems is addressed. Of interest are sandwiched nonsmooth nonlinearities such as dead-zone, hysteresis and backlash between dynamic blocks. Some preliminary continuous-time control designs are proposed. A framework for hybrid control is developed that is used to design control schemes for different cases of the control problem with required modifications. Friction compensation is addressed for systems with sandwiched friction along with sandwiched dynamics. An open problem of the control of sandwich nonlinear systems with actuator failures is introduced by a control design for an illustrative special case of the problem.; The proposed hybrid control framework employs an inner-loop discrete-time feedback design and an outer-loop continuous-time feedback design, combined with a nonlinearity inverse to cancel the nonlinearity effect, for improving output tracking. The compensator neural network has neurons that can approximate jump functions such as a dead-zone inverse. The weights of the two neural networks are tuned using a modified gradient algorithm. For an adaptive inverse or neural network based inverse, a control error equation is derived based on which a desirable tracking error equation is obtained for an adaptive update or tuning law design. Stability and tracking performance of the closed-loop control system are analyzed. Simulations are used to illustrate the effectiveness of the proposed hybrid control designs.; Friction compensation is addressed for a benchmark sandwich system having sandwiched friction between linear dynamic blocks as illustrated by a two-body system with load friction plus joint flexibility and damping. Several non-adaptive and adaptive compensation designs are analyzed, based on a model reference adaptive control (MRAC) scheme that uses static state feedback for control and dynamic output feedback for parameter adaptation to achieve output tracking.; A new class of open problem: output tracking control of sandwich nonlinear systems with actuator failures is presented and control design is developed for an illustrative special case of the problem. The background for this design is built by the design of direct adaptive state feedback control schemes to achieve state or output tracking, and an adaptive output feedback controller for output tracking for linear time-invariant plants with input actuator nonlinearities and failures. (Abstract shortened by UMI.)...