Funnel-control with integrating prefilter for nonlinear, time-varying two-mass flexible servo systems

A time-varying control strategy for the speed control of a nonlinear time-varying two-mass flexible servo system is investigated. The control strategy is based on a high-gain concept, which has been developed for systems with relative degree one, therefore a direct use in most industrial applications is inhibited. To be applicable for systems with higher relative degree - as the considered servo system - a state-feedback like extension is necessary. The problem of choosing feedback coefficients is solved such that a minimum-phase state-feedback is guaranteed. The goal is to control the speed of a load-machine in the sense of tracking a given reference signal by a prescribed limit function of the control error. To achieve exact tracking in presence of disturbances, external loads and time-varying system parameters an integrating self-adjusting prefilter is included, which reacts accordingly to occurring constraints of the control input. The implementation of the cascaded integrating prefilter and the adaptive concept yields overall robust control properties with its time-varying gain adaption only by measuring (noise admissible) the control error