Performance-Oriented Adaptive Robust Control of a Class of Nonlinear Systems Preceded by Unknown Dead Zone With Comparative Experimental Results

This paper presents an integrated direct/indirect adaptive robust control scheme for a class of nonlinear dynamic systems preceded by unknown nonsymmetric, nonequal slope dead-zone nonlinearity. Departing from existing approximate adaptive dead-zone compensations, this paper uses indirect parameter estimation algorithms along with on-line condition monitoring to obtain an accurate estimation of the unknown dead zone when certain relaxed persistent-excitation conditions are satisfied-a theoretical result that cannot be achieved with the existing methods. Such a result is obtained by making full use of the fact that though not being linearly parameterized globally, the unknown dead zone can still be linearly parameterized perfectly within certain known working ranges. With these accurate estimates of dead-zone parameters, perfect dead-zone compensation is then constructed and utilized in the development of a performance-oriented adaptive robust control algorithm for the overall system. Consequently, asymptotic output tracking is achieved even in the presence of unknown dead zone. In addition, the proposed algorithm achieves certain guaranteed robust transient performance and final tracking accuracy even when the entire system may be subjected to other uncertain nonlinearities and time-varying disturbances. The proposed algorithm is also experimentally tested on a linear motor drive system preceded by a simulated unknown nonsymmetric dead zone. Comparative experimental results obtained validate the effectiveness of dead-zone compensation and the high-performance nature of the proposed approach in practical implementation.