Improved observer-based robust adaptive control for a class of nonlinear systems with unknown deadzone

This paper presents an improved observer-based robust adaptive control strategy for a class of nonlinear systems that have two features; i. the coupling of unmeasured states and unknown parameters exist at the measured states dynamics, ii. unknown deadzone exists at the system actuation. At first, the bounds of the dead zone parameters are assumed to be known and a suitable control strategy is derived. This strategy involves the derivation of a control action, unmeasured states observer, and unknown parameters estimators such that global stable system performance is guaranteed. Then another control strategy is proposed when the bounds of the dead zone parameters are unavailable. The second control algorithm comprises the derivation of suitable control action, unmeasured states observer, and unknown parameters estimators such that global stable system performance is assured and the anonymity of the dead zone parameters bounds is accommodated. Simulations are performed when using both control strategies for a nonlinear system that falls in the category of systems addressed in this paper. The system is a singlelink mechanical joint that suffers from friction torque, modeled by LuGre friction model, with unknown dead zone exists at its actuation. The simulation results show the high performance of the suggested control approaches.