Nonlinear observers in closed-loop trajectory tracking

One of the difficulties for the application of geometric control methods in control engineering is that, in general, the full state has to be measured. In this paper we design a nonlinear-observer in order to estimate the states variables to be used in the control loop. The control problem we deal with is the trajectory tracking for general nonlinear (smooth) systems of the type x˙=f(x,u), y=h(x), and the nonlinear observer presented has the following characteristics: (1) the speed of convergence is adjustable; (2) the closed-loop control for trajectory tracking-with the observer in the loop-is stable. An application to a robot manipulator is included