A sliding observer for the elastic modes of the flexible forearm of a two-joint robot arm

The problem is considered of estimating the dynamic characteristics of the elastic modes excited by the control input in the flexible forearm of a two-joint robot. The complexity of the nonlinear model of the elastic link is substantially reduced, at least with reference to the estimation problem, by assuming the availability of direct measurements or estimates of the state variables of the rigid component of the motion of both the rigid and elastic link. An observer equation is proposed based on the well-known technique of sliding modes. A strategy for the choice of the observer parameters is developed to guarantee the asymptotic convergence to zero of the components of the estimation error. Several experiments have been carried out by digital simulation to confirm the validity of the proposed sliding mode observer and also its robustness with respect to system parameter variations