A simple application of GPI observers to the force control of robots

In this work the design of a linear observer-linear controller robust output feedback scheme is introduced for simultaneous trajectory tracking of position and force in fully actuated robot manipulators. The unknown state-dependent additive nonlinearity influencing the input-output description is modeled as an absolutely bounded “time-varying perturbation”. Generalized Proportional Integral (GPI) observers are shown to naturally estimate the unknown perturbation and a certain number of its time derivatives in an arbitrarily close manner. This information is used to advantage on the linear feedback controller design via a simple cancelation effort. To the best of the authors´ knowledge GPI observers have not been used before for robot force control. A experimental analysis/comparison is presented to show the good performance of the proposed approach.