Generalized Proportional Integral observer-based force control in robot manipulators

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 comparison experimental analysis is presented to show the good performance of the proposed approach.