IJCAS

A function approximation technique (FAT) based force sensorless adaptive impedance controller is proposed in this paper for rigid robot manipulators without using force estimators. The basic idea is to rewrite the traditional impedance controller by replacing the contact force with the target impedance so that a force sensorless impedance controller is obtained. A lumped uncertainty can then be found by collecting all the uncertainties in the new controller. The FAT is employed to facilitate the design of the adaptive loop justified by the Lyapunov stability theory. In this new design, computation of tedious regressor matrix used in most traditional robot adaptive designs are avoided. Both the renowned singularity problem and the joint acceleration feedback problem are circumvented. The number of functions to be estimated is reduced to be linear to the number of robot joints which is a great simplification in real-time computation. Simulation results show that the proposed design can give good performance regardless of various uncertainties and unavailability of the contact force signals.

Keywords: Adaptive control, force control, force estimator, impedance control.