Robust adaptive control of underactuated robot manipulators in Cartesian space

In this paper, a study on the control of robot manipulators with free-swinging passive joints overcoming actuator failures is performed. In the case that the passive joints have neither actuators nor brakes, a robust adaptive control scheme overcoming the uncertainties is proposed in Cartesian space where tasks are planned, for underactuated manipulators. The proposed control scheme does not need a priori knowledge of the accurate dynamic parameters and the exact uncertainty bounds. The availability of the proposed control scheme is guaranteed by the assumption that the joint configurations remains in the inside of nonsingular regions during the total control process. To overcome this dynamic singularity problem for a nominal decoupling matrix in the controller, a singularity-free desired Cartesian path-planning in the outside of singular regions is achieved via a computer simulation. To illustrate the feasibility and validity of the proposed control scheme, simulation results for a three-link planar robot manipulator with one passive joint are presented.