DYNAMIC DECOUPLING FOR HYBRID CONTROL OF RIGID-JOINT FLEXIBLE-JOINT ROBOTS INTERACTING WITH THE ENVIRONMENT

In this paper a nonlinear decoupling and linearizing feedback control for force-controlled robots with constrained end-effector motion is considered. A general method is presented that assures an exact feedback linearization for both cases of rigid- and flexible-joint robots, as the joint flexibility can cause instability or robot control. The application of feedback control linearizes and decouples the original nonlinear system into a number of decoupled linear subsystems. The controllers for a part of these subsystems take as inputs the commands in the robot task space, in which the end-effector trajectory and/or orientation is originally specified. The remaining subsystems have as inputs signals corresponding to contact force mismatching. The effect of stiction on the end-effector contact with the environment is inherently incorporated in the formulation, using the same constrained system formalism. A version of the controller with improved robustness characteristics is proposed, based on the robust servomechanism theory. The derivation of the control algorithm for a two-link planar robot interacting with a rough plane surface is presented as an example. Numerical simulation results confirm the effectiveness of the method. The issues associated with real-time robot control, such as the choice of sampling frequency and the influence of modeling errors, are discussed.