It is shown that the Reaction Null Space formulation — a method developed for motion analysis and reactionless motion generation of free-floating and flexible-base robots — can be used to fully decouple the end-link dynamics of a kinematically redundant fixed-base robot. Decoupling is achieved thereby via the pseudoinverse of a coupling-inertia submatrix, in quite a different way from the dynamic decoupling achieved via the inertia-weighted generalized inverse of the manipulator Jacobian and known from the Operational Space formulation. The properties of the new formulation are clarified with the help of a comparative study on a representative motion/force control scenario. The simulation results show that the two formulations deliver identical results as far as end-link dynamics are concerned. The new method has an advantage with regard to joint space dynamics, though, which becomes apparent especially in the neighborhood of kinematic singularities, where the inertiaweighted generalized inverse of the manipulator Jacobian is ill-behaved.

We aim at experimental verification of the efficiency of natural-motion path tracking (i.e. tracking speed in proportion to the determinant of the Jacobian) in comparison to constant-speed path tracking. This is done first via simulations, with a simple planar manipulator and then with a six-DOF manipulator. From the results it becomes apparent that natural-motion path tracking outperforms constant-speed path tracking in terms of peak joint speed, peak joint torque and total mechanical power, ensuring thereby a higher average tracking speed. The results are also confirmed via experiments with a real six-DOF robotic limb.