Experiments on command shaping control of a manipulator with flexible links

Minimizing vibrations of a maneuvered flexible manipulator is a challenging task. Results are presented of a series of experimental tests carried out on the Space Robot Simulator assembly, which has been set up at the Spacecraft Research and Design Center of the Naval Postgraduate School. The manipulator is planar with two rotational degrees of freedom and two links, of which either one or both can be flexible in bending. The manipulator floats on air cushions on a granite table. The task of the experiments was to test the effectiveness of the command input shaping technique on the near-minimum-time tracking control of a flexible manipulator. A recently introduced sliding mode control method with smooth joint friction compensation was applied to track either an open- or a closed-reference end-effector path, mapped into joint space. This controller guarantees a very precise tracking of the joint reference motion, despite the high and poorly modeled joint friction torques. Satisfying results, in terms of vibration reduction, have been obtained on point-to-point trajectories and on closed-path trajectories, The results are compared with those obtained with a different command shaping technique.