Underactuated Manipulators: Control Properties and Techniques

Abstract

We consider planning and control problems for underactuated manipulators, a special instance of mechanical systems having fewer input commands than degrees of freedom. This class includes robots with passive joints, elastic joints, or flexible links. Structural control properties are investigated, showing that manipulators with passive joints in the absence of gravity are the most difficult to control. With reference to these, solutions are proposed for the typical problems of trajectory planning, trajectory tracking, and set-point stabilization. The relevance of nonlinear control techniques such as dynamic feedback linearization and iterative steering is clarified through illustrative examples.