Whole-Body Control of Series-Parallel Hybrid Robots

Abstract :

Parallel mechanisms are becoming increasingly popular as subsystems in various robots due to their superior stiffness, payload-to-weight ratio and dynamic properties. The serial connection of parallel subsystems leads to series-parallel hybrid robots, which are more difficult to model and control than serial or tree-type systems. At the same time, Whole-Body Control WBC has become the method of choice in the control of robots with redundant degrees of freedom, e.g. legged robots. However, most state of the art WBC frameworks can only deal with serial or tree-type robot topologies. In this paper, we describe a computationally efficient framework for Whole-Body Control of series-parallel hybrid robots subjected to a large number of holonomic constraints. In contrast to existing WBC frameworks, our approach describes the optimization problem in the actuation space of a series-parallel robot, which provides better exploitation of the feasible workspace, higher accuracy, and more transparent behavior near singularities. We evaluate the proposed framework on two different humanoids with series-parallel architecture and compare its performance to a WBC approach for tree-type robots.