Modeling and Control of a Hybrid Locomotion System

This paper describes a hybrid mobility system that combines the advantages of both legged and wheeled locomotion. The legs of the hybrid mobility system permit it to surmount obstacles and navigate difficult terrain, while the wheels allow efficient locomotion on prepared surfaces and a reliable passive mechanism for supporting the weight of the vehicle. The paper addresses the modeling, analysis and control of such hybrid mobility systems using the specific example of a wheelchair with two powered rear wheels, two passive front casters, and two powered articulated 2 degree-of-freedom legs. Such systems, typically, rely on multiple frictional contacts with the ground for support and for locomotion. They also exhibit redundancy in actuation, which is used here to actively control and optimize the contact forces. The scheme for active traction optimization developed here minimizes the tendency to slip at the frictional contacts by redistributing the contact forces so as to minimize the l..