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 syst em permit it to surmount obstacles and navigate difficult terrain, while th e wheels allow efficient locomotion on prepared surfaces and provide a reli able passive mechanism for supporting the weight of the vehicle. We address the modeling, analysis and control of such hybrid mobility systems using t he specific example of a wheelchair with two powered rear wheels, two passi ve front casters, and two articulated two-degree-of-freedom legs. We exploi t the redundancy in actuation to actively control and optimize the contact forces at the feet and the wheels. Our scheme for active traction optimizat ion redistributes the contact forces so as to minimize the largest normaliz ed ratio of tangential to normal forces among all the contacts Simulation a nd experimental results for the prototype are presented to demonstrate and evaluate the approach.