Force Guided Docking Control of an Omnidirectional Holonomic Vehicle and its Application to Wheelchairs

A new hybrid wheelchair/bed system for assisting the bedridden has been developed and tested. The powered wheelchair docks with a stationary bed and reconfigures to a chair to provide full mobility assistance by eliminating the need to transfer the bedridden person from bed to chair. Furthermore, the chair can dock directly and automatically with a toilet to eliminate the need to change seating. The chair is driven by an omnidirectional holonomic vehicle with ball wheel mechanisms. The omnidirectional and precise dead reckoning characteristics of the vehicle provide the chair with superior maneuverability and ability to navigate in closely confined environments. The holonomic nature of the vehicle adds to this the ability to dock easily and precisely against a fixture using force guided control. A clear set of functionalities were defined for the wheelchair. The omnidirectional vehicle was mechanically redesigned to ensure stability without sacrificing performance. A new control system was developed, allowing the chair to be driven both manually and automatically. An instrumented bumper system was designed and installed on the vehicle. A force-guided docking control method was developed and tested, consisting of a combination of impedance control based on force feedback from the bumpers and active compliant control through servo stiffness. The vehicle was successfully docked to the bed despite a small clearance ratio as well as large lateral and angular initial errors. Thesis Supervisor: Haruhiko H. Asada Title: Professor of Mechanical Engineering