Docking control of holonomic omnidirectional vehicles with applications to a hybrid wheelchair/bed system

Abstract

A method for docking a vehicle with a fixture is developed and applied to a hybrid wheelchair/bed system. A powered wheelchair is docked to a bed portion and reconfigured to a flat stationary bed so that the bedridden person does not have to change seating when transferring between the chair and bed. A holonomic omnidirectional vehicle with a ball wheel mechanism is used for the wheelchair. The high maneuverability and holonomic nature of the vehicle allow the wheelchair to be docked precisely with a fixture. An instrumented bumper is developed to detect contacts with the fixture and ensure rider comfort. Using sensor information from the bumpers, the contact state of the vehicle is recognized at all times. Moreover, the orientation of the fixture is estimated from the contact information, and using a framework of discrete event control, the vehicle is aligned and guided towards the fixture despite large misalignments. A prototype system was designed and tested. The vehicle was successfully docked to the bed despite a small clearance ratio as well as large lateral and angular initial misalignments.