A hybrid wheelchair/bed system for eliminating transfer between the bed and chair is developed and tested. A powered wheelchair can be 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. Moreover the powered wheelchair can be docked to a toilet directly and automatically so that the bedridden can use the toilet without changing seating. 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 chair to be docked easily and precisely against a fixture. First, this paper describes the basic concept of the reconfigurable holonomic omnidirectional mobile bed with unified seating, or RHOMBUS for short. Issues on the mechanical design of the vehicle, chair, and bed are addressed, followed by control issues. A compliant bumper mechanism is used to assist in both bed and toilet docking control as well as to ensure rider comfort. A hybrid stiffness control docking method using force sensors embedded at optimal locations within the bumper is developed. 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 errors.

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