Kinematic Model of a New Staircase Climbing Wheelchair and its Experimental Validation

This paper describes the mechanical devices, the movements and the associated kinematic models of a novel wheelchair prototype capable of climbing staircases. The key feature of the mechanical design is the use of two decoupled mechanisms in each axle, one used to negotiate steps, and the other to position the axle with respect to the chair to accommodate the overall slope. This decoupling makes possible many different climbing strategies, the overall mechanism being extraordinarily versatile from a control point of view. Kinematic models have been developed for the different mechanical configurations that appear during all the ascend/descend processes. These models are required to control the actuators of the wheelchair in such a way that its centre of mass is able to follow arbitrary spatial trajectories. This is very important as one has to design very smooth spatial trajectories, keeping a near null inclination of the seat all the time in order to guarantee the comfort of the passenger, usually a handicapped or injured person. A real prototype is presented, and experimental results are reported that show the efficiency of the mechanism and the accuracy of the kinematic models developed. KEY WORDS—wheelchair, stair climbing, kinematic model, trajectory generation o N 1. www.thewheelchairlift.co.uk 2. R. Misawa “Stair-climbing vehicle for wheelchair,” Japan Patent 8-286 753, Oct. 29, 1996. 3. “Stair-climbing vehicle for wheelchair,” U. S. Patent 6 158 386, Dec. 12, 2000.