Stable Step Climbing and Descending for Tandem Wheelchairs Connected by a Passive Link

This paper describes a new cooperative strategy for two wheelchairs system to climb up or descend down a step which is a typical obstacle in the daily active of wheelchair users. These two wheelchair robots are connected with a simple linkage mechanism between the rear of one wheelchair and the front of another. Even without using a method by which a robot lifts up and supports its weight using any special actuator, each wheelchair can overcome the step stably and relatively easily because wheelchair´s moment of rotation during climbing the step is controlled by the force passed through by the link from its partner wheel chair. In the design, the assistant effect is especially influenced by the height of the two robot´s link positions. So in the paper, we provide detailed discussion on changing the two-link positions during the different stages of the step climbing and descending. Numerical calculation and experiment results are shown for illustrating the validity of the proposed strategy.