Abstract: The characteristics of interaction between WT wheelchair robot and stair environments is analyzed and possible patterns of WT wheelchair robot during the stair-climbing process are summarized, with the criterion to determine the pattern of the wheelchair robot proposed. Aiming at wheelchair robot^s complicated hybrid mechanism with holonomic constraints, the theorems of simplification for the mechanism with symmetric independent generalized coordinates and symmetric holonomic constraints are proposed, as well as a novel control law designed for holonomic or nonholonomic robot systems. The Lagrange equation of WT wheelchair robot in each pattern during the stair-climbing process and the generalized coordinate curve of each joint when keeping wheelchair^s seat horizontal are obtained. Combined with the computed torque method, a so called active tension control law for WT wheelchair robot, which can track the reference input curve of holonomic constraint force when tracking reference input curve of each joint, is obtained. STATEFLOW module in Matlab is used to simulate the whole stair-climbing process for WT wheelchair robot. Finally, there is an experiment verifying the dynamic model and the control law.

Key words: wheelchair robot;stair-climbing process;holonomic system;dynamics;control law