Dynamic modeling and sliding mode control of a five-link biped during the double support phase

An improved approach to the dynamic modeling of a five-link biped and a sliding mode control algorithm for motion regulation are developed during the double support phase (DSP). By modifying the conventional definition of certain physical parameters of the biped system, it is shown that the procedure of the derivation of the dynamic equations and their final forms are significantly simplified. The dynamic model of the five-link biped during the DSP is first formulated as the motion of robot system under holonomic constraints, and then, the horizontal and vertical displacements of the hip and the orientation of the trunk are selected as independent generalized coordinates to describe the constraint system and to eliminate the constraint forces from the equation of motion. Based on the presented dynamic formulation, we develop a sliding mode controller for biped motion regulation. The stability and the robustness of the controller are investigated. The control scheme is evaluated by computer simulations. To the best of our knowledge, it is the first time that a robust sliding mode controller is developed for biped walking during the DSP. This work makes it possible to provide robust sliding mode control to a full range of biped walking and yield dexterity and versatility for performing specific gait patterns.