| Compared with traditional means of locomotion, like wheels, which require con- tinuous contact with the locomotion surface, legged locomotion has big advantage that it has discontinuous contact with the ground, which enable the bipedal robot to handle rough terrain easily. However, despite decades of progress, the bipedal robot locomo- tion is still far from achieving the elegant motions observed in human walking. In this thesis, an underactuated five-link planar bipedal robot is modeled to walk on flat ground, upstairs, downstairs, and the transitions between different modes of locomo- tion, which has "natural" walking gaits similar to human walking. Lagrange method is used to derive the mathematical equations of the dynamics model. The complete model of the bipedal robot walking, which is a nonlinear system with impulse effects, consists of a continuous stance phase model and a discrete instantaneous impact phase model. By imposing holonomic constraints to the bipedal robot, continuous controller is developed which can force the bipedal robot state to evolve in the Zero Dynamics Surface as desired. The method of Poincare map is used to determine the existence and local stability of the fixed points of periodic walking gaits. Finally, in order to realize a smooth switching of the bipedal robot walking from one mode of locomotion to another one, a transition step and the corresponded controller are designed between the two modes of locomotion. |
