عنوان مقاله [English]
Over the last decade, the zero dynamic concept in controlling under-actuated systems is an emerging viewpoint in the study of the generation and stabilization of the walking gait for biped robots. The main feature of this method relies on planning and tracking the reference paths, considered virtual constraints on biped configuration, during their motion. The virtual constraints do not arise from a physical connection between the two variables but rather from the actions of a feedback controller. These virtual constraints are defined as a set of outputs, equal in number to the inputs. Then, by designing a feedback controller that asymptotically drives the outputs to zero, the evolution of the joints of the robot would be synchronized in order to emerge as a walking gait. The virtual constraints are formulated in terms of some functions of a passive coordinate variable of biped configuration that is a strictly monotonic variable during completion of a one step course. It is important to note that this is not a classical trajectory tracking scheme, because the desired evolution of outputs is enslaved to a variety of biped configurations and not time. In this paper, at first, the hybrid dynamic model, which includes motion deferential equations describing the continuous biped evolution during the swing phase, is derived, together with a discrete map for jumping state variables at the impact event. Then, a coherent framework for generation and stabilization of the walking gait on a slope for a planar three link biped robot with pointed feet will be outlined. This method is based on orbital stabilization of the hybrid zero dynamic via Poincare return map analysis. Indeed, the dimension of the zero dynamics is considerably less than the dimension of the model itself; the task to be achieved by the robot is implicitly encoded into a lower-dimensional system. The successfulness of the ethod is verified by simulation results.