An Extension of Kinematic Model for the Linkage Mechanism to Analyze the Workspace and Gait Trajectory Induced by the Swing Leg Motion

The anatomical structure of animal leg repeatedly represented by open and closed kinematic chains. The open-chain has flexibility in producing functional gait trajectories, while it loses structural strength. On the other hand, closed linkages has well organized structural arrangement that could mobilize or stabilize large anatomical areas, and the range of movement has a limitation due to constraints in the system. In the present study, we focused on the partial extension of the closed linkage mechanism to be able to reproduce particular animal gait trajectories by adding a new link to control the leg's swinging. In the multibody dynamics, the proposed mechanism was analyzed to work as a simple oscillatory control associated with the movement of the constrained part of the leg mechanism. The reachable workspace was derived from the motion range of joints and extension/retraction of the leg mechanism. The extended analysis showed that animal gait trajectories were generated flexibly according to control parameters with driver constraints. It suggests that the specific locomotor behavior differentiate in trajectory due to the amplitude oscillation of swinging motion in the estimated leg workspace.