A Proposal of the Kinematic Model of the Horse Leg Musculoskeletal System by Using Closed Linkages In part, closed loop mechanisms can be found in musculoskeletal systems in animals, which are not only composed of combinations with bones and muscles but also of tendons in proper positions. Indeed, the mechanism provides flexible animal gait patterns which is associated with different leg trajectories depending on the ground condition and the purpose. In this paper, we focused on the horse leg mechanism as an animal to be able to adapt to the guidance of the house rider and hypothesized that the principle mechanism can be modeled with closed linkages with a changeable length link, which is formulated as a distance driver. The horse hind limb is driven in a complex manner by kinematic joints and forces generated by muscles and tendons, while in the viewpoint of the geometrical structure of principal joints were selected from the original structure and coupling with other reconstructed linkages as a simple form. In the computer experiment based on the multibody dynamics, the proposed linkage system demonstrated that horse leglike trajectories were provided by the proposed model with eleven fixed links and a relative distance driver as a function of muscletendon unit. In the closed linkage, a uniform circular motion is assumed in the input driving force and the force is transmitted to the endeffector as toe and then a desired locomotive trajectory is provided. The important finding is that a kicking force is generated in the toe just before the grounding. This nonlinear kinematic transmission may provide a hint to analyze adaptive capabilities in the animal locomotion even by the simple closed linkage without a complex actuator control system.

2DOF link mechanism mimicking cheetahxe2x80x99s spine and leg movement A spine of a quadruped animal has compliantly connected several segments. This structure enables the animal to realize bendingstretching motion during running along with the motion of the legs. In this paper, we describe a link mechanism for mimicking such bendingstretching motion of the spine and the leg with few degrees of freedom. By designing a linkage mechanism, we try to realize a similar motion of the spine and the hind leg as that of a cheetah. We developed a prototype with such a structure and demonstrate that it can realize the similar movement of the spine and the leg as that of a cheetah with a simple control strategy.