Design and control of robot legs with bi-articular muscle-tendon complex

The musculoskeletal system of animals is evolved to an optimal form for their locomotion in their living environments. Their phenomenal dynamic motions are performed by synergistically using those muscles and tendons. In particular, it is known that the muscle-tendon complex in lower leg greatly contributes to the fast running and jumping of felidae like cats and cheetahs. This complex, which is composed of gastrocnemius and Achilles' tendon, generates large output by storing and reusing the kinetic energy during their locomotions. To realize creature-like dynamic motion, we have developed leg mechanism called elastic four-bar linkage mechanism, which is made of four-bar linkage mechanism with one elastic linkage and electrical motor, inspired by bi-articular muscle-tendon complex of cats. In this paper, we optimize the design of the four-bar linkage mechanism including elasticity characteristics of elastic linkage in this leg mechanism by vertical jump simulation. Moreover, we propose the motion control strategy for drop jump inspired from the Stretch-Shortening Cycle (SSC) of bi-articular muscle-tendon complex. As a result of drop jump experiment using two-legged robot, the robot realized high jumps owing to the optimal design and the new control strategy.