Development of a flexible coupled spine mechanism for a small quadruped robot

Abstract

Quadruped animals realize dynamic motions such as fast running and high and long jumping with the utilization of the flexibility of their bodies. It is known that the motions of their front and rear legs couple with the flexion and extension of their spine when running or jumping. In recent years, quadruped robots inspired by cats and cheetahs have been developed. In our group, a small quadruped robot has been developed with leg mechanisms which consist of spring and damper systems inspired by bi-articular muscle-tendon complexes of animals. The robot is able to perform various motions such as walking, running and jumping. In this paper, flexibility features as in animal bodies are to be introduced to make the robot run fast and jump long (or high) by coupling the motions of their spine and legs. In our design, the flexion and extension of the spine are realized by a spine joint with a torsion spring, and the coupling to the front and rear legs has been realized by cables. Driving the scapula or hip joints causes flexion of the spine and stores the elastic energy in the spring. The extension of the spine with the spring assists in driving the scapula or hip joints. As a result, in the jump experiment, the robot with a flexible spine can realize longer jump distance than that by a robot with a rigid spine.