Development of a biologically inspired hopping robot-"Kenken"

As many biomechanists indicate, a tendon plays an important role in running or jumping motions. It stores the kinetic energy as a potential energy during stance and also absorbs the impulse at touch down. Inspired by such biomechanical studies, we propose a simple mechanical model for the hindlimb of a dog to realize a robot that imitates a dog running, and the hardware design of a one-legged running robot, "Kenken". The robot has an articulated leg and uses two hydraulic actuators as muscles and a tensile spring as a tendon. The spring being attached like the gastrocnemius or plantaris enables the robot to produce sufficient propulsion force by virtue of the "energy transfer" from the knee, even if there is no actuator at the ankle joint. Using an empirical controller based on the characteristic dynamics of the model, the robot has succeeded in planar one-legged hopping. Although the problem related to the stability at higher speeds remains, experimental results demonstrate that the proposed hindlimb mechanism is effective for legged running.