Abstract

A Spring-Loaded-Inverted Pendulum (SLIP) model has been applied to many legged robots, such as quadruped robots, for realizing trotting, bounding, and galloping motions. The indecipherable damping factors, however, hindered the implementation of the SLIP model in practice. In this paper, a control algorithm is proposed to realize the ideal springy motion of a robotic leg. A Kalman filter with a damped SLIP model as the reference system is utilized for estimating a longitudinal velocity of the robotic leg (i.e., the length change rate between the proximal joint and the tip toe). By cancelling the undesired damping factors through positive feedback based on the Kalman filter estimate, the robotic leg is controlled to realize an undamped SLIP model. The proposed method is verified by simulation and experiment. The results showed that the proposed control algorithm enabled the robotic leg to keep continuously hopping as a spring even in the presence of nonlinear frictions.