Mechanistic Properties of Five-bar Parallel Mechanism for Leg Structure Based on Spring Loaded Inverted Pendulum

Abstract

To achieve robotic walking, a successful approach is to approximate a robots dynamics as a simplified model. However, the difference between the mechanistic properties of a robot and the simplified model causes a problem of unstable and inefficient walking. To solve this problem mechanically, this paper proposes a design principle for the leg structures of bipedal robots that match the mechanistic properties of a simplified model, specifically the spring-loaded inverted pendulum (SLIP) model. The SLIP model is widely applied to robots because it has passive stability and dynamic properties similar to those of animal gaits. We have analyzed the effects of parameters of five-bar linkages with springs as a part of the leg structure of a bipedal robot. Our analysis showed that the spring parameters can impart the same mechanistic properties as the SLIP model in any configuration of a five-bar parallel mechanism. Moreover, a simplified case of a parallel linkage structure using two springs with the same properties also produced the mechanical properties of the SLIP model. These theoretical analyses were also validated with an experimental model.