Design and Dynamic Analysis of a Compliant Leg Configuration towards the Biped Robot’s Spring-Like Walking

The spring-loaded inverted pendulum (SLIP) model has been proven successfully applied to implement spring-like walking for biped robots. This work presents a compliant leg configuration that can meet the requirements of the SLIP model. The leg is characterized by the fact that most of the mass is concentrated in the hip, and the leg is spring-like and light in weight. Numerical models were introduced to analyze the stiffness of the leg, and its dynamic characteristics with the mass of the leg being taken into account. Using the proposed model, the analysis on the stiffness showed that the leg could be taken as a variable stiffness spring with respect to the length of the leg, the longer the leg, the greater the stiffness. In addition to this, it suggested that the mass of the leg should be maintained below one-tenth of the mass concentrated in the hip to perform spring-like walking. Experiments regarding the stiffness and dynamic characteristics showed a good agreement with the simulation results, thus verifying the presented leg configuration and the numerical models. Afterwards, experiments were conducted on vertical jumps of the leg, demonstrating the feasibility of the leg to perform the biped’s spring-like walking, regardless of being at a certain speed, or at varying speeds.