A SLIP-based Robot Leg for Decoupled Spring-like Behavior: Design and Evaluation

We present a spring loaded inverted pendulum (SLIP) based robot leg to enable decoupled swing motion and spring-like behavior. The two SLIP principles (decoupled swing motion and spring-like behavior) allow an improved understanding of robot locomotion and its control. Proposed leg mechanism include one degree of freedom (DOF) straight-line generating mechanism to perform ideal spring-like behavior and the pantograph to amplify that. The spring-like behavior can be implemented using mechanical constraints with Chebyshev linkage and the virtual spring method. For applying the virtual spring method to the radial motion controlled by one actuator, the relationship between the actuator force and radial force acting on the foot end was determined by using a kinematic interpretation. A 1-DOF test bed including the suggested leg was built and tested to verify the decoupled motions. The spring-like leg behavior was demonstrated during the free fall experiment and the experiment in which external force was applied.