Moment arm analysis of the biarticular actuators in compliant robotic leg carl

Abstract

The biarticular actuators are widely used in the musculoskeletal bipedal robots. We derive the mathematical formulations to explain the static function of the leg muscles. The goal is to report analytical and biological observations to facilitate the design of the anthropomorphic robotic leg. Our analysis indicates that the ratio of the moment arms, in two spanning joints, has the profound influence on the function of the biarticular muscles. Detailed moment arm dataset of the human body is applied to verify the role of the biarticular muscles in various forms of locomotion. Satisfying the technical constraints, we provide a guideline on the structural design of the biarticular actuators based on the associated action directions. Our analyses are investigated using the compliant robotic leg Carl. A vertical jump experiment is performed to demonstrate the action of each actuator and the influence of the moment arm values.