Diaphragm Ankle Actuation for Efficient Series Elastic Legged Robot Hopping

The observation of the anatomy of agile animals and their locomotion capabilities emphasizes the importance of fast and lightweight legs and confirms the intrinsic compliance integrated into muscle-tendon units as a major ingredient for energy efficient and robust locomotion. This quality is especially relevant for distal leg segments which are subject to aggressive dynamics. Legged robots are accordingly designed to improve dynamic performance by lightweight mechanisms combined with series elastic actuation systems. However, so far no designs are available that feature all characteristics of a perfect distal legged locomotion actuator such as a lightweight and low-inertia structure, with high mechanical efficiency, no stick and sliding friction, and low mechanical complexity. With this goal in mind, we propose a novel robotic leg which integrates all above features. Specifically, we develop, implement, and characterize a bioinspired robot leg that features a lightweight Series ELastic Diaphragm distal Actuator (SELDA) for active control of foot motion. We conducted experiments to compare two leg configurations, with and without foot actuation, to demonstrate the effectiveness of the proposed solution in agile forward hopping controlled by a central pattern generator. We studied how tuning SELDA's activation timing can adjust the robot's hopping height by 11% and its forward velocity by 14%, even with comparatively low power injection to the distal joint.