Gastrocnemius and Power Amplifier Soleus Spring-Tendons Achieve Fast Human-like Walking in a Bipedal Robot

TL;DR

This study demonstrates that spring-tendon configurations in a bipedal robot can replicate human-like walking, with specific tendons influencing speed, energy efficiency, and joint coordination, advancing understanding of leg mechanics in locomotion.

Contribution

The paper introduces a robot model with simplified muscle-tendon units that elucidate how ankle and knee mechanics contribute to efficient, human-like walking.

Findings

Soleus spring-tendon modulates walking speed and energy efficiency.

Gastrocnemius spring-tendon influences joint coordination during push-off.

Different spring-tendon configurations affect ankle power and gait dynamics.

Abstract

Legged locomotion in humans is governed by natural dynamics of the human body and neural control. One mechanism that is assumed to contribute to the high efficiency of human walking is the impulsive ankle push-off, which potentially powers the swing leg catapult. However, the mechanics of the human lower leg with its complex muscle-tendon units spanning over single and multiple joints is not yet understood. Legged robots allow testing the interaction between complex leg mechanics, control, and environment in real-world walking gait. We developed a 0.49m tall, 2.2kg anthropomorphic bipedal robot with Soleus and Gastrocnemius muscle-tendon units represented by linear springs, acting as mono- and biarticular elastic structures around the robot's ankle and knee joints. We tested the influence of three Soleus and Gastrocnemius spring-tendon configurations on the ankle power curves, the coordination of the ankle and knee joint movements, the total cost of transport, and walking speed. We controlled the robot with a feed-forward central pattern generator, leading to walking speeds between 0.35m/s and 0.57m/s at 1.0Hz locomotion frequency, at 0.35m leg length. We found differences between all three configurations; the Soleus spring-tendon modulates the robot's speed and energy efficiency likely by ankle power amplification, while the Gastrocnemius spring-tendon changes the movement coordination between ankle and knee joints during push-off.