Capturability-Based Analysis and Control of Legged Locomotion

Abstract

This three-part paper discusses the analysis and control of legged locomotion in terms of N-step capturability: the ability of a legged system to come to a stop without falling by taking N or fewer steps. We consider this ability to be crucial to legged locomotion and a useful, yet not overly restrictive criterion for stability. Part 1 introduces the theoretical framework for assessing N-step capturability. Formal definitions of N-step capturability and related terms are given, and general disturbance robustness metrics based on capturability are proposed. Part 2 uses the theoretical framework developed in the current part to analyze N-step capturability for three simple gait models. Part 3 describes how the results for the simple models were used to control a complex lower body humanoid robot with two six degree of freedom legs.