Quadrupedal Spine Control Strategies: Exploring Correlations Between System Dynamic Responses and Human Perspectives
Nicholas Hafner, Chaoran Liu, Carlos Ishi, Hiroshi Ishiguro
TL;DR
The paper investigates how a quadrupedal robot with an actively actuated four-DoF spine affects gait naturalness and system dynamics, contextualized for human-robot interaction. It introduces four spine trajectory strategies integrated with a model predictive controller to drive foot-ground reactions, and evaluates both energy efficiency and subjective naturalness against a fixed-spine baseline. Results show that while some spine strategies yield more natural motion, none improve energy efficiency relative to the fixed spine, highlighting a trade-off between natural movement and CoT. The work underscores the potential of spine-enabled quadrupeds in social and healthcare contexts and points to hardware and design refinements, such as passive/hybrid spine options and roll DoF exploration, to achieve better energy efficiency without sacrificing naturalness.
Abstract
Unlike their biological cousins, the majority of existing quadrupedal robots are constructed with rigid chassis. This results in motion that is either beetle-like or distinctly robotic, lacking the natural fluidity characteristic of mammalian movements. Existing literature on quadrupedal robots with spinal configurations primarily focuses on energy efficiency and does not consider the effects in human-robot interaction scenarios. Our contributions include an initial investigation into various trajectory generation strategies for a quadrupedal robot with a four degree of freedom spine, and an analysis on the effect that such methods have on human perception of gait naturalness compared to a fixed spine baseline. The strategies were evaluated using videos of walking, trotting and turning simulations. Among the four different strategies developed, the optimised time varying and the foot-tracking strategies were perceived to be more natural than the baseline in a randomised trial with 50 participants. Although none of the strategies demonstrated any energy efficiency improvements over the no-spine baseline, some showed greater footfall consistency at higher speeds. Given the greater likeability drawn from the more natural locomotion patterns, this type of robot displays potential for applications in social robot scenarios such as elderly care, where energy efficiency is not a primary concern.