From template to anchors: transfer of virtual pendulum posture control balance template to adaptive neuromuscular gait model increases walking stability.

Ayoob Davoodi,Andre Seyfarth,Maziar A Sharbafi,Omid Mohseni

doi:10.1098/rsos.181911

Ayoob Davoodi, Andre Seyfarth + Show 2 more

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https://doi.org/10.1098/rsos.181911

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Abstract

Biomechanical models with different levels of complexity are of advantage to understand the underlying principles of legged locomotion. Following a minimalistic approach of gradually increasing model complexity based on Template & Anchor concept, in this paper, a spring-loaded inverted pendulum-based walking model is extended by a rigid trunk, hip muscles and reflex control, called nmF (neuromuscular force modulated compliant hip) model. Our control strategy includes leg force feedback to activate hip muscles (originated from the FMCH approach), and a discrete linear quadratic regulator for adapting muscle reflexes. The nmF model demonstrates human-like walking kinematic and dynamic features such as the virtual pendulum (VP) concept, inherited from the FMCH model. Moreover, the robustness against postural perturbations is two times higher in the nmF model compared to the FMCH model and even further increased in the adaptive nmF model. This is due to the intrinsic muscle dynamics and the tuning of the reflex gains. With this, we demonstrate, for the first time, the evolution of mechanical template models (e.g. VP concept) to a more physiological level (nmF model). This shows that the template model can be successfully used to design and control robust locomotor systems with more realistic system behaviours.

Highlights

Building a legged system with agile, efficient and robust functionality requires appropriate design and control
We use the VBLA for leg adjustment and force feedback-based strategies by modulating the hip spring stiffness (FMCH) or muscle activation for balance control
These models can be extended to anchor models such that they can be implemented on robots or be verified in biological gait experiments. One of such template models is based on the virtual pivot point (VPP) concept [11], which is selected for posture control in this paper

Summary

Introduction

Building a legged system with agile, efficient and robust functionality requires appropriate design and control. To this end, roboticists can learn from biological locomotor systems. The biological body as the representative of the mechanical design and the neural system as the controller can be considered for understanding the basic concepts of legged locomotion. Detailed modelling of such an intricate phenomenon is challenging and computationally expensive. Employing template (conceptual) models were introduced as an alternative method for realizing the fundamentals of locomotion [1]. The striking feature of templates is that they ignore all the redundancies and still lend themselves to be used as simple conceptual models explaining complex problems [2]

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