A Double-Layered Elbow Exoskeleton Interface With 3-PRR Planar Parallel Mechanism for Axis Self-Alignment

Mohammad I Awad,Irfan Hussain,Yahya Zweiri,Dongming Gan,Shramana Ghosh

doi:10.1115/1.4048428

Abstract

Abstract Designing a mechanism for elbow self-axis alignment requires the elimination of undesirable joint motion and tissue elasticity. The novelty of this work lies in proposing a double-layered interface using a 3-PRR planar parallel mechanism as a solution to the axis alignment problem. 3-PRR planar parallel mechanisms are suitable candidates to solve this as they can span the desired workspace in a relatively compact size. In this paper, we present the modeling, design, prototyping, and validation of the double-layered elbow exoskeleton interface for axis self-alignment. The desired workspace for the self-axis alignment mechanism is specified based on the estimated maximum possible misalignment between the exoskeleton joint and the human anatomical elbow joint. Kinematic parameters of the 3-PRR planar mechanism are identified by formulating an optimization problem. The goal is to find the smallest mechanism that can span the specified workspace. The orientation angle of the mechanism’s plane addresses the frontal frustum vertex angle of the elbow’s joint, while the translational motion allows the translational offsets between the user’s elbow and the exoskeleton joint. The designed exoskeleton axis can passively rotate around the frontal plane ±15 deg and translate along the workspace 30 mm in the frontal plane. Experimental results (quantitative and qualitative) confirmed the capability of the proposed exoskeleton in addressing the complex elbow motion, user’s satisfaction, and ergonomics.

Highlights

IntroductionIn the last two decades, several rehabilitation teams have started to integrate robotic-aided therapies in their rehabilitation projects
It’s worthy to highlight that the theoretical workspace covers more area due to the fact that it does not include the physical constraints imposed by different parts of the mechanism like the width of the links and dimensions of the slider bases that affect the workspace as the links collide with each other
A methodology for obtaining the smallest 3-PRR planar parallel mechanism geometry that has the workspace characteristics required for self-alignment of exoskeleton axes at the elbow joint is presented

Summary

Introduction

In the last two decades, several rehabilitation teams have started to integrate robotic-aided therapies in their rehabilitation projects Such treatments represent a novel and promising approach in rehabilitation of the post stroke paretic upper limb. The use of robotic devices in rehabilitation can provide high-intensity, repetitive, task-specific, and interactive treatment of the impaired upper limb and can serve as an objective and reliable means of monitoring patient progress [3,4,5]. A major source of user’s discomfort in wearing an exoskeleton is caused by the misalignment between the joint axes of the exoskeleton and the anatomical axes of the human joints [16]. Several complications that must be addressed to achieve axes alignment between the exoskeleton axes and the human joint axes like the added redundancy, complexity and the variability of the human musculoskeletal system [18]

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Results

Conclusion