A Tendon-Driven Wrist Abduction-Adduction Joint Improves Performance of a 5 DoF Upper Limb Exoskeleton -- Implementation and Experimental Evaluation

2026-04-21

AI Summary

This study addresses a critical limitation in current upper-limb exoskeletons—their inability to effectively assist wrist abduction–adduction (Ab-Ad) motion—which hinders users with severe motor impairments from performing activities of daily living. To overcome this, the authors integrated a compact, lightweight hybrid-driven wrist module into the five-degree-of-freedom exoskeleton EXOTIC2, employing tendon actuation for active abduction and spring-assisted adduction. For the first time, experimental results demonstrate that incorporating active Ab-Ad significantly enhances assistance performance: spillage during a drinking task decreased from 56% to 3%, and success rate in horizontal positioning for a scratching task improved from 28% to 75%, without increasing task completion time. This work provides crucial empirical evidence supporting the inclusion of active wrist Ab-Ad in high-functionality upper-limb exoskeleton design.

Technology Category

Intelligent Robots: ManipulationHumans and AI: Interaction Techniques and DevicesPlanning, Routing, and Scheduling: Activity and Plan Recognition

Application Category

User Modeling, Personalization and Recommendation: Practical large-scale studies of user experienceResponsible Web: Machine-in-the-loop, human agency and autonomyGraph Algorithms and Modeling for the Web: Efficient manipulation of static and dynamic Web-related graphs

Abstract

Wrist function is essential in performing activities of daily living (ADLs). However, there is limited experimental evidence on the functional impact of wrist Abduction-Adduction (Ab-Ad) joint assistance in upper limb exoskeletons (ULEs) for rehabilitation. This study evaluates the effect of implementing an active wrist Ab-Ad joint in a five degree of freedom (DoF) ULE, EXOTIC2 exoskeleton, to support individuals with severe motor impairments. Methods: A compact, lightweight wrist module with tendon-driven abduction and spring-driven adduction was integrated into the EXOTIC exoskeleton. Eight adults with no motor disabilities completed drinking and scratching tasks under randomized wrist-enabled and wrist-locked conditions along with a preliminary feasibility test in one individual with Amyotrophic lateral sclerosis (ALS). Kinematic and task performance metrics including wrist range of motion, task completion time, spillage and leveling metrics were assessed. Results: Implementing the wrist Ab-Ad DoF improved task success metrics. Spill incidence during the drinking task decreased from 56% to 3%, and leveling success for scratching task improved from 28% to 75%. Conclusion: Integrating wrist Ab-Ad assistance improved key functional task outcomes without increasing execution time. Significance: The study provides the experimental evidence that active wrist Ab-Ad control enhances task-level performance in exoskeleton-assisted ADLs.

Problem

• wrist abduction-adduction
• upper limb exoskeleton
• activities of daily living
• rehabilitation robotics
• functional assistance

Innovation

• tendon-driven actuation
• wrist abduction-adduction
• upper limb exoskeleton
• functional task performance
• rehabilitation robotics