Design and Development of a 3D-Printed Metamaterial Actuator for Finger Rehabilitation

Applying NASA Fabric Geometry in a Novel Device for Stroke Therapy

Master thesis (2024)

Authors

S.J.L. Hoving Mechanical Engineering

Contributors

A.H.A. Stienen Biomechatronics & Human-Machine Control - Mechanical, Maritime and Materials Engineering (mentor)
F. C T Van Der Helm Biomechatronics & Human-Machine Control - Mechanical, Maritime and Materials Engineering (graduation committee member)
Faculty
Mechanical Engineering
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Published Date

12-12-2024

Language

English

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Faculty

Mechanical Engineering

Abstract

Assistive devices are crucial to support rehabilitation, as the increasing shortage of healthcare professionals limits the availability of consistent, hands-on therapy. Rehabilitation for stroke patients is necessary to regain motor function, but most current assistive devices face challenges in balancing effectiveness, comfort, and portability, limiting their practicality for independent use. This research presents a 3D-printed metamaterial actuator glove designed to address these challenges, providing stroke survivors with an effective, comfortable tool for finger movement recovery. The actuator aims to improve upon the limitations of existing rigid and soft exoskeletons.ย 

The actuator features a NASA-inspired chainmail material, combining flexibility and strength in a dorsally mounted leaf spring actuator to facilitate natural finger motion. Artificial ligaments and tendons were implemented to stabilize the components during movement. The ligaments maintain the alignment of thimbles and distribute forces evenly, preventing displacement during actuation, while the tendons generate additional moments to improve force application during flexion. A Design Thinking approach guided iterative improvements in actuation, fixation, and user interaction to meet the functional requirements of rehabilitation devices.

Testing confirmed the actuatorโ€™s ability to deliver up to 16.4๐‘ of fingertip force in fully extended, 15.2๐‘ in the half-flexed, and 7.6๐‘ in fully flexed position. Joint angles of 85.9ยฐ (MCP), 106.3ยฐ (PIP), and 69.9ยฐ (DIP) were achieved, enabling a full range of motion for activities of daily living (ADLs). The artificial ligaments ensured alignment and stability across all positions, while the tendons enhanced flexion efficiency by generating positive moments during bending. Input-output force relationships exhibited high reliability in half-flexed (๐‘…2 = 0.9334) and fully flexed (๐‘…2ย = 0.9196) positions, though variations were observed in fully extended positions due to spring buckling and contact inconsistencies. Despite
limitations in elongation and spring stability under high input forces (> 130๐‘), the actuator demonstrated significant advantages over comparable devices like the ETH Tenoexo, which demonstrates maximum forces of 5.2๐‘.ย 

Overall, this actuator has shown potential for use in at-home stroke rehabilitation, offering a lightweight solution that supplies sufficient force for ADLs. Further improvements are needed to increase efficiency, reduce friction, and improve fixation to the hand for better reliability and comfort during extended use.

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