A Self-Aligning Upper-Limb Exoskeleton Preserving Natural Shoulder Movements: Kinematic Compatibility Analysis

Area of Science:

• Rehabilitation Engineering
• Biomechanics
• Robotics

Background:

• Stroke survivors often experience upper-limb motor dysfunction.
• Exoskeletons show promise for motor function training.
• Accurate kinematic alignment is crucial for effective exoskeleton use.

Purpose of the Study:

• To evaluate the self-aligning performance of the NESM-γ upper-limb exoskeleton.
• To assess the impact of passive degrees of freedom on kinematic compatibility during reaching tasks.
• To compare movement patterns and muscle activation with and without the exoskeleton, and with locked vs. unlocked passive joints.

Main Methods:

• Kinematic and electromyographic data were collected from eight healthy subjects.
• Subjects performed reaching tasks under three conditions: no exoskeleton (baseline), exoskeleton with unlocked passive joints (HIL-unlocked), and exoskeleton with locked passive joints (HIL-locked).
• Movement patterns, joint deviations, and peak muscle activations were analyzed.

Main Results:

• The HIL-unlocked condition closely matched baseline movement patterns, with minimal shoulder angle error (<5 deg) and glenohumeral center of rotation deviation (<20 mm).
• No significant differences in peak muscle activations were observed between baseline and HIL-unlocked conditions.
• The HIL-locked condition resulted in significant deviations in trunk and glenohumeral trajectory (up to 50 mm) and increased muscle activation.

Conclusions:

• The NESM-γ exoskeleton, with its self-aligning passive joints, demonstrates kinematic compatibility with the human shoulder complex and trunk.
• Kinematic solutions that accommodate natural movement are essential for shoulder exoskeleton design.
• This technology has the potential to improve motor function training for post-stroke patients.