Fiber Bragg grating-based three-dimensional human-robot interaction force sensor with high precision and large range...

Area of Science:

• Biomedical Engineering
• Materials Science
• Optical Sensing

Background:

• Rehabilitation exoskeletons require precise measurement of human-robot interaction forces.
• Existing force sensors may lack the necessary precision, range, or stability for dynamic rehabilitation scenarios.

Purpose of the Study:

• To develop and validate a high-precision, large-range three-dimensional (3-D) fiber Bragg grating (FBG) force sensor.
• To enable accurate measurement and decoupling of interaction forces between a patient's lower limb and a rehabilitation exoskeleton.
• To ensure reliable performance through integrated temperature compensation and a novel mechanical design.

Main Methods:

• Integration of four FBG-inscribed optical fibers circumferentially within an elastomer, with an additional fiber for temperature compensation.
• Implementation of a simply supported beam structure and optimization of FBG sensor parameters to enhance sensitivity and resolution.
• Development of a novel measurement method combining temperature compensation and differential decoupling for accurate 3-D force measurement.

Main Results:

• The FBG sensor achieved force measurement ranges of 0-300 N (Z-axis) and -50 to 50 N (X/Y-axes).
• Achieved resolutions were 0.046 N (X), 0.047 N (Y), and 0.093 N (Z) after calibration.
• Validation experiments confirmed favorable force decoupling performance and dynamic response to walking speed variations.
• A 600-gait-cycle test demonstrated a coefficient of variation below 10%, confirming sensor stability and effective temperature compensation.

Conclusions:

• The developed 3-D FBG force sensor provides high precision and large range for measuring human-exoskeleton interaction forces during lower limb rehabilitation.
• The novel measurement method integrating temperature compensation and differential decoupling effectively achieves accurate 3-D force decoupling.
• The sensor exhibits excellent stability and reliability in practical application, validated through extensive testing on a rehabilitation exoskeleton.