Gravity Compensation of an Exoskeleton Joint Using Constant-Force Springs

Area of Science:

• Biomedical Engineering
• Rehabilitation Robotics
• Biomechanics

Background:

• Stroke is a leading cause of long-term upper-limb impairment.
• Exoskeleton devices aim to aid stroke patient assessment and rehabilitation.
• Reducing exoskeleton weight is a critical design challenge, often requiring oversized motors for gravity balancing.

Purpose of the Study:

• To investigate the effectiveness of constant-force springs for gravity balancing in upper-limb exoskeletons.
• To determine if elastic elements can replace heavy motors for torque generation.
• To reduce the overall weight of rehabilitation exoskeleton devices.

Main Methods:

• Experimental testing of C-shaped constant-force springs in single, back-to-back, and double-wrapped configurations.
• Analysis of force output fluctuations over 180° of wrapping.
• Measurement of friction values for different spring configurations.

Main Results:

• Constant-force springs demonstrated force output fluctuation below 8.6% over 180° wrapping.
• Friction values were measured to be below 2.6%.
• The back-to-back configuration offered better force consistency, while the double-wrapped configuration exhibited lower friction.

Conclusions:

• Constant-force springs are a viable solution for gravity balancing in upper-limb exoskeletons.
• Using springs can potentially lead to lighter and more effective rehabilitation devices.
• Specific configurations (back-to-back, double-wrapped) offer trade-offs between force consistency and friction.