A Bioinspired Gear-Rolling Knee Exoskeleton for Enhanced Human-Exoskeleton Kinematic Compatibility.

Area of Science:

• Robotics
• Biomechanics
• Mechanical Engineering

Background:

• Human-exoskeleton interaction often suffers from knee joint misalignment due to complex tibiofemoral motion.
• Subject-specific joint dynamics pose challenges for kinematic compatibility in wearable robotic systems.

Purpose of the Study:

• To reduce human-exoskeleton knee joint misalignment.
• To improve kinematic compatibility between users and knee exoskeletons.
• To accommodate non-uniform and subject-specific tibiofemoral joint motion.

Main Methods:

• A bioinspired, gear-based knee exoskeleton with a planetary gear mechanism and a three-stage compensatory transmission was designed.
• A virtual human-exoskeleton interaction model quantified kinematic misalignment using a sliding misalignment metric.
• Design optimization was guided by the developed model, with evaluation via simulations, prototype testing, and human-subject experiments.

Main Results:

• The proposed mechanism reduced knee joint misalignment by approximately 70% compared to single-axis designs.
• Torque transmission tests showed high accuracy, with peak deviations of 8%-15% during extension and 5%-13% during flexion.
• Back-drivability tests confirmed low passive resistance, with back-driving torque below 5% of the rated assistive torque.

Conclusions:

• The developed gear-based knee joint effectively approximates anatomical motion and accommodates internal misalignment.
• The system maintains reliable torque transmission within a deterministic kinematic structure.
• This research offers a generalizable framework for addressing knee joint misalignment in wearable exoskeletons, enhancing human-robot kinematic compatibility.