Coordinated human-exoskeleton locomotion emerges from regulating virtual energy

Area of Science:

• Robotics
• Biomechanics
• Rehabilitation Engineering

Background:

• Lower-limb exoskeletons show promise for gait rehabilitation but struggle with human-exoskeleton coordination.
• Coordination issues, or mismatches in intended vs. desired trajectories, reduce gait performance, especially for users with residual motor ability.

Purpose of the Study:

• To investigate the virtual energy regulator (VER)'s effectiveness in generating coordinated locomotion with lower-limb exoskeletons.
• To assess gait coordination, naturalness, and muscle effort reduction using VER compared to passive and natural walking.

Main Methods:

• Experimented VER on nine healthy individuals across various speeds (0.6-0.85 m/s).
• Compared VER-assisted gait with natural and passive (zero-torque) walking using muscle activity, kinematic, spatiotemporal, and kinetic measures.
• Presented VER convergence proof and a metric for user contribution to gait.
• Compared VER with a phase-based path controller for muscle effort and joint kinematics.

Main Results:

• VER demonstrated natural, coordinated locomotion with 13.1%-17.7% average muscle effort reduction compared to passive walking.
• VER improved natural gait indicators versus zero-torque walking, enhancing knee extension by 3.9-4.1 degrees.
• VER achieved 13.9%-15.1% muscle effort reduction compared to the phase-based path controller.
• A novel metric showed resultant locomotion is a linear combination of user and VER limit cycles.

Conclusions:

• The virtual energy regulator (VER) effectively promotes natural and coordinated locomotion in lower-limb exoskeletons.
• VER reduces user muscle effort and enhances gait kinematics, preserving natural variability and user engagement.
• Findings offer insights into the central nervous system's control of locomotion and VER's potential in rehabilitation.