Implementation and Tuning of Momentum-Based Controller for Standing Balance in a Lower-limb Exoskeleton with...

Area of Science:

• Robotics
• Biomechanics
• Rehabilitation Engineering

Background:

• Lower limb exoskeletons (LLEs) aim to restore mobility for paraplegic individuals.
• Current LLEs often require crutches for balance, limiting user autonomy.
• Advancements in robotic control enable autonomous balance capabilities.

Purpose of the Study:

• To implement and evaluate a momentum-based standing balance controller for the Symbitron LLE.
• To investigate the effect of control gain tuning on balancing performance.
• To demonstrate autonomous balance control for paraplegic users during stance.

Main Methods:

• Implemented a momentum-based controller with center of mass tracking in the Symbitron LLE.
• Tuned control gains and applied external pushes to assess balancing performance.
• Evaluated the controller's ability to prescribe joint torques for maintaining stability with a user.

Main Results:

• Heuristic guidelines for controller tuning were derived based on gain adjustments and push responses.
• The LLE autonomously balanced a paraplegic user, rejecting pushes up to 60 N (hip height) and 40 N (shoulder height).
• Successful balancing was demonstrated in various stances, including parallel and staggered stances with different foot heights.

Conclusions:

• The developed controller offers a viable strategy for torque-controlled, under-actuated LLEs to maintain stance balance in paraplegic users.
• This represents a significant step towards achieving autonomous balance control during gait in LLEs.
• The findings provide a foundation for future research in LLE control and user mobility restoration.