Encouraging Volitional Pedaling in Functional Electrical Stimulation-Assisted Cycling Using Barrier Functions

Area of Science:

• Rehabilitation Engineering
• Control Systems Theory
• Biomechanics

Background:

• Stationary cycling with functional electrical stimulation (FES) is a key therapy for movement impairments.
• Maximizing rider's volitional effort enhances long-term benefits like strength and endurance.
• Existing systems may not adequately balance safety, rider effort, and therapeutic assistance.

Purpose of the Study:

• To develop and validate a combined motor and FES control system for stationary cycling.
• To maximize rider's volitional contribution while ensuring safety within a defined cadence range.
• To investigate the use of barrier functions and robust control for guaranteed safety and stability.

Main Methods:

• A combined motor and FES control system was developed using safety-ensuring barrier functions.
• Robust control tools from Lyapunov theory were integrated to handle uncertain dynamics.
• The closed-loop system was modeled as a hybrid system to ensure asymptotic stability.
• Experimental validation was performed on five participants.

Main Results:

• The barrier function controller successfully constrained rider cadence within a 50 ± 5 RPM range.
• Minimal motor assistance (4.1% of trial duration) was required when prioritizing cadence stability.
• The system demonstrated effective control, prioritizing rider power output in a separate protocol.

Conclusions:

• The developed control system effectively maximizes rider effort in FES-assisted cycling while guaranteeing safety.
• Barrier function and robust control methods provide a reliable framework for therapeutic cycling systems.
• This approach holds promise for enhancing rehabilitation outcomes for individuals with movement impairments.