Regulating knee joint position by combining electrical stimulation with a controllable friction brake

Area of Science:

• Biomedical Engineering
• Rehabilitation Robotics
• Neuroprosthetics

Background:

• Hybrid functional electrical stimulation (FES) systems integrate muscle activation with mechanical components for improved gait restoration.
• Controlling limb motion effectively is crucial, especially when facing variations in muscle properties and fatigue.

Purpose of the Study:

• To compare the position tracking performance of three different controllers for a free-swinging shank in able-bodied subjects.
• To evaluate controllers under varying muscle fatigue states and different position tracking demands.

Main Methods:

• Evaluated three controllers: open-loop (OL), proportional-derivative closed-loop (PD), and bang-bang plus controlled-brake (CB).
• OL and PD controllers utilized a forward path model of the stimulated muscle-limb system.
• CB control involved maximal muscle activation against a controlled brake acting as a "moving-wall".

Main Results:

• The controlled-brake (CB) control demonstrated superior position tracking performance compared to OL and PD controllers.
• CB control maintained high performance across a wide range of tracking tasks and muscle fatigue levels.
• CB control did not require prior calibration or knowledge of individual muscle properties.

Conclusions:

• Controlled-brake (CB) control is a highly effective strategy for hybrid FES gait restoration, offering robust limb motion control.
• CB control's independence from muscle property calibration simplifies implementation.
• Potential drawbacks of CB control include significant mechanical power dissipation and skeletal impact forces.