A Phase Variable Approach for Improved Rhythmic and Non-Rhythmic Control of a Powered Knee-Ankle Prosthesis

Area of Science:

• Robotics
• Biomechanics
• Prosthetics

Background:

• Current multi-joint prosthetic leg control excels at rhythmic tasks like walking but struggles with non-rhythmic motions and real-world maneuvers.
• Developing adaptable control systems is crucial for enhancing prosthetic leg functionality and user independence.

Purpose of the Study:

• To develop a novel controller for multi-joint prosthetic legs capable of both rhythmic and non-rhythmic movements.
• To enable seamless transitions between different speeds and tasks, and to incorporate volitional leg motions.
• To reduce compensatory movements in amputee users during prosthetic leg use.

Main Methods:

• A new piecewise holonomic phase variable was developed as the controller's foundation.
• A finite state machine, using thigh angle measurements and foot contact sensing, managed transitions.
• The controller was implemented on a powered knee-ankle prosthesis and tested with a transfemoral amputee.

Main Results:

• The transfemoral amputee subject successfully performed diverse tasks: walking (slow/fast, backward), starting/stopping, obstacle negotiation, and kicking a ball.
• Clinically significant reductions in compensatory movements (e.g., vaulting, hip circumduction) were observed during rhythmic tasks compared to a passive prosthesis.
• Considerable improvements in performance were noted for non-rhythmic tasks.

Conclusions:

• The developed controller effectively manages both rhythmic and non-rhythmic tasks in multi-joint prosthetic legs.
• This unified framework offers a pathway to more reliable and versatile prosthetic leg control for diverse real-world activities.
• The findings suggest potential for improved user mobility and reduced physical strain for amputees.