Toward Phase-Variable Control of Sit-to-Stand Motion with a Powered Knee-Ankle Prosthesis.

Area of Science:

• Biomechanics
• Robotics
• Rehabilitation Engineering

Background:

• Sit-to-stand (STS) motion is crucial for daily living but challenging for above-knee amputees.
• Existing prosthetic knee controllers often lack adaptability to individual user parameters and dynamic conditions.

Purpose of the Study:

• To develop and evaluate a novel phase-variable controller for prosthetic knees in above-knee amputees during STS.
• To model the biomechanical interactions between the sound limb, residual limb, and prosthesis during STS.

Main Methods:

• A biomechanical model was created, incorporating the sound side and residual limb's work on the prosthesis.
• A phase-variable controller was designed, parametrized by a biomechanical phase, not time.
• The controller's performance was analyzed via simulation using the developed model, testing various initial conditions and biological parameters.

Main Results:

• The controller demonstrated robust performance with minimal tuning across diverse conditions.
• Simulated kinematic trajectories closely matched those observed in non-amputees.
• Generated prosthetic joint torques were consistent with normative human STS torque profiles.
• Simulated STS rise times were comparable to those of non-amputees.

Conclusions:

• The phase-variable controller offers a promising approach for improving STS function in above-knee amputees.
• This controller design shows advantages over traditional proportional-derivative controllers for prosthetic limb applications.
• The model effectively captures key biomechanical interactions relevant to prosthetic STS motion.