Stabilization of a three-dimensional limit cycle walking model through step-to-step ankle control

Area of Science:

• Biomechanics
• Robotics
• Prosthetics

Background:

• Unilateral, below-knee amputation increases fall risk, partly due to lost active ankle control.
• Robotic ankle-foot prostheses offer a potential solution for improving balance.

Purpose of the Study:

• To investigate ankle- and hip-based walking stabilization methods using a 3D gait model.
• To assess the effectiveness of different control inputs for balance improvement in simulated amputees.

Main Methods:

• Developed a 3D human gait model incorporating ankle and hip movements.
• Generated discrete feedback control laws (linear quadratic regulators) for step-to-step adjustments.
• Simulated environmental disturbances as random floor height changes and defined balance performance by maximum allowable disturbance.

Main Results:

• All tested control laws stabilized the initially unstable walking model.
• Step-by-step modulation of ankle push-off alone yielded superior balance performance (3.2% leg length) compared to lateral foot placement (1.2% leg length).

Conclusions:

• Robotic ankle-foot prosthesis control, particularly ankle push-off, can significantly enhance balance during walking.
• Optimized prosthetic ankle control may reduce fall risk and improve mobility for amputees.