A prosthetic leg that learns from the user's motion could help amputees walk more naturally

Andrew Ng, A prosthetic leg that learns from the user's motion could help amputees walk more naturally, The Batch, August 05, 2020.

What’s new: Researchers from the University of Utah designed a robotic leg that uses machine learning to generate a human-like stride. It also helps wearers step over obstacles in a natural way.

How it works: Rather than trying to recognize obstacles in the user’s path, the prosthesis relies on cues from the user’s body to tell it when something is in the way. Sensors in the user’s hip feed data a thousand times per second into a processing unit located in the unit’s calf. For instance, the way a user rotates their hip might tell the leg to tuck its knee to avoid tripping over an obstacle.

• A finite state machine (a logic-based controller) determines when and how to flex the knee based on angles of the ankle and thigh and the weight on the prosthetic foot.
• A second model called the minimum-jerk planner kicks in when the angle and speed of the artificial limb reach a certain point. It works to minimize sharp, sudden actions.
• The prosthesis applies reinforcement learning to adjust its motion as the user walks, using smoothness as the cost function.