Emulator helps iteration of prosthetic lower leg

A prosthetic lower leg that lets users take on challenging terrain has been developed in the US, an advance that takes advantage of a new emulator tool for quicker prototyping.

Prosthetic lower leg

Stanford University mechanical engineers used the emulator to develop a ‘tripod foot’ that responds to rough terrain by actively shifting pressure between three different contact points.

Graduate student Vincent Chiu, postdoctoral researcher Alexandra Voloshina and Steven Collins, an associate professor of mechanical engineering and a member of Stanford Bio-X describe the construction and first tests of their prosthetic emulator in a paper published in IEEE Transactions on Biomedical Engineering.

“Prosthetic emulators allow us to try lots of different designs without the overhead of new hardware,” said Collins. “Basically, we can try any kind of crazy design ideas we might have and see how people respond to them.”

To make rougher terrain more manageable for lower leg prosthetics, the team looked at a tripod with a rear-facing heel and two forward-facing toes. Outfitted with position sensors and motors, the foot could adjust its orientation to respond to varying terrain, much as someone with an intact foot could move their toes and flex their ankles to compensate while walking over rough ground.

However, even with simple designs, a conventional approach can take years to develop. “First you have to come up with an idea and then you prototype it and then you make a nice machined version,” Chiu said in a statement. “It could take several years, and most of the time you find out that it doesn’t actually work.”

Rather than building a prosthetic limb someone could test in the real world, the team instead built a basic tripod foot, then hooked it up to powerful off-board motors and computer systems that control how the foot responds as a user moves over all kinds of terrain.

In doing so, the team can put their design focus on how the prosthesis should function – how hard one toe should push off while walking, how springy the heel should be and so forth – without having to worry about how to make the device lightweight and inexpensive at the same time.

So far the team has reported results from work with one participant, a 60-year-old man who lost his leg below the knee due to diabetes, and the early results are said to be promising – making the team hopeful they can take those results and turn them into more capable prosthetics.

“One of the things we’re excited to do is translate what we find in the lab into lightweight and low power and therefore inexpensive devices that can be tested outside the lab,” Collins said. “And if that goes well, we’d like to help make this a product that people can use in everyday life.”