Science

AMP-Foot 2.0 prosthesis mimics human ankle's spring

AMP-Foot 2.0 prosthesis mimics...
An amputee tests the AMP-Foot 2.0 on a treadmill
An amputee tests the AMP-Foot 2.0 on a treadmill
View 2 Images
An amputee tests the AMP-Foot 2.0 on a treadmill
1/2
An amputee tests the AMP-Foot 2.0 on a treadmill
CAD rendering of the AMP-Foot 2.0
2/2
CAD rendering of the AMP-Foot 2.0

The majority of protheses available today that replace the lower leg, ankle, and foot are passive devices that store energy in an elastic element (similar to a coiled spring) at the beginning of a step and release during push-off to give you some added boost. While this type of prosthetic is energy efficient, it doesn't replicate the full power we get from our muscles. In order to provide that kind of energy an actuator is required, and these are often heavy and bulky. Researchers at Belgium's Vrije Universiteit Brussel have streamlined the technology in a device they call the AMP-Foot (Ankle Mimicking Prosthetic Foot).

The latest version, AMP-Foot 2.0, uses an actuator to store energy in springs, which is released when needed. By using a smaller, low-power actuator, the device is lighter and its batteries last longer, even though the actuator is essentially always busy. It is also one of the first prostheses to gather and store energy when the foot naturally bends upwards (towards the shin) during each step. A pair of force sensors (one in the heel and one at the toes) detect the leg's stance, so the locking device knows when to store and when to release its power.

CAD rendering of the AMP-Foot 2.0
CAD rendering of the AMP-Foot 2.0

The result is a prosthesis that, despite utilizing actuators, weighs just five and a half pounds (2.5 kg), which is roughly the weight of a healthy foot. Currently it can provide enough power to replicate 100 percent of push-off for someone weighing up to 165 lbs (75 kg) during normal walking on flat ground. It is currently being tested with amputees.

This isn't the only prosthesis with an actuated ankle, but the low power is key. For example, researchers at Arizona State University are working on one called SPARKy, but it relies on a 150 W motor, whereas the AMP-Foot 2.0 uses just 30-60 W. You can see the AMP-Foot 2.0 in action in the following video.

Source: Vrije Universiteit Brussel

The AMP-Foot 2.0 : A Powered Transtibial Prosthesis That Mimics Intact Ankle Behavior

1 comment
Gregg Eshelman
The video is a 20 or 21 second sequence looped multiple times. Watch how the treadmill scoots a bit to the left every time the prosthetic foot comes down. At 20~21 seconds the position of the treadmill jumps to the right, then the cycle repeats.