A new robotic prosthetic leg prototype offers a more natural gait while also being quieter and more energy efficient than other designs.
The study is published in the journal IEEE Transactions on Robotics.
The key is the use of new small and powerful motors, originally designed for a robotic arm on the International Space Station. The streamlined design offers a free-swinging knee and regenerative braking, which charges the battery with energy captured when the foot hits the ground. This feature enables the leg to more than double a typical prosthetic user’s walking needs with one charge per day.
Using conventional prosthetics, amputees must raise their hips to lift the prosthetic foot from the floor and swing the leg forward. This unnatural gait takes more energy than ordinary walking, causes extra stress and pain in the hips and lower back, and eventually damages the joints. Robotic legs have the potential to provide a much more comfortable gait, but one of their drawbacks is stiffness in the joints.
Motors in robotic legs need to fit into the space that an ordinary limb would take up. In the past, this has meant using small motors that spin quickly, and then using a series of gears to convert the fast spin into a more powerful force.
The problem is that the gears are noisy, inefficient, add weight and make it harder for the joints to swing. The researchers surmounted this by incorporating two of those stronger space station motors, one powering the knee and the other powering the ankle.
There are many benefits to using fewer gears. In addition to enabling the free-swinging knee, removing gears brought the noise level down from the scale of a vacuum cleaner to a refrigerator. Also, the regenerative braking absorbs some of the shock when the prosthetic foot hits the ground.
If the joints are stiff or rigid, the force is transferred to the residual limb, and that can be painful. Instead, the researchrers use that force to charge the battery.
The amputees who test drive the prosthetics say they can feel the leg helping them push off the ground as they walk.
The team’s next step is to improve the control algorithms that can help the leg automatically adjust to different terrain, changes in pace and transitions between different types of activity.
News Source: University of Michigan
