Polio is a disease that effects the joints of the lower limbs. In particular, it attacks motor nerves and causes muscle atrophy. Despite this loss individuals with polio can regain some mobility by using orthotics which prevent knee buckling under a constant load.
Unfortunately, the standard solution in developing countries does not allow for knee flexion during swing — their legs are rigid from the hip down. However, some models do allow for flexion by having a lock and release mode at the knee; this allows for a more biological gait.
The current technology forces wearers to unlock the latch after each step. The goal of the free-swing knee is to give the user more autonomy by using their natural gait to lock and unlock the knee during locomotion.
During heel-strike the latch opens to allow the knee to bend naturally. There is a stop to prevent the knee from buckling during loading. Finally, when the leg is straight again during swing phase the mechanism locks, preparing the user again for heel-strike.
For additional information check out the final project presentation from our course Developing World Prostheses: free_swing_knee.