Design and Implementation of a Swing Phase Control System for a Prosthetic Knee

Lower limb prostheses for above knee (AK) amputees require very challenging technology. All prosthetic knees require some degree of swing phase control to maintain a smooth gait. Swing control designs differ in complexity according to the mechanism used to change the rate of motion of the knee. The simplest knees use mechanical friction at the axis of rotation and only allow a constant walking speed. The more complex knees use fluid dynamics to provide variable resistance and the most complex knees use microprocessor technology to allow the knee to respond instantly to the amputees desired changes in speed. However, this superior gait performance comes at an extremely high financial cost to the amputee. In this work, a low cost swing phase control system for a prosthetic knee is designed, implemented and tested. The control system continuously monitors the subject´s gait, detects the maximum hip flexion angle and recognizes his desired walking speed before the end of each gait cycle. It then outputs a trigger signal to the knee unit to adjust the damping coefficient accordingly, thus permitting fast automatic matching of the desired slow, normal or fast walking speed. The results show the ability of the system to recognize the required speeds after a sufficient training period for the subject.