Position and Weight Activated Passive Knee Mechanism

The human knee is a complex and robust system. It is the most important joint for human gait because of its immense load bearing ability. The loss of such an important joint often makes it difficult for a person to ambulate. Because of this and the resulting unnatural application of forces, many trans-femoral amputees develop an asymmetric gait that leads to future complications. Prosthetic knees are required to be well-designed to cope with all variabilities. There have been many prosthetic knee designs, some more complex than others. This paper describes the design and preliminary testing of a novel passive position and weight activated knee locking mechanism for use in lower limb prosthetics. This knee mechanism is designed to be a simple and economical alternative to existing knee mechanisms. The mechanism utilizes the dynamics of the user to lock the knee during stance and unlock during the swing phase. The presence of one moving component and a simple assembly makes this design a good base for customization. Results from testing the knee mechanism shows trends that are different from a normal human knee, which is to be expected. The prosthetic knee is designed to have low friction during swing of the shank and, hence, the flexion and extension angles and angular velocities are larger compared to a normal knee. The kinematics show a cyclic trend that is highly repeatable. Further refinement and testing can make this mechanism more efficient in mimicking a normal knee.