Prosthetic Leg Dynamic Simulation

Effect of a spring constant on travel and mechanical efficiency

http://www.youtube.com/watch?v=BKGvEKk1nkQ&feature=share&list=PLLBUgWXdTBDhUyN1Kur1XbDG4p7W9OKom&index=8

Our objective was to successfully simulate and optimize a prosthetic knee. We developed a dynamic nonlinear model based on the prosthetic apparatus as shown in the Figure. The spring constant of the prosthetic was optimized in order to achieve the highest overall efficiency of the leg. Overall efficiency was determined by comparing the mechanical efficiency to the distance efficiency. Mechanical efficiency was defined as the energy output over the work required to move the leg and the distance efficiency was defined as the distance our prosthetic moved over the desired distance of movement. The model was successfully optimized with a spring constant value of 1.94 N/m.

Method/Procedure

In order to optimize the spring constant in our prosthetic leg, we began by creating a dynamic nonlinear model. This involved determining mathematical relationships between body velocity and the force on our knee, which acted on the spring system inside our prosthetic. This was then mathematically related to the knee’s torque and angular velocity, which resulted in a model of the prosthetic leg’s motion. This model was entered into Simulink in which the overall velocity of our body became the input and the movement of our leg became the output.
Within this dynamic model, one important factor was the spring constant (k) inside the prosthetic knee. Our focus in this lab was to optimize the k value in a way that would maximize both the accuracy of each step and the mechanical efficiency of the prosthetic. We simulated our model across a range of k values and compared the resulting distance efficiencies and mechanical efficiencies. After determining our optimal k, we used this in our simulation to check its accuracy.