A Study of Tibial Motion Accuracy using Circular and Noncircular Gears in a Transfemoral Prosthetic Knee Part 2: Motion and Axode Generation and Curve Fitting

This is the second part of a two-part work where the authors' design method for gear-based transfemoral prosthetic knees is demonstrated using knee motion data from 7 clinical knee motion studies. The purpose of this two-part work is to determine if circular gears can consistently exhibit accurate tibial motion during gait versus noncircular gears in a transfemoral prosthetic knee. In part 2, RRSS linkages are calculated to approximate the tibial positions produced in part 1. The axodes for these linkages are also generated and circle dimensions are calculated that best fit the centrodes. These circles become the pitch circles for gear pairs to be included in the prosthetic knee design. Lastly, a tibial position accuracy comparison between the knee design using circular gears versus noncircular gears is made. Unlike noncircular gears, which are custom-made, circular gears can offer advantages in manufacturing cost and design simplicity since it is a standard component. However, to justify the use of circular gears in the knee design, it must be determined if it can consistently exhibit tibial motion that is as accurate as noncircular gears.