DEVELOPMENT OF ANKLE-FOOT ORTHOSIS DESIGN

Abstract

This report outlines the final design process for the Ankle-foot orthosis (AFO) in partnership with Anderson Orthopedics. The project objectivewasto create an AFO prototype that aimed to compensate for muscle weakness in gait,and maximizeforward propulsion, while providing quantifiable justification of critical design choices.The first section of the report detailsthe concept generation phase. In this phase, the needs ofthe client and patient were first determined. Our team then generated21 concepts, which were narrowed down to four main options. Then a kinematic and dynamicmodel was generatedto determine the target stiffness of the AFO,which had a value of 1.4 Nm/deg. Then, the safety factor of the AFO was determined to be 2.52 and the final material was determined to be Windform SP. The last section of the concept generation was to create 3D models of the four main concepts using CanFit, to input into Hyperworks foroptimization.The second section of the reportpertains tospecific design details. The optimizationprocess was conductedfor the two most desirableconcepts, an optimized version of the pre-existing prototype,and a posterior strut design. It was thendetermined that the lateral strutdesign was infeasible due to excessive lateral bending during gait. From this, it was determined that thefunctionality needscould only be met by a design iterating upon a posterior strut concept. The final design had an achieved height of 38.1cm, width of 9.5cm, length 27.8cm, and weight of 575g. The linear stiffness attained was 1.88N/mm, and overall bending stiffness 4.01Nm/degrees. The approximate cost to manufacture the device was about $3000 USD. Given the limited design space, a design was achieved utilizingan attainedstiffness of 4.1 Nm/deg. The achieved FOS was 1.33 as detailed by stress contour results. These numbers deviate in some magnitude from the targets sought out at the onset of the project, but the overall goal of proving feasibility of 3D printing for this specific application was achieved, and the device produced should in theory provide quantifiable benefits to the specific patient’s gait.