Design of Transfemoral Prosthesis

Chin, Jia Dong (2020) Design of Transfemoral Prosthesis. Final Year Project (Bachelor), Tunku Abdul Rahman University College.

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Abstract

The patients with lower extremity amputations face variety physical difficulties as the surgical removal of lower extremity negatively affected the mobility of the amputees and their ability to perform daily activities. Hence, the resources such as wheelchairs, walkers, crutches and peg leg were developed to assist the amputees on restore of mobility. While they can assist in restore of the mobility of amputees, however, the mobility restored was insufficient as they could not restore the natural human locomotion. After centuries of development, the lower limb prosthesis was introduced to restore the human locomotion which is then reflects in restore of higher mobility of the amputees. Then, the transfemoral prosthetic knee joints are developed as one of the enhancements on the overall structure of transfemoral prosthesis. The knee joints are typically designed to mimic the flexion-extension motion of biological knees during human locomotion. While the knee joints required to provide sufficient rotation for locomotion, it also required to support the human body weight during knee flexion-extension. Current prosthetic knee joints available are all rigid link mechanisms knee joints. However, the rigid link designs of current prosthetic knee joints subject to various limitations such as the wear and backlash of interconnection parts could result in the short lifespan of expensive knee joints. This project is to utilise compliance mechanism to design a prosthetic knee joints which able to provide same functions as rigid link knee joints. The proposed compliant mechanism prosthetic knee joints utilize and enhances the structure of the compliant iris to provide flexion-extension motion for locomotion. Moreover, the designed knee joints should be able to withstand the human body weight during the extension motion. The research scope in this project covers the medical analysis on the amputation level and residual limb condition, the gait analysis on human locomotion, the components of transfemoral prosthesis, the design of compliance mechanisms and the design methods of compliance mechanism. Different structures with various geometries were investigated to test on the results obtained under rotation and forces. The methodology to choose on the Al7178-T76 as the material of compliant prosthetic knee based on the consideration on properties and cost of materials are provided. At the end of the project, the characteristics and behaviors of compliant mechanisms were studied. The relationship between the parameters and the ability of the profile to perform rotation were analyzed and the final design that could provide sufficient rotation were presented.