Graduation Year

2008

Document Type

Thesis

Degree

M.S.M.E.

Degree Granting Department

Mechanical Engineering

Major Professor

Craig Lusk, Ph.D.

Committee Member

Rajiv Dubey, Ph.D.

Committee Member

Nathan Crane, Ph.D.

Keywords

compliant mechanisms, proprioception, knee disarticulation, polycentric 4- bar, prosthetic, interface mechanics, design by specialization

Abstract

Compliant mechanisms offer several design advantages which may be exploited in prosthetic joint research and development: they are light-weight, have low cost, are easy to manufacture, have high-reliability, and have the ability to be designed for displacement loads. Designing a mechanism to perform optimally under displacement rather than force loading allows underlying characteristics of the swing phase of gait, such as the maximum heel rise and terminal swing to be developed into a prosthetic knee joint. The objective of this thesis was to develop a mechanical add-on compliant link to an existing prosthetic knee which would perform to optimal standards of prosthetic gait, specifically during the swing phase, and to introduce a feasible method for increasing proprioceptive feedback to the amputee via transferred moments and varying surface tractions on the inner part of a prosthetic socket. A finite elements model was created with ANSYS to design the prosthetic knee compliant add-on and used to select the geometry to meet prosthetic-swing criteria. Data collected from the knee FEA model was used to apply correct loading at the knee in a SolidWorks model of an above-knee prosthesis and residual limb. Another finite element model was creating using COSMOSWorks to determine the induced stresses within a prosthetic socket brought on by the compliant link, and then used to determine stress patterns over 60 degrees of knee flexion (standard swing). The compliant knee add-on performed to the optimal resistance during swing allowing for a moment maxima of 20.2 Newton-meters (N-m) at a knee flexion of 62 degrees. The moments applied to the prosthetic socket via the compliant link during knee flexion and extension ranged from 5.2 N-m (0 degrees) in flexion, to 20.2 N-m (62 degrees) in extension and induced a varying surface tractions on the inner surface of the socket over the duration, thus posing a possible method of providing proprioceptive feedback via surface tractions. Developing a method for determining the level of proprioceptive feedback would allow for less expensive and more efficient methods of bringing greater control of a prosthesis to its user.

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