Prosthetic Foot Coupling Assembly with Interlocking Rings
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Solution Overview
Problem
Prosthetic feet for Syme amputees often require a prosthetic ankle capable of complex motion, but this adds bulk and weight, and existing coupling systems can lead to stress concentrations that result in premature wear and breaking, particularly in geriatric, young, or weak patients who prefer a lighter option.
Innovation Solution
A prosthetic foot design featuring a keel with a coupling assembly that includes a bearing member, support sleeve, and embedding member with interlocking rings, which distributes stress and allows for motion around three axes while minimizing weight and bulk, using materials like polypropylene and polyethylene blends for flexibility and durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a prosthetic ankle capable of complex motion is included, then the simulation of anatomical ankle operation is improved, but the weight and bulk of the prosthetic foot increases
Solution Approach 1:
The prosthetic foot is divided into distinct functional segments: a keel body for structural support, a coupling assembly with bearing member for motion, and a cosmesis for appearance. This segmentation allows the complex motion function to be isolated in the coupling assembly rather than requiring the entire prosthetic to be heavy and bulky.
Solution Approach 2:
The patent uses polypropylene-polyethylene blend materials with specific flexibility characteristics to create a lightweight keel that can still support complex ankle motion. By changing material parameters (flexibility, strength-to-weight ratio), the design achieves motion capability without excessive weight.
2Strength
If a coupling system is used to connect the prosthetic foot, then the connection strength is improved, but stress concentrations occur that lead to premature wear and breaking
Solution Approach 1:
The embedding member with interlocking rings is designed to distribute stresses throughout the keel body before they can concentrate at critical points. This stress-distributing feature acts as a cushioning mechanism that prevents premature failure at the coupling connection points.
Solution Approach 2:
The coupling assembly uses a combination of materials including polypropylene, polyethylene blends, and potentially metal bearing components. This composite approach allows each material to contribute its superior properties: polypropylene for flexibility, polyethylene for wear resistance, and metal for bearing load capacity, thereby preventing premature failure.
3Weight of moving object
If a lightweight design is used to reduce weight, then the ease of use for geriatric and weak patients is improved, but the durability and stress resistance may be reduced
Solution Approach 1:
The keel is constructed from polypropylene-polyethylene blend materials that provide an optimal balance of strength-to-weight ratio. These composite materials maintain sufficient stress resistance for lightweight construction, enabling geriatric and weak patients to use the prosthetic without excessive weight while retaining adequate durability.
Solution Approach 2:
Different regions of the prosthetic foot have different material properties optimized for their specific functions: the keel body uses flexible polypropylene-polyethylene blends for lightweight support, while the coupling assembly incorporates harder materials for stress-bearing connections. This local quality differentiation maintains strength where needed while minimizing overall weight.
Data Source
AI summary
A prosthetic foot, including a keel having a longitudinal axis. The keel includes a keel body including a heel portion, a forefoot portion, and an ankle portion positioned between the heel portion and the forefoot portion. The ankle portion includes a housing having a vertically oriented central axis. In addition, the prosthetic foot includes a coupling assembly disposed within the housing of the ankle portion. The coupling assembly includes a bearing member disposed about the central axis, a support sleeve concentrically disposed about the bearing member, and an embedding member disposed about the support sleeve. The embedding member includes a plurality of interlocking rings.