Variable-Stiffness Orthopedic Hinge for Guided Joint Motion
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Solution Overview
Problem
Existing lightweight orthopedic device hinges lack adaptability to different activity levels, rigidity, strength, and motion control, and fail to dynamically conform to the user's limb shape, particularly between flexion and extension, while providing sufficient support and cooperation with other orthopedic device components.
Innovation Solution
A monolithic hinge body made from a flexible polymeric material that extends continuously from one end to another, with an articulating section that can bend both angularly and transversely, featuring a variable radius and adjustable stiffness through an insert, allowing for better fit and motion control without additional moving parts or fasteners.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a robust hinge with multiple parts and structural elements is used, then the hinge facilitates and guides joint movement effectively, but the weight, cost, bulk, and complexity of the orthopedic device increase
Solution Approach 1:
The hinge is divided into distinct functional zones: a first end portion with first stiffness for structural support, a second end portion with second stiffness for joint articulation, and a middle portion with intermediate stiffness for smooth transition. This segmentation allows each zone to optimize its properties for specific functions, reducing overall weight while maintaining reliability.
Solution Approach 2:
Different portions of the hinge have different stiffness properties tailored to their specific functions. The first end portion is stiffer for structural support, the middle portion has intermediate stiffness for transition, and the second end portion has lower stiffness for flexible articulation. This local differentiation eliminates the need for a uniformly robust structure throughout, reducing overall weight and complexity.
2Weight of moving object
If a lightweight hinge such as a stay or flexible bar is used, then the weight and complexity are reduced, but the hinge provides insufficient control and guidance of motion
Solution Approach 1:
The hinge employs a gradient stiffness structure that dynamically adapts to different operational conditions. The varying stiffness along the length of the hinge allows it to provide firm control where needed (at the joint articulation point) while remaining flexible elsewhere, enabling effective motion control in a lightweight design.
Solution Approach 2:
The hinge is formed from a composite structure with varying material properties or density distribution along its length. This allows the creation of a lightweight hinge that nonetheless provides sufficient motion control through strategic placement of stiffer materials in critical zones and more flexible materials in non-critical zones.
3Shape
If a lightweight hinge is embedded within a tubular sleeve, then the orthopedic device maintains a streamlined outline, but the hinge cannot adapt to different characteristics including rigidity, strength, and range of motion control
Solution Approach 1:
The hinge incorporates variable stiffness parameters along its length, with the first end portion having higher stiffness for structural support, the middle portion having intermediate stiffness for smooth transitions, and the second end portion having lower stiffness for flexible joint articulation. This parameter variation allows the hinge to adapt to different motion control requirements while maintaining a streamlined appearance when embedded in the tubular sleeve.
4Adaptability or versatility
If a monolithic hinge body made from flexible polymeric material is used, then the hinge conforms dynamically to the user's limb shape, but additional moving parts and fasteners are eliminated which may reduce adjustability
Solution Approach 1:
The hinge combines multiple functions into a single monolithic polymeric structure: articulation, conformability to limb shape, and structural support. The gradient stiffness design within the monolithic structure provides the necessary adjustability and adaptability without requiring separate moving parts or fasteners, simplifying the overall device while maintaining ease of operation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The hinge provides enhanced strength, stability, and dynamic accommodation to the user's limb dimensions, minimizing interference with natural leg motion while maintaining structural integrity and flexibility, thus offering improved support and fit for orthopedic devices.
Implementation Method 1
The single material structure may be compliant and adapted to flexibly bend not just within an angular range, but also transversely relative to a neutral longitudinal axis of a leg or joint in extension
Implementation Method 2
The articulating section has an adjustable floating center variable radius within the angular range because the variable radius changes according to flexion of the hinge
Data Source
AI summary
A hinge has a hinge body forming an articulating section extending between a first end and a second end of the hinge. The articulating section is adapted to bend from a neutral axis when the first and second ends are parallel to an angular range in which the first end is arranged among a plurality of angles within the angular range relative to the second end. The hinge body may define a receptacle along the articulating section, and an insert may be provided for insertion into the receptacle. The insert can modify the stiffness of the hinge in the angular range and is arranged parallel to the neutral axis.