Conical External Fixator Spring Jamming
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Solution Overview
Problem
Existing elastic external fixators for bone traction or distraction suffer from involuntary modifications in force intensity due to vibrations and friction, particularly when using cylindrical-shaped components, leading to inconsistent treatment outcomes in applications like articular fractures.
Innovation Solution
The improved elastic external fixator features a conical-shaped projecting part with a continuously increasing cross-section, which prevents the helical spring from pivoting around its longitudinal axis, ensuring the force intensity remains consistent by jamming the spring's end on the conical surface, thereby maintaining adjusted force application.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a cylindrical-shaped projecting part is used in the external fixator, then the structure is simple and easy to manufacture, but the helical spring can pivot around its longitudinal axis due to vibrations and friction, causing involuntary modifications in force intensity
Solution Approach 1:
The projecting part is changed from a cylindrical symmetric shape to a conical asymmetric shape. The conical surface creates a wedge effect that prevents the helical spring from pivoting around its longitudinal axis, thereby eliminating involuntary force modifications while maintaining manufacturing simplicity
Solution Approach 2:
The friction and vibrations that previously caused harmful pivoting motions are converted into a beneficial jamming effect. The conical surface transforms the spring's tendency to pivot into a self-locking mechanism where friction prevents unwanted motion and stabilizes the applied force
2Adaptability or versatility
If the helical spring is allowed to pivot around its longitudinal axis, then the device has more degrees of freedom and adaptability, but the force intensity applied between bone portions becomes inconsistent
Solution Approach 1:
The conical shape of the projecting part creates an asymmetric constraint that allows the spring to be installed at the correct orientation while preventing unwanted pivoting. This asymmetric geometry provides the necessary adaptability for installation while ensuring precise and consistent force application
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
This design ensures a stable and consistent elastic force application between bone portions, reducing the risk of involuntary force modifications and enhancing the effectiveness of treatments like ligamentotaxis for articular fractures by maintaining precise traction or distraction.
Implementation Method 1
the spring 11 could, for various reasons (vibrations, friction, etc.), pivot around its longitudinal axis
Implementation Method 2
an elastic external fixator capable of exerting an elastic force adjustable in intensity between a first and a second portion of bone
Data Source
AI summary
The present invention relates to external fixators that are resilient between two first and second bone portions O1, O2. The fixator comprises a spring (11) having an axis (12), a body (14), means (15) for mounting said body (14) such as to be in engagement with the spring (11), a pin (16) attached to the bone O1 and passing through the spring, a second body (22) comprising a base (122) and a projecting portion (44) secured to the base (122), one end (47) of the helical spring (11) being mounted such as to abut about the projecting portion (44), and means (24) for linking the body (22) to the bone portion O2 and the helical spring (11). The fixator is characterised in that the projecting portion (44) has a section that increases continuously from the end (48) thereof until the end (46) thereof, the end (47) of the spring having an inner section that is larger than the section of the end (48) and smaller than the cross-section of the end (46).