Elliptical Bone Screw Asymmetric Thread Geometry
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Solution Overview
Problem
Existing screw locking methods require materials with high modulus of elasticity and additional components to prevent loosening, which is inadequate for elastic materials like bone, where a reliable and durable connection is critical, especially in medical implants.
Innovation Solution
A bone screw with an elliptical screw body, where the ratio of semi-axes R/r allows for secure engagement with elastic materials, providing intrinsic protection against loosening through mechanical integration and osseointegration, and can be designed to accommodate the regenerative capacity of bone tissue.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional screw locking methods (cotter pins, locknuts, washers, adhesive) are used, then the screw connection is secured against loosening, but additional components or materials are required and the method requires materials with high modulus of elasticity
Solution Approach 1:
The invention extracts and eliminates the need for additional locking components (cotter pins, locknuts, washers, adhesive) by integrating the locking function directly into the screw thread geometry itself. The asymmetric thread profile with different pitch angles for tightening and loosening creates intrinsic locking that prevents loosening without any extra parts.
Solution Approach 2:
The screw thread employs asymmetric geometry with different pitch angles - a first pitch angle for tightening and a second, smaller pitch angle for loosening. This asymmetry creates different mechanical interactions during tightening versus loosening, providing inherent locking during normal operation while still allowing controlled removal when needed.
2Reliability
If conventional screw locking methods are used, then the screw connection is secured, but materials with high modulus of elasticity (stiff materials) are required
Solution Approach 1:
The invention changes the geometric parameters of the screw thread - specifically the pitch angles - to create different mechanical advantages for tightening versus loosening. By optimizing these angular parameters, the screw achieves reliable locking in elastic materials like bone without requiring the material itself to have high modulus of elasticity.
3Ease of manufacture
If a round screw body is used, then the screw can be easily manufactured and inserted, but the connection may loosen over time in elastic materials
Solution Approach 1:
The screw thread employs asymmetric geometry with different pitch angles - a first pitch angle for tightening and a second, smaller pitch angle for loosening. This asymmetry creates different mechanical interactions during tightening versus loosening, providing inherent locking during normal operation while still allowing controlled removal when needed.
Data Source
Figure 1~2
Figure 3
AI summary
The invention relates to self-locking screws. Said claimed self-locking screws have an elliptical screw body. They are particularly suitable for use in elastic materials.