Flexible Bone Screw Coupling for Torque and Tensile Load
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Solution Overview
Problem
Existing bone screws face challenges in transmitting torque and absorbing tensile forces while maintaining mobility between bone parts, often resulting in imprecise torque transmission and limited ability to handle high tensile forces due to structural limitations in their flexible connections.
Innovation Solution
A screw design with a concentric arrangement of a coupling and flexible connection, where the coupling absorbs torsional forces and the flexible connection absorbs tensile forces, allowing for a compact structure and optimized functionality for both functions, using a combination of form-fitting connections like dovetail and tongue-and-groove to enhance flexibility and torque transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a ball joint with octagonal head is used to transmit torque, then torque transmission is enabled, but the corners round off and the ball shell widens at higher torques, limiting the transmissible torque
Solution Approach 1:
The coupling is divided into multiple segment elements (first coupling element, second coupling element, etc.) that can rotate relative to each other. This segmentation allows the coupling to transmit torque through the flexible connection without requiring a rigid octagonal geometry, thereby avoiding corner rounding and shell widening while maintaining torque transmission capability.
Solution Approach 2:
The coupling transitions from a static rigid connection to a dynamic flexible connection that allows relative movement. The segment elements can rotate relative to each other, enabling the coupling to adapt to the flexible connection's movement while still transmitting torque, thus maintaining strength at higher torques.
2Power
If a universal joint is used for flexible connection, then larger torques and tensile forces can be transmitted, but the filigree universal joint connection is not possible with small shaft diameters
Solution Approach 1:
The coupling and flexible connection are merged into a single integrated component rather than separate universal joint mechanisms. This combining allows the structure to transmit both torque and tensile forces through a simplified design that is compatible with small shaft diameters, reducing device complexity while maintaining power transmission capability.
Solution Approach 2:
The flexible connection is designed to perform multiple functions simultaneously: it transmits torque, absorbs tensile forces, and allows relative movement between the head part and threaded part. This multi-functionality eliminates the need for separate universal joint mechanisms, simplifying the overall structure.
3Adaptability or versatility
If the screw is made highly elastic in longitudinal extent to allow bending movements, then mobility between bone parts is maintained, but precise distance maintenance between bone parts and torque transmission become imprecise
Solution Approach 1:
The coupling is segmented into multiple elements that can rotate relative to each other, allowing bending movements while maintaining a defined mechanical connection. This segmentation enables the screw to accommodate mobility between bone parts without compromising the precision of distance maintenance or torque transmission, as each segment contributes to the overall flexibility while maintaining structural integrity.
4Stability of the object's composition
If a wire rope or wire bundle is used as flexible connection, then axial elasticity is achieved, but torque transmission without special socket wrench is not possible
Solution Approach 1:
The coupling and flexible connection are merged into an integrated structure where the coupling elements are directly connected to the flexible connection (wire rope or wire bundle). This integration allows torque to be transmitted directly through the flexible connection without requiring special socket wrenches, while the wire rope or bundle maintains its axial elasticity property.
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
Enables efficient transmission of large tensile forces and torques, maintaining precise distance between bone parts and allowing for natural joint movement, suitable for various applications including medical stabilization of bone fractures.
Implementation Method 1
The spring part in the shaft of the bone screw gives it a certain axial elasticity (axial compression or distraction)
Implementation Method 2
The connection between the coupling elements and the flexible connection is made form-fitting, for example in the form of a dovetail connection or a tongue-and-groove connection
Data Source
Figure 1~8
Figure 9~16
Figure 17~18
AI summary
The invention relates to a screw with a head part, a threaded part and a flexible connecting part between the head part and the threaded part, in order to transmit a torsional force between the head part and the threaded part and to allow two opposing buckling movements between the head part and the threaded part in the longitudinal axis of the screw, wherein the head part and the threaded part each have a longitudinal axis which can be arranged offset parallel to each other, and the screw, when the head part and the threaded part are arranged on a longitudinal axis, has an ε-modulus between 20,000 and 100,000 N/mm2 against elongation.