Dual-Interface Screw with Reverse-Threaded Extraction
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Solution Overview
Problem
Screws often disengage from drivers during insertion or require excessive torque for extraction, especially when dealing with non-magnetic materials or materials that have been in place for a long time, leading to misalignment and torque limitations.
Innovation Solution
A dual interface screw element with a first engagement interface for insertion and a second reverse-threaded interface for extraction, allowing for secure torque application in both directions using complementary tools.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single engagement interface is used for both insertion and extraction, then the device complexity is reduced, but the torque required for extraction becomes excessively large and may exceed the torque deliverable through the interface
Solution Approach 1:
The engagement interface is segmented into two distinct interfaces: a first engagement interface for insertion and a second engagement interface for extraction. This segmentation allows each interface to be optimized for its specific function, enabling the extraction interface to handle higher extraction torques without requiring excessive complexity in a single unified interface design.
Solution Approach 2:
Different local qualities are provided at different locations on the screw head. The first engagement interface has properties optimized for insertion torque application, while the second engagement interface has properties optimized for extraction torque application. This local differentiation allows each interface to perform its specific function efficiently without compromising the other.
2Reliability
If a strong forward axial force is applied to maintain reliable engagement during insertion, then the engagement reliability is improved, but the desired rearward extraction force is hindered
Solution Approach 1:
The engagement interface is divided into two separate interfaces located at different axial positions on the screw head. The first engagement interface is optimized for insertion operations with appropriate axial force characteristics, while the second engagement interface is optimized for extraction operations. This segmentation resolves the conflict by providing dedicated interfaces for each operation type.
Solution Approach 2:
The second engagement interface uses a reverse thread configuration (left-handed thread when the external thread is right-handed, or vice versa). This inversion allows the extraction tool to apply rearward axial force effectively while the screw is being unscrewed, counteracting the forward axial force that maintains engagement during insertion.
3Reliability
If a magnetic bit is used to prevent screw disengagement, then the engagement reliability is improved for non-magnetic materials, but misalignment between driver and screw still occurs
Solution Approach 1:
The engagement interface is segmented into two distinct interfaces with different geometries and functions. The first engagement interface provides precise alignment during insertion through its specific geometric configuration, while the second engagement interface handles extraction. This segmentation eliminates the need for magnetic bits and provides inherent mechanical alignment precision.
Data Source
AI summary
A dual interface screw element includes a screw body (10) with an external thread (12) and two distinct engagement interfaces (13, 15), one for inserting the screw and another for removing it. The removal engagement interface (15) includes a reverse thread (16) located in an axial recess (36) such that a complementary reverse-threaded tool (24) applying torque to extract the screw body is tightened against the second engagement interface. The screw is part of a system including an extraction tool (24) and an insertion tool (18). Applications include medical applications such as dental implants and bone screws, domestic applications such as headless wall mounting anchors, and a wide range of other industrial and aerospace applications.