Ball-and-Socket Prosthesis Pin Fastening Shear Lock
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Solution Overview
Problem
Existing ball-and-socket prostheses face issues with secure fastening, as the screws used to hold the cap and base together can fail due to repeated thrusts, leading to undesirable unthreading, especially when the ball bears against the bearing surface, and permanent securing hampers later replacement of worn components.
Innovation Solution
A secure assembly arrangement where a pin is inserted cross-wise to the pin's axis, putting it in shear, and the cap and base have parallel legs and grooves that receive the pin, providing a strong, secure connection without relying on thread engagement, allowing for easy disassembly and replacement of components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If screws are used to hold the cap and base together, then the components can be securely fastened, but the screws can fail due to repeated thrusts and unthreading
Solution Approach 1:
The fastening function is segmented into two independent mechanisms: legs embedded in grooves for positional stability and a pin providing shear-based mechanical locking. This separation allows each component to optimize for its specific function, with the pin handling thrust loads through shear rather than tension on threads.
Solution Approach 2:
The threaded mechanical fastening system is replaced with a shear-based pin mechanism. Instead of relying on thread engagement and tensile strength, the pin utilizes shear strength to resist thrust forces, providing more reliable fastening under repeated loading conditions.
2Strength
If screws are used to fasten the cap and base, then the components can be securely held, but permanent securing hampers later replacement of worn components
Solution Approach 1:
The fastening system transitions from a permanent threaded connection to a reversible mechanical lock. The pin can be easily inserted and removed, allowing the cap and base to be disassembled and reassembled multiple times without degradation, enabling straightforward component replacement and maintenance.
Solution Approach 2:
The fastening element (pin) is designed as a separate, removable component that can be extracted without damage to the cap or base. This allows the joint to be easily disassembled for maintenance or replacement of worn components, then reassembled with the same pin or a replacement pin.
3Strength
If a pin is inserted cross-wise to put it in shear, then a stronger connection is provided, but the structure becomes more complex
Solution Approach 1:
The pin fastening mechanism is merged with the existing leg-groove structure. The legs and grooves provide the basic alignment and positioning, while the pin adds shear-based locking. This integration creates a unified fastening system where components work together rather than adding separate, complex mechanisms.
Solution Approach 2:
Instead of using threads that engage through axial loading, the design inverts the approach by using a pin that engages through shear loading in a cross-wise direction. This inversion provides superior strength for thrust resistance while maintaining structural simplicity through the straightforward pin insertion geometry.
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 solution provides a stronger, more secure connection that resists shear forces, preventing unthreading and allowing for easy disassembly and replacement of components, enhancing the durability and maintainability of the prosthesis.
Implementation Method 1
forces put the pin in shear, which provides a very secure connection
Data Source
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AI summary
A two-piece socket for a ball-and-socket arrangement, including a base and a cap. The socket includes a leg on one of the cap or base of the socket and a receiving groove on the other of the cap or base of the socket, wherein there is at least one opening in the leg which lines up with a corresponding opening in the groove for a fastener to extend through these openings to releasably secure the cap to the base of the socket. The orientation of the fastener is such that the fastener is under shear loading when the cap is pulled apart from the base.