Captive Fastener Assembly with Angular Motion Standoff
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Solution Overview
Problem
The existing captive fastener assemblies for field replaceable units (FRU) in telecommunication systems often result in misalignment and damage due to the floating nature of captive screws, leading to improper attachment and increased replacement costs.
Innovation Solution
A captive fastener assembly featuring a standoff with an internally threaded cylindrical structure and a shaft allowing for angular and circular motion, enabling alignment with the receiving nut and reducing the risk of damage, along with a deformed frusto-conical joint for secure fastening.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a floating captive screw is used to fasten the FRU, then the screw can be retained in position without losing it, but the floating nature causes misalignment with the receiving nut and improper attachment
Solution Approach 1:
A standoff is introduced as an intermediary component between the captive screw and the FRU faceplate. The standoff provides a fixed reference point that guides the screw's angular motion, ensuring the threaded portion remains properly aligned with the receiving nut on the card cage throughout the fastening process.
Solution Approach 2:
The invention allows the captive screw to have controlled angular motion within a specified range relative to the standoff. This dynamic capability enables the screw to self-align with the receiving nut while maintaining the floating retention function, resolving the contradiction between flexibility and precision.
2Ease of operation
If the threaded portion of the captive screw is projected towards the card cage, then the screw can engage with the receiving nut, but it causes FRU misalignment and incomplete insertion
Solution Approach 1:
The standoff extends in the vertical dimension from the FRU faceplate, creating a three-dimensional arrangement where the captive screw can move angularly around the standoff axis. This dimensional arrangement separates the engagement function from the alignment function, allowing proper insertion without misalignment.
3Manufacturing precision
If repeated screwing and unscrewing is performed to align the captive screw, then alignment with the receiving nut can be achieved, but damage to the screw head and face plate occurs
Solution Approach 1:
The standoff is pre-installed on the FRU faceplate before the captive screw is attached. This preliminary action establishes a fixed geometric reference that guides the screw's position from the beginning, eliminating the need for repeated screwing and unscrewing operations that cause damage.
4Manufacturing precision
If the captive screw gets stuck in an inclined position, then alignment is maintained, but the threaded portion remains in-between the face plate and card cage causing damage
Solution Approach 1:
The standoff structure provides a cushioning effect by absorbing misalignment forces through its rigid support. When the captive screw moves during insertion, the standoff prevents excessive inclination and ensures the threaded portion does not get stuck in damaging positions, protecting both the screw and card cage.
Data Source
AI summary
A method and device for a captive fastener assembly comprising of a fastener including a head and a shaft, the shaft comprising of a threaded section and an unthreaded section being interposed between the head and the threaded section. A standoff accommodating the fastener permanently fastened to the first surface and enabling the fastener to have an angular and circular motion within the standoff and fastening the first surface with the other surface by placing the surfaces together so that the fastener is substantially aligned with the receiving nut on the other surface for coupling, wherein a marginal offset for the alignment of fastener with the female part of the other surface is allowed.