Load-Indicating Fastener With External Alignment for Small Bolts
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Solution Overview
Problem
Existing bolt load measurement methods suffer from inaccuracies due to misalignment and require complex machining, limiting their applicability to smaller bolts and increasing costs.
Innovation Solution
A fastener design with external alignment protrusions and a strain datum on the outer end, allowing for accurate load measurement with a measuring tool that aligns via a cavity and engagement length, reducing machining complexity and accommodating smaller bolt sizes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If contact type bolt load measuring methods are used with dial gauges, then load measurement capability is provided, but measurement accuracy deteriorates due to misalignment between the gauge and bolt axis
Solution Approach 1:
The patent introduces an alignment protrusion as an intermediary feature between the bolt and measuring tool. This protrusion provides a mechanical guide that automatically aligns the measuring tool with the bolt axis, eliminating the misalignment problems that occur with direct dial gauge contact. The alignment protrusion acts as a mediator that ensures accurate positioning without requiring complex alignment procedures by the operator.
Solution Approach 2:
The alignment protrusion enables the measuring system to self-align through its own geometric features rather than requiring external alignment procedures. The protrusion's shape and positioning allow the measuring tool to automatically find its correct orientation when engaged with the bolt, making the system self-aligning and eliminating the need for operator skill in alignment.
2Measurement precision
If complex machining methods are used to create internal alignment features, then measurement accuracy is improved, but manufacturing complexity and cost increase
Solution Approach 1:
Instead of creating complex internal alignment features within the bolt (as done in prior art), the patent inverts the approach by providing alignment features on the external surface of the bolt. The alignment protrusion extends from the bolt's outer surface, transforming an internal alignment problem into an external alignment solution that is much simpler to manufacture using standard machining operations.
Solution Approach 2:
The patent extracts the alignment function from the internal structure of the bolt and places it on the external surface. By taking out the alignment feature from the bolt's interior and positioning it on the exterior as a protrusion, the design simplifies manufacturing while maintaining alignment accuracy. This external positioning allows for easier access during both manufacturing and measurement operations.
3Measurement precision
If internal alignment features are used, then measurement accuracy is maintained, but applicability to smaller bolts is limited due to space constraints
Solution Approach 1:
The alignment protrusion utilizes the asymmetric available space on the external surface of the bolt rather than requiring symmetric internal cavity space. By positioning the protrusion on the outer surface, the design can accommodate smaller bolt diameters where internal cavity space would be insufficient. The external placement allows the alignment feature to be sized appropriately for small bolts without compromising the bolt's structural integrity.
Data Source
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AI summary
A bolt load measuring arrangement 31 has a bolt 4 with a reference pin 10 extending from the root 12 of a hole 11 in the bolt. Shoulder 23 of a bore 22 defines a strainable portion datum shoulder located within the strainable portion 7 of the bolt 4. The strain datum sleeve 32 has a hole 33 to allow it to pass around the reference pin 10 which extends to the end of the strain datum sleeve. The reference datum 15 is on the outer end of the reference pin 10 and the strain datum 16 is on the outer end of the strain datum sleeve 32. The outer end of the strain datum sleeve includes an alignment protrusion 34 over which the measuring tool 40 engages. For the alignment of the measuring tool 40 to be sufficiently accurate, the engagement length 37 is at least 0.9 times the engagement width 38, or diameter of the alignment protrusion.