Female Fastener Load Sensing for Accurate Preload Verification
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Solution Overview
Problem
Existing methods for tightening fasteners, such as torque wrenches and hydraulic tensioners, provide poor control of preload, leading to fatigue failure and fluid leakage due to unknown thread friction and uncertain load transfer, and lack a reliable way to check bolt load after assembly.
Innovation Solution
A female fastener with a sealed, internal load measuring device featuring an electrical switch mechanism that measures compressive load and communicates this to an external system, allowing for remote monitoring and adjustment of the tightening process to ensure a safe preload is maintained.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If torque wrenches are used to tighten fasteners, then the tightening process is simple and quick, but the preload control is poor due to unknown thread friction
Solution Approach 1:
The patent replaces mechanical torque-based tightening with an electrical/ electronic measurement system. A load cell integrated into the fastener directly measures the compressive load on the bolt, converting mechanical force into an electrical signal that can be read by external equipment. This substitution eliminates the uncertainty of thread friction effects and provides precise preload measurement while maintaining efficient tightening processes.
Solution Approach 2:
The patent introduces a load cell as an intermediary element between the bolt and nut. This load cell acts as a mediator that directly experiences the compressive load and translates it into measurable electrical signals. By placing the measurement device within the load path itself rather than relying on indirect torque measurements, the system achieves accurate preload control without sacrificing tightening speed.
2Measurement precision
If hydraulic tensioners are used to tighten fasteners, then higher preload control is achieved, but the final fastener load remains uncertain due to load transfer loss
Solution Approach 1:
The fastener performs its own measurement of the compressive load through an integrated load cell. The measurement system is self-contained within the fastener assembly, eliminating the need for external measurement devices that might introduce additional uncertainty. The load cell directly measures the force it experiences, providing reliable feedback on the actual preload achieved regardless of the tightening method used.
Solution Approach 2:
The patent replaces indirect mechanical measurement methods with direct electrical measurement. Instead of relying on mechanical linkages or hydraulic pressure readings that may not accurately reflect the actual bolt load, the load cell converts the compressive force directly into an electrical signal, providing certain and reliable measurement of the final fastener load.
3Device complexity
If no load measurement device is installed, then the fastener structure remains simple, but there is no way to check bolt load after assembly
Solution Approach 1:
The load cell serves multiple functions: it acts as both a structural element within the fastener assembly and a measurement device. The same component that experiences the mechanical load also converts it into an electrical signal for measurement and monitoring. This multi-functionality minimizes the increase in device complexity while enabling complete load information capture throughout the fastener's service life.
Solution Approach 2:
The load cell is nested within the fastener assembly, with the measurement device integrated into the existing structural components. The load cell fits within the space between the bolt and nut, utilizing the existing geometry of the fastener system. This nesting approach allows load measurement capability to be added without significantly increasing the overall size or complexity of the fastener structure.
4Measurement precision
If a load measuring device is installed inside the fastener, then bolt load can be measured accurately, but the device complexity increases
Solution Approach 1:
The patent uses an electrical load cell to replace complex mechanical measurement systems. The load cell employs strain gauges or piezoelectric elements that convert mechanical stress directly into electrical signals, eliminating the need for mechanical linkages, levers, or other complex mechanical transmission components. This substitution achieves high measurement precision while keeping the added complexity minimal.
Solution Approach 2:
The load cell utilizes thin flexible elements such as strain gauge foils or piezoelectric films that can be bonded to the fastener components. These thin-film sensors conform to the geometry of the fastener parts and provide accurate measurement without adding significant bulk or complexity. The flexible nature of these elements allows them to integrate seamlessly into the existing fastener structure.
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
The female fastener accurately measures and indicates preload, enabling early detection of unsafe joint conditions, ensuring reliable assembly and preventing fatigue failure or leakage by automatically adjusting tightening tools and transmitting data to remote monitoring stations.
Implementation Method 1
a load measuring device having an electrical switch mechanism disposed sealed and contained inside the threaded body for measuring compressive load on the female fastener
Data Source
AI summary
A female fastener for receiving and engaging with a threaded male fastener, the female fastener comprising a threaded body, a load measuring device having an electrical switch mechanism disposed sealed and contained inside the threaded body for measuring compressive load on the female fastener and for communicating a signal representing said measured compressive load to an external system.