Threaded Fastener Installation With Ultrasonic Tension Control
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Solution Overview
Problem
Existing methods for installing threaded fasteners fail to accurately control axial tension due to variations in structure thickness and overheating, which affect the measurement of installed tension.
Innovation Solution
A method that determines the structure thickness and adjusts the target tension value based on geometric characteristics of the fastener, using ultrasonic waves to measure axial tension, and monitors temperature to correct for overheating effects, ensuring precise tension control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If ultrasonic waves are used to measure axial tension in the screw, then the installation process can be controlled to a target tension, but the measurement becomes inaccurate when the structure thickness varies or when the screw heats up during tightening
Solution Approach 1:
The patent measures the structure thickness before tightening the nut, and determines the initial position of the nut on the screw before tightening begins. This preliminary measurement allows the system to compensate for thickness variations during the tightening process by adjusting the target value of the first parameter based on the pre-measured thickness and pre-determined nut position
Solution Approach 2:
The patent continuously monitors the first parameter (time of flight of ultrasonic waves) during tightening and compares it to a target value that has been adjusted based on the pre-measured structure thickness. The tightening process is controlled by stopping when the measured parameter reaches the adjusted target value, creating a feedback loop that compensates for thickness variations and thermal effects
2Strength
If the nut is tightened onto the screw to secure the structure, then the structure is firmly assembled, but the screw heats up which amplifies elongation and reduces axial tension
Solution Approach 1:
The patent determines the initial position of the nut on the screw before tightening begins. This preliminary positioning, combined with pre-measured structure thickness, allows the system to calculate a corrected target value for the first parameter that compensates for the expected thermal expansion during tightening, ensuring accurate tension control despite temperature increases
Solution Approach 2:
The patent replaces direct mechanical tension measurement with ultrasonic wave time-of-flight measurement. This non-contact acoustic measurement method is less sensitive to thermal effects and provides more accurate real-time monitoring of axial tension during the tightening process
3Measurement precision
If the screwing process is monitored using ultrasonic waves, then axial tension can be measured, but the measurement is affected by thermal expansion which reduces tension accuracy
Solution Approach 1:
The patent performs preliminary measurements of structure thickness and initial nut position before tightening. These preliminary data are used to determine a corrected target value for the first parameter that accounts for expected thermal expansion, allowing the system to maintain measurement reliability throughout the heating process
Solution Approach 2:
The patent changes the target value of the first parameter based on the pre-measured structure thickness and determined initial nut position. This parameter adjustment compensates for thermal expansion effects, allowing the ultrasonic measurement system to maintain accuracy despite temperature increases during tightening
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 method ensures accurate and controlled installation of threaded fasteners by accounting for structure thickness and temperature variations, providing reliable axial tension measurements and preventing over-tightening.
Implementation Method 1
emission of ultrasonic waves into the fastener, reception of reflected ultrasonic waves and measurement of a first parameter representative of a variation of said waves, said first parameter providing an indirect measurement of an axial tension in the screw
Implementation Method 2
measuring for example the variation of the time of flight of ultrasonic waves emitted and received in the screw, the time of flight providing an indirect measurement of the axial tension in the screw
Implementation Method 3
a resonance frequency shift of the screw
Implementation Method 4
tightening the nut onto the screw heats the screw
Data Source
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AI summary
The invention relates to a method for installing a threaded fastener (10) in a structure, the threaded fastener comprising a screw (20) and a nut (28). The method comprises the steps of: a) inserting the screw into the structure and tightening the nut onto the screw; b) simultaneously emitting and receiving ultrasonic waves in the fastener and measuring a parameter representative of a variation in said waves, said first parameter providing an indirect measurement of an axial tension in the screw; c) stopping the tightening when a target value of the first parameter is reached. The method further comprises determining the thickness of the structure to be clamped and determining the target value of the first parameter as a function of the thickness of the structure to be clamped and the geometric characteristics of the fastener (10).