Variable Torque Rate Test Joint With Inverted Rotation
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Solution Overview
Problem
Existing test joints for rotary tools used in threaded fasteners face challenges in accurately simulating the torque and clamping force, particularly for smaller nuts and bolts, due to high moment of inertia and the need for laborious tool removal for reverse rotation, and they lack direct measurement of clamping force.
Innovation Solution
A variable torque rate test joint design with a fixed threaded shaft and rotating nut, utilizing a collar and spring beams to adjust torque rate, and an integrated torque sensor to measure torque directly, allowing for reduced moment of inertia and efficient resetting without tool removal, and providing a direct measure of clamping force through strain gauges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a traditional test joint with a rotating bolt is used, then the torque pattern can be simulated, but the moment of inertia is too high to accurately test impulse drive tools
Solution Approach 1:
The patent inverts the traditional test joint configuration by making the nut the rotating component instead of the bolt. The bolt head is fixed to the test rig, and the nut rotates on the bolt shaft. This inversion dramatically reduces the moment of inertia of the rotating mass, making it comparable to actual fastener bolts and enabling accurate testing of impulse drive tools.
2Weight of moving object
If the test joint is designed with a fixed bolt and rotating nut, then the moment of inertia is reduced, but the tool cannot be reset without removal
Solution Approach 1:
The patent implements a dynamic locking mechanism that can switch between locked and unlocked states. During testing, the bolt head is locked to the test rig to maintain the reduced moment of inertia configuration. After testing, the locking mechanism is released, allowing the bolt head to rotate and the nut to be unscrewed for resetting, thus enabling both accurate testing and easy resetting operations.
3Measurement precision
If torque is measured using an intermediate torque sensor, then the torque reading can be obtained, but the moment of inertia increases and clamping force cannot be directly measured
Solution Approach 1:
The patent extracts the torque measurement function from a separate intermediate torque sensor and integrates it directly into the bolt shaft through strain gauges. This eliminates the need for an additional rotating torque sensor, thereby reducing the moment of inertia while maintaining accurate torque measurement capabilities.
Solution Approach 2:
The patent merges the torque measurement function with the bolt shaft structure itself by incorporating strain gauges directly on the shaft. This combination allows simultaneous measurement of both torque and clamping force (through axial strain) using the same integrated sensor system, eliminating the need for separate measurement devices.
4Measurement precision
If strain gauges are mounted on the bolt shaft, then direct clamping force measurement is achieved, but the bolt rotation during testing becomes problematic
Solution Approach 1:
The patent resolves this contradiction by inverting the rotation assignment: the bolt shaft remains fixed and does not rotate, while the nut rotates instead. The strain gauges mounted on the fixed bolt shaft can therefore maintain stable electrical connections while accurately measuring both torque (through twisting strain) and clamping force (through axial strain).
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 design provides a more accurate simulation of torque and clamping force, reduces the moment of inertia, and improves testing efficiency by allowing the test joint to be reset without reversing the rotary tool, enabling precise calibration and measurement of torque and clamping force.
Implementation Method 1
A torque rate adjustment device comprises at least one spring beam that is anchored to a reaction point at one end and flexes as it extends in cantilever over a pivot point
Implementation Method 2
The shaft may comprise strain gauges that provide a direct measure of the clamping force
Data Source
AI summary
In a variable torque rate test joint, screw-threaded first and second elements are rotated relative to one another by a tool under test. At least one spring beam is cantilevered over a pivot point to exert an axial force between the first and second elements and the torque rate of the test joint can be varied by moving the pivot point to change the axial force. The first element may be a shaft that is fixed during testing and the second element is a nut rotatably mounted on the shaft, whereby the element rotated by the tool has a minimal moment of inertia. Whichever of the first and second elements is held stationary during the test may be mounted in a hub that is locked during the test but can be rotated at the end of the test to reset the test joint. Measurements may be made of the torque and the rotation angle to derive an actual torque rate of the joint, which allows correction of errors by moving the pivot point.