Bolt Pre-Tension Tightening for Accurate Clamp Force Control
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Solution Overview
Problem
Existing methods for tightening bolts and nuts often fail to maintain the target tightening force effectively, particularly due to backlash and inconsistent force distribution, leading to suboptimal fastening of target objects.
Innovation Solution
A method and device that utilize sensors to detect tensile force and angle of rotation, controlling the tightening process to terminate when a specific inflection point in the force-to-angle ratio change occurs, ensuring the tightening force equals the target force by synchronizing the rotation of the nut or bolt with the tension rod, thereby maintaining the predetermined tensile force.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the nut is rotated and tightened until the tightening force equals the predetermined tensile force, then the tightening force reaches the target value, but backlash between the bolt and nut causes inconsistent force distribution and prevents accurate achievement of target tightening force
Solution Approach 1:
The patent applies preliminary action by pre-tensioning the bolt to a predetermined tensile force before initiating nut rotation. This preliminary tensile force eliminates backlash between the bolt and nut threads, ensuring that subsequent tightening force is accurately transmitted without loss. The bolt is stretched to a specific elongation amount that corresponds to the predetermined tensile force, creating a stable baseline condition for precise tightening control.
Solution Approach 2:
The patent employs feedback by continuously monitoring the elongation amount of the bolt during the tightening process and using this information to control the termination of tightening. Sensors detect the real-time elongation of the bolt, and this feedback signal is used to determine when the target tightening force has been achieved, allowing for precise control and consistent results across multiple fastening operations.
2Ease of operation
If tightening operation is terminated when the state changes from tightening force equal to tensile force to tightening force differing from tensile force, then the process is simplified, but the timing is difficult to detect accurately due to backlash
Solution Approach 1:
The patent replaces the traditional mechanical torque-based tightening control with an elongation-based control system. Instead of relying on torque sensors and mechanical feedback that are affected by backlash, the system uses elongation sensors to directly measure the bolt's deformation. This substitution of the control mechanism eliminates the influence of thread backlash on termination timing detection, providing accurate and consistent results.
Solution Approach 2:
The patent changes the control parameter from torque to elongation amount. By monitoring the elongation of the bolt rather than the torque applied to the nut, the system achieves precise control over the tightening force. The termination of tightening is determined by a predetermined elongation amount, which directly correlates to the target tightening force, providing both simplicity and accuracy.
3Measurement precision
If three tightening steps are used to achieve target tightening force, then the tightening force can be controlled, but the process complexity increases and productivity decreases
Solution Approach 1:
The patent implements continuous useful action by performing the entire tightening process in a single continuous operation rather than dividing it into separate steps. The bolt is pre-tensioned and the nut is rotated to the target elongation amount in one continuous sequence, eliminating the need for intermediate stopping and measurement steps. This continuous process maintains the beneficial effects of multi-step tightening while improving productivity.
Solution Approach 2:
The patent merges the pre-tensioning step and the tightening step into a single integrated process. Instead of performing pre-tensioning, checking the state, then performing tightening, the system combines these operations continuously with elongation-based control. The predetermined tensile force is applied and the nut is rotated to the target elongation in one seamless operation, reducing process complexity while maintaining precision.
Data Source
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AI summary
[Problem] To make the tightening force resulting from a nut and bolt to have a target tightening force. [Solution] Provided is a nut and a bolt tightening method for fastening an object, wherein a tightening force is applied on the object by rotating a nut or a bolt in a state in which a predetermined tension force is applied on the bolt in the axial direction of the bolt. When the tensile force exerted on the bolt decreases as the tightening force increases and after a timing when an inflection point occurs in a time course change in a ratio of an amount of change in the tensile force exerted on the bolt to an amount of change in an angle of rotation of the nut or the bolt, the tightening resulting from the rotation of the nut or bolt is terminated and the tensile force applied on the bolt is removed.