Bolt Tension Tightening Control Using Inflection-Point Detection
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Solution Overview
Problem
Existing methods for tightening bolts and nuts to a target tightening force often fail to accurately terminate the tightening operation at the correct timing, leading to inconsistencies in the achieved tightening force.
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 occurs in the change rate of tensile force relative to angle, ensuring the tightening force equals the target force by synchronizing the rotation of the nut or bolt with the tension rod and drive socket.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If tightening operation is terminated when tensile force decreases as tightening force increases, then tightening force can be controlled, but precise termination timing is difficult to determine due to backlash between bolt and nut
Solution Approach 1:
The invention uses feedback control by monitoring the relationship between tensile force and angle of rotation during tightening. The controller detects when the tensile force starts to decrease as tightening force increases, and terminates the operation at this specific feedback signal, achieving precise tightening force control despite backlash in the system.
Solution Approach 2:
The invention replaces traditional mechanical tightening control methods with a sensor-based detection system. Instead of relying solely on mechanical indicators, the system uses sensors to detect tensile force and angle of rotation, substituting mechanical sensing with electronic measurement to achieve more precise control.
2Measurement precision
If three tightening steps are used to achieve target tightening force, then tightening accuracy is improved, but tightening time and process complexity increase
Solution Approach 1:
The invention performs preliminary action by applying predetermined tensile force to the bolt before the tightening operation. This preliminary tensioning prepares the bolt-nut assembly in advance, allowing the tightening to be completed more efficiently by simply detecting the inflection point where tensile force begins to decrease, rather than requiring multiple separate tightening steps.
Solution Approach 2:
The invention extracts the essential control criterion from the complex three-step process: instead of requiring three separate tightening operations, the system identifies and uses the critical moment when tensile force starts to decrease as the termination signal. This extracts the key control point from the multi-step process, simplifying the overall procedure while maintaining accuracy.
3Measurement precision
If predetermined tensile force is applied to bolt with nut pressed, then tightening force can be controlled, but device complexity increases due to additional sensors and control mechanisms
Solution Approach 1:
The invention makes the sensors serve multiple functions: the tensile force sensor not only monitors the preliminary tensioning but also detects the termination point of the tightening operation. The angle of rotation sensor similarly tracks both the application of tensile force and the detection of the inflection point. This multi-functionality reduces the need for separate detection systems for each stage.
Solution Approach 2:
The invention merges the control of preliminary tensile force application and tightening termination detection into a single integrated process. By combining the detection of tensile force and angle of rotation data and analyzing their relationship, the system uses one control logic to manage both the application of predetermined tensile force and the determination of tightening completion, reducing overall system complexity.
Data Source
AI summary
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.