Screw Tightening Bottom-Touch Detection via Axial Force Calibration

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Solution Overview

Problem

Existing methods for detecting bottom-touching defects in screw tightening, such as those using axial force meters, increase the number of parts and costs, and suffer from low precision and potential erroneous determinations due to indirect measurement of axial force.

Innovation Solution

A method involving a measuring system with a screw hole member and an axial force measuring device to directly measure the compressive force between the screw hole member and the bearing surface, allowing for precise determination of bottom-touching based on acquired parameters, which are then used to set a reliable standard for determining the presence or absence of this defect.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a probe with vibration generator and vibration detector is used to measure axial force, then axial force measurement capability is achieved, but the number of parts and cost increase

Engineering Contradiction:

Improveaxial force measurement capabilityVSAvoidnumber of parts

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent extracts the axial force measurement function from a separate probe device and integrates it into the existing screw tightening device's control unit. The control unit calculates axial force indirectly using the relationship between tightening torque and axial force, eliminating the need for separate vibration generators and detectors while maintaining measurement capability

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent uses tightening torque as an intermediary parameter to determine axial force. Instead of directly measuring axial force with complex sensors, the control unit measures tightening torque during screw tightening and calculates axial force based on the known relationship between torque and axial force, thus using torque as a mediator to achieve the measurement goal

Inventive Principle:

Principle #24Intermediary (Mediator)

2Measurement precision

If vibration detection method is used to indirectly measure axial force, then measurement can be performed, but precision is low and erroneous determination may occur

Engineering Contradiction:

Improveaxial force measurement precisionVSAvoiddetermination accuracy

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent implements feedback control by continuously monitoring tightening torque during the screw tightening process and using this real-time data to calculate axial force. The control unit compares the calculated axial force against expected values and can detect bottom-touching defects by identifying deviations from the normal torque-axial force relationship, thereby improving measurement reliability through continuous feedback

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent changes the measurement parameter from direct axial force measurement (using vibration) to tightening torque measurement. By measuring torque instead of vibration and calculating axial force through the torque-axial force relationship, the system achieves more precise and reliable measurements without the errors associated with vibration-based indirect measurement

Inventive Principle:

Principle #35Parameter changes

3Reliability

If bottom-touching is determined by gap detection between bearing surface and object, then obvious bottom-touching can be detected, but bottom-touching without gap cannot be detected

Engineering Contradiction:

Improvebottom-touching detection capabilityVSAvoiddetection method limitation

Core Design Contradiction:

ReliabilityVSDifficulty of detecting and measuring

Solution Approach 1:

The patent replaces the mechanical gap detection method with a torque-based measurement system. Instead of physically detecting gaps between the bearing surface and object, the control unit measures tightening torque and calculates axial force to determine bottom-touching. This substitution allows detection of bottom-touching cases where no visible gap exists, as the torque-axial force relationship reveals the defect

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent uses axial force calculation as an intermediary to detect bottom-touching. Rather than directly observing gaps or contact, the system calculates axial force from torque measurements and identifies bottom-touching by detecting abnormal axial force values or deviations from expected patterns, thus using axial force as a mediator to reveal hidden defects

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS11759898B2Method for setting bottom-touching-determination standard and non-transitory computer readable storage medium

Publication Date: 2023.09.19 OMRON CORP

AI summary

Provided is a method for setting bottom-touching-determination standard capable of setting a bottom-touching-determination standard based on parameters with high reliability. The method for setting bottom-touching-determination standard includes a screwing step of screwing a measurement screw (11) into a measurement screw hole (13a), a parameter acquisition step of acquiring parameters in the screwing step, a bottom-touching-determination step of determining the presence or absence of bottom-touching on the basis of an axial force of the measurement screw, and a determination standard setting step of collating the determination result in the bottom-touching-determination step and the parameters to set the bottom-touching-determination standard.