Screw Tightening Torque Variation Detection During Temporary Tightening

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Solution Overview

Problem

Existing screw tightening systems struggle to reliably detect abnormalities during the temporary tightening period due to variations in screw size, material, tightening torque, and rotation speed, often requiring high threshold values that delay detection.

Innovation Solution

A screw tightening system that calculates the standard deviation of torque values during the temporary tightening period and compares it to a reference standard deviation to determine abnormalities, allowing for reliable detection without needing to adjust threshold values based on screw size, material, or equipment differences.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a high threshold value is set for torque abnormality detection, then false detection is reduced, but detection timing is delayed

Engineering Contradiction:

Improveabnormality detection reliabilityVSAvoiddetection timing

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent changes the detection parameter from absolute torque value to standard deviation of torque values. This allows using a fixed threshold (e.g., 3 standard deviations) that adapts to different screw specifications and equipment variations, resolving the contradiction between reliable detection and timely detection.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The system continuously monitors torque values and calculates standard deviation in real-time during the tightening process. This feedback mechanism enables dynamic abnormality detection that responds immediately to variations in torque patterns, achieving both high reliability and timely detection.

Inventive Principle:

Principle #23Feedback

2Measurement precision

If threshold value is adjusted for each screw specification and equipment, then detection accuracy is improved, but system complexity increases

Engineering Contradiction:

Improveabnormality detection accuracyVSAvoidthreshold setting complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent transforms the detection approach from using absolute torque thresholds (which require adjustment for each screw specification) to using standard deviation of torque values. This parameter change creates a universal detection method that works across different screw sizes, materials, and equipment without requiring threshold reconfiguration.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The standard deviation-based detection method serves as a universal solution that can detect abnormalities across all screw specifications and equipment types using a single threshold setting, eliminating the need for multiple customized threshold configurations.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS12440933B2Screw tightening system, controller, and non-transitory storage medium

Publication Date: 2025.10.14 OMRON CORP

AI summary

A screw tightening system includes an actuator including a driver bit that rotationally drives a screw and a motor coupled with driver bit, and a controller that controls actuator. Controller includes an acquirer that acquires torque values of a torque generated in a motor, a calculator that calculates a standard deviation of the torque values in a temporary tightening period, and a determiner that determines that there is an abnormality when a ratio of the standard deviation to a reference standard deviation exceeds a first threshold value.