Screw Joining Control Using Optical Distance Difference Quotients

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Solution Overview

Problem

Existing screw joining methods face challenges in accurately determining the head support position due to manufacturing and application-related component tolerances, leading to inefficient speed changes and potential over-torquing, especially with self-tapping screws and non-precut threads.

Innovation Solution

The method employs difference quotients ΔL/Δt and ΔL/Δϕ to monitor and control the joining movement, allowing for precise detection of head contact independent of tolerances, enabling optimal speed adjustments and torque control by tracking the distance covered relative to time and angle of rotation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If speed is switched early to account for all component tolerances, then head contact detection reliability is improved, but cycle time increases due to unnecessarily long reduced speed operation

Engineering Contradiction:

Improvehead contact detection reliabilityVSAvoidcycle time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent replaces mechanical/torque-based detection methods with an optical measurement system. A sensor measures the actual distance between the fastener head and receptacle surface, substituting mechanical tolerance accommodation with direct optical measurement, thereby eliminating the need for conservative early speed switching.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The system continuously measures the actual distance between the fastener head and receptacle surface using a sensor, providing real-time feedback to the control unit. This feedback enables dynamic speed adjustment based on actual position rather than predetermined conservative timing, optimizing both reliability and cycle time.

Inventive Principle:

Principle #23Feedback

2Difficulty of detecting and measuring

If torque monitoring is used to detect head contact, then detection capability is improved, but speed switching becomes impossible in time for self-tapping screws due to irregular and high torque before head seating

Engineering Contradiction:

Improvehead contact detection capabilityVSAvoidspeed switching time

Core Design Contradiction:

Difficulty of detecting and measuringVSLoss of time

Solution Approach 1:

The patent replaces torque-based mechanical detection with optical distance measurement. By measuring the actual distance between the fastener head and receptacle surface, the system avoids the problematic torque signals that occur during self-tapping screw formation, enabling reliable and timely head contact detection.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Productivity

If fastener joining speed is increased, then productivity is improved, but risk of over-torquing increases when head contact position is uncertain

Engineering Contradiction:

Improvefastening speedVSAvoidtorque control reliability

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The control unit receives real-time feedback from the sensor measuring the actual distance between fastener head and receptacle surface. Based on this feedback, the control unit dynamically adjusts the driving speed, allowing high speed when head contact is not yet reached and automatically reducing speed when head contact is detected, thereby preventing over-torquing while maximizing productivity.

Inventive Principle:

Principle #23Feedback

Data Source

PatentEP1995021B1Method for assembling a fastener and device for implementing the method

Publication Date: 2014.04.02 WEBER SCHRAUBAUTOMATEN GMBH & CO KG

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AI summary

In a process to determine the optimum engagement and securing of screw fixtures, the absolute position or its head are established by mathematical differential quotients ?L/ ?t or ?L/ ??.