Contactless Web Dimension Measurement Using Reference Shadow
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Solution Overview
Problem
Existing non-contact methods for determining the dimensions of a moving web of material, particularly opaque materials, are prone to inaccuracies due to changes in detection means such as camera positions and ambient conditions, leading to measurement errors.
Innovation Solution
An arrangement using a backlight and optical detection means with a shading element between the background lighting and the material web, where the evaluation means compare instantaneous contrast images with a reference contrast image to determine a correction factor, accounting for changes in the detection setup and accurately calculating the real dimension of the material web.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If optical detection means (cameras) are used to determine web width during production, then continuous measurement is enabled, but measurement accuracy deteriorates due to changes in camera position and ambient conditions
Solution Approach 1:
A shading element with a slot is introduced as an intermediary object between the light source and the material web. This slot serves as a reference object whose shadow position remains stable despite changes in camera position or ambient conditions. By comparing the web edge shadow position relative to this stable reference shadow, accurate width measurement is maintained during continuous production operation.
Solution Approach 2:
The system changes the reference parameter from absolute camera coordinates to relative positions based on the shading element's shadow. The evaluation unit determines web width by measuring the distance between the web edge shadow and the shading element shadow, rather than relying on fixed camera calibration parameters that drift during operation.
2Measurement precision
If camera calibration is performed using a slit aperture during production breaks, then initial measurement accuracy is achieved, but reliability deteriorates due to frequent changes in detection means properties
Solution Approach 1:
The shading element is pre-positioned in the measurement path before production begins. Its slot creates a persistent reference shadow that is captured in every measurement image. This preliminary setup eliminates the need for repeated calibration during production breaks, as the reference shadow continuously compensates for detection means drift throughout operation.
Solution Approach 2:
The evaluation unit continuously compares the position of the web edge shadow relative to the shading element shadow in each captured image. This feedback mechanism automatically compensates for changes in camera position or ambient conditions, maintaining measurement reliability without requiring manual recalibration during production breaks.
3Measurement precision
If multiple cameras are used to avoid height deviation errors, then measurement accuracy improves, but device complexity increases
Solution Approach 1:
The shading element acts as a mediator that provides a reference shadow visible to the camera system. This reference shadow enables accurate width measurement with a single camera by providing a stable positional reference, eliminating the need for multiple cameras or stereoscopic systems while maintaining measurement precision.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables precise and reliable determination of the material web's dimensions by accounting for changes in the detection system, reducing measurement errors and ensuring accurate width measurement during production.
Implementation Method 1
the instantaneous contrast image represents a shadowing of the backlight by the material web and by the shading element
Data Source
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AI summary
The invention relates to an arrangement (2) for the contactless determination of at least one dimension of a moving material web, more particularly a material web (4) made of light-impenetrable material, with a backlighting, with optical detection means for detecting at least one current contrast image, and with evaluation means, wherein the backlighting (6) is arranged opposite the optical detection means, wherein the material web (4) moves in a plane between the at least one optical detection means (8) and the backlighting (6), and wherein the current contrast image has at least one piece of information about at least one light intensity laterally next to the material web (4). The present invention also relates to a corresponding method. To simplify and improve the contactless determination of the dimension, the present invention proposes that a shading element (36) is provided and the current contrast image is compared with a reference contrast image, wherein the current contrast image renders a shading of the backlighting (6) through the material web (4) and through the shading element (36).