Optical Tissue Softness Detection via Multi-Angle Shadow Imaging
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Solution Overview
Problem
Current methods for measuring the softness of tissue paper are unreliable, particularly in detecting surface softness, as they fail to accurately quantify the slight surface feeling and often conflict with human subjective evaluations, and existing devices are not suitable for online applications in tissue manufacturing.
Innovation Solution
A method and arrangement using digital imaging to detect free fibre ends on the surface of tissue paper by illuminating the sample from multiple directions, estimating surface normals, reconstructing reflectance images, and comparing them to construct difference images that represent shadows of fibre ends, allowing for on-line softness measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current measurement devices are used to measure tissue softness, then bulk softness can be measured reliably, but surface softness measurement is not straightforward and conflicts with panel test results
Solution Approach 1:
The patent replaces mechanical contact-based softness measurement devices with an optical imaging system. By using digital images captured from multiple angles and analyzing shadow patterns of free fibre ends, the system achieves surface softness measurement that correlates with human panel tests without mechanical contact, thereby resolving the conflict between instrumental measurements and subjective evaluations
Solution Approach 2:
The patent utilizes variations in light reflectance and shadow intensity (optical property changes) to detect free fibre ends on the tissue surface. By analyzing the visual contrast and shadow patterns in images captured under different lighting conditions, the system quantifies surface characteristics that correlate with perceived softness
2Measurement precision
If artificial robotic fingers are used to measure surface softness, then slight surface feeling can be detected, but online application is not currently realistic
Solution Approach 1:
The patent replaces mechanical robotic fingers with a non-contact optical imaging system that captures digital images of the tissue surface. This substitution enables online measurement capability while maintaining the sensitivity to detect free fibre ends, as the optical system can rapidly capture images during production without mechanical contact or folding requirements
Solution Approach 2:
The patent creates optical copies (digital images) of the tissue surface from multiple angles. By analyzing these image copies and the shadow patterns they contain, the system achieves surface softness measurement without requiring physical contact or complex mechanical probes, enabling practical online implementation
3Measurement precision
If folding of paper is required for fibre measurement, then fibre amount can be measured, but additional devices are required and online measurement is impossible
Solution Approach 1:
Instead of folding the paper to make fibres visible (as in prior art), the patent inverts the approach by illuminating the surface from multiple angles and analyzing shadow patterns of free fibre ends in the original flat configuration. This eliminates the need for folding devices while maintaining measurement capability
Solution Approach 2:
The patent transitions from measuring fibres in a single dimension (requiring folding to expose fibre ends) to utilizing the third dimension (lighting angle variation) to create shadow patterns. By capturing images from multiple angular dimensions, the system detects free fibre ends without altering the paper's physical configuration
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 reliable and repeatable measurement of tissue paper softness, comparable to human panel tests, with small standard deviation, and can be implemented on-line without requiring additional paper folding, improving the accuracy and consistency of softness assessment.
Implementation Method 1
illuminating a target sample surface, which comprises free fibre ends, from at least two directions one direction at a time, with at least one light source, obtaining for each light source direction an original reflectance image for the target sample surface with an imaging device
Data Source
AI summary
The invention relates to a method and arrangement for detecting free fiber ends in a paper surface. The method comprises illuminating a target sample (6) surface, which comprises free fiber ends, from at least two directions one at the time, with at least one light source (1). Original reflectance images are obtained for the target sample (6) surface with an imaging device (4), and a surface normal is estimated for each image pixel of the original reflectance image. Thus it is possible to reconstruct a reconstructed reflectance image from the estimated surface normals, and to compare the reconstructed reflectance image and the corresponding original reflectance image and to construct a difference image, where the differences represent shadow objects of the free fiber ends in a paper surface.