Real-Time Color Control for Moving Articles
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Solution Overview
Problem
Current color control methods in industrial printing, such as those using RGB cameras and spectrophotometers, struggle with absolute measurement of color on moving articles, especially on small surfaces and gradients, and are limited by the need for calibration and subjective human interpretation.
Innovation Solution
A system comprising a lighting device that illuminates a moving article with successive lighting cycles of distinct spectral bands, a detection device to capture backscattered light, and a processing unit to determine color values in real-time across the entire surface, using CIE L*a*b* coordinates and color difference formulas for precise color control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If an RGB camera is used for automatic color control, then color measurement can be performed in real-time on moving articles, but only relative measurement is achieved requiring prior calibration and unable to provide absolute color values
Solution Approach 1:
A calibration target with known spectral properties is introduced as an intermediary reference object. The system captures images of this target alongside the moving article, uses the target's known spectral characteristics to calculate a correction matrix, and applies this matrix to convert relative RGB measurements into absolute color values (L*a*b* coordinates), thereby resolving the contradiction between real-time measurement capability and absolute measurement accuracy
Solution Approach 2:
The system transforms the measurement parameters from simple RGB values to corrected RGB values using a calibration-based correction matrix, and further transforms these to absolute L*a*b* color space coordinates. This parameter transformation enables the system to maintain real-time measurement speed while achieving absolute color measurement accuracy by changing the mathematical representation of color data
2Measurement precision
If a spectrophotometer is used for automatic color control, then absolute color measurement is achieved independent of source profile, but sampling is limited to solid areas with minimum surface area of 5 mm x 5 mm
Solution Approach 1:
The imaging system divides the article surface into multiple small measurement points or regions, each capable of being analyzed independently for absolute color values. By capturing high-resolution images and processing them to extract color information from small features (characters, logos, gradients), the system achieves spectrophotometer-level accuracy without requiring large sampling areas, thus resolving the contradiction between measurement precision and area constraints
Solution Approach 2:
The system replaces the mechanical contact-based spectrophotometer probe with an optical imaging system that uses light reflection and image processing to determine absolute color values. This substitution allows non-contact measurement of small areas through digital image analysis, maintaining absolute measurement accuracy while eliminating the minimum area requirement of physical spectrophotometer probes
3Measurement precision
If human color control is used, then closeness to customer validation criteria is achieved, but extensive experience is required for training and subjectivity makes control unreliable
Solution Approach 1:
The system performs self-calibration using a calibration target with known spectral properties. The calibration process is automated, requiring no human expertise to execute - the system automatically captures images of the target, calculates the correction matrix, and stores calibration data. This eliminates the need for trained operators while maintaining high color judgment accuracy, resolving the contradiction between measurement precision and operational complexity
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
Enables absolute, real-time color measurement over the entire surface of moving articles, differentiating colors with sensitivity matching human perception, and improving precision without the need for extensive calibration or human intervention.
Implementation Method 1
a lighting device configured to illuminate said moving article according to successive lighting cycles, each lighting cycle comprising the successive formation, at a given frequency, of a given number N of lighting lines having distinct spectral bands
Implementation Method 2
a detection device configured to detect, during each lighting cycle, the light backscattered by the article illuminated successively by each of said lighting lines
Data Source
Figure 1
Figure 2A~2B
Figure 3
AI summary
The present invention relates to a system (100) for controlling the colour, in real time, of an article (10) positioned on a travelling carrier. The system comprises: an illumination device (101, 105) configured to illuminate the moving article in successive illumination cycles, each illumination cycle comprising the successive formation, at a given rate, of a given number N of illumination lines having separate spectral bands, where N ≥ 4, the illumination lines being substantially perpendicular to the movement direction, the set of illumination lines being formed during an illumination cycle defining on the moving article an illumination strip with a given dimension in the movement direction; a detection device (102, 106) configured to detect, during each illumination cycle, the light backscattered by the article successively illuminated by each of the illumination lines so as to form, during each illumination cycle, at each point of a given number of points of an observation band (20) perpendicular to the movement direction, a number N of signals respectively corresponding to the light backscattered by the point in each of the spectral bands; a processing unit (104) configured to determine, at each of the points of the observation band and from the N signals, at least one value representative of the colour of the point.