Adaptive Dye Response Modeling for Moving Web Color Control
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Solution Overview
Problem
Existing methods for controlling sheet color in paper manufacturing using dyes and optical brightening agents are limited by the need for traditional on-line step response tests, which are time-consuming and result in 'off-spec' products due to grade-dependent dye response models and inaccurate base flow estimation, especially when producing deep shade colors or using high amounts of recycled material.
Innovation Solution
A method that models the coloring process using a-priori measured reflectance spectra of sample sheets to determine a model, which is applied on-line to regulate the flow of colorants and optical brightening agents, eliminating the need for traditional bump tests and accounting for variations in dye response shape and gain through adaptive interpolation based on measured reflectance spectra.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional on-line step response tests (bump tests) are used to determine dye response models, then the model can be obtained through direct measurement, but the process is time-consuming and results in off-spec products during testing
Solution Approach 1:
The patent performs dye response measurements offline on sample sheets before actual production. The reflectance spectra of sample sheets with different dye concentrations are measured in advance, and the dye response model is determined from these pre-collected data. This eliminates the need for time-consuming online bump tests during production while maintaining model accuracy.
Solution Approach 2:
The patent uses sample sheets as copies or representatives of the actual production web. By measuring the reflectance spectra of these sample sheets with known dye concentrations, the system creates a model that can be applied to control the actual production process without needing to physically test the production web itself.
2Reliability
If grade-dependent dye response models are used, then the model reflects specific production conditions, but the model becomes inaccurate when producing deep shade colors or using high amounts of recycled material
Solution Approach 1:
The patent determines the dye response model by measuring reflectance spectra across a range of dye concentrations and using this data to establish a comprehensive model. The model accounts for variations in dye response shape and gain by using multiple sample sheets with different concentrations, enabling accurate prediction across different shades and material compositions without requiring separate grade-specific models.
Solution Approach 2:
The patent creates a universal dye response model that can be applied across different production conditions, including various shades and recycled material contents. The model uses the relationship between dye concentration and reflectance spectrum changes to provide a generalizable approach that works for both light and deep shade colors, as well as different fiber stock compositions.
3Ease of operation
If traditional color control methods are used, then the process is simple to operate, but off-spec products are generated during and after color changes
Solution Approach 1:
The patent uses an online spectrophotometer to continuously measure the reflectance spectrum of the production web in real-time. The measured spectrum is compared with the target spectrum, and the color control system adjusts the dye flow rate based on this feedback to minimize color difference. This closed-loop control ensures continuous production of on-spec products during and after color changes.
Solution Approach 2:
The patent pre-determines the dye response model offline using sample sheets with different concentrations. This preliminary modeling allows the control system to predict the effect of dye additions accurately and make precise control decisions without needing to perform trial additions during production, thereby preventing off-spec product generation.
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 reduces the generation of off-spec products by enabling precise control of sheet color, minimizing errors, and adapting to changes in dye concentrations and paper shade, thereby improving production efficiency and reducing costs.
Implementation Method 1
The spectrophotometer is typically mounted to a scanning device for continuously measuring sheet color reflectance spectrum from a standard light source that is directed at one side of the sheet
Data Source
AI summary
A method and apparatus are set forth for modeling a coloring process in moving web manufacturing through dye response gain adaptation using measured sheet color spectrum; and dye response shape adaptation using measured color spectrum of the production sheet. The adaptation of colorant (dye) response gain uses the measured sheet color spectrum value at the value of maximum light absorbance of the dye. The adaptation of dye response spectrum uses the measured sheet color reflectance spectrum and sample sheet color spectrum with a corresponding response shape calculated using a formula to adapt the current sheet condition dye response shape using the dye response from the sample sheet on the assumption of a constant ratio of absorption change to dye concentration change.