Flat Field Density Correction in Inkjet Printing Systems
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Solution Overview
Problem
Commercial inkjet printing systems face challenges in fabricating uniformly sized nozzles, leading to non-uniform ink laydown characteristics and resulting in unpredictable variations in dark and light density regions, causing waste and increased costs due to the need for extensive corrections across large print media lengths.
Innovation Solution
A printing system with integrated imaging and motion encoding that captures images of printed content, uses test blocks to create density variation traces, and adjusts printhead data with negative masks to achieve flat field and density correction, ensuring uniformity and reducing waste by correcting deviations in real-time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple nozzle plates with precisely sized and spaced nozzles are used to increase printing capacity, then the printing system can handle larger print media and higher volumes, but manufacturing precision deteriorates due to the difficulty of fabricating uniformly sized nozzles across 12,000 to 30,000 nozzles
Solution Approach 1:
The system performs preliminary characterization of each nozzle's ink laydown characteristics before actual printing by printing test patterns and measuring density variations. This preliminary data is stored and used to create correction factors that compensate for manufacturing non-uniformities during production printing, allowing the system to maintain high productivity while accounting for manufacturing variations.
Solution Approach 2:
The system changes the parameters of the printing process by adjusting ink quantities for individual nozzles based on their measured characteristics. By varying the ink amount deposited by each nozzle according to its specific performance, the system compensates for manufacturing non-uniformities and achieves consistent overall print density across all nozzles.
2Productivity
If corrections for non-uniform ink laydown are delayed, then the printing system can continue operating without interruption, but loss of time increases as corrections may not occur for hundreds or thousands of feet of print media
Solution Approach 1:
The system performs correction setup in advance by characterizing all nozzles and generating correction factors before production printing begins. This preliminary correction setup eliminates the need for interruptions during printing, as the correction data is ready to be applied immediately throughout the printing process.
Solution Approach 2:
The system maintains continuous printing operation by applying correction factors in real-time during the printing process. The correction is not a separate post-processing step but is integrated into the printing workflow, allowing continuous operation without interruptions while still achieving uniform print quality.
3Manufacturing precision
If extensive corrections are applied across large print media lengths, then density uniformity can be improved, but loss of substance increases due to waste from unusable printed content
Solution Approach 1:
The system adjusts ink quantities for individual nozzles to compensate for manufacturing variations, achieving uniform density without requiring reprints. By changing the ink amount parameter for each nozzle based on its characteristics, the system produces usable printed content throughout the entire media length, eliminating waste.
Solution Approach 2:
The system converts the harmful effect of manufacturing non-uniformities into a benefit by using the measured variations to create targeted correction factors. Instead of treating non-uniform nozzles as defects requiring wasteful reprints, the system uses the variation data to optimize ink distribution, turning the manufacturing limitation into a basis for precise correction.
4Manufacturing precision
If real-time imaging and correction systems are implemented, then manufacturing precision of ink laydown is improved, but device complexity increases due to integrated imaging systems and processing requirements
Solution Approach 1:
The imaging system serves multiple functions: it captures images of test patterns for nozzle characterization, monitors print quality during production, and provides data for correction factor generation. By making the imaging system multi-functional, the patent reduces the need for separate dedicated systems for each function, thereby managing complexity while achieving precise ink laydown control.
Solution Approach 2:
The system uses its own imaging capability to automatically characterize and correct its printing performance without requiring external measurement equipment or manual intervention. The printing system self-diagnoses nozzle variations and self-corrects by applying generated correction factors, reducing the need for additional complex external systems.
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
The system effectively corrects for non-uniformities in ink laydown, minimizing waste and reducing the time and cost associated with correcting density variations across extensive print media, resulting in more consistent and efficient printing.
Implementation Method 1
an opening in the housing for receiving light reflected from the print media
Implementation Method 2
a folded optical assembly in the housing that receives the reflected light and transmits the light a predetermined distance
Implementation Method 3
an image sensor within the housing that receives the light and captures one or more images of the printed content on the moving print media
Implementation Method 4
at least one motion encoder that transmits an electronic pulse or signal proportional to a fixed amount of incremental motion of the print media
Data Source
AI summary
A density variation correction method for a printing system includes printheads in at least one linehead printing a test block pattern on a print media. A density variation trace is produced for each printed test block in the test block patterns by capturing an image of each test block and averaging pixel data in a transport direction. The density variation traces associated with a known print density represented in the test block pattern are compared with a respective reference density value. A determination is made as to whether there is a difference between each density variation trace and the respective reference density value. If there is a difference, the density variation trace is adjusted to match the reference density value. The method can be repeated for all of the known print densities represented in the test block pattern and for all of the lineheads in the printing system.