Inkjet Head Dot Ratio Control for Bidirectional Banding
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Solution Overview
Problem
Inkjet recording apparatuses face challenges with gloss banding and density unevenness during bidirectional printing, where the order of dot color layering leads to surface shape differences and banding issues, compromising image quality and productivity.
Innovation Solution
A liquid jetting apparatus with a recording head unit, gradation setting unit, and irregular pattern setting unit that adjusts the dot ratio and gradation patterns at the ends of the recording head to randomize the number of dots per unit area, preventing density and gloss banding by complementing image layers and reducing granularity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If bidirectional printing is performed to increase productivity, then output speed is improved, but gloss banding and density unevenness occur due to differences in dot color layering order
Solution Approach 1:
The patent applies different dot ratio settings to different regions of the recording head. Specifically, the dot ratio is set to decrease toward the ends of the head in the sub-scanning direction, creating local variations in dot density that compensate for the banding effects caused by bidirectional printing. This local quality adjustment ensures uniform overall appearance despite directional printing differences.
Solution Approach 2:
The gradation setting unit pre-adjusts the dot ratios before actual printing occurs. By calculating and setting appropriate gradation values for each nozzle based on its position, the system prepares compensation data in advance that prevents gloss banding and density unevenness from occurring during bidirectional printing operations.
2Device complexity
If dot ratio is uniformly set across all nozzles to simplify control, then device complexity is reduced, but density unevenness occurs at the ends of the recording head
Solution Approach 1:
Instead of uniform dot ratios, the system implements position-dependent dot ratio settings where nozzles at different locations along the sub-scanning direction have different dot ratios. The dot ratio decreases toward the ends of the recording head, creating local variations that compensate for edge effects and ensure uniform density across the entire printed area.
Solution Approach 2:
The system dynamically changes the dot ratio parameter based on nozzle position in the sub-scanning direction. By adjusting this key parameter locally rather than maintaining a constant value, the system achieves uniform density distribution while accounting for the specific printing conditions at different head positions.
3Device complexity
If regular dot patterns are used to maintain simple image data processing, then processing complexity is reduced, but periodic unevenness and granularity occur in the printed image
Solution Approach 1:
The system introduces irregular patterns that break the symmetry and periodicity of regular dot arrangements. By randomizing dot positions and ratios according to calculated gradation values, the system eliminates periodic unevenness and granularity while maintaining simple processing through algorithmic generation of these irregular patterns.
Solution Approach 2:
The irregular patterns and gradation settings are calculated and applied in advance to the image data before printing. This preliminary processing step incorporates all necessary compensations for uniformity, allowing the actual printing process to proceed with simple, straightforward execution without requiring complex real-time adjustments.
Data Source
AI summary
A liquid jetting apparatus includes a recording head unit including nozzles; a moving mechanism configured to alternately perform a scanning operation of moving the recording head unit in a scanning direction while causing the recording head unit to discharge a liquid and a sub-scanning movement operation of moving the recording head unit or the recording medium in a sub-scanning direction without causing the recording head unit to discharge the liquid; a gradation setting unit configured to set gradation on portions of image data corresponding to setting regions at ends of the recording head unit; an irregular pattern setting unit configured to set an irregular pattern on the image data to randomize a dot ratio indicating the number of dots per unit area; and a head discharge drive unit configured to cause the nozzles to discharge the liquid based on the image data.