Inkjet Head Raster Correction for Banding Reduction
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Solution Overview
Problem
Color ink-jet printers face issues with banding due to errors in the feed mechanism, leading to white streaks and reduced print accuracy, especially at higher speeds where dot overlap occurs, resulting in a grainy image instead of high-resolution output.
Innovation Solution
The image forming apparatus adjusts the relative positions of the recording head and medium by transporting the medium in the auxiliary-scanning direction and employs error diffusion techniques, converting image data bit sizes and applying coefficients to distribute errors among multiple pixels, and rearranging errors between low and high-resolution buffers to minimize banding and maintain print quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the printing medium is transported in the auxiliary-scanning direction between main scans, then the ink head can be repositioned for the next scan, but feed mechanism errors cause excessive transport distance, creating wider raster intervals and banding
Solution Approach 1:
The control apparatus performs preliminary actions by storing correction values that compensate for feed mechanism errors before they cause banding. The apparatus predicts and prepares correction data based on detected feed errors, applying corrections in advance to maintain precise raster intervals even when transport deviations occur.
Solution Approach 2:
The system implements feedback by detecting actual feed distances during auxiliary scanning, comparing them against expected values, and using the difference to generate correction values. These corrections are then applied to subsequent main scan positioning, creating a closed-loop system that continuously compensates for feed mechanism variations.
2Ease of operation
If the printing medium is transported excessively in the auxiliary-scanning direction, then the ink head can be repositioned, but the distance between rasters increases causing visible banding
Solution Approach 1:
The system converts the harmful effect of feed errors into beneficial correction data. By detecting the actual deviation caused by excessive transport and using it to generate correction values, the system transforms the error into a useful compensation mechanism that prevents banding in subsequent scans.
Solution Approach 2:
The control apparatus changes the parameter of raster positioning by applying correction values to the expected transport distance. This parameter adjustment compensates for the excessive feed error, restoring the correct raster interval and eliminating the visual banding effect.
3Productivity
If the movement speed in the main scanning direction is increased, then productivity improves, but the time interval between dot formation decreases causing dot overlap and reduced accuracy
Solution Approach 1:
The control apparatus performs preliminary positioning adjustments by calculating and applying correction values before the high-speed main scan completes. This advance preparation ensures that even at increased speeds, dots are placed accurately without overlap by compensating for the reduced time interval between scans.
Solution Approach 2:
The system uses feedback from detecting feed errors to generate correction values that compensate for reduced dot formation time intervals. This feedback mechanism allows the system to maintain dot placement accuracy even when printing speed increases, preventing the harmful effect of dot overlap.
Data Source
Figure 1
Figure 2A~2B
Figure 3A~3B
AI summary
A print method and apparatus for minimizing effects of error in repositioning during printing process may include generating successive scans of a recording head, wherein the scans may partially overlap to account for the error in repositioning. As an example, after the recording head makes one scan across the document being printed, the document (or the head) may be repositioned for the next scan so that several print elements of the recording head are aligned to lie between certain rows of dots printed in the previous scan, resulting in a higher number of rows in the overlapping portion of the scans. Additional features may include varying the row/column arrangement of dots in the overlap portion, or performing error diffusion and correction for different areas of resolution in the scans.