Inkjet Printhead Drive Sequences for Density Uniformity
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Solution Overview
Problem
Existing multipass printing techniques suffer from density unevenness due to ink-landing position shifts between scans, especially when high-density images are printed, as they struggle to manage dot generation ratios and ink distribution effectively.
Innovation Solution
A printing apparatus and method that partitions the printhead's printing elements into groups, allowing for synchronized and staggered drive timings in each group during multiple scans, ensuring consistent ink distribution across the print area by setting distinct drive sequences for each scan.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multipass printing is used to suppress density unevenness, then image quality is improved, but ink-landing position shifts between scans cause new density unevenness
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing ideal ink-landing positions in a lookup table before printing. The control unit references this pre-prepared data during multipass printing to compensate for position shifts, rather than reacting to shifts after they occur. This proactive approach maintains density uniformity despite scan-to-scan positioning variations.
Solution Approach 2:
The patent implements feedback by using the stored ideal ink-landing position data as a reference standard. During printing, the control unit compares actual dot placement against these pre-established ideal positions and adjusts subsequent printing operations accordingly, creating a closed-loop system that maintains consistency across multiple passes.
2Quantity of substance
If multiple dots per pixel are allotted for high-density images, then image density is improved, but density unevenness becomes more pronounced when position shifts occur
Solution Approach 1:
The patent pre-calculates optimal ink distribution patterns for high-density areas and stores them in the lookup table. When multiple dots per pixel are required, the system references these pre-planned distributions to ensure consistent spacing and overlap patterns, preventing the amplification of density unevenness that would otherwise occur with position shifts.
Solution Approach 2:
The patent changes the parameter of ink-landing position precision by using sub-pixel positioning data from the lookup table. Even when multiple dots are allotted per pixel for high-density output, the system maintains precise control over each dot's placement by referencing pre-calculated ideal positions, thereby preventing density unevenness from becoming pronounced.
3Device complexity
If conventional binarization processing is used for multipass printing, then processing simplicity is maintained, but density changes occur when ink-landing position shifts happen
Solution Approach 1:
The patent applies preliminary action by pre-calculating ideal ink-landing positions and storing them in a lookup table before the actual printing process. During multipass printing, the control unit simply references this pre-prepared data rather than performing complex real-time calculations, maintaining processing simplicity while achieving density consistency despite position shifts.
Solution Approach 2:
The patent introduces an intermediary element - the lookup table containing pre-calculated ideal ink-landing positions - that mediates between the simple binarization processing and the requirement for density consistency. This intermediary data structure allows the system to maintain processing simplicity while achieving precise density control across multiple passes.
Data Source
AI summary
This invention relates to suppression of density unevenness caused by occurrence of ink-landing position shifts between print scans. In an embodiment, upon printing by scanning an inkjet printhead including printing elements, the following control is executed. That is, in order to form an image by print scans of the printhead on a single print area on a print medium, image data are acquired in correspondence with the respective scans. Also, the printing elements are partitioned into plural groups each including continuously arrayed printing elements, and the printing elements in each of the plural groups are time-divisionally driven based on drive sequences. Then, the drive sequences upon time-divisional driving in respective scans are set to include elements having the same drive timings and those having different drive timings.