Ink Jet Print Gap Compensation via Topography Mapping
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Solution Overview
Problem
Ink jet printers face defects in printing due to variations in the print gap between the print head and substrate, caused by factors like substrate thickness variations, thermal distortions, and inaccuracies in the print head transport system, leading to placement errors and image distortions, especially in bi-directional printing and large format printing.
Innovation Solution
A method to compensate for print gap variations by obtaining a working measure of the topography of the substrate surface, using stored representations of the surface conditions and parameters such as temperature, to adjust the timing of ink release from the print head, ensuring accurate droplet placement despite changes in the print gap.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the print gap is kept constant through precise manufacturing and adjustment, then manufacturing precision is improved, but thermal distortions during use cause print gap variations leading to placement errors
Solution Approach 1:
The system performs preliminary mapping of the print table surface topography before printing operations. This pre-acquired topographic data is stored and used to compensate for thermal distortions and surface variations during actual printing, allowing the system to predict and correct droplet placement positions in advance rather than reacting to errors after they occur
Solution Approach 2:
The system uses encoder feedback to continuously monitor the actual position of the print head and combines this with the stored topographic map to calculate real-time compensation values. This closed-loop feedback mechanism adjusts droplet ejection timing based on the actual print gap variations detected during operation, maintaining placement accuracy despite thermal expansion and table deformation
2Productivity
If the print table area is increased for large format printing, then productivity is improved, but thermal expansion causes significant distortions affecting print quality
Solution Approach 1:
The large print table surface is divided into multiple smaller measurement zones or segments. The topographic mapping system acquires data for each segment separately and stores them as distinct representations. During printing, the system selects and applies the appropriate segment data based on the current print head position, enabling precise compensation across the entire large format area while managing thermal distortion effects locally in each segment
Solution Approach 2:
The system adds a temporal dimension to the topographic data by capturing surface variations at different times or temperature conditions. This allows the system to select pre-acquired topographic representations that match current thermal conditions, effectively compensating for thermal expansion effects in large format printing by choosing the most appropriate reference surface map
3Productivity
If bi-directional printing is used to increase productivity, then printing speed is improved, but print gap variations cause double images and fuzzy text
Solution Approach 1:
The system applies different compensation values for forward and backward printing directions based on the local print gap conditions at each position. Instead of using a single global compensation value, the system queries the stored topographic map for the specific location and direction of travel, retrieving direction-specific encoder pulse adjustments that account for the asymmetric effects of print gap variations in each direction, thereby preventing double imaging and fuzzy text in bi-directional printing
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 method improves print quality by accurately compensating for print gap variations, reducing errors in ink droplet placement and maintaining image registration, even on non-flat surfaces, with minimal adjustments to existing electronic systems and without complex image data processing.
Implementation Method 1
the position in which the ink droplet lands on the substrate, relative to the point of release from the print head, is affected by the droplet velocity, the speed of the print heads relative to the substrate and the gap between print heads and substrate
Data Source
AI summary
In an ink jet printer (2), where there is relative movement between a print carriage (4) and a print table (6) to print on to a substrate mounted on the table (6), the gradient of the print table at each position of the print carriage (4) is used to produce a compensated position of the print carriage (4), and printing data is sent to the print head according to the compensated position instead of the actual position. This delays or advances the release of ink, to compensate for the difference in the time taken for the ink to reach a substrate mounted on the print table (6) when the print gap between print heads and print table (6) is not constant.