Automated Image Sensor Calibration via Circular Disc Test Charts
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Solution Overview
Problem
Existing methods for automated image sensor calibration and print head adjustment in inkjet printing machines are inefficient due to the use of test print charts not optimized for digital printing, which are difficult to evaluate with automated systems and require external measurement tools, leading to inaccuracies and increased complexity.
Innovation Solution
A method that prints and evaluates test print charts with filled circular discs, allowing for accurate alignment of individual printing nozzles and camera calibration using specific algorithms, eliminating outliers, and reducing the need for external sensors, thereby simplifying the process and improving accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional test print charts with lines or dot patterns are used for calibration, then measurement precision can be achieved, but device complexity increases and ease of operation deteriorates due to requiring external microscopes and manual evaluation
Solution Approach 1:
The test print chart automatically generates calibration data that can be evaluated by the existing image recording system without requiring external measurement tools. The pattern is designed to be self-evaluating through automated image processing algorithms that detect geometric features and calculate coordinate transformations, making the system self-sufficient for calibration purposes
Solution Approach 2:
The patent replaces manual microscope-based measurement with automated image processing. The image recording system captures the test print chart, and software algorithms automatically identify pattern features, calculate positions, and determine coordinate transformations, substituting mechanical measurement processes with optical-digital automation
2Measurement precision
If high-resolution external microscopes are used for pattern evaluation, then measurement precision improves, but productivity decreases and loss of time increases
Solution Approach 1:
The image recording system serves multiple functions: it performs both quality control monitoring of printed outputs and calibration measurement of the test print chart. This multi-functional approach eliminates the need for separate dedicated measurement devices and enables automated calibration evaluation within the existing production workflow
Solution Approach 2:
The test print chart is printed as part of the normal printing process before quality control evaluation. The calibration pattern is prepared in advance on the same substrate using the same print heads, allowing calibration data to be collected proactively without requiring separate measurement steps or interrupting the production flow
3Measurement precision
If specialized image sensors are used for specific pattern evaluation, then measurement precision improves, but device complexity increases
Solution Approach 1:
The existing image recording system, designed for quality control, is made multi-functional by enabling it to perform both print quality monitoring and calibration pattern evaluation. The same camera and image processing software handle both tasks, eliminating the need for specialized dedicated sensors and reducing overall system complexity
Data Source
AI summary
A method calibrates image sensors and adjusts print heads in an inkjet printing machine via a computer. The method includes printing a test print chart, recording the printed test print chart via an image sensor to create a digital image, determining a coordinate transformation between the coordinates on the test print chart and the coordinates of the image sensor and the print heads, implementing a computer-assisted evaluation process of the digital image to determine the coordinates on the test print chart, deriving correction values for print head adjustment and camera calibration from results of the coordinate transformation and/or the comparison thereof with the determined measured values, and implementing the print head adjustment and the camera calibration by the computer. The test print chart has filled circular discs. The filled circular discs have a minimum diameter that is selected for them to function even if defective printing nozzles occur.