Skew Correction in Digital Photo Printers Using Test Pattern Analysis
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Solution Overview
Problem
Existing digital photo printers face challenges in accurately correcting the skew of photosensitive material relative to the main scan direction, leading to image distortion due to detection errors and tolerance issues in skew correction devices.
Innovation Solution
A method involving the use of test prints with specific patterns to measure and calculate skew characteristics, allowing for precise adjustment of skew correction parameters, ensuring accurate alignment of the leading edge of the recording material with the main scan direction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Difficulty of detecting and measuring
If two detecting sensors are used to detect the leading edge of the photosensitive material, then the skew detection function is provided, but detection errors occur due to transport speed variations and sensor mounting position deviations
Solution Approach 1:
A test pattern is introduced as an intermediary element. The test pattern includes a leading edge and reference lines that are printed on the photosensitive material itself. By detecting the position of these reference lines after image recording, the skew can be calculated indirectly through the displacement of the reference lines, rather than directly detecting the leading edge of the material. This intermediary approach eliminates the errors caused by sensor mounting position deviations and transport speed variations.
2Ease of operation
If a skew correction device with movable roller pair is used, then skew correction function is provided, but tolerance in the skew correction device itself prevents feedback control based on sensor outputs
Solution Approach 1:
The invention implements a feedback control system where the skew degree is calculated based on the position of reference lines in the test pattern, and this calculated skew degree is used to adjust the skew correction device. The feedback loop compensates for the inherent tolerance in the skew correction device by continuously monitoring the actual skew through the reference line positions and making real-time adjustments to the roller pair position accordingly.
Solution Approach 2:
The invention replaces direct mechanical leading edge detection with an optical/image-based detection method. Instead of relying on mechanical sensors to detect the physical leading edge of the material, the system uses image recording and processing to detect the position of reference lines in a test pattern, thereby substituting mechanical detection with optical field-based measurement that has higher precision.
3Measurement precision
If test prints with patterns are used to calculate skew characteristics, then high-accuracy skew correction is achieved, but additional processing steps and time are required
Solution Approach 1:
The test pattern is recorded in advance on the photosensitive material before actual image printing. This preliminary action allows the skew characteristics to be measured and the skew correction parameters to be determined beforehand. By performing the skew measurement and correction setup in advance using the test pattern, the actual production printing process can proceed without time-consuming skew adjustments, thus reducing the time loss during normal operation.
Data Source
AI summary
A printer processor prints out two sheets of test prints by printing a test pattern on two recording sheets of different lengths. The test pattern consists of eight straight-linear lines that are parallel to a main scan direction or a sub scan direction of an exposure section. Dimensions of designated portions of the test pattern are measured on each of the test prints, to detect skew characteristics of the recording sheets, deviations of print starting positions in the main and sub scan directions and fluctuations in transport speed of the recording sheets. Based on the detected values, a skew correcting section, the exposure section and a conveyer device for the recording sheets are controlled to correct skew of the recording sheets, the print starting positions in the main and sub scan directions and the transport speed.