Line Image Sensor Calibration via Dot Pattern Coordinates
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Solution Overview
Problem
Existing image reading apparatuses with line image sensors face accuracy issues during calibration due to inclination and diameter errors of the document conveyance rollers, which affect the precision of error component derivation and overall image correction.
Innovation Solution
An image reading apparatus that includes a line image sensor, a first derivation unit for determining dot pattern coordinates, a second derivation unit for calculating the inclination angle of the line image sensor, and a calculation unit for generating correction values using a chart with isolated dot patterns, where the dot patterns are arranged such that their coordinates sum to zero, thereby accurately correcting for sensor inclination and roller errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If straight-line patterns are used for calibration, then the inclination of the line image sensor can be derived, but diameter errors of the document conveyance roller affect the reading accuracy of the calibration document
Solution Approach 1:
The calibration document is divided into multiple dot patterns (first dot pattern, second dot pattern, third dot pattern, fourth dot pattern) arranged at different positions. Each dot pattern serves as an independent reference point for coordinate derivation, allowing the system to segment the calibration process into multiple discrete measurement points that can be individually processed to eliminate roller error effects.
Solution Approach 2:
The patent transitions from using straight-line patterns (one-dimensional reference) to using dot patterns arranged in two-dimensional space. By deriving coordinates in both main scanning and sub scanning directions from multiple dot patterns, the system adds a dimensional aspect to the calibration process, enabling more robust error compensation that accounts for roller diameter errors.
2Ease of manufacture
If a plurality of line image sensors is used to reduce cost, then cost merit is improved, but connection errors occur due to positional misalignment and inclination
Solution Approach 1:
The dot pattern calibration document serves multiple functions: it calibrates each line image sensor individually, provides reference points for connection processing between sensors, and enables error derivation for both main scanning and sub scanning directions. This universal calibration approach replaces the need for separate calibration procedures for each sensor.
Solution Approach 2:
The system derives inclination angles and correction values from the dot pattern coordinates, then applies these correction values to compensate for misalignment errors in connection processing. This feedback mechanism continuously corrects for manufacturing tolerances and positional errors, maintaining high connection accuracy despite using multiple sensors.
Data Source
AI summary
An object of one embodiment of the present invention is to accurately derive an inclination of a line image sensor. One embodiment of the present invention is an image reading apparatus including: a line image sensor in which reading elements for reading an image are arrayed in a predetermined direction; a first derivation unit configured to, based on read data acquired by reading a chart on which a plurality of dot patterns is printed with the line image sensor, derive coordinates of each of the plurality of dot patterns; a second derivation unit configured to derive an inclination angle of the line image sensor based on the coordinates derived by the first derivation unit; and a first calculation unit configured to calculate a first correction value for correcting the inclination of the line image sensor based on the inclination angle derived by the second derivation unit.