Image Forming Apparatus Calibration Using Displaced Multi-Beam Dot Patterns
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Solution Overview
Problem
In electrophotographic image forming apparatuses, changes in photosensitive member and toner properties, along with environmental factors, cause variations in image density, particularly due to beam pitch deviations in multi-beam optical scanning devices, leading to uneven dot patterns and inaccurate light amount calibration.
Innovation Solution
The apparatus includes an image forming section with a control unit that adjusts developing voltage for solid images and exposure amount for halftone images using a dot pattern with dots arranged at regular intervals and displaced in the sub scanning direction, allowing for precise image density correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a multi-beam optical scanning device is used to form halftone images, then productivity is improved through faster scanning, but manufacturing precision deteriorates due to beam pitch deviation causing uneven dot patterns
Solution Approach 1:
The invention divides the reference image into multiple measurement regions, each corresponding to different beam positions. By segmenting the measurement approach, the system can detect beam pitch deviations for each beam individually and perform separate light amount corrections, thereby maintaining dot pattern uniformity despite using multi-beam scanning for productivity improvement
Solution Approach 2:
The invention changes the parameter being measured from overall image density to per-beam light amount based on dot pattern variations. By detecting deviations in dot pattern density caused by beam pitch changes and adjusting light amount parameters individually for each beam, the system maintains manufacturing precision while using multi-beam scanning
2Device complexity
If beam pitch deviation occurs in the optical scanning device, then device complexity is reduced by using fixed beam positions, but measurement precision deteriorates due to inaccurate density detection
Solution Approach 1:
The invention applies local quality by creating measurement regions with different dot densities corresponding to different beam positions. Each region is optimized for detecting specific beam characteristics, allowing precise measurement of beam pitch deviations without adding complexity to the optical scanning system itself
Solution Approach 2:
The invention uses a dot pattern reference image that copies the expected ideal dot arrangement. By comparing the actual scanned dot pattern against this reference copy, the system can detect beam pitch deviations and correct light amount without requiring complex real-time beam position sensing
3Ease of operation
If conventional solid image patches are used for density calibration, then ease of operation is improved through simple calibration procedures, but reliability deteriorates because they cannot correct beam pitch deviation effects on halftone images
Solution Approach 1:
The invention transitions from static solid image patches to dynamic dot pattern reference images that reveal beam position variations. The dot pattern's periodic structure allows detection of beam pitch deviations that solid images cannot detect, improving reliability of halftone calibration while maintaining operational simplicity through automated detection algorithms
Solution Approach 2:
The invention changes the calibration parameter from overall image density to per-beam light amount by using dot pattern density variations. This parameter change enables detection and correction of beam pitch deviation effects, improving halftone image density stability without complicating the calibration procedure
Data Source
AI summary
An image forming apparatus includes an image forming section, an optical scanning device, an image density sensor, and a control unit. The optical scanning device scans the surface of the image carrying member with light emitted from light sources to form an electrostatic latent image. The control unit can perform light amount calibration to adjust the exposure amount of the light scanning device based on the density of a reference image detected by the image density sensor. The reference image used for light amount calibration has a dot pattern in which as many individual dots as there are light sources are arrayed at regular intervals in the main scanning direction. The dot pattern is formed repeatedly in the main and sub scanning directions. The dots forming the dot pattern are arranged at different positions in the sub scanning direction to be displaced in units of pixels from each other.