Polygon Mirror Speed Control for Density Evenness
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Solution Overview
Problem
Conventional electro-photographic image forming apparatuses face challenges in maintaining image size consistency between the front and back faces of a sheet due to sheet shrinkage and density unevenness in the vertical scanning direction, which hinders high-speed processing when adjusting image magnification.
Innovation Solution
An image forming apparatus with a polygon mirror that adjusts rotating speed to change image magnification, includes a reference position detecting unit, a target component position calculating unit, a storage unit for correction data, and a parameter correcting unit to accurately calculate and correct the position of the photoreceptor drum in the vertical scanning direction, even when the signal cycle changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the rotating speed of the polygon motor is changed to adjust magnification between front and back faces, then image size consistency is improved, but the line cycle changes causing the calculated position of the photoreceptor drum to become inaccurate
Solution Approach 1:
The patent applies dynamics by making the counting value dynamic rather than fixed. When the polygon motor rotating speed changes to adjust magnification, the system automatically updates the counting value used in position calculations to match the new line cycle. This dynamic adjustment ensures that the position calculation remains accurate despite changes in scanning speed and line cycle duration.
Solution Approach 2:
The patent changes the parameter (counting value) based on the polygon motor rotating speed. By establishing a correspondence between different rotating speeds and their respective counting values, the system can accurately calculate the photoreceptor drum position regardless of whether the motor operates at high or low speed for magnification adjustment.
2Measurement precision
If the counter is reset by waiting for the photoreceptor drum to return to reference position, then position calculation accuracy is improved, but processing speed decreases and sheet interval increases
Solution Approach 1:
The patent performs preliminary action by pre-establishing the correspondence between polygon motor rotating speeds and counting values. This allows the system to immediately use the appropriate counting value when speed changes occur, without needing to wait for the photoreceptor drum to return to a reference position to reset the counter, thereby maintaining high processing speed.
Solution Approach 2:
The patent maintains continuity of useful action by eliminating the need to stop or wait for counter reset. The system continuously calculates positions using the currently applicable counting value, ensuring uninterrupted processing and minimizing the interval between sheets while maintaining calculation accuracy.
3Device complexity
If a simple counter configuration is used to correct density unevenness, then device complexity is reduced, but the system cannot handle magnification changes accurately
Solution Approach 1:
The patent enhances universality by making the counter configuration adaptable to multiple operating conditions. By establishing a set of counting values corresponding to different polygon motor rotating speeds, the simple counter structure gains the capability to handle both standard and magnified imaging operations accurately, serving multiple functions without increasing hardware complexity.
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
Enables accurate correction of density unevenness and maintains high-speed processing by continuously calculating the photoreceptor drum's position without requiring it to return to a reference position, thus reducing the interval between sheets.
Implementation Method 1
an image forming unit which scans a laser light based on image data with a polygon mirror to expose light to a photoreceptor drum to form an electrostatic latent image
Implementation Method 2
the position of the photoreceptor drum, etc. in the vertical scanning direction is calculated and the density unevenness in the vertical scanning direction is corrected
Data Source
AI summary
An image forming apparatus includes the following. An image forming unit forms an image. An image magnification changing unit changes a rotating speed of a polygon motor to change magnification of the image. A reference position detecting unit detects a reference position of a predetermined target component in a vertical scanning direction. A target component position calculating unit calculates a position of the target component based on a detecting result and a signal of a predetermined cycle according to the rotating speed of the polygon motor. A storage unit stores a correction table to correct density unevenness. An image data correcting unit obtains correction data based on the position of the target component and corrects the image data. A parameter correcting unit corrects a parameter according to a timing that the rotating speed of the polygon motor is changed.