Polygon Mirror Dot Position Correction via Write Clock Adjustment
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Solution Overview
Problem
Image forming apparatuses using rotary polygon mirrors experience dot position shifts due to rotation irregularities and reflection surface errors, leading to image quality degradation, particularly in high-speed operations where centrifugal forces cause changes in mirror flatness and jitter over time, which existing correction methods cannot effectively address.
Innovation Solution
An image forming apparatus that includes a rotary polygon mirror, a photodetector to measure jitter at multiple positions, and a hardware processor that adjusts the write clock's frequency and phase based on measured jitter information to correct dot position shifts, using both first and second jitter data to account for changes over time and across all reflection surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high-speed rotation of the polygon mirror is used to increase productivity, then image formation speed is improved, but dot position shift and jitter increase due to centrifugal force causing changes in mirror flatness
Solution Approach 1:
The patent applies preliminary action by measuring and storing jitter characteristics at multiple positions across the reflection surface before image formation occurs. The correction values are pre-calculated and stored in memory, allowing the system to compensate for dot position shifts without real-time measurement delays. This enables high-speed operation while maintaining precision through pre-prepared correction data.
Solution Approach 2:
The patent changes parameters by measuring jitter at multiple positions across the reflection surface and using these measurements to dynamically adjust correction values for each position. The system varies correction parameters based on the specific location on the reflection surface, allowing precise compensation for centrifugal force effects at different radial distances from the rotation axis.
2Manufacturing precision
If frequency and phase adjustment of write clock is used to correct dot position shift, then manufacturing precision is improved, but existing methods cannot cope with changes in jitter over time
Solution Approach 1:
The system performs preliminary measurement of jitter characteristics at multiple positions across the reflection surface and stores these correction values in advance. This allows the system to adapt to changing jitter conditions over time by having pre-measured correction data that can be applied immediately without delay, maintaining precision even as operational conditions change.
Solution Approach 2:
The patent implements feedback by using measured jitter information from multiple positions to continuously refine and update correction values. The system monitors actual jitter behavior and adjusts correction parameters accordingly, creating a closed-loop system that adapts to time-varying conditions while maintaining dot position accuracy.
3Device complexity
If correction is applied only at start and end positions of main scanning, then device complexity is reduced, but manufacturing precision deteriorates in intermediate areas due to remaining errors from polygon mirror flatness
Solution Approach 1:
The patent applies segmentation by dividing the reflection surface into multiple measurement positions rather than treating it as a single unit. Jitter is measured at multiple discrete locations across the surface, and correction values are calculated for each position independently. This segmented approach captures the spatial variation in jitter caused by polygon mirror flatness errors, enabling precise correction throughout the entire scanning area.
Solution Approach 2:
The system changes parameters by applying position-specific correction values rather than a single uniform correction. Each measurement position on the reflection surface has its own corrected frequency and phase values stored in memory, allowing the system to adapt correction parameters based on the specific location being scanned, thereby maintaining high precision across all intermediate areas.
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
This solution effectively suppresses dot position shifts in the main scanning direction across the entire scanning area, including changes over time, thereby enhancing image quality by aligning start and end positions of laser beams and maintaining uniform scanning lengths.
Implementation Method 1
a photodetector that detects scanning of the light beam at a start position and an end position in the main scanning direction
Data Source
AI summary
An image forming apparatus includes: an image carrier on which an image is formed; a light source that generates a light beam; an optical scanner that executes scanning of the light beam; a reflection surface identifier that identifies each reflection surface of a rotary polygon mirror; a sub-scanning direction driver that relatively moves the image carrier and the light beam to each other; a storage that stores first jitter information; a photodetector that detects scanning of the light beam; a measurement device that generates second jitter information; and a hardware processor that uses the first and second jitter information to change a frequency of a write clock and adjust a phase of the write clock, wherein the hardware processor obtains a correction characteristic for a dot position shift, and changes the frequency of the write clock and adjusts the phase of the write clock.