Polygon Mirror Phase Control for Color Drift Reduction
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Solution Overview
Problem
Color drift occurs in image forming apparatuses due to phase differences in the rotation phases of polygon mirrors when transitioning from a standby state to an operating state, leading to inefficiencies in matching rotation phases and potential overshoot or undershoot of rotation frequencies.
Innovation Solution
An image forming apparatus that includes a polygon driving portion, beam detecting portions, a reference phase setting portion, and a phase control portion to efficiently match the rotation phases of polygon mirrors by setting a reference phase based on detected laser beam positions and controlling rotation frequencies in stages, using a Phase Locked Loop (PLL) to prevent frequency overshoot and undershoot.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the rotation frequency of the polygon motor is changed to decrease the phase control time, then the phase matching speed is improved, but overshoot or undershoot of the rotation frequency occurs
Solution Approach 1:
The phase control process is divided into multiple stages with different frequency adjustment rates. In the first stage, a larger frequency adjustment rate is applied for rapid phase correction. In the second stage, a smaller frequency adjustment rate is applied to fine-tune the phase matching, preventing overshoot and undershoot while completing the phase alignment.
Solution Approach 2:
The frequency adjustment rate is made dynamic rather than fixed. The control system automatically switches between different frequency adjustment rates based on the current phase difference and control progress. This dynamic adjustment allows the system to achieve both fast phase matching and stable frequency control.
2Productivity
If a large frequency adjustment is applied to reduce phase control time, then the phase matching speed is improved, but the rotation frequency becomes unstable
Solution Approach 1:
The frequency adjustment is segmented into two distinct stages: a first stage with larger frequency adjustment for rapid phase correction, and a second stage with smaller frequency adjustment for stable fine-tuning. This segmentation enables the system to achieve both high phase matching speed and frequency stability.
Solution Approach 2:
The control system performs preliminary large-frequency adjustments to eliminate the majority of the phase difference quickly, then transitions to small-frequency adjustments for precise final alignment. This preliminary action approach allows the system to achieve phase matching speed while maintaining frequency stability in the final stage.
3Loss of time
If the rotation frequency is changed significantly to match phases quickly, then the phase control time is reduced, but overshoot or undershoot occurs
Solution Approach 1:
The phase control process is segmented into coarse adjustment and fine adjustment stages. The first stage uses larger frequency changes for rapid coarse phase matching, while the second stage uses smaller frequency changes for precise fine phase matching, ensuring both speed and precision are achieved.
Solution Approach 2:
The frequency adjustment rate is dynamically changed based on the control stage. The system transitions from high-speed coarse adjustment to high-precision fine adjustment, dynamically adapting the adjustment rate to match the current control requirements and eliminate overshoot/undershoot.
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
The solution enables efficient matching of rotation phases between polygon mirrors, reducing color drift and improving the accuracy of color image formation by setting a reference phase as an intermediate phase between leading and lagging phases and controlling frequencies in a staged manner, thereby preventing overshoot and undershoot.
Implementation Method 1
beam detecting portions that detect laser beams scanning by the predetermined number of polygon mirrors at preset positions on scanning paths
Data Source
AI summary
A CPU (91) of an image forming apparatus includes a beam detecting part (911) that detects each of laser beams scanning by a predetermined number (e.g., four) of polygon mirrors (332) at a preset position (where a beam sensor (335) is disposed), a reference phase setting part (912) that sets a reference phase that is a phase to be a reference of the predetermined number of rotation phases of the polygon mirrors (332) based on a result of detection by the beam detecting part (911), and a phase control part (913) that controls polygon motor (330) so that predetermined number of rotation phases of the polygon mirrors (332) match the reference phase.