Multi-beam Light Scanning Apparatus Correcting Color Shifts
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Solution Overview
Problem
In multi-beam light scanning apparatuses using an oblique-incidence optical system, color shifts occur in the sub scanning direction, particularly at the end portions of the main scanning direction, due to non-uniform imaging magnification ratios, leading to inconsistent scanning line pitches and poor image quality across the entire effective image region.
Innovation Solution
The apparatus adjusts the positions of light emitting portions for the head line in the sub scanning direction, ensuring that the number of folds in the optical path from the rotational polygon mirror to the scanned surface differs by an even or odd number, depending on the direction of light incidence, to maintain consistent scanning line intervals and correct color shifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the imaging magnification ratio in the sub scanning section is set to be constant in the entire effective scanning region, then the imaging system is simplified, but the scanning line pitch of the plurality of beams on the scanned surface becomes different between the scanning start side and the scanning end side, causing color shifts
Solution Approach 1:
The patent applies local quality by differentiating the imaging magnification ratio settings for different regions of the scanned surface. Specifically, the imaging optical system is configured to provide a first imaging magnification ratio in the sub scanning section for scanned surfaces corresponding to colors C and M, and a second imaging magnification ratio for scanned surfaces corresponding to colors K and Y. This regional differentiation ensures that scanning line pitches remain consistent across the entire effective scanning region, including both the scanning start side and the scanning end side, thereby preventing color shifts while maintaining a relatively simple overall system architecture.
2Volume of moving object
If multiple scanned surfaces are scanned by a single rotational polygon mirror to satisfy small size requirements, then the apparatus size is reduced, but color shifts occur in the sub scanning direction due to non-uniform imaging magnification ratios
Solution Approach 1:
The patent implements local quality by configuring the imaging optical system to provide different imaging magnification ratios for different color groups. The system sets a first imaging magnification ratio for the sub scanning section when scanning surfaces corresponding to colors C and M, and a second imaging magnification ratio for surfaces corresponding to colors K and Y. This approach enables a single rotational polygon mirror to accurately scan multiple scanned surfaces while maintaining consistent scanning line pitches across the entire effective scanning region, thereby preventing color shifts and maintaining compact apparatus size.
Solution Approach 2:
The patent applies parameter changes by adjusting the imaging magnification ratio parameter in the sub scanning section of the imaging optical system. By changing this parameter to different values (first imaging magnification ratio for C and M colors, second imaging magnification ratio for K and Y colors), the system compensates for the non-uniformity caused by the oblique-incidence optical system and the single rotational polygon mirror configuration, ensuring accurate color alignment across all scanned surfaces.
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 adjustment ensures high-definition image output with minimized color shifts across the entire scanning region, maintaining uniform scanning line pitches and improving image quality by aligning scanning lines from different light emitting portions.
Implementation Method 1
a deflection surface of a rotational polygon mirror has a conjugate relationship with a scanned surface in a sub scanning section
Data Source
AI summary
A multi-beam light scanning apparatus includes incident optical systems each of which allows a light beam to enter a deflection surface of a rotational polygon mirror in a sub scanning section from above and below directions obliquely with respect to a surface perpendicular to a rotation axis of the rotational polygon mirror at a finite angle, and a light source unit which is disposed for each of the incident optical systems and has light emitting portions. A light emitting portion corresponding to printing of a head line in the sub scanning direction among the light emitting portions of the light source unit that are disposed obliquely in the upward direction, and a light emitting portion corresponding to the printing of the head line in the sub scanning direction, that are disposed obliquely in the downward direction are different from each other in the sub scanning direction.