Scanning Optical System Stop Placement for Multi-Beam Focus Control
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Solution Overview
Problem
In scanning optical systems for laser beam printers and copying machines, achieving a balance between reduced costs, higher definition, and enhanced speed is challenging due to variations in focus and asymmetrical light intensity distributions, especially with multi-beam systems where the stop placement is limited, affecting the depth of focus and spot diameter.
Innovation Solution
A scanning optical system is configured to control the focal length and aperture size of optical components such that the intensity at the edge of the stop is maintained at a predetermined level, ensuring a sufficient depth of focus, achieved through specific expressions involving distances, focal lengths, and aperture diameters, which allows for reduced costs, higher definition, and enhanced speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the stop is provided in proximity to the focal point on the image side of the collimator to equalize vignetting among multi-beams, then the spot diameter and depth of focus are equalized among beams, but the stop cannot be provided in proximity to the light deflector, causing writing location displacement due to focus displacement
Solution Approach 1:
The patent transitions from a two-dimensional stop placement problem (either near focal point or near light deflector) to a three-dimensional solution by positioning the stop at an intermediate location along the optical path. This intermediate positioning, combined with specific optical design parameters, allows the stop to fulfill multiple functions: equalizing vignetting among multi-beams while maintaining writing location accuracy, thus resolving the spatial conflict in stop placement.
2Manufacturing precision
If the aperture of the stop is reduced to control spot diameter, then higher definition is achieved, but the width of depth of focus is reduced, making the system more sensitive to focus displacement
Solution Approach 1:
The patent optimizes the F-number of the optical system by carefully selecting the aperture diameter of the stop relative to the focal length of the collimator. This parameter optimization achieves a balance where the spot diameter is sufficiently small for high definition while the depth of focus remains adequate to tolerate focus displacements, thus resolving the contradiction between spot size and depth of focus width.
3Reliability
If the stop aperture is increased to maintain depth of focus, then focus displacement tolerance is improved, but the spot diameter increases, reducing definition
Solution Approach 1:
The patent achieves optimal balance by precisely controlling the F-number parameter of the optical system. The aperture diameter of the stop is set to a specific value relative to the collimator's focal length, creating an optimized optical configuration that simultaneously achieves adequate spot diameter for high definition and sufficient depth of focus width for focus displacement tolerance.
4Productivity
If multiple light emission points are used to enhance speed, then productivity is improved, but asymmetrical intensity distribution occurs due to vignetting, increasing spot diameter and reducing depth of focus
Solution Approach 1:
The patent handles multi-beam systems by treating each light emission point as a separate beam that requires individual vignetting control. The stop is designed to equalize the vignetting effect across all segmented beams, ensuring that each beam maintains uniform spot diameter and depth of focus characteristics despite originating from different positions, thus preserving productivity while maintaining precision.
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 secures a stable depth of focus while maintaining high definition and speed, even with multi-beam systems, by optimizing the placement and size of optical components, thereby addressing the limitations of existing technologies.
Implementation Method 1
a collimator lens 2 having a positive power, into which a light beam from the light source 1 enters
Implementation Method 2
a stop 4 for blocking a part of the light beam emitted from the collimator lens 2
Data Source
AI summary
A scanning optical system includes a light source including light emission points, a deflector for deflecting a beam in main scanning direction, an optical element for guiding the beam from the light source to the deflector, and a stop for limiting the beam from the optical element, sets the followings appropriately: distance from the light source to the stop; focal length of the optical element; distance in main scanning direction from an intersection of optical axis and the light source at a farthest light emission point from the optical axis in main scanning direction; stop aperture diameter in main scanning direction; total angle at half maximum of a far-field pattern of emitted light; and angle between a marginal ray within main scanning section at the farthest light emission point from the optical axis in main scanning direction and a ray of a maximum intensity.