Asymmetric Imaging Optical Element for Scanning Line Uniformity
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Solution Overview
Problem
Multi-beam optical scanning apparatuses with obliquely-incident optical systems face uneven scanning line intervals due to manufacturing and assembly errors, leading to degraded printing performance, and existing solutions either limit design freedom or increase size and cost.
Innovation Solution
An imaging optical element with a non-circular optical surface shape in the sub-scanning section, featuring a specific curvature radius and aspherical surface coefficients that change asymmetrically along the main scanning direction, is used to deflect light fluxes and adjust scanning line intervals without compromising design freedom or increasing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If an obliquely-incident optical system is used to downsize the apparatus, then the apparatus size is reduced, but the intervals between scanning lines become uneven due to manufacturing and assembly errors
Solution Approach 1:
The patent applies asymmetry by making the optical surface shape asymmetric with respect to the main scanning direction. Specifically, the aspherical surface coefficients are designed to differ between the light source side and anti-light source side, creating an asymmetric optical path that compensates for the unevenness caused by oblique incidence and manufacturing errors.
Solution Approach 2:
The patent applies local quality by varying the aspherical surface coefficients at different locations along the main scanning direction. The coefficients are specifically optimized for different regions (light source side vs. anti-light source side) to locally compensate for position-dependent deviations caused by manufacturing and assembly errors.
2Manufacturing precision
If the sub-scanning magnification is varied to uniformize scanning line intervals, then the uniformity of intervals is improved, but the complexity of the optical system increases
Solution Approach 1:
The patent applies parameter changes by modifying the aspherical surface coefficients of the optical surface. Instead of varying the sub-scanning magnification through complex mechanical adjustments, the invention changes the optical parameters (aspherical coefficients) to achieve uniform scanning line intervals while maintaining a simpler optical system configuration.
3Manufacturing precision
If existing correction methods are applied to compensate for manufacturing errors, then the scanning line uniformity is improved, but the design freedom is limited or size and cost increase
Solution Approach 1:
The patent provides design freedom by allowing flexible adjustment of aspherical surface coefficients without imposing strict limitations on other optical parameters. The method enables compensation for manufacturing errors while maintaining flexibility in designing the incident optical system, avoiding the need for fixed configurations of stops and collimator lenses.
Solution Approach 2:
The patent extracts the error compensation function from the overall optical system design by independently optimizing the aspherical surface coefficients. This separates the correction mechanism from the main optical path design, allowing the incident optical system to be designed freely while the aspherical surface handles the uniformization task.
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 reduces the unevenness in scanning line intervals and maintains satisfactory printing performance by effectively managing wavefront aberration and spot diameter enlargement, ensuring consistent image formation across the scanning area.
Implementation Method 1
an imaging optical element used therefor, and is suitable for an image forming apparatus such as a laser beam printer
Implementation Method 2
effectively managing wavefront aberration and spot diameter enlargement, ensuring consistent image formation across the scanning area
Data Source
AI summary
The imaging optical element includes an optical surface whose shape within a sub-scanning section has a non-circular shape. Assuming that a coordinate along a main scanning direction is Y and a coordinate along a sub-scanning direction is Z and that, within the sub-scanning section, a curvature radius on an optical axis of the optical surface is r, an eccentricity is k, a coefficient of variation in the curvature radius of the optical surface is Di, and an aspherical surface coefficient is GmnYm, when a shape S of the optical surface within the sub-scanning section is defined by an expression:S=Z2r′1+1-(1+k)(Zr′)2+∑n=116∑m=016GmnYmZn,r′=r(1+∑i=214DiYi)the expression includes a term in which n is an odd number equal to or larger than 3, and the aspherical surface coefficient of at least one of the terms in which n is an odd number equal to or larger than 3 is changed asymmetrically along the main scanning direction.