Scanning Optics Surface Shaping to Suppress Molding Birefringence
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Solution Overview
Problem
Conventional imaging optical elements suffer from deformation and birefringence due to mold release and shrinkage during molding, particularly in regions with discontinuous thickness changes, which affect printing performance and optical quality.
Innovation Solution
The light scanning apparatus incorporates imaging optical elements with continuous sagittal line tilt and curvature functions, ensuring smooth transitions at non-effective portions to suppress deformation and birefringence by using a spline shape for at least part of the non-effective regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the thickness continuously changes between the non-effective portion and the outer portion in the main scanning cross section, then the deformation of the optical surface due to mold release or shrinkage is suppressed, but a discontinuous change in thickness occurs in cross sections not including the optical axis, forming steps that cause deformation and birefringence
Solution Approach 1:
The patent applies parameter changes by modifying the sagittal line tilt and curvature functions to be continuous but not infinitely differentiable at predetermined positions in the non-effective portions. This mathematical parameter adjustment ensures that the thickness transitions smoothly in the main scanning direction while preventing discontinuous changes and step formation in the sub-scanning direction, thereby suppressing both optical surface deformation and birefringence without compromising manufacturing precision
2Adaptability or versatility
If the shape of the optical surface in the sub-scanning cross section has an inclination (sagittal line tilt), then the imaging optical element can be designed with specific optical properties, but steps are formed between the non-effective portion and the outer portion, causing deformation and large birefringence
Solution Approach 1:
The patent resolves this contradiction by carefully controlling the parameters of the sagittal line tilt and curvature functions. By making these functions continuous but not infinitely differentiable at specific positions, the design maintains the necessary optical surface inclination for versatile optical performance while preventing the formation of steps that would cause birefringence and deformation, thus achieving both adaptability and manufacturing precision
3Ease of manufacture
If the thickness changes discontinuously in the imaging optical element, then the flow path of resin during molding changes according to the sub-scanning position, but this causes large birefringence in the effective portion of the optical surface
Solution Approach 1:
The patent addresses this contradiction by optimizing the mathematical parameters of the sagittal line tilt and curvature functions. By designing these functions to be continuous but not infinitely differentiable at predetermined positions, the patent ensures uniform resin flow during molding while suppressing birefringence in the effective portion, thus maintaining both ease of manufacture and manufacturing precision
Data Source
AI summary
Provided is a light scanning apparatus wherein each of optical surfaces of an imaging optical element includes an effective portion on which a light flux traveling toward an effective region of a scanned surface is incident, and two non-effective portions provided on both sides in main scanning direction of effective portion, wherein, when each of a change in a sagittal line tilt amount and a change in a sagittal line curvature in main scanning direction on at least one of optical surfaces is represented by a function, at least one of functions is continuous and is not infinitely differentiable at a predetermined position on each of two non-effective portions, and wherein, with respect to at least one of sagittal line tilt amount and sagittal line curvature, an absolute value at a first end of non-effective portion on a side opposite to effective portion is smaller than that at predetermined position.