Optical Scanning Lens Thickness Control for Birefringence Stability
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Solution Overview
Problem
Existing optical scanning apparatuses for color image forming devices face issues with uneven thickness of image forming optical elements in the sub-scanning cross section due to sagittal line tilt changing surfaces, leading to fluctuations in optical performance due to birefringence and polarization changes.
Innovation Solution
The optical scanning apparatus employs image forming lenses with aspherical shapes and sagittal line tilt changing surfaces, ensuring that the thickness deviation ratio is controlled within specific limits to minimize birefringence fluctuations, thereby stabilizing optical performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a sagittal line tilt changing surface is used to correct curvature of scanning line and wavefront aberration, then optical performance is improved, but thickness of the optical element becomes uneven in the sub-scanning cross section causing birefringence fluctuations
Solution Approach 1:
The patent applies local quality by making the optical element have different thickness characteristics in different regions. Specifically, the optical element is designed with a first region (where |y| ≤ ymax1) having controlled thickness variation and a second region (where |y| > ymax1) with different thickness characteristics. This local differentiation allows the optical element to correct aberrations while controlling birefringence in the critical region where light beams pass through.
Solution Approach 2:
The patent changes the thickness parameter of the optical element in a controlled manner. By defining specific relationships between thickness t(y) and position y, and by controlling the ratio |yΔs|max−ydmax|/W to be 0.05 or less, the patent optimizes the thickness distribution to balance aberration correction with birefringence control. This parameter optimization resolves the contradiction between optical performance and thickness uniformity.
2Reliability
If thickness deviation is reduced to minimize birefringence fluctuations, then optical performance stability is improved, but ability to correct curvature of scanning line and astigmatism is compromised
Solution Approach 1:
The patent resolves this contradiction by applying different thickness control strategies to different regions. In the first region (|y| ≤ ymax1), the thickness is controlled with tight constraints (|yΔs|max−ydmax|/W ≤ 0.05) to maintain optical performance stability. In the second region (|y| > ymax1), the thickness can vary more freely, allowing the optical element to achieve the necessary aberration correction while maintaining stability in the critical region.
Solution Approach 2:
The patent introduces a new dimensional constraint by defining the ratio |yΔs|max−ydmax|/W as a control parameter. This dimensionless parameter combines multiple factors (position y, maximum thickness deviation Δs|max, maximum thickness position ydmax, and aperture W) into a single figure of merit that simultaneously addresses both stability and correction capability. By controlling this parameter, the patent achieves both reliability and 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 effectively corrects curvature of scanning lines and astigmatism while maintaining consistent optical performance by reducing thickness deviations and birefringence fluctuations, enhancing the overall optical quality.
Implementation Method 1
a deflector that deflects a light beam from a light source to scan a scanned surface in a main scanning direction
Implementation Method 2
an optical system including at least one optical element that guides the light beam from the deflector to the scanned surface
Data Source
AI summary
An optical scanner includes: deflector deflecting a beam from a light source to scan scanned surface in main-scanning direction; and a first element closest to scanned surface and guides the beam to scanned surface, in which thickness of first element in optical-axis direction in main-scanning section changes in main-scanning direction, first element includes an optical surface whose normal on main-scanning section is tilted thereto, the normal tilt amount changes in main-scanning direction, and a position in main-scanning direction where interval in optical-axis direction between both ends in sub-scanning direction of effective region of the optical surface in sub-scanning section is maximum, a position in main-scanning direction where a thickness in optical-axis direction of first element in main-scanning section is maximum, and maximum image height in main-scanning direction on scanned surface are appropriately set in region on one side of the optical surface relative to optical axis in main-scanning direction.