Scanning Lens Incident Surface Shape for Error Sensitivity Reduction
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Solution Overview
Problem
In optical scanning devices, particularly in color image forming apparatuses, the dimensional errors in scanning lenses lead to high error sensitivity, complicating the manufacturing and optical performance, especially for common scanning lenses that handle multiple laser beams.
Innovation Solution
The optical scanning device incorporates a first scanning lens with an incident surface and an exit surface, both having positive refractive power in the main scanning direction, where the oblique angle of the light beam varies from the center to the ends, with specific constraints on the rate of change and its second derivative to reduce error sensitivity and manufacturing complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a common scanning lens is used to scan multiple laser beams, then device complexity is reduced, but manufacturing precision requirements increase due to high error sensitivity
Solution Approach 1:
The incident surface of the scanning lens is designed with a specific asymmetric shape where the oblique angle θ varies from center to end according to controlled rates of change (dθ and d2θ). This local variation in surface geometry compensates for mold errors at different positions, reducing error sensitivity while maintaining the common scanning lens configuration
Solution Approach 2:
The patent controls specific optical parameters of the incident surface, namely the oblique angle θ and its rates of change (dθ and d2θ), to satisfy predetermined conditions. By adjusting these parameters, the lens achieves reduced error sensitivity without requiring higher manufacturing precision
2Reliability
If the oblique angle varies significantly from center to end, then optical performance improves, but manufacturing complexity increases
Solution Approach 1:
Instead of allowing complete freedom in oblique angle variation, the patent applies partial control by specifying that dθ and d2θ satisfy predetermined conditions. This partial constraint approach achieves sufficient optical performance improvement without requiring excessively complex surface shape control
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 configuration minimizes the influence of mold errors on optical properties, allowing for reduced focus point shifts and improved field curvatures, even with surface displacements, thus enhancing the optical performance and manufacturing ease of scanning lenses.
Implementation Method 1
The incident surface allows the oblique angle θ of the light beam entering the incident surface with respect to the normal to the incident surface to vary from a center to an end of the incident surface in the main scanning direction
Implementation Method 2
scanning lenses configured to image the deflected laser beam onto a circumferential surface (surface to be scanned) of a photoconductive drum
Data Source
AI summary
An optical scanning device includes a light source, a deflector, and a plurality of scanning lenses. A scanning lens lying closest to the deflector has a positive refractive power and the incident surface of it allows the oblique angle θ of the light beam entering the incident surface to vary from a center to an end of the incident surface. The incident surface satisfies the following conditions, where Δθ is the amount of change and dθ is the rate of change in the oblique angle θ of the light beam in the main scanning direction, d2θ is the rate of change in dθ, and Δ2θ is the amount of change in Δθ:d2θ<|0.036| when Δ2θ increases from the center to the end in the main scanning direction; andd2θ<|0.061| when Δ2θ decreases from the center to the end in the main scanning direction.