Polygon Mirror Coating for Uniform Light Across Image Heights
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Solution Overview
Problem
Existing light scanning apparatuses using polygon mirrors face issues with non-uniform light amounts at different image heights due to varying reflectivities at varying incident angles, and existing solutions to mitigate this often result in increased apparatus size.
Innovation Solution
A polygon mirror with a multilayer film structure on its reflecting surfaces, where the physical film thickness and reflectivity are carefully controlled to ensure uniform light distribution across the scanned surface, achieved through vacuum vapor deposition and precise film formation techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a flat mirror is arranged between the polygon mirror and the scanned surface to cancel reflectivity differences, then the light amount difference among respective image heights is reduced, but the size of the apparatus is increased
Solution Approach 1:
The patent applies local quality by creating non-uniform film thickness distribution across the reflecting surface of the polygon mirror. The film thickness is deliberately made thicker at the incident angle end and thinner at the reflection angle end, allowing different regions of the mirror to have different optical properties that compensate for incident angle variations without adding external components
Solution Approach 2:
The patent changes the physical parameter of film thickness across the reflecting surface to control reflectivity characteristics. By varying the film thickness parameter from one end of the reflecting surface to the other, the patent achieves uniform light distribution while maintaining a compact apparatus structure
2Ease of manufacture
If the reflectivity is made uniform across the entire reflecting surface, then the manufacturing process is simplified, but the light amount difference among respective image heights cannot be reduced
Solution Approach 1:
The patent deliberately creates non-uniform film thickness distribution across the reflecting surface, making different parts of the mirror have different optical properties. This local variation in film thickness allows the system to achieve uniform light output despite the complexity of the manufacturing process
Solution Approach 2:
The patent converts the naturally occurring non-uniform film thickness (which could be considered a defect or harmful variation) into a beneficial feature. By controlling and optimizing this non-uniformity, the patent achieves uniform light distribution across the scanned surface
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 provides a high-quality, cost-effective polygon mirror that maintains uniform light amounts across the scanned surface without increasing the apparatus size, enhancing environmental durability and reducing manufacturing costs.
Implementation Method 1
A polygon mirror according to the present invention has a plurality of rectangular reflecting surfaces 5a in which the following conditional expression (2) is satisfied: 0.02≤|1−B/A|≤0.10, where A represents a reflectivity at a center of the reflecting surface 5a with respect to a light flux which is incident at a predetermined incident angle, and B represents the reflectivity at a predetermined point between the center and an end in a longitudinal direction of the reflecting surface 5a with respect to a light flux which is incident at the predetermined incident angle
Data Source
AI summary
In order to provide a polygon mirror which can reduce a light amount difference among respective image heights on a scanned surface with suppressing an increase in size in a light scanning apparatus, the polygon mirror according to the present invention includes a plurality of rectangular reflecting surfaces in which the following condition is satisfied:0.02<|1−B/A|<0.10where A represents a reflectivity at a center of the reflecting surface with respect to a light flux which is incident at a predetermined incident angle, and B represents the reflectivity at a predetermined point between the center and an end in the longitudinal direction of the reflecting surface with respect to the light flux which is incident at the predetermined incident angle.