Polygon Mirror Cover Window Stray Light Management
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Solution Overview
Problem
High-speed optical beam scanning devices face issues with stray light from the cover window of the polygon mirror, which degrades image quality due to reflection, and existing solutions complicate optical characteristics and increase the number of parts.
Innovation Solution
The optical beam scanning device incorporates a light deflecting device with a cover window and a post-deflection optical system, where the reflection light from the cover window is shielded from striking outside the effective area of optical elements, preventing it from affecting the image forming process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the rotation speed of the polygon motor is increased to achieve high-speed scanning, then the scanning speed is improved, but wind noise and heat generation increase
Solution Approach 1:
A cover is introduced as an intermediary component between the polygon mirror and the external environment. This cover includes a light-transmitting window that allows the light beam to pass through while protecting the polygon mirror from direct exposure to air currents, thereby reducing wind noise and heat generation without compromising scanning speed.
Solution Approach 2:
The cover is designed with a thin, light-transmitting window that selectively transmits the light beam while blocking harmful environmental factors. This thin film structure allows optical functionality to be maintained while providing protection against wind noise and heat.
2Reliability
If a cover with window is provided on the polygon mirror, then protection from dust and cooling is improved, but reflection light from the window causes stray light on the image surface
Solution Approach 1:
The harmful reflection light is extracted from the optical path by positioning it outside the effective scanning area. The cover window is designed and positioned such that reflection light from the window strikes only the effective area of the scanning optical system, preventing it from reaching the image surface as stray light.
Solution Approach 2:
The cover window is designed with specific local properties: its position, angle, and dimensions are optimized so that reflection light is directed to a specific location (outside the effective scanning area) while the transmitted light maintains proper optical characteristics for image formation.
3Object-generated harmful factors
If the cover glass is inclined to make reflection light escape, then stray light is reduced, but optical characteristics deteriorate and a correction flat plate is required
Solution Approach 1:
Instead of completely eliminating reflection light through complex measures, the solution accepts partial reflection but directs it to a harmless location. The cover window is positioned and angled so that reflection light escapes in a direction that does not affect the image quality, making additional correction components unnecessary.
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 effectively prevents the deterioration of picture quality caused by stray light from the cover window, maintaining optical integrity without increasing the number of parts or degrading optical characteristics.
Implementation Method 1
a cover having a cover window portion for keeping a passage for an entering/emitting light
Data Source
AI summary
An optical beam scanning device includes a light deflecting device with at least a polygon mirror portion of which is covered by a cover having a cover window portion for keeping a passage for an entering/emitting light, a pre-deflection optical system for entering an optical beam from a light source into said light deflecting device and a post-deflection optical system for focusing a reflection light from said light deflecting device on a surface to be scanned. The light deflecting device, post-deflection optical system and the cover window portion are so disposed that the pretreated light-shielding reflection light from the cover window portion avoids from striking upon a flange portion and an edge portion of one or a plurality of the optical element parts within the post-deflection optical system, with respect the entering light.