Scanning Unit Optical Design for Stable Beam Pitch
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Solution Overview
Problem
Conventional scanning units face challenges in maintaining high image density and output speed while minimizing noise, power consumption, and durability issues, particularly due to deviations in sub-scanning beam pitch and beam quality degradation with increased light sources.
Innovation Solution
A scanning unit is designed with a light source of surface-emitting lasers, a coupling lens, an aperture, an image forming lens, and an optical deflector, where the focal length of the image forming lens in the sub-scanning direction is equal to or smaller than the optical path length between the lens and the aperture, ensuring stable beam pitch and improved beam quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the polygon scanner is rotated at high speed to increase output speed, then image density and output speed are improved, but noise increases, power consumption increases, and durability drops
Solution Approach 1:
The patent divides a single high-speed scanning task into multiple parallel scanning operations by using multiple light beams. The array of light-emitting members emits multiple beams that scan the target surface simultaneously, achieving high output speed without requiring a single polygon scanner to rotate at excessively high speeds, thereby reducing noise and improving durability.
Solution Approach 2:
The patent transitions from temporal multiplexing (single beam scanning sequentially) to spatial multiplexing (multiple beams scanning in parallel). By arranging light-emitting members in a two-dimensional array and using a diffusion lens to expand the beam profile, multiple scan lines are generated simultaneously across the target surface, increasing productivity without proportionally increasing the scanning mechanism's rotational speed.
2Productivity
If multiple beams are produced from a light flux to increase image density and speed, then output speed is improved, but beam quality degrades and scan line interval becomes uneven
Solution Approach 1:
The patent introduces a diffusion lens as an intermediary optical element between the light-emitting members and the target surface. This diffusion lens serves as a mediator that transforms the divergent beams from multiple light sources into a unified, evenly spaced scan line pattern. The diffusion lens ensures that even though multiple light-emitting members are used, the resulting scan lines have uniform intervals and maintained beam quality.
3Productivity
If the number of light sources is increased to improve image density, then productivity is improved, but device complexity increases and beam quality degrades
Solution Approach 1:
The patent merges multiple light-emitting members into a single integrated array structure mounted on one substrate. Instead of treating each light source as a separate complex component, the array configuration combines them into a unified light generation unit. The diffusion lens further merges the optical paths of all light-emitting members into a single expanded beam profile, simplifying the overall optical system while maintaining high image density through parallel scanning capability.
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 achieves a stable sub-scanning beam pitch, reduces noise and power consumption, and enhances image resolution and speed, enabling high-quality and high-speed image formation.
Implementation Method 1
a coupling lens that receives the light beams from the light source and renders the light beams as substantially parallel light
Implementation Method 2
an image forming lens that receives the diameter-defined parallel light and forms an image in a sub-scanning direction
Implementation Method 3
an image forming lens that receives the diameter-defined parallel light and forms an image in a sub-scanning direction
Implementation Method 4
an optical deflector that is arranged close to a focal point of the image forming lens, and that receives light beams of the image and deflects the light beams for scanning a target surface
Data Source
AI summary
A scanning unit in an image forming apparatus includes a light source, a coupling lens, an aperture, an image forming lens, and a polygon mirror. The light source includes a plurality of surface-emitting lasers. The coupling lens, the aperture, and the image forming lens are arranged on the optical path of light beams emitted by the light source. The polygon mirror deflects light beams of an image formed by the coupling lens towards a photosensitive drum for scanning. The focal length of the image forming lens in a sub-scanning direction is set to be equal to or smaller than an optical path length between the image forming lens and the aperture.