Image Forming Apparatus Laser Scanning Clock Correction
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Solution Overview
Problem
Existing image forming apparatuses without a scanning lens having the fθ characteristic face challenges in maintaining uniform image widths due to varying exposure amounts across the scanning direction, leading to issues like thicker latent images at the center portion compared to the end portion.
Innovation Solution
The apparatus employs a rotatable photosensitive member and a light emitting means that scans laser light based on image data, with a correcting means that adjusts the image data according to continuous pixel numbers and pixel positions to ensure uniform exposure across the scanning direction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a scanning lens having fθ characteristic is used, then the spot of laser light moves at constant speed on the photosensitive member, but the apparatus becomes large and costly
Solution Approach 1:
The patent extracts the fθ characteristic requirement from the scanning lens itself and implements it through electrical correction of the image clock frequency instead. By removing the need for a specialized optical lens and replacing it with electronic timing adjustment, the apparatus achieves constant spot speed without the associated size and cost increases
Solution Approach 2:
The patent replaces the mechanical/optical solution (scanning lens with fθ characteristic) with an electrical/electronic solution (correction of image clock frequency). This substitution eliminates complex optical components while achieving the same functional result of uniform pixel spacing and constant spot speed
2Manufacturing precision
If electrical correction is performed to dispose pixels evenly, then pixel spacing is uniform, but exposure amounts per unit area differ between center and end portions
Solution Approach 1:
The patent applies different image clock frequencies to different regions (center vs. end portions) of the scanning area. By making the timing correction location-specific rather than uniform across the entire scan, it compensates for the varying spot speeds at different positions, ensuring that each region receives appropriate exposure amounts while maintaining overall pixel spacing uniformity
Solution Approach 2:
The patent dynamically changes the image clock frequency parameter based on the scanning position. By adjusting this timing parameter locally across different portions of the scan, it compensates for the non-uniform spot speed caused by using a simple scanning lens, thereby achieving uniform exposure amounts across the entire photosensitive member surface
3Productivity
If the spot moves at different speeds at center and end portions, then scanning is faster overall, but image widths become non-uniform
Solution Approach 1:
The patent implements dynamic adjustment of the image clock frequency during the scanning process. Rather than using a fixed timing rate, the system dynamically changes the timing parameter based on position, allowing it to accommodate the varying spot speeds at different locations while maintaining uniform image widths throughout the scanned area
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 effectively reduces the difference in image widths in the scanning direction of the laser, even without using a scanning lens with the fθ characteristic, thereby improving image quality and consistency.
Implementation Method 1
an optical scanning unit for exposing a photosensitive member. The optical scanning unit emits a laser light based on image data, and the laser light is reflected by a rotating polygon mirror and is allowed to transmit through a scanning lens to irradiate and expose the photosensitive member
Data Source
AI summary
An image forming apparatus includes a photosensitive drum, an optical scanning device and a controller. The optical scanning device forms a latent image on the photosensitive drum by scanning laser light based on image data in a scanning direction. The controller corrects the image data. In the image forming apparatus, a scanning speed which is a speed of the laser light scanned on the photosensitive member is slower at a center portion than at an end portion. The controller corrects the image data according to a continuous pixel number which is a number of pixels, for forming the latent image, continued in the scanning direction and a pixel position which is a position within continuous pixels which are a plurality of pixels continued.