Optical Writing Device Pixel Clock Alignment
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Solution Overview
Problem
Optical writing devices with multiple light sources face challenges in maintaining image alignment due to varying distances, leading to uneven scanning line widths, and existing solutions either increase circuit complexity or fail to correct misalignment when sharing a pixel clock signal among light sources.
Innovation Solution
An optical writing device with a pixel clock generator that measures scanning speed and generates a corrected pixel clock, along with pulse data and shift data, to align image pulses across multiple light sources using a common pixel clock, thereby correcting misalignment without increasing circuit scale.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a pixel clock generating function is provided for each of the light sources, then the misalignment among images for each scanning line can be corrected, but the scale of the circuit increases and leads to cost overruns
Solution Approach 1:
The patent merges multiple pixel clock generating functions into a single shared pixel clock generating unit that serves all light sources. This single unit generates a common pixel clock signal that is distributed to all light sources, eliminating the need for separate pixel clock generators for each light source while still enabling correction of image misalignment through centralized control.
Solution Approach 2:
The single pixel clock generating unit is designed to serve multiple light sources simultaneously, making it a universal component that performs the function of multiple individual generators. This multi-functional design reduces circuit scale while maintaining the capability to correct misalignment for all light sources through a unified approach.
2Device complexity
If one pixel clock generating function is shared by all light sources, then cost can be reduced, but the misalignment among images for each scanning line cannot be corrected
Solution Approach 1:
The patent introduces a feedback mechanism where the single pixel clock generating unit receives information about the scanning speeds of individual light sources and adjusts the pixel clock signal accordingly. This feedback loop enables the system to compensate for variations in scanning speeds and correct image misalignment while still using a shared pixel clock generator.
Solution Approach 2:
The system dynamically changes parameters of the pixel clock signal, such as frequency or phase, based on the specific requirements of each light source. By adjusting these parameters in response to measured scanning speeds, the single pixel clock generator can accommodate multiple light sources with different characteristics and correct their misalignment.
3Manufacturing precision
If oblique-incidence keystone correction is used to correct misalignment among images, then image alignment can be improved, but pixel clock correction cannot be performed
Solution Approach 1:
The patent segments the correction process into two distinct functions: oblique-incidence keystone correction for geometric distortion and pixel clock correction for timing synchronization. The single pixel clock generating unit is designed to handle both types of correction independently, allowing the system to perform pixel clock frequency adjustment in addition to the existing keystone correction capability.
Data Source
Figure 1~2
Figure 3
Figure 4A
AI summary
An optical writing device (3) and an image forming apparatus (1, 5) incorporating the optical writing device (3). The optical writing device (3) includes two or more light sources (31a), a pixel clock generator (323) to measure a scanning speed of one of the two or more light sources (31a) and generate a pixel clock of a cycle corrected according to the measured scanning speed, a pulse data generation and output unit (324) to generate pulse width data and shift data for the pixel clock generated by the pixel clock generator (323) to output the generated pulse width data and the generated shift data for each one of the two or more light sources (31a), and a plurality of image pulse generation and output units (325) to generate an image pulse. In the optical writing device (3), the plurality of image pulse generation and output units (325) are supplied with the pixel clock in common.