Polygon Mirror Scanning Timing Control for Image-Forming Devices
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Solution Overview
Problem
Conventional image-forming devices face challenges in precisely controlling the scanning of a photosensitive member with a light beam due to the sensitivity limitations of beam detect sensors and manufacturing errors in polygon mirrors, which affect the accuracy of exposure positions.
Innovation Solution
An image-forming device with a scanning unit that includes a polygon mirror, a reference mark, a detecting unit, and a memory system to measure and store the time period from reference mark detection to the arrival of the light beam at the photosensitive member, allowing precise modulation of the light beam with image data, accounting for manufacturing errors and improving scanning accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a beam detect sensor is used to control the timing of light beam irradiation, then the scanning timing can be controlled, but the sensor's low sensitivity and unstable sensing level cause imprecise exposure positioning
Solution Approach 1:
The patent removes the beam detect sensor from the system entirely and replaces it with a reference mark detection method. The reference mark on the polygon mirror is detected by a reference mark detection unit, and the timing is controlled based on this detection rather than using a sensor to detect the light beam itself. This extraction of the problematic sensor eliminates the sensitivity and stability issues while maintaining timing control capability.
Solution Approach 2:
The patent introduces a reference mark as an intermediary element between the polygon mirror and the detection system. Instead of directly detecting the light beam or relying on sensor sensitivity, the reference mark serves as a stable, detectable feature that mediates the timing control process. The reference mark detection unit detects this intermediary mark to determine the correct timing for light beam irradiation.
2Manufacturing precision
If conventional timing control methods are used without accounting for polygon mirror manufacturing errors, then the system is simpler, but the exposure position becomes offset with each scanning line
Solution Approach 1:
The patent implements a feedback mechanism where the reference mark detection unit continuously monitors the position of the reference mark on the polygon mirror. The detected timing information is fed back to the control unit, which adjusts the light beam irradiation timing accordingly. This feedback loop compensates for manufacturing errors in the polygon mirror, ensuring accurate exposure positioning without requiring complex pre-calibration systems.
Solution Approach 2:
The patent replaces complex mechanical timing adjustment mechanisms with an optical detection and electronic control system. Instead of using mechanical means to precisely position and adjust timing components, the system uses optical detection of the reference mark and electronic timing control based on detected signals. This substitution reduces mechanical complexity while improving precision.
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 enables precise control of the light beam scanning on the photosensitive member, enhancing the accuracy and reliability of image formation by accounting for manufacturing errors in the polygon mirror, thus improving the overall image quality and consistency.
Implementation Method 1
a polygon mirror having a plurality of facets, each of the plurality of facets deflects the light beam to the photosensitive member
Implementation Method 2
a reference mark detecting unit that detects the reference mark
Data Source
AI summary
A scanning unit of an image-forming device has a polygon mirror for deflecting a laser beam across the surface of a photosensitive member. A disc that rotates together with the polygon mirror is provided with a reference mark. When the reference mark passes a photointerrupter, the photointerrupter detects the rotating position of the polygon mirror. A counter measures the number of pulses in a reference clock from the moment the photointerrupter detects the reference mark until a sensor provided in a measuring device detects the laser beam deflected by the polygon mirror, and the value of the counter is stored in memory as timing data. When the scanning unit is subsequently mounted in an image-forming device, the count value stored in memory is used to control the exposure timing for irradiating the photosensitive member in the image-forming device with the laser beam.