Rotary Polygonal Mirror Ghost Suppression via Timing Control
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Solution Overview
Problem
Image forming apparatuses with rotary polygonal mirrors suffer from reflection ghosts due to chamfers on the deflecting surfaces, leading to density unevenness and unsatisfactory image formation, especially when the rotating speed increases or when higher image accuracy requires wider light beams.
Innovation Solution
The image forming apparatus includes a synchronism detecting system that detects a light beam from a light source device other than the one emitting for black color, ensuring the light source emits at a timing when the beam is incident on the chamfer, and the BD optical system is disposed at the side of the imaging optical system for a color least conspicuous in the image, minimizing the influence of reflection ghosts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the rotating speed of the rotary polygonal mirror is increased to improve printing speed, then productivity is improved, but the angle through which the mirror rotates during light emission increases, causing the light beam to impinge on the chamfer and producing reflection ghosts that deteriorate image quality
Solution Approach 1:
The light source is controlled to emit light in advance before the light beam reaches the chamfer region, and to stop emitting before the beam would impinge on the chamfer. This preliminary timing control prevents reflection ghost formation while allowing high rotating speeds for maintained productivity
Solution Approach 2:
The light source emits light periodically only during the specific angular range where the light beam reflects off the deflecting surface toward the photosensitive drum, and remains off when the beam would hit the chamfer. This periodic emission pattern eliminates reflection ghosts while maintaining high printing speed
2Measurement precision
If the light beam width is increased to improve image accuracy, then measurement precision is improved, but the likelihood of the light beam impinging on the chamfer increases, producing reflection ghosts that worsen image quality
Solution Approach 1:
The light source timing is controlled to emit and stop emitting light in advance relative to the beam's angular position, ensuring that even wider light beams do not impinge on the chamfer during emission, thus preventing reflection ghosts while maintaining high image accuracy
Solution Approach 2:
The emission timing parameters of the light source are precisely adjusted based on the angular position of the rotary polygonal mirror, creating a temporal parameter control that prevents spatial overlap between the light beam and chamfer region, eliminating reflection ghosts regardless of beam width
3Manufacturing precision
If chamfering is applied to the deflecting surfaces to improve manufacturing precision, then manufacturing precision is improved, but reflection ghosts are produced when light beams impinge on the chamfers, worsening image quality
Solution Approach 1:
The harmful effect of the chamfer (reflection ghost) is extracted and isolated by controlling the light source to not emit during the angular range where the beam would hit the chamfer. This separates the useful function (chamfer for manufacturing precision) from its harmful effect (reflection ghost), allowing both to coexist
Solution Approach 2:
The chamfer, which initially causes reflection ghosts, is retained for its manufacturing precision benefits. The light source timing control converts the potential harm into a benefit by using the chamfer's fixed angular position as a reference to precisely control light emission timing, thereby eliminating ghosts while maintaining manufacturing advantages
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 reduces the impact of ghost light on the image, enabling the production of satisfactory images by preventing reflection ghosts from reaching the photosensitive drums, particularly for the black color, which is most conspicuous.
Implementation Method 1
a rotary polygonal mirror (5) having a plurality of deflecting surfaces (6) for scanningly deflecting a plurality of light beams (LB)
Implementation Method 2
synchronism detecting means for obtaining a synchronizing signal (BD signal) when the photosensitive drum (13a, 13b, 13c or 13d) is to be scanned
Implementation Method 3
a plurality of imaging optical systems (LB) provided in relation to the plurality of light beams (LB), respectively, scanningly deflected by the different deflecting surfaces (6) and configured to image the plurality of light beams (LB) upon different photosensitive members (13a, 13b, 13c and 13d), respectively
Data Source
AI summary
An image forming apparatus includes photosensitive drums including one for black, light source devices, a rotary polygonal mirror having deflecting surfaces with chamfers, input optical systems, imaging optical systems and a synchronism detecting system for detecting a synchronizing light beam for determining the timing for scanning each of the photosensitive drums in a main scan direction, wherein the synchronism detecting system detects a light beam for forming an image of a color different from the black, and wherein the timing as the synchronism detecting device obtains a synchronizing signal and the timing as a light beam from the input optical system, which is at the side where the synchronism detecting device is provided, is incident on the chamfer of the deflecting surface of the rotary polygonal mirror, are at least partly overlapping.