Laser Beam Diameter Correction for Uniform Image Density
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Solution Overview
Problem
Existing image forming apparatuses face irregularities in output image density due to fluctuations in laser beam diameter in both the main and sub-scanning directions, with the sub-scanning direction fluctuations having a greater impact, which previous techniques have failed to adequately address.
Innovation Solution
An image forming method that detects the laser beam diameter in the sub-scanning direction and adjusts the pulse width accordingly to ensure uniform image output density, using a combination of measurement and two-dimensional interpolation to correct for variations in beam diameter and power along the image height.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a pulse width modulated signal is used for laser beam scanning, then the image forming speed is improved, but the uniformity of output image density deteriorates due to fluctuations in laser beam diameter
Solution Approach 1:
The patent implements feedback control by detecting the actual laser beam diameter with a sensor and adjusting the pulse width based on the detected value. The control unit compares the detected beam diameter with the standard value and modifies the pulse width to compensate for deviations, ensuring uniform exposure energy despite beam diameter fluctuations during scanning
Solution Approach 2:
The patent dynamically changes the pulse width parameter based on the detected laser beam diameter. When the beam diameter deviates from the standard value, the pulse width is adjusted accordingly to maintain constant exposure energy, transforming a static parameter into a dynamically adaptable one to compensate for beam fluctuations
2Speed
If the laser beam scanning operation is performed in the main scanning direction, then the scanning speed is improved, but the uniformity of laser beam position and diameter deteriorates
Solution Approach 1:
The patent uses a sensor to detect the actual laser beam diameter during scanning and feeds this information back to the control unit, which adjusts the pulse width in real-time to compensate for position and diameter variations caused by high-speed scanning in the main scanning direction
Solution Approach 2:
The patent performs preliminary detection of the laser beam diameter before exposure and uses this information to pre-adjust the pulse width, ensuring that compensation is already in place before the actual exposure occurs, thereby maintaining uniformity despite high-speed scanning
3Ease of manufacture
If resin-made lenses are used in the optical scanning apparatus, then the manufacturing cost is reduced, but the molding precision and resulting beam diameter uniformity deteriorate
Solution Approach 1:
The patent implements a feedback control system that detects the actual laser beam diameter produced by the resin-made lens and adjusts the pulse width accordingly, compensating for the inherent molding precision limitations of resin lenses and achieving uniform exposure energy despite the lower cost optical components
Solution Approach 2:
The patent accepts the use of lower-cost resin-made lenses with shorter operational life and lower molding precision, but compensates for these deficiencies through active feedback control, allowing the system to achieve required performance using cheaper optical components
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 approach significantly reduces irregularities in image density by accurately correcting pulse widths based on sub-scanning direction fluctuations, improving gray levels and color consistency across the image, even with resin-made lenses that sacrifice molding precision for cost.
Implementation Method 1
a laser beam output section for outputting a laser beam in response to a pulse width modulated signal
Implementation Method 2
the laser beam is applied onto a surface of a photoreceptor to perform scanning and exposure operations so that a latent image is formed on the photoreceptor
Data Source
Figure 1
Figure 2a~2c
Figure 3
AI summary
An image forming method including: inputting a pulse width modulated signal into a laser beam output section and thereby outputting a laser beam, wherein a pulse width of the pulse width modulated signal is changed based on image data containing density information; scanning the laser beam onto a surface of a photoreceptor through an optical scanning apparatus and thereby outputting an image; detecting a diameter of the laser beam in a sub-scanning direction formed on the surface of the photoreceptor, the diameter of the laser beam inherent to each optical scanning apparatus and changing along an image height in a main scanning direction; and correcting the pulse width in response to the diameter in the sub-scanning direction so that the image output density is uniform with respect to one and the same input density in the image data.