Optical Scanning Device Variable Sub-Scanning Magnification
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Solution Overview
Problem
Conventional optical scanning devices using over-filled optical systems face challenges in maintaining accurate focusing of light beams onto photoreceptors while correcting errors in the angle of reflecting surfaces of polygon mirrors, especially when downsizing, leading to issues with sub-scanning magnification and image quality.
Innovation Solution
The use of a free-form-surface lens and scanning lenses in an optical scanning device that adjusts the light beam's width and curvature to maintain conjugation with the photoreceptor surface, even at varying deflection angles, allowing for effective correction of errors in the angle of reflecting surfaces and suppression of wobbling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If an over-filled optical system is used to downsize the device, then the device size is reduced, but the converging point of the light beam is displaced from the photoreceptor surface due to movement of reflecting surfaces along with polygon mirror rotations
Solution Approach 1:
The patent introduces a variable sub-scanning magnification parameter that changes according to the deflection angle. By making the sub-scanning magnification angle variable rather than constant, the system can compensate for the displacement of the converging point caused by polygon mirror rotations, thereby maintaining focusing accuracy while using an over-filled optical system for downsizing.
Solution Approach 2:
The patent implements dynamic adjustment of the light beam's curvature and width through variable magnification optics. The sub-scanning magnification is dynamically changed based on the deflection angle to maintain the conjugate relationship between the reflecting surfaces and photoreceptor surface throughout the scanning range.
2Manufacturing precision
If the reflecting surfaces and photoreceptor surface are maintained in conjugation, then focusing accuracy is improved, but errors in the angle of reflecting surfaces cannot be corrected adequately
Solution Approach 1:
The patent employs variable sub-scanning magnification that changes with deflection angle to simultaneously address both focusing accuracy and angle error correction. By adjusting the magnification parameter dynamically, the system can correct angular errors from the polygon mirror while maintaining the conjugate relationship for accurate focusing.
Solution Approach 2:
The patent introduces an intermediate optical system with variable magnification capability between the polygon mirror and photoreceptor. This intermediate system acts as a mediator that can compensate for angular errors while preserving the conjugate relationship, allowing both focusing accuracy and angle error correction to be achieved.
3Volume of moving object
If sub-scanning magnification is increased to downsize the device, then device size is reduced, but it becomes impossible to correct both errors in the angle of reflecting surfaces and errors in the sub-scanning-direction image surface
Solution Approach 1:
The patent makes the sub-scanning magnification dynamic rather than static. By varying the magnification according to the deflection angle, the system can correct both angular errors and sub-scanning surface errors simultaneously, even with increased magnification required for downsizing. The dynamic adjustment compensates for the increased sensitivity to errors.
Solution Approach 2:
The patent introduces a variable magnification parameter that changes with operating conditions (deflection angle). This parameter change allows the system to maintain error correction capability across the entire scanning range, despite using higher sub-scanning magnification to reduce device size.
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 achieves a balance between focusing the light beam on the photoreceptor surface and correcting errors in the polygon mirror's reflecting surfaces, reducing wobbling and maintaining image quality even with increased sub-scanning magnification, thus addressing the trade-offs in conventional techniques.
Implementation Method 1
a light beam incident to a plurality of reflecting surfaces of a polygon mirror is wider in a main-scanning direction than a single reflecting surface of the polygon mirror, and a width of the light beam in a sub-scanning direction is adjusted by a free-form-surface lens so that an average wavefront curvature in a sub-scanning direction of the light beam immediately after reflection from the reflecting surfaces of the polygon mirror varies according to a deflection angle
Implementation Method 2
the light beam is incident to a plurality of reflecting surfaces of a polygon mirror... and focused on a photoreceptor by way of scanning lenses
Implementation Method 3
a width of the light beam in a sub-scanning direction is adjusted by a free-form-surface lens so that an average wavefront curvature in a sub-scanning direction of the light beam immediately after reflection from the reflecting surfaces of the polygon mirror varies according to a deflection angle
Data Source
Figure 1
Figure 2A~2D
Figure 3A~3B
AI summary
An optical scanning device having: a light source (11) for emitting a light beam; a deflector (14) having a plurality of flat reflecting surfaces; a first optical system (12, 13) disposed between the light source (11) and the deflector (14); and a second optical system (1, 2) disposed between the deflector (14) and a photoreceptor surface (10), and configured such that the reflecting surfaces of the deflector (14) and the photoreceptor surface (10) are conjugated in a sub-scanning direction at every deflection angle in a main-scanning range. In the optical scanning device, the light beam traveling from the first optical system (12, 13) to the deflector (14) has a width greater than a dimension in a main-scanning direction of each reflecting surface of the deflector (14), and the light beam passes through different portions of the first optical system (12, 13) depending on whether the light beam is to be deflected by the deflector (14) to be directed to an edge portion of the main-scanning range or to be directed to a center portion of the main-scanning range such that the light beam traveling to the deflector (14) has a smaller average wavefront curvature in a sub-scanning direction when the light beam is to be deflected by the deflector to be directed to an edge portion of the main-scanning range than when the light beam is to be deflected by the deflector to be directed to the center portion of the main-scanning range.