Scanning Device Post-Scan Optics Distortion Correction
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Solution Overview
Problem
Conventional scanning devices with F-Theta lenses suffer from significant size and weight issues due to bulky mirror arrangements, particularly for long scan lengths, leading to increased space, weight, and cost requirements, along with challenges in minimizing distortions like scan arc and keystone distortion.
Innovation Solution
A scanning device design featuring prescan optics arranged upstream of a polygon mirror and postscan optics downstream, utilizing a correction objective with at least one first and second correction lens, a cylindrical mirror, and a cylindrical lens, where the cylindrical mirror is tilted and one correction lens is offset to minimize distortions and reduce the number of optical components, resulting in a more compact and stable structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If a conventional mirror arrangement with F-Theta lenses is used for long scan lengths, then the scan length is achieved, but the size and weight of the scanning device become excessively large
Solution Approach 1:
The patent changes the optical parameters by replacing the conventional F-Theta lens system with a catadioptric post-scan optics system that includes a spherical mirror and cylindrical lenses. This parameter change allows achieving long scan lengths (e.g., 600mm) with significantly reduced device weight and size, as the catadioptric design is more compact than the all-refractive F-Theta lens approach.
Solution Approach 2:
The patent employs a composite optical system combining reflective elements (spherical mirror) and refractive elements (cylindrical lenses with different refractive indices). This composite approach allows the system to achieve long scan lengths while maintaining compact dimensions, as the combination of reflection and refraction enables more efficient light path folding and focusing compared to pure refractive systems.
2Manufacturing precision
If the post-scan optics are arranged centered on the polygon mirror to minimize distortion, then image distortion is reduced, but the device becomes bulky for larger angles of incidence
Solution Approach 1:
The patent segments the post-scan optics into functionally distinct components: a spherical mirror for beam deflection and cylindrical lenses for distortion correction. This segmentation allows the spherical mirror to be positioned at a smaller angle of incidence (reducing device volume) while the cylindrical lenses compensate for the resulting distortion, effectively decoupling the angle of incidence from the distortion level.
Solution Approach 2:
The patent introduces cylindrical lenses as intermediary elements between the spherical mirror and the target surface. These intermediary lenses serve to correct the image distortion introduced by the non-centered mirror arrangement, allowing the mirror to be positioned at smaller angles for compactness while maintaining image quality through the mediating correction function of the cylindrical lenses.
3Device complexity
If fewer optical components are used to reduce size and weight, then device complexity is reduced, but the ability to correct image errors and maintain imaging quality may be compromised
Solution Approach 1:
The patent designs the spherical mirror to perform multiple functions: primary beam deflection, focal length determination, and partial distortion correction. The cylindrical lenses are designed to simultaneously correct residual distortion in one direction while maintaining beam collimation. This multi-functionality reduces the total component count compared to conventional systems that require separate elements for each function.
Solution Approach 2:
The patent merges the distortion correction function with the beam deflection function by integrating cylindrical lenses directly into the catadioptric post-scan optics assembly. This merging allows the system to achieve both compact size (through reduced component count) and high imaging quality (through combined correction functions), as the cylindrical lenses and spherical mirror work together in a unified optical path rather than as separate correction stages.
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 significantly reduces distortions, minimizes the size and weight of the scanning device, and facilitates easier production, while maintaining high imaging quality and stability, especially for large scan lengths and high numerical apertures.
Implementation Method 1
The polygon mirror facets reflect the bundle of rays in the crossscan plane at an angle of reflection that is the same as the angle of incidence
Implementation Method 2
the post-scan optics, arranged one after the other in the direction of the axial beam, include a correction objective with at least one first and one second correction lens
Implementation Method 3
The cylinder mirror is tilted by a first tilt angle with respect to the surface normal of the polygon mirror in the crossscan plane, the first tilt angle β being determined by the angle of incidence α
Implementation Method 4
One of the two correction lenses is tilted by a second tilt angle γ relative to the optical axis of the post-scan optics and offset by a distance a
Data Source
Figure 1
Figure 2
AI summary
The invention relates to a scanning device, comprising a light source (1), a scanning unit (2) having a polygon mirror (2.1), a pre-scanning optical unit (3), and a post-scanning optical unit (4), wherein the pre-scanning optical unit (3) is arranged in front of the polygon mirror (2.1) in such a way that a beam (1.1) coming from the light source (1) hits the polygon mirror (2.1) at an angle of incidence (α) in a cross scanning plane and the optical axis of the post-scanning optical unit (4.0) is arranged in a reflection direction of the polygon mirror (2.1). Arising distortions, a trapezoidal distortion and a scanning bow, in the imaging of the light source (1) onto a scanning line (5) are minimized in that the cylindrical mirror (4.2) of the post-scanning optical unit (4) is tilted in the cross scanning plane by a first tilting angle (β) with respect to the surface normal of the polygon mirror (2.1) and one of the two correction lenses (4.1.1, 4.1.2) of the post-scanning optical unit (4) is tilted by a second tilting angle (ϒ) with respect to the optical axis of the post-scanning optical unit (4.0) and is arranged at an offset (a).