Telecentric Mirror Array Reading Module for Deep Depth of Field
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Solution Overview
Problem
Conventional optical imaging systems in image reading devices face challenges such as deep depth of field in reduction systems leading to increased costs due to long optical path lengths and chromatic aberration, and shallow depth of field in unity magnification systems causing image blurring, especially when dealing with documents of varying sizes or surfaces.
Innovation Solution
A reading module utilizing a telecentric optical system with a mirror array and aperture stop portion, where the mirror array is composed of aspherical concave reflection mirrors and the aperture stop is strategically positioned to minimize optical path length and prevent image blurring, achieving a deep depth of field without chromatic aberration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a reduction optical system is used, then a deep depth of field is achieved, but the optical path length becomes very long (200 to 500 mm) and the cost increases
Solution Approach 1:
The patent divides the optical system into multiple rod lenses arranged in an array, where each rod lens corresponds to a specific region of the document. This segmentation allows the system to achieve deep depth of field characteristics similar to reduction systems while maintaining a compact overall structure with shorter optical path length.
Solution Approach 2:
The patent transitions from a single optical path to a two-dimensional array of rod lenses. By arranging multiple rod lenses in a matrix configuration, the system processes different document regions simultaneously through parallel optical paths, achieving both compactness and deep depth of field without requiring a long single optical path.
2Stability of the object's composition
If a reduction optical system is used, then a deep depth of field is achieved, but the number of components increases and cost increases
Solution Approach 1:
The patent merges multiple rod lenses into a single integrated array structure that functions as one unified optical component. This consolidation reduces the number of separate components and assembly steps compared to traditional reduction systems that require multiple discrete lenses and mirrors, thereby lowering cost and simplifying the device while maintaining deep depth of field.
3Length of stationary object
If a unity magnification optical system is used, then the optical path length is short (10 to 20 mm) and the construction is simple, but the depth of field is very small causing image blurring
Solution Approach 1:
The patent applies local quality by designing each rod lens in the array to have specific optical characteristics optimized for its corresponding document region. This allows the system to achieve deep depth of field locally at each rod lens while maintaining overall system compactness, overcoming the shallow depth of field limitation of unity magnification systems.
4Device complexity
If a unity magnification optical system is used, then the construction is simple and cost is reduced, but image blurring occurs due to different magnifications of individual lenses
Solution Approach 1:
The patent employs rod lenses with precisely controlled curved surfaces to ensure uniform magnification across all lenses in the array. The spherical or aspherical curvature of each rod lens is optimized to produce consistent image magnification, eliminating the image blurring and distortion that occurs in unity magnification systems where individual lenses have varying magnifications.
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 a compact, cost-effective image reading device with a deep depth of field, capable of uniformly reading documents of varying sizes and surfaces without image blurring, by using a telecentric optical system with a mirror array and aperture stop, effectively addressing the limitations of both reduction and unity magnification systems.
Implementation Method 1
a mirror array 35 composed of a plurality of aspherical concave reflection mirrors 35a to 35c
Implementation Method 2
the reflection mirrors 35a to 35c converge the image light d on the sensor 41 to form an inverted image
Implementation Method 3
an aperture stop portion 37 that the image light d passes through on its way from the reflection mirrors 35a to 35c to the sensor 41
Data Source
Figure 1
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AI summary
A reading module (50) has a light source (31), an optical system (40), and a sensor (41). The light source (31) radiates light to a document (60). The optical system (40) images, as image light (d), reflected light of the light radiated from the light source (31) to the document (60). In the sensor (41), the image light (d) imaged by the optical system (40) is converted into an electrical signal. The optical system (40) has a mirror array (35) and an aperture stop portion (37). In the mirror array (35), reflection mirrors (35a, 35b, 35c) are coupled together in an array in the main scanning direction. The aperture stop portion (37) has a first aperture (37a) adjusting the amount of the image light (d) reflected from a reflection mirror (35a, 35b, 35c) and a second aperture (37b) shielding stray light entering the first aperture (37a) from an adjacent reflection mirror (35a, 35b, 35c). Between the first and second apertures (37a, 37b), a reflection reduction mechanism (S, 70, 71, 37d) is provided that reduces reflection, toward the first aperture (37a), of light other than the image light (d) traveling from the second aperture (37b) to the first aperture (37a).