Circular Aperture Diaphragm for Fixed Focus Camera Depth of Field
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Solution Overview
Problem
Fixed focus cameras used in optical devices face challenges in maintaining image quality across varying distances due to limited depth of field, especially when capturing images of objects with arbitrary shapes like 2-D optical codes, where existing solutions either provide directional improvements or are costly and complex.
Innovation Solution
The use of a circular aperture diaphragm in conjunction with evenly distributed LED illumination sources around the optical axis enhances the depth of field, ensuring consistent image quality regardless of object orientation, and allows for flexible camera-object distance adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a fixed focus camera is used to reduce costs, then manufacturing cost is reduced, but the depth of field is limited and image quality varies with distance
Solution Approach 1:
The patent applies parameter changes by modifying the optical parameters of the fixed focus camera system. Specifically, it introduces a diaphragm with a circular aperture to control the light beam diameter, and adjusts the focal length and aperture size to optimize the depth of field. These parameter changes enable the camera to maintain acceptable image quality across a broader range of distances while keeping the fixed focus design for cost effectiveness.
2Manufacturing precision
If the distance between camera and object is adjusted to improve image quality, then image quality improves, but flexibility in positioning is reduced
Solution Approach 1:
The patent changes the optical parameters including focal length (1.8mm to 3.6mm), aperture diameter (0.9mm to 1.8mm), and diaphragm positioning to expand the depth of field from 1.2mm to 2.4mm. This allows the camera to maintain acceptable image quality across a broader range of distances, providing positioning flexibility without sacrificing image quality for barcode reading applications.
3Reliability
If a rectangular aperture diaphragm is used to improve depth of field in one direction, then depth of field increases in that direction, but it is not adapted for objects with arbitrary shapes
Solution Approach 1:
The patent applies spheroidality by using a circular aperture diaphragm instead of a rectangular one. The circular aperture with diameters of 0.9mm to 1.8mm provides uniform depth of field enhancement in all directions (360-degree rotational symmetry), making it adaptable for capturing images of objects with arbitrary shapes including 2-D barcodes, QR codes, and other circular or non-linear geometries.
4Manufacturing precision
If illumination sources are positioned to evenly illuminate the object, then image quality consistency improves, but device complexity increases
Solution Approach 1:
The patent applies segmentation by using multiple LED illumination sources (at least two, preferably three or four) positioned at different locations around the optical axis. Each LED illuminates a specific sector of the object, and their combined effect provides uniform 360-degree illumination. This segmented approach achieves illumination uniformity without requiring a complex single-source illumination system.
Solution Approach 2:
The patent transitions from a single-point or single-plane illumination source to a multi-dimensional arrangement of LED sources positioned around the optical axis in a circular or radial pattern. This spatial distribution in multiple dimensions enables uniform illumination across the entire field of view, eliminating shadows and hot spots while maintaining system simplicity.
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 increases the depth of field, enabling high-quality image capture across a broader range of distances and orientations, improving the flexibility and reliability of image recognition in optical devices, particularly for applications like 2-D barcode reading.
Implementation Method 1
The diaphragm is provided with a circular aperture and the centre point of this aperture coincides with the optical axis of the camera. The use of a circular aperture in the diaphragm significantly increases the depth of field of the camera
Implementation Method 2
The optical device is provided with a plurality of LED illumination sources, positioned around the optical axis to allow the illumination sources to evenly, that is homogeneously, illuminate an object
Implementation Method 3
The optical device comprises a camera. The camera is connected to a support which is adapted to fix the optical device at an appropriate position with an appropriate inclination with respect to a support
Data Source
Figure 1
Figure 2
Figure 3~5
AI summary
An optical device (1) including a fixed focus camera having a predetermined depth of field with an optical axis (55), wherein the optical device (1) comprises a diaphragm (5) positioned in the optical axis (55) of the camera and comprising a light passing aperture (53) for increasing the predetermined depth of field of said camera to provide an increased depth of field, wherein the diaphragm is attached to the camera, wherein the light passing aperture (53) of the diaphragm (5) is circular shaped within an opaque screen and positioned to have its centre point coincide with the optical axis (55) of the camera and wherein the optical device (1) further comprises illumination means evenly positioned around the optical axis (55)for evenly illuminating an object positioned within the increased depth of field of the camera.