Toroidal Lens Astigmatism Balance for Barcode Readers
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Solution Overview
Problem
Imaging-based bar code readers face challenges in achieving adequate light throughput and resolution due to limitations in pinhole camera designs and single lens systems, with astigmatism issues affecting image quality, especially off-axis performance, and manufacturing complexities.
Innovation Solution
A single lens element design with a toroidal surface and cylindrical aperture stop that balances astigmatism across the field of view, allowing for a larger aperture and improved light throughput, while reducing manufacturing costs through a fixed lens and aspherical surface configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a pinhole camera design is used, then no lens is required and the design is simple, but light throughput is low and resolution is limited
Solution Approach 1:
The patent extracts the essential function of the pinhole (aperture control) while removing the limitation of no lens by introducing a specialized lens element. The pinhole aperture is retained to control light paths and reduce aberrations, while a lens is added to improve light throughput and resolution simultaneously.
Solution Approach 2:
The patent changes the optical parameters by introducing a lens with specific focal length and aperture characteristics. The lens parameters (focal length, aperture size, curvature) are optimized to achieve both high light throughput and high resolution, overcoming the pinhole's inherent limitations.
2Device complexity
If a pinhole camera design is used, then no lens is required and the design is simple, but resolution is limited due to diffraction
Solution Approach 1:
The patent extracts the essential function of the pinhole (aperture control) while removing the limitation of no lens by introducing a specialized lens element. The pinhole aperture is retained to control light paths and reduce aberrations, while a lens is added to improve light throughput and resolution simultaneously.
Solution Approach 2:
The patent changes the optical parameters by introducing a lens with specific focal length and aperture characteristics. The lens parameters (focal length, aperture size, curvature) are optimized to achieve both high light throughput and high resolution, overcoming the pinhole's inherent limitations.
3Adaptability or versatility
If a single lens design is used, then more flexibility is achieved, but off-axis performance is poor due to astigmatism
Solution Approach 1:
The patent applies asymmetry by introducing a cylindrical surface element that is oriented at a specific angle (e.g., 45 degrees) relative to the optical axis. This asymmetric cylindrical component compensates for the astigmatism caused by the main lens, balancing the focal points for different orientations and improving off-axis image quality.
Solution Approach 2:
The patent introduces a cylindrical surface as an intermediary element between the main lens and the image plane. This cylindrical component acts as a mediator that corrects the astigmatic aberration by providing additional refractive power in specific directions, thereby improving off-axis performance.
4Illumination intensity
If a larger aperture stop is used, then light throughput is improved, but astigmatism increases
Solution Approach 1:
The patent applies asymmetry by introducing a cylindrical surface element that is oriented at a specific angle (e.g., 45 degrees) relative to the optical axis. This asymmetric cylindrical component compensates for the astigmatism caused by the main lens, balancing the focal points for different orientations and improving off-axis image quality.
Solution Approach 2:
The patent introduces a cylindrical surface as an intermediary element between the main lens and the image plane. This cylindrical component acts as a mediator that corrects the astigmatic aberration by providing additional refractive power in specific directions, thereby improving off-axis performance.
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 enhances light throughput, reduces astigmatism-related image distortions, and improves signal-to-noise ratio, enabling better barcode reading performance and cost-effectiveness in mass production.
Implementation Method 1
Light reflected from a target image, e.g., a target bar code is focused through a lens of the imaging system onto the pixel array
Implementation Method 2
an aperture stop fixed in relation to the focusing lens having an opening that allows light from the target object to impinge upon the lens for focusing onto the light detecting array
Data Source
AI summary
An exemplary imaging based barcode reader has an imaging system that includes a photosensitive array, a focusing lens fixed with respect to the light detecting array which creates an image of a target object on the light detecting array; and an aperture stop fixed in relation to the focusing lens having an opening that allows light from the target object to impinge upon the lens for focusing onto the light detecting array. The focusing lens has a surface facing the aperture stop that is toroidal and in one exemplary embodiment approximates a cylinder that balances or optimizes. Astigmatism of the lens in the imaging plane located in the close proximity to the photosensitive array.