Tilted Sensor Array for Keystone Correction in Optical Fingerprint Readers
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Solution Overview
Problem
Prism-based optical fingerprint readers face challenges with keystone distortion and limited image resolution due to oblique viewing angles, which affect the quality and accuracy of fingerprint images.
Innovation Solution
The solution involves tilting the image plane of the image sensor relative to the imaging lens to correct keystone distortion and using an array of imagers to increase resolution and scalability, while inscribing fiducial marks on the platen for simplified image stitching and correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If an oblique viewing angle is used in prism-based optical fingerprint readers, then the device can achieve compact size and simple structure, but keystone distortion occurs and image resolution is limited
Solution Approach 1:
The patent divides the imaging system into multiple discrete imagers arranged in an array, where each imager captures a specific portion of the fingerprint image. This segmentation allows the system to maintain the compact oblique viewing angle configuration while achieving high overall resolution through the combined output of multiple imaging elements.
2Manufacturing precision
If a single imager is used, then the device structure is simple, but image resolution is limited
Solution Approach 1:
The imaging system is segmented into multiple imagers that work together as an array. Each imager is a simple component, but their collective arrangement provides high resolution while maintaining individual component simplicity.
Solution Approach 2:
The patent transitions from a single-point imaging approach to a distributed array configuration, adding spatial dimensionality to the imaging system. This allows resolution improvement without requiring each individual imager to be overly complex.
3Ease of manufacture
If fiducial marks are inscribed on the platen, then image stitching and correction become simplified, but the platen manufacturing complexity increases
Solution Approach 1:
Fiducial marks are pre-inscribed on the platen during manufacturing, establishing reference points before the imaging process begins. This preliminary action simplifies subsequent image stitching and correction operations by providing known reference locations for alignment.
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 keystone distortion, enhances image resolution, and makes the fingerprint reader more compact and scalable, improving the overall quality and accuracy of fingerprint imaging.
Implementation Method 1
Light from the light source reaches the contact surface after passing through the prism. If the light reaches a valley, total internal reflection causes all the light to reach the image sensor after passing through the lenses. On the other hand, if the light reaches ridges pushed onto the surface, some light reaches to the image sensor and some light is absorbed in the ridges.
Data Source
AI summary
A fingerprint reader for acquiring a fingerprint image has a platen with a micro prism sheet on its underside. An arrangement of fold mirrors is used to receive light from the platen and fold the optical path twice before reaching the imagers. The reader has multiple imagers, each imager having at least an imaging lens and an image sensor. Each imager is configured so that the image plane of the image sensor is tilted relative to the optical axis of the imaging lens, such that keystone distortion in the fingerprint image is corrected.