Fingerprint Sensor Finger Movement Estimation
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Solution Overview
Problem
Existing fingerprint sensor technologies face challenges in accurately estimating finger movement direction and speed, particularly when using small sensors with low memory and computational complexity, as ridges in the periphery of the fingerprint pattern can be near parallel, making it difficult to distinguish between movement directions.
Innovation Solution
A method involving acquiring reference and candidate fingerprint images, determining match parameter values for different finger movement directions, and evaluating local extremum match parameters to estimate finger movement direction and speed, even in areas with parallel ridges, by considering multiple candidate directions and varying acquisition frequencies to improve accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a small fingerprint sensor is used to reduce hardware size and cost, then device complexity and power consumption are reduced, but measurement precision of finger movement direction and speed deteriorates due to parallel ridges in the periphery
Solution Approach 1:
The fingerprint sensor area is divided into multiple reference areas, with each reference area having associated candidate areas displaced in different candidate finger movement directions. This segmentation allows the system to evaluate multiple directional hypotheses simultaneously, resolving the ambiguity caused by parallel ridges in small sensor areas.
Solution Approach 2:
The patent introduces a temporal dimension by acquiring fingerprint images at multiple different times and evaluating match parameter values across time sequences. This temporal dimension provides additional information to disambiguate movement direction, complementing the spatial information from the small sensor area.
2Device complexity
If block matching method is used to track finger movement, then computational complexity and memory requirements are reduced, but measurement precision of finger movement estimation deteriorates
Solution Approach 1:
The reference fingerprint image is divided into multiple reference areas, each with corresponding candidate areas displaced in different directions. This segmentation enables parallel evaluation of multiple movement hypotheses using simple block matching, achieving both low computational complexity and high precision through systematic comparison.
Solution Approach 2:
The system evaluates match parameter values for multiple candidate directions and uses feedback from these evaluations to determine the most likely finger movement direction. The local extremum match parameter values provide feedback that guides the selection of the correct movement direction, improving precision without increasing computational complexity.
3Measurement precision
If multiple candidate finger movement directions are evaluated to improve measurement precision, then finger movement estimation accuracy improves, but use of energy increases due to additional processing
Solution Approach 1:
Instead of evaluating all possible movement directions exhaustively, the patent uses partial action by selecting a limited set of candidate finger movement directions based on the specific reference area and its associated candidate areas. This partial evaluation approach achieves sufficient precision while minimizing energy consumption.
Solution Approach 2:
The system pre-establishes the relationship between reference areas and candidate areas, including the displacement vectors for candidate finger movement directions. This preliminary preparation allows the actual movement estimation to proceed with minimal computational steps, reducing real-time energy consumption while maintaining precision.
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 approach allows for accurate estimation of finger movement direction and speed, even with small fingerprint sensors, by evaluating multiple candidate directions and optimizing image acquisition and processing, resulting in improved navigation system performance with reduced complexity and energy consumption.
Implementation Method 1
a capacitive fingerprint sensor detecting a measure indicative of the capacitive coupling between each sensing element in an array of sensing elements and a finger surface touching the fingerprint sensor surface
Data Source
AI summary
The present invention relates to a method of estimating a finger movement direction of a finger, comprising the steps of: a) acquiring a reference fingerprint image; b) acquiring at least one candidate fingerprint image at each acquisition time in a time sequence of acquisition times; c) determining, for each of the acquisition times, a match parameter value for each of a plurality of candidate finger movement directions, the match parameter value being indicative of a correlation between a reference fingerprint image portion and a candidate fingerprint image portion corresponding to displacement in the candidate finger movement direction; d) determining, for each of the candidate finger movement directions, a local extremum match parameter value indicating a maximum correlation for the time sequence of acquisition times; and e) estimating the finger movement based on an evaluation of the determined local extremum match parameters.