Non-Contact Thin Medium Detection via Laser Interferometry
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Solution Overview
Problem
Existing methods for detecting foreign bodies on banknotes, such as mechanical thickness measurement, infrared detection, and ultrasound detection, face challenges with low accuracy and limited applicability, particularly in identifying thin foreign bodies and those with different reflection characteristics.
Innovation Solution
A non-contact detection method using a light source, optical splitter, reference plane, and linear array photoelectric detector to calculate optical distances and fringes, determining the presence of foreign bodies by comparing the number of fringes with a predetermined threshold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a mechanical thickness measurement device is used to detect foreign bodies on banknotes, then the detection process is simple, but the measurement accuracy is low and thin foreign bodies cannot be effectively detected
Solution Approach 1:
The patent replaces the mechanical thickness measurement system with an optical measurement system using laser interferometry. The laser beam interacts with the banknote surface and foreign bodies, creating interference patterns that are analyzed to detect foreign bodies with high precision without mechanical contact.
Solution Approach 2:
The patent changes the measurement parameter from mechanical thickness to optical path difference. By measuring the phase shift of laser light caused by foreign bodies on the banknote surface, the system achieves high-resolution detection of thin foreign bodies that mechanical devices cannot detect.
2Measurement precision
If an infrared detection device is used to detect foreign bodies on banknotes, then certain foreign bodies with different reflection characteristics can be detected, but the application field is narrow and only works for specific types of foreign bodies
Solution Approach 1:
The patent creates a universal detection system that can identify various types of foreign bodies (adhesive tapes, thin papers, glue, etc.) regardless of their material composition or reflection characteristics. The optical interferometry method measures physical presence and thickness rather than relying on specific optical properties, making it applicable to diverse foreign body types.
3Ease of operation
If an ultrasound detection device is used to detect foreign bodies on banknotes, then non-contact detection is achieved, but the measurement wavelength is long and accuracy is low
Solution Approach 1:
The patent replaces the ultrasound detection system with an optical detection system using laser interferometry. Light waves have much shorter wavelengths compared to ultrasound waves, enabling the detection of thinner foreign bodies with higher precision while maintaining non-contact operation.
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 enhances detection accuracy and sensitivity, effectively identifying foreign bodies on banknotes with improved measurement precision and broader applicability compared to existing technologies.
Implementation Method 1
obtaining time instants when target light, which is generated by reflecting light emitted by a light source via the thin medium, reaches a linear array photoelectric detector
Implementation Method 2
calculating first optical distances and second optical distances corresponding to the target light and the reference light based on the obtained time instants when the target light and the reference light reach the linear array photoelectric detector, and obtaining, by a signal processing module through using a predetermined calculation method, the number of bright and dark fringes in interference fringes
Data Source
AI summary
A method and device for non-contact detection of a thin medium (5) is disclosed. The device comprises a light source (1), an optical splitter (2), a reference plane (3), a linearly arrayed photoelectric detector (6), a signal processing module (4) and the thin medium (5). The method involves the following steps: acquiring time for targeted light which is emitted by the light source (1) and reflected by the thin medium (5) to the linearly arrayed photoelectric detector (6), and acquiring time for reference light which is emitted by the light source (1) and reflected by the reference plane (3) to the linearly arrayed photoelectric detector (6); according to the acquired time that the targeted light and the reference light arrive at the linearly arrayed photoelectric detector (6), computing a first optical path and a second optical path corresponding to the targeted light and the reference light respectively, and acquiring quantity of bright fringes and dark fringes of interference fringes according to a predetermined computing manner by the signal processing module (4); conducting difference comparison between the quantity of the bright fringes and dark fringes of the interference fringes and the quantity of the bright fringes and dark fringes of standard interference fringes according to the predetermined manner, and if the value of the comparison result is larger than the predetermined threshold value, determining that the foreign matters are positioned on the thin medium (5). The detection method and device solves the technical problems that precision is low and measuring wavelength is long caused by an existing mechanical thickness measuring device, an infrared detector and an ultrasonic detector used to detect the foreign substance on the surface of the thin medium.