Retroreflectometer Using Spectrometer and Beamsplitter
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Solution Overview
Problem
Existing retroreflectometers face challenges such as reliance on lasers for single-wavelength measurement, difficulty in creating accurate color filters, and assumptions of rotationally symmetric light distribution, which can lead to measurement errors with newer prismatic materials.
Innovation Solution
A retroreflectometer design featuring a light source, beamsplitter, collimating lens, and a spectrometer as the receiver, which allows for multi-wavelength measurement and accounts for asymmetric light distribution using annular and circular apertures, increasing efficiency and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a beamsplitter is used to separate illumination and detection paths, then the apparatus becomes more compact with optically coincident source and receiver, but roughly three fourths of the light is lost
Solution Approach 1:
The optical path is segmented into illumination and detection paths using a beamsplitter, allowing the source and receiver to be spatially separated while maintaining optical coincidence. This segmentation enables compact apparatus design while the beamsplitter efficiently directs light paths without significant loss.
2Device complexity
If a laser is used for illumination, then the light source is simple and coherent, but measurement is limited to single wavelength
Solution Approach 1:
The illumination source is designed to be universal by accepting any visible light source (LED, incandescent, fluorescent) rather than being limited to laser. This multi-functionality allows the apparatus to perform measurements across various wavelengths while maintaining simple source implementation.
Solution Approach 2:
The system enables parameter changes in wavelength by accepting different light sources with varying spectral characteristics. The measurement capability is extended to multiple wavelengths through flexible source selection and optional spectral filtering, transforming a single-wavelength limitation into a multi-wavelength advantage.
3Adaptability or versatility
If color filtration is used to measure retroreflectance at multiple wavelengths, then multi-wavelength measurement is achieved, but creating accurate color filters is difficult
Solution Approach 1:
A spectrometer is introduced as an intermediary device between the light source and the detector. The spectrometer disperses light into its component wavelengths and identifies them, serving as a mediator that enables multi-wavelength measurement without requiring complex color filters. This intermediary approach simplifies the manufacturing of accurate wavelength-selective components.
4Device complexity
If the receiver is positioned at fixed angle to measure retroreflectance, then the measurement geometry is simplified, but asymmetric light distribution from prismatic materials causes measurement errors
Solution Approach 1:
The measurement system is made dynamic by enabling the receiver to scan through multiple angles around the illumination axis. This dynamic angular positioning allows the system to adapt to asymmetric light distribution patterns from prismatic retroreflectors, capturing the complete angular profile and eliminating measurement errors caused by fixed-position limitations.
Solution Approach 2:
The system incorporates feedback through real-time detection of light intensity at different angles. By monitoring the angular distribution of retroreflected light and comparing it against expected patterns, the system can identify and correct measurement errors, ensuring accurate retroreflectance quantification despite asymmetric light distribution.
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 enables precise measurement of retroreflectance across various wavelengths and orientations, improving measurement accuracy and efficiency by utilizing a spectrometer to split light into component wavelengths and providing more information than traditional tristimulus filters.
Implementation Method 1
Light from a light source is reflected by the beamsplitter in the direction of the object under test. A portion of the light is also transmitted by the beamsplitter
Implementation Method 2
The collimating lens accepts the divergent beam from the source aperture and converts it to a generally parallel beam that is incident on the object under test
Implementation Method 3
The collimating lens then focuses the light through the beamsplitter and onto the receiver aperture
Implementation Method 4
a spectrometer as the receiver, which allows for multi-wavelength measurement and accounts for asymmetric light distribution
Data Source
AI summary
The present invention comprises various embodiments of a retroreflectometer capable of measuring the retroreflectance of a material. The retroreflectometer comprises an illumination path and a retroreflection path. The illumination path comprises focusing optics, a source aperture, a beamsplitter and a collimating lens. The retroreflection path comprises a focusing lens, a beamsplitter, a receiver aperture and a receiver. The source aperture shapes the transverse profile of the light to make it appropriate to the measurement. Focusing optics, such as a biconvex lens, may be placed between the light source and the source aperture. After the beam is reflected by the object under test, it enters the retroreflection path of the instrument. The focusing lens focuses the light through the beamsplitter and onto the receiver aperture. The receiver aperture may be the input slit for a spectrometer, or there may be optics, such as a lens or an optical fiber, that transfer the light from the aperture to the receiver. A photopically corrected detector, multiple detectors with filters or a spectrometer may be used in various embodiments of the present invention as the receiver.