Optical Displacement Sensing With Talbot-Length Grating Alignment
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Optical displacement sensors using diffraction gratings suffer from significant light loss due to diffraction, which impairs their performance by reducing sensitivity and signal-to-noise ratio.
Innovation Solution
The optical path length between the diffraction grating and reflective surface is configured to satisfy specific relationships with the Talbot length, such as L = Tz² or L = Tz⁴, to ensure that the diffracted light patterns coincide with the grating positions, minimizing light loss through multiple reflections and absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a laser beam is used to irradiate the measurement object, then measurement precision is improved, but the device complexity increases due to requiring precise positioning mechanisms
Solution Approach 1:
The patent replaces mechanical positioning mechanisms with a magnetic field-based tracking system. Magnets are embedded in the measurement object, and magnetic field sensors detect the position of these magnets, eliminating the need for complex mechanical positioning while maintaining measurement precision. This substitutes mechanical systems with magnetic field interactions.
2Ease of operation
If the measurement object is made small and lightweight, then ease of operation is improved, but the area for mounting measurement markers decreases
Solution Approach 1:
Traditional visual markers are replaced with magnets embedded directly into the measurement object. This allows position detection through magnetic field sensors without requiring large surface areas for markers, enabling small and lightweight objects to be measured effectively while maintaining ease of operation.
3Ease of operation
If the sensor system is made portable for field use, then ease of operation is improved, but power consumption increases
Solution Approach 1:
The system uses periodic pulsed laser irradiation instead of continuous illumination, and the measurement object is moved periodically through the measurement field. This periodic operation reduces average power consumption while maintaining measurement capabilities, enabling portable field use with limited battery power.
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 enhances light coupling to photo detectors, potentially doubling the sensitivity of the sensor by allowing light to make multiple round trips, thereby reducing light losses and improving the signal-to-noise ratio.
Implementation Method 1
a laser beam is used to irradiate the measurement object
Implementation Method 2
a magnetic field is generated in a measurement object to move the measurement object along a measurement path
Data Source
Figure 1
Figure 2
Figure 3
AI summary
An optical displacement sensor (2) comprises a reflective surface (4) and one or more diffraction gratings (6) which, together with the reflective surface, each define a respective interferometric arrangement. The reflective surface (4) is moveable relative to the diffraction grating(s) (6) or vice versa. Light from a light source (8) propagates via the interferometric arrangement(s) to produce an interference pattern at a respective set of photo detectors (10). Each interference pattern depends on the separation between the reflective surface (4) and the respective grating (6). A collimating optical arrangement (14) at least partially collimates the light between the light source (8) and the diffraction grating(s) (6). For the or each interferometric arrangement, when the reflective surface (4) or the diffraction grating (6) is in a zero-displacement position, the optical path length L of the light propagating between the diffraction grating (6) and the reflective surface (4) satisfies the relationship: to within 20% of j, where n is an integer; where Tz is the Talbot length, defined by: where λ is the wavelength of the light, and where p is the grating period of the respective diffraction grating (6). Alternatively, L may satisfy: to within 20% of p where m is an odd integer. Additionally or alternatively, the optical displacement sensor (34; 112) may comprise two or more diffraction gratings (44, 46; 116) and may be configured to provide a respective separate light beam (62, 64; 132) to each grating (44, 46; 116) using a beam-separating arrangement (48; 126) or plural light source elements.