Linear displacement measurement device and method based on young's double-slit interference fringes

Abstract

The application provides a linear displacement measurement device and method based on Young's double-slit interference fringes, which comprises a double-slit diaphragm, a linear array camera, a displacement measurement sliding platform, a light source and an image processing system; the displacement measurement sliding platform is a sliding table moving at a linear guide rail, the sliding table is a position of a measured object, the sliding table is connected with the linear array camera, so that the optical axis of the camera and the laser output by the light source and the double-slit diaphragm are at the same horizontal height; when measurement is performed, the laser of the light source passes through the double-slit diaphragm to form interference fringes; the linear array camera collects the interference fringe images and transmits the collected data to the image processing system; the sliding table drives the linear array camera to perform horizontal linear displacement, so that the linear array camera collects interference fringe image information corresponding to different distances; the image processing system analyzes the obtained fringe image information to obtain distance information between the measured object and the light source; the measurement device has simple structure, the measurement method is easy to implement, and the measurement precision is high and the measurement range is large.

Description

Technical Field

[0001] The present invention relates to the field of optical displacement measurement technology, in particular to a linear displacement measurement device and method based on Young's double-slit interference fringes. Background Art

[0002] Large-scale precision displacement measurement technology and equipment are the core technologies and key functional components of ultra-precision high-end equipment. Currently, common displacement measurement methods include electrical measurement, optical grating measurement, etc. The electrical measurement method has high reliability, a wide range of applications, and considerable measurement accuracy, but requires high installation and maintenance costs and a demanding measurement environment; the optical grating measurement method can meet the requirements of large scale, high speed, and high precision, but it also has problems such as periodic error accumulation or line errors, and has high requirements for manufacturing or installation. Although the holographic grating has high accuracy, it has low measurement efficiency and limited applicable occasions. The linear large-scale displacement measurement device and method based on Young's double-slit interference fringes proposed in the present invention have the advantages of high measurement accuracy, large measurement range, and non-contact. In addition, compared with the shortcomings of the traditional laser interferometer measurement device system, the system structure of this device is simple, the installation is convenient, and the scope of application is greatly improved. Summary of the Invention

[0003] The present invention proposes a linear displacement measurement device and method based on Young's double-slit interference fringes. The measurement device has a simple structure, the measurement method is easy to implement, and the measurement accuracy is high and the range is large.

[0004] The present invention adopts the following technical solutions.

[0005] A linear displacement measurement device based on Young's double-slit interference fringes includes a double-slit diaphragm, a linear array camera, a displacement measurement sliding platform, a light source, and an image processing system. The displacement measurement sliding platform is a slide that moves on a linear guide rail. The slide is the position of the object to be measured. The slide is connected to the linear array camera so that the camera optical axis is at the same horizontal height as the laser output by the light source and the double-slit diaphragm. When performing a measurement operation, the light source laser passes through the double-slit diaphragm to form interference fringes. The linear array camera collects interference fringe images and transmits the collected data to the image processing system. The slide drives the linear array camera to perform horizontal linear displacement so that the camera collects interference fringe image information corresponding to different distances. The image processing system analyzes the obtained fringe image information to obtain distance information between the object to be measured and the light source.

[0006] The light source is a semiconductor laser light source, and the linear guide is a linear guide rail with an electric ball screw mechanism.

[0007] The linear displacement measurement method based on Young's double-slit interference fringes adopts the linear displacement measurement device described above, and includes the following steps:

[0008] Step S1: Secure the linear scan camera to the slide of the displacement measurement platform and adjust the camera's optical axis to the same level as the laser light path and double-slit diaphragm output by the semiconductor laser. Adjust the lens's focus and aperture, and set the corresponding parameters in the acquisition software so that the interference fringes formed by the laser passing through the double-slit diaphragm are uniformly and clearly imaged on the linear scan camera's sensor.

[0009] Step S2: As the slide moves horizontally, the position of the interference center fringe produced by the laser passing through the double-slit aperture remains unchanged, while the spacing between the fringe periods changes. The fringe signal imaged in the sensor of the linear array camera also changes accordingly. During the horizontal displacement of the slide, the linear array camera continuously images the received interference fringes.

[0010] Step S3: The collected fringe signal is transmitted to the image processing system, which pre-processes the fringe signal and preliminarily calculates the distance information between the object to be measured and the light source.

[0011] The step S3 specifically includes the following steps:

[0012] Step S31: performing fringe preprocessing on the obtained fringe signal in units of lines;

[0013] Step S32: Except for the first row, the real-space distance ΔX(i) corresponding to the ith period fringe pixel is calculated based on the normalized fringe amplitude-frequency correction information obtained through fringe preprocessing and the imaging range of the linear array camera. The distance between the slide and the light source is preliminarily determined by calculating the relationship between ΔX(i) and the displacement value-pixel point-real-space mapping formula.

[0014] Step S33: 500 distance value points are evenly spaced within the range of 0.98 to 1.02 times before and after the initially determined displacement value. The corresponding ΔX(i) is obtained by reversely applying the mapping relationship formula based on the distance values ​​represented by the 500 points. 500 lines of superimposed light intensity images are constructed using the superimposed light intensity image, where each line of the superimposed light intensity image is the ideal interference fringe pattern formed by the distance value of the point.

[0015] Step S34: performing correlation calculation on the superimposed light intensity image and the original image to obtain correlation coefficients corresponding to different points;

[0016] Step S35: Take the maximum correlation coefficient among 500 points, and take 40 distance values ​​with equal spacing before and after the corresponding distance value within a certain range for weighted average to obtain the final accurate distance value, where the weight is the correlation coefficient corresponding to each distance value.

[0017] The fringe preprocessing includes: first performing a Hamming window algorithm correction on the original fringe signal, then performing Fourier transform on the corrected fringe signal to obtain amplitude-frequency information, and then taking the 6 points before and after the maximum power point of the frequency signal and the 6 points before and after the maximum power point of the frequency signal, performing normalization processing on the frequency signal to obtain a normalized frequency signal.

[0018] The mapping relationship formula of the displacement value-pixel point-real space determined by the stripes is:

[0019] L(i)=(ΔX(i)*d) / λ

[0020] Among them, L(i) is the actual spatial displacement value corresponding to the i-th periodic fringe, ΔX(i) is the real space distance corresponding to the i-th periodic fringe pixel, d is the spacing between the two slits, λ is the laser wavelength of the interference fringe formed, and the L(i) obtained by calculating the actual spatial displacement value ΔX(i) corresponding to each fringe period through the mapping relationship formula is the preliminarily determined distance value between the object to be measured and the light source.

[0021] The present invention relates to a linear large-range displacement measurement device and method based on Young's double-slit interference fringes. The method uses a linear array camera to collect interference fringes formed by laser passing through a double-slit aperture, and transmits the collected fringe signals to an image processing system. The image processing system measures linear displacement parameters through steps such as preprocessing and multiple corrections. Compared with the prior art, the present invention has the following beneficial effects: a linear large-range displacement measurement device and method based on Young's double-slit interference fringes are provided. Interference fringes are formed by passing laser through a double-slit aperture, and interference fringe images of an object to be measured during horizontal motion are obtained by a linear array camera. Finally, the fringe images are analyzed and processed by the image processing system to obtain horizontal displacement information of the object to be measured. The entire measuring device has a simple structure, the measuring method is easy to implement, the measurement accuracy is high and the range is large, and the device has strong practicality and broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0023] Attachment Figure 1 is a schematic structural diagram of a measuring device according to an embodiment of the present invention (wherein the direction perpendicular to the placement surface of the displacement measurement sliding platform is the Z-axis, the direction of the camera optical axis is the X-axis, the direction perpendicular to the intersection plane formed by the X-axis and the Z-axis is the Y-axis, and the dot-dash line indicates the imaging position of the laser relative to the double-slit aperture and the linear array camera, i.e., the laser path);

[0024] Attachment Figure 2Schematic diagram of the simulation of the present invention in Matlab software (wherein, (a) is the fringe image corresponding to different distances between the camera and the object to be measured obtained by continuous shooting of the simulated linear array camera; (b) is the normalized frequency information of the frequency of the highest power point and the six frequency values ​​before and after it in the Fourier transform of each row of fringe in Figure (a) after weighted average, where the weight is the power value at each frequency; (c) is the actual fringe spacing and the calculated fringe spacing obtained based on the frequency information in Figure (b), as well as the error in the calculated fringe spacing; (d) is the actual distance and the preliminary calculated distance obtained based on the calculated fringe spacing in Figure (c) , and the error of the preliminary calculated distance. (e) is the correlation result obtained after reconstructing the interference fringes at the dotted line in Figure (a) and their corrected distance. Among them, the corrected distance is 500 equally divided values ​​obtained by equally dividing within a certain range before and after the preliminary calculated distance value. (f) shows the final accurate distance value of each row of stripes and its error. Among them, the final accurate distance value is obtained by reconstructing the stripes with the corrected distance of each row of stripes in Figure (a), and then selecting the distance value at the point where the correlation coefficient between the reconstructed stripes and the original stripes is the largest and the 20 distance values ​​before and after it for weighted averaging, where the weight is the correlation coefficient corresponding to each distance value). DETAILED DESCRIPTION

[0025] As shown in the figure, a linear displacement measurement device based on Young's double-slit interference fringes includes a double-slit diaphragm, a linear array camera, a displacement measurement sliding platform, a light source and an image processing system; the displacement measurement sliding platform is a slide that moves on a linear guide rail, the slide is the position of the object to be measured, and the slide is connected to the linear array camera so that the camera optical axis and the laser output by the light source and the double-slit diaphragm are at the same horizontal height; when performing a measurement operation, the light source laser passes through the double-slit diaphragm to form interference fringes; the linear array camera collects the interference fringe image and transmits the collected data to the image processing system; the slide drives the linear array camera to perform horizontal linear displacement so that the camera collects interference fringe image information corresponding to different distances; the image processing system analyzes the obtained fringe image information to obtain the distance information between the object to be measured and the light source.

[0026] The light source is a semiconductor laser light source, and the linear guide is a linear guide rail with an electric ball screw mechanism.

[0027] The linear displacement measurement method based on Young's double-slit interference fringes adopts the linear displacement measurement device described above, and includes the following steps:

[0028] Step S1: Secure the linear scan camera to the slide of the displacement measurement platform and adjust the camera's optical axis to the same level as the laser light path and double-slit diaphragm output by the semiconductor laser. Adjust the lens's focus and aperture, and set the corresponding parameters in the acquisition software so that the interference fringes formed by the laser passing through the double-slit diaphragm are uniformly and clearly imaged on the linear scan camera's sensor.

[0029] Step S2: As the slide moves horizontally, the position of the interference center fringe produced by the laser passing through the double-slit aperture remains unchanged, while the spacing between the fringe periods changes. The fringe signal imaged in the sensor of the linear array camera also changes accordingly. During the horizontal displacement of the slide, the linear array camera continuously images the received interference fringes.

[0030] Step S3: The collected fringe signal is transmitted to the image processing system, which pre-processes the fringe signal and preliminarily calculates the distance information between the object to be measured and the light source.

[0031] The step S3 specifically includes the following steps:

[0032] Step S31: performing fringe preprocessing on the obtained fringe signal in units of lines;

[0033] Step S32: Except for the first row, the real-space distance ΔX(i) corresponding to the ith period fringe pixel is calculated based on the normalized fringe amplitude-frequency correction information obtained through fringe preprocessing and the imaging range of the linear array camera. The distance between the slide and the light source is preliminarily determined by calculating the relationship between ΔX(i) and the displacement value-pixel point-real-space mapping formula.

[0034] Step S33: 500 distance value points are evenly spaced within the range of 0.98 to 1.02 times before and after the initially determined displacement value. The corresponding ΔX(i) is obtained by reversely applying the mapping relationship formula based on the distance values ​​represented by the 500 points. 500 lines of superimposed light intensity images are constructed using the superimposed light intensity image, where each line of the superimposed light intensity image is the ideal interference fringe pattern formed by the distance value of the point.

[0035] Step S34: performing correlation calculation on the superimposed light intensity image and the original image to obtain correlation coefficients corresponding to different points;

[0036] Step S35: Take the maximum correlation coefficient among 500 points, and take 40 distance values ​​with equal spacing before and after the corresponding distance value within a certain range for weighted average to obtain the final accurate distance value, where the weight is the correlation coefficient corresponding to each distance value.

[0037] The fringe preprocessing includes: first performing a Hamming window algorithm correction on the original fringe signal, then performing Fourier transform on the corrected fringe signal to obtain amplitude-frequency information, and then taking the 6 points before and after the maximum power point of the frequency signal and the 6 points before and after the maximum power point of the frequency signal, performing normalization processing on the frequency signal to obtain a normalized frequency signal.

[0038] The mapping relationship formula of the displacement value-pixel point-real space determined by the stripes is:

[0039] L(i)=(ΔX(i)*d) / λ

[0040] Among them, L(i) is the actual spatial displacement value corresponding to the i-th periodic fringe, ΔX(i) is the real space distance corresponding to the i-th periodic fringe pixel, d is the spacing between the two slits, λ is the laser wavelength of the interference fringe formed, and the L(i) obtained by calculating the actual spatial displacement value ΔX(i) corresponding to each fringe period through the mapping relationship formula is the preliminarily determined distance value between the object to be measured and the light source.

[0041] In this example, the linear displacement measuring device is used to directly measure the displacement accuracy of the slide, and the object to be measured is the slide itself.

Claims

1. A linear displacement measurement method based on Young's double-slit interference fringes, characterized by: The following steps are included: Step S1: Secure the linear scan camera to the slide of the displacement measurement platform and adjust the camera's optical axis to the same level as the laser light path and double-slit diaphragm output by the semiconductor laser. Adjust the lens's focus and aperture, and set the corresponding parameters in the acquisition software so that the interference fringes formed by the laser passing through the double-slit diaphragm are uniformly and clearly imaged on the linear scan camera's sensor. Step S2: As the slide moves horizontally, the position of the interference center fringe produced by the laser passing through the double-slit aperture remains unchanged, while the spacing between the fringe periods changes. The fringe signal imaged in the sensor of the linear array camera also changes accordingly. During the horizontal displacement of the slide, the linear array camera continuously images the received interference fringes. Step S3: The collected fringe signal is transmitted to the image processing system, which pre-processes the fringe signal and preliminarily calculates the distance information between the object to be measured and the light source; The step S3 specifically The following steps are included: Step S31: performing fringe preprocessing on the obtained fringe signal in units of lines; Step S32: Except for the first row, the real-space distance ΔX(i) corresponding to the ith period fringe pixel is calculated based on the normalized fringe amplitude-frequency correction information obtained through fringe preprocessing and the imaging range of the linear array camera. The distance between the slide and the light source is preliminarily determined by calculating the relationship between ΔX(i) and the displacement value-pixel point-real-space mapping formula. Step S33: 500 distance value points are evenly spaced within the range of 0.98 to 1.02 times before and after the initially determined displacement value. The corresponding ΔX(i) is obtained by reversely applying the mapping relationship formula based on the distance values ​​represented by the 500 points. 500 lines of superimposed light intensity images are constructed using the superimposed light intensity image, where each line of the superimposed light intensity image is the ideal interference fringe pattern formed by the distance value of the point. Step S34: performing correlation calculation on the superimposed light intensity image and the original image to obtain correlation coefficients corresponding to different points; Step S35: Take the maximum correlation coefficient among the 500 points, and take the corresponding distance value within a certain range of equal intervals before and after it, and take a total of 40 distance values ​​for weighted average to obtain the final accurate distance value, where the weight is the correlation coefficient corresponding to each distance value; The fringe preprocessing includes: firstly performing a Hamming window algorithm correction on the original fringe signal, then performing a Fourier transform on the corrected fringe signal to obtain amplitude-frequency information, and then taking the maximum power point of the frequency signal and the six points before and after the maximum power point of the frequency signal, performing a normalization process on the frequency signal to obtain a normalized frequency signal; The mapping relationship formula of the displacement value-pixel point-real space determined by the stripes is: L(i)=(ΔX(i)*d) / λ Among them, L(i) is the actual spatial displacement value corresponding to the i-th periodic fringe, ΔX(i) is the real space distance corresponding to the i-th periodic fringe pixel, d is the spacing between the two slits, λ is the laser wavelength of the interference fringe formed, and the L(i) obtained by calculating the actual spatial displacement value ΔX(i) corresponding to each fringe period through the mapping relationship formula is the preliminarily determined distance value between the object to be measured and the light source.

2. A linear displacement measurement device based on Young's double-slit interference fringes, employing the linear displacement measurement method based on Young's double-slit interference fringes as claimed in claim 1, characterized in that: The system comprises a double-slit diaphragm, a linear array camera, a displacement measurement sliding platform, a light source, and an image processing system. The displacement measurement sliding platform is a slide that moves on a linear guide rail. The slide is the location of the object to be measured and is connected to the linear array camera so that the camera optical axis is at the same horizontal height as the laser output by the light source and the double-slit diaphragm. When performing a measurement operation, the light source laser passes through the double-slit diaphragm to form interference fringes. The linear array camera collects the interference fringes image and transmits the collected data to the image processing system. The slide drives the linear array camera to perform horizontal linear displacement so that the camera collects interference fringes image information corresponding to different distances. The image processing system analyzes the obtained fringes image information to obtain the distance information between the object to be measured and the light source.

3. The linear displacement measurement device based on Young's double-slit interference fringes according to claim 2, characterized in that: The light source is a semiconductor laser light source, and the linear guide is a linear guide rail with an electric ball screw mechanism.

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