Displacement triangulation apparatus and method based on laser interference fringes

Abstract

The application provides a displacement triangulation device and method based on laser interference fringes, which comprises a linear array camera, a double-slit diaphragm, a laser light source and an image processing system; the linear array camera is used to collect interference fringe signals received after laser passes through the double-slit diaphragm and is reflected by the surface of a to-be-measured object, and transmit the collected fringe signals to the image processing system; the double-slit diaphragm is assembled with the laser light source as a module to generate interference fringes; the laser light source is used to emit laser to pass through the double-slit diaphragm to form interference fringes; and the image processing system analyzes and processes the fringe image to obtain displacement information of the to-be-measured object. Compared with the traditional circular spot laser triangulation technology, the measurement device combines the advantages of laser triangulation and interference fringes, the fringe spot contains more characteristic information, the structure is simple, the measurement method is easy to realize, and the measurement precision is high.

Description

Technical Field

[0001] The present invention relates to the field of optical displacement measurement technology, and in particular to a displacement triangulation measurement device and method based on laser interference fringes. Background Art

[0002] Precision displacement measurement technology and equipment are core functional components in industrial production. Currently, common displacement measurement methods include optical interferometry measurement, time-grating measurement, etc. The time-grating measurement method relies on traveling wave signals containing spatial and temporal information, and the displacement measurement accuracy is relatively high, but it requires extremely high-precision installation and manufacturing to prevent the consistency between the gratings from being destroyed; the traditional optical interferometry measurement method can meet the requirements of large range and high precision, but it also has problems such as complex optical interference systems and high costs, and is easily affected by factors such as air disturbances and humidity changes. Compared with the traditional circular spot laser triangulation measurement technology, the displacement triangulation measurement device and method based on laser interference fringes proposed in the present invention have the advantages of high measurement accuracy, more characteristic information contained in the fringed light spot, simple system structure, convenient installation, and non-contact, and its scope of application is greatly improved. Summary of the Invention

[0003] The purpose of the present invention is to provide a displacement triangulation measurement device and method based on laser interference fringes; the measurement device has a simple structure, the measurement method has high measurement accuracy and is easy to implement.

[0004] To achieve the above object, the technical solution of the present invention is as follows:

[0005] A displacement triangulation measurement device based on laser interference fringes comprises a line array camera, a double-slit aperture, a laser light source, and an image processing system. The line array camera is used to collect interference fringe signals formed by laser light passing through the double-slit aperture and reflected by the surface of an object to be measured, and transmit the collected fringe signals to the image processing system. The double-slit aperture and the laser light source are assembled into a module to generate interference fringes. The laser light source is used to emit laser light through the double-slit aperture to form interference fringes. The image processing system analyzes and processes the fringe images to obtain displacement information of the object to be measured.

[0006] A displacement triangulation measurement method based on laser interference fringes is implemented using a displacement triangulation measurement device based on laser interference fringes, and includes the following steps:

[0007] Step S1: A laser light source emits a laser beam that passes through a double-slit aperture, forming interference fringes. The laser beam then reaches the smooth surface of the object to be measured at a certain incident angle θ, which reflects the interference fringes at the same height. A linear array camera's photosensitive unit receiving surface is then parallel to the smooth surface of the object to be measured and fixed on the laser reflection path, maintaining an angle of π / 2-θ between the receiving surface and the reflection path, and receiving a clear interference fringe image signal.

[0008] Step S2: As the object to be measured moves in a direction perpendicular to the normal of the surface of the object to be measured, the direction of the laser light path remains unchanged, and the incident point on the surface of the object to be measured shifts. The interference fringe image signal formed in the sensor of the linear array camera also shifts horizontally in the time domain. During the displacement of the object to be measured, the interference fringes received are continuously imaged by the linear array camera.

[0009] Step S3: The collected interference fringe image signal is transmitted to an image processing system, and the image processing system pre-processes the interference fringe image signal and preliminarily extracts the displacement information of the object to be measured.

[0010] Preferably, the step S3 specifically includes the following steps:

[0011] Step S31: performing image preprocessing on the obtained interference fringe image signal;

[0012] Step S32: performing a Fourier transform operation on the pre-processed time domain interference fringe signal to obtain a spectrum; performing a zero matrix filling operation on the interference fringe signal spectrum;

[0013] Step S33: performing an inverse Fourier transform operation on the zero-filled interference fringe signal spectrum to obtain a time-domain interference fringe signal with an increased number of sampling points;

[0014] Step S34: performing a first cross-correlation calculation on the first frame of up-sampled time domain signal acquired by the line scan camera after processing in steps S31-S33 and each frame of up-sampled time domain signal, wherein the first frame of up-sampled time domain signal is subjected to the first cross-correlation calculation with the first frame of up-sampled time domain signal to obtain a first frame of autocorrelation sequence, and the first frame of up-sampled time domain signal is subjected to the first cross-correlation calculation with each of the remaining frames of up-sampled time domain signal to obtain multiple groups of first cross-correlation sequences; then, each first cross-correlation sequence is subjected to a cross-correlation operation with the first frame of autocorrelation sequence to obtain multiple groups of second cross-correlation sequences, and a cross-correlation pixel offset value is calculated.

[0015] Step S35: Substitute the obtained cross-correlation pixel offset value into the relative displacement-cross-correlation offset value mapping relationship to obtain the relative displacement of the object to be measured.

[0016] Preferably, the image preprocessing includes performing a Gaussian filtering operation on the original time-domain fringe signal to filter out high-frequency burr noise.

[0017] Preferably, the relative displacement-cross-correlation offset value mapping formula is:

[0018] d(i)=(ΔX(i)*p) / (2*N*tan(θ))

[0019] Where d(i) is the real-space displacement of the fringe in the i-th frame relative to the fringe in the first frame, ΔX(i) is the pixel offset corresponding to the second cross-correlation sequence between the fringe in the i-th frame and the fringe in the first frame, p is the pixel size of the linear array camera, θ is the incident angle between the laser optical path and the surface of the object to be measured, and N is the time domain upsampling factor.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention provides a displacement triangulation measurement device and method based on laser interference fringes. Interference fringes are formed by passing laser light through a double-slit aperture. The interference fringes are emitted onto the surface of the object to be measured and then reflected and captured by a linear array camera. Finally, the fringe images are analyzed and processed by an image processing system to obtain displacement information of the object to be measured along the reflection normal direction. Compared with traditional circular spot laser triangulation measurement technology, the entire measurement device has a simple structure, low cost, easy measurement method, high measurement accuracy, and the fringe spots contain rich feature information. It has strong practicality and broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the structure of the displacement triangulation measurement device based on laser interference fringes of the present invention;

[0023] Figure 2 This is a flow chart of interference fringe processing and relative displacement calculation of the present invention;

[0024] Figure 3 Schematic diagram of the displacement triangulation method process in one embodiment of the present invention.

[0025] In the picture:

[0026] 1-Double slit aperture; 2-Laser light source module; 3-Image processing system; 4-Linear array camera with imaging plane perpendicular to the displacement direction of the object to be measured; 5-Initial position of the object to be measured; 6-Position of the object to be measured during displacement; Red dotted line - Surface normal of the object to be measured; Black arrow - Displacement direction of the object to be measured; Red arrow - Laser centerline path; Blue thin line - Distribution of the interference field in space when the object to be measured is in its initial position; Orange dotted line - Distribution of the interference field in space after the object to be measured has been displaced. DETAILED DESCRIPTION

[0027] The following is combined with Figure 1-3 , the technical solution of the present invention is described in detail.

[0028] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present application belongs.

[0029] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0030] like Figure 1 As shown, this embodiment provides a displacement triangulation measurement device based on laser interference fringes, including a line array camera, a double-slit aperture, a laser light source, and an image processing system. The line array camera is used to collect interference fringe signals formed by laser light passing through the double-slit aperture and reflected by the surface of the object to be measured, and transmit the collected fringe signals to the image processing system. The double-slit aperture is assembled into a module with the laser light source to generate interference fringes. The laser light source is used to emit laser light through the double-slit aperture to form interference fringes. The image processing system analyzes and processes the fringe images to obtain displacement information of the object to be measured.

[0031] In this embodiment, the image processing system is implemented on a computer, which is equipped with a preprocessing module and a displacement information extraction module. The preprocessing module can obtain interference fringes after noise is filtered out by preprocessing the original fringes, and calculate the relative displacement of the object based on the pixel offset values ​​obtained by fringes upsampling and two consecutive cross-correlations between the first frame and other frames. In addition, it should be noted that the above image processing process, including the preprocessing module and the displacement information extraction module, is based on Figure 1 This is accomplished based on the interference optical path shown.

[0032] like Figure 2 As shown, this example also provides a linear large-range displacement measurement method based on the above-mentioned device and Young's double-slit interference fringes, comprising the following steps:

[0033] Step S1: A laser beam emitted from a laser light source passes through a double-slit aperture, forming interference fringes. The beam then reaches the surface of the object under test at a specific angle of incidence, θ, where θ is the angle of incidence formed between the laser beam path and the surface normal. The surface of the object under test then reflects the interference fringes at the same height. The receiving surface of the line scan camera's photosensitive unit is then positioned parallel to the surface of the object under test and fixed in the reflected laser beam path, maintaining an angle of π / 2-θ with the reflected beam path. This allows for the detection of a clear interference fringe image signal.

[0034] Step S2: As the object to be measured moves in a direction perpendicular to the normal of its surface, the direction of the laser light path remains unchanged, and the incident point on the surface of the object to be measured produces horizontal displacement. The fringe signal imaged in the sensor of the linear array camera also produces horizontal displacement in the time domain. During the displacement of the object to be measured, the interference fringes received are continuously imaged by the linear array camera.

[0035] Step S3: The collected interference fringe signal is transmitted to the image processing system, and the image processing system pre-processes the interference fringe signal and preliminarily extracts the displacement information of the object to be measured.

[0036] In this embodiment, step S3 specifically includes the following steps:

[0037] Step S31: performing image preprocessing on the obtained interference fringe signal;

[0038] Step S32: Perform Fourier transform operation on the pre-processed time domain interference fringe signal to obtain its spectrum. Then, perform zero matrix filling operation on the interference fringe signal spectrum.

[0039] Step S33: performing an inverse Fourier transform operation on the zero-filled interference fringe signal spectrum to obtain a time-domain interference fringe signal with an increased number of sampling points.

[0040] Step S34: Perform a first cross-correlation calculation on the first frame of upsampled time domain signals acquired by the line scan camera and each frame of upsampled time domain signals to obtain a first cross-correlation sequence. Each cross-correlation sequence is then cross-correlated with the first frame of autocorrelation sequence to obtain a second cross-correlation sequence, and their cross-correlation offset values ​​are calculated.

[0041] Step S35: Substitute the obtained cross-correlation offset value into the relative displacement-cross-correlation offset value mapping relationship to obtain the relative displacement of the object to be measured.

[0042] The relative displacement-cross-correlation offset value mapping formula is:

[0043] d(i)=(ΔX(i)*p) / (2*N*tan(θ))

[0044] Where d(i) is the real-space displacement of the fringe in the i-th frame relative to the fringe in the first frame, ΔX(i) is the pixel offset corresponding to the second cross-correlation sequence between the fringe in the i-th frame and the fringe in the first frame, p is the pixel size of the linear array camera, θ is the incident angle between the laser optical path and the surface of the object to be measured, and N is the time domain upsampling factor.

[0045] like Figure 3 As shown in the figure, a schematic diagram of specific operation steps is provided; among them, (a) is a multi-frame interference fringe image continuously captured by the linear array camera during the displacement process; (b) is the intensity curve of the dotted interference fringes in Figure (a); (c) is the cross-correlation sequence of the dotted interference fringes in Figure (a) after two consecutive cross-correlation operations; (d) is the relative displacement curve calculated after the interference fringes of all frames in Figure (a) are processed and the relevant parameters are substituted into the relative displacement-cross-correlation offset value mapping relationship formula.

[0046] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other manner. Any person skilled in the art may utilize the above-disclosed technical content to modify or modify the present invention into equivalent embodiments. However, any simple modifications, equivalent variations, and modifications to the above embodiments that do not depart from the technical content of the present invention and are based on the technical essence of the present invention remain within the scope of protection of the present invention.

Claims

1. A displacement triangulation measurement method based on laser interference fringes, characterized in that: The method is implemented using a displacement triangulation measurement device based on laser interference fringes, comprising a line array camera, a double-slit aperture, a laser light source, and an image processing system. The line array camera is used to collect interference fringe signals formed by laser light passing through the double-slit aperture and reflected by the surface of the object to be measured, and transmit the collected fringe signals to the image processing system. The double-slit aperture and the laser light source are assembled into a module to generate interference fringes. The laser light source is used to emit laser light through the double-slit aperture to form interference fringes. The image processing system analyzes and processes the fringe images to obtain displacement information of the object to be measured. The measuring method comprises the following steps: Step S1: A laser light source emits a laser beam that passes through a double-slit aperture, forming interference fringes. The laser beam then reaches the smooth surface of the object to be measured at a certain incident angle θ, which reflects the interference fringes at the same height. A linear array camera's photosensitive unit receiving surface is then parallel to the smooth surface of the object to be measured and fixed on the laser reflection path, maintaining an angle of π / 2-θ between the receiving surface and the reflection path, and receiving a clear interference fringe image signal. Step S2: As the object to be measured moves in a direction perpendicular to the normal of the surface of the object to be measured, the direction of the laser light path remains unchanged, and the incident point on the surface of the object to be measured shifts. The interference fringe image signal formed in the sensor of the linear array camera also shifts horizontally in the time domain. During the displacement of the object to be measured, the interference fringes received are continuously imaged by the linear array camera. Step S3: transmitting the collected interference fringe image signal to an image processing system, which pre-processes the interference fringe image signal and preliminarily extracts the displacement information of the object to be measured; The step S3 specifically includes the following steps: Step S31: performing image preprocessing on the obtained interference fringe image signal; Step S32: performing a Fourier transform operation on the pre-processed time domain interference fringe signal to obtain a spectrum; performing a zero matrix filling operation on the interference fringe signal spectrum; Step S33: performing an inverse Fourier transform operation on the interference fringe signal spectrum after the zero matrix filling operation to obtain a time domain interference fringe signal with an increased number of sampling points; Step S34: performing a first cross-correlation calculation on the first frame up-sampled time domain signal acquired by the line scan camera after the processing in steps S31-S33 and each frame up-sampled time domain signal, wherein the first frame up-sampled time domain signal is first cross-correlated with the first frame up-sampled time domain signal to obtain a first frame autocorrelation sequence, and the first frame up-sampled time domain signal is first cross-correlated with each of the remaining frames up-sampled time domain signals to obtain multiple groups of first cross-correlation sequences; then, cross-correlating each first cross-correlation sequence with the first frame autocorrelation sequence to obtain multiple groups of second cross-correlation sequences, and calculating a cross-correlation pixel offset value; Step S35: Substitute the obtained cross-correlation pixel offset value into the relative displacement-cross-correlation offset value mapping relationship to obtain the relative displacement of the object to be measured.

2. The displacement triangulation measurement method based on laser interference fringes according to claim 1, characterized in that: The image preprocessing includes performing a Gaussian filtering operation on the original time domain fringe signal to filter out high-frequency burr noise.

3. The displacement triangulation measurement method based on laser interference fringes according to claim 1, characterized in that: The relative displacement-cross-correlation offset value mapping formula is: d(i)=(ΔX(i)*p) / (2*N*tan(θ)) Where d(i) is the real-space displacement of the fringe in the i-th frame relative to the fringe in the first frame, ΔX(i) is the pixel offset corresponding to the second cross-correlation sequence between the fringe in the i-th frame and the fringe in the first frame, p is the pixel size of the linear array camera, θ is the incident angle between the laser optical path and the surface of the object to be measured, and N is the time domain upsampling factor.

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