Displacement triangulation device and method based on laser interference fringes

Abstract

The invention provides a displacement triangulation measuring device and method based on laser interference fringes. The measuring device comprises a linear array camera, a double-slit diaphragm, a laser light source and an image processing system. The line-scan digital camera is used for collecting interference fringe signals which are formed by laser penetrating through the double-slit diaphragm and received after the laser is reflected by the surface of an object to be measured, and transmitting the collected fringe signals to the image processing system; the double-slit diaphragm and the laser light source are assembled into a module for generating interference fringes; the laser light source is used for emitting laser to pass through the double-slit diaphragm to form interference fringes; and the image processing system analyzes and processes the stripe image to obtain displacement information of the object to be measured. Compared with a traditional circular light spot laser triangulation measurement technology, the measurement device integrates the advantages of a laser triangulation method and interference fringes, the fringe light spots contain more feature information, the structure is simple, the measurement method is easy to implement, 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 and time-grating measurement. 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 spot, simple system structure, convenient installation, and non-contact, and the 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 measuring device based on laser interference fringes comprises a linear array camera, a double slit aperture, a laser light source and an image processing system; the linear array camera is used for collecting interference fringe signals formed by laser passing through the double slit aperture and received after being reflected by the surface of an object to be measured, and the collected fringe signals are transmitted 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 for emitting laser light to pass 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, the method is implemented by a displacement triangulation measurement device based on laser interference fringes, and comprises the following steps:

[0007] Step S1: A laser light source emits a laser beam that passes through a double slit aperture to form interference fringes, and reaches the smooth surface of the object to be measured at a certain incident angle θ, and the smooth surface of the object to be measured reflects the fringe interference field at the same height; then the receiving surface of the linear array camera photosensitive unit is kept parallel to the smooth surface of the object to be measured, and fixed on the laser reflection light path, so that the receiving surface of the linear array camera photosensitive unit maintains an angle of π / 2-θ with the reflection light path, and a clear interference fringe image signal is received;

[0008] Step S2: As the object to be measured moves in a direction perpendicular to the normal line of the surface of the object to be measured, the direction of the laser light path remains unchanged, the incident point on the surface of the object to be measured is displaced, and the interference fringe image signal formed in the sensor of the linear array camera also moves 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 the 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 Fourier transform operation on the pre-processed time domain interference fringe signal to obtain a spectrum diagram; performing a zero matrix filling operation on the interference fringe signal spectrum;

[0013] Step S33: performing an inverse Fourier transform operation on the interference fringe signal spectrum after zero filling 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 up-sampled time domain signal collected by the linear array camera after the processing of steps S31-S33 and each frame up-sampled time domain signal, wherein the first frame up-sampled time domain signal and the first frame up-sampled time domain signal perform a first cross-correlation calculation to obtain a first frame autocorrelation sequence, and the first frame up-sampled time domain signal and each of the remaining frames up-sampled time domain signals perform a first cross-correlation calculation to obtain multiple groups of first cross-correlation sequences; then, each first cross-correlation sequence is respectively cross-correlated with the first frame 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 relationship formula is:

[0018] d(i)=(ΔX(i)*p) / (2*N*tan(θ))

[0019] Among them, d(i) is the real space displacement value of the fringe of the i-th frame relative to the fringe of the first frame, ΔX(i) is the pixel offset value corresponding to the second cross-correlation sequence between the fringe of the i-th frame and the fringe of 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 multiple.

[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 through a double-slit aperture. The interference fringes are emitted to the surface of an object to be measured and then captured by a linear array camera after reflection. 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 the 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 more characteristic information. The device has strong practicality and broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic structural diagram of a 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 figure:

[0026] 1- double slit aperture; 2- laser light source module; 3- image processing system; 4- linear array camera with imaging plane perpendicular to 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- path of laser center line; blue thin line- distribution of interference field in space when the object to be measured is in the initial position; orange dotted line- distribution of interference field in space after displacement of the object to be measured. DETAILED DESCRIPTION

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

[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 meanings as those 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, it indicates 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 linear array camera, a double slit aperture, a laser light source and an image processing system; the linear array camera is used to collect interference fringe signals formed by laser passing through the double slit aperture and received after being 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 used to be assembled into a module with the laser light source to generate interference fringes; the laser light source is used to emit laser to pass 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 based on a computer, on which a preprocessing module and a displacement information extraction module are installed. 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 value obtained by fringes upsampling and two consecutive cross-correlation operations between the first frame and other frames. In addition, 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 Young's double-slit interference fringes based on the above device, comprising the following steps:

[0033] Step S1: The laser light source emits a laser beam that passes through a double slit aperture to form interference fringes, and reaches the surface of the object to be measured at a certain incident angle θ, where θ is the incident angle formed by the laser light path and the normal line of the surface of the object to be measured. The surface of the object to be measured then reflects the fringe interference field at the same height. After that, the receiving surface of the linear array camera photosensitive unit is kept parallel to the surface of the object to be measured and fixed on the laser reflection light path, so that it maintains an angle of π / 2-θ with the reflection light path, and receives 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, the incident point on the surface of the object to be measured produces a horizontal displacement, and the fringe signal imaged in the sensor of the linear array camera also produces a 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 signals are transmitted to an image processing system, and the image processing system pre-processes the interference fringe signals 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 diagram. Then, perform zero matrix filling operation on the interference fringe signal spectrum;

[0039] Step S33: performing an inverse Fourier transform operation on the interference fringe signal spectrum after zero filling 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 up-sampled time domain signal collected by the linear array camera and each frame up-sampled time domain signal to obtain a first cross-correlation sequence. Then, perform a cross-correlation calculation on each cross-correlation sequence with the first frame autocorrelation sequence to obtain a second cross-correlation sequence, and calculate the cross-correlation offset value.

[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 relationship formula is:

[0043] d(i)=(ΔX(i)*p) / (2*N*tan(θ))

[0044] Among them, d(i) is the real space displacement value of the fringe of the i-th frame relative to the fringe of the first frame, ΔX(i) is the pixel offset value corresponding to the second cross-correlation sequence between the fringe of the i-th frame and the fringe of 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 multiple.

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

[0046] The above is only a preferred embodiment of the present invention, and does not limit the present invention in other forms. Any technician familiar with the profession may use the above disclosed technical content to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention still belongs to the protection scope of the technical solution of the present invention.

Claims

1. A displacement triangulation measurement device based on laser interference fringes, characterized in that: The invention comprises a linear array camera, a double slit aperture, a laser light source and an image processing system; the linear array camera is used for collecting interference fringe signals formed by laser passing through the double slit aperture and received after being reflected by the surface of the object to be measured, and the collected fringe signals are transmitted 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 for emitting laser light passing through the double slit aperture to form interference fringes; the image processing system analyzes and processes the fringe images to obtain the displacement information of the object to be measured.

2. A displacement triangulation measurement method based on laser interference fringes, characterized in that: The method is implemented by using the displacement triangulation measurement device based on laser interference fringes as claimed in claim 1, and comprises the following steps: Step S1: A laser light source emits a laser beam that passes through a double slit aperture to form interference fringes, and reaches the smooth surface of the object to be measured at a certain incident angle θ, and the smooth surface of the object to be measured reflects the fringe interference field at the same height; then the receiving surface of the linear array camera photosensitive unit is kept parallel to the smooth surface of the object to be measured, and fixed on the laser reflection light path, so that the receiving surface of the linear array camera photosensitive unit maintains an angle of π / 2-θ with the reflection light path, and a clear interference fringe image signal is received; Step S2: As the object to be measured moves in a direction perpendicular to the normal line of the surface of the object to be measured, the direction of the laser light path remains unchanged, the incident point on the surface of the object to be measured is displaced, and the interference fringe image signal formed in the sensor of the linear array camera also moves 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: The collected interference fringe image signal is transmitted to the 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.

3. The displacement triangulation measurement method based on laser interference fringes according to claim 2 is characterized in that: The step S3 specifically comprises the following steps: Step S31: performing image preprocessing on the obtained interference fringe image signal; Step S32: Performing Fourier transform operation on the pre-processed time domain interference fringe signal to obtain a spectrum diagram; 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 zero filling 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 collected by the linear array camera after the processing of steps S31-S33 and each frame up-sampled time domain signal, wherein the first frame up-sampled time domain signal and the first frame up-sampled time domain signal perform a first cross-correlation calculation to obtain a first frame autocorrelation sequence, and the first frame up-sampled time domain signal and each of the remaining frames up-sampled time domain signals perform a first cross-correlation calculation to obtain multiple groups of first cross-correlation sequences; then, each first cross-correlation sequence is respectively cross-correlated with the first frame autocorrelation sequence to obtain multiple groups of second cross-correlation sequences, and a cross-correlation pixel offset value is calculated. 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.

4. The stripe preprocessing method according to claim 3, 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.

5. The displacement triangulation measurement method based on laser interference fringes according to claim 3 is characterized in that: The relative displacement-cross-correlation offset value mapping relationship formula is: d(i)=(ΔX(i)*p) / (2*N*tan(θ)) Among them, d(i) is the real space displacement value of the fringe of the i-th frame relative to the fringe of the first frame, ΔX(i) is the pixel offset value corresponding to the second cross-correlation sequence between the fringe of the i-th frame and the fringe of 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 multiple.

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