A synchronous speed and distance measurement system and method based on laser triangulation

Abstract

This invention provides a system and method for synchronously measuring speed and distance based on laser triangulation. The method includes: moving a surface to be measured; an image acquisition module acquiring a light spot at a preset frequency and transmitting it to a processor in real time; the processor calculating the movement distance of the internal texture of the speckle and the interval value of the spot edge on the photosensitive surface of the image acquisition module based on the light spot; calculating the lateral movement distance of the surface to be measured based on the movement distance of the internal texture of the speckle; calculating the lateral movement speed of the surface to be measured based on the lateral movement distance of the surface to be measured; and calculating the axial movement distance of the surface to be measured based on the interval value of the light spot edge on the photosensitive surface of the image acquisition module. This achieves real-time monitoring of the lateral movement speed of the surface to be measured while simultaneously reconstructing its surface undulations, thus expanding the multi-degree-of-freedom measurement field of laser triangulation sensors and giving it broader application potential in industrial inspection and quality control.

Description

Technical Field

[0001] This invention relates to the field of laser triangulation technology, and more particularly to a system and method for synchronously measuring speed and distance based on laser triangulation. Background Technology

[0002] Currently, the surface topography inspection of precision parts mainly relies on coordinate measuring machines (CMMs). The high cost of these systems and the need for regular maintenance greatly increase the economic burden of production. Moreover, as contact measuring devices, they pose a risk of damaging the surface of the object being measured.

[0003] Laser triangulation systems, which have the advantages of simple principle, compact structure, low cost and non-contact measurement, mainly focus on improving the accuracy and measurement range of the axial movement distance of the measured object and optimizing the digital image processing algorithm of the collected light spot. Research on multidimensional measurement has not been carried out in depth and is still in the exploratory stage.

[0004] In view of this, the present invention provides a speed and distance synchronous measurement system and method based on laser triangulation. Summary of the Invention

[0005] To address the aforementioned shortcomings, this invention provides a synchronous speed and distance measurement system and method based on laser triangulation. This invention primarily utilizes the principles of geometric triangulation and the speckle effect to construct a direct-fire laser triangulation measurement system that satisfies Scheimpflug's imaging law. By deriving and establishing the lateral and axial movement distance relationships between the object under test and the imaging spot, the system enables real-time monitoring of the lateral movement speed and surface undulation changes of the metal object under test. Digital image correlation (DIC) technology is introduced to capture the internal texture displacement values ​​of the speckle acquired by CMOS, and the lateral movement speed of the object under test is calculated in conjunction with the CMOS acquisition frequency. This low computational complexity allows for real-time monitoring. The Canny operator and Zernike moments are introduced to locate the sub-pixel edge differences between adjacent spots, and the grayscale changes in the spot edge region are used for filtering to calculate the surface undulation changes of the object under test, achieving micron-level measurement accuracy. This invention expands the multidimensional measurement research of the laser triangulation principle, making it potentially widely applicable in industrial inspection and quality control.

[0006] The technical means employed in this invention are as follows:

[0007] On one hand, the present invention provides a speed and distance synchronous measurement system based on laser triangulation, comprising:

[0008] The surface being tested;

[0009] A single-mode optical fiber is located on one side of the surface being measured;

[0010] A laser triangulation sensor module includes a collimating lens and an imaging lens. The collimating lens is located between the surface being measured and the single-mode optical fiber, and is parallel to the surface being measured. Along a direction perpendicular to the surface being measured, the optical center of the collimating lens overlaps with the light-emitting end of the single-mode optical fiber. The imaging lens is located to one side of the collimating lens, along a direction perpendicular to the surface being measured. The imaging lens does not overlap with the single-mode optical fiber and is not parallel to the surface being measured.

[0011] An image acquisition module is located on the side of the imaging lens away from the surface being measured;

[0012] The processor is connected to the image acquisition module.

[0013] On the other hand, the present invention also provides a speed and distance synchronization measurement method based on laser triangulation, applied to the above-mentioned speed and distance synchronization measurement system based on laser triangulation, comprising:

[0014] A preset resolution is established, and the imaging lens and the image acquisition module are adjusted according to the preset resolution.

[0015] The light-emitting end projects a Gaussian beam onto the surface under test, and the Gaussian beam forms a light spot through the laser triangulation sensor module and the surface under test;

[0016] The measured surface is moved, and the image acquisition module acquires the light spot at a preset frequency and transmits it to the processor in real time.

[0017] The processor calculates the movement distance of the internal texture of the speckle and the interval value of the edge of the speckle on the photosensitive surface of the image acquisition module based on the speckle movement distance; calculates the lateral movement distance of the tested surface based on the movement distance of the internal texture of the speckle, calculates the lateral movement speed of the tested surface based on the lateral movement distance of the tested surface; and calculates the axial movement distance of the tested surface based on the interval value of the edge of the speckle on the photosensitive surface of the image acquisition module.

[0018] Preferably, the processor calculates the movement distance of the speckle texture within the speckle based on the light spot, including:

[0019] The processor selects the Tth-th acquired light spot and the T+1th acquired light spot from the light spots, and establishes a square region with a side length of (2m+1)×(2m+1) pixels as the reference region, with the centroid of the Tth acquired light spot as the center.

[0020] The zero-mean normalized sum of squared differences function in DIC is used to search for the target region with the highest correlation to the reference region in the light spot acquired in the (T+1)th acquisition. The target region has the same size as the reference region.

[0021] The distance the speckle texture moves within the target area is calculated based on the center point of the target area and the centroid.

[0022] Preferably, the processor calculates the interval value of the light spot edge on the photosensitive surface of the image acquisition module based on the light spot, including:

[0023] The processor selects the light spot acquired in the Tth acquisition and the light spot acquired in the T+1th acquisition from the light spots;

[0024] A Gaussian filter is used to smooth the light spot acquired in the Tth and T+1th acquisitions.

[0025] The Canny operator is used to determine the integer pixel edge points of the light spot acquired in the Tth time. Based on the Zernike moment and the integer pixel edge points of the light spot acquired in the Tth time, sub-pixel localization is performed on the light spot acquired in the Tth time to obtain the edge sub-pixel points of the light spot acquired in the Tth time.

[0026] The Canny operator is used to determine the integer pixel edge points of the light spot acquired in the (T+1)th acquisition. Based on the Zernike moment and the integer pixel edge points of the light spot acquired in the (T+1)th acquisition, sub-pixel localization is performed on the light spot acquired in the (T+1)th acquisition to obtain the sub-pixel edge points of the light spot acquired in the (T+1)th acquisition.

[0027] The interval value of the edge of the light spot on the photosensitive surface of the image acquisition module is calculated based on the edge sub-pixel points of the light spot acquired in the Tth acquisition and the edge sub-pixel points of the light spot acquired in the (T+1)th acquisition.

[0028] Preferably, the lateral movement distance of the tested surface is calculated based on the movement distance of the speckle internal texture, and is calculated in the following manner:

[0029]

[0030] Wherein, S2 is the lateral movement distance of the measured surface, S2 ′ L1 is the distance the speckle texture moves within the surface under test in its initial state, L2 is the object distance during the process of the principal ray passing through the imaging lens, and the principal ray is the ray that emerges from the Gaussian beam in a direction perpendicular to the surface under test, passes through the optical center of the collimating lens, and after diffuse reflection on the surface under test, the reflected ray passes through the optical center of the imaging lens, f is the focal length of the imaging lens, β is the angle between the principal ray and the image acquisition module after passing through the imaging lens, and α is the reflection angle of the principal ray when it is reflected on the surface under test.

[0031] Preferably, the lateral movement velocity of the measured surface is calculated based on the lateral movement distance of the measured surface, and is calculated in the following manner:

[0032]

[0033] Where v is the lateral movement speed of the measured surface, S2 is the lateral movement distance of the measured surface, and t is the time taken for the measured surface to move the lateral distance.

[0034] Preferably, the axial movement distance of the measured surface is calculated based on the interval value of the light spot edge on the photosensitive surface of the image acquisition module, and is calculated in the following manner:

[0035]

[0036] Where S1 is the axial movement distance of the measured surface. In the initial state, the perpendicular distance between the measured surface and the collimating lens is A. When the perpendicular distance between the measured surface and the collimating lens is less than A, S1 is a positive value; when the perpendicular distance between the measured surface and the collimating lens is greater than or equal to A, S1 is a negative value. ′ L1 is the interval value of the light spot on the photosensitive surface of the image acquisition module, L1 is the object distance of the principal ray as it passes through the imaging lens when the surface under test is in its initial state, the principal ray is the ray that emerges from the Gaussian beam in a direction perpendicular to the surface under test, passes through the optical center of the collimating lens, and after diffuse reflection on the surface under test, the reflected ray passes through the optical center of the imaging lens, f is the focal length of the imaging lens, β is the angle between the principal ray and the image acquisition module after passing through the imaging lens, and α is the reflection angle of the principal ray when it is reflected on the surface under test.

[0037] Preferably, a preset resolution is used, and the imaging lens and the image acquisition module are adjusted according to the preset resolution, including:

[0038] The focal length and position of the imaging lens are determined based on the resolution.

[0039] The image acquisition module is determined based on the positions of the surface under test, the single-mode optical fiber, the collimating lens, and the imaging lens, and the image acquisition module satisfies Scheimpflug's law.

[0040] Compared with the prior art, the present invention has the following advantages:

[0041] 1. The speed and distance synchronous measurement system and method based on laser triangulation provided by this invention provides a formula for the lateral movement distance of the measured surface and a speed monitoring theory, which opens up the field of multi-degree-of-freedom measurement of laser triangulation sensors, giving them a wider range of application potential in industrial inspection and quality control.

[0042] 2. The speed and distance synchronous measurement system and method based on laser triangulation provided by this invention introduces DIC technology and combines it with a cubic spline interpolation fitting function, which can accurately capture the displacement of the internal texture of the elliptical speckle on the image sensor. This enables the system to monitor the lateral movement speed of the measured surface in real time, providing strong technical support for precision measurement and industrial automation control.

[0043] 3. The velocity and distance synchronous measurement system and method based on laser triangulation provided by this invention, by introducing the Canny operator and Zernike moment, can achieve precise monitoring of real-time changes in the edge of the imaging spot, thereby reconstructing the surface morphology of the measured metal surface and determining whether its surface roughness meets industrial production requirements. The micron-level measurement accuracy achieved not only enhances the system's practicality but also provides strong technical support for precise measurement in complex or dynamic measurement environments.

[0044] 4. The speed and distance synchronous measurement system and method based on laser triangulation provided by the present invention can realize real-time monitoring of the lateral movement speed of the measured surface, while restoring its surface undulation morphology and judging whether its surface roughness meets the production requirements. It is suitable for dealing with the challenges of large individual differences in blanks, tight tolerances and poor processing consistency in the processing and delivery of complex surfaces in precision industrial manufacturing. Attached Figure Description

[0045] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0046] Figure 1 This is a schematic diagram of a speed and distance synchronous measurement system based on laser triangulation provided by the present invention.

[0047] Figure 2 This is a schematic diagram of a light spot.

[0048] Figure 3 This is a schematic flowchart of a method for synchronously measuring speed and distance based on laser triangulation provided by the present invention.

[0049] Figure 4 This is a schematic diagram of edge ranging.

[0050] Figure 5 This is another schematic diagram of edge ranging.

[0051] In the figure: 1. Surface under test; 2. Single-mode optical fiber; 3. Collimating lens; 4. Imaging lens; 5. Image acquisition module. Detailed Implementation

[0052] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0053] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0054] Combination Figure 1 and Figure 2 , Figure 1 This is a schematic diagram of a speed and distance synchronization measurement system based on laser triangulation provided by the present invention. Figure 2 This is a schematic diagram of a light spot, illustrating a specific embodiment of the speed and distance synchronization measurement system based on laser triangulation provided by the present invention, including:

[0055] Surface to be tested 1;

[0056] Single-mode fiber 2 is located on one side of the surface 1 being measured;

[0057] The laser triangulation sensor module includes a collimating lens 3 and an imaging lens 4. The collimating lens 3 is located between the measured surface 1 and the single-mode fiber 2. The collimating lens 3 is parallel to the measured surface 1 and overlaps with the light-emitting end of the single-mode fiber 2 in a direction perpendicular to the measured surface 1. The imaging lens 4 is located on one side of the collimating lens 3 and does not overlap with the single-mode fiber 2 in a direction perpendicular to the measured surface 1. The imaging lens 4 is not parallel to the measured surface 1.

[0058] Image acquisition module 5 is located on the side of imaging lens 4 away from the surface 1 being measured;

[0059] The processor is connected to the image acquisition module 5.

[0060] It should be noted that the single laser beam is emitted from the semiconductor laser diode in the light source module and connected to the incident end of the laser triangulation sensor module through the single-mode optical fiber 2. The image acquisition module 5 is tilted relative to the main light beam passing through the imaging lens 4. The image acquisition module 5 can be a CMOS image sensor with an acquisition frequency of 100Hz, but it is not limited to this and can be set according to actual needs.

[0061] Understandably, the collimated Gaussian beam is projected perpendicularly onto the surface being measured 1, and a light spot is formed by the reflected light from the surface being measured 1. The image acquisition module 5 acquires the light spot, and the light spot is referenced... Figure 2 This method obtains diffuse reflection images of the circular area covered by incident light on the tested surface 1 at different times. By performing relevant image processing on each acquired image, the lateral movement speed, undulation morphology, and surface roughness of the tested surface 1 can be monitored in real time. This method can realize the real-time monitoring of the lateral movement speed of the tested surface 1, the restoration of its surface undulation morphology, and the determination of whether its surface roughness meets production requirements. It is suitable for dealing with the challenges of large individual differences in blanks, tight tolerances, and poor processing consistency in the processing and delivery of complex surfaces in precision industrial manufacturing.

[0062] Based on the same inventive concept, and referring to Figure 3 , Figure 3 This is a flowchart illustrating a speed and distance synchronization measurement method based on laser triangulation provided by the present invention, to illustrate a specific embodiment of the speed and distance synchronization measurement method based on laser triangulation provided by the present invention, applied to a speed and distance synchronization measurement system based on laser triangulation, including:

[0063] Set the preset resolution and adjust the imaging lens and image acquisition module according to the resolution.

[0064] The light-emitting end projects a Gaussian beam onto the surface being measured, and the Gaussian beam forms a light spot through the laser triangulation sensor module and the surface being measured.

[0065] The moving surface under test is used to acquire light spots at a preset frequency and transmit them to the processor in real time.

[0066] The processor calculates the movement distance of the internal texture of the speckle and the interval value of the speckle edge on the photosensitive surface of the image acquisition module based on the speckle movement distance; it calculates the lateral movement distance of the measured surface based on the movement distance of the internal texture of the speckle, and calculates the lateral movement speed of the measured surface based on the lateral movement distance of the measured surface; it calculates the axial movement distance of the measured surface based on the interval value of the speckle edge on the photosensitive surface of the image acquisition module.

[0067] It is understood that the speed and distance synchronous measurement method based on laser triangulation provided in this embodiment provides a formula for the lateral movement distance of the measured surface and a speed monitoring theory, opening up the field of multi-degree-of-freedom measurement of laser triangulation sensors, and giving them a wider range of application potential in industrial inspection and quality control.

[0068] In some optional embodiments, the processor calculates the distance the internal texture of the speckle moves based on the light spot, including:

[0069] The processor selects the light spot acquired in the Tth acquisition and the light spot acquired in the T+1th acquisition from the light spot, and establishes a square region with a side length of (2m+1)×(2m+1) pixels as the reference region, with the centroid of the light spot acquired in the Tth acquisition as the center.

[0070] The zero-mean normalized sum of squared differences function in DIC is used to search for the target region with the highest correlation to the reference region in the spot acquired in the (T+1)th acquisition. The target region and the reference region have the same size.

[0071] Calculate the internal texture movement distance of the speckle pattern based on the center point and centroid of the target area.

[0072] Understandably, the spot acquired in the Tth acquisition serves as the baseline spot image, with its centroid (x1, y1). A square region with a side length of (2m+1) × (2m+1) pixels is established centered on the centroid (x1, y1) as the reference region, denoted by f(x, y). The spot acquired in the T+1th acquisition is the spot image adjacent to the spot acquired in the Tth acquisition, i.e., the subsequent spot image. Using the zero-mean normalized sum of squared differences function in DIC, a target region g(x, y) centered at point (x2, y2) is searched in the subsequent spot image to maximize its correlation with the reference region. This refers to the distance the internal texture of the speckle pattern has moved.

[0073] Specifically, the zero-mean normalized sum of squared differences function in DIC is calculated as follows:

[0074]

[0075] Where, f(x) i y j () represents the grayscale value of a point within the reference area. g(x) is the average grayscale value of all pixels within the reference region. i y j () represents the grayscale value of a point within the target area. This is the average grayscale value of all pixels within the target area.

[0076] The introduced DIC technology can accurately capture the displacement of the internal texture of the elliptical speckle on the image sensor. The combination of this technology with the cubic spline interpolation fitting function enables the system to monitor the lateral movement speed of the measured surface in real time, providing strong technical support for precision measurement and industrial automation control.

[0077] In some optional embodiments, the processor calculates the interval value of the light spot edge on the photosensitive surface of the image acquisition module based on the light spot, including:

[0078] The processor selects the light spot acquired in the Tth acquisition and the light spot acquired in the (T+1)th acquisition from the light spots;

[0079] A Gaussian filter is used to smooth the light spot acquired in the Tth and T+1th acquisitions.

[0080] The Canny operator is used to determine the integer pixel edge points of the light spot acquired in the Tth acquisition. Based on the Zernike moment and the integer pixel edge points of the light spot acquired in the Tth acquisition, the sub-pixel localization of the light spot acquired in the Tth acquisition is performed to obtain the sub-pixel edge points of the light spot acquired in the Tth acquisition.

[0081] The Canny operator is used to determine the integer pixel edge points of the light spot acquired in the (T+1)th acquisition. Based on the Zernike moment and the integer pixel edge points of the light spot acquired in the (T+1)th acquisition, sub-pixel localization is performed on the light spot acquired in the (T+1)th acquisition to obtain the sub-pixel edge points of the light spot acquired in the (T+1)th acquisition.

[0082] The interval value of the light spot edge on the photosensitive surface of the image acquisition module is calculated based on the edge sub-pixel points of the light spot acquired in the Tth acquisition and the edge sub-pixel points of the light spot acquired in the (T+1)th acquisition.

[0083] Understandably, given the integer pixel edge points, the image rotation angle φ and the vertical distance l from the center of the circle to the edge are calculated based on the Zernike moment and its rotation invariance to obtain the sub-pixel points. Finally, the grayscale changes in the edge region of the light spot are used for filtering to locate the sub-pixel edge displacement of adjacent light spots.

[0084] Specifically, in the discrete case, the nth-order m-th Zernike moment of the image I(x, y) within the unit circle is calculated as follows:

[0085]

[0086] Where I(x, y) is a two-dimensional image representation, and ρ is the edge position. θ is the angle between vector ρ and the x-axis.

[0087] Rotation invariance is calculated as follows:

[0088] Z′ nm =Z nm ·e -imφ

[0089] Rotation invariance means that the phase of the Zernike moments changes before and after image rotation, while the magnitude remains unchanged.

[0090] Among them, Z nm Let Z′ be the Zernike moments of the image before rotation. nm Let φ be the Zernike moments of the rotated image, and φ be the rotation angle of the image.

[0091] The image rotation angle is calculated as follows:

[0092]

[0093] Among them, m[Z 11 [Zernike moments for the image] 11 The imaginary part, Re[Z] 11 [Zernike moments for the image] 11 The real part.

[0094] The vertical distance from the center of the circle to the edge is calculated as follows:

[0095]

[0096] Among them, Z 20 Z is a 2nd-order, 0th-order Zernike moment. 11 It is a first-order Zernike moment.

[0097] The introduced Canny operator and Zernike moment enable precise real-time monitoring of changes in the edge of the imaging spot, allowing for the reconstruction of the surface morphology and determination of whether its surface roughness meets industrial production requirements. The achieved micron-level measurement accuracy not only enhances the system's practicality but also provides strong technical support for precise measurements in complex or dynamic environments.

[0098] In some optional embodiments, the lateral movement distance of the measured surface is calculated based on the movement distance of the speckle internal texture, as follows:

[0099]

[0100] Where S2 is the lateral movement distance of the measured surface, S2 ′ L1 is the distance the speckle texture moves within the surface under test in its initial state, and L2 is the object distance during the process of the principal ray passing through the imaging lens. The principal ray is the ray that emerges from a Gaussian beam perpendicular to the surface under test, passes through the optical center of the collimating lens, and after diffuse reflection on the surface under test, the reflected ray passes through the optical center of the imaging lens. f is the focal length of the imaging lens, β is the angle between the principal ray after passing through the imaging lens and the image acquisition module, and α is the reflection angle of the principal ray when it is reflected on the surface under test.

[0101] It should be noted that when capturing the left side of the incident light spot, the texture movement S2 is set to "+", and when capturing the right side of the incident light spot, the texture movement S2 is set to "-".

[0102] Furthermore, L1 and β are calculated as follows:

[0103]

[0104] Where H is the vertical distance from the optical center of the imaging lens to the surface being measured.

[0105] In some optional embodiments, the lateral movement velocity of the measured surface is calculated based on the lateral movement distance of the measured surface, as follows:

[0106]

[0107] Where v is the lateral movement speed of the measured surface, S2 is the lateral movement distance of the measured surface, and t is the time taken for the measured surface to move the lateral distance.

[0108] In some optional embodiments, the axial movement distance of the measured surface is calculated based on the interval value of the light spot edge on the photosensitive surface of the image acquisition module, and is calculated in the following manner:

[0109]

[0110] Where S1 is the axial movement distance of the measured surface. When the measured object moves upward relative to the reference surface along the optical axis, the denominator of the formula is "+", otherwise, the denominator is "-". ′1 represents the interval value of the light spot on the photosensitive surface of the image acquisition module, L1 represents the object distance of the principal ray as it passes through the imaging lens when the surface under test is in its initial state, the principal ray is the ray that emerges from a Gaussian beam perpendicular to the surface under test, passes through the optical center of the collimating lens, and after diffuse reflection on the surface under test, the reflected ray passes through the optical center of the imaging lens, f is the focal length of the imaging lens, β is the angle between the principal ray and the image acquisition module after passing through the imaging lens, and α is the reflection angle of the principal ray when it is reflected on the surface under test.

[0111] It is understood that by sequentially processing the texture movement distance and edge changes within adjacent light spots, the method of the present invention can synchronously monitor the lateral movement speed and surface undulation changes of the measured surface in real time.

[0112] In some optional embodiments, a preset resolution is established, and the imaging lens and image acquisition module are adjusted according to the resolution, including:

[0113] The focal length and position of the imaging lens are determined based on the resolution.

[0114] The image acquisition module is determined based on the positions of the surface under test, single-mode fiber, collimating lens, and imaging lens. The image acquisition module satisfies Scheimpflug's law.

[0115] The determination of system structural parameters, taking into account system resolution, imaging spot size, and mechanical structure geometry, is an existing technology and will not be elaborated upon in this embodiment. Based on the determined system structural parameters, the imaging lens and image acquisition module are selected and adjusted to achieve synchronous measurement of the speed and surface undulations of the measured surface. As the measured surface moves at different lateral speeds, the CMOS photosensitive surface acquires the light spot in real time at a certain frequency and processes adjacent light spots.

[0116] In some alternative embodiments, refer to Figure 1 , Figure 4 and Figure 5 , Figure 4 This is a schematic diagram of edge ranging. Figure 5 This is another schematic diagram illustrating edge ranging, to demonstrate another specific embodiment of the laser triangulation-based synchronous speed and distance measurement method provided by the present invention. The method includes: vertically projecting a collimated Gaussian beam onto the surface to be measured 1; using a reflected light image acquisition module 5 to acquire light spot data on the surface of the surface to be measured 1, obtaining diffuse reflected light images of the circular area covered by incident light on the surface of the surface to be measured 1 at different times; and monitoring the lateral movement speed, undulation morphology, and surface roughness of the surface to be measured 1 in real time by performing relevant image processing on each acquired image. The specific steps are as follows:

[0117] System setup:

[0118] A laser triangulation system with a resolution of 5µm was constructed. The system's structural parameters are as follows: the ideal focal length of collimating lens 3 is f1 = 2mm, its distance from the laser fiber port is 2mm, its distance from the measured surface 1 is 70mm, the reflection angle α when the principal ray is reflected from the measured surface 1 is 31.1414°, the distance H from the optical center of imaging lens 4 to the measured surface 1 is 59.2681mm, the ideal focal length of imaging lens 4 is f = 25mm, the tilt angle β of the CMOS photosensitive surface is 46.9208°, and its distance from the imaging lens 4 is 35.925mm.

[0119] Adjust the relative position of the measured surface 1 and the laser triangulation system to ensure that the emitted laser is perpendicularly projected onto the rightmost side of the measured surface 1. Set the acquisition frequency of the CMOS image sensor to 100Hz to acquire the imaging spot. Then, use a lateral displacement device to control the measured surface 1 to move to the right at a certain speed until the Gaussian beam is projected onto the leftmost side of the measured surface 1.

[0120] During the movement of the measured surface 1, the collected light spots are processed using MATLAB, with each spot serving as a reference for the next. Texture movement values ​​within adjacent spots are captured to monitor the lateral movement speed in real time. See details... Figure 1 The edge variation distance between adjacent light spots is detected to determine the surface undulation variation. See details in [link to documentation]. Figure 4 and Figure 5 .

[0121] Measurement process:

[0122] The center of the reference spot is determined using the gray-scale centroid method, and a reference region with a radius of 20 is created based on this. Within the target spot, a target region of the same radius is created by moving 20 pixels laterally to the left, using the centroid of the reference spot as the initial point. The cross-correlation coefficient between the two regions is calculated using the zero-mean normalized sum of squared differences function in DIC. After calculation, the target region is moved one pixel to the right, and the cross-correlation coefficient is calculated again. This process continues until the target region is moved 20 pixels to the right of the centroid of the reference spot.

[0123] The zero-mean normalized sum of squared differences function in DIC is calculated as follows:

[0124]

[0125] Where, f(x) i y j () represents the grayscale value of a point within the reference area. g(x) is the average grayscale value of all pixels within the reference region. i y j () represents the grayscale value of a point within the target area. This is the average grayscale value of all pixels within the target area.

[0126] Based on the cross-correlation coefficients of 41 coordinates, a cubic spline interpolation function is used for fitting, and the maximum value of the function is obtained. The coordinates corresponding to this value are the sub-pixel positions of the centroid of the reference spot in the target spot, and the interval between the two coordinates is the internal texture displacement of the speckle. Substituting these values ​​into the formula, the lateral movement distance of the measured surface 1 is calculated, and then divided by the CMOS spot acquisition interval to determine its lateral movement velocity v.

[0127]

[0128] Adjacent light spots are subjected to the same degree of Gaussian filtering to remove noise and smooth the image. The Canny operator is used to determine the integer pixel coordinates of the light spot edges, and the direction of texture movement within the speckle is used to determine which side of the edge of the detected imaging light spot is being detected.

[0129] Based on integer pixel coordinates, and utilizing the Zernike polynomial and its rotation invariance, the angle φ between the perpendicular line and the x-axis, and the vertical distance l from the center to the edge, required to determine the sub-pixel coordinates of the spot edge, are calculated, where V nm For Zernike polynomials, * denotes conjugation.

[0130] Zernike moments are calculated as follows:

[0131]

[0132] Where I(x, y) is a two-dimensional image representation, and ρ is the edge position. θ is the angle between vector ρ and the x-axis.

[0133] The image rotation angle is calculated as follows:

[0134]

[0135] Among them, m[Z 11 [Zernike moments for the image] 11 The imaginary part, Re[Z] 11 [Zernike moments for the image] 11 The real part.

[0136] The vertical distance from the center of the circle to the edge is calculated as follows:

[0137]

[0138] Among them, Z 20 Z is a 2nd-order, 0th-order Zernike moment. 11 It is a first-order Zernike moment.

[0139] In practical discrete scenarios, Zernike moments are calculated using convolutions of different orders of templates with pixels. This invention uses a 7x7 template for sampling within a unit circle. Considering the effect of template magnification, the radius of the circle becomes 7 / 2, therefore the vertical distance *l* from the origin to the edge should be magnified by a factor of 7 / 2. The formula for the sub-pixel edge coordinates of the light spot is shown below, where *x* and *y* are obtained by the Canny operator:

[0140]

[0141] Where (x, y) are the integer pixel coordinates of the light spot edge, and (x′, y′) are the sub-pixel coordinates of the light spot edge.

[0142] Substituting the subpixel edge coordinates of adjacent light spots into the axial distance variation formula yields the surface undulation variation of the metal surface under test 1. A leftward shift of the reference light spot edge indicates that during the lateral movement of the surface under test 1, the newly covered area of ​​the laser is farther away from the collimating lens 3 relative to the initial state of the surface under test 1; in this case, the distance formula takes a "-" sign. Conversely, a leftward shift indicates that the newly covered area of ​​the laser is closer to the collimating lens 3 relative to the initial state of the surface under test 1; in this case, the distance formula takes a "+" sign.

[0143]

[0144] In this embodiment, a metal block with a surface roughness of 6.3 μm, milled to conform to GB / T6060.2-2006 standard, was selected as the test sample. The test surface 1 was controlled to move at different lateral speeds, and the present invention was used to repeat the measurement 10 times at different speeds to verify the accuracy and stability of the laser triangulation system. The experimental results are shown in the table below:

[0145]

[0146] During the experiment, the experimental data of the laser triangulation sensor constructed in this invention showed that its relative error was less than 2% and its relative uncertainty was less than 3%. This result proves that the sensor has reached high industry standards in terms of accuracy and stability. Specifically:

[0147] At different lateral movement speeds (1 mm / s to 7 mm / s), the relative error of the sensor's lateral velocity measurement is between 0.2908% and 1.7202%, and the relative error of the surface roughness measurement is between 0.0399% and 1.6855%, both of which are far below the industry-accepted upper limit of 2% error.

[0148] The relative uncertainties for velocity measurements ranged from 0.0331% to 0.5651%, and the relative uncertainties for surface roughness measurements ranged from 0.7282% to 2.0733%. These are significantly lower than the 3% uncertainty standard.

[0149] The above results demonstrate that the laser triangulation sensor invented in this study can maintain highly consistent measurement results and has significant feasibility and superiority in precision measurement.

[0150] The sequence numbers of the above embodiments of the present invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0151] In the above embodiments of the present invention, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0152] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for synchronously measuring velocity and distance based on laser triangulation, characterized in that, include: A speed and distance synchronization measurement system based on laser triangulation includes: The surface being tested; A single-mode optical fiber is located on one side of the surface being measured; A laser triangulation sensor module includes a collimating lens and an imaging lens. The collimating lens is located between the surface being measured and the single-mode optical fiber, and is parallel to the surface being measured. Along a direction perpendicular to the surface being measured, the optical center of the collimating lens overlaps with the light-emitting end of the single-mode optical fiber. The imaging lens is located to one side of the collimating lens, along a direction perpendicular to the surface being measured. The imaging lens does not overlap with the single-mode optical fiber and is not parallel to the surface being measured. An image acquisition module is located on the side of the imaging lens away from the surface being measured; The processor is connected to the image acquisition module; The specific steps of the laser triangulation-based method for synchronously measuring speed and distance are as follows: A preset resolution is established, and the imaging lens and the image acquisition module are adjusted according to the preset resolution. The light-emitting end projects a Gaussian beam onto the surface under test, and the Gaussian beam forms a light spot through the laser triangulation sensor module and the surface under test; The measured surface is moved, and the image acquisition module acquires the light spot at a preset frequency and transmits it to the processor in real time. The processor calculates the movement distance of the internal texture of the speckle and the interval value of the edge of the speckle on the photosensitive surface of the image acquisition module based on the speckle; calculates the lateral movement distance of the measured surface based on the movement distance of the internal texture of the speckle, calculates the lateral movement speed of the measured surface based on the lateral movement distance of the measured surface; and calculates the axial movement distance of the measured surface based on the interval value of the edge of the speckle on the photosensitive surface of the image acquisition module. The processor calculates the movement distance of the speckle texture within the speckle based on the light spot, including: The processor selects the light spot acquired in the Tth acquisition and the light spot acquired in the (T+1)th acquisition from the light spots, and establishes a side length of (2) with the centroid of the light spot acquired in the Tth acquisition as the center. m +1)×(2) m A square region of +1 pixel is used as the reference region; The zero-mean normalized sum of squared differences function in DIC is used to search for the target region with the highest correlation to the reference region in the light spot acquired in the (T+1)th acquisition. The target region has the same size as the reference region. Calculate the internal texture movement distance of the speckle based on the center point of the target region and the centroid point; The lateral movement distance of the tested surface is calculated based on the movement distance of the speckle internal texture, as follows: in, The lateral movement distance of the measured surface. The distance the internal texture of the speckle pattern has moved. The object distance during the process of the principal ray passing through the imaging lens when the surface under test is in its initial state is defined as follows: the principal ray is the ray emitted from the Gaussian beam in a direction perpendicular to the surface under test, passes through the optical center of the collimating lens, and after diffuse reflection on the surface under test, the reflected ray passes through the optical center of the imaging lens. The focal length of the imaging lens is... The angle between the main ray and the image acquisition module after the imaging lens passes through it. The reflection angle of the principal ray when it is reflected from the surface being measured; The lateral movement velocity of the measured surface is calculated based on the lateral movement distance of the measured surface, and is calculated in the following manner: in, The lateral movement velocity of the measured surface. The lateral movement distance of the measured surface. The time taken for the lateral movement distance of the measured surface.

2. The method for synchronously measuring speed and distance based on laser triangulation according to claim 1, characterized in that, The processor calculates the interval value of the light spot edge on the photosensitive surface of the image acquisition module based on the light spot, including: The processor selects the light spot acquired in the Tth acquisition and the light spot acquired in the T+1th acquisition from the light spots; A Gaussian filter is used to smooth the light spot acquired in the Tth and T+1th acquisitions. The Canny operator is used to determine the integer pixel edge points of the light spot acquired in the Tth time. Based on the Zernike moment and the integer pixel edge points of the light spot acquired in the Tth time, sub-pixel localization is performed on the light spot acquired in the Tth time to obtain the edge sub-pixel points of the light spot acquired in the Tth time. The Canny operator is used to determine the integer pixel edge points of the light spot acquired in the (T+1)th acquisition. Based on the Zernike moment and the integer pixel edge points of the light spot acquired in the (T+1)th acquisition, sub-pixel localization is performed on the light spot acquired in the (T+1)th acquisition to obtain the sub-pixel edge points of the light spot acquired in the (T+1)th acquisition. The interval value of the edge of the light spot on the photosensitive surface of the image acquisition module is calculated based on the edge sub-pixel points of the light spot acquired in the Tth acquisition and the edge sub-pixel points of the light spot acquired in the (T+1)th acquisition.

3. The method for synchronously measuring speed and distance based on laser triangulation according to claim 1, characterized in that, The axial movement distance of the measured surface is calculated based on the interval value of the light spot edge on the photosensitive surface of the image acquisition module, and is calculated in the following manner: in, Let A be the axial movement distance of the measured surface. In the initial state, the perpendicular distance between the measured surface and the collimating lens is A. When the perpendicular distance between the measured surface and the collimating lens is less than A, A is a positive value when the perpendicular distance between the measured surface and the collimating lens is greater than or equal to A. Negative value The interval value of the light spot on the photosensitive surface of the image acquisition module. The object distance during the process of the principal ray passing through the imaging lens when the surface under test is in its initial state is defined as follows: the principal ray is the ray emitted from the Gaussian beam in a direction perpendicular to the surface under test, passes through the optical center of the collimating lens, and after diffuse reflection on the surface under test, the reflected ray passes through the optical center of the imaging lens. The focal length of the imaging lens is... The angle between the main ray and the image acquisition module after the imaging lens passes through it. The reflection angle is the angle at which the principal ray is reflected from the surface being measured.

4. The method for synchronously measuring speed and distance based on laser triangulation according to claim 1, characterized in that, The preset resolution, and adjusting the imaging lens and the image acquisition module according to the preset resolution, includes: The focal length and position of the imaging lens are determined based on the resolution. The image acquisition module is determined based on the positions of the surface under test, the single-mode optical fiber, the collimating lens, and the imaging lens, and the image acquisition module satisfies Scheimpflug's law.

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