A cylindrical part diameter measuring device and method based on fringe projection

Abstract

The application provides a cylindrical part diameter measuring device and method based on fringe projection, which comprises a projection lamp, a 50 / 50 beam splitter, a two-dimensional camera and an image processing unit; the projection lamp projects a fringe to the surface of a measured structure for measuring the diameter information of the cross section of the measured part; the two-dimensional camera collects the projected fringe image of the surface of the measured part and transmits the collected fringe signal sequence to the image processing unit through a data line; and the image processing unit analyzes the fringe signal sequence in real time to obtain the diameter size of the measured part. The application realizes high-precision measurement of the diameter of the cylindrical part, effectively reduces the hardware cost, improves the processing efficiency of the measurement data, and achieves high-efficiency and high-precision detection of the geometric characteristics of the cylindrical part.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of machine vision measurement, and in particular to a cylindrical part diameter measurement device and method based on fringe projection. BACKGROUND

[0002] In the field of steel metal processing and detection, the diameter size of cylindrical parts is a key parameter affecting their quality and performance. Traditional detection methods usually use contact measurement tools such as calipers and micrometers, or use laser diameter measuring instruments and three-coordinate measuring instruments. However, these methods have certain limitations. Contact measurement can damage the measured surface and is difficult to implement online measurement. Non-contact laser measurement devices, although high in precision, are high in cost and difficult to be widely applied in production line environments.

[0003] In recent years, with the development of machine vision technology, visual measurement methods based on fringe projection have gradually been applied in industrial detection. Fringe projection technology projects a structured light pattern onto the surface of an object and calculates the geometric information of the object based on the deformation characteristics of the projected fringe. This method has the advantages of non-contact, high precision, and real-time measurement, and is suitable for automatic detection of the diameter of cylindrical parts on the production line. However, there is currently a lack of a low-cost, high-efficiency fringe projection system specifically for the detection of geometric characteristics of cylindrical parts, which can meet the needs of rapid detection on the production line. SUMMARY

[0004] In view of the above, the present application aims to provide a cylindrical part diameter measurement device and method based on fringe projection, which effectively reduces hardware costs and improves the processing efficiency of measurement data, achieving high-efficiency and high-precision detection of the geometric characteristics of cylindrical parts.

[0005] To achieve the above-mentioned purpose, the present application adopts the following technical solution: a cylindrical part diameter measurement device based on fringe projection, comprising a projection lamp, a 50 / 50 beam splitter, a two-dimensional camera, and an image processing unit, the two-dimensional camera being connected to the image processing unit; the projection lamp projects a fringe onto the surface of the measured structure to measure the diameter information of the measured part; the two-dimensional camera collects the projected fringe image on the surface of the measured part and transmits the collected fringe signal sequence to the image processing unit; the image processing unit analyzes the fringe signal sequence in real time to obtain the diameter size of the measured part.

[0006] In a preferred embodiment, the projection lamp comprises an LED light source and a sinusoidal fringe sheet, and the LED light source projects a sinusoidal fringe with a fixed period onto the surface of the measured structure.

[0007] In a preferred embodiment, the 50 / 50 beam splitter is placed in front of the projection lamp and the two-dimensional camera, and the 50 / 50 beam splitter is inclined at an angle of 45° with respect to the optical axis of the projection lamp and the two-dimensional camera. The 50 / 50 beam splitter is used to uniformly refract the light beam of the projection lamp to the surface of the measured structure, and the two-dimensional camera collects the projected fringe image reflected from the surface of the measured structure through the 50 / 50 beam splitter.

[0008] In a preferred embodiment, the two-dimensional camera includes a surface array sensor, an integrated circuit board, a device interface, and a power supply.

[0009] In a preferred embodiment, the projection lamp is arranged in front of the left of the axis of the measured structure, and the projection axis of the projection lamp is parallel to the axis of the measured structure. The projection axis is inclined at an angle of 45° with respect to the arrangement of the 50 / 50 beam splitter. The light beam of the projection lamp is refracted to the surface of the measured structure through the 50 / 50 beam splitter, and the fringe pattern uniformly covers the measured region of the measured structure.

[0010] The present application also provides a cylindrical part diameter measurement method based on fringe projection, which uses the cylindrical part diameter measurement device based on fringe projection.

[0011] Step S1: A designed sinusoidal fringe pattern is projected to the measurement region of the measured structure by using a fringe projection lamp, and the fringe beam is refracted by a 50 / 50 beam splitter to uniformly cover the measured region. The acquisition parameters of the two-dimensional camera are set, and the position and angle of the camera are adjusted to ensure that the camera can image and collect the projected fringe on the surface of the measured structure through the beam splitter, and the projected fringe pattern is clearly imaged at the center position of the two-dimensional camera. The camera is fixed to ensure the stability of imaging.

[0012] Step S2: The fringe image on the surface of the measured structure is continuously collected by the two-dimensional camera.

[0013] Step S3: The fringe image signal sequence collected by the two-dimensional camera is transmitted to the image processing unit through the data line, and the fringe signal sequence is analyzed by the image processing module. The diameter information of the measured structure is extracted by processing the density change and image deformation of the fringe.

[0014] In a preferred embodiment, step S3 is specifically as follows:

[0015] Step S31: The intensity signal of each row of fringes is extracted by performing grayscale processing on each row of fringe images collected in the measurement region of the fringe image.

[0016] Step S32: The frequency density distribution of each row of fringes is calculated by performing Fourier transform on the intensity of each row of fringes to obtain the main component in the frequency spectrum.

[0017] Step S33: The accurate density information of each row of fringes is obtained by using a spectrum correction technique, and a density variation curve of the fringes on the surface of the measured part is obtained, and a fringe density distribution map is generated.

[0018] Step S34: The fringe density variation curve is mapped to a surface profile curve of the measured structure measurement area by using a mapping relationship between the fringe density and the actual size.

[0019] In a preferred embodiment, the step S34 is specifically:

[0020] Step S341: The collected fringe density of each row is converted into an actual height h(x), and the calculation formula is:

[0021]

[0022] wherein D is the camera object distance, p0 is the reference row fringe density, p(x) is the fringe density of each row, x = 1, 2,..., n, and n is the number of pixel rows. o

[0023] Step S342: The size of the pixel point where the fringe density of each row is located is converted into an actual width w(x), and the calculation formula is:

[0024]

[0025] wherein D is the camera object distance, h(x) is the actual height of the fringe density of each row, a is the camera field of view angle, and P is the number of pixel points corresponding to the imaging width size. o

[0026] Step S343: The actual width w(x) and the actual height h(x) of the pixel point where each row of fringes is located are one-to-one mapped to obtain a point set (x i , y i ), and the point set is fitted to satisfy the standard form of a circular curve:

[0027] (x i -x c ) 2 +(y i -y c ) 2 =R 2

[0028] wherein (x c , y c ) is the center coordinates of the fitted circle, and R is the radius of the fitted circle.

[0029] Step S344: The point set (x i , y i ) is fitted by using a least square method.​) is carried out, the measurement error of the fitting result is calculated, the measured diameter D m is compared with the standard value D s , and the measurement error is calculated:

[0030] e r = |D m -D s |

[0031] Wherein the least square fitting principle is: the best fitting parameters (x c , y c , R) are found by minimizing the geometric error of the point set to the circle; the error calculation formula is:

[0032]

[0033] The total error is the sum of the error squares of all points:

[0034]

[0035] The circular equation is re-expressed in a linear form:

[0036] x 2 +y 2 +Ax+By+C=0

[0037] Wherein: A=-2x c , B=-2y c ,

[0038] According to the data of the point set (x i , y i ), a matrix form is constructed for solving:

[0039]

[0040] After A, B and C are solved, the center and the radius are calculated by minimizing the error function E:

[0041]

[0042] According to the fitting result, the diameter calculation formula of the circle is:

[0043] D=2R

[0044] Wherein R is the radius of the circle obtained by fitting.

[0045] Compared with the prior art, the present application has the following beneficial effects: the present application realizes non-contact high-precision measurement of the diameter of the cylindrical part, effectively reduces the hardware cost, improves the processing efficiency of the measurement data, and achieves high-efficiency and high-precision detection of the geometric characteristics of the cylindrical part. BRIEF DESCRIPTION OF DRAWINGS

[0046] Figure 1 is a schematic diagram of the diameter measuring device of the cylindrical part of the embodiment of the present application;

[0047] Figure 2 is a flow chart of the image processing of calculating the diameter of the cylindrical part of the embodiment of the present application; (a) is the intensity signal of each row of the fringe in the measuring area; (b) is the density variation curve of the fringe on the surface of the measured structure obtained from the fringe image of each area; (c) is the actual diameter curve obtained from the fringe density variation curve; (d) is the diameter fitting and error calculation.

[0048] Figure 1 In the figure, 1 is a projection lamp, 2 is a 50 / 50 beam splitter, 3 is a two-dimensional camera, 4 is a data transmission line, and 5 is a computer. DETAILED DESCRIPTION

[0049] The present application will be further described below in conjunction with the drawings and embodiments.

[0050] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present application. Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application pertains.

[0051] It should be noted that the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application; as used herein, the singular form is intended to include the plural form unless the context clearly indicates otherwise, and furthermore, it should be understood that when the terms "comprise" and / or "include" are used in the specification, there is a presence of a feature, step, operation, device, component, and / or a combination thereof.

[0052] A cylindrical part diameter measuring device and method based on fringe projection, referring to Figures 1-2 , comprising a projection lamp 1, a 50 / 50 beam splitter 2, a two-dimensional camera 3, and an image processing unit 5; the projection lamp 1 projects a fringe onto the surface of the measured part to measure the diameter information of the measured cylindrical part; the two-dimensional camera 3 collects the projected fringe image on the surface of the measured cylindrical part and transmits the collected fringe signal sequence to the image processing unit 5 through the data line 4; the image processing unit 5 analyzes the fringe signal sequence in real time to obtain the diameter size information of the cylindrical part.

[0053] The projection lamp 1 comprises an LED light source and a sinusoidal fringe sheet, the LED light source irradiates the sinusoidal fringe sheet to project a sinusoidal fringe with a fixed period onto the surface of the measured structure, and the size and position of the projected fringe pattern can be adjusted.

[0054] The 50 / 50 beam splitter 2 is placed in front of the projection lamp and the two-dimensional camera, and is inclined at 45° to the optical axis of the two devices. The 50 / 50 beam splitter 2 is used to uniformly refract the light beam of the projection lamp to the surface of the measured part, while allowing the two-dimensional camera 3 to collect the projected fringe image reflected from the surface of the measured part through the 50 / 50 beam splitter 2.

[0055] The two-dimensional camera 3 includes a surface array sensor, an integrated circuit board, a device interface, and a power supply. The imaging range can be reduced according to the pixel area where the projected fringe is located, so as to improve the sampling frame rate of the camera. When the two-dimensional camera 3 collects the projected fringe, the imaging optical axis thereof is perpendicular to the plane of the projected fringe, and the projected fringe is imaged at the center position of the image of the two-dimensional camera 3.

[0056] The projection lamp 1 is arranged in front of the left side of the shaft of the cylindrical part, and the projection axis thereof is parallel to the shaft of the measured structure. The projection axis is inclined at 45° to the 50 / 50 beam splitter 2, so that the light beam of the fringe projection lamp can be effectively refracted to the surface of the measured part after passing through the 50 / 50 beam splitter. The position and angle of the projection axis are optimized to ensure that the fringe pattern can uniformly cover the measured region of the measured part, thereby enhancing the clarity and measurement accuracy of the fringe pattern.

[0057] A cylindrical part diameter measurement method based on fringe projection, comprising the following steps:

[0058] Step S1: using a fringe projection lamp to project a designed sinusoidal fringe pattern to the measurement region of the measured cylindrical part, and refracting the fringe light beam through a 50 / 50 beam splitter so as to uniformly cover the measured region. The acquisition parameters of the two-dimensional camera are set, and the position and angle of the camera are adjusted, so that the camera can image and collect the projected fringe on the surface of the cylindrical part through the beam splitter, and ensure that the projected fringe pattern is clearly imaged at the center position of the two-dimensional sensor; and the camera is fixed to ensure the imaging stability;

[0059] Step S2: continuously collecting the fringe image on the surface of the measured cylindrical part through the two-dimensional sensor;

[0060] Step S3: transmitting the fringe image signal sequence collected by the two-dimensional camera to an image processing unit through a data line, and analyzing the fringe signal sequence through an image processing module. The diameter information of the measured part is extracted through the processing of the phase change of the fringe and the image deformation.

[0061] The step S3 is specifically:

[0062] Step S31: performing gray scale processing on each row of fringe images collected in the measurement region of the fringe image, and extracting the intensity signal of each row of fringe;

[0063] Step S32: Extract the main component in the fringe spectrum by Fourier transforming the intensity of each row of fringe to obtain the frequency domain information, and calculate the frequency density distribution of each row of fringe;

[0064] Step S33: Obtain the accurate density information of each row of fringe by using the spectrum correction technique, and then obtain the density variation curve of the fringe on the shaft surface to generate the fringe density distribution map.

[0065] Step S34: Convert the fringe density variation curve into the actual diameter curve of the measurement region of the cylindrical part by using the mapping relationship between the fringe density and the actual size obtained by system calibration.

[0066] The step S34 is specifically:

[0067] Step S341: Convert the collected fringe density of each row into the actual height, and the calculation formula is:

[0068]

[0069] Wherein: D o is the camera object distance, ρ0 is the reference row fringe density, ρ(x) is the fringe density of each row, x = 1, 2, …, n, and n is the number of pixel rows.

[0070] Step S342: Convert the pixel size of each row of fringe density into the actual width, and the calculation formula is:

[0071]

[0072] Wherein: D o is the camera object distance, h(x) is the actual height of each row of fringe density, α is the camera field of view angle, and P is the corresponding pixel number in the imaging width size.

[0073] Step S343: One-to-one map the actual width w(x) and the actual height h(x) of each row of fringe to obtain the point set (x i , y i ), and fit the point set to satisfy the standard form of the circular curve:

[0074] (x i -x c ) 2 +(y i -y c ) 2 =R 2

[0075] Wherein: (x c , y c ) is the center coordinates of the fitted circle, and R is the radius of the fitted circle.

[0076] Step S344: fitting the point set (x i ,y i ) using least square method, calculating the measurement error of the fitting result, comparing the measured diameter D m and the standard value D s , and calculating the measurement error:

[0077] e r = |D m -D s |

[0078] wherein the least square method fitting principle is: finding the best fitting parameters (x c ,y c , R) by minimizing the geometric error of the point set to the circle. The error calculation formula is:

[0079]

[0080] The total error is the sum of the error squares of all points:

[0081]

[0082] Express the circle equation in linear form again:

[0083] x 2 +y 2 +Ax+By+C=0

[0084] wherein: A = -2x c , B = -2y c ,

[0085] According to the data of the point set (x i ,y i ), construct a matrix form for solving:

[0086]

[0087] After solving A, B, and C, calculate the center and radius by minimizing the error function E:

[0088]

[0089] According to the fitting result, the diameter calculation formula of the circle is:

[0090] D = 2R

[0091] wherein R is the radius of the fitted circle.

Claims

1. A device for measuring the diameter of cylindrical parts based on fringe projection, characterized in that, The system includes a projection lamp, a 50 / 50 beam splitter, a 2D camera, and an image processing unit. The 2D camera is connected to the image processing unit. The projection lamp projects stripes onto the surface of the structure under test to measure the diameter of the part. The 2D camera acquires the projected stripe image on the surface of the part under test and transmits the acquired stripe signal sequence to the image processing unit. The image processing unit analyzes the stripe signal sequence in real time to obtain the diameter of the part under test. The measurement method based on the measuring device includes the following steps: Step S1: Project the designed sinusoidal stripe pattern onto the measurement area of ​​the structure under test using a stripe projection lamp, and refract the stripe beam through a 50 / 50 beam splitter to uniformly cover the measurement area; set the acquisition parameters of the two-dimensional camera, adjust the position and angle of the camera so that the camera can image and acquire the projected stripes on the surface of the structure under test through the beam splitter, and ensure that the projected stripe pattern is clearly imaged at the center of the two-dimensional camera; fix the camera to ensure imaging stability. Step S2: Continuously acquire stripe images of the surface of the structure under test using a two-dimensional camera; Step S3: The stripe image signal sequence acquired by the two-dimensional camera is transmitted to the image processing unit via a data cable. The image processing module analyzes the stripe signal sequence and extracts the diameter information of the measured structure by processing the density change and image deformation of the stripes. Step S3 specifically involves: Step S31: Extract the intensity signal of each stripe by performing grayscale processing on each row of stripe images acquired in the measurement area of ​​the stripe image; Step S32: By performing a Fourier transform on the intensity of each row of stripes, frequency domain information is obtained, the main components in the stripe spectrum are extracted, and the frequency density distribution of each row of stripes is calculated. Step S33: By using spectral correction technology to obtain the precise density information of each row of stripes, the density variation curve of the stripes on the surface of the tested part can be obtained, and a stripe density distribution map can be generated. Step S34: Using the mapping relationship between stripe density and actual size, the stripe density variation curve is mapped to the surface profile curve of the measurement area of ​​the structure under test.

2. The device for measuring the diameter of cylindrical parts based on fringe projection according to claim 1, characterized in that, The projection lamp includes an LED light source and a sinusoidal stripe sheet. The LED light source illuminates the sinusoidal stripe sheet and projects sinusoidal stripes with a fixed period onto the surface of the structure being measured.

3. The diameter measuring device for cylindrical parts based on fringe projection according to claim 1, characterized in that, The 50 / 50 beam splitter is placed in front of the projector and the 2D camera. The 50 / 50 beam splitter is tilted at 45° to the optical axis of the projector and the 2D camera. The 50 / 50 beam splitter is used to uniformly refract the beam of the projector onto the surface of the structure under test. At the same time, the 2D camera acquires the projected fringe image reflected from the surface of the structure under test through the 50 / 50 beam splitter.

4. The diameter measuring device for cylindrical parts based on fringe projection according to claim 1, characterized in that, The two-dimensional camera includes an area array sensor, an integrated circuit board, a device interface, and a power supply.

5. The diameter measuring device for cylindrical parts based on fringe projection according to claim 1, characterized in that, The projection lamp is positioned to the left front of the axis of the structure under test, with the projection axis of the projection lamp parallel to the axis of the structure under test. The angle between the projection axis and the 50 / 50 beam splitter is 45°, so that the beam of the projection lamp is refracted onto the surface of the structure under test after passing through the 50 / 50 beam splitter, and the stripe pattern uniformly covers the test area of ​​the structure under test.

6. The diameter measuring device for cylindrical parts based on fringe projection according to claim 1, characterized in that, Step S34 specifically involves: Step S341: Convert the collected stripe density of each row into actual height. The calculation formula is as follows: in: For camera object distance, For reference row fringe density, For the density of each row of stripes, , The number of rows of pixels; Step S342: Convert the pixel size of each row of stripe density to the actual width. The calculation formula is as follows: in: For camera object distance, The actual height of each row of stripes density. For the camera's field of view, This represents the number of pixels corresponding to the image width dimension; Step S343: Set the actual width of the pixels containing each row of stripes. Compared to actual height By performing a one-to-one mapping, we obtain the point set. Fit a set of points to make it conform to the standard form of a circular curve: in: To fit the coordinates of the center of the circle, Let be the radius of the fitted circle; Step S344: Use the least squares method to divide the point set Perform a fitting operation, calculate the measurement error of the fitting result, and measure the diameter. and standard value Compare and calculate the measurement error: The principle of the least squares fitting method is as follows: the optimal fitting parameters are found by minimizing the geometric error from the point set to the circle. The error calculation formula is: The total error is the sum of the squared errors at all points: Re-express the circular equation in linear form: in: , , ; Based on point set The data is used to construct a matrix to solve the problem: Solving , , Then, by minimizing the error function Calculate the center and radius of the circle: Based on the fitting results, the formula for calculating the diameter of a circle is: Where R is the radius of the fitted circle.

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