Cylindrical part diameter measuring device and method based on fringe projection

Abstract

The invention provides a device and a method for measuring the diameter of a cylindrical part based on fringe projection. The device comprises a projection lamp, a 50 / 50 spectroscope, a two-dimensional camera and an image processing unit, the projection lamp projects the fringes to the surface of the measured structure so as to measure the diameter information of the section of the measured part; the two-dimensional camera collects projection fringe images on the surface of a measured part and transmits a collected fringe signal sequence to the image processing unit through a data line. And the image processing unit analyzes the stripe signal sequence in real time so as to obtain the diameter size of the measured part. According to the invention, the high-precision measurement of the diameter of the cylindrical part is realized, the hardware cost is effectively reduced, the processing efficiency of the measured data is improved, and the high-efficiency and high-precision detection of the geometrical characteristics of the cylindrical part is realized.

Description

Technical Field

[0001] The invention relates to the technical field of machine vision measurement, and in particular to a device and method for measuring the diameter of cylindrical parts based on fringe projection. Background Art

[0002] In the field of steel metal processing and inspection, the diameter size of cylindrical parts is a key parameter affecting their quality and performance. Traditional inspection methods usually use contact measurement, such as tools such as calipers and micrometers, or use equipment such as laser diameter gauges and three-coordinate measuring machines. However, these methods have certain limitations. Contact measurement may cause damage to the measured surface and it is difficult to achieve online measurement; and non-contact laser measurement equipment has higher accuracy but higher cost, which makes it difficult to be widely used in assembly line production environments.

[0003] In recent years, with the development of machine vision technology, visual measurement methods based on fringe projection have gradually been applied to industrial inspection. 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 fringes. This method has the advantages of non-contact, high precision, and real-time measurement, and is suitable for automated 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 that can meet the needs of rapid detection on the production line. Summary of the invention

[0004] In view of this, the purpose of the present invention is to provide a cylindrical parts diameter measurement device and method based on fringe projection, which effectively reduces the hardware cost, improves the processing efficiency of measurement data, and achieves efficient and high-precision detection of the geometric characteristics of cylindrical parts.

[0005] To achieve the above-mentioned purpose, the present invention adopts the following technical scheme: a cylindrical part diameter measuring device based on fringe projection, comprising a projection lamp, a 50 / 50 beam splitter, a two-dimensional camera and an image processing unit, wherein the two-dimensional camera is connected to the image processing unit; the projection lamp projects fringes 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 includes an LED light source and a sinusoidal stripe sheet, and the LED light source illuminates the sinusoidal stripe sheet to project sinusoidal stripes with a fixed period onto the surface of the structure to be measured.

[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 45° to the optical axis of the projection lamp and the two-dimensional camera. The 50 / 50 beam splitter is used to evenly refract the light beam of the projection lamp to the surface of the structure to be measured, and the two-dimensional camera collects the projection fringe image reflected from the surface of the structure to be measured through the 50 / 50 beam splitter.

[0008] In a preferred embodiment, the two-dimensional camera includes an 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 side of the axis where the measured structure is located, so that the projection axis of the projection lamp is parallel to the axis where the measured structure is located, and the arrangement angle between the projection axis and the 50 / 50 beam splitter is 45°, so that the light beam of the projection lamp is refracted to the surface of the measured structure after passing through the 50 / 50 beam splitter, and the stripe pattern evenly covers the measured area of ​​the measured structure.

[0010] The present invention also provides a method for measuring the diameter of a cylindrical part based on fringe projection, using the device for measuring the diameter of a cylindrical part based on fringe projection, comprising the following steps:

[0011] Step S1: Use a stripe projector to project the designed sinusoidal stripe pattern onto the measuring area of ​​the structure to be measured, and refract the stripe beam through a 50 / 50 beam splitter to evenly cover the measured 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 collect the projected stripes on the surface of the structure to be measured 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;

[0012] Step S2: continuously collecting fringe images on the surface of the structure to be measured by a 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. The image processing module analyzes the fringe signal sequence and extracts the diameter information of the measured structure by processing the density change and image deformation of the fringe.

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

[0015] Step S31: extracting the intensity signal of each row of stripes by grayscale processing on each row of stripe images collected in the measurement area of ​​the stripe image;

[0016] Step S32: Perform Fourier transform on the intensity of each row of fringes to obtain frequency domain information, extract the main components in the fringes spectrum, and calculate the frequency density distribution of each row of fringes;

[0017] Step S33: using spectrum correction technology to obtain accurate 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 diagram can be generated;

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

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

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

[0021]

[0022] Where: 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, n is the number of pixel rows;

[0023] Step S342: Convert the pixel size of each row of stripe density to the actual width w(x), and the calculation formula is:

[0024]

[0025] Where: 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 number of pixels corresponding to the imaging width size;

[0026] Step S343: Map the actual width w(x) and the actual height h(x) of the pixel points where each row of stripes is located one by one to obtain a point set (x i ,y i ), and fit the point set to satisfy the standard form of a circular curve:

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

[0028] Where: (x c ,y c ) is the coordinate of the center of the fitting circle, and R is the radius of the fitting circle;

[0029] Step S344: Use the least squares method to transform the point set (x i ,y i) to fit the measured diameter D m and standard value D s For comparison, calculate the measurement error:

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

[0031] The least squares fitting principle is to find the best fitting parameter (x c ,y c , R); the error calculation formula is:

[0032]

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

[0034]

[0035] Re-express the circle equation in linear form:

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

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

[0038] According to the point set (x i ,y i ) data, construct a matrix form to solve:

[0039]

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

[0041]

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

[0043] D=2R

[0044] Where R is the radius of the fitted circle.

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

[0046] Figure 1 2 is a schematic structural diagram of a cylindrical parts diameter measuring device according to an embodiment of the present invention;

[0047] Figure 2 1 is an image processing flow chart for calculating the diameter of cylindrical parts according to an embodiment of the present invention; wherein (a) is the intensity signal of each row of stripes in the measurement area; (b) is the density variation curve of the stripes on the surface of the measured structure obtained by the stripe image of each area; (c) is the actual diameter curve obtained by the stripe density variation curve; and (d) is the diameter fitting and calculation error.

[0048] Figure 1 Among them, 1-projection lamp, 2-50 / 50 beam splitter, 3-two-dimensional camera, 4-data transmission line, 5-computer. DETAILED DESCRIPTION

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

[0050] It should be noted that the following detailed descriptions are illustrative 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.

[0051] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application; as used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or their combinations.

[0052] A cylindrical parts diameter measurement device and method based on fringe projection, reference Figure 1-2 , including 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 stripes 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 stripe image on the surface of the measured cylindrical part, and transmits the collected stripe signal sequence to the image processing unit 5 via a data line 4; the image processing unit 5 analyzes the stripe 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 stripe sheet. The LED light source irradiates the sinusoidal stripe sheet to project sinusoidal stripes with a fixed period onto the surface of the structure to be measured. The size and position of the projected stripe 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 axes of the two devices. The 50 / 50 beam splitter 2 is used to evenly refract the light beam of the projection lamp to the surface of the part to be measured, while allowing the two-dimensional camera 3 to collect the projection fringe image reflected from the surface of the part to be measured through the 50 / 50 beam splitter 2.

[0055] The two-dimensional camera 3 includes an 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 projection stripes are located to improve the sampling frame rate of the camera. When the two-dimensional camera 3 collects the projection stripes, its imaging optical axis is perpendicular to the projection stripe plane, and the projection stripes are placed at the center of the image of the two-dimensional camera 3 for imaging.

[0056] The projection lamp 1 is arranged in the front left of the axis of the cylindrical part, so that its projection axis is parallel to the axis of the measured structure, and the arrangement angle between the projection axis and the 50 / 50 beam splitter 2 is 45°, so that the light beam of the stripe 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 stripe pattern can evenly cover the measured area of ​​the measured part, thereby enhancing the clarity and measurement accuracy of the stripe pattern.

[0057] A method for measuring the diameter of cylindrical parts based on fringe projection comprises the following steps:

[0058] Step S1: Use a stripe projector to project the designed sinusoidal stripe pattern onto the measuring area of ​​the cylindrical part to be measured, and refract the stripe beam through a 50 / 50 beam splitter to evenly cover the measured 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 collect the projected stripes on the surface of the cylindrical part through the beam splitter, and ensure that the projected stripe pattern is clearly imaged at the center of the two-dimensional sensor; fix the camera to ensure imaging stability;

[0059] Step S2: continuously collecting fringe images on the surface of the cylindrical part to be measured by a two-dimensional sensor;

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

[0061] The step S3 is specifically as follows:

[0062] Step S31: extracting the intensity signal of each row of stripes by grayscale processing on each row of stripe images collected in the measurement area of ​​the stripe image;

[0063] Step S32: Perform Fourier transform on the intensity of each row of fringes to obtain frequency domain information, extract the main components in the fringes spectrum, and calculate the frequency density distribution of each row of fringes;

[0064] Step S33: using spectrum correction technology to obtain accurate density information of each row of stripes, the density variation curve of the stripes on the surface of the shaft can be obtained, and a stripe density distribution diagram can be generated;

[0065] Step S34: using the mapping relationship between the fringe density calibrated by the system and the actual size, the fringe density variation curve is converted into the actual diameter curve of the cylindrical part measurement area.

[0066] The step S34 is specifically as follows:

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

[0068]

[0069] Where: 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 stripe density to actual width, and the calculation formula is:

[0071]

[0072] Where: 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 number of pixels corresponding to the imaging width size.

[0073] Step S343: Map the actual width w(x) and the actual height h(x) of the pixel points where each row of stripes is located one by one to obtain a point set (x i ,y i ), and fit the point set to satisfy the standard form of a circular curve:

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

[0075] Where: (x c ,y c ) is the coordinate of the center of the fitting circle, and R is the radius of the fitting circle.

[0076] Step S344: Use the least squares method to transform the point set (x i ,y i ) to fit the measured diameter D m and standard value D s For comparison, calculate the measurement error:

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

[0078] The least squares fitting principle is to find the best fitting parameter (x c ,y c ,R). The error calculation formula is:

[0079]

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

[0081]

[0082] Re-express the circle equation in linear form:

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

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

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

[0086]

[0087] After solving A, B, and C, the center and radius of the circle are calculated by minimizing the error function E:

[0088]

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

[0090] D=2R

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

Claims

1. A cylindrical parts diameter measuring device based on fringe projection, characterized in that: It includes a projection lamp, a 50 / 50 beam splitter, a two-dimensional camera and an image processing unit, wherein the two-dimensional camera is connected to the image processing unit; the projection lamp projects stripes onto the surface of the measured structure to measure the diameter information of the measured part; the two-dimensional camera collects the projected stripe image on the surface of the measured part and transmits the collected stripe signal sequence to the image processing unit; the image processing unit analyzes the stripe signal sequence in real time to obtain the diameter size of the measured part.

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

3. The cylindrical parts diameter measuring device based on fringe projection according to claim 1 is characterized in that: The 50 / 50 beam splitter is placed in front of the projection lamp and the two-dimensional camera. The 50 / 50 beam splitter is inclined at 45° to the optical axis of the projection lamp and the two-dimensional camera. The 50 / 50 beam splitter is used to evenly refract the light beam of the projection lamp to the surface of the structure to be measured. At the same time, the two-dimensional camera collects the projection fringe image reflected from the surface of the structure to be measured through the 50 / 50 beam splitter.

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

5. The cylindrical parts diameter measuring device based on fringe projection according to claim 1 is characterized in that: The projection lamp is arranged in front of the left of the axis where the measured structure is located, so that the projection axis of the projection lamp is parallel to the axis where the measured structure is located, and the arrangement angle between the projection axis and the 50 / 50 beam splitter is 45°, so that the light beam of the projection lamp is refracted to the surface of the measured structure after passing through the 50 / 50 beam splitter, and the stripe pattern evenly covers the measured area of ​​the measured structure.

6. A method for measuring the diameter of cylindrical parts based on fringe projection, characterized in that The cylindrical parts diameter measuring device based on fringe projection as claimed in any one of claims 1 to 5 comprises the following steps: Step S1: Use a stripe projector to project the designed sinusoidal stripe pattern onto the measuring area of ​​the structure to be measured, and refract the stripe beam through a 50 / 50 beam splitter to evenly cover the measured 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 collect the projected stripes on the surface of the structure to be measured 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 collecting fringe images on the surface of the structure to be measured by a two-dimensional camera; Step S3: The fringe image signal sequence collected by the two-dimensional camera is transmitted to the image processing unit through the data line. The image processing module analyzes the fringe signal sequence and extracts the diameter information of the measured structure by processing the density change and image deformation of the fringe.

7. The method for measuring the diameter of cylindrical parts based on fringe projection according to claim 6, characterized in that: The step S3 is specifically as follows: Step S31: extracting the intensity signal of each row of stripes by grayscale processing on each row of stripe images collected in the measurement area of ​​the stripe image; Step S32: Perform Fourier transform on the intensity of each row of fringes to obtain frequency domain information, extract the main components in the fringes spectrum, and calculate the frequency density distribution of each row of fringes; Step S33: using spectrum correction technology to obtain accurate 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 diagram can be generated; Step S34: using the mapping relationship between the fringe density and the actual size, the fringe density variation curve is mapped into a surface profile curve of the measurement area of ​​the measured structure.

8. The method for measuring the diameter of cylindrical parts based on fringe projection according to claim 7, characterized in that: The step S34 is specifically as follows: Step S341: convert the collected stripe density of each row into the actual height h(x), and the calculation formula is: Where: 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, n is the number of pixel rows; Step S342: Convert the pixel size of each row of stripe density to the actual width w(x), and the calculation formula is: Where: 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 number of pixels corresponding to the imaging width size; Step S343: Map the actual width w(x) and actual height h(x) of the pixel points where each row of stripes is located one by one to obtain the point set ( x i ,y i) , fit the point set so that it satisfies the standard form of a circular curve: (x i -x c) 2 + ( y i -y c) 2 =R 2 in: ( x c ,y c) is the coordinate of the center of the fitting circle, and R is the radius of the fitting circle; Step S344: Use the least squares method to transform the point set ( x i ,y i) Perform fitting, calculate the measurement error of the fitting result, and measure the diameter D m and standard value D s For comparison, calculate the measurement error: e r = | D m -D s | The least squares fitting principle is to find the best fitting parameters by minimizing the geometric error from the point set to the circle. ( x c ,y c ,R ) ; The error calculation formula is: The total error is the sum of squared errors of all points: Re-express the circle equation in linear form: x 2 +y 2 +Ax+By+C=0 Where: A = -2x c , B=-2y c , According to the point set ( x i ,y i) The data is constructed in matrix form to solve: After solving A, B, and C, the center and radius of the circle are calculated by minimizing the error function E: According to the fitting results, the calculation formula for the diameter of the circle is: D=2R Where R is the radius of the fitted circle.

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