CN111815575A - Bearing steel ball part detection method based on machine vision - Google Patents

Bearing steel ball part detection method based on machine vision Download PDF

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CN111815575A
CN111815575A CN202010564947.0A CN202010564947A CN111815575A CN 111815575 A CN111815575 A CN 111815575A CN 202010564947 A CN202010564947 A CN 202010564947A CN 111815575 A CN111815575 A CN 111815575A
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steel ball
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CN111815575B (en
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产思贤
胡超群
周小龙
陈小佳
陈胜勇
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Zhejiang University of Technology ZJUT
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    • G06T7/00Image analysis
    • G06T7/0002Inspection of images, e.g. flaw detection
    • G06T7/0004Industrial image inspection
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Abstract

A bearing steel ball part detection method based on machine vision comprises steel ball circularity detection and part scratch detection and comprises the following steps: the method comprises the following steps of firstly, detecting the circularity of a steel ball, and the process is as follows: 1.1) preprocessing an input image; 1.2) acquiring the outline of the steel ball; 1.3) screening the obtained edges, and outputting the outline and circle center radius of the steel ball qualified by detection; step two, detecting scratches of the parts: 2.1) detecting the edge of the front surface of the part; 2.2) detecting the side edge of the part. The invention provides a bearing steel ball part detection method based on machine vision, which can overcome various interference factors and establish a high-efficiency and stable detection system.

Description

Bearing steel ball part detection method based on machine vision
Technical Field
The invention relates to the field of part detection, in particular to a bearing steel ball part detection method based on machine vision.
Background
While promoting social progress, humans have given machines a lot of complex work with a great deal of repeatability, and machine vision systems are in this category. Generally, machine vision systems are industrial test monitoring systems. In some dangerous work places or situations where the identification by human eyes is difficult, machine vision systems are often used to improve the quality or automation of the production line. Machine vision technology is one direction in the detection field, and aims to replace human eyes with machines to complete tasks of detection, identification, classification and the like. The complete machine vision technology comprises the technologies of light source illumination, optical imaging, digital image processing, machine classification, industrial control and the like, and has high stability and accuracy. Machine vision is mainly used in semiconductor, electronic, and mechanical industries, such as integrated circuit manufacturing, electronic molding, screen printing, and component molding. In addition, machine vision is also widely used in product quality inspection systems, and plays a significant role in industrial production.
The existing part detection method is generally based on a machine vision technology. A set of circular part detection framework is developed by researchers based on a machine vision technology, the precision measurement of the circular part is realized through simple camera calibration and sub-pixels, and an algorithm model mainly comprises four parts of system correction, preprocessing, image binarization and circular detection. The precision machining technology of the aspheric surface curved surface optical part is analyzed and researched, a set of ultra-precision air compression spindle system is developed, and the detection precision is improved to the international standard. Scanning an image of a computer hard disk sheet part to be detected by a linear array industrial camera, providing a new calibration algorithm and a new contour vectorization algorithm according to the characteristics of image scanning, and combining calibration, binaryzation, edge detection, contour vectorization and the like to obtain the size parameter of the part to be detected. Some researchers detect the defects on the surface of the part, accurately extract the detection area of the target part by performing a dynamic extraction algorithm twice, and then generate detection parameters based on a statistical chart classification algorithm and edge information such as the width, thickness, dispersion degree, deflection degree and the like of the part. On a modern automatic assembly line, the detection system can confirm the size, the number, the defect and the like of parts at any time and any place, and the industrial production efficiency is greatly improved. However, the problem of the current machine vision is also obvious, and the problems of time lag, low precision, poor stability and the like of the system are all needed to be solved urgently.
Disclosure of Invention
In order to overcome the defects that the parts cannot be detected quickly and accurately in the prior art and to solve the technical problems, the invention provides a bearing steel ball part detection method based on machine vision, which can overcome various interference factors and establish a high-efficiency and stable detection system.
The technical scheme adopted by the invention for solving the technical problems is as follows:
a bearing steel ball part detection method based on machine vision is characterized by comprising the following steps:
the method comprises the following steps of firstly, detecting the circularity of a steel ball, and the process is as follows:
1.1) image preprocessing: preprocessing an input image by using Gaussian filtering to remove high-frequency signals in the image;
1.2) extracting superior mesenteric artery mouth: the image is converted by methods such as gray level conversion, threshold segmentation and the like, so that the subsequent algorithm can more easily identify image information; through this step, the system will get several closed edge profiles;
1.3) screening edge profiles: in order to obtain a better detection edge, three screening conditions are adopted: contour pixel domain detection, ellipse fitting detection and circularity detection, wherein the contour pixel domain detection is to count the pixel area of each contour; because the circular outline of the steel ball can form an ellipse similar to a circle after imaging, ellipse fitting is carried out, and noise interference can be effectively eliminated; finally, after the edge profile information of the steel ball is obtained, the circularity of the ellipse is detected, and the purpose of the step is to detect whether the shape of the steel ball meets the production specification;
secondly, detecting scratches of the parts, wherein the process is as follows:
2.1) detecting scratches on the side surfaces of the parts: detecting the scratches on the side surfaces of the parts by using an edge detection method, firstly determining edge pixels in an image, and then connecting the pixels together to form a required area boundary;
2.2) detecting scratches on the front surface of the part: because too much edge information on the front side can cause serious influence on the classification result, a method for eliminating redundant edge information is adopted to remove high-frequency signals in the image.
Further, 2.1), the image edge represents the beginning of one region and another region in the image, and the set of pixels between adjacent regions in the image constitutes the edge of the image, so the edge of the image can be understood as the set of pixels with spatial abrupt change of the gray level of the image, and the image edge has two important concepts: the direction and gradient of the pixel change along the edge direction are smooth, and the pixel change perpendicular to the edge direction is severe, so according to the characteristic, the edge detection is usually performed by using a first derivative and a second derivative, so that the edge detection in an image can be determined by differentiating the gray value, and the derivative operation can be performed by a differential operator.
Further, the step of 2.2) is as follows:
2.2.1) preprocessing the image by using smooth filtering to remove high-frequency signals in the image;
2.2.2) detecting the image edge information by adopting an edge detection method and extracting a closed contour of the image;
2.2.3) carrying out ellipse fitting on the outline by using an ellipse fitting method, wherein the ellipse fitting is carried out because the target area to be extracted is a circular ring;
2.2.4) selecting a proper threshold value according to the fixed information of the image, screening the obtained elliptic contour to obtain the inner circle contour and the outer circle contour of the circular ring area, and finally obtaining the target area to be extracted by adopting an image subtraction method.
The invention has the following beneficial effects: based on machine vision, the problem that defective products are difficult to distinguish manually in the industrial production process is solved. And the method has high stability and portability and wide application prospect.
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FIG. 1 is a machine vision inspection system of the present invention;
FIG. 2 is a schematic view of the circularity detection of the present invention;
fig. 3 is a front surface inspection flow of the component of the present invention.
Detailed Description
The invention is further described below with reference to the accompanying drawings.
Referring to fig. 1 to 3, a bearing steel ball part detection method based on machine vision mainly solves steel ball circularity detection and part scratch detection, and comprises the following steps:
the first step, steel ball circularity detection, the flow of the detection method is shown in figure 2, and the process is as follows:
1.1) preprocessing an input image, which comprises the following specific steps:
firstly, preprocessing an input image by using Gaussian filtering to remove high-frequency signals in the image;
1.2) obtaining the steel ball profile, which comprises the following steps:
after the preprocessed information is obtained, the image is converted by methods such as gray level conversion, threshold segmentation and the like, so that the subsequent algorithm can more easily distinguish the image information. Through the step, the system can obtain a plurality of closed edge profiles, wherein only one closed edge profile is the edge profile of the steel ball, and the other closed edge profiles are noise interference generated by illumination;
1.3) screening the obtained edge profile, and outputting the profile and the circle center radius of the steel ball qualified by detection, wherein the steps are as follows:
in order to obtain a better detection edge, the invention adopts three screening conditions: contour pixel domain detection, ellipse fitting detection and circularity detection. Contour pixel domain detection is the statistics of the pixel area of each contour. Because the circular outline of the steel ball can form an ellipse similar to a circle after imaging, the ellipse fitting is carried out, and noise interference can be effectively eliminated. And finally, after the edge profile information of the steel ball is obtained, performing circularity detection on the ellipse, wherein the circularity of the profile is changed within a certain error range after the system is imaged in order to detect whether the appearance of the steel ball meets the production specification, and the steel ball beyond the range is likely to be a part which has defects and needs to be removed. The pixel threshold herein is: 1600. 2000, threshold of circularity 0.980;
circularity is the complexity used to delineate the boundaries of an image object, the value of which is minimal when the object is a perfect circle. The most common circularity is the ratio of the square of the circumference to the area, which is larger the more complex the shape, and the circularity index takes a minimum value of 4 pi when it is perfectly circular. Taking C as a circularity index, P as a perimeter and A as an area, the calculation formula is as follows:
Figure BDA0002547495200000051
the above calculation method is relatively rough, and the invention adopts boundary energy to measure. Taking p as the distance from any point on the boundary to some starting point. At any point, the boundary has an instantaneous radius of curvature r (p), which is the radius of the circle tangent to the boundary from the geometric relationship. The curvature function at point p is as follows:
Figure BDA0002547495200000052
the function K (p) is a periodic function with a period p. The average energy per unit boundary length is calculated as follows:
Figure BDA0002547495200000061
the radius of the circle is taken as R. The curvature can be calculated from the chain code, so the boundary energy can be easily obtained. For a boundary of fixed area, the minimum boundary energy E of a circle0Comprises the following steps:
Figure BDA0002547495200000062
wherein p is the distance from any point on the boundary to a certain starting point, and R is the radius of the circle;
secondly, detecting scratches of the parts, wherein the process is as follows:
2.1) detecting the scratches on the side surfaces of the parts, which comprises the following basic steps:
the invention uses an edge detection method to detect the side scratch of the part, firstly determines edge pixels in the image, and then connects the pixels together to form the required area boundary. The image edge represents the beginning of one region and another region in the image, and the set of pixels between adjacent regions in the image constitutes the edge of the image. Therefore, the edge of the image can be understood as a collection of pixels in which the gray level of the image has a spatial abrupt change. There are two important concepts of image edges: direction and gradient. The pixel variation along the edge direction is relatively smooth, while the pixel variation perpendicular to the edge direction is relatively sharp. Therefore, according to this feature, edge detection is usually performed using first and second derivatives. Therefore, edge detection in an image can be determined by deriving the gray value, and the derivative operation can be performed by a differential operator;
the Sobel operator is a first order differential operator, which calculates the gradient of each pixel by the gradient value of the adjacent area of the pixel, and finally performs the selection according to a fixed threshold value. The calculation formula is as follows:
Figure BDA0002547495200000063
the Sobel operator is a three-layer operator template, and is formed by two convolution kernels of dx and dy. One convolution kernel carries out calculation of a vertical edge, one convolution kernel carries out calculation of a horizontal convolution kernel, and the maximum value of the two convolution kernels is used as the final output result of the calculation.
In addition to the Sobel operator, Canny operator is also used herein for edge detection. The Canny operator is used herein to calculate local maxima of the image gradient, finding strong and weak edges of the target by two thresholds. The method is essentially to carry out smoothing treatment through a quasi-Gaussian function, and then locate the maximum value of the derivative through a first-order differential operator. The mean of the finite differences can be calculated in the second order square to find the partial derivative gradient at a point in the image. The direction angle and the amplitude can be calculated by a coordinate conversion formula from a rectangular coordinate system to a polar coordinate system:
Figure BDA0002547495200000071
Figure BDA0002547495200000072
where M [ i, j ] reflects the edge strength of the image and θ [ i, j ] reflects the edge direction of the image. When M [ i, j ] obtains a local maximum, θ [ i, j ] is the edge direction at that time. For the gradient amplitude, extracting a pixel with the maximum gradient value in each gradient direction by adopting a non-maximum value inhibition method;
2.2) detecting the front edge of the part, wherein the detection process is as shown in fig. 3, and because too much front edge information can seriously affect the classification result, the invention provides a method for eliminating redundant edge information, which removes high-frequency signals in an image, and comprises the following steps:
2.2.1) preprocessing the image by using smooth filtering to remove high-frequency signals in the image;
2.2.2) detecting the image edge information by adopting an edge detection method and extracting a closed contour of the image;
2.2.3) carrying out ellipse fitting on the outline by using an ellipse fitting method, wherein the ellipse fitting is carried out because the target area to be extracted is a circular ring;
2.2.4) selecting a proper threshold value according to the fixed information of the image, screening the obtained elliptic contour to obtain the inner circle contour and the outer circle contour of the circular ring area, and finally obtaining the target area to be extracted by adopting an image subtraction method.
The above description is only an embodiment of the present invention, and not intended to limit the scope of the present invention, and all equivalent structures or equivalent flow transformations made by using the contents of the specification and drawings, or applied directly or indirectly to other related technical fields are included in the scope of the present invention.

Claims (3)

1. A bearing steel ball part detection method based on machine vision is characterized by comprising the following steps:
the method comprises the following steps of firstly, detecting the circularity of a steel ball, and the process is as follows:
1.1) image preprocessing: preprocessing an input image by using Gaussian filtering to remove high-frequency signals in the image;
1.2) acquiring the steel ball profile: the image is converted by methods such as gray level conversion, threshold segmentation and the like, so that the subsequent algorithm can more easily identify image information; through this step, the system will get several closed edge profiles;
1.3) screening edge profiles: in order to obtain a better detection edge, three screening conditions are adopted: contour pixel domain detection, ellipse fitting detection and circularity detection, wherein the contour pixel domain detection is to count the pixel area of each contour; because the circular outline of the steel ball can form an ellipse similar to a circle after imaging, ellipse fitting is carried out, and noise interference can be effectively eliminated; finally, after the edge profile information of the steel ball is obtained, the circularity of the ellipse is detected, and the purpose of the step is to detect whether the shape of the steel ball meets the production specification;
secondly, detecting scratches of the parts, wherein the process is as follows:
2.1) detecting scratches on the side surfaces of the parts: detecting the scratches on the side surfaces of the parts by using an edge detection method, firstly determining edge pixels in an image, and then connecting the pixels together to form a required area boundary;
2.2) detecting scratches on the front surface of the part: because too much edge information on the front side can cause serious influence on the classification result, a method for eliminating redundant edge information is adopted to remove high-frequency signals in the image.
2. The method for detecting a steel ball part of a bearing based on machine vision as claimed in claim 1, wherein in 2.1), the image edge represents the beginning of one region and the other region in the image, and the set of pixels between adjacent regions in the image forms the edge of the image, so that the edge of the image can be understood as the set of pixels with spatial abrupt change of the gray level of the image, and the image edge has two important concepts: the direction and gradient of the pixel change along the edge direction are smooth, and the pixel change perpendicular to the edge direction is severe, so according to the characteristic, the edge detection is usually performed by using a first derivative and a second derivative, so that the edge detection in an image can be determined by differentiating the gray value, and the derivative operation can be performed by a differential operator.
3. A bearing steel ball part detection method based on machine vision as claimed in claim 1 or 2, characterized in that the steps of 2.2) are as follows:
2.2.1) preprocessing the image by using smooth filtering to remove high-frequency signals in the image;
2.2.2) detecting the image edge information by adopting an edge detection method and extracting a closed contour of the image;
2.2.3) carrying out ellipse fitting on the outline by using an ellipse fitting method, wherein the ellipse fitting is carried out because the target area to be extracted is a circular ring;
2.2.4) selecting a proper threshold value according to the fixed information of the image, screening the obtained elliptic contour to obtain the inner circle contour and the outer circle contour of the circular ring area, and finally obtaining the target area to be extracted by adopting an image subtraction method.
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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN112613523A (en) * 2020-12-15 2021-04-06 中冶赛迪重庆信息技术有限公司 Method, system, medium and electronic terminal for identifying steel flow at converter steel tapping hole
CN116363136A (en) * 2023-06-01 2023-06-30 山东创元智能设备制造有限责任公司 On-line screening method and system for automatic production of motor vehicle parts

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CN106053485A (en) * 2016-08-01 2016-10-26 苏州宙点自动化设备有限公司 Machine vision-based novel algorithm of intelligent circular inspection of steel ball surface defects
CN109003258A (en) * 2018-06-15 2018-12-14 广东工业大学 A kind of high-precision sub-pix circular pieces measurement method
CN111862037A (en) * 2020-07-17 2020-10-30 华中科技大学无锡研究院 Method and system for detecting geometric characteristics of precision hole type part based on machine vision

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Publication number Priority date Publication date Assignee Title
CN103175844A (en) * 2012-03-16 2013-06-26 沈阳理工大学 Detection method for scratches and defects on surfaces of metal components
CN106053485A (en) * 2016-08-01 2016-10-26 苏州宙点自动化设备有限公司 Machine vision-based novel algorithm of intelligent circular inspection of steel ball surface defects
CN109003258A (en) * 2018-06-15 2018-12-14 广东工业大学 A kind of high-precision sub-pix circular pieces measurement method
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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN112613523A (en) * 2020-12-15 2021-04-06 中冶赛迪重庆信息技术有限公司 Method, system, medium and electronic terminal for identifying steel flow at converter steel tapping hole
CN112613523B (en) * 2020-12-15 2023-04-07 中冶赛迪信息技术(重庆)有限公司 Method, system, medium and electronic terminal for identifying steel flow at converter steel tapping hole
CN116363136A (en) * 2023-06-01 2023-06-30 山东创元智能设备制造有限责任公司 On-line screening method and system for automatic production of motor vehicle parts
CN116363136B (en) * 2023-06-01 2023-08-11 山东创元智能设备制造有限责任公司 On-line screening method and system for automatic production of motor vehicle parts

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