CN115326835A

CN115326835A - Cylinder inner surface detection method, visualization method and detection system

Info

Publication number: CN115326835A
Application number: CN202211254437.9A
Authority: CN
Inventors: 崔超; 徐健; 周美兰; 陆振; 李振国; 李正明; 陆虎
Original assignee: Huiding Zhilian Equipment Technology Jiangsu Co ltd
Current assignee: Huiding Zhilian Equipment Technology Jiangsu Co ltd
Priority date: 2022-10-13
Filing date: 2022-10-13
Publication date: 2022-11-11
Anticipated expiration: 2042-10-13
Also published as: CN115326835B

Abstract

The invention provides a method for detecting the surface and the inner surface of a cylinder, a visualization method and a detection system, wherein the method for detecting the inner surface of the cylinder comprises the following steps: (a) Scanning the cylinder inner surface to obtain a point cloud data set consisting of 3D point cloud data; (b) Splicing the 3D point cloud data in the point cloud data set into a cylindrical model; and (c) judging whether the current point is a defective point.

Description

Cylinder inner surface detection method, visualization method and detection system

Technical Field

The invention relates to the technical field of visual detection, in particular to a detection method, a visualization method and a detection system for the inner surface of a cylinder.

Background

In industrial applications, cylindrical parts are found everywhere, such as cylindrical pipes, cylindrical missiles, etc. Due to corrosion and friction of materials and uncontrollable manufacturing process, the surface of the object is easy to deform and fall off, so the surface of the object needs to be detected regularly. In particular, for some precision parts, it is necessary to perform defect detection on the inner surface and the outer surface of the cylinder to meet the requirement of equipment, wherein the defect detection refers to detecting defects on the surface of an object, such as bulges, pits, scratches and the like. The detection of defects on the surface of an object is of great significance to the safety of the production process and the avoidance of economic losses.

The surface defect detection of the cylinder part, particularly the defect detection of the inner surface, has higher difficulty, and for some precise cylindrical parts, large detection equipment such as a panoramic camera cannot be placed in the cylinder because the space in the cylinder is smaller. The existing equipment inner surface detection method mainly comprises the following steps: radiographic testing, ultrasonic testing, and the like. The methods need to transmit and receive signals on the outer surface of the equipment for multiple times to complete the detection of the defects on the inner surface of the equipment, and have the characteristics of low detection efficiency, invisibility and the like.

In addition, the detection method and the detection device of the prior art cannot realize visualization of the inside of the cylinder, that is, the detection method and the detection device of the prior art only detect the type of the defect inside the cylinder, and cannot provide an accurate position of the defect, which also brings uncertainty to the detected result. The user is difficult to repair the defects in the cylinder according to the detection result.

Disclosure of Invention

The invention has a main advantage of providing a cylinder inner surface detection method, a visualization method and a detection system, wherein the cylinder inner surface detection method is a visual detection technology based on line structured light, and can acquire three-dimensional point cloud data of the cylinder inner surface, and perform defect detection and texture mapping on the cylinder three-dimensional point cloud data to realize visualization of the cylinder inner wall.

Another advantage of the present invention is to provide a method, a visualization method and a system for detecting defects on an inner surface of a cylinder, wherein the method for detecting defects on an inner surface of a cylinder is based on three-dimensional point cloud data, and realizes automation and visualization of the detection of defects on the inner surface and the outer surface of the cylinder.

Another advantage of the present invention is to provide a method, a visualization method, and a detection system for detecting an inner surface of a cylinder, wherein the method for detecting an inner surface of a cylinder is based on splicing of 3D point cloud data into a cylinder model, and whether a current point is a defect point is determined based on a difference between a distance from a point to an axis and a radius of the fitted cylinder model.

Another advantage of the present invention is to provide a cylinder inner surface inspection method, a visualization method, and an inspection system, in which the cylinder inner surface inspection method uses a 3D camera to scan the cylinder inner surface from front to back, thereby improving data integrity.

Another advantage of the present invention is to provide a method, a visualization method, and a detection system for detecting an inner surface of a cylinder, wherein the method estimates a transformation matrix based on a direction of a cylinder axis of a first point cloud and a point on the axis to achieve an initial registration, and the detection method has the advantages of high speed, high accuracy, and good stability.

Another advantage of the present invention is to provide a method for detecting an inner surface of a cylinder, a visualization method, and a detection system, wherein the method for detecting an inner surface of a cylinder determines whether a current point is a defect point based on a difference between a distance from a point to an axis and a radius of the fitted cylinder model, and a user can set a required detection accuracy as needed, which is beneficial to improving the applicability of the detection method.

Another advantage of the present invention is to provide a method, a method and a system for detecting the surface defects of a cylindrical object, wherein the detection system realizes automatic detection and texture mapping of the surface defects of the cylindrical object, provides a three-dimensional model for the cylindrical object, facilitates visualization of the detection, and facilitates a user to observe a detection result according to the three-dimensional model.

Another advantage of the present invention is to provide a method, a visualization method, and a detection system for detecting an inner surface of a cylinder, wherein the detection system scans an inner surface of a cylinder object by using a 3D camera to obtain a depth image, analyzes point cloud data of the inner surface of the cylinder according to the obtained depth image, and detects defects on the inner surface of the cylinder according to the depth information obtained by scanning, which is beneficial to improving the detection accuracy.

In accordance with one aspect of the present invention, the foregoing and other objects and advantages are achieved by a cylinder inside surface detecting method of the present invention, comprising the steps of:

(a) Scanning the cylinder inner surface to obtain a point cloud data set consisting of 3D point cloud data;

(b) Splicing the 3D point cloud data in the point cloud data set into a cylindrical model; and

(c) And judging whether the point of the cylindrical model is a defect point or not.

According to an embodiment of the present invention, the step (a) further comprises the steps of:

(a.1) scanning the cylinder inner surface along the cylinder axial direction O with a specific scanning field of view and obtaining a corresponding depth image;

and (a.2) adjusting the relative angle of the scanning view field and the surface of the object to be measured, and scanning the inner surface of the cylinder of the object to be measured and obtaining a corresponding depth image according to the step (a.1) after each adjustment, so that the inner surface of the cylinder of the object to be measured is completely scanned.

According to one embodiment of the present invention, in the step (a.2), the object is rotated by a specific rotation angle, so that the scanning field of view of the depth camera is switched to a specific position of the cylindrical inner surface of the object.

According to one embodiment of the present invention, in the step (a.2), the depth camera is rotated at a specific rotation angle so that a scanning field of view of the depth camera is switched to a specific position of the cylindrical inner surface of the object.

According to an embodiment of the present invention, the step (a) of the cylinder inner surface detecting method further comprises the steps of:

and (a.3) analyzing each depth image into a plurality of pieces of 3D point cloud data to form the point cloud data set.

According to an embodiment of the present invention, the step (b) of the cylinder inner surface detecting method further includes the steps of:

(b.1) calculating the rotation amount and the translation amount of each piece of other 3D point cloud data in the point cloud data set based on one piece of 3D point cloud data;

and (b.2) rotating and translating the cloud data of other points to obtain cylindrical point cloud data.

According to one embodiment of the present invention, the step (b.1) of the cylinder inner surface detecting method further comprises the steps of:

(b.1.1) estimating cylinder parameters based on the first piece of 3D point cloud data, and obtaining a point on the cylinder axis

Direction of cylinder axis

And a radius r; and

(b.1.2) for the ith slice of 3D Point cloud data

Knowing the rotation angle theta and the rotation axis v, an initial rotation matrix R and an initial translation t are calculated, wherein

。

According to one embodiment of the present invention, the step (b.2) of the cylinder inner surface detection method further comprises the steps of:

(b.2.1) estimating the rotation matrix R and the translational vector t based on the initialComputation transformation matrix

(ii) a And

(b.2.2) based on transformation matrices

To rotate and translate the ith piece of 3D point cloud data

Is carried out to obtain

Wherein

And

the final rotation and translation matrices are the respective,

。

according to an embodiment of the present invention, the step (c) of the cylinder inner surface detecting method further comprises the steps of:

(c.1) setting a Cylinder Defect determination threshold

In which

(ii) a And

(c.2) calculating the distance from each point in the cylindrical point cloud to the cylindrical axis if

If at all

Then point of

Is a concave point; if it is

Then point of

Are raised points.

According to one embodiment of the present invention, the method further comprises the step of, before the step (c.1) of the cylinder inner surface detecting method;

(c.0.1) in

And

dividing the cylindrical point cloud Q into a plurality of small point clouds in direction

(ii) a And

(c.0.2) cylindrically fitting each small point cloud of the cylindrical point cloud Q

And obtaining parameters of the fitting cylinder.

(c.3) clustering the concave points and the convex points to obtain concave and convex parts of the cylindrical surface.

According to another aspect of the present invention, the present invention further provides a method for visualizing an inner surface of a cylinder, wherein the method for visualizing an inner surface of a cylinder comprises the steps of:

(A) Scanning the inner surface of the cylinder to obtain a point cloud data set consisting of 3D point cloud data and an image set consisting of images;

(B) -stitching the 3D point cloud data of the point cloud data set into a cylindrical model, and stitching the image of the image set into a cylindrical image point cloud; and

(C) Aligning the cylindrical model with the cylindrical image point cloud to obtain a 3D texture map of the cylinder interior surface.

According to an embodiment of the present invention, the step (B) of the method for visualizing an inner surface of a cylinder further comprises the steps of:

(B.3) centralizing the cylindrical point cloud based on the center of mass of the cylindrical point cloud to obtain a centralized point cloud; and

(B.4) estimating cylinder parameters of the centralized point cloud to obtain the radius of the cylinder.

According to an embodiment of the present invention, in the step (B) of the cylinder inner surface visualization method, the centroid of the cylindrical point cloud Q is calculated

The points after the centralization are:

wherein

As a point cloud

To (1)

And (4) point.

(B.5) splicing the shot images to form a rectangular image; and

and (B.6) mapping the spliced rectangular image into a 3D cylindrical image to obtain the cylindrical image point cloud.

According to one embodiment of the invention, in said step (B.6) of the method for visualizing the internal surface of a cylinder, the measurement is carried outThe angle between two adjacent points in each row of the image corresponding to the inner surface of the object cylinder is:

height values corresponding to two adjacent points in each column:

wherein

And

respectively the width and height of the image.

And

respectively point cloud

The minimum height and the maximum height value of (c).

According to one embodiment of the invention, a cylindrical image point cloud

Wherein in the image is

Go to the first

The image points of a column correspond to spatial points of

Wherein

Is as follows

Go to the first

Corresponding to image points of a column

The value is obtained.

According to an embodiment of the present invention, the step (C) of the method for visualizing an inner surface of a cylinder further comprises the steps of:

(C.1) estimating a transformation matrix between the cylindrical image point cloud and the centered point cloud

；

(C.2) based on transformation matrices

Rotating and translating the centered point cloud or the cylindrical image point cloud such that the centered point cloud is aligned with the cylindrical image point cloud; and

and (C.3) fusing the centralized point cloud and the cylindrical image point cloud, so that the points in the centralized point cloud obtain RGB information from the cylindrical image point cloud.

According to one embodiment of the invention, in step (C.3) of the method for visualizing the internal surface of a cylinder, the point cloud is centered

The color of each point is a cylindrical picture point cloud

The color of the closest point to the current point.

According to another aspect of the present invention, the present invention further provides a cylinder inner surface detection system comprising:

the scanning device is used for scanning the surface of an object to be detected so as to acquire depth image information of the surface of the object to be detected;

the point cloud processing module analyzes the depth image information into 3D point cloud data and splices the 3D point cloud data into a cylindrical point cloud; and

and the detection module calculates the distance from each point in the point cloud data to the cylindrical axis and judges whether the point is a defect point.

According to one embodiment of the invention, the scanning device comprises a depth camera, and the depth camera scans the inner surface of the object to be measured from front to back along the axial direction O to obtain depth image information corresponding to the surface of the object to be measured.

According to one embodiment of the invention, the point cloud processing module further comprises an image parsing unit for parsing the depth image taken by the depth camera into 3D point cloud data and a point cloud stitching unit for moving and rotating the point cloud data to stitch into a cylindrical point cloud.

According to one embodiment of the invention, the detection module comprises a cylinder fitting unit and a defect determination unit, wherein the cylinder fitting unit divides the cylinder point cloud into a plurality of small blocks

Parallel point cloud

The data in (3) are subjected to cylinder fitting to obtain cylinder parameters, and the defect judgment unit calculates each point in the point cloud

Distance to the axis

If, if

Then point of

Is a concave trap point; if it is

Then point of

Are raised points.

According to one embodiment of the invention, the texture mapping method further comprises a texture mapping module, wherein the texture mapping module fuses 3D point cloud data and 2D image information corresponding to the inner surface of the cylinder into a texture map with color information.

According to one embodiment of the invention, the texture mapping module comprises a picture processing unit, a point cloud mapping unit and a fusion unit, wherein the picture processing unit is used for splicing the images, and the picture processing unit is used for splicing the images shot by the image shooting unit into a rectangular plane image. The point cloud mapping unit maps rectangular plane images into cylinders, and the fusion unit fuses cylinder point cloud data spliced by the point cloud data and cylinder image point clouds spliced by the images into a cylinder surface model with color information.

Further objects and advantages of the invention will be fully apparent from the ensuing description and drawings.

These and other objects, features and advantages of the present invention will become more fully apparent from the following detailed description and accompanying drawings.

Drawings

Fig. 1 is a schematic view of a system for detecting an inner surface of a cylinder according to a first preferred embodiment of the present invention.

FIG. 2 is a scanning schematic diagram of the cylinder inner surface detection system according to the first preferred embodiment of the present invention.

FIG. 3 is a schematic diagram of a piece of 3D point cloud data scanned by the cylinder inner surface detecting system according to the first preferred embodiment of the present invention.

Fig. 4A and 4B are schematic diagrams illustrating the cylinder inner surface detection system according to the first preferred embodiment of the present invention.

Fig. 5 is a schematic view illustrating a detection flow of the method for detecting the inner surface of the cylinder according to the first preferred embodiment of the invention.

FIG. 6 is a schematic diagram illustrating the steps of the method for detecting the inner surface of the cylinder according to the first preferred embodiment of the present invention.

Fig. 7 is a flow chart illustrating a method for visualizing the inner surface of the cylinder according to a second preferred embodiment of the invention.

FIG. 8 is a schematic step diagram of a method for visualizing the inner surface of a cylinder according to a second preferred embodiment of the present invention.

Fig. 9 is a schematic structural diagram of a system for detecting an inner surface of a cylinder according to a third preferred embodiment of the invention.

Detailed Description

The following description is presented to disclose the invention so as to enable any person skilled in the art to practice the invention. The preferred embodiments in the following description are given by way of example only, and other obvious variations will occur to those skilled in the art. The underlying principles of the invention, as defined in the following description, may be applied to other embodiments, variations, modifications, equivalents, and other technical solutions without departing from the spirit and scope of the invention.

It will be understood by those skilled in the art that in the present disclosure, the terms "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," and the like are used in an orientation or positional relationship indicated in the drawings for ease of description and simplicity of description, and do not indicate or imply that the referenced devices or components must be in a particular orientation, constructed and operated in a particular orientation, and thus the above terms are not to be construed as limiting the present invention.

It is understood that the terms "a" and "an" should be interpreted as meaning that a number of one element or element is one in one embodiment, while a number of other elements is one in another embodiment, and the terms "a" and "an" should not be interpreted as limiting the number.

Referring to fig. 1 to 9 of the drawings accompanying the present specification, a method of inspecting an inner surface of a cylinder, a method of visualizing the same, and an inspection system according to the present invention will be explained in the following description. The detection method, the visualization method and the detection system for the inner surface of the cylinder can acquire the three-dimensional point cloud data of the inner surface of the cylinder by using a line structured light-based visual detection technology, and perform defect detection and texture mapping on the three-dimensional point cloud data of the cylinder to realize visualization of the cylinder wall. It should be noted that the method, the method and the system for detecting the inner surface of the cylinder can detect defects on the inner surface (inner wall) or the outer surface (outer wall) of the cylinder to be detected, and perform texture mapping based on the three-dimensional point cloud data of the cylinder to realize visualization of the cylinder wall. It should be noted that, in the present application, the object to be detected, which is suitable for the cylinder inner surface detection method, the visualization method and the detection system, is a cylindrical structure object, such as a cylindrical part like a cylinder pipe, a cylinder missile, etc., wherein the inner surface of the object to be detected is a hollow cylinder structure or the outer surface of the object to be detected is a cylinder structure.

The method for detecting the inner surface of the cylinder, the method for visualizing the inner surface of the cylinder and the detection system for detecting the defects on the inner surface of the cylinder are further explained as an example below. It can be understood that the same method and system can be used for detecting defects on the outer surface of the cylinder and realizing visualization of the outer surface of the cylinder, which are not described herein again.

As shown in fig. 1 to 6, a method for inspecting an inner surface of a cylinder according to a first preferred embodiment of the present invention will be explained in the following description. In the method for detecting the inner surface of the cylinder, a depth camera is used for scanning the surface of a cylinder object to generate 3D point cloud data of different parts of the object; splicing the 3D point cloud data under different viewing angles into a cylindrical model; determining whether the current point is a defect point or not according to the difference between the distance from the point to the axis and the radius based on the fitted cylindrical model; the defective portion of the cylindrical object is found by a clustering method.

In detail, the method for detecting the inner surface of the cylinder comprises the following steps:

(a) Scanning the inner surface of the cylinder to obtain a point cloud data set consisting of 3D point cloud data;

(c) It is determined whether the current point is a defective point.

Acquiring a plurality of pieces of point cloud data through the step (a) of the cylinder inner surface detection method, wherein the plurality of pieces of point cloud data correspond to the inner surface of the object to be detected. The object to be measured is provided with an axial direction O, wherein the axial direction O of the object to be measured is a central axis of the object to be measured or the axial direction is parallel to the central axis of the object to be measured. In detail, in the preferred embodiment of the present application, the surface of the object to be measured is scanned in the axial direction O of the object to be measured by a depth camera. The depth camera scans the inner surface of the object to be measured from front to back along the axial direction O to obtain depth information corresponding to the surface of the object to be measured. Preferably, in this preferred embodiment of the present application, the depth camera may be, but is not limited to, a 3D camera. The depth camera obtains a depth image corresponding to the surface of the object to be measured by shooting the surface of the object to be measured.

And analyzing the depth image obtained by scanning to generate corresponding 3D point cloud data. Accordingly, a plurality of depth images captured by the depth camera are resolved into pieces of 3D point cloud data.

As shown in fig. 1 to 3, in the preferred embodiment of the present application, the depth camera has a specific scanning field of view, and when the depth camera scans from front to back along the axial direction O, the depth camera photographs a region corresponding to a specific central angle R of the inner surface of the object cylinder based on the scanning field of view. By way of example, in the preferred embodiment of the present application, the central angle R of the depth image obtained by a single scan of the depth camera corresponding to the inner surface of the object is 10 °, 12 °, 20 °, or the like.

Therefore, in step (a) of the method for detecting an inner surface of a cylinder according to the present application, the position of the inner surface of the object corresponding to the field of view of the depth camera during a single scan of the depth camera needs to be adjusted by adjusting the relative angle between the depth camera and the object. Adjusting the relative angle of the depth camera and the object to be measured for multiple times, so that the depth camera scans the surface of the object to be measured completely, and multiple depth images corresponding to the surface of the object to be measured are obtained through scanning of the depth camera; and analyzing the obtained depth images to obtain corresponding pieces of 3D point cloud data.

The step (a) of the method for detecting an inner surface of a cylinder according to the above preferred embodiment of the present invention further includes the steps of:

In the step (a.2) of the method for detecting an inner surface of a cylinder according to the above preferred embodiment of the present invention, the object is rotated by a specific rotation angle during a single adjustment, so that the scanning field of the depth camera is switched to a specific position of the inner surface of the cylinder of the object. Optionally, in the step (a.2) of the method for detecting an inner surface of a cylinder according to the above preferred embodiment of the present invention, the depth camera is rotated by a specific rotation angle during a single adjustment, so that a scanning field of the depth camera is switched to a specific position of the inner surface of the cylinder of the object.

In this preferred embodiment of the present application, the depth camera scans the inner surface of the cylinder and obtains the depth image corresponding to the inner surface of the cylinder, and the depth image obtained based on the scanning is resolved into pieces of 3D point cloud data corresponding to the inner surface of the cylinder. It will therefore be appreciated that in this preferred embodiment of the present application, the depth camera is adapted to move reciprocally inside the cylinder of the object while detecting the inner surface (inner wall) of the object, the depth image of the inner surface of the cylinder being scanned by the depth camera.

The step (a) of the method for detecting the inner surface of the cylinder according to the above preferred embodiment of the present invention further includes the steps of:

And (c) splicing the point clouds under different viewing angles into a cylindrical point cloud through the step (b) of the cylinder inner surface detection method. Specifically, the step (b) of the cylinder inner surface detecting method further comprises the steps of:

In detail, in the preferred embodiment of the present invention, in the step (b.1) of the cylinder inner surface detection method, a RANSAC (Random sample consensus) algorithm is used to perform cylinder parameter estimation on the first piece of 3D point cloud data to obtain a point on the cylinder axis

Direction of cylinder axis

And a radius r. It is understood that, in the preferred embodiment of the present invention, any piece of 3D point cloud data may be selected for cylinder parameter estimation, and cylinder parameters corresponding to the cylinder axis direction are obtained.

For the ith piece of 3D point cloud data

The known rotation angles θ andthe initial rotation matrix R is calculated at the rotation axis v, and the formula is as follows:

for the ith piece of 3D point cloud data

The initial translation vector t is:

estimating a transformation matrix using an NDT algorithm based on an initial rotation matrix R and a translational vector t

. Based on transformation matrices

To the ith 3D point cloud data

Rotating and translating to obtain

：

Wherein

And

are respectively finalThe matrix of rotations and translations is then used,

。

and

respectively representing point clouds

And

point j in (d).

Specifically, the step (b.1) of the cylinder inner surface detection method further comprises the steps of:

Direction of cylinder axis

And a radius r; and

(b.1.2) for the ith slice of 3D Point cloud data

。

Step (b.2) of the method for detecting the inner surface of a cylinder further comprises the steps of:

(b.2.1) estimating a transformation matrix based on the initial rotation matrix R and the translational vector t

(ii) a And

(b.2.2) based on transformation matrices

To rotate and translate the ith piece of 3D point cloud data

Is carried out to obtain

：

Wherein

And

the final rotation and translation matrices are respectively,

。

the spliced cylindrical point cloud is obtained through the steps

，

The number of the point clouds.

In step (c) of the method for detecting the inner surface of the cylinder, it is determined whether the current point is a defect point based on the difference between the distance from the point to the axis and the radius of the cylinder model obtained by splicing.

The defect detection of the inner surface of the cylinder is realized through the step (c) of the cylinder inner surface detection method. Specifically, the step (c) of the cylinder inner surface detecting method further comprises the steps of:

(c.1) setting a Cylinder Defect determination threshold

In which

(ii) a And

If at all

Then point of

Is a concave trap point; if it is

Then point of

Are raised points.

In detail, a cylindrical point cloud

In that

And

divided into a plurality of small blocks in the direction

Point-to-point cloud

And (4) performing cylinder fitting on the data to obtain cylinder parameters. Computing point clouds

Each point in

Distance to fitting cylindrical axis

If, if

Then point of

Is a concave trap point; if it is

Then point of

Is a convex point, wherein

In order to fit the radius of the cylinder,

is a given threshold. And performing Euclidean clustering on the abnormal (namely concave and convex) points to obtain concave and convex parts of the cylindrical surface.

The method for detecting the inner surface of the cylinder of the present invention further comprises the step of (c) before step (c.1);

(c.0.1) in

And

directionally dividing cylindrical point cloud Q into a plurality of small point clouds

；

(c.0.2) Cylinder fitting each small point cloud of the cylindrical point cloud Q

And obtaining parameters of the fitting cylinder.

The step (c) of the cylinder inner surface detecting method further comprises the steps of:

(c.3) clustering the concave and convex points to obtain concave and convex portions of the cylindrical surface.

It should be noted that, according to the method for detecting the inner surface of the cylinder in the first preferred embodiment of the present invention, the 3D camera is used to scan the inner surface of the cylinder from front to back, so as to improve the integrity of data. The transformation matrix is estimated based on the direction of the cylindrical axis of the first point cloud and one point on the axis to realize initial registration. Whether the current point is a defect point (i.e. a concave or convex point) is determined according to the difference between the distance from the point to the axis and the radius based on the fitted cylinder model.

It can be understood that the inner wall of the cylinder can be detected by the detection method of the inner surface of the cylinder, and 3D point cloud data corresponding to the inner wall of the cylinder is spliced according to the scanned data of the inner surface of the cylinder; and judging the defect type and defect point information of the inner wall of the cylinder based on the spliced point cloud data information. The detection result obtained by the above-mentioned method for detecting the inner surface of the cylinder is point cloud information, such as gray-scale point cloud information, for the defect position, and the defect position is displayed by a method for visualizing the inner surface of the cylinder as described below, so that the defect position and the type of the defect position can be more clearly viewed.

As shown in fig. 7 to 8, a method for visualizing an inner surface of a cylinder according to a second preferred embodiment of the present invention will be explained in the following description. The method for visualizing the inner surface of the cylinder comprises the following steps:

(B) Stitching the 3D point cloud data of the point cloud data set into a cylindrical model, and stitching the image of the image set into a cylindrical image point cloud; and

It should be noted that, by scanning and splicing the inner surfaces of the cylinders into a 3D texture map by the method for visualizing the inner surfaces of the cylinders according to the preferred embodiment of the present application, a user can visually observe the texture effect of the inner surfaces of the cylinders, and a visualization effect is provided. It can be understood that, by visualizing the inner surface of the cylinder by the above method for visualizing the inner surface of the cylinder, the texture inspection, especially the defect detection of the protrusions and the depressions, of the inner surface of the cylinder can be facilitated for the user to conveniently find the positions of the defect points from the 3D texture map.

Step (a) of the method for visualizing the inner surface of the cylinder according to the preferred embodiment of the present invention is to scan the inner surface of the cylinder by a depth camera (e.g. a 3D camera) and obtain a 3D point cloud data set corresponding to the inner surface of the cylinder; the cylinder inner surface is scanned by a planar camera (2D camera) and a set of 2D images corresponding to the cylinder inner surface is acquired.

It should be noted that the acquisition of the 3D point cloud data and the 2D image may be completed by scanning with the same device, or completed by scanning with different devices simultaneously. Therefore, in the preferred embodiment of the present application, the manner of acquiring the 3D point cloud data and the 2D image is not limited herein.

Preferably, the scanning process of the 3D point cloud data set is the same as the process of step (a) of the cylinder inner surface detection method in the first preferred embodiment. That is, the surface of the object is scanned in the axial direction O of the object by the depth camera. The depth camera scans the inner surface of the object to be measured from front to back along the axial direction O to obtain depth information corresponding to the surface of the object to be measured.

The step (a) of the method for visualizing an inner surface of a cylinder according to the above preferred embodiment of the present invention further comprises the steps of:

In the step (a.2) of the method for visualizing an inner surface of a cylinder according to the above preferred embodiment of the present invention, the object is rotated by a specific rotation angle during a single adjustment, so that the scanning field of view of the depth camera is switched to a specific position of the inner surface of the cylinder of the object. Optionally, in the step (a.2) of the method for visualizing an inner surface of a cylinder according to the above preferred embodiment of the present invention, the depth camera is rotated by a specific rotation angle during a single adjustment, so that a scanning field of view of the depth camera is switched to a specific position of the inner surface of the cylinder of the object.

The step (a) of the method for visualizing the inner surface of the cylinder according to the above preferred embodiment of the present invention, wherein the scanning process of the 2D image set is similar to the depth image scanning process, further comprises the steps of:

(A.3) scanning the inner surface of the cylinder along the axial direction O of the cylinder with a specific scanning view field and obtaining a corresponding plane image;

and (A.4) adjusting the relative angle of the scanning view field and the surface of the object to be measured, and scanning the inner surface of the cylinder of the object to be measured and obtaining a corresponding plane image according to the step (A.3) after each adjustment, so that the inner surface of the cylinder of the object to be measured is completely scanned.

It should be noted that, in step (a) of the method for visualizing the inner surface of the cylinder according to the preferred embodiment of the present application, the process of acquiring the depth image and the process of acquiring the plane image are not sequential.

Preferably, the process of stitching the 3D point cloud data set is the same as the process of step (b) of the method for detecting an inner surface of a cylinder in the first preferred embodiment, and is not repeated herein.

And (B) splicing the point clouds under different viewing angles into a cylindrical point cloud by the step (B) of the cylinder inner surface visualization method. Specifically, step (B) of the method for visualizing an inner surface of a cylinder further includes the steps of:

(B.1) calculating the rotation amount and the translation amount of other 3D point cloud data in the point cloud data set based on one piece of 3D point cloud data;

The step (b.1) of the method for visualizing the inner surface of a cylinder further comprises the steps of:

Direction of cylinder axis

And a radius r; and

(B.1.2) for the ith piece of 3D point cloud data

。

The step (b.2) of the method for visualizing the internal surface of a cylinder further comprises the steps of:

(ii) a And

(B.2.2) based on transformation matrices

To rotate and translate the ith 3D point cloud data

Is carried out to obtain

：

Wherein

And with

The final rotation and translation matrices are respectively,

。

the spliced cylindrical point cloud is obtained through the steps

，

The number of the point clouds is shown.

In this preferred embodiment of the present invention, the step (B) of the method for visualizing the inner surface of the cylinder further comprises the steps of:

In detail, a cylindrical point cloud

Centralizing, wherein the cylinder point cloud Q is centralized to obtain a centralized point cloud

. The centralization process of the cylindrical point cloud is as follows: firstly, calculating the mass center of the cylindrical point cloud Q

The points after the centralization are:

wherein

As a point cloud

To

And (4) points. Point cloud based on RANSAC algorithm

Performing cylindrical parameter estimation to obtain the radius of the cylinder

。

(B.5) splicing the shot images to form a rectangular image; and

In the step (b.6) of the method for visualizing the inner surface of the cylinder in the preferred embodiment of the present invention, the angle between two adjacent points in each row in the image corresponding to the inner surface of the cylinder of the object to be measured is:

height values corresponding to two adjacent points in each column:

wherein

And

respectively the width and height of the image.

And

respectively point cloud

The minimum height and the maximum height value of (c).

Each pixel point in the image corresponds to one point in the space, thereby generating a cylindrical image point cloud

Wherein in the image is

Go to the first

The image points of a column correspond to spatial points of

Wherein

Is as follows

Go to the first

To which image point of the column corresponds

The value is obtained.

In the preferred embodiment of the present invention, the step (C) of the method for visualizing the inner surface of a cylinder further comprises the steps of:

；

(C.2) based on transformation matrices

It is worth mentioning that in this preferred embodiment of the present invention, since the 3D cylindrical point cloud obtained by stitching does not have a color sheet and has spatial data information corresponding to the inner surface of the cylinder, the cylindrical image point cloud obtained by stitching pictures does not have accurate spatial information but has corresponding color information. Therefore, in step (C) of the method for visualizing the inner surface of a cylinder according to the preferred embodiment of the present invention, a 3D texture map having both color information and spatial data information corresponding to the inner surface of the cylinder can be obtained by aligning and fusing the 3D cylindrical point cloud obtained by stitching and the cylindrical image point cloud obtained by stitching pictures.

It is understood that in the step (c.3) of the method for visualizing the inner surface of the cylinder according to the above preferred embodiment of the present invention, the point cloud is centered

The color of each point in the point cloud is a cylindrical picture point cloud

The color of the closest point to the current point, i.e. the assigned centered point cloud

The color of each point in the point cloud C is the closest point in the point cloud C of the cylindrical picture.

It should be noted that, in the method for visualizing the inner surface of the cylinder in the preferred embodiment of the present application, the method for visualizing the inner surface of the cylinder may be combined with the method for detecting the inner surface of the cylinder in the first preferred embodiment, that is, after the method for detecting the inner surface of the cylinder detects the defect position and the type of the defect point, the defect position and the type of the defect are displayed according to the method for visualizing the inner surface of the cylinder, that is, the defect information detected by the 2D image and the defect detected by the 3D image are integrated, and finally the type of the defect position is output together and displayed on the 3D model of the texture map. Therefore, the defect position and the defect type of the inner surface of the cylinder can be detected, and the defect position and the defect type can be displayed in a highlight mode, so that the detection effect is further improved.

It can be understood by those skilled in the art that, in the preferred embodiment of the present application, the detection step (C) in the method for detecting the inner surface of the cylinder is performed sequentially with the texture mapping step (C) in the method for visualizing the inner surface of the cylinder, that is, the defect position and the defect type of the inner surface of the cylinder may be detected first, and the texture mapping may be performed on the inner surface of the cylinder after the detection, so as to form a highlighted 3D texture mapping model; or combining the 2D image and the 3D splicing model to form a visual texture mapping model, detecting the defect position and the defect type of the 3D mapping model by a defect detection method, and displaying the defect position and the defect type on the 3D model of the texture mapping to obtain a visual cylinder inner surface defect detection model.

Referring to fig. 9 of the drawings accompanying this specification, a cylinder inner surface detection system according to a third preferred embodiment of the present application will be explained in the following description. The cylinder inner surface detection system comprises a scanning device 10, a point cloud processing module 20 and a detection module 30, wherein the scanning device 10 is used for scanning the surface of an object to be detected to obtain depth information of the surface of the object to be detected, the depth information obtained by scanning of the scanning device 10 is transmitted to the point cloud processing module 20, the point cloud processing module 20 analyzes a depth image into 3D point cloud data information, the 3D point cloud data information is spliced into a cylindrical point cloud Q, and the detection module 30 judges whether defects, such as sunken points and raised points, exist on the cylinder inner surface according to the spliced cylindrical point cloud Q.

In detail, the scanning device 10 includes a depth camera 11, wherein the depth camera 11 is adapted to photograph the surface of the object and obtain depth image information corresponding to the surface of the object. Preferably, in the preferred embodiment of the present invention, the depth camera 11 of the scanning device 10 is a 3D camera, and the depth camera 11 scans the inner surface of the object to be measured from front to back for a plurality of times to obtain a plurality of depth images corresponding to the inner surface of the cylinder.

In detail, in the preferred embodiment of the present application, the surface of the object is scanned along the axial direction O of the object by the depth camera 11. The depth camera 11 scans the inner surface of the object to be measured along the axial direction O from front to back to obtain depth information corresponding to the surface of the object to be measured. The depth camera obtains a plurality of depth images corresponding to the surface of the object to be measured by shooting the surface of the object to be measured.

In the preferred embodiment of the present application, the depth camera 11 has a specific scanning field of view, and when the depth camera 11 scans from front to back along the axial direction O, the depth camera 11 captures an area corresponding to a specific central angle R of the inner surface of the cylinder of the object based on the scanning field of view. As an example, in the preferred embodiment of the present application, the central angle R of the depth image obtained by a single scan of the depth camera 11 corresponding to the inner surface of the object is 10 °, 12 °, 20 °, or the like.

Therefore, the position of the inner surface of the object corresponding to the field of view of the depth camera 11 during a single scan needs to be adjusted by adjusting the relative angle between the depth camera 11 and the object. Adjusting the relative angle between the depth camera 11 and the object to be measured a plurality of times, so that the depth camera 11 scans the surface of the object to be measured completely, and a plurality of depth images corresponding to the surface of the object to be measured are obtained by scanning through the depth camera 11; and analyzing the obtained depth images to obtain a plurality of pieces of corresponding 3D point cloud data.

The depth image scanned by the depth camera is transmitted to the point cloud processing module 20, and the point cloud processing module 20 analyzes and splices the depth image to obtain a spliced cylindrical point cloud Q.

Accordingly, the point cloud processing module 20 further includes an image parsing unit 21 and a point cloud stitching unit 22, wherein the image parsing unit 21 is configured to parse the depth image captured by the depth camera 11 and parse the depth image into 3D point cloud data. In the preferred embodiment of the present application, the image analysis unit 21 analyzes a plurality of depth images captured by the depth camera 11 into a plurality of pieces of 3D point cloud data. The point cloud splicing unit 22 splices the 3D point cloud data obtained by the analysis into a cylindrical point cloud Q.

Specifically, in the preferred embodiment of the present invention, the point cloud registration unit 22 uses a Random sample consensus (Random sample consensus) algorithm to perform a first 3D point cloud data registrationPerforming cylindrical parameter estimation to obtain a point on the cylindrical shaft

Direction of cylinder axis

For the ith piece of 3D point cloud data

Knowing the rotation angle θ and the rotation axis v, an initial rotation matrix R is calculated, as shown below:

for the ith piece of 3D point cloud data

The initial translation vector t is:

. The point cloud stitching unit 22 is based on a transformation matrix

To the ith 3D point cloud data

Rotating and translating to obtain

：

Wherein

And

the final rotation and translation matrices are the respective,

。

and

respectively representing point clouds

And

the jth point in (1).

In the preferred embodiment of the present invention, the point cloud registration unit 22 moves the remaining other point cloud data according to the final rotation and translation matrix based on the first point cloud, thereby obtaining the cylindrical point cloud Q. The spliced cylindrical point cloud is obtained through the steps

，

The number of the point clouds is shown.

The detection module 30 detects defects according to the cylindrical point cloud Q. Specifically, the detection module 30 calculates the distance from each point in the point cloud data to the cylindrical axis, and calculates the distance from each point in the point cloud data to the cylindrical axis according to a set threshold

) And judging whether the defect point is a defect point. Accordingly, the detection module 30 further comprises a cylinder fitting unit 31 and a defect determining unit 32, wherein the cylinder fitting unit 31 is used for point cloud of the cylinder point

In that

And

divided into a plurality of small blocks in the direction

Parallel point cloud

And (4) performing cylinder fitting on the data to obtain cylinder parameters. The defect determining unit 32 of the detecting module 30 calculates a point cloud

Each point in

Distance to the axis

If, if

Then point of

Is a concave trap point; if it is

Then point of

Are raised points. Wherein

Is the radius of the cylinder and is,

is a given threshold. The detection module 30 further comprises a clustering unit 33, wherein the clustering unit 33 performs euclidean clustering on the abnormal (i.e. concave and convex) points to obtain concave and convex portions of the cylindrical surface.

The system for detecting the inner surface of the cylinder further comprises a texture mapping module 40, wherein the texture mapping module 40 fuses 3D point cloud data and 2D image information corresponding to the inner surface of the cylinder into a texture map with color information. That is, in the preferred embodiment of the present application, the 3D point cloud data and the 2D image information corresponding to the inner surface of the cylinder are mapped into a cylinder model with color information, which facilitates visual observation of the inner surface of the cylinder, especially the information of the inner surface of the object to be measured.

Accordingly, in the preferred embodiment of the present application, the scanning device 10 further includes an image capturing unit 12, wherein the image capturing unit 12 is adapted to capture the surface of the object to be measured, and obtain image information corresponding to the inner surface of the cylinder of the object to be measured. It should be noted that, in the preferred embodiment of the application, the image capturing unit 12 scans in the same manner as the depth camera 11. The image capturing unit 12 scans the inner surface of the cylinder along the axial direction O of the cylinder with a specific scanning view field and obtains a corresponding plane image, and scans the inner surface of the cylinder of the object to be measured and obtains a corresponding plane image according to the above scanning method after each adjustment by adjusting the relative angle between the scanning view field and the surface of the object to be measured, so as to completely scan the inner surface of the cylinder of the object to be measured.

The image capturing unit 12 transmits the captured image information to the texture mapping module 40, and the texture mapping module 40 fuses the image information and the 3D point cloud data into a cylindrical model. The texture mapping module 40 includes a picture processing unit 41, a point cloud mapping unit 42 and a fusion unit 43, wherein the picture processing unit 41 is configured to stitch images, and the picture processing unit 41 stitches the images captured by the image capturing unit 12 into a rectangular planar image. The point cloud mapping unit 42 maps the rectangular planar image into a 3D cylinder, and in the preferred embodiment of the present invention, the angle value between two adjacent points in each row in the image corresponding to the inner surface of the object cylinder is:

height values corresponding to two adjacent points in each column:

wherein

And

respectively the width and height of the image.

And

respectively point cloud

The minimum height and the maximum height value of (c).

Wherein in the image is the first

Go to the first

The image points of a column correspond to spatial points of

In which

Is a first

Go to the first

To which image point of the column corresponds

The value is obtained.

The fusion unit 43 fuses the cylindrical point cloud data spliced by the 3D point cloud data and the cylindrical image point cloud spliced by the 2D image into a cylindrical surface model with color information, i.e. a 3D texture mapping model. In detail, after the fusion unit 43 aligns the cylindrical point cloud data and the cylindrical image point cloud, a mapping relationship between the cylindrical point cloud data and the cylindrical image point cloud is constructed, so that the cylindrical point cloud data and the cylindrical image point cloud are fused to obtain the 3D texture map. It is understood that the 3D texture map obtained by the texture mapping module 40 corresponds to the cylindrical inner surface image and the 3D point cloud information of the object, and the 3D texture map further provides the visual stereo image information for the user to observe, so as to facilitate the user to find the defect position and defect type, such as concave and convex points, of the corresponding cylindrical inner surface from the 3D texture map.

It will be appreciated by persons skilled in the art that the embodiments of the invention described above and shown in the drawings are given by way of example only and are not limiting of the invention. The objects of the invention have been fully and effectively accomplished. The functional and structural principles of the present invention have been shown and described in the embodiments, and any variations or modifications may be made to the embodiments of the present invention without departing from the principles described.

Claims

1. A method for inspecting an inner surface of a cylinder, the method comprising the steps of:

(a) Scanning the inner surface of a cylinder to be measured to obtain a point cloud data set consisting of 3D point cloud data;

2. The cylinder inside surface inspection method according to claim 1, wherein the step (a) further comprises the steps of:

and (a.2) adjusting the relative angle of the scanning view field and the inner surface of the cylinder to be measured, and scanning the inner surface of the cylinder of the object to be measured and obtaining a corresponding depth image according to the step (a.1) after each adjustment, so that the inner surface of the cylinder of the object to be measured is completely scanned.

3. The cylinder inner surface detecting method according to claim 2, wherein in the step (a.2), the object to be measured is rotated at a specific rotation angle so that the scanning field of view is switched to a specific position of the cylinder inner surface of the object to be measured.

4. The cylinder inner surface detection method according to claim 2, wherein in the step (a.2), the depth camera is rotated at a specific rotation angle so that a scanning field of view of the depth camera is switched to a specific position of the cylinder inner surface of the object.

5. The cylinder inner surface detecting method according to claim 2, wherein the step (a) of the cylinder inner surface detecting method further comprises the steps of:

6. The cylinder inner surface detecting method according to claim 2, wherein the step (b) of the cylinder inner surface detecting method further comprises the steps of:

7. The cylinder inside surface inspection method according to claim 6, wherein the step (b.1) of the cylinder inside surface inspection method further comprises the steps of:

Direction of cylinder axis

And a radius r; and

(b.1.2) for the ith slice of 3D Point cloud data

。

8. The cylinder inside surface inspection method according to claim 6, wherein the step (b.2) of the cylinder inside surface inspection method further comprises the steps of:

(ii) a And

(b.2.2) based on transformation matrices

To rotate and translate the ith 3D point cloud data

Is carried out to obtain

：

Wherein

And

the final rotation and translation matrices are respectively,

，

。

9. the cylinder inner surface detecting method according to claim 6, wherein in the step (c), it is determined whether the current point is a defect point based on a difference between a distance from the point to the axis and a radius of the cylinder model obtained by the splicing.

10. The cylinder inside surface inspection method according to claim 8, wherein the step (c) of the cylinder inside surface inspection method further comprises the steps of:

(c.1) setting a cylinder defect judgment threshold value

Wherein

(ii) a And

If, if

Then point of

Is a concave trap point; if it is

Then point of

Are raised points.

11. The cylinder inside surface inspection method according to claim 10, further comprising the step of;

(c.0.1) in

And

(ii) a And

And obtaining parameters of the fitting cylinder.

12. The cylinder inside surface inspection method according to claim 10, wherein the step (c) of the cylinder inside surface inspection method further comprises the steps of:

13. A method for visualizing an inner surface of a cylinder, wherein the method for visualizing an inner surface of a cylinder comprises the steps of:

(A) Scanning the inner surface of a cylinder to be measured to obtain a point cloud data set consisting of 3D point cloud data and an image set consisting of images;

14. The method for visualizing an inner surface of a cylinder as in claim 13, wherein step (B) of the method for visualizing an inner surface of a cylinder further comprises the steps of:

15. The method for visualizing an inner surface of a cylinder as in claim 13, wherein in the step (B) of the method for visualizing an inner surface of a cylinder, the centroid of the point cloud Q of a cylinder is calculated

The points after the centralization are:

in which

As a point cloud

To (1)

And (4) points.

16. The method for visualizing an inner surface of a cylinder as in claim 13, wherein the step (B) of the method for visualizing an inner surface of a cylinder further comprises the steps of:

(B.5) splicing the shot images to form a rectangular image; and

17. The method for visualizing an inner surface of a cylinder as in claim 16, wherein in said step (b.6) of the method for visualizing an inner surface of a cylinder, the values of the angles between two adjacent points in each row in the image corresponding to the inner surface of the cylinder of the object are:

height values corresponding to two adjacent points in each column:

in which

And

respectively the width and the height of the image,

and

respectively point cloud

The minimum height and the maximum height value of (c).

18. The method for visualization of an interior surface of a cylinder of claim 16, wherein the cylindrical image point cloud

Wherein in the image is the first

Go to the first

The image points of a column correspond to spatial points of

In which

Is a first

Go to the first

Corresponding to image points of a column

The value is obtained.

19. The method for visualizing an inner surface of a cylinder as in claim 13, wherein the step (C) of the method for visualizing an inner surface of a cylinder further comprises the steps of:

；

(C.2) based on transformation matrices

(C.3) fusing the centralized point cloud and the cylindrical image point cloud, so that the points in the centralized point cloud obtain RGB information from the cylindrical image point cloud.

20. The method for visualization of the inside surface of a cylinder as in claim 16, wherein in step (c.3) of the method for visualization of the inside surface of a cylinder, a cloud of points is centered

The color of each point in the point cloud is a cylindrical picture point cloud

The color of the closest point to the current point.

21. A cylinder interior surface inspection system, comprising:

the scanning device is used for scanning the surface of the object to be detected so as to obtain the depth image information of the surface of the object to be detected;

22. The system for inspecting the inner surface of a cylinder of claim 21, wherein said scanning device comprises a depth camera for scanning the inner surface of the object to be inspected along the axial direction O from front to back, resulting in depth image information corresponding to the surface of the object to be inspected.

23. The cylinder inner surface detection system of claim 21, wherein the point cloud processing module further comprises an image parsing unit for parsing a depth image taken by the depth camera into 3D point cloud data and a point cloud stitching unit for moving and rotating the point cloud data to stitch into a cylindrical point cloud.

24. The cylinder inner surface inspection system of claim 21, wherein the inspection module comprises a cylinder fitting unit and a defect determination unit, wherein the cylinder fitting unit divides the cylinder point cloud into a plurality of patches

Parallel-to-point cloud

The data in (2) is subjected to cylinder fitting to obtain cylinder parameters, and the defect judgment unit calculates each point in the point cloud

Distance to the axis

If, if

Then point of

Is a concave trap point; if it is

Then point of

Are raised points.

25. The system of claim 21, further comprising a texture mapping module, wherein the texture mapping module fuses 3D point cloud data and 2D image information corresponding to the inner surface of the cylinder into a texture map with color information and displays defect information of the inner surface of the cylinder.

26. The system for detecting the cylinder inner surface according to claim 25, wherein the texture mapping module comprises a picture processing unit for stitching images, a point cloud mapping unit for stitching the shot images into rectangular planar images, and a fusion unit for fusing the cylindrical point cloud data stitched by the point cloud data and the cylindrical image point cloud stitched by the images into a cylindrical surface model with color information.