1. A three-dimensional scanning-based assembly nail head levelness detection method is characterized in that a plurality of assembly nail heads are arranged on the surface of a structural member, the height difference between the surfaces of the assembly nail heads and the surface of the structural member is a preset value, and the method comprises the following steps: 1) scanning the surface of the assembled structural part by using three-dimensional scanning equipment to obtain point cloud data and image patterns of the surface of the structural part; 2) identifying the center position of the assembling nail head and the surface contour of the nail head according to the image pattern of the surface of the structural member and the diameter of the assembling nail head; 3) respectively extracting characteristic points of the surface profile of each assembling nail head and point cloud data of the surface of the structural member around the assembling nail head from the point cloud data of the surface of the structural member; 4) fitting the point cloud data of the surface of the structural member around the assembling nail head into a structural plane corresponding to the assembling nail head; 5) respectively calculating the height difference between the characteristic point of the surface profile of each assembling nail head and the structural plane corresponding to the assembling nail head; 6) and comparing the height difference between the characteristic point of the surface profile of the assembling nail head and the structural plane corresponding to the assembling nail head with a preset value, wherein if the height difference is within the range of the preset value, the product is qualified, and otherwise, the product is unqualified.

2. The assembled nail head flushness detection method based on three-dimensional scanning according to claim 1, wherein in step 2, the center position of the assembled nail head and the surface contour of the nail head are identified by extracting the center position of the nail head and the radius of the nail head through the color difference of the assembled nail head in the image pattern and the surface of the structural member around the nail head.

3. The three-dimensional scanning-based assembly nail head flushness detection method according to claim 1, wherein in step 3, 30 to 50 pieces of feature point data on the surface contour of the assembly nail head are selected from the point cloud data of the surface contour of each assembly nail head as analysis objects, and the feature point data are uniformly distributed in the surface contour of the assembly nail head.

4. The method for detecting the levelness of the assembled nail head based on the three-dimensional scanning according to claim 1, wherein in the step 3, the point cloud data range of the surface of the structural member around the assembled nail head is selected within 2.5 times of the radius of the assembled nail head around the assembled nail head.

Background

The newly-developed model has the characteristics of large size, complex structure, great use of composite materials and the like of the airplane, and has extremely high requirements on the control of the surface assembly error of the airplane due to the performance requirements of the newly-developed model. The composite material structure has large deformation, large connection difficulty and high technical requirement in the assembling process, has important influence on the control of the surface error of the airplane, and the leveling degree of the pin head is a main factor influencing the surface error of the airplane. The nail head flushness is that the countersunk head fastener is connected the back, and the difference in height size on nail head and aircraft combined material structure surface, its connection quality directly determines local pneumatic continuity and the electromagnetic reflection performance in surface, need detect the nail head flushness after the fastener is connected for this.

The difficulty in detecting the levelness of the nail head is the accurate extraction of the points of the assembled nail head and the points of the surface of the structural member around the assembled nail head. Because the height difference between the nail head of the new type airplane and the surrounding surface of the new type airplane is about 0.01mm, the new type airplane not only puts high requirements on measuring equipment, but also sets a small rivet extraction threshold value aiming at a nail head identification algorithm in the whole measuring point cloud, so that a lot of error identifications are possibly generated, and in addition, a great amount of calculation time and calculation memory are consumed for searching the point cloud belonging to the rivet from the point cloud with huge volume.

Therefore, a method for rapidly extracting the point cloud of the assembled nail head and accurately identifying the surface profile of the assembled nail head is urgently needed, so that the high-precision detection of the leveling degree of the nail head is carried out.

Disclosure of Invention

The method can meet the analysis and detection of the levelness of the assembled nail head of the composite material structure of the airplane, is used for detecting and analyzing the levelness of the nail head of the installed countersunk head fastener on the surface of the composite material structure of the airplane, provides data of the detection result of the levelness of the nail head, and judges whether the levelness of the nail head is qualified or not by a quantitative method.

In order to achieve the purpose, the technical scheme is as follows:

a three-dimensional scanning-based assembly nail head levelness detection method is characterized in that a plurality of assembly nail heads are arranged on the surface of a structural member, the height difference between the surfaces of the assembly nail heads and the surface of the structural member is a preset value, and the method comprises the following steps: 1) scanning the surface of the assembled structural part by using three-dimensional scanning equipment to obtain point cloud data and image patterns of the surface of the structural part; 2) identifying the center position of the assembling nail head and the surface contour of the nail head according to the image pattern of the surface of the structural member and the diameter of the assembling nail head; 3) respectively extracting characteristic points of the surface profile of each assembling nail head and point cloud data of the surface of the structural member around the assembling nail head from the point cloud data of the surface of the structural member; 4) fitting the point cloud data of the surface of the structural member around the assembling nail head into a structural plane corresponding to the assembling nail head; 5) respectively calculating the height difference between the characteristic point of the surface profile of each assembling nail head and the structural plane corresponding to the assembling nail head; 6) and comparing the height difference between the characteristic point of the surface profile of the assembling nail head and the structural plane corresponding to the assembling nail head with a preset value, wherein if the height difference is within the range of the preset value, the product is qualified, and otherwise, the product is unqualified.

The utility model provides an advantage lies in accurate discernment assembly body assembly pin head surface profile, and the ration reachs assembly pin head parallel and level degree, has realized that aircraft combined material assembly pin head parallel and level degree high accuracy detects, requires to provide reliable detection method for new model aircraft surface assembly pin head parallel and level degree high accuracy index to the ration gives detects the numerical value. The method can be used for detecting and analyzing the installation quality of the outer surface fastener of the airplane during the production process of the airplane or during the accident elimination of an outfield, judging whether the installation of the outer surface fastener of the airplane structure has faults or not, achieving the purpose of accurately detecting the levelness of the assembled nail head, and providing detection data support for the qualification of the levelness of the assembled nail head.

Drawings

FIG. 1 is a schematic view of a point cloud data and image pattern of a surface of a structure.

FIG. 2 is a schematic view of a set of height differences between a feature point of a surface profile of an assembly nail head and a plane of a structure corresponding to the assembly nail head.

The numbering in the figures illustrates: 1 structural part surface, 2 assembling nail heads, 3 structural part surface point cloud data and 4 assembling nail head surface contour characteristic points.

Detailed Description

Referring to the drawings, the invention aims to provide an assembly nail head flushness detection method based on three-dimensional scanning, which mainly comprises the following steps:

1. scanning the surface of the assembled structural part by using three-dimensional scanning equipment to obtain the characteristic point cloud data and the image pattern of the surface of the structural part, as shown in figure 1;

2. assembling the nail head point cloud, and extracting and accurately identifying the surface contour of the nail head; calibrating a color camera and measuring equipment together, shooting an image pattern of the surface of a structural member containing the assembled nail head by the color camera, extracting the actual central position of the assembled nail head through the color difference of the assembled nail head in the image pattern and the surface of the structural member around the nail head, taking the extracted center of the assembled nail head as a seed point, searching the radius of the assembled nail head and extracting the surface contour area of the nail head of each nail head;

and extracting the center position of the nail head and the radius of the nail head through the color difference of the surfaces of the assembled nail head and the structural part around the nail head in the image pattern, thereby identifying the center position of the assembled nail head and the surface contour of the nail head.

3. And respectively extracting characteristic points of the surface profile of each assembling nail head and the point cloud data of the surface of the structural member around the assembling nail head from the point cloud data of the surface of the structural member. Extracting characteristic points of the surface profile of the assembled nail head as first point set data, and extracting point cloud of the surface of the structural member around the nail head as second point set data;

and selecting 30 to 50 feature point data on the assembly nail head surface contour from the point cloud data of each assembly nail head surface contour as a first point set data analysis object, wherein the feature point data are uniformly distributed in the assembly nail head surface contour. And selecting the point cloud data range of the surface of the structural member around the assembling nail head as second point set data in the range of 2.5 times of the radius of the assembling nail head around the assembling nail head.

4. Fitting the second point set data on the surface of the structural member around the nail head to obtain a structural plane corresponding to the assembled nail head by using a least square method;

5. respectively calculating the height difference from each point in the first point set data to the fitted corresponding structural plane; and obtaining a height difference set of the surface profile characteristic point of the assembling nail head and the structural plane corresponding to the assembling nail head.

6. And comparing the maximum value in the obtained height difference with a theoretical preset value to obtain whether the levelness of the assembled nail head is qualified or not. And calculating the average value, the standard deviation, the maximum value and the minimum value of the deviation of each assembling nail head by using the obtained height difference set, and calculating the mounting inclination angle of the fastener according to the maximum value, the minimum value and the nail head diameter of the deviation, so as to judge the mounting verticality of the fastener, quantitatively judge the leveling degree of the assembling nail head and evaluate whether the leveling degree of the nail head meets the requirement of a preset index.