As we all know, the accuracy of the production of aircraft dynamic components is a complex task, which greatly affects the pneumatic performance of the entire aircraft.
In addition, the development of the aircraft may lead to some significant changes in its aerodynamic surface.
Therefore, the shape and surface defects of the fair process element should be controlled very precisely (1-5mm).
Although the shape of the aerodynamic surface has an effect on the aircraft's flight performance, the geometry of these aerodynamics elements is rarely precisely controlled due to the complexity of this control. The surface (
And general shape)
Due to the large size of the entire aircraft, it is difficult for the assembled aircraft to be controlled by contact measurements;
This large coordinate measuring machine can be installed in special factories and is very expensive.
Size controlled by arm-
The type coordinate measurement machine is possible, but the instrument needs to be positioned due to a very complex surface, and this method is not always applicable (
Generate additional errors)
The price of the instrument is also quite high.
In addition, this method requires mechanical contact with the aircraft surface with a touch probe, so it is time consuming to obtain the large point cloud needed to evaluate the shape and surface.
The application of laser scanning coordinate meter probes is also possible, but these probes are more expensive.
Measure the shape of the aircraft (
Using a classic hard template does not give accurate surface errors, nor does it determine the entire shape of the element, and it is time consuming.
Used to determine the shape of aircraft components such as wings, fuselage, rudder, etc.
Mainly optical (non-contact)
Measurement methods can be used successfully.
In this paper, we have made a very simple review of two measurement methods that can determine the shape of aircraft components by collecting optical surface points.
These methods are: collect points by an electronic thickness gauge working in surface scan mode and collect surface points by photographic measurement.
The results of the implementation of the two methods for the same aircraft components under laboratory conditions are also compared. 2.
In the experiment of measuring the shape of aircraft components under laboratory conditions, a part of the aircraft wing was selected.
The experiment consists of two parts: surface measurement (
Get point cloud)
The point cloud is obtained by laser scanning and photographic measurement of the land meter.
The overall arrangement of the instrument is shown in Figure 1;
Wing Ameasured (2)
Placed on the viewing table and on special marks (3)
The direction of the image used in the photographic measurement process is attached to the bracket and the wing itself.
Three arm 5503 electronic step gauge for wing segment surface scanning and obtaining marked coordinates (3)
In order to locate the image in the space, better point cloud coincidence needs to be obtained through photographic measurement and step scanning.
Obtaining the surface point cloud of the wing section by photographic measurement includes shooting multiple images using a Canon EOS 350D digital camera (
Calibration with TCC software at Bonn University of Technology)
From different directions (
Get a stereo view).
Determined from forpoint (
Especially in automatic mode)
By photographic measurement, some different color or shape points must be visible to the surface (
Because the location of the exact same point needs to be determined on multiple images)
The surface of the fiberglass plastic wing part is absolutely smooth, the color is single, and the surface draws some lines with a simple permanent mark (Atkinson2001).
The image of the wing part is taken from all sides with special marks on the side (Fig 1,3)
Used to determine the exact location of the camera when taking an image (
Absolute direction of image).
In addition, using tacheometer (1)
Therefore, a single coordinate system is introduced in photographic measurement and tacheometer measurement (Ruzgiene et al. 2005). [
Figure 1 slightly]
After the image is collected, further data processing is carried out using special photographic measurement software.
Use an automatic collection of points from different images (
Digital ground model of module PhotoMod (DTM)
The 3D point cloud on the surface of the wing section is obtained (Fig 2). [
As can be seen from Figure 2, in some areas, the density of point clouds obtained from different pairs of images is insufficient or there are some gaps (
Mathematical model of geometry).
Since there are too few images taken in certain areas, this error occurs and can be corrected by taking some additional images.
These areas were later manually eliminated and were not used for further data processing (
Use existing data around to fill these gaps).
Determination of expected RMS (
Root of Square
3D coordinate error of photographic measurement model (Generation . . . 2009): [
Mathematical expressions that cannot be reproduced in ASCII. ](1)here [m. sub. x,y]--
RMS error measured by image points when creating geometric mathematical models; [m. sub. mod]--
RMS error in image geometry Mathematical model[M. sub. x,y],[M. sub. H]--
RMS error of plane and height control point positiont--image scale; e--
Image inclination; r,f--
Photographic measurement parameters of images; n--
Number of control points.
Determined results of the calculation (theoretical)
The point location of the PhotoMod software is shown in the table.
After obtaining the point cloud through the photographic measurement software, the data is transmitted to the Unigraphics CAD software, in which the surface using the point cloud will be created.
Due to the complexity of the surface (
Closed Loop surface)
, Decided to make multiple point clouds at a certain spacing, and create the most suitable splicing through these slice points.
The reverse engineering surface of the wing is created through these tooth lines (Fig 3). [
Figure 3 slightly]
Check the surface quality created using mirror reflection surface control mode (Fig 4)
Or mitigation mode (Fig 5). [
Figure 4 slightly][
Figure 5 Slightly]
As can be seen from these two graphs, there are some differences in the surface of the wing part created at the leading edge (1)
And the smaller ones near the trailing edge (2)of the wing (Figs 4-5).
The reason for the difference in the trailing edge is obvious--
Gap of point cloud (
Visible in figure 2)
Therefore, the accuracy of the surface is insufficient.
After doing some additional images of the analysis section of the wing, and then getting more points in the Gap area, the difference is easily eliminated.
The reason for the difference in the surface of the leading edge is not so obvious, and may also be due to the insufficient number of images taken in the part of the complex shape of the wing and some light reflections that occur when these images are taken (
Figure 4, 1, Figure 5).
This difference can be eliminated by obtaining more cutting-edge images, or by collecting more attention points in the above section.
Although manual collection of point clouds increases the time required to collect point clouds, it also improves accuracy. 3.
Control the results to control the surfaces obtained through photographic measurements and to obtain a clear deviation result using Trimble 5503 electronic thickness gauge to measure the surface of the wing.
The measurement is carried out in scan mode, so the point cloud of the surface is obtained at a certain distance.
In order to obtain the point cloud of the entire wing part, several times were positioned in the case of two stable points as a reference.
Scanning the working mode of the height meter is generally a very similar working mode of the conventional photoelectric height meter;
The position of the point is obtained by measuring the horizontal and vertical angles and the distance (
By laser distance meter).
The same principle is used by modern ground laser scanners, but since ordinary tacheometer is often not used for surface scanning applications, the scanning process is more time-saving, although scanning accuracy is generally considered higher.
In the case of Trimble 5503, the point measurement accuracy stated by the manufacturer is within the range of 3mm. Therefore (
This method of surface measurement can be considered as a reference to control the surface obtained through photographic measurement.
After the surface of the wing section (
It takes about 5 hours for the whole scan process)
Scanned, data (point cloud)
Transferred to the graphic CAD software, in which, similar to the case where the point cloud is obtained by a photographic measurement, the point cloud is sliced and the best fitting curve is drawn by the slice point, A 3D surface is drawn using these curves (Fig 6). [
Figure 6 slightly]
Since the coordinate system in the photographic measurement and the taht measurement is the same (
Using the same control point with the same coordinates)
, It is easy to match the surface created from the point cloud obtained from photographic measurements and tachetermeasures (Fig 7). [
Figure 7 Slightly]
As can be seen from Figure 7, the surface difference obtained by photographic measurement is obvious at the front of the wing section, although the posterior margin difference is not obvious.
Generally speaking, after Visual comparison of the two surfaces, it can be considered that the difference is very small.
Figure 8 shows the exact deviation of the rose part with the biggest difference. [
From the cut section shown in figure 8, the maximum deviation between the point cloud obtained by the photographic measurement and the point cloud obtained by The tacheometer measurement does not exceed 2mm (
The area with the largest deviation).
Therefore, this measurement shows quite good accuracy. 4.
Summarize the comparison of measurement methods to get a free full picture
Description of formal surface measurements, advantages and disadvantages of some measurement methods (
Photographic measuring and thickness gauge
Laser scanning based)
Can be highlighted.
Main advantages of Tacheometer-
High measurement accuracy based on laser scanning;
The specified accuracy of the thickness gauge used is 3mm (
Although for normal laser scanning, seldom is over 4mm);
* Measurements can be made on almost any surface (
Although there are some errors in the color and texture of the surface);
* Point clouds are generated almost immediately after measurement, so measurement errors can be found and repeated if necessary (Suchocki 2008);
* Instruments such as electronic tape measure are widely used in the economic, construction and other industrial sectors, so they are quite available. Tacheometer-
The method based on laser scanning also has its disadvantages: * This method is very time consuming (
It takes about 20 minutes to get 100 points)
Although the point acquisition time is very short when using the ground laser scanner;
* High Price of instruments (
Laser scanner on the ground is particularly expensive).
Advantages of freedom of photographic measurement-
The point cloud measurement of the shape surface is: * The measurement is relatively cheap--
Only a high-precision camera and special software is required (Ruzgiene 2008);
* The possibility of obtaining a fairly high precision point cloud (
In the classical digital close-range photography, it is believed that the accuracy of the determination of the [point coordinates] is realized. + or -]0.
01% from the object is very possible)
Although highly dependent on the environment (Karara 1997);
* Possibility to correct the result (
Get extra points)
Only images, no need to measure the object itself.
The main shortcomings of the photographic measurement method in the case (
Measurement of aircraft surface)
Yes: * need to produce some artificial color difference on the surface, because it is absolutely smooth and colorless on most modern aircraft.
Usually, this color difference is produced by projecting different color light on the object under test (
Then there is no need to do any temporary marking)(Atkinson 1980);
* The measurement is highly dependent on environmental conditions due to its complete optical properties;
* The accuracy of the measurement is highly dependent on the camera calibration, which is difficult to complete and requires special facilities and software (
Although such calibration is rarely needed)(Sonka et al. 1998);
* It is not possible to see and evaluate the measurement results immediately;
Data processing must be performed primarily on a dedicated computer in an office environment, and all data processing takes time even in automatic mode. 5.
The conclusion can be said: * two methods for determining the surface dimensions of complex shapes (
Photographic measuring and thickness gauge-
Laser scanning based)
Tests were carried out in laboratory conditions, both of which can be used to measure aircraft surfaces.
* Although the principle of measuring a single part of the wing with two different measurement methods is different, the deviation between the two methods does not exceed 2mm, which is a change in the accuracy of the method (
Considered one of the references.
Both methods have their own advantages and disadvantages, so (
Under different conditions)
It can be used for the measurement of the surface of a boat with complex shapes.
* Additional testing of the methods used should be carried out under different environmental conditions, such as open-air aircraft warehouses, aircraft hangars and building facilities. DOI: 10. 3846/1648-7788. 2009. 13. 44-
49 received in March 18, 2009;
Atkinson, a referee accepted in May 5, 2009, K. B. 1980.
Development of photographic measurement and measurement.
London: Applied Science Press Ltd. 222 p. Atkinson, K. B. 2001.
Close-range photography and machine vision.
Scotland, UK: KW5 6DW white paper. 371 p.
DTM is generated using Russian images (online). 2009.
Availablefrom Internet access: . Karara, H. M. 1997.
Photographic survey of terrain
VA: American Society of photography and measurement, Virginia Avenue North, Falls Church. 206 p. Ruzgiene, B. 2008. Fotogrametrija.
Vilnius: Technika, page 203Ruzgiene, B. ; Frohner, W. 2005.
RANSAC for exception detection.
Surveying and Mapping, 31 (3).
Vilnius: Technika, 83-87. Sonka, M. , Hlavac, V. , Boyle, R. 1998.
Image processing, analysis and machine vision. Iowa: PWS. 260 p. Suchocki, C. 2008.
Application of scanning technology in coastal monitoring.
Selected Papers of the Seventh International Conference on Environmental Engineering, Volume 1. 3. May22-
On the 23rd, Vilnius, Lithuania.
Vilnius: Tech Card, 1493-1496.
Domantas Brucas (1)
Juror of Soji Alice. Visockiene (2)
Department of surveying and cadastral, Technical University of Vilnius Gediminas, Sauletekio al. 11, LT-
10223 Vilnius, Lithuania, E-mails: (1)domka@kttv. lt, (2)
J_visockene @ hotmail.
Date and place of Dr birth: 1979, Vilnius, Lithuania.
Education: Technical University of Vilnius Gadi Minas.
Affiliation and functions: Professor Assoc, University of Vilnius GediminasTechnical.
Research interests: Development and Research of comparator for angle measurement, automation of measurement result processing.
Publications: more than 15.
Juror of Soji Alice.
Doctor, date and place of birth: 1971, Lithuania.
Education: Technical University of verniusidi Minas.
Affiliation and functions: Professor Assoc, University of Vilnius GediminasTechnical.
Research direction: digital photography and land management.
Publications: more than 15.