DE102017102338A1 - Method and apparatus for finding or examining surface defects in a multi-layered surface - Google Patents

Abstract

The present invention relates to a method and apparatus for finding and / or examining surface defects (8) in a multi-layered surface (6). For this purpose, at least one camera (2) is moved over the surface (6) and successively different subregions (7) of the surface (6) are detected, wherein at least two images of each detected subregion (7) upon illumination of the subregion (7) with differently polarized Light and a polarizing filter (3) between the surface (6) and camera (2) are recorded. In this case, a movement of the camera (2) between the two images of a partial area (7) is preferably detected and taken into account during a processing of the images by a correction. In particular, the described method enables reliable detection and quantitative evaluation, for example with regard to an affected area, of lightning strikes in commercial aircraft as part of conventional inspection measures and shortens the duration of the investigation while at the same time significantly increasing the reliability with respect to visual inspections by maintenance personnel. An application for other components and similar inspection tasks is possible.

Description

The present invention relates to a method and apparatus for inspecting a surface constructed of two or more layers. In particular, it is about finding and / or investigating damage or surface defects in which an outer layer has been at least partially removed, so that an underlying layer is visible.

Such a task is present, for example, in the investigation of aircraft for lightning damage. Such studies have been performed visually by maintenance personnel and require great attention and expertise.

In the US 2010/0063650 A1 In addition, a method has already been proposed for inspecting an aircraft, in which a missile, in particular a so-called quadrocopter, uses a camera to inspect the top of an aircraft and thereby fly off certain orbits in order to check the outer integrity of an aircraft and to determine certain parameters from its surface measure up. However, not all damage to the surface can be detected or even classified by this method, in particular it is not possible to detect lightning damage with an area of typically 1 to 50 mm ² . Even with an increase in the resolution, small flash strikes on conventional camera images look just like foreign objects (dirt), painted rivets or other optical artifacts, so that a distinction is not possible.

The object of the present invention is to enable a method and a device for effectively finding and / or investigating damage in a multi-layered surface and to perform it in a time-saving manner.

To achieve this object, a method according to claim 1 and a device according to claim 8. Advantageous embodiments are given in the respective dependent claims. The embodiments can be used individually or in technically meaningful combinations with each other.

For this purpose, a method for finding and / or investigating damage in a multilayered surface with at least one camera, in which the camera is moved over the surface and successively different partial areas of the surface are detected, wherein at least two images of each detected partial area in the illumination of the Subarea with differently polarized light and a polarizing filter between the surface and the camera (or in the light path in the camera in front of a recording medium) are recorded. With a mobile camera large surface areas can be examined relatively quickly, whereby an automation of examinations and the evaluation of the recorded images is possible. Human errors in a visual examination due to inattention or lack of training can thus be avoided and investigations accelerated. Multilayered surfaces are here understood to mean surfaces, in particular a metallic structure, with at least one layer applied thereto, in particular protective layer and / or color layer.

This is based on the knowledge that with certain surface damage typically one or more layers are removed locally, so that underlying layers are visible. Different layers usually also have different reflection properties, which is why such damage is often recognizable by optical investigations. However, it is difficult to correctly interpret different surface changes and distinguish different types of damage. However, it has been found that different materials often differ not only in the reflection properties in terms of color and / or brightness, but also in the way in which polarized light is reflected. For example, a metallic surface, such as aluminum, changes the polarization of injected light much less than, for example, paints of different colors, or other matter adhering to a surface (soils). If one illuminates a surface with polarized light, then the reflected light is generally not or hardly polarized unless it is a metallic surface. In this case, the polarization is maintained substantially also in the reflected light. In any case, different materials have different properties that can be exploited in investigations. The principle is that one illuminates a surface with light of two different polarization planes, the polarization planes of the two illuminations should advantageously be approximately perpendicular to each other. In both types of lighting, an image is taken by a camera, with a polarization filter in front of or in the camera in the light path, which acts essentially in one of the two polarization planes. For materials that reflect or scatter polarized light without any polarization, the two images are still identical for differently polarized illumination, but for materials, the polarized light is at least partially identical polarized reflect or scatter, the two images are different.

So goes z. B. from the DE 10 2005 062 439 B3 a method for particle analysis in which a microscopic analysis of a collection of particles on a slide is made. In this case, differently polarized light is used for the illumination of the substance to be examined and a polarizing filter is used in front of the camera, so that the polarization of reflected light provides additional information about the sample to be examined. However, the described microscopic analysis system is not suitable for examining large surfaces, for example the outer skin of an aircraft. Here, such an effect or such a method of determination (modified) is now used to examine surfaces for damage. Substantially polarized filters or polarized light sources that are to be considered here allow substantially only the components of light in a predeterminable polarization plane to pass through, while all other polarizations are blanked out. The transmitted light thus has a predeterminable plane of polarization, which can either be retained (partially) during reflection or scattering, or can be canceled out again by uniform reflection or scattering in all polarization planes. Light polarized in a predetermined plane is completely transmitted in a second polarization filter of the same plane, but substantially completely absorbed in a polarization filter with a polarization plane formed perpendicular to the first polarization plane. When arranged at a non-right angle to each other polarizing filters, the effect correspondingly weaker.

Since a moving camera does not capture two consecutive images from exactly the same relative position to a sub-region even under favorable conditions, it may be necessary to accurately detect the movement of the camera and correct it while processing the images. This is relatively easy to accomplish today with available motion sensors (mostly inertial unit sensors or acceleration sensors). A corresponding geometric correction of the images taken from slightly different angles is also easily possible with modern image processing. Typically, a six-degree-of-freedom transformation matrix is used to account for all possible shifts and rotations. In principle, such a transformation matrix can also be obtained from orientation marks on the images themselves, if suitable optical artifacts are present on the surface to be examined.

In a preferred embodiment, therefore, two successive images taken at different levels of polarized light are digitally constructed from individual pixels and digitally processed by geometrically correcting the movement of the camera so that two images appearingly taken at the same angle are formed, like two can be further processed with fixed camera, in particular by subtracting the brightness and / or color of each pixel of the one image of the brightness or color of each pixel of the other image. As a result of the difference formation described, an image is produced in which the areas in which polarized light was still polarized even after reflection or scattering are highlighted. In this way it is possible in particular to reliably detect and better investigate metallic surfaces exposed by a coating.

Most sensitive is the method described when the two polarization planes of the differently polarized illumination are approximately perpendicular to one another and preferred that the polarization filter in the light path in or in front of the camera coincides with one of these two polarization planes. Deviations from these conditions lead to a lower quality of the examination results. The differently polarized light can be generated by a light source whose polarization changes, for example by a rotating polarizing filter or it can be generated by two light sources with differently oriented polarization filters. Of course, it is also possible to use a plurality of light sources with the same polarization direction for each of the two types of illumination if the illumination of the surface to be examined requires it.

The accuracy of the examination when moving the camera can be increased if the camera is preferably moved parallel to one of the two polarization planes, which is why this direction of movement is preferred.

In order to facilitate a correction of the movement or even be able to waive a correction in particularly favorable conditions, it is particularly advantageous to comply with certain conditions. The camera has an optical axis A and a distance a to the surface along the optical axis A, and the optical axis A forms an angle α to a vertical S on the surface, the camera moving at a speed v and two related images of a portion at a time interval .DELTA.t receives. Under these conditions, the distance a, the angle a, the speed v and the time interval Δt should be chosen in such a combination that a maximum angle βmax for an angle β between the joint V of a surface defect on the surface and the camera at the first shot and the corresponding joint V 'between the surface defect and the camera at the second shot is not exceeded. If the parameters can be selected such that the maximum angle βmax is very small, for example below 0.1 °, then no correction may be required. Otherwise, up to an angle of 1 ° or even 5 ° geometric correction methods can be applied. In simple terms, this means that the quality of the examination increases as the speed v of the camera decreases, whose distance a from the surface increases (if the illumination and the camera optics permit this) and / or the time Δt between two associated images decreases. The relevant parameters can be selected suitably for each examination task.

The method described is particularly suitable for the examination of a coated outer skin of an aircraft, in particular for the purpose of detecting and / or investigating lightning damage. Commercial aircraft are typically complete with paint, which in turn can be made up of different layers, with a lightning strike removing all coatings on a small area and exposing the underlying metal. Especially such damage can be examined particularly well with the described method, because metallic surfaces reflect or scatter polarized light while retaining at least part of the polarization, while the materials used for aircraft coatings do less or not at all.

While sufficient for the investigation of the underside of an aircraft, a hand-held or a robot arm camera support, it is advantageous for the investigation of the top, to move the camera by means of a flying machine, in particular with a remotely controllable drone, for example a so-called quadrocopter. This movement should be substantially parallel to the surface of the aircraft, which of course can not be done with great accuracy because of the irregular curvature of an aircraft fuselage. However, one can fly over the surface of an aircraft in suitable orbits with sufficient accuracy and in this way preferably record a multiplicity of image pairs of successive surface regions.

• - mindestens eine Kamera, der ein Polarisationsfilter vorgeschaltet ist,
• - mindestens eine erste Lichtquelle mit einer ersten Polarisationsebene und mindestens eine zweite Lichtquelle mit einer zweiten Polarisationsebene, die abwechselnd die Oberfläche beleuchten können, und
• - einen beweglichen Kameraträger.

An associated apparatus for finding and / or examining damage in a multi-layered surface has the following features:

• at least one camera, preceded by a polarizing filter,
• at least one first light source with a first plane of polarization and at least one second light source with a second plane of polarization, which can alternately illuminate the surface, and
• - a mobile camera carrier.

It is particularly preferred that the light sources are also attached to the camera support, so that a uniform movement with the camera and illumination of different subregions of the surface are possible.

To compensate for geometric differences in the associated images due to the movement of the camera support, it is advantageous if the camera carrier has a motion sensor for measuring movements and a memory for digital recording of recorded images of the camera and the measured movements. Depending on the requirements, it is thus possible either to carry out an evaluation during the examination or to perform this later on the basis of stored data. If the camera carrier is a flying machine, in particular a remotely controllable drone, it may also be advantageous to provide a device for the wireless transmission of recorded images and / or movement data to a stationary receiver in the flying machine in order to at least partially evaluate data during the examination to be able to.

• 1: eine Situation bei der Untersuchung einer Oberfläche,
• 2: geometrische Verhältnisse bei der Durchführung des beschriebenen Verfahrens, und
• 3: eine Situation bei der Inspektion einer Oberseite eines Flugzeugs.

The principles and a schematic embodiment of the invention, to which, however, is not limited, are described below with reference to the drawing. They show schematically:

• 1 : a situation when examining a surface,
• 2 : geometric conditions in carrying out the described method, and
• 3 : a situation when inspecting a top of an aircraft.

1 shows a camera carrier 1 with a camera 2 pointing to a surface 6 is directed. This surface can be divided into different parts 7 subdivided, with surface defects 8th in every section 7 be recognized and / or investigated. For this every subsection becomes 7 successively from a first polarized light source 4 and a second polarized light source 5 illuminated. The camera 2 takes during the illumination by the first light source 4 at least one image on and illuminated by the second light source 5 also at least one picture. A polarizing filter 3 in the light path from the surface 6 to the camera 2 causes only in a certain plane polarized light is transmitted. In case of a surface defect 8th In particular, if at this point metal is freed from a color coating, polarized light is thrown back differently than from the other areas. This can be determined in a later evaluation of the recorded images. If the camera carrier at a speed v (as indicated by an arrow) moves, so is the light path 9 slightly different at the first shot than at a later second shot. This may need to be corrected to better compare the two images.

In fact, the camera is on an irregularly curved surface 2 also not always exactly vertically above the part to be examined 7 so that there is a tilt angle α between a vertical S and an optical axis A the camera 2 results. Also this angle of inclination α is important in defining the parameters that should be used to investigate. The camera carrier 1 also has a motion sensor 10 , a store 11 for storing image and / or movement data on and, if necessary, a device 12 for the wireless transmission of such data. The camera carrier 1 can along an inspection track 19 over the surface 6 be moved, either on a (not shown) movement arm or the accommodation in a flying apparatus 18 , In the latter case, a stationary receiving station 13 to receive data already during the investigation.

2 shows the camera 2 in a first position P above the surface 6 and a surface defect 8th when taking a first picture and in a further position P 'after moving at the speed v when taking a second picture with a time interval .DELTA.t , Next to the distance a between camera 2 and surface 6 along the optical axis A the camera 2 (which by the angle of inclination α to the vertical S on the surface 6 can be inclined) is also the connecting line V from the camera 2 to a certain point on the surface 6 , in particular to a surface defect 8th , significant. This connecting line V from the first position P the camera 2 forms to the corresponding connecting line V 'to the camera 2 in the second position P 'an angle β , which is a measure of how strong the image data due to the movement of the camera 2 need to be corrected. The surface 6 is multi-layered, here with a first layer 20 (eg formed with paint and / or a non-metal) and a second layer 21 (eg formed with metal).

3 shows the application of the invention for examination of the top 17 of an airplane 16 to find and / or investigate lightning damage. In this case, the camera is 2 on a flying machine 18 , in particular a quadrocopter, which also fixes the first polarized light source 4 and the second polarized light source 5 wearing. For the investigation of partial areas 7 the plane top 17 becomes the flying machine 18 along an inspection track 19 substantially parallel to the aircraft upper side 17 guided.

For example, according to current technology, a camera can be used which records 30 frames per second, whereby polarized light sources can be switched on and off in a corresponding time sequence, so that synchronization with the sequence of picture recordings is possible without problems. The method described enables a reliable detection and quantitative evaluation, for example with regard to an affected area, of lightning strikes in commercial aircraft as part of standard inspection measures and shortens the duration of the investigation while at the same time significantly increasing the reliability with respect to visual inspections by maintenance personnel. An application for other components and similar inspection tasks is possible.

LIST OF REFERENCE NUMBERS

1

Camera carrier (flying machine, drone)

2

camera

3

polarizing filter

4

first polarized light source

5

second polarized light source

6

surface

7

subregion

8th

surface defect

9

light path

10

motion sensors

11

Storage

12

Device for transmission

13

stationary receiving station

14

image analysis

15

information output

16

plane

17

Aircraft top

18

flying machine

19

inspection train

20

first shift

21

second layer

S

Vertical on the surface

A, A '

optical axis of the camera

V, V '

Connecting line between surface defect and camera

a, a '

Distance between camera and surface

v

Movement speed of the camera

.delta.t

Time interval between two recordings of a surface area

α

Angle between shooting direction of the camera and surface

β

Angle between connecting lines V and V'

βmax

Maximum angle between two shots

P, P '

position

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 2010/0063650 A1 [0003]
• DE 102005062439 B3 [0008]

Claims (10)

Method for finding and / or examining surface defects (8) in a multilayered surface (6) with at least one camera (2), wherein the camera is moved over the surface (6) and successively different subregions (7) of the surface (6) and at least two images of each detected partial area (7) are recorded when illuminating the partial area (7) with differently polarized light and a polarization filter (3) between the surface (6) and the camera (2). Method according to Claim 1 , wherein a movement of the camera (2) between the two images of a sub-area (7) is detected and taken into account in a processing of the images by a correction. Method according to Claim 2 , where two successive images recorded at different polarized light are digitally constructed of individual pixels and are processed digitally by geometrically correcting the movement of the camera (2) so that two images taken at almost the same angle are produced, like two fixed ones Camera (2) recorded images can be further processed, in particular by subtracting the brightness and / or color of each pixel of the one image of the brightness or color of each pixel of the other image. Method according to one of the preceding claims, wherein the differently polarized light is generated by at least one light source (4) with alternating polarization or by at least two light sources (4, 5) with different polarization, whereby the light has alternately substantially two mutually perpendicular polarization planes , Method according to one of the preceding claims, wherein the camera (2) has an optical axis (A) and a distance (a) from the surface (6) along the optical axis (A) and the optical axis (A) has an angle (a) forming a vertical (S) on the surface (6), and wherein the camera (2) moves at a speed (v) and takes two related images of a subregion (7) at a time interval (Δt), and further the distance (a), the angle (a), the velocity (v) and the time interval (Δt) are chosen so that a maximum angle (βmax) for an angle (β) between the compound (V) of a surface defect (8) on the surface (6) and the camera (2) at the first shot and the corresponding connection (V ') between the surface defect (8) and the camera (2) at the second shot is not exceeded. Method according to one of the preceding claims, wherein the surface (6) is a coated outer skin of an aircraft (16) and the method is carried out for the purpose of detecting and / or investigating lightning damage. Method according to one of the preceding claims, wherein the movable camera (2) by means of a flying apparatus (18) is moved substantially parallel to the surface (6). Device for finding and / or investigating surface defects (8) in a multi-layered surface (6), having the following features: at least one camera (2), which is preceded by a polarizing filter (3), at least one first light source (4) with a first polarization plane and at least one second light source (5) with a second polarization plane, which can alternately illuminate the surface (6), - A movable camera support (1). Device after Claim 8 in that the camera carrier (1) has a movement sensor system (10) for measuring movements of the camera carrier (1) and a memory (11) for digital recording of recorded images of the camera (2) and the measured movements. Device after Claim 8 or 9 , wherein the camera carrier (1) is a flying apparatus (18).

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