METHOD AND DEVICE FOR DETECTING LOCAL DEFECTS ON A REFLECTIVE SURFACE

Abstract

A method for detecting local defects on a reflective surface with a device having at least one pattern for reflection on the reflective surface, at least one camera and a data processing unit. The pattern has at least one substantially linear light-dark transition, the positioning and orientation of the camera are known, the camera captures the pattern reflected on the surface and generates image data of the reflected pattern which are transmitted by the camera to the data processing unit, and the data processing unit determines local defects on the surface on the basis of an evaluation of at least one property of the at least one light-dark transition in the image data of the reflected pattern. Also a device and a computer program.

Claims

1.-12. (canceled)

13. A method for detecting local defects on a reflective surface with a device comprising at least one pattern for reflection on the reflective surface, at least one camera and a data processing unit, wherein the at least one pattern comprises at least one line-shaped light-dark transition, and wherein a position and orientation of the at least one camera being known, wherein the method comprises: recording, by the at least one camera, a reflected pattern on the reflective surface and generating image data of the reflected pattern; transmitting the image data from the at least one camera to the data processing unit; and, determining, by the at least one data processing unit, one or more local defects on the reflective surface based on an evaluation of at least one property of at least one line-shaped light-dark transition in the image data of the reflected pattern.

14. The method according to claim 13, wherein the at least one property of the at least one line-shaped light-dark transition in the image data is selected from a group consisting of: a shape of the at least one line-shaped light-dark transition in the image data, a contrast in a predetermined area of the at least one line-shaped light-dark transition in the image data; a change in brightness over a predetermined distance across the at least one line-shaped light-dark transition in the image data; and combinations thereof.

15. The method according to claim 13, wherein a position of the at least one pattern with respect to the reflective surface is unknown.

16. The method according to claim 13, wherein the at least one pattern comprises at least one stripe forming two light-dark transitions, and wherein the data processing unit evaluates a width of the at least one stripe to determine the local defects on the reflective surface.

17. The method according to claim 13, wherein the at least one pattern, or the reflective surface, or both perform a relative movement with respect to each other during the recording of the reflected pattern by the at last one camera.

18. A device for detecting local defects on a reflective surface comprising: at least one pattern for reflection on the reflective surface, at least one camera, and a data processing unit, wherein the at least one pattern comprises at least one line-shaped light-dark transition, wherein a positioning and an orientation of the at least one camera are known, wherein the camera is configured to record a reflected pattern on the reflective surface, generate image data of the reflected pattern, and transmit the image data to the data processing unit, and, wherein the data processing unit is configured to determine local defects on the reflective surface based on an evaluation of at least one property of at least one line-shaped light-dark transition in the image data of the reflected pattern.

19. The device according to claim 18, wherein the at least one property of the at least one line-shaped light-dark transition in the image data is selected from a group consisting of: a shape of the at least one line-shaped light-dark transition in the image data; a contrast in a predetermined area of the at least one line-shaped light-dark transition in the image data; a change in brightness over a predetermined distance across the at least one line-shaped light-dark transition in the image data; and combinations thereof.

20. The device according to claim 18, wherein a position of the at least one pattern with respect to the reflective surface is unknown.

21. The device according to claim 18, wherein the at least one pattern comprises at least one stripe forming two line-shaped light-dark transitions, and wherein the data processing unit is configured to evaluate a width of the at least one stripe to determine local defects on the surface.

22. The device according to claim 18, wherein the at least one pattern, or the reflective surface, or both are configured to perform a relative movement with respect to each other during the recording of the reflected pattern by the at least one camera.

23. A non-transitory computer readable medium storing a computer program product comprising instructions which, when executed by a processor, cause the processor to perform the method of claim 13.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Further advantages, features and possible applications of the present invention are also apparent from the following description of examples of embodiments and the drawing. All the features described and/or illustrated form the subject matter of the invention either individually or in any combination, even independently of their summary in the claims or their references.

[0027] It shows schematically

[0028] FIG. 1 an embodiment of a device according to the invention for determining the shape of a reflective surface.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] FIG. 1 shows the basic structure of a device 10 for detecting defects in a reflective surface 13 of an object 3 to be inspected. The device 10 comprises a camera 1 which observes the pattern 12 of a pattern carrier 2 via the reflective surface 13. In order to be able to determine defects in the reflective surface 13 of the object 3, a coordinate system of the camera 1 is determined using a known camera calibration method. For example, a camera calibration method which observes a planar pattern in at least two different orientations and which is described in Zhang, Z., A flexible new technique for camera calibration, IEEE Transactions on Pattern Analysis and Machine Intelligence, vol. 22, no. 11, 2000, pages 1330-1334, may be used. Further camera calibration methods are described, for example, in Fraser, Clive S., Digital camera self-calibration, ISPRS Journal of Photogrammetry and Remote Sensing, No. 52(4), 1997, pages 149-159.

[0030] The digital camera 1 is configured to view the 2-dimensional pattern 12 reflected on the reflective surface 13 pixel-by-pixel.

[0031] The pattern 12 may have different characteristics. For this purpose, a flat screen, e.g. a TFT screen, is provided as pattern carrier 2, on which any pattern 12 can be displayed. Due to the known pixel dimensions of the flat screen 2, the geometry of the displayed pattern 12 is also precisely known. However, other realizations for a pattern carrier 2, e.g. exchangeable plates with a measured pattern in a holder, are also conceivable. For example, the pattern 12 may form two bright stripes with a width B1 and a width B2 on a dark background, having a distance which is greater than the width B1, B2 of the two stripes. Here, B1 and B2 may be the same or different. The distance between the two stripes is the distance between two neighboring light-dark transitions of the neighboring stripes. Each stripe comprises two light-dark transitions, namely a first light-dark transition from an area of low brightness to an area of high brightness and a second light-dark transition from an area of high brightness to an area of low brightness.

[0032] In practice, the objects to be examined for surface defects are, for example, a windshield of a motor vehicle. The reflective surface is the outer surface 13 of the windshield 3.

[0033] The camera 1 records an image of the stripe pattern and transmits the generated digital data to the data processing unit 7.

[0034] The detection of defects on the surface 13 is carried out by a processor contained in the data processing unit 7 based on the data transmitted by the camera 1 with the image of the light-dark transitions of the pattern reflected on the surface 13. For this purpose, the brightness and/or a color value or greyscale value received by the data processing unit 7 from the camera 1 is evaluated for each pixel of the camera that corresponds to a point of the image. For this purpose, the lines of the transitions are first searched for, which is done using threshold value operations. If the line is the brightest area of a transition, it is assumed that only the areas where the line is visible appear bright in the image. Accordingly, such a threshold value operation is of course also possible for a dark line. The line and its surroundings are extracted from the intensity maxima found; these surroundings are a curved stripe with a certain expansion of bright/dark areas perpendicular to the line, which follows the course of the reflected line. The subsequent calculations, such as determining the local contrast and determining the local shape of the line and its width, are then carried out on this strip. It is then determined whether the course of the lines comprises changes compared to the course of the pattern 12, for example changes in direction. Alternatively or additionally, the width of the stripes extending in the areas of high brightness between adjacent line-shaped light-dark transitions may be determined. If there are deviations from the pattern 12 in the light-dark transitions, the data processing unit detects a defect in the surface 13 of the windshield 3. The data processing unit 7 can also assign the defect to a specific position on the surface 13 of the windshield 3, as the camera 1 is calibrated with regard to position and viewing direction. The expansion/dimension of the defect may also be determined based on the size of the area in the image captured by the camera 1, in which a change in the respective light-dark transition is determined and linked to the corresponding positions of the area on the surface 13.

[0035] The above steps are easy to implement and result in a high inspection speed. Defect positions and dimensions are determined. The data processing unit may store the determined defects and their dimensions in a memory unit and/or show them on a display.

[0036] While at least one exemplary embodiment of the present invention(s) is disclosed herein, it should be understood that modifications, substitutions and alternatives may be apparent to one of ordinary skill in the art and can be made without departing from the scope of this disclosure. This disclosure is intended to cover any adaptations or variations of the exemplary embodiment(s). In addition, in this disclosure, the terms comprise or comprising do not exclude other elements or steps, the terms a or one do not exclude a plural number, and the term or means either or both. Furthermore, characteristics or steps which have been described may also be used in combination with other characteristics or steps and in any order unless the disclosure or context suggests otherwise. This disclosure hereby incorporates by reference the complete disclosure of any patent or application from which it claims benefit or priority.

LIST OF REFERENCE SIGNS

[0037] 1 Camera [0038] 2 Pattern carrier, flat screen [0039] 3 Windshield [0040] 7 Data processing unit [0041] 10 Device [0042] 12 Pattern [0043] 13 Reflective surface of the windshield 3