AT513560A1 - Device for the examination of surfaces of metal sheets - Google Patents

Abstract

A device (1) for inspecting surfaces (2) of metal sheets (3), the apparatus comprising a light field camera (4) with at least one image sensor (5) and at least one grid (6) of micro lenses arranged in front of the image sensor (5) (7, 8, 9), wherein viewed from a surface to be examined (2) in front of the image sensor (5) and the grating (6) of microlenses (7, 8, 9) to at least one magnification optics (10) is arranged , which produces an enlarged image of a surface portion (17) of the surface (2) to be examined, which is imaged by the microlenses (7, 8, 9) on the image sensor (5).

Description

1

The invention relates to a device for inspecting surfaces of metal sheets.

Furthermore, the invention relates to a method for examining surfaces of metal sheets.

For metal sheets, such as process or conveyor belts, press plates, etc., depending on the processes in which they are used, the quality of the surface may be of great importance. As part of a quality control, therefore, usually the surface of a metal sheet is checked. The examination of surfaces of metal sheets is conventionally in the form of a visual inspection. Here, the surface of a tape is checked by a person for damage. The disadvantage of this procedure is that it is very time consuming and expensive.

It is therefore an object of the invention to simplify the process of verification.

This object is achieved with a device of the type mentioned in the present invention, that the device comprises a light field camera with at least one image sensor and at least one arranged in front of the image sensor grid of microlenses, viewed from a surface to be examined from before the image sensor and the grid At least one magnifying optical system is arranged, which generates an enlarged image of a surface portion of the surface to be examined, which is imaged by the microlenses on the image sensor. 2/19 N2012 / 21100 2

Light field cameras, also called plenoptic cameras, enable a three-dimensional representation of objects. Such cameras are known to the person skilled in the art, for example from WO 2010/121637 A1 and EP 2 244 484 B1, in which parameters to be considered in the construction of such cameras are explained in more detail. In the case of the subject invention, the grating of microlenses can be located in the image plane of a main objective or a camera lens of the light field camera or of the magnification optics. However, it should be mentioned at this point that in principle the grating of microlenses can also be located before or after an image plane of the magnifying optics or of a camera lens of the light field camera. The term "image plane" is understood in this document to mean a plane in which the image of an object is sharply imaged. The image plane may also be an intermediate image plane of the optical system. If the image plane lies behind the image sensor, then in the present context a virtual image plane is spoken. The grating of microlenses can be viewed from the magnifying optics or the camera lens in the direction of the image sensor, in particular in front of the image plane of the magnifying optics or the image plane of the camera lens, if the image plane of the magnifying optics or of the camera lens is a virtual image plane lying behind the image sensor. Whereas, on the other hand, the grating of microlenses viewed from the magnifying optics or the camera lens can be arranged behind the image plane of the magnifying optics or the image plane of the camera lens, if a real image is shown in this image plane, which is imaged by the microlenses on the image sensor.

No further optical element is provided between the grating of microlenses and the image sensor, with the exception that behind a first grating of microlenses another grating of microlenses or a plurality of grids of microlenses may or may not be arranged. The grating of microlenses can be used to detect not only the coordinates in the xy / y plane of the image sensor, but also the direction of a light beam. From the angular coordinates provided by the grating of microlenses and the x / y coordinates of the light rays impinging on the image sensor, a three-dimensional image of the viewed surface can be created. 3/19 N2012 / 21100 3

The solution according to the invention thus makes it possible to produce an enlarged three-dimensional image of a viewed surface section, which is subsequently used as a basis for the examination. The examination of the three-dimensional image can be performed by a person in the form of a visual inspection, for example, when the three-dimensional image is displayed on a screen. Such a visual inspection can be carried out very quickly due to the enlarged three-dimensional representation of the surface. However, the digital image generated by the image sensor can also be further processed automatically, as a result of which the time required for the examination of the surface can be substantially reduced.

According to an advantageous variant of the invention, it is provided that the at least one magnification optical system is designed as a microscope. By using a microscope even very small imperfections in the surface can be detected very reliably and quickly. In this case, provision can be made for the microscope to have an eyepiece and a lens and for the microlens grid to be arranged between the eyepiece of the microscope and the image sensor.

A further structural and constructive simplification of the device can be achieved in that the microscope is designed without eyepiece and has a lens, wherein the grid of microlenses between the lens and the image sensor is arranged. In this case, according to an advantageous variant of the invention, it may be provided that the grid of microlenses is arranged in an image plane of the objective of the microscope.

In order to be able to ensure good illumination of the surface section to be examined, the microscope can be designed as a reflected-light microscope.

A better depth resolution of the image can be achieved in that the grid of microlenses has at least three types of lenses, which differ in their focal length from each other. The embodiment with microlenses of different focal lengths is suitable in particular for an arrangement of the crystal of microlenses also before or after an intermediate image plane in which the image to be imaged by the microlenses onto the image sensor is located.

An advantageous variant of the invention provides that the device has a control which is connected to the image sensor and is adapted to generate from signals generated by the image sensor a three-dimensional digital image of the surface of a metal sheet being examined.

An automation of the image evaluation is facilitated by the fact that the device has an evaluation unit which is set up to classify elevations of the surface occurring in the three-dimensional image as soiling and depressions in the surface as damage to the metal sheet.

The above object is also achieved with a method of the type mentioned above according to the invention in that a device according to one of claims 1 to 9 is used, wherein the device in a recording step, a three-dimensional image of a surface to be examined section is created and recorded and in a subsequent evaluation step, the three-dimensional image is analyzed and evaluated with respect to damage to the surface section examined.

A particularly reliable detection of actual damage to the surface of the metal sheet can be ensured by the fact that in the evaluation step elevations on the surface are classified as soiling of the surface and depressions in the surface as damage to the surface of the metal sheet. In this case, dirt is again understood to mean removable dirt which does not actually damage the surface. Such contamination can originate, for example, from dust grains.

The examination process can be significantly accelerated by the fact that before the recording step, the surface of the metal sheet is examined optically in a pre-examination step after any damage and only 5/19 N2012 / 21100 5

Surface portions of the surface are subjected to the recording step, which were classified in the pre-examination step as possibly having damage. This variant of the invention has the advantage that only those areas which are classified as possibly containing damage must be examined more closely. For example, the preliminary examination may be performed by a person in the form of a rough visual inspection. Alternatively, the preliminary examination can also be carried out automatically.

For a better understanding of the invention, this will be explained in more detail by way of example with reference to the following figures.

In each case, in a schematic and highly simplified representation:

1 shows a device according to the invention;

Fig. 2 is a light field camera of the apparatus of Fig. 1;

Fig. 3 is a three-dimensional image of a surface portion of a metal sheet produced by the apparatus of Fig. 1;

4 shows a variant of a device according to the invention;

5 shows a further variant of a device according to the invention;

Fig. 6 is a flowchart of a method according to the invention.

By way of introduction, it should be noted that in the differently described embodiments, the same parts are provided with the same reference numerals or the same component names, wherein the disclosures contained in the entire description can be mutatis mutandis to the same parts with the same reference numerals or component names. Also, the location information chosen in the description, such as top, bottom, side, etc. related to the immediately described and illustrated figure and are to be transferred to the new situation mutatis mutandis when a change in position. Furthermore, individual features or combinations of features from the illustrated and described different exemplary embodiments may themselves represent independent, inventive or inventive solutions. All statements on ranges of values in the description of the present invention should be understood to include any and all sub-ranges thereof, e.g. the indication 1 to 10 should be understood to include all sub-ranges, starting from the lower limit 1 and the upper limit 10, i. all subregions begin with a lower limit of 1 or greater and end at an upper limit of 10 or less, e.g. 1 to 1.7, or 3.2 to 8.1 or 5.5 to 10.

It should also be noted that the figures are described across.

According to FIG. 1, a device 1 for checking surfaces 2 of metal sheets 3 has a light field camera 4. The light field camera 4 illustrated in more detail in FIG. 2 comprises an image sensor 5, which may be constructed as an array or grid of individual light-sensitive sensors. In front of the image sensor 5, a grid 6 of microlenses 7, 8, 9 is arranged. Although only one grating 6 is arranged in the illustration shown here, two or more grids 6 of microlenses 7, 8, 9 can also be arranged one behind the other along the optical axis, as has become known, for example, from EP2244484B1. Also, the microlenses 7, 8, 9 of the grating 6 can all have the same focal lengths or else different focal lengths. Viewed from the surface 2 to be examined, at least one magnification optical system 10 is arranged in front of the image sensor 5 and the grating 6 of microlenses 7, 8, 9, which generates an enlarged image of the surface 2 to be examined, which is then guided by the microlenses 7, 8, 9 is imaged on the image sensor 5.

The apparatus 1 has a controller 12, for example a correspondingly programmed micro or signal processor, which is connected to the image sensor 5 and is adapted to generate a three-dimensional signal, which is identified by the reference symbol 13 in FIG. 3, from the signals generated by the image sensor 5. generate a digital image of the surface 2 of a metal sheet 3 under examination. 7/19 N2012 / 21100 7

Furthermore, the device 1 can have an evaluation unit 14, for example likewise in the form of a suitably programmed micro or signal processor, which is set up in the three-dimensional image 13 occurring elevations 15 of the surface 2 as removable dirt and depressions 16 in the surface 2 as Classify damage to the metal sheet 3. The evaluation unit 14 and the controller 12 can be realized in a single component or as physically separate units from each other. In the first case, the controller 12 and the evaluation unit 14 may be realized as different programs or program parts which run on one or more parallel processors. If the controller 12 and the evaluation unit 14 are physically separated from each other, then the evaluation unit 14 can also be, for example, a computer that is external to the controller 12 with its own output unit, such as a screen. It should also be noted at this point that the three-dimensional images 13 generated by the device 1 can also be stored in a memory connected to the controller 12 in order to enable a documentation of the check. Also, the images 13 generated by the controller 12 can be stored together with the results of the evaluation unit 14. The images 13 and the results of the evaluation can be displayed together or separately on an evaluation unit, for example a screen.

Before discussing the exemplary structure of the magnifying optical system 10 shown in FIGS. 4 and 5 in further detail, the method according to the invention will be briefly explained with reference to the flowchart shown in FIG.

In a preliminary investigation step I, the surface 2 of the metal sheet 3 is examined visually for any damage. Only surface portions 17 that have been classified as potentially damaged in the pre-examination step I will be further examined below. The pre-examination step may be performed by a person in the form of a visual inspection or also automated. 8/19 N2012 / 21100 8

In a recording step II, a three-dimensional image 13 of the surface section 17 to be examined is created and recorded with the light field camera 1. In this case, in a subsequent evaluation step III, the three-dimensional image 13 is analyzed and evaluated with regard to damage to the examined surface section 17.

As already mentioned above, in the evaluation step III, elevations 15 on the surface 2 of the metal sheet 3 are classified as soiling of the surface 2, as caused for example by dust grains, and only depressions 16 in the surface as actual damage to the surface 2 of the metal sheet 3.

According to FIG. 4, the magnification optical system 10 can be designed as a microscope 11 with an objective 19 and an eyepiece 18. In the exemplary case illustrated here, the objective 19 has two lenses, while the eyepiece 18 is formed by a lens. It should be noted at this point, however, that in principle also any other structures of the microscope 11 not shown here are possible. The light rays emerging from the eyepiece 18 are focused by a camera lens 20 of the light field camera 4. Behind an image plane of the camera lens, the grating 6 is arranged from microlenses 7, 8, 9, which image the image of the examined surface portion 17 in a manner known per se on the image sensor 5.

FIG. 5 shows another structure of a microscope 21 according to the invention. In this case, an eyepiece is dispensed with and the grating 6 made of microlenses 7, 8, 9 is arranged in an image plane of the objective 22, which is indicated here by way of example by an objective lens. Behind the grating 6 is the image sensor 5.

The variants illustrated in FIGS. 4 and 5 are preferably reflected-light microscopes in order to ensure good illumination of the examined metallic surfaces.

The embodiments show possible embodiments of the device according to the invention and of the method according to the invention, wherein at this 9/19 N2012 / 21100 9

It should be noted that the invention is not limited to the specifically illustrated embodiments of the same, but also various combinations of the individual embodiments are mutually possible and this possibility of variation due to the teaching of technical action by representational invention in the skill of those working in this technical field , So there are also all conceivable embodiments that are possible by combinations of individual details of the illustrated and described embodiments and fall within the literal sense of the independent claims covered by the scope. 10/19 N2012 / 21100

LIST OF REFERENCE NUMBERS

contraption

surface

metal sheet

Light field camera

image sensor

Grid of microlenses

microlens

microlens

microlens

magnification optics

microscope

Control 3D image

evaluation

survey

deepening

surface section

eyepiece

lens

camera lens

microscope

Lens 11/19 N2012 / 21100

Claims (12)

1. Device (1) for the examination of surfaces (2) of metal sheets (3), characterized in that the device comprises a light field camera (4) with at least one image sensor (5) and at least one in front of the image sensor (5) arranged grid (6) consists of microlenses (7, 8, 9), wherein viewed from a surface (2) to be examined from the image sensor (5) and the grating (6) of microlenses (7, 8, 9) at least one magnification optics ( 10), which generates an enlarged image of a surface section (17) of the surface (2) to be examined, which is imaged by the microlenses (7, 8, 9) on the image sensor (5). 2. Apparatus according to claim 1, characterized in that the at least one magnifying optical system (10) as a microscope (11,21) is formed. 3. Apparatus according to claim 2, characterized in that the microscope (11) has an eyepiece (18) and a lens (19) and the grating (6) of microlenses (7, 8, 9) between the eyepiece (18) of the microscope (11) and the image sensor (5) are arranged. 4. Apparatus according to claim 2, characterized in that the microscope (21) is designed without eyepiece and having a lens (22), wherein the grid (6) of microlenses (7, 8, 9) between the lens (22) and the image sensor (5) is arranged. 5. Apparatus according to claim 4, characterized in that the grating (6) of microlenses (7, 8, 9) in an image plane of the lens (22) is arranged. 6. Device according to one of claims 2 to 5, characterized in that the microscope (11,21) is designed as a reflected light microscope. 12/19 N2012 / 21100 2 7. Device according to one of claims 1 to 6, characterized in that the grid (6) of microlenses (7, 8, 9) has at least three types of lenses which differ in their focal length from one another. 8. Device according to one of claims 1 to 7, characterized in that the device (1) comprises a controller (12) which is connected to the image sensor (5) and adapted to, from the image sensor (5) signals generated to produce a three-dimensional digital image (13) of the surface (2) of an inspected metal sheet (3). 9. Apparatus according to claim 8, characterized in that it comprises an evaluation unit (14), which is arranged in the three-dimensional image (13) occurring elevations (15) of the surface (2) as soiling and depressions (16) in the Surface (2) as damage to the metal sheet (3) to classify. 10. A method of inspecting surfaces (2) of metal sheets (3), characterized in that a device (1) according to any one of claims 1 to 9 is used, wherein with the device (1) in a recording step (II) a three-dimensional Image (13) of a surface section (17) to be examined is created and recorded and in a subsequent evaluation step (III) the three-dimensional image (13) is analyzed and evaluated with regard to damage to the surface section (17). 11. The method according to claim 10, characterized in that in the evaluation step (III) elevations (15) on the surface (2) as soiling of the surface (2) and depressions (16) in the surface as damage to the surface (2) of the Metal sheets (3) are classified. 12. The method according to claim 11, characterized in that prior to the recording step (II), the surface (2) of the metal sheet (3) in a preliminary examination step (I) is examined visually for any damage and only Surface portions (17) of the surface (2) are subjected to the recording step (II) classified as having damages in the preliminary examination step (I). 14/19 N2012 / 21100