DE102017110080B4 - Method and device for detecting surface defects of a surface - Google Patents

Abstract

A method of detecting surface defects (28, 30, 32, 38) of a surface (14) comprising the steps of:
- Providing at least a portion of the surface (14) in a detection area (16);
- providing a first dark field light source (18) directed in a first direction to the detection area (16);
- providing a second dark field light source (22) directed in a second direction onto the detection area (16);
- providing a detector (26) directed towards the detection area (16);
- illuminating the surface (14) in the detection area (16) with the two dark field light sources (18, 22); and
- detection of surface defects (28, 30, 32, 38) illuminated by the dark field light sources (18, 22) by means of the detector (26); characterized in that the first and the second dark field light source (18, 22) radiate approximately parallel and directed light at an angle significantly shallower than the reflection angle to the detection area.

Description

The invention relates to a method and a device for detecting surface defects of a surface. More particularly, the invention relates to a method and apparatus for detecting surface defects of a surface having at least two dark field light sources.

Depending on the application, different methods are used in the detection of surface defects of a surface. While automated detectors or sensors are used in many areas, other areas of the world still require human viewers, such as in the inspection of footage.

The common method for assessing the film surface is purely visually at the viewing table. In the care and copying of film material, it is important to examine the condition of the film material and to detect defects, in particular surface defects. This information is then used during film restoration or scanning.

The method of dark field illumination is an established method to visually contrast small objects, especially in microscopy, from the background. Also in the material technology this method is used to represent small surveys in high contrast. In this approach, a dark field illumination or darkfield light source is placed flat with the object while the camera is perpendicular or normal to the object or surface. In this way, most of the light is reflected away from the camera. The camera detects only the scattered light, which is reflected by a surface defect, which is then visible in high contrast.

DE 10 2008 012 478 A1 discloses an apparatus for spatially illuminating an object having a plurality of light sources disposed about the object and means for selectively driving the plurality of light sources. The light sources are radiant surface light sources and can be designed as light or dark field illuminated.

DE 10 2013 108 457 A1 discloses a device for illuminating an object by means of a flatly formed illumination source, wherein the radiation emanating from the illumination source can be coupled into the beam path of an optical sensor and can be imaged onto the object. You can switch between bright or darkfield incident light.

The invention is based on the object to improve the detection of surface defects.

This object is achieved by a method according to claim 1 or a device according to claim 9.

• Bereitstellen zumindest eines Teils der Oberfläche in einem Detektionsbereich;
• Bereitstellen einer ersten Dunkelfeld-Lichtquelle, welche in einer ersten Richtung auf den Detektionsbereich gerichtet ist;
• Bereitstellen einer zweiten Dunkelfeld-Lichtquelle, welche in einer zweiten Richtung auf den Detektionsbereich gerichtet ist;
• Bereitstellen eines auf den Detektionsbereich gerichteten Detektors;
• Beleuchten der Oberfläche in dem Detektionsbereich mit den beiden Dunkelfeld-Lichtquellen; und
• Detektion von durch die Dunkelfeld-Lichtquellen beleuchteten Oberflächendefekten mittels des Detektors, wobei die erste und die zweite Dunkelfeld-Lichtquelle fast paralleles und gerichtetes Licht in einem Winkel deutlich flacher als der Reflexionswinkel auf den Detektionsbereich ausstrahlen.

The method according to the invention for detecting surface defects of a surface comprises the steps:

• Providing at least a portion of the surface in a detection area;
• Providing a first dark field light source which is directed toward the detection area in a first direction;
• Providing a second dark field light source which is directed in a second direction onto the detection area;
• Providing a detector directed to the detection area;
• Illuminating the surface in the detection area with the two dark field light sources; and
• Detecting surface defects illuminated by the dark field light sources by means of the detector, wherein the first and second dark field light sources emit nearly parallel and directed light at an angle significantly shallower than the reflection angle to the detection area.

As a dark field light source is understood here a light source, which emits almost parallel and directional light. The light source may have a plurality of parallel LEDs, lasers or other bulbs. To better parallelize the emitted light, the light source may have additional optics, such as one or more collimators. In addition, the dark-field light source is arranged very close to the detection area or the surface to be tested, so that the emitted light impinges on the detection area or the surface to be tested at a very shallow angle. With a trouble-free surface then no light gets to the detector. Only light scattered by a surface defect reaches the detector.

The dark field light sources are arranged in two differently aligned directions. For example, the two dark field light sources can be arranged at an angle of 90 ° to each other. To achieve a larger illumination range, two dark field light sources may be arranged opposite one another, so that the almost parallel emitted light of these two dark field light sources in one direction. Overall, therefore, four dark-field light sources may be present in this example. One may then designate two opposite dark field light sources as the first dark field light source and the other two opposite dark field light sources as the second dark field light source.

The detector used is, for example, an optical camera. The term detector here comprises an area detector, a line detector and a point detector. In general, any detector can be used which has a detection range or spectral range which is suitable for detecting the radiation emitted by the dark-field light sources or the radiation reflected by the surface. It is possible to use a plurality of detectors, which are tuned, for example, in each case to different spectral ranges of the two dark field light sources. As a detector, the human eye or a human observer can be considered.

The illumination by the two dark field light sources can take place simultaneously or with a time offset.

The surface must be smooth in principle, but may consist of all materials which are suitable to reflect light of the dark field light source. For example, surfaces of films, microfilm, microplan films, polished diamonds, foils, skis, sliding surfaces, and so on may be analyzed for surface defects according to the method proposed herein. The term surface defects is not limited to defects on the surface that have no extension in depth. Rather, the term surface defects includes all defects that have a share of the surface. Accordingly, defects which completely penetrate the surface beneath the surface are also referred to herein as surface defects.

The method according to the invention has the advantage that surface defects can be detected quickly and reliably by the two differently aligned dark-field light sources. The different illumination of the surface defects increases the information provided and improves the detection rate. For film material, a reliable, fully automated detection is provided for the first time. All surface defects common to a film, such as longitudinal scratches due to film transport, transversal splices and soiling such as dust, can be detected. Due to the geometry of the structure, the different types of surface defects can be categorized. Thus, for example, the longitudinal scratches are illuminated by one of the two dark field light sources, the splices by the other of the two dark field light sources and contamination by both dark field light sources. By means of suitable evaluations such as color coding of the light sources or time-shifted illuminations and images, the surface defects or defects can be categorized during the recording, regardless of their form. As a result, an additional information level is created, which can significantly simplify a subsequent evaluation and / or correction of the errors.

It can be provided that the dark-field light sources are oriented in preferred directions in which surface defects in the surface preferably occur. Respectively preferred directions of the detection area are aligned or predetermined, by means of which then the surface to be examined are aligned. This ensures that the surface defects or defects are optimally illuminated.

It can be provided that, during lighting and / or detection, a relative movement takes place between the surface and the detection area, the dark field light sources being operated in a pulse mode. During the relative movement, the surface and / or the detection area is moved. For example, a film may be moved through the detection area. This allows a much faster analysis. The dark field light sources are operated in a pulse mode, for example like a flash. This provides a good image quality with simultaneous fast passage of the film or the surface available. The two dark field light sources can be activated simultaneously or in a very short time interval from each other. In the case of staggered images, the images can be shifted for later processing of the detection so that the images of both dark field light sources comprise the identical section in the surface or the film material.

It may further be provided that the dark field light sources emit in different spectral ranges. This has the advantage that, with simultaneous activation of the dark field light sources, the surface defects illuminated by the respective dark field light source are assigned to a fixed spectral range. Thus, the detector, for example an optical camera or a human observer, can select or select the surface defects on the basis of the spectral range, for example of a color. Preferably, the spectral ranges are distant from each other, such as the two colors blue and red. In this way, overlaps of the spectral regions are avoided, which increases the accuracy and reliability of the detection. The choice of spectral ranges is not limited to the visible wavelengths. For example, range in the IR and UV spectrum can be used for the two darkfield light sources.

It can further be provided that a light source with respect to the detector is arranged on the other side of the surface, the light source radiating in a further spectral range. With this arrangement in the form of a transparency unit perforations or holes in the surface can be detected by the then translucent light. This light source is not a darkfield light source but is normal to the surface. The spectral range is preferably different from the spectral ranges of the dark field light sources, so that it is possible to deduce the type of defect even from the light color.

It can be provided that the surface defects are categorized on the basis of the spectral ranges and / or combinations of the spectral ranges. This allows a sort of physical pre-sorting of the surface defects before the actual processing, for example by means of a software for image recognition. In this way, the computational effort and processing time can be significantly reduced. For example, if one dark field light source emits red and the other dark field light source emits blue, the surface defects mainly perpendicular to the respective light are marked in one of these colors. In the case of punctiform or flat disturbances, such as elevations due to contamination or depressions such as holes, color can be seen combined. In the case of a transmitted-light unit, there is another color available for even better detection and marking of very small holes.

It can further be provided that based on the number, the area and / or the amount of light of the detected surface defects a quality measure of the surface is created. With such a quality measure can be made a reliable and very fast to make statement regarding the quality of the surface. This can be used in the quality inspection of materials such as a film or to prepare for a restoration of a film. Due to the two differently aligned darkfield light sources, in addition to the pure number of surface defects, it is also possible to specify categories of surface defects. For example, in a film this may be scratches in the longitudinal direction, splices in the transverse direction and soiling such as dust.

It can further be provided that an image is taken of the surface in the detection area and that the detected surface defects are corrected taking into account the surrounding image material. This is particularly suitable for archiving or digitizing film material. Now, with algorithms for error correction or image processing, the detected surface defects can be corrected automatically or even in real time. After the correction of the surface defects, the digital storage of the film material takes place. This method works very reliable and fast. The detection and correction can be much faster than the normal playback speed of the film.

The device according to the invention for detecting surface defects of a surface comprises a detection region in which at least a part of the surface can be arranged, a first dark-field light source which is directed in a first direction onto the detection region, and a detector directed onto the detection region. A second dark field light source is provided, which is directed in a second direction onto the detection area. The first and second dark field light sources radiate nearly parallel and directed light at an angle much shallower than the reflection angle to the detection area. The same advantages and modifications apply as described above. The device may also comprise a plurality of units in the form of the described detection area with dark field light sources and detector. It can be provided that a unit is provided on both sides of the surface, such as a film or a film. For example, with larger surfaces, several of these units may be arranged side by side. So a kind of line scanner can be realized. Likewise, a matrix arrangement of several units is possible.

It can be provided that the dark field light sources are arranged perpendicular to one another. This arrangement provides a large ninety degree angular separation between the two directions of light, which improves the detection and differentiability of surface defects. In the case of films, for example, typical scratches in the longitudinal direction and splices in the transverse direction can be optimally illuminated, which leads to a high degree of reflection and thus to recognizability.

Further preferred embodiments of the invention will become apparent from the remaining, mentioned in the dependent claims characteristics.

The various embodiments of the invention mentioned in this application are, unless otherwise stated in the individual case, advantageously combinable with each other.

• 1 eine perspektivische Darstellung einer Vorrichtung zur Detektion von Oberflächendefekten einer Oberfläche; und
• 2 eine perspektivische Darstellung einer weiteren Vorrichtung zur Detektion von Oberflächendefekten einer Oberfläche.

The invention will be explained below in embodiments with reference to the accompanying drawings. Show it:

• 1 a perspective view of an apparatus for detecting surface defects of a surface; and
• 2 a perspective view of another device for detecting surface defects of a surface.

1 shows a spatial representation of the device 10 for the detection of surface defects. Here is a material in the form of a film 12 reviewed or analyzed. The film 12 has a surface 14 and becomes along a transport direction T through a detection area 16 the device 10 emotional. The detection area 16 can be structurally defined, for example, by a diaphragm or aperture. On the other hand, the detection area 16 be defined by optical properties such as illumination or detection range. Finally, the detection area 16 also be defined by an image processing software.

Next to the detection area 16 is a first darkfield light source 18 arranged. It is at a 90 ° angle to the transport direction T aligned. Here, for the sake of simplicity, there is a single first dark field light source 18 shown. To improve the illumination, another darkfield light source can be found at the opposite end of the detection area 16 be arranged. The first darkfield light source 18 emits almost parallel light or light rays 20 out which the surface 14 transverse to the transport direction T in the detection area 16 spotlighting.

A second darkfield light source 22 is in the direction of the transport direction T arranged and aligned. Again, for simplicity, only a second dark field light source 22 shown; a second opposite dark field light source may also be provided. The second darkfield light source 22 emits almost parallel light or light rays 24 out which the surface 14 long to the transport direction T in the detection area 16 spotlighting.

A detector 26 for example in the form of a digital camera is above the detection area 26 and thus normal to the surface 14 arranged. The arrangement and / or optics of the detector 26 is formed such that the detection area 16 is completely recorded. Depending on the application, the detection range 16 to the surface to be examined 14 be adjusted. In the analysis of film material, the detection range 16 for example, be adapted to a picture of the footage.

Both darkfield light sources 18 . 22 or their optics and / or lighting means are arranged such that the light beams 20 . 26 at a very shallow angle to the surface 14 or the detection area 16 incident. The angle is much flatter than the angle of reflection. This causes the light rays 20 and 26 with a flawless surface 14 completely from the detector 26 Way to be reflected. Therefore, a captured image provides no information or is black.

The device 10 can work in a continuous mode and in a start-stop mode. In the continuous mode, the surface becomes 14 of the film 12 continuously that means without a break through the detection area 16 guided. The two darkfield light sources 18 and 22 and optionally also the detector 26 are synchronized with the speed of film transport. This ensures that every single image of the film 12 through the two darkfield light sources 18 and 22 lit and from the detector 26 is recorded. The two darkfield light sources 18 and 22 can be operated in a flash mode, increasing the transport speed of the film 12 can be significantly increased. This allows a very fast analysis of the surface 14 of the film 12 , In the start-stop mode, the surface becomes 14 always a section, the detection area 16 corresponds, moves further. This new section is then illuminated and detected again, resulting in quasi-continuous processing. The details of illumination of surface defects by the dark field light sources 18 and 22 is described below.

Two types of lighting through the two darkfield light sources 18 and 20 are possible. The two darkfield light sources 18 and 20 can be operated offset in time, with two images of the detection area 16 or the surface arranged there 14 arise. In the continuous transport mode compensation of the resulting image offset is then required. This compensation can be performed by a software routine.

On the other hand, the two dark field light sources 18 and 20 be activated at the same time so that the light rays 20 and 24 at the same time the detection area 16 or the surface arranged therein 14 illuminate. To the To simplify identification and assignment of surface defects, the dark field light sources radiate 18 and 22 Light in different spectral ranges. In this example, the first darkfield light source works 18 in a blue spectral range and the second darkfield light source 22 in a red spectral range. These two spectral ranges are sufficiently separated in their wavelengths so that the detector 26 the differences can dissolve well. In the detection area 16 is a longitudinal surface defect 28 such as one in the transport of the film 12 resulting scratch shown. When illuminated by the first darkfield light source 18 meet their rays of light 20 on the longitudinal edge of the surface defect 28 on, causing stray light in the direction of the detector 26 is reflected. The rays of light 24 the second darkfield light source 22 however, they are parallel to the longitudinal surface defect 28 so that there is little or no scattered light from the light rays 24 the second darkfield light source 22 in the direction of the detector 26 be reflected. Thus, the longitudinal surface defect appears 28 in one of the detector 26 taken picture in the color blue.

In the detection area 16 is also a transverse surface defect 30 such as a splice of the film 12 shown. When illuminated by the second darkfield light source 22 meet their rays of light 24 on the transverse edge of the surface defect 30 on, causing stray light in the direction of the detector 26 is reflected. The rays of light 20 the first dark field light source 18 however, they are parallel to the transverse surface defect 30 so that there is little or no scattered light from the light rays 20 the first dark field light source 18 in the direction of the detector 26 be reflected. Thus, the transverse surface defect appears 30 in one of the detector 26 taken picture in the color red.

In the detection area 16 is still a surface-shaped surface defect 32 such as a pollution caused by dust. When illuminated by the first darkfield light source 18 meet their rays of light 20 on longitudinal edges of the surface defect 32 on, causing stray light in the direction of the detector 26 is reflected. The rays of light 24 the second darkfield light source 22 meet on transverse edges of the surface defect 32 on, causing stray light in the direction of the detector 26 is reflected. Because of this surface defect 32 Edges, elevations or depressions transverse to the light propagation of both dark field light sources 18 and 22 has, stray light from both darkfield light sources 18 and 22 to the detector 26 reflected. Thus, the surface-shaped surface defect appears 32 in one of the detector 26 taken picture in both the color blue and in the color red.

This allows a classification of the surface defects 28 . 30 and 32 already based solely on the color of the surface defects in that of the detector 26 taken picture. This allows for fast typing of surface defects, for example, to create a measure of goodness or to facilitate subsequent correction of surface defects, for example by presorting.

In 2 is an extension of the device 10 shown. The device has as well as in 1 represented over the detection area 16 , the two darkfield light sources 18 and 22 as well as the detector 26 to surface defects in the surface 14 of the film 12 to recognize.

In addition, the device has 10 here about another light source 34 that are below the detection area 16 or the movie 12 is arranged. The light source 34 is thus opposite to the detector 26 arranged. The light rays of the light source, not shown here for reasons of clarity 34 are in the direction of the detector 26 directed. The light source 34 is formed or arranged such that it the detection area 16 illuminates.

This light source 34 serves to check the light transmission of the surface 14 or the movie 12 , For typical perforations 36 who are watching movies 12 On the long sides for film transport are present, the film 12 rayed. This is done by the detector 26 detected. Likewise, surface defects become 38 illuminated in the form of holes. The through the perforations 36 and surface defects 38 passing light beams are from the detector 26 detected or recorded. Depending on the color of the emitted light of the light source 34 These surface defects can also be typified in the form of perforations. For example, the light source 34 Emit light in a spectral range corresponding to the color green. Then appear on one of the detector 26 captured image of these surface defects in the color green.

The surface defects 32 and 38 can also through the two dark field light sources 18 and 22 be detected. However, it may be advantageous to use the additional light source 34 to use these surface defects 32 and 38 even better visible. In particular, very small holes or perforations can be better recognized.

Ideally, each of the light sources points 18 . 22 and 34 a different spectral range whose wavelengths are still spaced apart. Then, with a simple optical camera, all types of surface defects in a picture can be made distinguishable.

In summary, it should be noted that with the method described here or the device for the detection of surface defects 28 . 30 . 32 and 38 These can be reliably and quickly detected. In addition, by a color coding of the types of surface defects 28 . 30 . 32 and 38 a physical presorting of the defects possible, which allows statistical analysis and facilitates subsequent correction of the surface.

LIST OF REFERENCE NUMBERS

10

device

12

Movie

14

surface

16

detection range

18

first darkfield light source

20

light rays

22

second darkfield light source

24

light rays

26

detector

28

surface defect

30

surface defect

32

surface defect

34

light source

36

perforation

38

hole

T

transport direction

Claims (10)

A method of detecting surface defects (28, 30, 32, 38) of a surface (14) comprising the steps of: - providing at least a portion of the surface (14) in a detection region (16); - providing a first dark field light source (18) directed in a first direction to the detection area (16); - providing a second dark field light source (22) directed in a second direction onto the detection area (16); - providing a detector (26) directed towards the detection area (16); - illuminating the surface (14) in the detection area (16) with the two dark field light sources (18, 22); and - detecting surface defects (28, 30, 32, 38) illuminated by the dark field light sources (18, 22) by means of the detector (26); characterized in that the first and the second dark field light source (18, 22) radiate approximately parallel and directed light at an angle significantly shallower than the reflection angle to the detection area. Method according to Claim 1 , characterized in that the dark field light sources (18, 22) are aligned in preferred directions in which surface defects (28, 30, 32, 38) in the surface (14) preferably occur. Method according to Claim 1 or 2 , characterized in that during the lighting and / or the detection, a relative movement between the surface (14) and the detection area (16) takes place, wherein the dark field light sources (18, 22) are operated in a pulse mode. Method according to one of the preceding claims, characterized in that the dark-field light sources (18, 22) emit in different spectral ranges. Method according to Claim 4 , characterized in that a light source with respect to the detector is arranged on the other side of the surface (14), the light source (34) radiating in a further spectral range. Method according to Claim 4 or 5 , characterized in that the surface defects (28, 30, 32, 38) are categorized on the basis of the spectral ranges and / or combinations of the spectral ranges. Method according to one of the preceding claims, characterized in that based on the number, the area and / or the amount of light of the detected surface defects (28, 30, 32, 38) a quality measure of the surface (14) is created. Method according to one of the preceding claims, characterized in that an image is taken of the surface (14) in the detection area (16) and that the detected surface defects (28, 30, 32, 38) are corrected taking into account the surrounding image material. Device for detecting surface defects (28, 30, 32, 38) of a surface (14) comprising a detection region (16) in which at least a part of the surface (14) can be arranged, a first dark field light source (18) directed in a first direction to the detection area (16), a second dark field light source (22) directed in a second direction to the detection area (16) and one on the detection area (16) directed detector (26), characterized in that the first and the second dark field light source (18, 22) radiate approximately parallel and directed light at an angle significantly shallower than the reflection angle to the detection area. Device after Claim 9 , characterized in that the dark field light sources (18, 22) are arranged perpendicular to each other.

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