Method and detection device for optically detecting a surface

Abstract

A method and a detection device (9) for optically detecting a surface (10) of an object (1) are described. Using the method, during an image recording sequence, a time periodic pattern (13) with different illumination patterns (130) is generated on the surface (10) by an illumination device (8) of the detection device (9), and in the image recording sequence, a plurality of images of the pattern (13) on the surface (10) is recorded by an image recording device (7) of the detection device (9), wherein the generation of one of the different illumination patterns (130) is respectively synchronized with the image recording of one of the images of the pattern (13), the phase of the pattern (13) is determined from a sequence of the recorded illumination patterns (130) in at least one image point, and defects (4, 5) of the surface (10) are detected from deviations between the recorded illumination patterns (130) and the generated known illumination patterns (130). The illumination device (8) and the recording device (7) of the images are arranged at a reflection angle (α), wherein the object (1) is moved relative to the detection device (9), and the duration of the image recording sequence is selected such that the sequence reflection area (17) can be regarded as constant (Fig. 4b).

Description

TECHNICAL FIELD

[0001] The present invention relates to a method and a detection device for the optical detection of a surface of an object, as well as to the use of the method and the detection device. When using the method, during an image recording sequence, a time periodicity of patterns with different illumination patterns is generated on the surface by an illumination device of the detection device. During the image recording sequence, a plurality of images of the pattern of the surface is recorded by an image recording device of the detection device. BACKGROUND

[0002] In this process, the generation of one of the different illumination patterns is synchronized with the image recording of one of the images of the pattern, respectively, so that each image from the image recording sequence is recorded with a known illumination pattern of the different illumination patterns, respectively; in other words, this means that in each camera image only one illumination pattern is visible. By synchronizing the image recording and the pattern generation, in particular, it is achieved that the illumination pattern does not change during the exposure time of the image recording. From the sequence of the recorded known illumination patterns, the phase of the pattern is determined in at least one image point. Since the pattern / patterns of the different illumination patterns are known, the image point can be associated with a point of the known pattern. From the deviation between the recorded illumination pattern in at least one image and the generated known illumination pattern, defects of the surface are detected. Defects on the surface lead to a distortion of the known pattern / one of the known illumination patterns recorded in one image. This makes it possible to identify and output the defects by image evaluation, which is basically known to the skilled person, using suitable algorithms, for example by a suitable computing unit. By scanning a plurality of surface regions one after the other, i.e. by repeated application at different regions of the surface, the entire surface or selected parts of the surface can be detected.

[0003] One of the most important tasks in the surface detection process is the detection and classification of defects, since the topography of these defects can lead to a deflection of light. These defects are often not perceived at all by the naked eye as topographical defects, but only as changes in surface brightness or subtle differences. Usually, it is necessary or at least advantageous to carry out the detection during movement. According to the invention, particularly preferred applications of such surfaces will be described at a later stage.

[0004] In principle, the method according to the invention is suitable for the optical detection of reflective surfaces. According to the invention, reflective surfaces include ideal reflective, i.e. mirror, surfaces as well as surfaces which exhibit a certain scattering effect in addition to the reflective properties. The criterion here is that the surface illuminated with the pattern, also including the pattern projected onto the surface, is optically recordable in the image.

[0005] For a long time, the method used for detecting surfaces has been deflection measurement. This comprises recording an image of the reflection of a known pattern on a surface with a camera and evaluating it in a computer. Defects in the surface lead to distortions of the pattern on the surface, which can be detected. If the recording geometry and the pattern geometry are known, this can also be used to determine the 3D topography of the surface. The skilled person knows various methods of how to do this. These are known as such and are not described in detail with regard to the present invention.

[0006] The basic principle of deflection measurement is that the deflection of a light ray incident on a surface is determined by identifying a point in the pattern, onto which the visible ray emanating from the camera (recording device) and reflected on the surface is incident. In other words, the deflection of the visible ray on the surface is determined by the reflection, which depends on the direction of the surface normal in the respective point (reflection point), which is the straight line perpendicular to the surface in the reflection point. From the normal field thus determined, the topography of the surface can be determined by, for example, integration.

[0007] A method often used for locating points is the so-called phase shift method, in which a periodic pattern is used and it is determined in which phase position of the pattern the point to be determined lies.

[0008] In principle, a distinction must be made here between methods for which one image of the pattern is sufficient or for which multiple images are required.

[0009] The advantage of methods for which one image is sufficient is that these methods can also be used for moving surfaces, so they are initially more suitable for, for example, web-like products or detection in production processes. However, their disadvantage is that they are more susceptible to defects or require a second physical pattern to be present in the beam path. For example, WO 98 / 17971 A1 discloses how a minimum beam deviation can be detected and determined. In essence, a stripe pattern is observed here by a camera. For the described method, a single image is sufficient, since the pixel grid of the camera is used as a second pattern. However, the disadvantage here is that both the camera and the pattern need to be very precisely adjusted. In an industrial environment, for example in a production process, this is very difficult to achieve or is only achieved at unreasonable cost.

[0010] The method using multiple image operations is more robust to defects and does not require time-consuming adjustments. The pattern is displayed and recorded successively in several phase positions offset relative to each other. If a fringe pattern with a sinusoidal brightness curve is used, particularly simple evaluation results are obtained, which are recorded four times each, offset by a quarter of the period length. But other patterns and sequences of patterns are possible as well. From the sequence of gray values in each pixel, the phase position in the pattern is derived. This method is comprehensively described in relevant textbooks and articles (e.g. Gorthi and Rastogi, Fringe Projection Techniques: Whither we are?, Proc. Optics and Lasers in Engineering, 48(2): 133-140, 2010). The disadvantage, however, is the need for multiple images from the same location on the surface. In the detection of film and other web products in a production process, or in principle in the detection of surfaces that move relative to the detection device, it is not possible in practice to take multiple images from the same location on the surface, since the surface is continuously moving. For example, a path that runs at high speed in a production process cannot be stopped. This problem can be solved by using a detection device that moves in synchronism with the path. Such a solution is admittedly technically complex and therefore costly and requires a great deal of space, which is often not available, particularly in a production environment.

[0011] EP 2 390 656 B1 discloses a method in which a running path surface is observed, preferably using an inline camera. The illumination comprises a fast switchable pattern illumination, preferably LED illumination, which is laterally connected to the path. This illumination consists of individually controllable LEDs or LED modules, with which different illumination patterns can be quickly and dynamically generated. The switching and the image recording are synchronized, so that images with different illumination patterns can be recorded from the surface quickly and successively. In particular, the scanning and switching speed is so fast that the distance between the images recorded in the feed direction is much smaller than the range of the pixels in the feed direction. Thus, the images can be recorded at almost the same location. However, recording at exactly the same location is not possible. SUMMARY

[0012] It is an object of the present application to propose a reliable alternative for the detection of moving surfaces, which can in particular be implemented in a simple manner in an industrial environment, such as a production process.

[0013] According to the application, this object is achieved by the method according to claim 1 and the detection device according to claim 12.

[0014] According to the method described at the outset, the illumination device and the image recording device are arranged in a reflection angle (with respect to the surface normal aligned perpendicularly on the surface in the reflection region, respectively). "Within the reflection angle" means that the edge rays of the imaging point, i.e. the visible rays emanating from the imaging point edge, are reflected in the reflection point on the surface and mark the visible area of the illumination pattern (pattern area) in the imaging point. In other words, the illumination pattern of the pattern is reflected on the surface exactly mapped in the image point of the image recording device. The camera (as recording device) thus precisely observes the pattern (i.e. the illumination device, which can be designed as an illumination line, for example).

[0015] For moving objects, the reflection angle does not change as long as the shape of the surface and its arrangement relative to the stationary detection device remain unchanged. This applies to flat or slightly curved surfaces if the average curvature is constant and the direction of the surface normal of the surface (at least with respect to the direction of the visible rays) only changes negligibly. This can be the case, for example, with a wavy surface structure, in which the direction of the surface normal changes only slightly. Small means that the change is only large enough for the pattern area to remain visible at the image point. The pattern area must therefore be correspondingly wide in the feed direction. As soon as this is no longer possible, the method according to the application cannot be applied to the stationary detection device. However, in this case, the method according to the application proposed, the detection device can be moved on the curved surface in the reflection device, respectively.

[0016] Since the periodicity of the change in the direction of the surface normal is known, the normal mechanical tracking of the detection device can follow the reflection condition or the reflection angle lies within the recording area using flat illumination and recording devices, and the image point is selected according to the periodically occurring reflection angle, this method can also be used for curved surfaces.

[0017] As long as the detection device can unambiguously detect the change in the pattern, this method can be used independently to determine the topology of the defect.

[0018] For example, in order to be able to detect larger surface areas or to allow continuous detection in the production process, according to the application, the object is moved during the detection of the surface relative to the detection device, preferably in a defined / strictly controlled direction of movement, so that the surface of the object is moved.

[0019] For the phase shift method described at the beginning, it is essential that the images belonging to the image sequence always record the same location of the surface. Since here a moving surface is detected, for example a material path which moves relative to the recording device, this is not possible. However, in order to be able to use the method and to detect the phase of the pattern, the duration of the image recording sequence is chosen to be so short that the sequence reflection area can be regarded as constant. The sequence reflection area is defined as the total surface area which is covered / recorded by the reflection area in the individual images of the image recording sequence. Expressed in simplified terms, the images of the image recording sequence are recorded one after the other at such a speed that the travel from the first image to the last image of the image recording sequence is so small that the surface area (reflection area) captured can still be regarded as virtually the same location of the surface.

[0020] The surface area which is completely covered by the reflection area in the individual images from the image recording sequence is produced by the combination of all reflection areas of all individual images recorded during the image recording sequence in a common area, which is referred to as the sequence reflection area. This surface area can be regarded as at least approximately constant if the reflection areas of all images from the image recording overlap by at least 40% or more, preferably at least 60%. However, these values are not to be understood as fixed values, but rather as typical guide values which the skilled person can adjust (possibly experimentally) to the respective conditions. In principle, these methods can work as long as the optical conditions show a pattern on the image point which has a period length which is significantly smaller than one period length. Of particular importance is the concave curvature of the surface, which maps large pattern areas onto the image point due to the concave mirror effect. For fault detection, an overlap area of 40% to 70% should be sufficient, and an estimate of the surface normal, i.e. an estimate of the surface topology, is an overlap area of 60% to 80%. Depending on the shape of the surface and the type of defect which occurs, other areas can also occur, which the skilled person can determine and / or predefine when setting up the corresponding detection device according to the teaching of the present application (possibly with the aid of empirical measurements). That is to say, according to the present application, it is proposed to choose the duration of the image recording sequence in such a way that the images recorded in the image recording sequence are recorded quickly one after the other in chronological order, and the path of displacement of the surface due to the movement of the object from the first image to the last image of the image recording sequence is so small that the reflection areas of the first image and the last image can be regarded as one and the same area on the surface. The smaller the measurement error compared to a measurement with a stationary object, the better the above-mentioned condition is met.

[0021] The reflection area of the surface captured in an imaging point (defined by a camera pixel or possibly by a combination of multiple camera pixels at a minimum resolution) is predefined by the recording geometry (distance, recording angle) and the recording optics. Due to the reflection angle of the arrangement of the recording device and the illumination device relative to the surface normal, a change in the angle of one of the two devices must also be reproduced in the other device, respectively. This makes a change in the reflection angle relatively complex. The same applies to a change in the recording optics, respectively. According to the application, the size of the reflection area and / or of the pattern area mapped in the reflection area can be changed or adjusted in a relatively simple manner by the distance of the recording device and / or the illumination device. This does, admittedly, also require a change in the structure of the detection device.

[0022] When the method according to the application is carried out, influencing the other parameters according to the application is easier. Suitable parameters when carrying out the method will now be described. In order to adjust the duration of the image recording sequence according to the predetermined speed and direction of movement of the object, so that the sequence reflection area can be regarded as constant, according to a preferred embodiment of the application, one or more of the measures listed below can be taken.

[0023] Thus, when the method according to an embodiment of the application is carried out, the size of the image point to be set can be specified. In the simplest case, the size of the image point can correspond to the pixel resolution of the camera (used as image recording device). This represents the highest resolution that can be achieved with a given distance of the camera and a given focal length of the camera. The higher the camera resolution, the smaller the reflection area associated with the image point on the surface, the smaller the defects that can be detected on the surface. One way of changing the size of the image point is to change the pixel resolution of the camera. The pixel resolution of a camera used for digital image recording according to the preferred application is predetermined by the optoelectronic chip used as recording sensor of the camera, on which a single pixel (sensor pixel) captures (integrates) the light incident on this pixel over the exposure time. By reducing the resolution, it is also possible to achieve the size of the image point by combining multiple sensor pixels of the camera to form one image point. One image point can also be referred to as one pixel. However, if multiple sensor pixels are combined to form one image pixel, the image pixel and the sensor pixel are different.

[0024] According to one embodiment, the size of the image point can be set by combining a plurality of pixels of the recording sensor (sensor pixels) of the recording device into one image pixel. In a variant, the number of pixels combined along the direction of movement of the object and transverse to the direction of movement of the object can be chosen in various ways according to the application. It can be meaningful to increase the size of the reflection area along the direction of movement of the object at the expense of the resolution in order to achieve a higher coverage of the reflection area of the individual images in one image recording sequence. This increases the sequence reflection area in the direction of movement of the object. The resolution transverse to this can be kept higher. The resolution transverse to the direction of movement of the object and its surface is determined only by the recording geometry, i.e. essentially by the size of the image point (limited by the size of the pixels of the recording sensor of the image recording device, taking into account the smallest possible range), the focal length of the lens and the viewing distance. The resolution transverse to the direction of movement is not affected by the movement.

[0025] The movement blur develops along the longitudinal direction of the movement. Since during the image recording all light rays in one image point (pixel of the image, not necessarily coinciding with a pixel of the recording sensor) are integrated together, which light rays have been incident on this image point during the exposure, the surface observed, which is mapped on one image point, is enlarged in the direction of movement. Relative to the moving surface (also referred to as the reflection area associated with the image point), it can be said that the length of the image point appears stretched. Here, "longitudinal" and "transverse" refer to the direction of movement, not necessarily to the row direction and column direction of the camera. At an oblique viewing angle, each pixel appears stretched obliquely in a manner corresponding to the row direction and column direction of the camera.

[0026] In a sequence of images recorded for a multi-image phase shift method (during the image recording sequence), all images in each image point (image pixel) should be mapped to the same location on the surface. However, when a plurality of images is recorded consecutively, these images move relative to the moving surface with respect to each other. Therefore, in order to compensate for this, measures are taken according to the application, which can result in the reflection areas of the different images still being able to be considered approximately as the same location on the surface. Changing the size of the image point in the above-described manner can contribute to this.

[0027] According to the application, further measures can include setting the duration of the image recording sequence during the execution of the method. The duration of the image recording sequence, i.e. the time required to record all images in one image recording sequence, determines - for a predetermined movement speed of the object / surface - the distance to which the surface area of the reflection area corresponding to the first image has moved until the last image is recorded. This results in the size of the sequence reflection area and the overlap of the reflection areas of the individual images to be set according to the application. Basically, the shorter the duration of the image recording sequence, the greater the overlap.

[0028] In addition to the limitations of the maximum scanning frequency of the recording sensor and the possible shortest exposure time of the recording device, the scanning frequency (defined as the frequency of the consecutive image recordings) and / or the exposure time can also be adjusted. The shorter the exposure time, the sharper the recorded images (reduced motion blur) and the faster the consecutive images can be recorded (scanning speed). The exposure time can be shortened by increasing the brightness of the pattern generated on the surface and / or opening the aperture of the recording optics. By increasing the brightness / enlarging the aperture opening (typically defined by the smaller number of apertures in the optics), the exposure time can be shortened. Therefore, it makes sense to use a high-brightness but adjustable light illumination device.

[0029] A suitable illumination device can consist of individual adjustable light LEDs, which can be individually adjusted to generate a pattern and together to adjust the overall light intensity. Basically, it is preferable to operate the illumination device at maximum light intensity and to reduce the exposure time until a properly exposed image is recorded.

[0030] Therefore, according to the present application, when adjusting the duration of an image recording sequence, at least one of the following variables can be adjusted: the exposure time of the images, the brightness of the pattern generated on the surface, the scanning frequency of the recording sensor and / or the number of images in each image recording sequence. All or several of the variables can also be adjusted.

[0031] Therefore, according to the present application, the duration of an image recording sequence can of course also be changed by changing the number of images in each image recording sequence, wherein the image recording sequence can be shortened by reducing the number of images and vice versa.

[0032] Furthermore, according to the present application, the measurement sensitivity can be influenced by choosing the illumination distance (while also choosing the sight distance between the recording device and the pattern) and the viewing angle. The further the distance, the flatter the viewing angle (i.e. flatter with respect to the surface; the steeper the angle perpendicular to the surface), the higher the sensitivity. Especially for partially reflective and partially diffusive reflective surfaces, it is preferred to choose a flatter viewing angle and illumination angle between (e.g. < 30°) and / or the maximum illumination distance. According to the present application, the maximum illumination distance can mean to utilize the available space to arrange the illumination device. The illumination distance (distance between the illumination device and the surface) can for example be chosen to be larger than the distance between the recording device and the surface, wherein typical values can be between 1 times and e.g. 10 times. The skilled person will choose values experimentally suitable for the respective application, wherein according to the basic teaching of the present application, in many cases, a smaller illumination angle and viewing angle and / or a larger illumination distance (between the recording device and the illumination device) will increase the sensitivity.

[0033] The purpose of recording a plurality of images is to determine the phase of the pattern in order to identify from it the position of the known illumination pattern in the recorded image points. This will allow the detection of surface defects by distortion of the surface pattern. According to one embodiment, for example, three images can be recorded. For example, the generated pattern can be made periodically asymmetrically, so that the phase of the pattern can be determined unambiguously from the three images. Alternatively, the pattern can also be periodically symmetric, and the recording of the images is asymmetric, for example, by changing the scanning / image recording frequency between different images in the same image recording sequence.

[0034] However, according to a preferred application of the present application, at least or exactly four images are scanned in the same image recording sequence. For example, the pattern itself can be a sinusoidal distribution of the intensity, which is recorded in four different phase positions with the same scanning sequence. Thereby, the phase of the pattern in each image can be determined accurately in a simple manner. For example, the phase shift between the phase positions in the image recording sequence of the successive images can be only 1 / 4 of the length of the pattern period. However, other phase shifts between the images of the image recording sequence are also possible.

[0035] According to another aspect of the present application, the illumination device can generate the illumination pattern in such a way that the visible area of the recorded illumination pattern in the image points of the recorded images can be considered constant during the respective image recording sequence.

[0036] The area of the visible illumination pattern (pattern area) in the image points can be considered constant during the image recording sequence as long as the pattern area remains visible in the image points and the intensity of the recorded pattern area does not change significantly. For example, this can be assumed if the recorded intensity does not change by more than 10%, preferably not more than 8%, particularly preferably not more than 4% during the image recording sequence, or another defined criterion is maintained. In principle, the above-mentioned criterion also applies here.

[0037] For this purpose, according to a preferred aspect of the present application, the length of the period of the pattern in the illumination pattern can be chosen so that the intensity change can be considered sufficiently constant depending on the topology of the surface in the direction of the pattern course, in other words, this means that the intensity change does not exceed a criterion which is suitable for the respective case. The selection of the criterion can be determined by the skilled person by experiment when setting up the system and the specific pattern.

[0038] The topology of the surface is determined, inter alia, by its curvature, which requires a change in the direction of the surface normal. The direction of the surface normal is related to the angle of reflection. By the topology of the surface to be examined with the method according to the application, it is possible to determine, by means of the resulting angle of reflection of a known arrangement of the detection device, which pattern region of the illumination pattern is mapped in the image point during the defined duration of the image recording sequence. By means of a predefined period length, the illumination pattern can be specified in such a way that the above-mentioned criteria are met. The method is thus flexible for the prescribed detection task.

[0039] According to a further aspect of the method according to the application, it can be provided that the periodic pattern is generated along the movement direction of the object, transversely to the movement direction of the object or alternately along and transversely to the movement direction of the object.

[0040] For a pattern along the movement direction of the object, for a surface to be detected which is curved, the aforementioned movement blur and the shift of the reflection zone will overlap with the shift of the pattern region observed by the image point, since the change in the angle of reflection is associated with a change in the intensity, since the intensity of the pattern changes in this direction.

[0041] For a pattern transversely to the movement direction, the reflection zone also changes. However, since the pattern along the shift direction of the object has the same intensity, the change in the angle of reflection does not necessarily result in a change in the intensity. As long as the image point captures the same pattern region and the pattern region captured by the image point does not shift transversely to the movement direction due to the curvature of the surface, the intensity measured in the image point remains unchanged.

[0042] According to the application, this difference can be taken into account during the adjustment of the period length of the pattern described above according to the alignment of the pattern along or transversely to the movement direction of the object. In particular, according to the application, the period length of the pattern can be particularly preferably different for the pattern along and transversely to the movement direction.

[0043] In addition, the known curvature of the surface of the object in the defined surface region to be detected can also be used according to the application to determine suitable criteria for distinguishing between non-defective and defective surfaces and / or to correct deviations caused by the known (expected) surface shape when evaluating the recorded images as part of the detection of defects.

[0044] Since the pattern is generated alternately along and transversely to the movement direction, different defects (in particular directional defects in the surface) can be detected more reliably and systematically.

[0045] In one embodiment of the method according to the application, the recording device can be focused so that the illumination pattern recorded in the image becomes blurred.

[0046] This can be achieved, for example, by focusing the recording device on the surface or another defined point instead of the pattern, through predefined specific aperture and focal length settings, and also by selectively selecting the focal length / depth of field according to the invention, so as to map the illumination pattern in the image, making it blurred, but with the surface in focus. The effect of doing so is to make a sharp brightness distribution appear diluted. Thus, for example, a sharp pattern simply composed of alternating, separable bright / dark areas can be mapped as an approximately sinusoidal brightness curve. In this case, a particularly simple illumination device can be used, without requiring additional optical elements to generate the desired brightness curve. Furthermore, when a shifted patterned area is mapped onto an image recorded in an image recording sequence, the brightness distribution becomes less sharp, which can particularly have a positive effect on curved surfaces and the effects associated with them.

[0047] In many cases, the surface to be detected is not an ideal reflector, but rather a semi-diffuse reflector. While the reflection is directional, its scattering solid angle is relatively large, meaning the bidirectional reflection distribution function (BRDF) has a scattering lobe of moderate width. As long as the scattering lobe remains narrow enough that the camera image can sufficiently modulate the mirrored pattern, and even on a non-ideal reflective surface, it can work on a reflective basis, which also results in a washout of the pattern's brightness distribution in the image. This property of the surface can also be used to achieve effects similar to those achieved by the described camera defocus setup on the pattern. However, this (additional) effect must be considered during the defocus setup, as the partial blur (which is desired in this case) is in any case generated by the surface itself.

[0048] On the other hand, the surface must be sufficiently mirror-like to allow the pattern to be fully observed. Therefore, for surfaces with relatively few reflections, it is advantageous to choose the flattest possible viewing angle and illumination angle, as well as to increase the illumination distance.

[0049] It may be particularly advantageous to determine the three-dimensional topography of an object's surface during surface inspection via a deflection measurement process according to the invention. The 3D topography of the surface can also be determined if the recorded geometry and pattern geometry are known, as in the method proposed according to the invention. Many options are known regarding how to do this. In the deflection measurement method, the deflection of light incident on the surface can be determined because points in the pattern are identified, and visible rays emitted by the camera (recording device) and projected (reflected) onto the surface are incident on said points. Therefore, the deflection of the visible rays can be determined, depending on the surface normal at the corresponding point. The topography of the surface can be determined from the resulting surface normal field, for example, by integration.

[0050] It is particularly preferred to use the method described above or parts thereof and / or the detection apparatus described below to detect net-shaped products, for example during the production process or after their manufacture, or to detect surfaces, in particular treated, curved or flat surfaces.

[0051] An important specific example is the detection of FCCL films during or after production. FCCL films (flexible copper clad laminate) are the core material for the manufacture of flexible printed circuit boards. FCCL films are usually about 100-150 pm thick and comprise, for example, a polyamide core (usually a plastic film) which is laminated on one or both sides with a copper film. During the lamination process, creases can occur which will be detected by the method according to the application. During surface detection, it can also be necessary to detect lamination defects, in particular so-called lamination creases 4 (as shown in Figure 1) or internal creases 5 (as shown in Figure 2). With lamination creases, the material forms a slight fold which is flattened again during lamination. Internal creases are formed from folds in the internal plastic film which are laminated together.

[0052] Both defects are difficult to detect with the naked eye because the film is so thin that the surface is not affected by the creases to a great extent. Only when observing the direct reflection of the observation light on the surface of the film can the defects be detected. This is due to the semi-diffuse reflection of the copper film. For other laminated films, the appearance is important and is adversely affected by such defects, although the features of the topography are small.

[0053] When detecting curved surfaces, for example painted containers or vehicle bodies, the detection apparatus is programmed by means of the corresponding processing device and guided through the curved surface according to the preferred embodiment, so that the illumination device and the recording device are kept at a reflection angle to the surface. In this case, the detection apparatus is moved relative to the mostly stationary object. This results in a relative movement of the object / object surface relative to the detection apparatus. In the present description, when talking about a moving object relative to the detection apparatus, this also means this relative movement. It is most important to find defects in the topography of the curved surface which have the smallest flatness in this way, which can have an adverse effect on the appearance or function of the surface. It is also often helpful to measure such defects in three dimensions, i.e. to determine the 3D topology of the surface and the defects.

[0054] The present application also relates to a detection device for the optical detection of a surface of an object and its use in the above-mentioned applications. The detection device comprises an illumination device and a recording device, which are aligned to each other such that the visible light emitted from the recording device is incident on the illumination device as reflected visible light at the surface when halving the angle between the output visible light and the reflected visible light with the surface normal in the point of incidence of the visible light perpendicular to the surface. In other words, the recording device and the illumination device of the detection device are arranged at a reflection angle with respect to the surface. The illumination device is designed to generate a temporal periodicity of patterns with different illumination patterns during an image recording sequence, while the recording device is designed to record images of the pattern reflected on the surface in synchronization with the generation of the illumination patterns during the image recording sequence. The detection device further comprises a computing unit for controlling the detection device and evaluating the recorded images, wherein the processor of the computing unit is designed to execute the above-mentioned method or parts thereof.

[0055] According to a preferred embodiment of the detection device according to the present application, the illumination device comprises individually controllable light elements arranged in a row or matrix. Furthermore, preferably, the recording device can comprise a recording sensor for recording an image mapped on the recording sensor by recording optics, wherein the recording sensor comprises individual sensor pixels (camera pixels) arranged in a row or matrix.

[0056] For example, the illumination device can be designed as an illumination line, which is preferably arranged transversely or along the feed direction (direction of movement of the object / surface relative to the detection device). The illumination line consisting of individually controllable illumination elements arranged in a line can consist of a plurality of LEDs or LED modules arranged side by side, which can be individually switched in synchronization with the image recording. The illumination device serves to quickly and continuously generate the periodicity of patterns required for the phase shift process. For example, the recording device can also be designed as a line camera, which can also be assembled from a plurality of line camera modules arranged side by side as required. In this arrangement, the composite image field of the line camera is a line (so-called scan line) on the surface. This scan line can be aligned transversely to the direction of relative movement of the surface and, in the direction of movement, has a very small width compared to its length (lateral extension), which depends on the pixel resolution of the line camera.

[0057] The illumination line can be very long (transversely to the direction of movement) to cover the entire width of the path (or the required detection area on the surface) to be detected at the reflection angle. When the camera and the illumination are arranged at the same distance from the surface, the illumination line on each side must be longer than the scan line on the surface observed by all cameras by about half the width of the scan line of a single line camera, for other distances the illumination line must be longer or shorter (as the case can be).

[0058] The width of the illumination line (in the direction of movement) can determine a maximum surface angle which can still be measured using the device. If the surface angle is greater than the maximum surface angle, the visible rays of the camera reflected by the surface no longer fall on the illumination and the camera cannot see anything either.

[0059] The method is also suitable for use with an area scan camera (matrix arrangement). The scan line then becomes an image field, since the width in the direction of movement becomes greater. The width of the illumination line in the direction of movement can also be increased accordingly. In a variant, an illumination matrix can be used instead of an illumination line. This consists of a number of individual LEDs or LED modules which are arranged in several seamlessly connected illumination lines which can all be switched independently of one another in synchronism with the image recording. Thus, by switching several illumination lines in the same way, the width of the illumination line can easily be changed.

[0060] The illumination matrix can not only be used to switch the pattern transversely to the path direction, but also to switch the pattern in the path direction. This has the advantage that the deflection measurement process mainly measures the surface angle / surface normal, i.e. the direction of the periodic pattern. Thus, when using an illumination line, only the angle transversely to the direction of movement can be measured, whereas using an illumination matrix makes it possible to measure in all directions, preferably in both the direction of movement and transversely to the direction of movement. BRIEF DESCRIPTION OF DRAWINGS

[0061] In the drawings:

[0062] Fig. 1 shows a schematic sectional view of an object with a surface to be detected, the surface having a first typical defect;

[0063] Fig. 2 shows a schematic sectional view of an object with a surface to be detected according to Fig. 1, the surface having a second typical defect;

[0064] Fig. 3a shows a top view of a detection device for detecting a flat surface according to an embodiment of the application;

[0065] Fig. 3b shows a side view of the detection device according to Fig. 3a. DETAILED DESCRIPTION

[0066] The object 1 shown in Figs. 1 and 2 is an FCCL film which is used as a raw material for printed circuit boards, the surface 10 of which is to be detected by the detection device according to the application. It is a laminated film 1 consisting of three layers, a plastic film 3 in the middle as an intermediate layer, and a copper film 2 as an outer layer laminated on the intermediate layer. It is usually detected whether the surface 10 of the object 1 has surface defects.

[0067] This surface detection can also be used to detect lamination defects, in particular so-called lamination wrinkles 4 (Fig. 1) and internal wrinkles 5 (Fig. 2). With a lamination wrinkle 4, the material forms a slight wrinkle, which is flattened again during lamination. An internal wrinkle 5 is caused by wrinkles already formed in the inner plastic film 3, which are laminated together.

[0068] Fig. 3b shows a side view of the detection device 9 with the illumination device 8 and the recording device 7. On the illumination device 8, a pattern 13 with a temporal periodicity of different illumination patterns 130 is depicted, which illuminate the surface 10 of the object 1 (see also the top view according to Fig. 3a). The illumination patterns 130 comprise a luminance profile 14. This also results in the generation of the pattern 13 on the surface 10. The recording device 7 records the pattern 13 on the surface 10 in an image.

[0069] The recording device 7 also comprises a recording sensor 11, which generates an image with a plurality of image points 12. Since the optics of the recording device are not depicted, the visible rays 15 emanating from the (each) image point 12 are reflected to the surface 10 and incident on the pattern 13 generated on the illumination device 8 as reflected visible rays 19. Fig. 3b draws the edge rays of these visible rays 15, 19. The edge rays emanate from the edge of the image point 12 and delimit a reflection area 17 on the surface 10. All visible rays 15 emanating from the image point 12 with the reflection angle a and incident on the surface lie in the reflection area 17 on the surface 10 and are also reflected from the surface as reflected visible rays 19 with the reflection angle a. They are incident on the illumination device 8 in the pattern area 17, since according to the arrangement according to the application, the recording device 7 and the illumination device 8 are arranged with the reflection angle a with respect to the surface 10.

[0070] The reflection angle a is defined as the angle between the incident (emanating from the image point 12) / emergent (reflected from the surface 10) visible rays 15, 19 and the associated surface normal 16. The surface normal 16 belonging to the visible rays 15, 19 extends perpendicularly to the surface in the reflection point 170 at which the visible rays 15, 19 intersect the surface 10.

[0071] Fig. 3a shows in detail the lines of the recording sensor 11 of the recording device 7, which extend along the width of the surface 10, like for example a web-like product, such as a FCCL film, which moves along the movement direction 6 like the object 1. The recording device 7 can be configured as a line camera with only one sensor line of the recording sensor 11 or as an area scan camera with multiple such sensor lines. The image point 12 can be formed by one or more sensor pixels. Through the not depicted optics, the image point 12 of the recording device (camera) captures the reflection area 17 on the surface 10. The visible ray 15 is deflected on the surface 10 and captures the pattern area 18, which at the point in time of the image recording, is given by the area of the pattern 13 / the corresponding illumination pattern 130 of the pattern 13. In the example shown in Figs. 3a and 3b, the illumination device is designed as an illumination line, which is aligned transversely to the movement direction 6 of the surface 10.

[0072] Fig. 3b shows the same arrangement in a side view, wherein the reflection of the visible ray 15, 19 (depicted as edge ray in all figures) can be clearly identified by the reflection angle a with respect to the surface normal 16. The depicted edge ray of the visible ray 15, 19 shows the size / area of the reflection area 17 on the surface 10 and the pattern area 18 in the pattern 13.

[0073] Figs. 3a and 3b show the state during image recording, wherein it is assumed that the movement of the surface 10 along the movement direction can be neglected during the short exposure time of the image recording. If this is not the case, the recorded image would show a certain motion blur, which can be counteracted by shortening the exposure time (assuming that the illumination is bright enough).

[0074] As already described before, during the image recording sequence, a plurality of images is recorded in chronological order with the method according to the present application. Since the surface moves along the movement direction 6 during the image recording sequence, the image points 12 in the respective reflection area 17 of the consecutively recorded images no longer see the same surface area. Rather, the reflection areas 17 on the surface 10 move relative to each other in the consecutively recorded images.

[0075] This is shown in Figures 4a and 4b, in which the movement 61 of the surface 10 between the first and the last image recording of the image recording sequence is plotted. The reflection area 17a is plotted as the reflection area of the first image recording, and the reflection area 17b is plotted as the reflection area from the last image recording in the image recording sequence (each image rotated by 90° in the hatching). In the overlap area, the two hatches overlap. The entire reflection area 17 on all images of the recording sequence is enlarged accordingly (relative to the surface 10 covered as a whole by the reflection area of the individual recordings). This effect is basically similar to the motion blur described above, with the difference that the entire reflection area is integrated in one image. This makes the image appear blurred, as long as the motion blur is fully recognizable.

[0076] Since the recording geometry does not change with a flat surface, the movement of the surface 10 has no effect on the pattern area 18; this remains unchanged during the recording sequence, in which, of course, the pattern illumination produces a phase shift, as described above. For the sake of clarity, this is not shown in Figure 4a.

[0077] Figure 4b shows the same situation as in Figure 4a in a side view. The surface normal 16a during recording of image a is in the same position at the same time as the surface normal 16b during recording of image b, which is shown here as an instantaneous recording of the arrangement. Due to the flat surface 10, the alignment of the surface normals 16a and 16b is the same, so the pattern area 18 also does not change.

[0078] Figures 3c and 4c show an arrangement of the detection device 9 in which the illumination device 8 comprises an illumination line aligned along the movement direction 6 of the surface 10. This can be realized by a line illumination device (with a correspondingly aligned line) or by a correspondingly controlled matrix illumination device. Due to the flat surface, this arrangement also leads to a situation similar to that shown in Figures 3a, 3b and Figures 4a, 4b. For a detailed description, reference is made to the above description.

[0079] Figures 3d and 4d show an arrangement of the detection device 9 similar to that in Figures 3c and 4c. In which not only the illumination line of the illumination device 8, but also the sensor line of the recording sensor 11 is aligned along the movement direction 6 of the surface 10. The recording device can be correspondingly designed as a line camera (with only one sensor line) or a matrix camera (with several sensor lines arranged side by side). Due to the flat surface, this arrangement also leads to a situation similar to that shown in Figures 3a, 3b, 3c and Figures 4a, 4b, 4c. For a detailed description, reference is made to the above description.

[0080] When the surface is indeed not flat, this is different. This is described in Figures 5a, 5b, 5c and 5d or Figures 6a, 6b, 6c and 6d, respectively. These views and arrangements correspond to the views and arrangements discussed with reference to the views and arrangements related to Figures 3a, 3b, 3c and 3d or Figures 4a, 4b, 4c and 4d. In view of the general description, reference should thus be made to the above. Since the curvature of the surface 10 influences the alignment of the surface normals 16, 16' and since the reflection of the visible rays 15, 19 is influenced, different pattern areas 18a, 18b result for different images of the image recording sequence.

[0081] Figures 5a, 5b, 5c and 5d show the situation for one image, e.g. the first image of an image sequence, respectively. Figure 5a essentially corresponds to Figure 3a, wherein the side of the surface 10 depicted in a curved manner indicates that the curvature of the surface 10 extends transversely to the movement direction 6. Due to the curvature of the surface 10, the visible rays in the top view do not reflect in a straight line, but are deflected at the reflection points 170, 170'. Correspondingly, the reflected visible rays 19 are incident on the pattern 13 in a pattern area 18, which is located at a different position than the pattern area 18 according to Figure 3a. Figure 5b accordingly shows that the alignment of the surface normals 16 and 16' in the reflection points 170 and 170' is different (hence the different reference numerals are indicated). The reflection angles a, a' are thus also different.

[0082] Figures 6a and 6b show the reflection areas 17a (for the visible rays 15, 19 reproduced in Figures 5a, 5b during recording) and 17b (for the visible rays 15, 19 reproduced in Figures 6a, 6b) and the overlap area 171. The pattern areas 18a and 18b and their overlap area 181 are shown in a corresponding manner.

[0083] The image point 12 is illuminated by the area 18, 18a, 18b of the pattern delimited by the edge visible rays 15 (before mirroring at the surface 10) or 19 (after mirroring at the surface 10), wherein this area 18, 18a, 18b is mapped onto the pattern 13 across the reflection area 17, 17a, 17b of the surface 10 in the recording device 7. However, each visible ray 15 is deflected according to the surface normal 16, 16', 16a, 16a' or 16b, 16b' present at this location.

[0084] The situation in the first image of a sequence is depicted in Figures 5a, 5b, 5c and 5d. Again, the camera pixel 12 in the image sensor 11 is illuminated by the area 18 of the pattern bounded by the edge ray 15 (before mirroring at the surface 10) or 19a (after mirroring at the surface 10), which maps across the area 17a of the surface 10 in the camera onto the pattern 13. However, now the view ray 15 is deflected according to the surface normal 16a or 16b present at this position. The situation in the last image of a sequence of images is shown in Figures 6a, 6b, 6c and 6d. Now, the area 18b of the pattern 13 maps onto the area 17b of the curved surface 10 moving in the image point 12. The surface normals 16b, 16b' now play a decisive role with the mirroring of the edge ray 15 emanating from the camera. Due to these differences from the first image (Figures 5a, 5b, 5c and 5d), the area of the illumination pattern 130 in the illumination device 8 seen or mapped in the image point 12 is also shifted. In summary, during the sequence of images from the first recording to the last recording, the image point 12 sweeps across the area 17 of the surface 10 in Figures 6a, 6b, 6c and 6d, thus across the entire area 18 of the pattern 13. The image point 12 can see this area, which lies in the reflection zones 17a and 17b on the surface 10, and in the pattern areas 18a and 18b on the pattern 13. It, i.e. the image point 12, cannot see during the entire image sequence the area which is present only in 17a or 17b / 18a or 18b.

[0085] However, it should be noted that the scales in Figures 3a, 3b, 3c, 3d, 4a, 4b, 4c, 4d, 5a, 5b, 5c, 5d, 6a, 6b, 6c, 6d are not realistic. The cut-out areas 171 and 181 depicted with cross-hatching also do not correspond to the actual size, respectively, but are only for illustrative purposes and to facilitate understanding. In fact, at least the wavelength of the pattern 13 or the illumination pattern should have a longer wavelength compared to the size described for the image point 12, so that the image point 12 covers only a small fraction of the wavelength. If the scale with regard to size were true, one would not be able to recognize the principle in the figures.

[0086] As already mentioned, in the sequence of image recordings recorded for the multi-image phase-shift process, the same location of the surface 10, i.e. the same reflection area 17, shall actually be mapped in all images of each image point 12. When recording a plurality of images in succession, these images will move relative to the moving surface 10. For the images recorded by the image point 12 during the sequence of images, it ultimately depends on the extent of the change in the mapping of the periodic pattern 13 on the surface 10 in the recording device 7 during the sequence of images, whether it can still be considered as "substantially the same location" in the sense of the present application. This in turn depends on the pattern 13 (illumination pattern 130) itself and its distance from the surface 10, on the other hand on the reflection area 17 mapped onto the image point 12 during the entire sequence of images, and how this area (reflection area 17) changes. The area of the reflection area depends on the optical pixel resolution (i.e. the area mapped in the observation plane on one pixel), the exposure time, the duration of the exposure sequence and the traversal speed (i.e. the distance the surface 10 moves through during the entire sequence of images). The change in the pattern area 18 depends on the surface topography (in particular the change in the surface normal).

[0087] If a phase-shift process is to be carried out, the pattern 13 and the image point 12 (again in the case of a stationary surface 10) must match one another in such a way that in the part of the illumination pattern 130 covered by the image point 12 on the illumination pattern 130, the brightness can be considered almost constant, or the average brightness actually represents the brightness measured at the image point 12. Likewise, a change in brightness is allowed to such an extent that the change in brightness of the required minimum surface deflection (caused by the defect to be detected) is sufficient for the detection device 9 to be able to perceive it. The former means that the surface 10 (covered by the image point 12 as reflection area 19) can be considered almost flat. If this is not the case, no further measurement of the topography is possible without further information; rather, only the presence of a surface deviation can be detected. Furthermore, the lateral resolution (i.e. the size of the surface area) must be adjusted to ensure that the smallest surface deviation detected during the detection is still resolved.

[0088] For a moving surface 10, it must also be taken into account that during the sequence of image recordings, a larger area (entire reflection area 17 on the surface 10 of Fig. 4a, Fig. 4b, Fig. 4c, Fig. 4d, for example Fig. 6a, Fig. 6b, Fig. 6c, Fig. 6d, is covered by an image point. This affects the lateral resolution. If the surface is additionally curved, a larger pattern area 18 on the pattern 13 is additionally covered by one image point. This affects the depth resolution. If the surface 10 moves during the recording of the images in the sequence of images, the deciding factor is how the respective visible ray 15, 19 of the image point 12 sweeps across the illumination pattern 130 (instantaneous recording of the pattern 13).

[0089] In the case of a flat surface 10, this effect according to Figures 3 and 4 does not occur in any case. Thus, no errors occur due to the mapping of different recorded pattern regions in the recorded sequence of images. But this only applies in the case of an undisturbed and error-free measurement. As soon as the surface exhibits any faults (or if the surface is curved), this is no longer the case. Thus, the situation shown in Figures 5 and 6 also occurs in the case of a measurement error.

[0090] Due to the method according to the application and the corresponding detection device, the system is arranged in such a way that the above-mentioned condition is also maintained for the exposure time / overall recording time of the complete image recording sequence. For this purpose, the images of the image recording sequence are recorded in rapid succession in chronological order at such a speed that the movement of the surface 10 during the recording is so small that the area (reflection region 17) covered by each image point 12 on the surface 10 can still be regarded as constant. Furthermore, the arrangement of the period length of the pattern 31 is such that during the recording of the image recording sequence, the area swept by the visible rays 15, 19 of the recording device 7 mirrored or reflected on the surface can still be regarded as constant / the resulting error is smaller than the required depth resolution.

[0091] The greater the degree of curvature of the surface 10, the faster the recording of the images and the longer the wavelength of the pattern 13. However, only the areas actually to be examined on the surface 10 need to meet these two conditions. In most cases, these are structurally defect-free surface areas and those areas in which flat, topographic long-wave defects are present. Furthermore, most of the defects in the surface 10 have a very small, usually very steep topography. With regard to these defects, these conditions can no longer be met in most cases, wherein this already applies to a large part of the static case. All that can be done is to detect these defects (detect defects), but it is no longer possible to measure them (measure topography).

[0092] In order to achieve the required lateral resolution for the entire image recording sequence, the method requires a very high image recording frequency. These, in turn, require very short exposure times, which, in turn, require very bright illumination.

[0093] For the phase-shift method used in this case in a very advantageous manner, it is most advantageous if the pattern 13, i.e. each illumination pattern 130, is a sinusoidal brightness curve. This is usually achieved by using a screen or pattern projected on the surface. A sinusoidal curve can be displayed very well. Unfortunately, it is usually not possible to use these illuminations economically to achieve sufficient brightness, and the possible image frequency is limited, so that it can only be used for slow processes.

[0094] With LED lines or LED matrices, individual LEDs or even individual LED modules (consisting of multiple individual LEDs) can be controlled individually to achieve the required brightness and the required switching frequency and in synchronization with the image recording of the camera. Alternatively, multiple lines can be combined into a matrix.

[0095] In the simplest form, only opening or closing is implemented using a single LED or LED module. This means that only a rectangular brightness curve can be implemented, which is only a rough approximation of the actually required sinusoidal brightness curve. This is already sufficient to perform the phase shift method, but with limited accuracy. By taking various measures, the required curve can be better approximated. The closer to the sinusoidal curve, the higher the accuracy. The illumination line or illumination matrix can be modified so that intermediate brightness can also be set for individual LEDs. Depending on the size of the LEDs or LED modules, the sinusoidal curve can be well approximated. This can be achieved, for example, by temporarily switching on individual LEDs or LED modules only during the actual exposure time. However, this method is complex, as it requires very fast control of the electronics. The preferred solution according to the application provides for the pattern of blurring to be mapped on the camera. This has already been described and will not be repeated here.

[0096] It should be noted that the terms "camera" and "image recording device" are synonymous in the context of the above description. All features and functions disclosed in connection with the camera also apply accordingly to the image recording device and vice versa. Reference is made to the following list of reference signs:

[0097] 1 object

[0098] 2 copper film

[0099] 3 plastic film

[0100] 4 first defect

[0101] 5 second defect

[0102] 6 movement direction

[0103] 61 movement

[0104] 7 recording device

[0105] 8 illumination device

[0106] 9 detection device

[0107] 10 surface

[0108] 11 recording sensor

[0109] 12 image point

[0110] 13 pattern

[0111] 130 illumination pattern

[0112] 14 luminance distribution

[0113] 15 visible ray

[0114] 16 surface normal

[0115] 17 reflection zone

[0116] 170 reflection point

[0117] 171 cut-out area of a single image reflection zone

[0118] 18 pattern area

[0119] 181 cut-out area of a single image reflection zone

[0120] 19 visible ray

[0121] a reflection angle

Claims

1. A method for optically inspecting a curved surface (10) of an object (1) using a detection device (9), the method comprising the following steps: During the image recording sequence, a time-periodic pattern (13) with different illumination patterns (130) is generated on the surface (10) by the illumination device (8) of the detection device (9), and multiple images of the pattern (13) on the surface (10) are recorded by the image recording device (7) of the detection device (9) during the image recording sequence. The generation of one of the different lighting patterns (130) is synchronized with the image recording of one of the images of the pattern (13), such that each image from the image recording sequence is recorded with a known lighting pattern (130) of the different lighting patterns (130); The phase of pattern (13) is determined by a sequence of known illumination patterns (130) recorded in at least one image point; Defects (4, 5) on the surface (10) are detected from the deviation between the illumination pattern (130) recorded in at least one image and the generated known illumination pattern (130); The feature is that the illumination device (8) and the image recording device (7) are arranged at a reflection angle (α), wherein During the detection of the surface (10), the object (1) moves relative to the detection device (9); The duration of the image recording sequence is selected, and the period length of the pattern (13) in the illumination pattern (130) is selected such that the intensity variation does not exceed the selected standard according to the topology of the surface (10) in the pattern direction. Thus, the illumination pattern (130) is generated by the illumination device (7) such that the area of ​​the illumination pattern (130) visible in the image point (12) of the image recorded during each image recording sequence is regarded as constant, and the sequence reflection area (17) can be regarded as constant. The sequence reflection area (17) is defined as the surface area completely covered by the reflection areas (17a, 17b) in each image from the image recording sequence.

2. The method according to claim 1, characterized in that, The size of the image point (12) is set during the execution of the method.

3. The method according to claim 2, characterized in that, The size of the image point (12) is set by combining multiple pixels of the recording sensor (11) of the recording device (7).

4. The method according to any one of the preceding claims, characterized in that, The duration of the image recording sequence is set during the execution of the method.

5. The method according to claim 4, characterized in that, When setting the duration of the image recording sequence, adjust at least one of the following variables: - Image exposure time; - The brightness of the pattern (13) generated at the surface (10); - Record the scanning frequency of the sensor (11); - The number of images in the sequence recorded for each image.

6. The method according to claim 1, characterized in that, The periodic pattern (13) is generated along the direction of movement of the object (10), laterally to the direction of movement of the object (10), or alternately along and laterally to the direction of movement of the object (10).

7. The method according to claim 1, characterized in that, The recording device (7) focuses, causing the illumination pattern (130) recorded in the image to become blurred.

8. The method according to claim 1, characterized in that, During the inspection of the surface (10), the three-dimensional morphology of the surface (10) of the object (1) is determined by a deflection measurement process.

9. Use of the method according to any one of claims 1 to 8 for detecting mesh products or treated surfaces (10).

10. A detection apparatus for optically detecting a curved surface (10) of an object (1) using an illumination device (8) and a recording device (7), the illumination device (8) and the recording device (7) being aligned with each other such that visible rays (15) emitted from the illumination device (8) are reflected as visible rays (19) on the surface and then incident on the recording device (7), wherein the surface normal (16) on the surface (10) at the point of incidence of the visible rays (15, 19) just halves the angle between the output visible ray (15) and the reflected visible ray (19), wherein, The illumination device (8) is designed to generate a pattern (13) with different time periodicity of illumination patterns (130) during the image recording sequence, and the recording device (7) is designed to record the pattern (13) reflected on the surface (10) synchronously with the generation of the illumination pattern (130) during the image recording sequence, wherein the detection device (9) includes a computing unit for controlling the detection device (9) and for evaluating the recorded image, characterized in that the processor of the computing unit is designed to perform the method according to any one of claims 1 to 8.

11. The detection device according to claim 10, characterized in that, The lighting device (8) includes individually controllable light elements arranged in rows or matrices, and the recording device (7) includes a sensor (11) for recording an image mapped onto the sensor (11) by recording optics, wherein the sensor (11) includes individual sensor pixels arranged in rows or matrices.

12. The detection device according to claim 10 or 11, characterized in that, The recording device (7) and the illumination device (8) are arranged such that a flat viewing and illumination angle of less than 30° is provided between the respective visible rays (15, 19) and the surface (10), and / or a large illumination distance is provided between the surface (10) and the illumination device (8), the illumination distance being between 1 and 10 times the distance between the recording device (7) and the surface (10).

Images