Method and device for compensating for material web offset during material web inspection

Description

Field of the invention

[0001] The present invention relates to a method and a device for compensating a material web offset in observation and inspection systems for machines with continuously moving products, such as material webs. Background of the invention

[0002] When producing products manufactured as material webs, especially printed products such as labels or packaging, observation and / or automated quality assurance after printing is of great importance in order to check the print result. In addition to automated monitoring, support for visual inspection by an operator can also be provided. With this type of quality assurance, the material webs are passed under observation or inspection systems that take images of the material webs. These images can be checked by an operator or automatically. To guarantee high image quality, the material webs can be illuminated for the images using appropriate devices. Web observation systems are known, for example, from JP 2008 286646 A, DE 10 2012 101 310 B3, DE 10 2015 105 656 A1 and US 2010 / 214416 A1.US 2012 / 281121 A1 describes a device for selective pixel binning. The aforementioned document JP 2008 286646 A discloses a device for inspecting material webs, in which two different sub-areas of a matrix camera chip in the transport direction of the material web are read at several times t, t+1, t+2. These two sub-areas are then each processed into a combined image, resulting in two combined images.

[0003] In a special type of inspection, the so-called multi-inspection, an attempt is made to capture the entire material web (100% inspection) using two types of illumination. However, more than two, i.e. three, four or five types of illumination can also be used. The conditional alternating or time-shifted image acquisition with different types of illumination and acquisition parameters enables, for example, the evaluation of two image sequences with different information. However, this results in an offset between the individual images or image sequences in the direction of the material web movement, which were acquired, for example, using incident light and transmitted light. The effects of the offset can become greater the faster the web speed, the more precise the resolution of the matrix chip and the longer the delay between the images or image sequences.In known inspection systems, attempts are made to compensate for this offset using complex software and corresponding computing power, since the image sequences of the two (or more) inspection types must be precisely superimposed for evaluation in order to be able to specify the same referencing or the same reference (in the case of inspection errors) to the moving object. On the other hand, it is also possible to ignore a small offset, but this is not satisfactory. Other systems with software compensation usually use an algorithm for image stabilization in which, after pattern matching, identical patterns are superimposed using registration zones. With different lighting and thus also different image information, however, there is the disadvantage that it may be difficult to find identical patterns. The same lighting is actually assumed here.Compensating for this via software is, on the one hand, very complex and, on the other hand, sometimes impossible or unsatisfactory in multi-inspection systems. The properties of the material web, which can be transparent, translucent, opaque, or mixed, can also impact unsatisfactory software compensation.

[0004] The aim of the present invention is therefore to provide a device and a method which eliminate the disadvantages of software compensation. Summary of the invention

[0005] The present invention relates to a method for compensating a material web offset in inspection systems for material webs according to claim 1 and to a device for observing and / or inspecting material webs according to claim 8.

[0006] The method according to the invention for compensating for a material web offset in inspection systems for material webs that move in the direction of a material web length and / or a material web width comprises the following steps: taking a first image of a first section of a material web at a first point in time with a camera that includes a matrix chip; and taking a second image of a second section of the material web at a second point in time with the camera, wherein for the first image, exclusively a first active partial area of ​​the matrix chip is activated at the first point in time and for the second image, exclusively a second active partial area of ​​the matrix chip is activated at the second point in time, and wherein the first active partial area and the second active partial area are not identical.A time shift between the first and the second recording is either fixed or is adjusted according to the material web movement and depends on a first trigger that triggers the first recording at the first time and a second trigger that triggers the second recording at the second time.

[0007] The dynamic adjustment of the active partial area used by the matrix chip enables direct and precise synchronization of two image sequences of a material web and is independent of the properties of the material web (which are required, for example, for software compensation of the offset). This control allows two (or more) image sequences taken at minimally different times to be directly acquired and precisely superimposed. This eliminates the need for complex, sometimes even impossible, or at least unsatisfactory, compensation of an offset along the length of the material web during recordings via software analysis. Furthermore, by reducing the active area of ​​the matrix chip, the image acquisition frequency can be increased. This is particularly advantageous for multiple inspections (i.e., inspections with different types of illumination) of moving objects.The method according to the invention thus enables optimal referencing (hardware compensation) of multiple image sequences. Consequently, an exact 100% inspection of a material web is possible, even for multi-inspection systems with different illumination types and without the use of additional software compensation for referencing. This also leads to potential savings in the required computing power.

[0008] In embodiments, a size and / or a position of the first and second active partial areas of the matrix chip and thus the field of view of the camera can be dynamically adjusted in the direction of the material web length and / or in the direction of the material web width.

[0009] In embodiments that can be combined with all previously described embodiments, the first section and the second section can be two identical material web sections. Alternatively, the first section and the second section can be two different material web sections.

[0010] The second active partial area is offset from the first active partial area by a specified offset in the direction of the material web length and / or in the direction of the material web width. This is advantageous because it allows both an offset of the material web in the direction of the material web length and an offset of the material web in the direction of the material web width to be compensated for via the hardware. This is particularly advantageous if, for example, the material web edges for an offset in the direction of the material web width cannot be detected (with regard to possible software compensation) or the field of view is adapted to the usefulness of the material web width. This makes it possible to further increase the image recording frequency if partial areas of the matrix chip that are restricted in both the direction of the material web length and the direction of the material web width are activated.With the help of a position sensor, it is also possible to adjust the field of view in the direction of the material web width to the material web width used without having to take the material web edges into account.

[0011] In embodiments that can be combined with all of the embodiments described so far, the first recording can be part of a first image sequence of the material web and the second recording can be part of a second image sequence of the material web. A first sequence can be created with a plurality of first recordings to generate the first image sequence of the material web, and a second sequence can be created with a plurality of second recordings to generate the second image sequence of the material web. In this case, all recordings of the first image sequence can be recorded with the first active partial area of ​​the matrix chip and all recordings of the second image sequence can be recorded with the second active partial area of ​​the matrix chip, or the second active partial area of ​​the matrix chip can be adapted for the recordings of the second image sequence.

[0012] In embodiments that can be combined with all of the embodiments described so far, the material web can be illuminated with a first type of illumination for the first and second images. Alternatively, the material web can be illuminated with a first type of illumination for the first image, and the material web can be illuminated with a second type of illumination for the second image. A first image can be taken with the first type of illumination and a second image can be taken with the second type of illumination for a plurality of successive sections of the material web in the direction of the material web length, the first images together resulting in a first image sequence of the material web, and the second images resulting in a second image sequence of the material web. At least one of the first and second image sequences can be used for web observation and / or inspection.In particular, the first and / or second image sequences can be visually displayed to a user.

[0013] The material web can be illuminated across the entire field of view of the camera for the first and / or second image capture. Alternatively, the material web can be selectively illuminated according to the first and second active partial areas of the matrix chip. The material web can be illuminated in a traversing manner relative to the direction of the material web width. Furthermore, further images of corresponding additional sections can be created at corresponding additional times using corresponding additional active partial areas of the matrix chip, whereby the additional sections are identical to the first section and / or the second section. For the further images, other types of illumination can be used to illuminate the material web.

[0014] The types of illumination can, for example, be selected from the group consisting of incident light illumination, background light illumination and transmitted light illumination.

[0015] In embodiments that can be combined with all previously described embodiments, the camera's field of view can be designed to cover at least the entire material web width. In particular, the camera's field of view can be larger in the direction of the material web width than the material web width. Based on a signal from a material web position sensor, the first and second active partial areas can be adjusted, in particular a size and / or a position of the first and second active partial areas in the direction of the material web width.

[0016] In embodiments that can be combined with all previously described embodiments, the second point in time can be offset from the first point in time by 0.0001 to 0.01 seconds, in particular by 0.0005 to 0.001 seconds.

[0017] The material web can be moved at a web speed of at least 150 m / min, in particular at least 500 m / min, preferably at least 900 m / min in the direction of the material web length.

[0018] In embodiments that can be combined with all previously described embodiments, a sensor can also be provided for determining the distance traveled or the speed of the material web in the direction of the material web length.

[0019] In embodiments that can be combined with all previously described embodiments, a distance traveled by the material web in the direction of the material web length can be measured and the first time point for the first recording and / or the second time point for the second recording can be calculated and provided to the camera.

[0020] Alternatively, a speed of the material web can be measured and a time shift between the first recording and the second recording can be controlled.

[0021] In embodiments that can be combined with all previously described embodiments, a plurality of cameras with matrix chips can be provided, wherein the cameras are arranged distributed over the material web width so that the fields of view of the cameras adjoin or overlap one another in the direction of the material web width, wherein the plurality of cameras create corresponding first and second images and the first and second images are combined to form two contiguous image sequences.

[0022] In embodiments that can be combined with all previously described embodiments, the field of view of the camera can be arranged traversing relative to the direction of the material web width. Additionally or alternatively, if a plurality of cameras is provided, the plurality of cameras can be arranged traversing relative to the direction of the material web width.

[0023] In embodiments that can be combined with all previously described embodiments, at least one camera can be provided on a front side of the material web and at least one camera on a back side of the material web and can each create first and second images of the front side and the back side of the material web.

[0024] The invention further comprises a device for observing and / or inspecting material webs that move in the direction of a material web length and / or a material web width. The device comprises a camera having a matrix chip, wherein partial areas of the matrix chip can be activated independently of one another, and a control unit. The control unit is designed to cause exclusively a first partial area of ​​the matrix chip to be activated in order to create a first image of a first section of the material web at a first point in time; exclusively a second partial area of ​​the matrix chip to be activated in order to create a second image of a second section of the material web at a second point in time, wherein the first active partial area and the second active partial area are not identical.A time shift between the first and the second recording is either fixed or is adjusted according to the material web movement and depends on a first trigger that triggers the first recording at the first time and a second trigger that triggers the second recording at the second time.

[0025] In embodiments, a size and / or a position of the first and second active partial areas of the matrix chip and thus the field of view of the camera can be dynamically adjusted in the direction of the material web length and / or in the direction of the material web width.

[0026] In embodiments of the device that can be combined with all previously described embodiments, the first section and the second section can be two identical material web sections. Alternatively, the first section and the second section can be two different material web sections.

[0027] The control unit is designed to select the first and second active partial areas such that the second active partial area is offset by a predetermined offset in the direction of the material web length and / or in the direction of the material web width compared to the first active partial area.

[0028] In embodiments of the device that can be combined with all of the embodiments described so far, the first recording can be part of a first image sequence of the material web and the second recording can be part of a second image sequence of the material web. The control unit can be designed to cause a first sequence with a plurality of first recordings to be created in order to generate the first image sequence of the material web and a second sequence with a plurality of second recordings to be created in order to generate the second image sequence of the material web. The control unit can be designed to cause all recordings of the first image sequence to be recorded with the first active partial area of ​​the matrix chip and all recordings of the second image sequence to be recorded with the second active partial area of ​​the matrix chip, or to adapt the second active partial area of ​​the matrix chip for the recordings of the second image sequence.

[0029] In embodiments of the device that can be combined with all previously described embodiments, the device can have a first illumination device, so that the material web can be illuminated with a first type of illumination for the first and second exposures. Alternatively, the device can have first and second illumination devices, so that a first type of illumination can be used for the first exposure of the material web and a second type of illumination can be used for the second exposure of the material web.The control unit can be designed to cause a first image to be taken with the first type of illumination and a second image to be taken with the second type of illumination of a plurality of successive sections of the material web in the direction of the material web length, the first images together resulting in a first image sequence of the material web and the second images resulting in a second image sequence of the material web. The control unit can be designed to cause the material web to be illuminated in the entire field of view of the camera for the first and / or the second image, or to cause the material web to be selectively illuminated in accordance with the first and second active partial areas of the matrix chip. The first and / or the second illumination device can be arranged so as to traverse the direction of the material web width.The control unit can be configured to activate additional partial areas of the matrix chip in order to create additional images of corresponding additional sections at corresponding additional times, wherein the additional sections are identical to the first section and / or the second section. In particular, the device can comprise additional illumination devices so that the material web can be illuminated with additional types of illumination for the additional images. The illumination devices can be configured to provide at least one type of illumination selected from the group consisting of incident illumination, background illumination, and transmitted illumination.

[0030] In embodiments of the device that can be combined with all previously described embodiments, the camera can have a field of view to cover at least the entire material web width. In particular, the field of view of the camera in the direction of the material web width can be larger than the material web width. The device can also have a material web position sensor, and the control unit can further be configured to cause the first and second active partial areas to be adjusted based on a signal from the material web position sensor, in particular to adjust a size and / or a position of the first and second active partial areas in the direction of the material web width.

[0031] In embodiments of the device which can be combined with all embodiments described so far, the control unit can be designed to cause the second point in time to be offset from the first point in time by 0.0001 to 0.01 seconds, in particular by 0.0005 to 0.001 seconds.

[0032] In embodiments of the device which can be combined with all the embodiments described so far, a sensor can also be provided for determining the distance travelled or the speed of the material web in the direction of the material web length.

[0033] In embodiments of the device that can be combined with all previously described embodiments, the device can be designed to measure a distance traveled by the material web in the direction of the material web length and to calculate the first time point for the first recording and / or the second time point for the second recording and to provide it to the camera.

[0034] Alternatively, the device can be designed to measure the speed of the material web and thereby control a time shift between the first recording and the second recording.

[0035] In embodiments of the device that can be combined with all previously described embodiments, a plurality of cameras with a matrix chip can be provided, wherein the cameras are arranged distributed across the material web width, so that the viewing areas of the plurality of cameras adjoin one another or overlap in the direction of the material web width. The control unit can be configured to cause the plurality of cameras to take corresponding first and second images and to combine the first and second images into two contiguous image sequences.

[0036] In embodiments of the device which can be combined with all previously described embodiments, the field of view of the camera can be arranged traversing with respect to the direction of the material web width and / or, if a plurality of cameras is provided, the plurality of cameras can be arranged traversing with respect to the direction of the material web width.

[0037] In embodiments of the device which can be combined with all previously described embodiments, at least one camera can be provided on a front side of the material web and at least one camera on a back side of the material web, wherein the control unit is designed to cause first and second images of the front side and the back side of the material web to be created.

[0038] In embodiments of the device that can be combined with all embodiments described so far, the device can also comprise a lens with a fixed focal length.

[0039] Further details and features of the invention are described with reference to the following figures. Short description of the characters

[0040] Fig. 1 shows a schematic representation of an inventive device for material web observation or material web inspection according to an exemplary embodiment; Fig. 2 shows two views of a material web with superimposed image sequences; Fig. 3 shows two schematic representations of a matrix chip with correspondingly activated partial areas; Fig. 4 shows two further schematic representations of a matrix chip with correspondingly activated partial areas. Detailed description

[0041] The term "material web" used below is to be understood broadly and refers to all types of products that are moved automatically during processing and for which observation or inspection is required. These include, among others, printed paper products, fabrics and textiles, packaging or packaging raw materials, labels, etc. The material webs do not have to be continuous but can also be in the form of successive sheets. The device and method according to the invention can be used for the observation and / or inspection of all these products.

[0042] Fig. 1shows a schematic side view of a device 100 for observing and / or inspecting a material web 10. The device 100 can be used for all methods for compensating a material web offset described below. In addition to web observation / inspection, the device can also be used for color density measurement or spectral color measurement. Device 100 comprises a camera 110 equipped with a matrix chip 20, for example a CCD or CMOS sensor. The camera 110 can be suitable for 1D, 2D and / or 3D recordings and can be a color or black-and-white camera. The camera 110 or the field of view of the camera 110 can be either parallel or traversing with respect to the direction of the material web width x (see Fig. 2 ). In an embodiment not shown, an additional camera for detailed shots may also be provided. Fig. 1also shows different devices for illuminating the material web 10. In the example shown, one or two lighting devices 130 are provided above the material web 10 and one lighting device 150 is provided below the material web 10. Alternative designs may also have only one lighting device or more than two lighting devices.

[0043] Also in Fig. 1A lens 112 for the camera 110 can be seen, which preferably has a fixed focal length (fixed focus). In alternative embodiments, a zoom lens can also be used. In addition, a sensor 140 is provided, which measures the distance traveled or the speed of the material web. Sensors that can be used here include encoders, proximity switches, print mark sensors or direct speed sensors. For example, rotary encoders (incremental rotary encoders, rotary pulse encoders) can be used, which are usually used with a running wheel. The running wheel, with a known rolling circumference, sits on the material web and, for example, several pulses are generated per revolution. The number of pulses detected can be used to determine the distance traveled by the material web in the direction of the material web length y.The material web speed can then be determined, for example, via the number of recorded pulses per unit of time and the distance traveled, i.e., via the time and distance values ​​(see example below). The material web 10 is preferably moved in the direction of a material web length y, but can also be moved in the direction of a material web width x (see . Fig. 2 ) The material web 10 can be moved, for example, at a web speed of at least 150 m / min, in particular at least 500 m / min, preferably at least 900 m / min in the direction of the material web length y.

[0044] In addition, the device 100 also comprises a (in Fig. 1not shown) control unit, which controls all activities of the device and processes corresponding signals, for example from the sensor 140 or other external sensors. In addition, one or more monitors can be provided for the visual display of the camera recordings or the created image sequences (in Fig. 1 not shown).

[0045] As mentioned at the beginning, the method according to the invention allows for a material web offset that occurs during two consecutive recordings to be compensated without complex software. This is made possible by the following procedure: Creating a first recording of a first section of the material web 10 at a first time with the camera 110, which includes the matrix chip 20, and then creating a second recording of a second section of the material web 10 at a second time with the camera 110. The special feature here is that, as shown in Fig. 3 and Fig. 4shown, a first active partial area 22 of the matrix chip 20 is used for the first recording and a second active partial area 24 of the matrix chip 20 is used for the second recording, wherein the first active partial area and the second active partial area are not identical.

[0046] The second point in time may, for example, be offset by 0.0001 to 0.01 seconds, in particular by 0.0005 to 0.001 seconds, from the first point in time.

[0047] An active area of ​​the matrix chip 20 is a partial area of ​​the matrix chip 20 that is activated for capturing an image. The principle of the "Region of Interest" (ROI, see Fig. 1 )used, in which the actual active area, i.e. the resolution, of a matrix chip 20 (as already mentioned, CMOS chips, CCD chips or chips with FPGA can be used here, for example) is adjusted. This means that not the entire chip area and thus not the maximum viewing area (in Fig. 1the maximum field of view 150 of the camera is shown in the direction of the material web length y), i.e. not the complete resolution of the chip, but only a partial area, i.e. a part of the resolution or a part of the available sensor points, is used to create a picture. This will be explained using a highly simplified example. For example, a matrix chip can have 20 x 20 = 400 fictitious pixels. For clarification, it should be mentioned again that this is a fictitious example to explain the principle of the invention, since the matrix chips actually used have a much larger number of pixels (up to over 100 megapixels).For a first recording, for example, a first active partial area 22 with 5 x 20 = 100 fictitious pixels can be used, which utilizes the entire width (in the x-direction corresponding to the direction of the material web width) of the matrix chip 20 but only a portion of its length (in the y-direction corresponding to the direction of the material web length). For a second recording, a second active partial area 24 can be used, which is one pixel width (the fictitious pixels of the representation in . Fig. 3 ) in the direction of the material web length y. With other parameters (for example, to compensate for a higher web speed and / or a larger time delay between the two images), the second image may be shifted by more than one pixel. Alternatively, as in Fig. 4As shown, an active partial area 22 restricted in the x direction can also be used for the first image, and a second partial area 24 correspondingly shifted in the x and y directions can be used for the second image. Using this method, corresponding first and second image sequences can then be created by continuously creating first and second images with the corresponding partial areas 22, 24 and combining them into image sequences (more on this below).

[0048] The device and method offer several advantages. The dynamic adjustment of the active partial areas 22, 24 used by the matrix chip 20 enables a direct and exact synchronization of two image sequences of a material web 10 and is independent of the properties of the material web 10 (which are required, for example, for software compensation of the offset). This control allows two (or more) image sequences taken at minimally different times to be directly acquired and precisely superimposed. A complex or sometimes even impossible or at least unsatisfactory compensation of a Y offset (see Δy in Fig. 2 ) This eliminates the need for software analysis during recordings. To illustrate the offset in the direction of the material web length y when the material web 10 moves in this direction, Fig. 2Two material webs 10 are shown, each of which has web sections captured at minimally different times, which can be combined into image sequences 30a, 30b. Although these image sequences cover the entire material web 10 (100% inspection), they are offset by Δy in the direction of the material web movement (in this case, in the y direction), since the material web 10 has always moved a little further between two consecutive images depending on the material web speed and the delay of the camera 110. The following offset Δy can arise, for example, for the following frame parameters: Path speed (in direction y): 180 m / min ≡ 3 m / sec ≡ 3000 mm / sec Camera resolution: 0.2 mm / pixel Image acquisition delay: 500 µs

[0049] This results in a line frequency of 15,000 lines / sec ≡ 15 lines / millisecond. With a delay between two image sequences of 500 microseconds (0.5 milliseconds), this would result in an offset Δy of 7.5 lines or 7.5 pixels, which corresponds to 1.5 mm.

[0050] Such offsets can be directly dynamically compensated with the device 100 according to the invention and the method according to the invention by activating corresponding partial areas 22, 24 of the matrix chip 20, so that identical sections can be captured in two consecutive recordings.

[0051] A further advantage of the invention is that the image acquisition frequency can be increased by reducing the size of the active areas 22, 24 of the matrix chip 20. This is particularly advantageous for multiple inspections (i.e., inspections with different types of illumination) of moving objects. The method and device 100 according to the invention thus enable optimal referencing (hardware compensation) of multiple image sequences. Consequently, an exact 100% inspection of a material web is also possible for multi-inspection systems with different types of illumination and without the use of additional software compensation for referencing. This also leads to potential savings in the required computing power.

[0052] Depending on the lens focal length and the ROIs used on the matrix chips, different geometric distortions may occur during image acquisition, leading to inaccuracies. These can be compensated for, for example, through distortion calibration.

[0053] As in Fig. 3 and Fig. 4As shown, a size and / or a position of the first and second active partial areas 22, 24 of the matrix chip 20 and thus the field of view of the camera 110 in the direction of the material web length y and / or in the direction of the material web width x can be dynamically adjusted. Factors that influence the adjustment of the active partial areas include, for example, the current web speed (for example measured via the sensor 140), the current camera resolution and the current delay between two image recordings, whereby the delay can either be fixed or also adjusted dynamically (see example below). These factors can be taken into account immediately and directly in the matrix chip 20 by adjusting the active partial areas 22, 24, whereby, for example, deviations in these factors can also be dynamically compensated.In addition, a position sensor can be provided, for example, to determine the position and width of the material web (in the x-direction). The signals from this sensor can also be directly incorporated into the adjustment of the active partial surfaces 22, 24.

[0054] As mentioned above, the device can be used for different purposes. For example, the first section and the second section can be two identical material web sections. This means that the same section of the material web 10 is imaged twice, for example to be able to use two different types of illumination during multi-inspection. Furthermore, it is also possible to use more than two types of illumination and take a corresponding number of images. Alternatively, the first section and the second section can be two different material web sections. In this case, two different sections of the material web are imaged, but also with different active partial areas 22, 24, in order to be able to compensate for a suddenly deviating condition regarding the offset of the material web 10 in the direction of the material web length y or the material web width x, for example.This can be used, for example, in devices with only one type of illumination. Here, only one-time compensations occur, i.e., there is only a one-time change, triggered by a specific event, for the images of the camera 110 from the first active partial area 22 of the matrix chip 20 to the second active partial area 24 of the matrix chip 20. Such an event can be, for example, an abrupt increase in the material web speed (and thus some type of offset, such as offset Δy of the material web 10 in the direction of the material web length y). Fig. 2 ) or a slipping of the material web transverse to the direction of movement (offset of the material web 10 in the direction of the material web width x).

[0055] As in Fig. 3 or Fig. 4As shown, the second active partial area 24 can be offset by a predetermined offset in the direction of the material web length y and / or in the direction of the material web width x compared to the first active partial area 22. This is advantageous because both an offset Δy of the material web 10 in the y-direction and an offset of the material web 10 in the x-direction can be compensated for via the hardware. This is particularly advantageous if, for example, the material web edges for an offset in the x-direction cannot be detected (with regard to possible software compensation) or the field of view of the camera 110 is adapted to the actual use of the material web 10. A further increase in the image recording frequency is made possible if partial areas of the matrix chip 20 that are restricted in both the x- and y-direction are activated.With the help of the position sensor mentioned above, it is also possible to adjust the field of view in the x-direction to the material web width without having to take the material web edges into account.

[0056] The first image can be part of a first image sequence of the material web 10 and the second image can be part of a second image sequence of the material web 10. The first image sequence of the material web 10 is created from a plurality of first images and the second image sequence from a plurality of second images. It can be provided that all images of the first image sequence are recorded with the first active partial area 22 of the matrix chip 20 and all images of the second image sequence are recorded with the second active partial area 24 of the matrix chip 20. It is also possible for the second active partial areas 24 of the matrix chip to be adapted for the recordings of the second image sequence. Factors such as the current web speed, the current camera resolution and the current delay between two image recordings can be taken into account.

[0057] As in Fig. 1As shown, the device has different illumination devices. The material web 10 can be illuminated with the same first type of illumination (for example, with illumination device 130) for the first and second exposures. Alternatively, the material web 10 can be illuminated with a first type of illumination (for example, with illumination device 130) for the first exposure, and the material web 10 can be illuminated with a second type of illumination (for example, with illumination device 120) for the second exposure.With regard to the multi-inspection, a first image can now be taken of a plurality of successive sections of the material web 10 in the direction of the material web length y, each of which has a first illumination type and a second image can be taken of the second illumination type, the first images together forming the first image sequence of the material web 10 and the second images forming the second image sequence of the material web 10. The image sequences generated in this way can then, for example, be visually displayed to a user on one or more monitors. For example, a user can simultaneously observe the web in an image sequence for the inspection. Alternatively, the web can also be observed using a separate image sequence.

[0058] Depending on the lighting devices 120, 130 used, the material web 10 can be illuminated for the first and / or second recording across the entire field of view 150 of the camera 110, or alternatively, it can be illuminated selectively according to the first and second active partial areas 22, 24 of the matrix chip. Furthermore, it is possible for the illumination of the material web 10 to be traversing relative to the direction of the material web width x.

[0059] In addition to a multi-inspection with two image sequences, the device can also be used for a multi-inspection with three or more image sequences. For this purpose, further images of corresponding further sections are then created at corresponding further times using corresponding further active partial areas of the matrix chip 20, wherein the further sections are identical to the first section and / or the second section. For these further images, further types of illumination can be used to illuminate the material web 10. Of course, in addition to the illustrated illumination devices 120, 130, further illumination devices can be provided. The illumination types can, for example, be selected from the group consisting of incident light illumination, background light illumination, and transmitted light illumination.A range of lighting properties can be implemented: homogeneous or inhomogeneous lighting, direct, diffuse, focused, or collimated lighting, coaxial, transmissive, and / or polarized lighting, different lighting angles and bright-field or dark-field lighting, light wavelengths in the UV, visible, or IR range (e.g., to enable the inspection of security features), single-color (monochrome), multi-color (polychrome), or color-tunable or controllable (RGB) lighting, area or line lighting, constant or flashed lighting. Incident and transmitted light can be used alternately or simultaneously. The lighting systems can be designed as tunnel lighting systems, tube lighting systems, or dome lighting systems, and can be modular or adapted to the material web width.Light sources such as incandescent lamps, gas discharge lamps, LED lighting, OLED lighting, or laser lighting can be used. The respective lighting types and properties can be used for the following multi-inspection applications, for example: print image inspection with visible incident light, label inspection with visible transmitted light, and inspection of UV security features with UV incident light.

[0060] The field of view of the camera 110 can be designed to cover at least the entire material web width. As already described above, the field of view of the camera 110 in the direction of the material web width x can be larger than the material web width. Based on a signal from the material web position sensor (in Fig. 1not shown), the first and second active partial areas 22, 24 can be adjusted, in particular a size and / or a position of the first and second active partial areas 22, 24 in the direction of the material web width x. In addition to the position of the material web 10, the following factors can also play a role in adjusting the active partial areas 22, 24: the current web speed, the current camera resolution and the current delay between two image recordings.

[0061] The delay, i.e. the time shift between the first and second recording, can either be fixed or adjusted according to the material web movement. The delay depends on a first trigger that triggers the first recording (at the first time) and a second trigger that triggers the second recording (at a second time). The delay between the first trigger and the second trigger creates the material web offset Δy (see Fig. 2). As already mentioned, a time interval between these two triggers (i.e. the two recordings) can be fixed and is limited, for example, by a maximum image recording frequency of the camera 110. The first and second times for the two triggers, i.e. the delay, can also be adjusted dynamically. The sensor 140 mentioned above can be used to measure the distance traveled or the speed of the material web 10. This will be described below using a simple numerical example for a sensor with a running wheel. The information for controlling the triggers comes, for example, from an encoder. This encoder is coupled to the running wheel and emits a certain number of pulses, e.g. 2048, per revolution of the running wheel.For example, if the impeller has a diameter of 100 mm, this results in a rolling circumference of 100 mm * π = 314.16 mm and a distance traveled by the material web in the direction of the material web length y of 314.16 mm / 2048 pulses per revolution, which corresponds to approximately 0.15 mm per pulse. Using a sensor with, for example, a resolution of 1600 x 1200 pixels and a material web width in the x direction of 350 mm, this results in 350 mm / 1600 pixels = 0.22 mm per pixel in the x direction (covering the entire material web width) and, since a matrix chip is used, also 0.22 mm per pixel in the y direction. Assuming the offset Δy is 132 mm and using the impeller / encoder combination described above, we get 132 mm / 0.15 mm per pulse = 880 pulses of the encoder.This means that between the activation of the first trigger for the first recording and the activation of the second trigger for the second recording, 880 encoder pulses were recorded. The second recording is therefore created with an offset of Δy = 132 mm. Since the 132 mm offset Δy corresponds to 600 pixels in the matrix chip example, the ROI for the second recording must be offset by 600 pixels in the direction of the material web length y in order to record the same material web section (with different lighting). The correction value for the ROI can therefore be determined using the number of pulses. The first time point for the first trigger or the first recording and the second time point for the second trigger or the second recording can therefore be determined using the travel distance of the impeller and the encoder pulses. For example, the first recording can be taken after a first number of pulses and the second recording after a second number of pulses.During continuous operation, the number of pulses is usually constant, as the material web sections should each cover 100% of the material web. Changing the material web speed only changes the time between the first and second shots, but not the number of pulses between the first and second shots. This means that the distance traveled by the material web remains the same, but the time shift between the shots changes or is adjusted. This means that with a sensor that can measure the distance (wheel with encoder), appropriate triggering for the first and second shots and a correction of the ROI can take place.

[0062] This approach can also be used to compensate for different material web speeds, for example, since triggering depends only on the predetermined number of pulses, which in turn are reached at an earlier or later point in time depending on the web speed. This means that the sensor 140 can, for example, take into account different material web speeds during start-up, stop-up, or even within a work process, and thus adjust the (times of the) first and second images taken by the camera 110 accordingly. The number of pulses to be waited for in each case can be determined, for example, depending on the properties and resolution of the matrix sensor 20 used.

[0063] For triggering, for example, the above-mentioned control unit or a control device can be used, which receives information from the sensor 140 to send a trigger signal for the first and second recordings to the camera 110. The control unit or control device can be provided as an external device. However, it is also possible for such a device or control logic to be built directly into the camera 110. Thus, for example, the sensor 140 can be connected directly to the control device or to the camera 110.

[0064] In addition to the Fig. 1In addition to the embodiment shown with a camera 110, it is also possible to equip the device 100 with a plurality of cameras with a matrix chip 20, wherein the cameras are then arranged distributed across the material web width so that the fields of view of the cameras adjoin or overlap one another in the direction of the material web width x. The plurality of cameras then creates corresponding first and second images, wherein the first and second images are combined to form two contiguous image sequences. If multiple cameras are used, they can be arranged traversing relative to the direction of the material web width x. In addition, mechanical offsets of the cameras in the direction of the material web length y can be compensated for by a corresponding selection of active partial areas of the matrix chips 20.

[0065] It can also be provided that at least one camera 110 is arranged on a front side of the material web 10 and at least one camera is arranged on a back side of the material web 10, each of which takes first and second images of the front and back of the material web 10. This enables the observation or inspection of both sides of the material web.

Claims

1. Method for compensating for a material web offset in inspection systems for material webs which are moving in the direction of a material web length (y) and / or a material web width (x), wherein the method comprises the following steps: taking a first picture of a first portion of a material web (10) at a first point in time with a camera (110) which comprises a matrix chip (20); and taking a second picture of a second portion of the material web (10) at a second point in time with the camera (110); wherein just a first active partial surface (22) of the matrix chip (20) is activated at the first point in time for the first picture and just a second active partial surface (24) of the matrix chip (20) is activated at the second point in time for the second picture, wherein the first active partial surface and the second active partial surface are not identical; wherein the second active partial surface (24) is offset in comparison with the first active partial surface (22) by a prescribed offset in the direction of the material web length (y) and / or in the direction of the material web width (x); and wherein a time lag between the first and the second picture is either prescribed as a fixed amount of time or adjusted according to the material web movement and is dependent on a first trigger, which triggers the first picture at the first point in time, and a second trigger, which triggers the second picture at the second point in time.

2. Method according to Claim 1, characterized in that a size and / or a position of the first and second active partial surfaces (22, 24) of the matrix chip (20) and thereby the field of view of the camera (110) in the direction of the material web length (y) and / or in the direction of the material web width (x) can be dynamically adjusted.

3. Method according to Claim 1 or Claim 2, <b>characterized in that the first portion and the second portion are two identical material web portions; or in that the first portion and the second portion are two different material web portions.

4. Method according to any one of the preceding claims, characterized in that the first picture is part of a first sequence of pictures of the material web (10) and the second picture is part of a second sequence of pictures of the material web (10), in particular wherein a first sequence is created with a plurality of first pictures in order to produce the first sequence of pictures of the material web (10) and a second sequence is created with a plurality of second pictures in order to produce the second sequence of pictures of the material web (10).

5. Method according to any one of the preceding claims, characterized in that the material web (10) is illuminated with a first type of lighting for the first and second pictures; or in that the material web (10) is illuminated with a first type of lighting for the first picture and the material web (10) is illuminated with a second type of lighting for the second picture.

6. Method according to Claim 5, characterized by the taking of further pictures of corresponding further portions at corresponding further points in time using corresponding further active partial surfaces of the matrix chip, wherein the further portions are identical to the first portion and / or the second portion, and optionally wherein further types of lighting are used for illuminating the material web (10) for the further pictures.

7. Method according to any one of the preceding claims, characterized in that a field of view of the camera (110) is designed to cover at least the entire width of the material web, in particular wherein the field of view of the camera (110) in the direction of the material web width (x) is greater than the material web width; optionally wherein the first and second active partial surfaces (22, 24) are set on the basis of a signal from a material web position sensor, in particular a size and / or a position of the first and second active partial surfaces (22, 24) in the direction of the material web width (x) is set.

8. Device for observing and / or inspecting material webs which are moving in the direction of a material web length (y) and / or a material web width (x), comprising: a camera (110) which comprises a matrix chip (20), wherein partial surfaces of the matrix chip (20) can be activated independently of one another; and a control unit; wherein the control unit is designed to cause just a first partial surface (22) of the matrix chip (20) to be activated in order to take a first picture of a first portion of the material web (10) at a first point in time; just a second partial surface (24) of the matrix chip (20) to be activated in order to take a second picture of a second portion of the material web (10) at a second point in time; wherein the first active partial surface (22) and the second active partial surface (24) are not identical; wherein the control unit is designed to select the first and second active partial surfaces (22, 24) such that the second active partial surface (24) is offset in comparison with the first active partial surface (22) by a prescribed offset in the direction of the material web length (y) and / or in the direction of the material web width (x); and wherein a time lag between the first and the second picture is either prescribed as a fixed amount of time or adjusted according to the material web movement and is dependent on a first trigger, which triggers the first picture at the first point in time, and a second trigger, which triggers the second picture at the second point in time.

9. Device according to Claim 8, characterized in that a size and / or a position of the first and second active partial surfaces (22, 24) of the matrix chip (20) and thereby the field of view of the camera (110) in the direction of the material web length (y) and / or in the direction of the material web width (x) can be dynamically adjusted.

10. Device according to Claim 8 or Claim 9, <b>characterized in that the first portion and the second portion are two identical material web portions; or in that the first portion and the second portion are two different material web portions.

11. Device according to any one of Claims 8 to 10, characterized in that the device (100) has a first lighting device (120, 130), so that the material web (10) can be illuminated with a first type of lighting for the first and second pictures; or in that the device (100) has first and second lighting devices (120, 130), so that a first type of lighting can be used for the first picture of the material web (10) and a second type of lighting can be used for the second picture of the material web (10).

12. Device according to Claim 11, characterized in that the control unit is designed to cause a first picture to be respectively taken with the first type of lighting and a second picture to be respectively taken with the second type of lighting of a plurality of portions of the material web (10) following one another in the direction of the material web length (y), wherein the first pictures together produce a first sequence of pictures of the material web (10) and the second pictures produce a second sequence of pictures of the material web (10).

13. Device according to Claim 11 or Claim 12, characterized in that the control unit is designed to cause further partial surfaces of the matrix chip (20) to be activated in order to take further pictures of corresponding further portions at corresponding further points in time, wherein the further portions are identical to the first portion and / or the second portion, and optionally wherein the device comprises further lighting devices, so that the material web (10) can be illuminated with further types of lighting for the further pictures.

14. Device according to any one of Claims 8 to 13, characterized in that a plurality of cameras with a matrix chip (20) are provided, wherein the cameras are arranged distributed over the material web width, so that the fields of view of the plurality of cameras in the direction of the material web width (x) adjoin one another or overlap, wherein the control unit is designed to cause the plurality of cameras to take corresponding first and second pictures and the first and second pictures to be combined to form two contiguous sequences of pictures.

15. Device according to any one of Claims 8 to 14, characterized in that at least one camera (110) is provided on a front side of the material web (10) and at least one camera is provided on a rear side of the material web (10), wherein the control unit is designed to cause first and second pictures to be respectively taken of the front side and the rear side of the material web (10).