Intelligent synchronization method for web inspection system

Abstract

The invention relates to a method of intelligent synchronization of a web inspection system (30) for monitoring a moving web and comprising a synchronization device (32) and at least one slave camera (31, 33), and at least one illumination device (35, 36) arranged to illuminate an area of the web arranged to be imaged by the camera (31, 32, 33). The method comprises: transmitting a synchronization signal (20) to the at least one slave camera (31, 33), wherein the synchronization signal (20) comprises at least a start pulse (22) and serial data (23) comprising additional information, and wherein all the cameras (31, 32, 33) of the web inspection system (30) are configured to be synchronized with each other based on a synchronization time instant (25) when the integration of the camera (31, 32, 33) ends; transmitting a light synchronization signal (21) to the at least one illumination device (35, 36) indicating the on and off times of the at least one illumination device (35, 36), the off time corresponding to the synchronization time instant (25); and calculating an integration start time based on the individual integration time of a camera (31, 32, 33) and the synchronization time instant (25) which is common for the cameras (31, 32, 33) of the web inspection system (30). The invention additionally relates to a web inspection system (30) and a computer program product causing the system (30) to perform the method.

Description

Technical Field

[0001] The present invention relates to a method for synchronizing cameras of a web inspection system that monitors a moving web of a continuous manufacturing process.

[0002] The invention also relates to a web inspection system and a computer program product for causing a web inspection system to perform the method. Background Art

[0003] In continuous manufacturing processes, material or products are constantly fed into the machine. In such processes, for example, in papermaking machines, the product must be monitored, for example, by a web inspection system, in order to detect possible deviations and achieve a high-quality end product. Such a web inspection system, for example, includes a camera system comprising multiple area scan (array) cameras with a large pixel matrix. These cameras capture a 2D image of a given area in one exposure cycle using horizontal and vertical elements, for example, with 640×480 pixels. In other words, with an area scan camera, the pixel matrix provides an image of the target. As the target moves past the area scan camera system, the camera's area image sensor captures an image of the target and transmits the image to a processing unit for analysis.

[0004] If there is more than one camera in the monitoring system, these cameras need to be synchronized so that they always take individual pictures at exactly the same time. In this way, when the results of adjacent cameras are processed later, the results and images of adjacent cameras can be combined. Due to the camera technology, the switching off of the pulsed light also needs to be precisely synchronized with the end of the camera integration.

[0005] Typically, cameras are synchronized with each other using a simple synchronization signal that defines the camera's image capture time. This type of synchronization is sufficient as long as a fixed frame rate is used. However, when using a simple synchronization signal that only defines the camera's image capture time, the camera does not accurately know the number of images from the other cameras or the distance the web has traveled. Therefore, combining the results with adjacent images later is difficult or nearly impossible. Furthermore, if the pulsed light is not turned off exactly at the same time as the camera integration ends, pixel integration will continue, which can result in poor image quality; for example, the image may be too bright.

[0006] CN204287062U discloses a synchronization method for a web inspection system for monitoring a moving web and comprising a master camera and an illumination device for synchronizing slave cameras. EP3343896A1 discloses a method and system for synchronizing active illumination pulses in a multi-sensor imager. Summary of the Invention

[0007] The present invention aims to provide and demonstrate a novel method for synchronizing a camera and at least one lighting device of a web inspection system for monitoring a moving web of a continuous manufacturing process. Another object is to provide a web inspection system and a computer program product for causing the web inspection system to perform the method. The synchronization method, system, and computer program product according to the present invention are characterized by what is presented in the independent claims, while the dependent claims relate to advantageous embodiments of the invention.

[0008] According to a first aspect, a method for intelligent synchronization of a web inspection system is provided, the web inspection system being for monitoring a moving web and comprising a synchronization device and at least one slave camera, and at least one lighting device arranged to illuminate an area of ​​the web arranged to be imaged by the camera, the method comprising: transmitting, by the synchronization device, a synchronization signal to the at least one slave camera, wherein the synchronization signal comprises at least a start pulse and serial data, the serial data comprising additional information for the at least one slave camera, and wherein all the cameras of the web inspection system are configured to synchronize with each other based on a synchronization pulse indicating a synchronization moment when camera integration ends; transmitting, by the synchronization device, an optical synchronization signal to the at least one lighting device, wherein optical control pulses of the optical synchronization signal indicate switch-on and switch-off times of the at least one lighting device, the switch-off times corresponding to the synchronization moments; and calculating an integration start time based on the individual integration times of the cameras and the synchronization moment that is common to the cameras of the web inspection system.

[0009] According to an example, the method further includes starting integration of the cameras at the calculated integration start time of the cameras and turning on the at least one lighting device for illuminating the area on the web imaged by the cameras; and ending integration of all cameras at the synchronization moment and turning off the at least one lighting device. According to an example, the method further includes reading intensity values ​​from pixels of the cameras measured during the integration and resetting the pixels; forming captured image data based on the read intensity values; and transmitting the captured image data together with the received additional information to an image data processing device. According to an example, the method further includes forming a combined image from the received image data using the received additional information by the image data processing device. According to an example, all cameras of the web inspection system are area scan cameras. According to an example, the synchronization device is a smart camera that is one of the cameras of the web inspection system. According to an example, the synchronization device is an external synchronization device.

[0010] According to a second aspect, a web inspection system for monitoring a moving web is provided, comprising a synchronization device and at least one slave camera, at least one lighting device and an image data processing device, wherein the cameras are synchronized with each other by using the method according to the first aspect and examples thereof.

[0011] According to an example, the at least one slave camera is an area scan camera. According to an example, the cameras of the web inspection system are arranged adjacently in a row. According to an example, the synchronization device is a smart camera of the web inspection system. According to an example, the synchronization device is an external synchronization device. According to an example, the web inspection system further includes an edge marking device.

[0012] According to a third aspect, a computer program product is provided, which is stored on a computer-readable medium and executable in a computing device, wherein the computer program product comprises instructions for a synchronization device of a web inspection system comprising at least one slave camera and at least one lighting device to perform the method according to the first aspect and its examples. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings, in which:

[0014] Figure 1a A web inspection system including adjacent camera groups and lighting devices synchronized with each other using an intelligent synchronization method is shown according to an embodiment of the present invention.

[0015] Figure 1b -e shows the Figure 1a images captured by the web inspection system's camera and a combined image of these images,

[0016] Figure 1f -g shows an image captured by a camera of a web inspection system including adjacent cameras but without using a synchronization method according to an embodiment of the present invention,

[0017] Figure 2 shows an intelligent synchronization signal of an intelligent synchronization method for a web inspection system according to an embodiment of the present invention,

[0018] Figure 3 A web inspection system is shown using an intelligent synchronization method according to an embodiment of the present invention for synchronizing its camera and lighting device, and

[0019] Figure 4 A block diagram illustrating an intelligent synchronization method for a web inspection system according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0020] Several adjacent image sensors are area scan cameras (also known as matrix cameras) used by the web inspection system to monitor a moving web. Each of these adjacent image sensors is arranged to capture an image frame—that is, one image matrix at a time—as the web being inspected moves through the camera's field of view. The captured adjacent images cover approximately the entire width of the web. Each image is captured by exposing a two-dimensional array of photosensitive elements to light focused on the array by lenses for a short period of time (called the integration or shutter time). The array can be referred to as an image, and the individual photosensitive elements can be referred to as pixels. Each pixel measures the intensity of the light falling on it during the integration period. After the integration is complete, the measured intensity value is read, and the pixel is reset, shorted to black level, until the next integration begins. The measured analog intensity value is then converted to digital information for subsequent processing to form the actual captured image. The integration is defined by the behavior of the readout electronics and is independent of the exposure performed by the shutter. The web to be monitored may be, for example, a web material of a paper or board machine or some other kind of machine comprising moving parts to be monitored, such as a printing press comprising moving rollers, or an assembly machine.

[0021] The image data for each captured image can then be transmitted to an image data processing device for processing. The image data processing device can be, for example, a computer, a logic circuit, a digital signal processor (DSP), an image data computer, or any other computing device suitable for processing images of this type. For processing, adjacent images can be combined into a single image having an expanded image field. For this combination, it is important that the images comprising the combined image are captured such that, at the time of capture, the web has traveled the same distance in the direction of travel for all images, so that adjacent images are parallel and aligned with each other and, when combined, form a longitudinal rectangular combined image perpendicular to the direction of travel of the web.

[0022] Simple synchronization pulses, provided by a master camera or an external module, can be used to synchronize adjacent cameras and lighting devices in a web inspection system by indicating a first time point for starting image capture (begin pixel integration) and turning on the lights, and a second time point for ending image capture (end pixel integration) and turning off the lights. The integration time depends on the interval between lighting ons. However, this type of simple start pulse is not sufficient in all situations; for example, it is not sufficient when the capture frequency (frame rate) needs to be changed on the fly. However, it is useful when the camera's image capture frequency is predetermined and remains constant. Furthermore, when this type of simple synchronization pulse is used, the camera does not include information, such as the image sequence number and / or the distance traveled by the web in the direction of movement at the time of image capture, with the captured images. This information is not otherwise available but is required when combining the images. Consequently, combining these images into a single composite image can be difficult, or at least sometimes impossible. Furthermore, the captured images may not be substantially parallel, and if at least one of the images includes an event and a defect map is formed based on these non-parallel images, the defect map cannot be reliably used to locate and / or correct defects in the web.

[0023] Therefore, in the present invention, instead of simple synchronization pulses, an intelligent synchronization method is used to synchronize a web inspection system with more than one adjacent camera. In this intelligent synchronization method, a master camera can be one of the cameras in the web inspection system, used to synchronize the other cameras in the web inspection system, known as slave cameras. At least one lighting device or an external synchronization device can be used to synchronize the cameras and the at least one lighting device in the web inspection system. If an external synchronization device is used for synchronization, all cameras are slave cameras. Regardless of whether the device transmitting the synchronization signal is the master camera or the external device, it can be referred to as a synchronization device.

[0024] The master camera synchronizes the slave cameras by transmitting a synchronization signal to them. Furthermore, in the case of an external synchronization device, this is the external synchronization device that transmits the synchronization signal to the cameras of the web inspection system. The synchronization signal indicates the synchronization time of the cameras. This synchronization time corresponds to the time when the light of at least one lighting device is turned off. The cameras define their integration start point so that their end time is synchronized with the transmitted light-off time. Because integration for all cameras ends and the lights are turned off simultaneously, adjacent images of the web are acquired simultaneously, i.e., synchronously. Furthermore, the synchronization signal may include a serial data field containing additional information that can be used when combining images from adjacent cameras or controlling camera settings. This additional information facilitates the combination of these images, allowing them to be reliably combined for processing, such as analysis and / or defect map generation. In the intelligent synchronization method, to synchronize at least one lighting device of the web inspection system with the camera, the synchronization device transmits an optical synchronization signal to the at least one lighting device. The optical control pulses of the optical synchronization signal indicate the on and off times of the at least one lighting device. The intelligent synchronization method includes transmitting two signals, namely transmitting a synchronization signal to at least two cameras and transmitting an optical synchronization signal to at least one lighting device.

[0025] The web inspection system may also include an edge marking device. A smart camera or an external synchronization unit can be used to control the edge marking device. The edge marking device sprays marks into the edge of the paper web. These marks can be, for example, so-called direction of travel (MD) marks, which are applied to the web at specific intervals. These intervals can be, for example, 25 m, 100 m, or 1000 m, or any other predetermined distance. These marks make it easier to locate defects and correct them. These marks can be visible to the naked eye or invisible, but visible under UV light, and can be dot or line codes, such as some type of binary code.

[0026] Figure 1aA web inspection system 10 is shown, according to one embodiment of the present invention, including a group of cameras 11, 12, 13, 14 and an illumination device 16 that are synchronized using an intelligent synchronization method. The intelligent synchronization method includes transmitting a synchronization signal and an optical synchronization signal. Web inspection system 10 includes four adjacent cameras 11, 12, 13, 14. Illumination device 16 is configured to illuminate the field of view of cameras 11, 12, 13, 14 on a web 15 being inspected. All cameras 11, 12, 13, 14 are area scan cameras that view different portions of the web. One of the cameras, in this embodiment, camera 11, is the master camera, while the other cameras 12, 13, 14 are slave cameras. The integration time of each camera 11, 12, 13, 14 is either predetermined or automatically controlled / adjusted based on the intensity of its previously captured image. This intensity can change, for example, due to lens contamination or changes in the monitoring target.

[0027] The master camera 11 synchronizes the slave cameras 12, 13, 14 by transmitting a synchronization signal to the slave cameras 12, 13, 14. The synchronization signal includes a start pulse. The synchronization signal indicates to the cameras 12, 13, 14 that the capture should be terminated. Figure 1b The synchronization moment for the integration of images 11', 12', 13', and 14' shown in FIG. This synchronization moment can be, for example, the trailing edge or rising edge of a start pulse. Based on this integration end time and their own integration time, the slave cameras 12, 13, and 14 and the master camera 11 calculate their own integration start times.

[0028] The main camera 11 further synchronizes the lighting device 16 via an optical synchronization signal, which indicates the on and off times of the lighting device 16 via an optical control pulse. In this embodiment, the on time is indicated by the rising edge of the optical control pulse. The lighting device 16 is turned on before integration of any of the cameras 11, 12, 13, and 14 begins. In this embodiment, the off time is indicated by the trailing edge of the optical control pulse, and this off time defines the time when the lighting device 16 is turned off and corresponds to the synchronization time of the cameras 11, 12, 13, and 14. If more than one lighting device is present, the main camera 11 synchronizes all lighting devices via the optical synchronization signal, so that all lighting devices are turned off at the defined synchronization time.

[0029] The web inspection system 10 further includes an edge marking device 18 for marking the edge of the web 15 at certain predetermined intervals, but the edge marking device 18 is an optional device in the web inspection system 10 .

[0030] The transmitted synchronization signal also includes serial data. The serial data field may include additional information for the slave cameras 12, 13, 14. This additional information may be used to combine the images or may be some other type of information, such as for controlling camera settings. Figure 2 Smart synchronization signals and optical synchronization signals are explained more precisely in the context of .

[0031] However, there may be embodiments in which line cameras are used instead of area scan cameras. In addition, it is also possible that all cameras 11, 12, 13, 14 are so-called slave cameras and an external synchronization unit is used to transmit synchronization signals to all cameras and transmit optical synchronization signals to the lighting device 16.

[0032] Figure 1b Shown correspondingly by Figure 1a 1 ', 12', 13', 14' captured by cameras 11, 12, 13, 14 of web inspection system 10. As explained above, the capturing of images 11', 12', 13', 14' is synchronized by an intelligent synchronization signal, and therefore images 11', 12', 13', 14' are parallel and taken at the same distance from the beginning of web 15 in the direction of travel. As can be seen, there are no defects or correspondences in any of images 11', 12', 13', 14'.

[0033] Figure 1c Shown by Figure 1b The combined image 17' is formed by the images 11', 12', 13', and 14'. Furthermore, because the images 11', 12', 13', and 14' are parallel and aligned, all their information is contained in the combined image 17'. The images 11', 12', 13', and 14' are successfully combined based on the orientation information transmitted by the synchronization signal.

[0034] Figure 1d Shown correspondingly by Figure 1a The images 11'', 12'', 13'', 14'' captured by the cameras 11, 12, 13, 14 of the web inspection system 10. As described above in Figure 1a As explained in the context of , the capture of images 11 ″, 12 ″, 13 ″, 14 ″ is also synchronized using an intelligent synchronization signal, and therefore the images 11 ″, 12 ″, 13 ″, 14 ″ are also parallel and aligned transversely to the direction of movement of the web 15 . As can be seen, a defect A is present in the border region of the images 11 ″ and 12 ″. The defect A is positioned such that a first portion of the defect A is in the image 11 ″ and a second portion is in the image 12 ″. The defect A is therefore a single error distributed over the region of two adjacent images 11 ″, 12 ″.

[0035] Figure 1e Shown by Figure 1dThe combined image 17" is formed by the images 11", 12", 13", 14". And, because the images 11", 12", 13", 14" are parallel and aligned, all their information is correctly contained in the combined image 17" and the defect A is correctly shown in the correct position, i.e. as a single defect.

[0036] Figure 1f Shown correspondingly by Figure 1a The cameras 11, 12, 13, 14 of the web inspection system 10 capture images 11'', 12''', 13''', 14'''. However, these images 11''', 12''', 13''', 14''' are not captured using an intelligent synchronization method and its synchronization signal, but rather using a simple synchronization signal. The image capture frequency of the cameras 11, 12, 13, 14 is also different, i.e., it is not the same and is not predetermined for the cameras 11, 12, 13, 14. Thus, also at the same time, adjacent images 11''', 12''', 13''', 14''' are captured synchronously, but because the simple synchronization signal does not send orientation information or other information suitable for use in the combination stage of the cameras 11, 12, 13, 14, 11''', 12''', 13''', 14''' are mixed, and one of the images 12''' is misplaced in the combination stage and ends up in a different combined image than the other images 11''', 13''', 14''', e.g. Figure 1g The other images 11''', 13''', 14''' are in the combined image 17'''a and the misplaced image 12''' is in the combined image 17'''b. The cameras 11 and 12 capture the same defect A as Figure 1d , but now the first and second parts of defect A are in two different combined images 17'''a and 17'''b. And, if a defect map is formed based on these combined images 17'''a and 17'''b and an attempt is made to correct defect A of the web 15 based on the defect map, the correction will not be successful because defect A is not correctly indicated in that defect map. However, if a defect map is formed based on image 1e and an attempt is made to correct defect A based on that defect map, the correction will be successful because defect A is correctly indicated in that defect map and is in the correct position.

[0037] Figure 2 The synchronization signal of a web inspection system according to an intelligent synchronization method according to an embodiment of the present invention is shown. The synchronization signal shown above is transmitted by a synchronization device, for example, a synchronization signal 20 transmitted by a master camera to a slave camera. The purpose of the synchronization signal 20 is to synchronize all cameras with each other to capture images synchronously so that image integration is completed at the same time, and also to provide additional information added to the image.

[0038] The synchronization signal 20 consists of a start pulse 22, serial data 23, and a pause 24 therebetween. The synchronization moment 25, when all cameras complete integration and the lights are turned off, is the trailing edge (i.e., the falling edge) of the start pulse 22. In other words, the start pulse 22 contains information indicating the synchronization moment 25 to the slave cameras. However, the leading edge (i.e., the rising edge) of the start pulse 22, rather than the trailing edge, may indicate the synchronization moment 25. Each camera calculates its own integration start time, i.e., the point in time at which integration begins from the synchronization moment 25 common to all cameras, based on its own integration time. The length of the start pulse 22 can be, for example, 30-80 µs, for example, 50 µs. For example, if the start pulse 22 indicates that the synchronization moment 25 is 50 µs later (i.e., the length of the pulse 22 is 50 µs), and the integration time of the first camera is 20 µs, then the first camera starts integrating 30 µs after the start pulse 22 (i.e., 20 µs before the synchronization moment 25), and if the integration time of the second camera is 15 µs, then the second camera starts integrating 35 µs after the start pulse 22 (i.e., 15 µs before the synchronization moment 25).

[0039] After the start pulse 22 ends and before the serial data 23, there is a pause 24. The length of pause 24 can be several µs, for example, 2-10 µs. Serial data 23 includes additional information for the slave camera. This information may include, for example, the precise end time of the next light pulse (i.e., the next synchronization moment), an illumination profile number to be used when capturing the next image, position information at the time of the next synchronization moment 25, the image number for the next image, a skip next image flag, some special data, a checksum, and so on. A suitable bit rate for the data field of serial data 23 may be, for example, approximately 1 Mbit / s. The camera may add this additional information along with the captured image data when it is transmitted to an image data processing device, and / or the camera may use this additional information to control its own settings or operation.

[0040] Shown below the smart synchronization signal 20 is a light synchronization signal 21 transmitted to the web inspection system's lighting device, which is also arranged to illuminate the imaged area of ​​the web via the main camera. Light synchronization signal 21 uses light control pulses 26 to indicate when the lighting device's light should be turned on and off. The trailing edge of light control pulse 26 indicates to the lighting device when it should be turned off, and this time corresponds to synchronization instant 25 of the smart synchronization signal 20. Thus, the lighting device switches on and off in synchronization with the time when the cameras end integration. The rising edge of light control pulse 26 indicates to the lighting device when it should be turned on, and this time is before any of the cameras are configured to begin integration. Alternatively, the trailing edge of light control pulse 26 indicates to the lighting device when it should be turned on, and the rising edge of light control pulse 26 indicates to the lighting device when it should be turned off.

[0041] Figure 3 A web inspection system 30 is shown synchronizing its cameras 31, 32, 33 and lighting devices 35, 36 using an intelligent synchronization method according to an embodiment of the present invention. The web inspection system 30 includes a group of three cameras 31, 32, 33, two lighting devices 35, 36, and image data processing devices 31', 32', 33' for each camera 31, 32, 33. However, the image data processing devices may be common to one or more cameras. The cameras 31, 32, 33 are arranged adjacently (i.e., side by side) in a row to expose image frames, i.e., capture a matrix of images from the web across the entire width of the web, such that adjacent images together cover an area across the entire width of the corresponding web. One of the cameras 32 is a master camera configured to act as a synchronization device, and the remaining cameras 31, 33 are slave cameras.

[0042] The lighting devices 35, 36 are arranged to illuminate areas on the web that are arranged to be imaged by the cameras 31, 32, 33. The lighting devices 35, 36 are switched off and on by a light synchronization signal 38 transmitted by the main camera 32. Figure 2 The optical synchronization signal 38 is explained in the context of FIG.

[0043] The cameras 31, 32, 33 are arranged to capture images at synchronization moments indicated by a single common smart synchronization signal 37. At the same synchronization moment, the lighting devices 35, 36 are switched off. The master camera 32 transmits the smart synchronization signal 37 to the cameras 31, 33. The smart synchronization signal 37 also includes serial data, which includes additional information for the slave cameras 31, 33. Figure 2The type of additional information will be explained more precisely in the context of [ ]. Cameras 31, 32, 33 can use the received additional information to adjust their settings for the next image capture. For example, cameras 31, 32, 33 may receive an illumination profile number, which is arranged to be used as additional information when capturing the next image, and may adjust their parameters based on this information. Their parameters may be predefined for each illumination profile number. Furthermore, after capturing an image, cameras 31, 32, 33 may add the received additional information to the context of the captured image data. For example, if cameras 31, 32, 33 receive the time of the synchronization moment, the number of the next image, and / or the position along the direction of movement at the synchronization moment as additional information, this information may be added to the captured image data. Thereafter, cameras 31, 32, 33 are arranged to transmit the captured image data, along with the additional information, to their image data processing devices 31', 32', 33' for processing, analysis, etc.

[0044] The image data processing devices 31', 32', and 33' can be external devices. They include at least one processor, at least one memory containing computer program code for one or more program elements, and means for receiving image data and additional data wirelessly or via a wired connection, such as a receiver for receiving data wirelessly or via a wired connection. Multiple processors (e.g., general-purpose processors, graphics processors, and DSP processors), field-programmable gate arrays (FPGAs), and / or multiple different memories can be present, such as volatile memory for runtime data and program storage and non-volatile memory, such as a hard disk, for permanent data and program storage. The image data processing devices 31', 32', and 33' can be any computing device suitable for processing image data, such as a computer. The image data processing devices 31', 32', and 33' can electronically communicate with the cameras 31, 32, and 33, respectively, via signal lines. To process signals sent to and from the signal lines, the image data processing device 32 includes I / O circuitry. The connection between the cameras 31, 32, 33 and the image data processing devices 31', 32', 33' can be a wired or wireless network. The image data processing devices 31', 32', 33' can also include a video controller and an audio controller that generate signals that can be transmitted to the user via the computer accessories. The simulator can generate outputs that are transmitted to the user via an output device. The video controller can be connected to a display. The display can be, for example, a flat-panel display or a projector for producing a larger image. The audio controller can be connected to a sound source, such as a speaker or headphones.

[0045] One of the image data processing devices 31', 32', 33' can combine adjacent images into a combined image based on additional information received in the context of the captured image data. The image data processing device 31', 32', 33' can also analyze the combined image to detect defects or other events. Additionally, the image data processing device 31', 32', 33' or an external computing device can create a defect map based on the captured images and the combined image, indicating the location of defects in the web relative to the distance traveled by the web. This makes correction of those defects easier because the distance of the defects from the beginning of the web can be accurately displayed. The defect map can be stored in a database and displayed.

[0046] The image data processing device 31 ′, 32 ′, 33 ′ may also be part of the camera 31 , 32 , 33 .

[0047] Cameras 31, 32, 33 form a first camera row. If there is more than one camera row, i.e., at least one other camera row including at least one slave camera, then the same master camera 32 can be used to transmit the smart synchronization signal for those slave cameras, or each row can include its own master camera that can be used to transmit the smart synchronization signal for the slave cameras in its own camera row. The first camera row can also include more than the three cameras 31, 32, 33 shown, as well as other possible camera rows. The number of cameras in a row can depend on the width of the web and / or the field of view of the cameras used.

[0048] The web inspection system 30 further includes an edge marking device 34 for marking the edge of the web at specific predetermined intervals, but the edge marking device 34 is also an optional device in the web inspection system 30 .

[0049] Figure 4 An embodiment of the present invention is shown, in which a block diagram of a synchronization method 40 for a web inspection system is disclosed. The web inspection system is configured to monitor a moving web and includes a synchronization device and at least one slave camera. The at least one lighting device is arranged to illuminate an area of ​​the web, the area being imaged by the camera. In step 41, a synchronization signal is transmitted by the synchronization device to the at least one slave camera, wherein the synchronization signal includes at least a start pulse and serial data, the serial data including additional information for the at least one slave camera, and wherein all cameras of the web inspection system are configured to synchronize with each other based on a synchronization pulse indicating a synchronization moment when camera integration ends. In step 41, an optical synchronization signal is transmitted by the synchronization device to the at least one lighting device, wherein optical control pulses of the optical synchronization signal indicate on and off times for the at least one lighting device, the off time corresponding to the synchronization moment. Furthermore, in step 43, an integration start time is calculated based on the individual integration times of the cameras and a common synchronization moment for all cameras of the web inspection system.

[0050] Various embodiments of the present invention may be implemented with the aid of computer program code residing in a memory and causing an apparatus to perform the invention. For example, the apparatus is a computing device, such as an image data processing device, which may include circuitry and electronics for analyzing, receiving, and transmitting data, computer program code residing in a memory, and a processor that, when executing the computer program code, causes the apparatus to perform the features of the embodiments. A processor, when executing computer program code, causes a web inspection system to perform all steps of the following method, the web inspection system comprising a synchronization device and at least one slave camera, and at least one lighting device arranged to illuminate an area of ​​the web arranged to be imaged by the camera, the steps comprising: transmitting, by the synchronization device, a synchronization signal to the at least one slave camera, wherein the synchronization signal comprises at least a start pulse and serial data, the serial data comprising additional information for the at least one slave camera, and wherein all the cameras of the web inspection system are configured to synchronize with each other based on a synchronization pulse indicating a synchronization moment when camera integration ends; transmitting, by the synchronization device, an optical synchronization signal to the at least one lighting device, wherein optical control pulses of the optical synchronization signal indicate on and off times of the at least one lighting device, the off times corresponding to the synchronization moments; and calculating an integration start time based on individual camera integration times and the synchronization moment common to the cameras of the web inspection system.

[0051] The present invention offers numerous advantages over existing methods and systems for web inspection systems comprising at least two area scan cameras. The arrangement according to the present invention makes it possible to synchronize the area scan cameras using an intelligent synchronization method, wherein an intelligent synchronization signal is transmitted by a master camera (one of the cameras in the web inspection system) to the other cameras in the web inspection system, the other cameras being slave cameras. Furthermore, the intelligent synchronization signal according to the present invention makes it possible to transmit additional information to the slave cameras and utilize this additional information not only for image capture but also when analyzing the captured image data. In the intelligent synchronization method, the lighting of the web inspection system can also be controlled by the optical synchronization signal to achieve the best possible imaging results.

[0052] It is obvious that the invention is not limited only to the embodiments presented above, but it can be modified within the scope of the appended claims.

Claims

1. A method for intelligent synchronization of a web inspection system (30) for monitoring a moving web and comprising a master camera (32) and at least one slave camera (31, 33) configured to act as synchronization means, and at least one lighting device (35, 36) arranged to illuminate an area of ​​the web arranged to be imaged, the method comprising: a synchronization signal (20) is transmitted to the at least one slave camera (31, 33) by the synchronization device (32), characterized in that the synchronization signal (20) comprises at least a start pulse (22) and serial data (23), the serial data comprising additional information for the at least one slave camera (31, 33), the additional information being configured to combine images of adjacent cameras and wherein all the cameras (31, 32, 33) of the web inspection system (30) are configured to synchronize with each other based on the start pulse (22), the start pulse indicating a synchronization moment (25) when integration of the cameras (31, 32, 33) is ended, An optical synchronization signal (21) is transmitted to the at least one lighting device (35, 36) via the synchronization device (32), wherein the optical control pulse (26) of the optical synchronization signal (21) indicates the on and off times of the at least one lighting device (35, 36), the off time corresponding to the synchronization moment (25), and An integration start time is calculated based on the individual integration times of the cameras (31, 32, 33) and the synchronization moment (25) which is common to the cameras (31, 32, 33) of the web inspection system (30).

2. The smart synchronization method according to claim 1, wherein the method further comprises: starting integration of the cameras (31, 32, 33) at their calculated integration start times and switching on the at least one lighting device (35, 36) for illuminating the area on the web imaged by the cameras (31, 32, 33), and At the synchronization point in time (25), the integration of all cameras (31, 32, 33) is terminated and the at least one lighting device (35, 36) is switched off.

3. The smart synchronization method according to claim 2, wherein the method further comprises: Read the intensity values ​​from the pixels of the cameras (31, 32, 33) measured during the integration and reset the pixels, forming captured image data based on the read intensity values, and The captured image data are transmitted together with the received additional information to an image data processing device (31', 32', 33').

4. The smart synchronization method according to claim 3, wherein the method further comprises: A combined image is formed from the received image data by the image data processing means (31', 32', 33') using the received additional information.

5. The intelligent synchronization method of claim 1, wherein all cameras (31, 32, 33) of the web inspection system (30) are area scan cameras.

6. A web inspection system for monitoring a moving web and comprising a master camera (32) and at least one slave camera (31, 33) as synchronization devices, at least one lighting device (35, 36) and image data processing devices (31', 32', 33'), wherein the cameras (31, 32, 33) are synchronized with each other by using the method according to any one of claims 1 to 5.

7. The web inspection system of claim 6, wherein the at least one slave camera (31, 33) is an area scan camera.

8. The web inspection system according to claim 6 or 7, wherein the cameras (31, 32, 33) of the web inspection system (30) are arranged adjacently in a row.

9. The web inspection system according to claim 6 or 7, wherein the web inspection system (30) further comprises an edge marking device (34).

10. A computer program product stored on a computer-readable medium and executable in a computing device, wherein the computer program product comprises instructions for causing a master camera (32) acting as a synchronization device of a web inspection system (30), comprising at least one slave camera (31, 33) and at least one lighting device (35, 36), to perform the method according to any one of claims 1 to 5.

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