A smart synchronization method for web inspection systems

Abstract

The present invention relates to a smart synchronization method for a web inspection system (30) for monitoring a moving web, the web inspection system (30) 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 cameras (31, 32, 33). The method includes transmitting a synchronization signal (20) to at least one slave camera (31, 33), the synchronization signal (20) including at least a start pulse (22) and serial data (23) including additional information, and all cameras (31, 32, 33) of the web inspection system (30) are configured to synchronize with each other based on a synchronization moment (25) when integration of the cameras (31, 32, 33) ends; transmitting an optical synchronization signal (21) to the at least one lighting device (35, 36) indicating on and off time switching of the at least one lighting device (35, 36), the off switch time corresponding to the synchronization moment (25); and calculating a start time of integration based on the individual integration times of the cameras (31, 32, 33) and the synchronization moment (25) common to the cameras (31, 32, 33) of the web inspection system (30). The present invention further relates to a web inspection system (30) and a computer program product for causing the system (30) to perform the method.

Description

[Technical field]

[0001] Technical Field The present invention relates to a method for synchronizing cameras in a web inspection system that monitors a moving web in 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 technology]

[0003] background In a continuous manufacturing process, there is a material or product that is constantly running through the machine. In such a process, for example a paper machine, the product must be monitored by a web inspection system, for example a camera system, to detect possible deviations and obtain a high quality final product. The camera system is a camera system with multiple area scan (array) cameras that contain a large matrix of pixels, for example an area scan camera with one matrix of horizontal and vertical elements or pixels of 640x480 pixels providing one image of the monitored object, capturing a 2D image of a given area in one exposure cycle. As the monitored object passes through the area scan camera system, its image is exposed by the area image sensor of the camera and transferred to a processing unit for analysis.

[0004] If there are two or more cameras in a surveillance system, they must be synchronized in such a way that they always take pictures of the subject at exactly the same time and can combine the image with the results of adjacent cameras when the results are processed later. Depending on the camera technology, the switching off of the pulsed light must also be precisely synchronized with the end of the camera's integration.

[0005] Usually, the cameras are synchronized with each other by a simple synchronization signal that defines the image capture time of the cameras. This kind of synchronization is provided well if a fixed frame rate is used. However, when a simple synchronization signal that only defines the image capture time of the cameras is used, the cameras do not know exactly the image number of the other cameras or the distance the web has traveled, making it difficult or nearly impossible to combine the results with adjacent images in a post-process. Furthermore, if the pulsed light is not switched off exactly at the same time as the integration of the cameras ends, the integration of the pixels may continue, resulting in poor image quality, for example the image may become too bright. Summary of the Invention

[0006] overview It is an object of the present invention to provide and present a novel method for synchronizing a camera and at least one lighting device of a web inspection system monitoring a moving web of a continuous production process. A further object is to provide a web inspection system and a computer program product for causing the web inspection system to execute the method. The synchronization method, system and computer program product according to the invention are characterized in what is presented in the independent claims, the dependent claims relate to advantageous embodiments of the invention.

[0007] According to a first aspect, there is provided a smart synchronization method for a web inspection system comprising a synchronization device and at least one slave camera for monitoring a moving web and at least one lighting device arranged to illuminate an area of ​​the web arranged to be imaged by the cameras, the smart synchronization method comprising: transmitting a synchronization signal by the synchronization device to the at least one slave camera, the synchronization signal comprising serial data including at least one start pulse and additional information for the at least one slave camera, all cameras of the web inspection system being configured to synchronize with each other based on a synchronization pulse indicating a synchronization moment when integration of the cameras ends; transmitting an optical synchronization signal by the synchronization device to the at least one lighting device, the optical control pulses of the synchronization signal indicating the on and off switch times of the at least one lighting device, the off switch time corresponding to the synchronization moment; and calculating a start time of integration based on individual integration times of the cameras and a synchronization moment common to the cameras of the web inspection system.

[0008] According to an embodiment, the method further comprises starting the integration of the cameras at their calculated integration start times and switching on at least one lighting device to illuminate the area on the web imaged by the cameras, and terminating the integration of all cameras and switching off at least one lighting device at the instant of the synchronization moment. According to an embodiment, the method further comprises reading intensity values ​​measured during integration from the pixels of the cameras 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 embodiment, the method further comprises forming a composite image from the received image data using the received additional information by the image data processing device. According to an embodiment, all the cameras of the web inspection system are area scan cameras. According to an embodiment, the synchronization device is a smart camera that is one of the cameras of the web inspection system. According to an embodiment, the synchronization device is an external synchronization device.

[0009] According to a second aspect, there is provided a web inspection system for monitoring a moving web comprising a synchronization device and at least one slave camera, at least one lighting device and an image data processing device, the cameras being synchronized with each other by using the method according to the first aspect and its embodiments.

[0010] According to one embodiment, at least one slave camera is an area scan camera. According to one embodiment, the cameras of the web inspection system are arranged adjacent to one another in a row. According to one embodiment, the synchronization device is a smart camera of the web inspection system. According to one embodiment, the synchronization device is an external synchronization device. According to one embodiment, the web inspection system further comprises an edge marking device.

[0011] According to a third aspect, there is provided a computer program product stored on a computer readable medium and executable within a computing device, the computer program product comprising 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 examples thereof. [Brief description of the drawings]

[0012] BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in more detail with reference to the accompanying drawings. [Figure 1a] 1 illustrates a web inspection system comprising a group of adjacent cameras and lighting devices that are synchronized with each other by using a smart synchronization method according to an embodiment of the present invention. [Figure 1b-e] 1 shows images captured by a camera of the web inspection system of FIG. 1a and a composite image of these images. [Figure 1f-g] 1 illustrates images captured by cameras of a web inspection system with adjacent cameras but without using a synchronization method according to an embodiment of the present invention. [Diagram 2] 4 illustrates a smart synchronization signal of a smart synchronization method for a web inspection system in accordance with an embodiment of the present invention. [Diagram 3] 1 illustrates a web inspection system that uses a smart synchronization method for synchronizing cameras and lighting devices of the system, according to an embodiment of the invention. [Figure 4] FIG. 2 illustrates a block diagram of a smart synchronization method for a web inspection system according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Detailed Description A number of adjacent image sensors, area scan cameras also called matrix cameras in web inspection systems, monitor the moving web and are positioned so that each of them captures images in one image frame, i.e., one image matrix at a time, as the inspected web moves through the camera's field of view. The captured adjacent images cover substantially 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 a lens for a short period of time called the integration or shutter time. The array may be called an image and the individual photosensitive elements may be called pixels. Each pixel measures the intensity of the light that falls on it during the integration. After the integration is finished, the measured intensity value is read and the pixel is reset, i.e., shorted to a black level until the next integration begins. The measured analog intensity value is then converted to digital information, which is then processed to form the actual captured image. The integration is delimited by the operation of the readout electronics and does not depend on the exposure by the shutter. The web being monitored may be, for example, a web-like material in a paper or corrugated machine, or some other type of machine with moving parts being monitored, such as a printing machine with moving rolls, or an assembly machine.

[0014] The image data of each captured image can then be sent 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), or an image data computer, or any other computing device suitable for processing this type of image. For processing, adjacent images can be combined into a single image with an enlarged image field, but for this combination, it is important that the images to be combined are captured such that in all images, the web has traveled the same distance in the direction of movement at the moment of capture, so that adjacent images are aligned parallel to each other and, when combined, form a longitudinal rectangular composite image perpendicular to the direction of web movement.

[0015] A simple synchronization pulse provided by the master camera or an external module may be used to synchronize adjacent cameras and lighting devices of a web inspection system with each other by indicating a first time point to start image capture (start pixel integration) and switch on the lighting, and a second time point to end image capture (end pixel integration) and switch off the lighting. The integration time depends on the time interval for which the lighting device is switched on. However, this kind of simple start pulse is not sufficient in various situations, for example when there is a need to change the capture frequency (frame rate) on the fly, but it can work when the image capture frequency of the camera is predetermined and remains the same. Furthermore, when using this kind of simple synchronization pulse, the camera does not add information about the captured image, for example related to the image sequence number and / or related to the distance traveled by the web in the direction of movement at the moment of image capture, even though such information is needed when the images are combined, or otherwise such information is not available. Therefore, it is very difficult, or at least sometimes impossible, to combine these images into a single combined image. Furthermore, the captured images may not be substantially parallel, and if an event is constituted by at least one of the images 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.

[0016] Therefore, in the present invention, instead of a simple synchronization pulse, a smart synchronization method is used to synchronize a web inspection system having two or more adjacent cameras. In the smart synchronization method, a master camera, which may be one of the cameras of the web inspection system, is used to synchronize the other cameras of the web inspection system, so-called slave cameras, and at least one lighting device or an external synchronization device may be used to synchronize the cameras of the web inspection system and at least one lighting device. If an external synchronization device is used for synchronization, all cameras are slave cameras. The device that sends the synchronization signal may be called a synchronization device, whether it is a master camera or an external device.

[0017] The master camera synchronizes the slave cameras by sending them a synchronization signal. And, in case of using an external synchronization device, it is the external synchronization device that sends the synchronization signal to the cameras of the web inspection system. The synchronization signal indicates a synchronization moment for the cameras. The synchronization moment corresponds to the switch-off time of the illumination of at least one lighting device. The cameras define the start of their integration to end in unison with the transmitted switch-off time of the illumination, and since the integration of all cameras ends in unison and the illumination is also switched off in unison, adjacent images of the web are taken at the same time, i.e. in unison. Furthermore, the synchronization signal may include a serial data field containing additional information to be transmitted that can be used when combining images of adjacent cameras or controlling camera settings. This additional information can ensure that the images are combined with each other to facilitate the combination of these images, e.g. for processing steps to analyze and / or form a defect map. In the smart synchronization method, in order to synchronize at least one lighting device of the web inspection system with the cameras, the synchronization device sends an optical synchronization signal to at least one lighting device. The optical control pulses of the optical synchronization signal indicate the on and off switch-off times of the at least one lighting device. The smart synchronization method includes transmitting both a synchronization signal to at least two cameras and a light synchronization signal to at least one lighting device.

[0018] The web inspection system may further comprise an edge marking device. A smart camera or an external synchronization unit may be used to control the edge marking device. The edge marking device sprays a marking on the edge area of ​​the paper web. The marking may for example be a so-called moving direction (MD) marking, which is sprayed on the web at regular intervals. The intervals may for example be 25 m, 100 m or 1000 m, or any other pre-determined distance. Based on the marking, defects are then more easily located for correction. The marking may be visible to the eye or invisible to the eye but visible to ultraviolet light, may be a dot or line code, or may for example be a binary code of a certain type.

[0019] FIG. 1a shows a web inspection system 10 with a group of cameras 11, 12, 13, 14 synchronized with each other by using a smart synchronization method according to an embodiment of the present invention, and a lighting device 16. The smart synchronization method includes transmitting a synchronization signal and an optical synchronization signal. The web inspection system 10 comprises four adjacent cameras 11, 12, 13, 14. The lighting device 16 is configured to illuminate the field of view of the cameras 11, 12, 13, 14 on the web 15 to be inspected. All the cameras 11, 12, 13, 14 are area scan cameras looking at different parts of the web. One of the cameras, the camera 11 in this embodiment, is a master camera, and the other cameras 12, 13, 14 are slave cameras. Each camera 11, 12, 13, 14 has its own integration time, which is either predetermined or automatically controlled / adjusted based on the intensity of a previously captured image. The intensity may change, for example, due to a dirty lens or a change in the monitored object.

[0020] The master camera 11 synchronizes the slave cameras 12, 13, 14 by sending them a synchronization signal. The synchronization signal comprises a start pulse. It indicates to the cameras 12, 13, 14 the time which is the synchronization moment at which they should end their integration in order to capture the images 11', 12', 13', 14' shown in Fig. 1b. The synchronization moment may for example be the trailing edge or the rising edge of the start pulse. Then, based on this end time of integration and their own integration times, the slave cameras 12, 13, 14 and the master camera 11 themselves calculate the start time for their own integration.

[0021] The master camera 11 further synchronizes the lighting device 16 by means of an optical synchronization signal indicating by means of an illumination control pulse the on and off switching times for the lighting device 16. In this embodiment the on switching time is indicated by the rising edge of the optical control pulse. The lighting device 16 is switched on before the integration of any of the cameras 11, 12, 13, 14 starts. In this embodiment the off switching time is indicated by the trailing edge of the optical control pulse and defines the time to switch off the lighting device 16 and corresponds to the synchronization moment of the cameras 11, 12, 13, 14. If several lighting devices are present, the master camera 11 synchronizes them all by means of an optical synchronization signal so that they are all switched off at the defined synchronization moment.

[0022] Web inspection system 10 also includes an edge marking device 18 for marking the edge of web 15 at regular, predetermined intervals, although edge marking device 18 is an optional device in web inspection system 10 .

[0023] The transmitted synchronization signal also contains serial data. The serial data field may contain additional information for the slaved cameras 12, 13, 14. This additional information may be used to synthesize images or may be some other type of information, for example to control camera settings. The smart sync signal and the optical sync signal are explained in more detail in connection with FIG. 2.

[0024] However, there can be embodiments in which a line camera is used instead of an area scan camera. It is even possible that all cameras 11, 12, 13, 14 are so-called slave cameras and an external synchronization unit is used to transmit a synchronization signal to them and an optical synchronization signal to the lighting device 16.

[0025] Figure 1b shows images 11', 12', 13', and 14' captured by cameras 11, 12, 13, and 14, respectively, of web inspection system 10 of Figure 1a. The capture of images 11', 12', 13', and 14' was synchronized by a smart synchronization signal as described above, so that images 11', 12', 13', and 14' are parallel and taken the same distance in the direction of travel from the leading edge of web 15. As can be seen, there are no defects or their equivalent in any of images 11', 12', 13', and 14'.

[0026] Figure 1c shows a composite image 17' formed from the images 11', 12', 13', 14' of Figure 1b. And since the images 11', 12', 13', 14' are parallel and aligned, all their information is included in the composite image 17'. The images 11', 12', 13', 14' are successfully composited based on the position information transmitted by the synchronization signal.

[0027] FIG. 1d shows images 11'', 12'', 13'', 14'', respectively, captured by cameras 11, 12, 13, 14 of web inspection system 10 of FIG. 1a. The capture of images 11'', 12'', 13'', 14'' has been synchronized again by using smart synchronization signals as described above with respect to FIG. 1a, so that images 11'', 12'', 13'', 14'' are again parallel and aligned laterally with respect to the moving direction of web 15. As can be seen, defect A is present in the border area of ​​images 11'' and 12''. Defect A is located such that a first portion of defect A is in image 11'' and a second portion is in image 12''. Thus, defect A is one error distributed in the area of ​​two adjacent images 11'', 12''.

[0028] FIG. 1e shows a composite image 17'' formed from images 11'', 12'', 13'', and 14'' of FIG. 1d. And because images 11'', 12'', 13'', and 14'' are parallel and aligned, all their information is correctly included in composite image 17'', and defect A is correctly shown in the correct location, i.e., as a single defect.

[0029] FIG. 1f shows images 11''', 12''', 13''', and 14''' of cameras 11, 12, 13, and 14, respectively, of web inspection system 10 of FIG. 1a. However, these images 11''', 12''', 13''', and 14''' are not captured by using the smart synchronization method and its synchronization signal, but rather by using a simple synchronization signal. The capture frequencies of cameras 11, 12, 13, and 14 are also varied, i.e., are not the same but remain predetermined for cameras 11, 12, 13, and 14. Thus, although adjacent images 11''', 12''', 13''', 14''' were captured simultaneously in unison, the simple synchronization signal did not transmit suitable positional or other information for cameras 11, 12, 13, 14 to use in the compositing phase, resulting in images 11''', 12''', 13''', 14''', blending together and one of the images, 12''', being misaligned in the compositing phase resulting in a different composite image than the other images 11''', 13''', 14''', as shown in FIG. 1g. The other images 11''', 13''', 14''', are in composite image 17''''a, and the misaligned image 12''' is in composite image 17''''b. Cameras 11, 12 imaged the same defect A as in FIG. 1d, but now the first and second portions of defect A are in two different composite images 17''''a and 17''''b. If a defect map were then formed based on these composite images 17'''a and 17'''b and an attempt was made to correct defect A in web 15 based on the defect map, the correction would be unsuccessful because defect A would not be correctly represented in the defect map. On the other hand, if a defect map were formed based on image 1e and an attempt was made to correct defect A based on the defect map, the correction would be successful because defect A would be correctly and in the correct location in the defect map.

[0030] 2 shows a synchronization signal of the smart synchronization method of the web inspection system according to one embodiment of the present invention. The synchronization signal shown above is a synchronization signal 20 sent by a synchronization device, e.g., a master camera, to the slave cameras. The purpose of the synchronization signal 20 is to synchronize all the cameras with each other to capture images at the same time and finish integrating the images at the same time, and also to provide additional information to be added to the image.

[0031] The synchronization signal 20 includes a start pulse 22, serial data 23 and a pause 24 between them. The synchronization moment 25 is the trailing edge, i.e. the falling edge of the start pulse 22, at which all cameras finish integration and the lighting is switched off, i.e. the start pulse 22 includes information indicating the synchronization moment 25 for the slaved cameras. However, instead of the trailing edge it may also be the leading edge, i.e. the rising edge of the start pulse 22 indicating the synchronization moment 25. The camera calculates the start time of integration, i.e. the point in time at which it starts integration, based on its own integration time from the synchronization moment 25, which is common for all cameras. The length of the start pulse 22 may be, for example, 30 to 80 μs, for example 50 μs. For example, if the start pulse 22 indicates that the synchronization moment 25 is 50 μsec later (i.e., the length of the pulse 22 is 50 μsec) and the integration time of the first camera is 20 μsec, the first camera will start integrating 30 μsec after the start of the start pulse 22, i.e., 20 μsec before the synchronization moment 25, and if the integration time of the second camera is 15 μsec, the second camera will start integrating 35 μsec after the start of the start pulse 22, i.e., 15 μsec before the synchronization moment 25.

[0032] After the end of the start pulse 22 and before the serial data 23 there is a pause 24. The length of the pause 24 may be a few μs, for example 2-10 μs. The serial data 23 contains additional information for the slaved camera. The information may for example be the exact end time of the next light pulse, i.e. the next synchronization moment, the lighting profile number arranged to be used when capturing the next image, position information at the moment of the next synchronization moment 25, the image number of the next image, a flag to skip the next image, some application specific data, a checksum, etc. A suitable bit rate for the data field of the serial data 23 may for example be around 1 Mbit / s. The camera may add this additional information to 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.

[0033] The signal shown below, smart sync signal 20, is a light synchronization signal 21 sent to the lighting devices of the web inspection system arranged to illuminate the imaged area of ​​the web, and is also sent by the master camera. The light synchronization signal 21 indicates the time of switching the light of the lighting devices on and off by light control pulse 26. The trailing edge of the light control pulse 26 indicates to the lighting devices the time to switch off, which time corresponds to the synchronization moment 25 of the smart sync signal 20. Thus, the lighting devices are switched on in unison at the time the cameras finish integrating. The rising edge of the light control pulse 26 indicates to the lighting devices the time to switch on, which time is before any of the cameras are configured to start integrating. Or, alternatively, the trailing edge of the light control pulse 26 indicates to the lighting devices the time to switch on, and the rising edge of the light control pulse 26 indicates to the lighting devices the time to switch off.

[0034] 3 shows a web inspection system 30 using a smart synchronization method for synchronizing cameras 31, 32, 33 and lighting devices 35, 36 according to an embodiment of the present invention. The web inspection system 30 comprises a group of three cameras 31, 32, 33, two lighting devices 35, 36, and an image data processing device 31', 32', 33' for each camera 31, 32, 33. However, one image data processing device can also be common for one or more cameras. The cameras 31, 32, 33 are arranged adjacently, i.e. in a line, to expose image frames, i.e. capture image matrices from the web over its entire width, such that adjacent images together cover an area corresponding to the entire width of the web. One of the cameras 32 is a master camera configured to act as a synchronization device, and the remaining cameras are slave cameras 31, 33.

[0035] Illumination devices 35, 36 are arranged to illuminate areas on the web arranged to be imaged by cameras 31, 32, 33. The switching off and on of illumination devices 35, 36 is controlled by an optical synchronization signal 38 transmitted by master camera 32. Optical synchronization signal 38 is described in connection with FIG.

[0036] The cameras 31, 32, 33 are arranged to capture images at a synchronization moment indicated by a single common smart sync signal 37. At the same synchronization moment the lighting devices 35, 36 are switched off. The master camera 32 transmits the smart sync signal 37 to the slave cameras 31, 33. The smart sync signal 37 also includes serial data containing additional information for the slave cameras 31, 33. The type of additional information is explained in more detail in connection with FIG. 2. The cameras 31, 32, 33 may use the received additional information to adjust their settings for the next image capture. For example, as additional information they may receive a lighting profile number that is arranged to be used when capturing the next image and may adjust their parameters based on that information. Those parameters may be predefined for each lighting profile number. Furthermore, after capturing an image the cameras 31, 32, 33 may add the received additional information in relation to the captured image data. For example, if additional information is received such as the time of the synchronization moment, the number of the next image and / or the position in the direction of movement at the moment of the synchronization moment, this information may be added to the captured image data, after which the cameras 31, 32, 33 are arranged to transfer the captured image data together with the additional information to their image data processing devices 31', 32', 33' for processing, analysis etc.

[0037] The image data processing devices 31', 32', 33' may be external devices. The image data processing devices 31', 32', 33' comprise at least one processor, at least one memory containing computer program code for one or more program units, and means for receiving image data and additional data wirelessly or via a wired connection, e.g. a receiver for receiving data wirelessly or via a wired connection. There may be multiple processors, e.g. a general purpose processor, as well as a graphics processor, and a DSP processor, a field programmable gate array (FPGA), and / or multiple different memories, e.g. a volatile memory for storing data and programs at run-time, and a non-volatile memory such as a hard disk for storing data and programs persistently. The image data processing devices 31', 32', 33' may be any computing device suitable for handling image data, such as a computer. The image data processing devices 31', 32', 33' may be in electronic communication with the cameras 31, 32, 33 correspondingly via signal lines. To handle signals to and from the signal lines, the image data processing device 32 comprises I / O circuits. The connection between the cameras 31, 32, 33 and the image data processing devices 31', 32', 33' may be a wired or wireless network. The image data processing devices 31', 32', 33' may also include a video controller and an audio controller for generating signals that can be generated to a user using a computer accessory. The simulator may generate an output to a user through an output means. The video controller may be connected to a display. The display may be, for example, a flat panel display or a projector for generating a larger image. The audio controller may be connected to a sound source such as a loudspeaker or earphones.

[0038] One of the image data processing devices 31', 32', 33' may combine adjacent images into a composite image based on additional information received related to the captured image data. The image data processing devices 31', 32', 33' may also analyze the composite image to detect defects or other events. Furthermore, one of the image data processing devices 31', 32', 33' or an external computing device may form a defect map based on the captured composite image showing the location of defects in the web with respect to the distance the web has traveled, making correction of those defects easier because their distance from the beginning of the web can be precisely indicated. The defect map may be stored in a database and displayed.

[0039] The image data processing devices 31 ′, 32 ′, 33 ′ may also be part of the cameras 31 , 32 , 33 .

[0040] The cameras 31, 32, 33 form a first camera row, and if there is more than one camera row, i.e. at least one other camera row with at least one slave camera, the same master camera 32 can be used to send the smart sync signal to those slave cameras, or each row may include its own master camera that can be used to send the smart sync signal to the slave cameras of its own camera row. The first camera row may also comprise more cameras than the three cameras 31, 32, 33 shown, and other possible camera rows. The number of cameras in a row may depend on the width of the web and / or the field of view of the cameras used.

[0041] Web inspection system 30 also includes an edge marking device 34 for marking the edge of the web at regular, predetermined intervals, although edge marking device 34 is again an optional device in web inspection system 30 .

[0042] 4 illustrates an embodiment of the present invention in which a block diagram of a method 40 for synchronizing 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 slaved camera and at least one illumination device arranged to illuminate an area of ​​the web arranged to be imaged by the camera. In step 41, a synchronization signal is sent by the synchronization device to the at least one slaved camera, where the synchronization signal includes serial data including at least one start pulse and additional information for the at least one slaved camera, and all cameras of the web inspection system are configured to be synchronized with each other based on a synchronization pulse indicating a synchronization moment when the integration of the cameras ends. Step 4 2 In step 42, an optical synchronization signal is sent by the synchronization device to the at least one lighting device, where optical control pulses of the synchronization signal indicate on and off switch times of the at least one lighting device, where the off switch times correspond to the synchronization moment. In step 43, a start time of integration is calculated based on the individual integration times of the cameras and the synchronization moment common to the cameras of the web inspection system.

[0043] 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 present invention. For example, a computing device, e.g., an image data processing device, may comprise circuitry and electronics for analyzing, receiving, and transmitting data, computer program code in a memory, and a processor that, when operating the computer program code, causes the apparatus to perform features of the embodiments. When the processor runs the computer program code, it may cause a 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 cameras to perform all of the following steps of a method: sending a synchronization signal by the synchronization device to the at least one slave camera, the synchronization signal including serial data including at least one start pulse and additional information for the at least one slave camera, and all cameras of the web inspection system are configured to synchronize with each other based on a synchronization pulse indicating a synchronization moment when integration of the cameras ends; sending an optical synchronization signal by the synchronization device to the at least one lighting device, the optical control pulses of the optical synchronization signal indicating the on and off switch times of the at least one lighting device, the off switch time corresponding to the synchronization moment; and calculating a start time of integration based on individual integration times of the cameras and a synchronization moment common to the cameras of the web inspection system.

[0044] Considerable advantages are achieved by the present invention compared to existing methods and systems of web inspection systems with at least two area scan cameras. The arrangement according to the present invention allows the area scan cameras to be synchronized by a smart synchronization method, where a smart synchronization signal is sent by one of the cameras of the web inspection system, the master camera, to the other camera of the web inspection system, the slave camera. Furthermore, the smart synchronization signal according to the present invention also allows additional information to be sent to the slave camera, which can be utilized not only for image capture but also when analyzing the captured image data. The smart synchronization method also allows the lighting device of the web inspection system to be controlled by the light synchronization signal in order to enable the best possible imaging results.

[0045] It is obvious that the invention is not limited solely to the embodiments presented above, but it can be modified within the scope of the appended claims. The present application provides the following aspects of the invention. (Aspect 1) 1. A smart synchronization method for a web inspection system (30) for monitoring a moving web, comprising a master camera (32) and at least one slave camera (31, 33) configured to act as synchronization devices, and at least one illumination device (35, 36) arranged to illuminate an area of ​​the web arranged to be imaged, comprising: transmitting a synchronization signal (20) by the synchronization device (32) to the at least one slaved camera (31, 33), the synchronization signal (20) including at least one start pulse (22) and serial data (23) including additional information for the at least one slaved camera (31, 33), all the cameras (31, 32, 33) of the web inspection system (30) being configured to synchronize with each other based on the start pulse (22) indicating a synchronization moment (25) when integration of the cameras (31, 32, 33) ends; - transmitting an optical synchronization signal (21) by said synchronization device (32) to said at least one lighting device (35, 36), where optical control pulses (26) of said optical synchronization signal (21) indicate on and off switch times of said at least one lighting device (35, 36), the off switch times corresponding to said synchronization moments (25); and calculating a start time of integration based on the individual integration times of the cameras (31, 32, 33) and the synchronization moment (25) common to the cameras (31, 32, 33) of the web inspection system (30). (Aspect 2) 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) to illuminate the area on the web imaged by the cameras (31, 32, 33); The smart synchronization method of embodiment 1, further comprising terminating integration of all cameras (31, 32, 33) and switching off the at least one lighting device (35, 36) at the instant of the synchronization moment (25). (Aspect 3) reading intensity values ​​measured during integration from pixels of the cameras (31, 32, 33) and resetting the pixels; forming captured image data based on the read intensity values; and The smart synchronization method of aspect 2, further comprising: transmitting the captured image data together with the received additional information to an image data processing device (31', 32', 33'). (Aspect 4) The smart synchronization method of embodiment 3, further comprising forming a composite image from the received image data using the received additional information by the image data processing device (31', 32', 33'). (Aspect 5) 5. The smart synchronization method of any one of aspects 1 to 4, wherein all the cameras (31, 32, 33) of the web inspection system (30) are area scan cameras. (Aspect 6) A web inspection system for monitoring a moving web, comprising a master camera (32), at least one slave camera (31, 33) as synchronization devices, at least one lighting device (35, 36), and an image data processing device (31', 32', 33'), wherein the cameras (31, 32, 33) are synchronized with each other by using the method according to any one of aspects 1 to 5. (Aspect 7) 7. The web inspection system of claim 6, wherein the at least one slave camera (31, 33) is an area scan camera. (Aspect 8) 8. The web inspection system of claim 6 or 7, wherein the cameras (31, 32, 33) of the web inspection system (30) are arranged adjacent to each other in a row. (Aspect 9) 9. The web inspection system of any one of aspects 6 to 8, wherein the web inspection system (30) further comprises an edge marking device (34). (Aspect 10) A computer program product stored on a computer-readable medium and executable within a computing device, the computer program product comprising instructions for 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 aspects 1 to 5.

Claims

1. 1. A smart synchronization method for a web inspection system (30) for monitoring a moving web, comprising a master camera (32) and at least one slave camera (31, 33) configured to act as synchronization devices, and at least one illumination device (35, 36) arranged to illuminate an area of ​​the web arranged to be imaged, comprising: transmitting a synchronization signal (20) by the synchronization device (32) to the at least one slaved camera (31, 33), the synchronization signal (20) comprising serial data (23) including at least one start pulse (22) and additional information for the at least one slaved camera (31, 33), the additional information being configured to be used for the merging of images of adjacent cameras, and all the cameras (31, 32, 33) of the web inspection system (30) being configured to synchronize with each other based on the start pulse (22) indicating a synchronization moment (25) when integration of the cameras (31, 32, 33) ends; transmitting an optical synchronization signal (21) by said synchronization device (32) to said at least one lighting device (35, 36), where optical control pulses (26) of said optical synchronization signal (21) indicate on and off switch times of said at least one lighting device (35, 36), the off switch times corresponding to said synchronization moments (25); and calculating a start time of integration based on the individual integration times of the cameras (31, 32, 33) and the synchronization moment (25) common to the cameras (31, 32, 33) of the web inspection system (30).

2. 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) to illuminate the area on the web imaged by the cameras (31, 32, 33); 2. The smart synchronization method according to claim 1, further comprising: terminating integration of all said cameras (31, 32, 33) and switching off said at least one lighting device (35, 36) at the instant of said synchronization moment (25).

3. reading intensity values ​​measured during integration from the pixels of said cameras (31, 32, 33) and resetting the pixels; forming captured image data based on the read intensity values; and The smart synchronization method of claim 2, further comprising: transmitting the captured image data together with the received additional information to an image data processing device (31', 32', 33').

4. The smart synchronization method of claim 3, further comprising forming a composite image from the received image data using the additional information received by the image data processing device (31', 32', 33').

5. The smart synchronization method of any one of claims 1 to 4, wherein all the cameras (31, 32, 33) of the web inspection system (30) are area scan cameras.

6. A web inspection system for monitoring a moving web, comprising as synchronization devices a master camera (32), at least one slave camera (31, 33), at least one lighting device (35, 36) and an image data processing device (31', 32', 33'), said cameras (31, 32, 33) being 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 slaved camera (31, 33) is an area scan camera.

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

9. The web inspection system of any one of claims 6 to 8, 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, the computer program product comprising instructions for 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 of any one of claims 1 to 5.

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