LED matrix lighting

Abstract

The present invention relates to an LED matrix lighting device (20) for illuminating a lighting pattern with uniform intensity. The LED matrix lighting device comprises a plurality of LEDs (22); a collimating lens (23) in front of each LED (22) for collimating the light of the LED (22); and a light refraction element (24) in front of the collimating lens (23), arranged to refract the light of at least a first portion of the LEDs (22) at a different refraction angle than that of at least a second portion of the LEDs (22). The present invention further relates to a machine vision system, a method and a computer program product.

Description

Technical Field

[0001] The present invention relates to an LED matrix lighting device arranged to produce a consistent and uniform lighting pattern on the surface of a monitoring target, such as a continuous wood fiber web. The present invention further relates to a machine vision system comprising at least one LED matrix lighting device, a method of utilizing the LED matrix lighting device, and a computer program product for causing the system to perform the method. Background Art

[0002] In continuous manufacturing processes, such as in paper, pulp and board machines, materials or products are continuously formed and moved through the machine. In such processes, multiple cameras, such as 10 to 40 cameras, are used to monitor the process in order to detect possible deviations or web breaks in different parts of the machine. For imaging, the continuous material web must be illuminated. The moving speed of the web may exceed 120 km / h, and therefore the camera must use a very short shutter speed time in order to freeze the frame. Therefore, the quality of the image of the moving web depends heavily on the lighting.

[0003] Nowadays, LED lighting is also often used to illuminate a moving web. The idea is to provide a consistent lighting pattern on the surface of the web. However, this is not always possible due to the lack of space above (or below) the moving web and it is therefore not possible to install LED lighting perpendicular to the web to be illuminated and monitored, but rather the web is usually illuminated from the side of the paper machine at an angle of 30 to 60 degrees relative to the web. As a result, the lighting pattern may not be consistent and different parts of the pattern have different brightness. Summary of the invention

[0004] An improved method and technical apparatus for implementing the method have now been invented. Various aspects of the invention include an LED matrix lighting device arranged to produce a consistent and uniform lighting pattern on the surface of a monitoring target, such as a continuous wood fiber web. The invention further relates to a machine vision system comprising at least one LED matrix lighting device, a method of utilizing and controlling the LED matrix lighting device, and a computer program product for causing a system to perform the method and control the LED matrix lighting device.

[0005] According to a first aspect of the present invention, there is provided an LED matrix lighting device for illuminating a lighting pattern with uniform intensity, the LED matrix lighting device comprising a plurality of LEDs, a collimating lens in front of each LED for collimating the light of the LED, and a light refraction element in front of the collimating lens, the light refraction element being arranged to refract at least a first portion of the light of the LEDs at a different refraction angle than at least a second portion of the LEDs.

[0006] According to one embodiment, the LED matrix lighting device further comprises at least one power supply circuit for LEDs, and the amount of current provided for the first part of LEDs is different from the amount of current provided for at least the second part of LEDs. According to one embodiment, the first part of LEDs comprises one LED, a row of LEDs of an LED matrix, or a column of LEDs of the LED matrix. According to one embodiment, the refraction angle is determined based on the position of the LED in the LED matrix lighting device. According to one embodiment, the refraction angle is the angle between the optical center axis of the collimated light of the LED and the optical center axis of the refracted light of the same LED. According to one embodiment, the FWHM viewing angle of the collimated light of the LED is at least as large as the difference between the refraction angles. According to one embodiment, the current provided for at least one LED is adjustable. According to one embodiment, the current provided for at least one LED is adjustable based on the detected intensity deviation in the captured image.

[0007] According to a second aspect of the invention, a machine vision system for detecting deviations from a wood fiber web is provided, wherein the machine vision system comprises: an LED matrix lighting device according to the first aspect and its embodiments, at least one imaging device for capturing an image of the illuminated area, and a data processing device.

[0008] According to an embodiment, the data processing means is arranged to analyse the image data to detect intensity deviations in the captured images.

[0009] According to an embodiment, the data processing means are arranged to adjust a current provided to the at least one LED based on the detected intensity deviation.

[0010] According to a third aspect of the present invention, a method is provided, comprising: obtaining image data; analyzing the image data; detecting intensity deviations in a lighting pattern provided by an LED matrix lighting device according to the first aspect and its embodiments in a captured image; and adjusting a current provided to at least one LED of the LED matrix lighting device.

[0011] According to a fourth aspect of the present invention, a computer program product implemented on a non-transitory computer-readable medium is provided, the computer program product comprising computer program code, which is configured to cause a system to perform a method comprising the following when executed on at least one processor: obtaining image data; analyzing the image data; detecting intensity deviations in a lighting pattern provided by an LED matrix lighting device according to the first aspect and its embodiments in the captured image; and adjusting a current provided to at least one LED of the LED matrix lighting device. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Hereinafter, various embodiments of the present invention will be described in more detail with reference to the accompanying drawings, in which:

[0013] Figure 1a , 1b The optical axes of LEDs of a conventional LED matrix lighting device viewed from above and from the side are shown;

[0014] Figure 1c , 1d It is shown accordingly Figure 1a and 1b The viewing angle of the LEDs of the LED matrix lighting device;

[0015] Figure 2a , 2b shows the optical axis of the LED of the LED matrix lighting device according to an example embodiment;

[0016] Figure 2c , 2d It is shown accordingly Figure 2a and 2b The viewing angle of the LEDs of the LED matrix lighting device;

[0017] Figure 3a An LED matrix lighting device according to an example embodiment is shown;

[0018] Figure 3b Shows Figure 3a An exploded view of an LED matrix lighting device;

[0019] Figure 4 A machine vision system including an LED matrix lighting device according to an example embodiment is shown; and

[0020] Figure 5 A machine vision system including an LED matrix lighting device according to an example embodiment is shown. DETAILED DESCRIPTION

[0021] In a continuous manufacturing process, such as in a paper, cellulose, and board machine, materials or products are continuously formed and moved through the machine. A machine vision system comprising a plurality of cameras (e.g., 10 to 40 cameras) can be used to monitor the process in different parts of the process. Monitoring can include imaging of a monitoring target (e.g., a moving web), storing image data, and analyzing image data. The camera (i.e., image sensor) can be, for example, a CMOS or CCD camera, a matrix camera or a line scan camera, a black and white camera or a color camera, a regular camera or a smart camera, or any suitable camera.

[0022] In order to image a monitoring target, the monitoring target must be illuminated. For example, in order to image a web product, the web product must be illuminated, for example, by an illumination pattern or lines whose width corresponds to the width of the web product. The term "web product" (i.e. "web") in this context refers to any type of wood fiber web produced by a paper machine, cellulose machine or board machine, while the term "wood fiber" in this context refers to any suitable wood fiber, such as paper fiber, cellulose fiber or board fiber. Depending on the monitoring target and / or the monitoring system, the wavelength of the light used can vary within a wide spectrum, and the wavelength can vary from the ultraviolet (UV) region to the short-wave infrared thermal region (SWIR).

[0023] As already described above, suitable illumination may depend on the monitoring target, but a consistent illumination pattern with uniform intensity throughout the entire pattern shining on the monitoring target provides a good starting point for high-quality imaging, because it increases the probability of detecting the predetermined object of interest (e.g., deviations (one or more) in the web product or web breaks (one or more)). The type of lighting device, the number of lighting devices, the direction of light, the operation of the lighting device, or the type of lighting device used may depend on the object arranged to be imaged and the type of (one or more) cameras used. The lighting device used to illuminate the monitoring target (e.g., web) typically includes at least two, several or more light sources, such as LEDs. The LED requires at least one LED circuit, LED driver, or current source circuit as an electronic circuit (i.e., power supply circuit) arranged to power the LED. Typically, one electronic circuit powers several or more LEDs. The power supply circuit is arranged to provide a current through (one or more) LEDs so that the LEDs reach the required or desired light intensity, and the power supply circuit is arranged to limit the current to prevent damage to the LEDs. Although LEDs are discussed throughout the application, other suitable light sources can also be used instead of LEDs.

[0024] The image data of the captured images may be stored and analyzed by a data processing device of each camera (e.g., a smart camera) used to image the manufacturing process, and / or the image data of the captured images may be transmitted to an external data processing device for storage and analysis. An external data processing device is a data processing device that is not an integral part of the camera. The data processing device monitors the data in order to find a predetermined object of interest. The image data may also be stored and analyzed in a system comprising the above two systems, i.e., (one or more) cameras with (one or more) integrated data processing devices and (one or more) external data processing devices. All systems, cameras with integrated data processing devices, cameras with external data processing devices, and combinations thereof include or are connected to a database, a user interface, and possible interfaces to factory systems and manufacturing processes.

[0025] Cameras that capture images of a continuous manufacturing process may be part of a web monitoring system (WMS) that monitors for web breaks. The web monitoring system may continuously store image data received from a plurality of cameras in a memory of a computer program product. Such stored image data may be used to determine the cause of a web break after it has occurred. Since the web may move at speeds exceeding 120 km / h, the camera must use very short shutter speed times in order to freeze the image. Therefore, the quality of images captured from such a fast moving web depends heavily on the uniform intensity of the illumination and how the illumination is distributed in the image area.

[0026] The camera may also be part of a web inspection system (WIS), i.e. an event capture camera system that monitors possible web deviations. The term "web deviation" in this context encompasses any deviation that can be detected from the web product, such as defects, holes, stains, noticeable changes, grey or black spots, streaks, wrinkles, bubbles or patterns in the web product. In a web inspection system, a camera is mounted to capture the entire web width in the cross direction of the web and store the captured image data. The lighting used may be, for example, reflected light, or the web may be illuminated through the web. The angle of the reflected light may also vary greatly, depending on the web defect that should be looked for. But again, the quality of the image depends on the quality of the lighting.

[0027] Based on the above, it is obvious that lighting is an important part of quality process monitoring.The idea of ​​the present invention is therefore to provide a lighting arrangement which provides conditions such that the detection of predetermined objects from a captured image is as efficient as possible.

[0028] The lighting device according to an exemplary embodiment of the present invention is a matrix-type light-emitting LED lighting device, i.e., an LED matrix lighting device configured to generate a consistent lighting pattern with uniform luminous intensity (i.e., brightness) throughout the pattern on the surface of the monitoring target (e.g., on a web product). The LED matrix lighting device may include a base, LEDs, at least one power supply circuit for the LEDs, a collimating lens, and a light refraction element. The LEDs are arranged in a matrix on the surface of the base, for example, by attaching (one or more) circuit boards or other surfaces or substrates, and the LEDs are attached to the other surfaces or substrates on the surface of the base.

[0029] The power supply circuit is arranged to provide a current through the LEDs so that the LEDs illuminate with a required or desired intensity. The driving mode of a part of the LEDs may be different from the driving mode of at least one other part of the LEDs, i.e. the amount of current provided by the power supply circuit to a part of the LEDs may be different from the amount of current provided to at least one other part of the LEDs. It is also possible that each LED is driven differently from the driving mode of the other LEDs, or that a column of LEDs of the LED matrix is ​​driven differently from the driving mode of at least one other column of LEDs of the LED matrix, or that a row of LEDs of the LED matrix is ​​driven differently from the driving mode of at least one other row of LEDs of the LED matrix. The amount of current provided may depend, for example, on the position of the LED in the matrix, i.e. the position to which the light beam of the LED is arranged to be directed (i.e. refracted by the light refraction element), i.e. which part of the surface the light of the LED is arranged to illuminate, taking into account the part of the surface illuminated by the position of the light of the other LEDs. For example, if a first portion of LEDs (e.g., a column of LEDs) is at a greater distance from the illuminated surface than at least one other portion of LEDs ((one or more) other columns) is at a greater distance from the illuminated surface, the first portion of LEDs is refracted so that a larger refraction angle is formed between the optical center axis of the LED beam (before the beam is refracted due to the refractive element) and the optical center axis of the refracted LED beam, and the amount of current provided to the first portion of LEDs may be higher than the current provided to at least one other portion of LEDs because the higher current makes these LEDs brighter, and despite the longer distance from the surface, the first portion of LEDs may now illuminate the surface similarly to the at least one other portion of LEDs that is closer to the surface and driven at a lower current. The amount of current provided may be controlled by a data processing device integrated in the LED matrix lighting device or by an external data processing device (e.g., a data processing device that also analyzes image data of the captured image), or a user may control the amount of current provided by configuring the amount of current of the LEDs.

[0030] A collimator is an optical element that collects light from an LED and refracts the light into parallel light rays. The collimator can be constructed of a parabolic mirror or a lens, and the LED can be positioned at its focus. A collimating lens can be arranged in front of each LED, i.e., a collimator matrix, i.e., a collimating lens matrix, is attached to the LED matrix to collimate the output light of the LEDs from the LED matrix. However, the collimating lens can be an integrated structure of the LED, in which case a separate collimating lens is not required on the LED. The LED and the collimating lens together define the viewing angle of the LED, i.e., the LED beam angle indicating the available light emitted from the LED source. The viewing angle can be defined by using the full width at half maximum (FWHM) method and can be indicated by degrees. FWHM defines the angle at which 50% peak intensity is reached. For example, if it is measured that the LED has 50% intensity at an angle of 40°, the viewing angle (FWHM) of the LED will be 40°.

[0031] The light refraction element is arranged in front of each collimating lens in the form of a refraction lens matrix attached to the LED matrix, so that each LED has a collimating lens and a refraction lens, or the light refraction element is arranged as a single refraction lens attached to all LEDs of the LED matrix. The lenses of the refraction lens matrix can be, for example, prisms, such as Fresnel prisms, and the single refraction lens can be, for example, a film or sheet forming a Fresnel-type lens or prism. The light refraction element is arranged to incrementally guide the central optical axis of each collimated LED light beam outward from the optical center axis of the collimated LED light, i.e., refract. The refraction element is configured to guide the light beam of the LED to a wider area, so that the refraction element does not guide the light to the same area on the surface of the monitoring target, or so that the illuminated areas on the surface overlap very little. Non-overlapping light beams (i.e., refracted light beams) can form a consistent illumination pattern with uniform luminous intensity (i.e., brightness) throughout the illumination pattern on the surface of the monitoring target because the current supplied to the LED is controlled and because the current control has an effect on the intensity of the illuminated area. If the light beams overlap, the current control of the LEDs has no effect on the lighting pattern, or at least is not as efficient as if each LED illuminates its own area in the lighting pattern because the same area is illuminated by several LEDs.

[0032] Figure 1aThe optical axis 14 of the LED 12 of the prior art LED matrix lighting device 10 as viewed from above is shown, that is, the horizontal optical axis of the LED matrix lighting device 10 is shown. The LED matrix lighting device 10 includes a base 11, an LED matrix, and a collimator matrix. The size of the LED matrix is ​​9*4, that is, there are 36 LEDs 12 in the LED matrix of the LED matrix lighting device 10. The electronic circuit of the LED 12 of the matrix lighting device is arranged in the base 11. The collimator matrix is ​​arranged on the LED 12 and its size is also 9*4. Each collimator lens 13 of the collimator matrix is ​​an optical element that collects light from the LED 12 and refracts the light into parallel light rays shown as the optical axis 14. Figure 1b FIG. 1 shows an optical axis 14 of the LED 12 of the prior art LED matrix 10 viewed from the side, that is, the vertical optical axis of the LED 12 is shown. Figure 1a and 1b As can be seen, each optical axis 14 extends straight from the LED 12, ie the optical axis is not refracted.

[0033] Figure 1c Shows Figure 1a The viewing angle of the LED 12 of the LED matrix lighting device 10 as viewed from above, and Figure 1d Shows Figure 1b The viewing angle 15 of the LED 12 of the LED matrix lighting device 10 as viewed from the side. The viewing angle 15 of the LED 12 has a conical shape; initially, the viewing angle has a narrow shape that widens as the light extends away from the LED 12. The full width at half maximum (FWHM) viewing angle of the LED 12 is 40 degrees. In order to achieve a consistent lighting pattern across the entire web from the side of the web, the FWHM (full width at half maximum) viewing angle of each LED of the lighting device must be wide, for example, 20 to 60 degrees.

[0034] The viewing angle 15 of the middle LED 12 is indicated by the line pattern. Since the optical axes 14 of the LEDs are straight and extend in parallel, when a certain distance from the LEDs is achieved, the viewing angles of the LEDs 12 overlap and the resulting illumination pattern on the surface 16 has a non-uniform luminous intensity; the central area of ​​the illumination pattern is illuminated by several LEDs 12 (all LEDs in this embodiment) and the outermost parts of the pattern are illuminated by light generated by only one LED. Thus, the central area of ​​the illuminated line or pattern is brighter than the edge areas and different parts of the paper web are illuminated with different intensities, depending on, for example, the distance of the parts from the central part of the illumination pattern; there is bright light near the center of the illumination pattern, but the amount of light is lower in the edge areas of the illumination pattern. Furthermore, even if the LED current of this prior art illumination device 10 is adjusted (which is not the case), the control of the LED power does not have much influence on the resulting pattern because the same area is illuminated by several LEDs.

[0035] Figure 2a An optical center axis 25 of a light beam of LED 22 of an LED matrix lighting device 20 viewed from above is shown after light of the LED 22 has passed through a collimating lens 23 and a light refraction element 24 according to an example embodiment of the present invention, i.e., a horizontal optical center axis 25 of the collimated and refracted LED light beam is shown. Figure 2b The optical center axes 25 obtained from the side view are shown, that is, the vertical optical center axes 25 of the collimated and refracted LED light beams of the LED 22 are shown. The LED matrix lighting device 20 includes a base 21, an LED 22, a collimating lens 23, and a light refraction element 24. In this embodiment, the size of the LED matrix is ​​9 * 4 (columns * rows), but the size can also be smaller or larger. In some embodiments, the number of columns can be, for example, 1 to 25, and the number of rows can be, for example, 1 to 25 or any other suitable number. In the smallest matrix, the number can be 2, that is, the matrix is ​​2 * 1. The LED 22 can be attached to (one or more) circuit boards or some other substrates attached to the base 21, for example.

[0036] The base 21 may have at least one power supply circuit for the LED 22 and other possible electronic circuits inside, or the at least one power supply circuit for the LED 22 may be an external power supply circuit for the LED 22, which is electrically connected to the LED 22. The at least one power supply circuit is arranged to power the LEDs 22 so that each LED 22 is illuminated with a required or desired intensity defined for the LED. The amount of current provided by the at least one power supply circuit may be controlled and / or determined by a data processing device integrated in the LED matrix lighting device 20 or by an external data processing device (not shown).

[0037] In front of each LED 22, a collimating lens 23 is arranged, i.e. a matrix of collimating lenses 23, i.e. a collimator matrix, is attached to the LED matrix to collimate the output light of the LED. The LED and the collimating lens together define the FWHM viewing angle of the LED (i.e. the light beam provided by each LED 22), and the viewing angle can be indicated in degrees, as explained above. It should be noted that the central axis of the collimated LED light beam corresponds to the central axis of the LED light that has not yet passed through the collimating lens.

[0038] The light refraction element 24 is arranged in front of each collimating lens 23 (and LED 22). In this embodiment, the light refraction element 24 is a single refractive film attached in front of the collimating lens 23 of the matrix of all LEDs 22 and collimating lenses 23 of the LED matrix. The light refraction element 24 can also be a matrix of refractive lenses / films attached to the matrix of collimating lenses 23. The light refraction element 24 is arranged to incrementally direct the central optical axis of the collimated LED light beam outward from the central axis of the collimated LED light (and the center of the LED matrix lighting device 20) so that a refraction angle is formed between the central optical axis of the collimated LED light beam and the central axis 25 of the refracted LED light beam. The refraction angle is determined based on the position of the LED 22 in the LED matrix lighting device 20. For example, if the LED 22 is arranged to illuminate a farther area, its refraction angle is greater than the refraction angle of the LED arranged to illuminate a closer area, so that the farther area can be illuminated. When the LED 22 is arranged to illuminate a farther area, its refraction angle is greater than the refraction angle of the LED arranged to illuminate a closer area, so that the farther area can be illuminated. Figure 2a and 2b The optical axis 25 of the refracted LED light beam of the LED 22 is Figure 1a and 1b When compared with the optical axis 14 of the unrefracted LED light beam of the LED 12 shown in FIG. Figure 2a and 2b This refraction can be seen in the figure. The light refraction element 24 is arranged to be easily changed. This is because the size of the required refraction angle caused by the light refraction element 24 depends on the distance of the LED from the surface to be illuminated, i.e. the distance from the surface of the monitoring target, and if the position of the LED matrix lighting device relative to the target surface 27 changes, the distance may change. Different refraction angles can be achieved by different kinds of light refraction elements. The refraction angle can be, for example, between 5° and 10°.

[0039] Figure 2c Shows Figure 2a The viewing angle 26 of the LED 22 of the LED matrix lighting device 20, and Figure 2d Shows Figure 2bThe viewing angle 26 of the LED 22 of the LED matrix lighting device 20 is shown in FIG. The viewing angle 26 of the LED 22 has a conical shape; initially, near the LED, the viewing angle has a narrow shape, and as the light extends away from the LED 22, the viewing angle widens. Figure 2c and 2d A central axis 25 of the refracted LED light beam is shown in FIG.

[0040] Figure 2c and 2d The viewing angle 26 of each LED 22 in the target surface 27 is indicated by a different grid pattern. Since the central optical axis 25 of the light beams of the LEDs 22 is straight and refracted outwardly by the light refraction element 24, the viewing angles 26 of the LEDs 22 do not overlap when they reach the target surface 27, and thus each portion of the illumination pattern is illuminated by only one LED 22, and since each LED, column or row of LEDs can be powered individually to provide the desired intensity, the illumination pattern formed on the surface 27 can have a uniform luminous intensity. In addition, the control of the power of the LED, column or row of LEDs has a significant effect on the intensity of the pattern formed on the target surface 27, because the viewing angles 26 of the LEDs 22 do not overlap when they reach the target surface 27, and thus each portion of the illumination pattern is illuminated by one LED 22.

[0041] In this example embodiment, the FWHM viewing angle of each LED 22 is 10 degrees in both the vertical and horizontal directions. In general, in an LED matrix lighting device according to an embodiment of the present invention, the FWHM viewing angle of the light beam of the LED is defined to be at least as large as the difference between the refraction angles of the optical axes of two adjacent LEDs. There is a difference between the refraction angles of the optical axes of adjacent LEDs because the light refraction element guides the central optical axis of the collimated LED light beam, for example, from the optical center axis of the collimated LED light and the center of the lighting device differently and incrementally outward to the side depending on the position of the LED in the LED matrix and therefore also depending on the distance from the monitoring target, so that each LED illuminates a different part of the illumination pattern, i.e., the viewing angles do not overlap. However, if the FWHM viewing angle of the light beam of the LED is large, such as 20 degrees or more, the adjustment accuracy of the illumination pattern may be reduced, i.e., the intensity adjustment performed by the power control of the LED may not be so accurate.

[0042] Figure 3aAn LED matrix lighting device 30 according to an example embodiment is shown. The LED matrix lighting device 30 comprises a body 31, a matrix of LEDs 32, a matrix of collimating lenses 33 and a matrix of light refraction elements 34. The LEDs 32 are arranged on the body 31, for example as such or by using a separate surface arranged to be attached to the body 31. The body 31 further comprises an electronic circuit 35 arranged to power (one or more) LEDs, but the body may also comprise a data processing device comprising at least one processor, at least one memory containing computer program code for one or more program units and means for receiving configuration information on how to power the LEDs from a data processing device of a machine vision system or other external data processing device, for example a receiver or a transceiver, wirelessly or by a wired connection. The collimating lenses 33 of the collimating lens matrix are arranged in front of each LED 32 of the LED matrix. The light refraction elements 34 of the light refraction element matrix are arranged in front of each collimating lens 33, on the other side of the collimating lens 33 than the side of the LED 32, so as to refract the collimated light of the LED 32 in the lateral direction from the optical center axis of the collimated LED light 37 of the LED 32. The optical center axis of the refracted light is at Figure 3b 38. The LED matrix lighting element 30 is connected to a power source. The refractive properties of one or more light refractive elements 34 may be different from the refractive properties of other light refractive elements 34, i.e. one or more light refractive elements 34 may have different refractive properties compared to other light refractive elements, because whether the optical center axis of the collimated light 37 needs to be refracted depends on the distance of the LED 32 (and the light refractive element 34) from the target / area of ​​the surface arranged to be illuminated. If there is only one light refractive element 34 instead of a matrix of light refractive elements 34, the refractive properties inside the element may vary.

[0043] Due to the collimating lens 33 and the refractive element 34, the LED matrix lighting device 30 illuminates the imaging target so that the light uniformly illuminates the imaging target. However, in order to perform imaging, the intensity of the illuminated pattern must also be uniform, and therefore the amount of current provided by the electronic circuit 35 to the first part of the LEDs is different from the amount of current provided to at least the second part of the LEDs. The amount of current provided depends, for example, on the placement of the LEDs in the LED matrix of the lighting device, and therefore also on the angle between the optical center axis of the LED (before refraction) and the optical center axis of the refracted LED light beam, and on the lighting angle, that is, how far the lighting device is positioned from the imaging target.

[0044] Figure 3b Shows Figure 3a An exploded view of an LED matrix lighting device 30 . Figure 3b3 shows the light ray 36 from the LED and the optical axis of the collimated LED light 37 and the optical center axis of the refracted LED light 38. The refraction angle 39 between the optical center axis of the collimated LED light 37 and the optical center axis of the refracted LED light 38 is also shown.

[0045] Figure 4 A WMS or WIS machine vision system 40 is shown according to an embodiment disclosed in connection with a moving paper web 43 as a target object. The moving direction of the web 43 is towards the image, away from a viewer of the image. The machine vision system 40 comprises a camera 41, an LED matrix lighting device 44 according to an embodiment of the invention, and a data processing device 42. The camera 41 is arranged to capture images from the illuminated paper web 43 and to transmit data of each image to the data processing device 42. The LED matrix lighting device 44 is a separate lighting device, but the lighting device 44 may also be an integrated part of the camera 41.

[0046] The data processing device 42 is configured to analyze the received image data captured and transmitted by the camera 41 in order to find deviations in the web 43. The data processing device 42 may further analyze the illumination pattern 46 in the image. If the data processing device 42 detects from the image data that the pattern 46 does not have a uniform luminous intensity across the pattern, the data processing device may reconfigure the electronic circuitry of the LED matrix illumination device 44 so that the amount of current provided to one or more LEDs is changed and the intensity of the illumination pattern becomes constant across the pattern, and deviations in the web 43 may be more accurately detected across the entire width of the web.

[0047] The data processing device 42 can control the power of the LEDs, for example, so that the amount of current provided for the first part of the LEDs is different from the amount of current provided for at least the second part of the LEDs. The amount of current provided can again depend on, for example, the placement of the LEDs in the LED matrix of the lighting device 44, i.e. on the refraction angle, and therefore also on the distance of the LEDs from the part of the paper web 43 that the LEDs are configured to illuminate. Therefore, the LED matrix lighting device 44 according to an embodiment of the present invention and comprising LEDs whose power is regulated individually or in groups is arranged to illuminate the paper web 43 (or other web material) so as to be imaged by means of an illumination pattern 46 with uniform intensity (e.g., illumination lines with uniform intensity).

[0048] The lighting angle is the angle between the horizontal center axis of the LED matrix lighting device 44 and the surface of the web 43. In this embodiment, the angle is 45 degrees, i.e. 45°, but the angle can also be larger or smaller and can depend on the space arranged for the lighting device 44, or, for example, on the width of the lighting pattern arranged to be illuminated.

[0049] The data processing device 42 includes: at least one processor; at least one memory, containing computer program code for one or more program units; and a member for receiving image data from the camera 41 wirelessly or through a wired connection, such as a receiver or a transceiver; and a member for transmitting a trigger signal wirelessly or through a wired connection, such as a transmitter or a transceiver. There may be multiple processors (e.g., general-purpose processors and graphics processors and DSP processors) and / or multiple different memories, such as volatile memories for storing data and programs at run time and non-volatile memories such as hard disks for permanent storage of data and programs. The data processing device 42 is an external data processing device, and the data processing device may be any computing device suitable for processing image data and possibly also determining or controlling the current provided to the LED, such as a computer. The data processing device 42 communicates electronically with the camera 41 and the lighting device 44 via a signal line or wirelessly. The camera 41 may also include a video controller and an audio controller for generating signals that can be generated for the user with a computer accessory. The camera 41 may generate output to the user through an output member. The video controller may be connected to a display. The display may be, for example, a flat panel display or a projector for producing a larger image. The audio controller may be connected to a sound source, such as a speaker or headphones. The camera 44 may also include an acoustic sensor, such as a microphone.

[0050] Figure 5 An embodiment of the invention is shown, wherein a WMS or WIS machine vision system 50 according to an embodiment is arranged to monitor a moving web 57. The machine vision system 50 comprises two LED matrix lighting devices 58, 59 according to an embodiment of the invention and two smart cameras 51, 54 comprising image sensors 52, 55 and data processing devices 53, 56. The LED matrix lighting devices 58, 59 may also be an integrated part of the smart cameras 51, 54. The LED matrix lighting devices 58, 59 illuminate the moving web 57 at an illumination angle of 40 degrees, and the LED matrix lighting device 59 illuminates the moving web 57 at an illumination angle of 50 degrees. The LED matrix lighting devices 58, 59 are positioned to the side, but from the side. Figure 5 It cannot be clearly seen that the LED matrix lighting device illuminates the pattern such that it is positioned away from the symmetry axis of the illuminated pattern. The image sensors 52,55 are arranged to capture images from the moving web 57 and transmit image data to the data processing devices 53,56 of the smart cameras 51,54.

[0051] The data processing devices 53 , 56 may include similar structures and functions as the data processing device 42 .

[0052] Image sensors 52, 55 are arranged to capture an image of web 57 and LED matrix lighting devices 58, 59 illuminate web 57 with lighting patterns 58a, 59a on the surface of web 57. Patterns 58a, 59a extend the entire width of web 57. However, it is also possible for the pattern to be narrower and extend the entire width of web 57.

[0053] The various embodiments of the present invention may be implemented with the aid of a computer program code that resides in a memory and causes a device to perform the present invention. For example, a device that is a computing device (e.g., a data processing device) may include circuits and electronic devices for analyzing, receiving, and transmitting data, a computer program code in a memory, and a processor that causes the device to perform the features of the embodiments when the computer program code is executed.

[0054] The present invention achieves considerable advantages when compared to existing methods and systems of LED matrix lighting devices or machine vision systems including at least LED matrix lighting devices. With the device according to the present invention, the LED matrix lighting device can be placed to the side of the web or other target to be illuminated and still illuminate the entire pattern with a consistent intensity, because the LED matrix lighting device has a light refracting element in front of the collimating lens and the LEDs (i.e., on the other side of the collimating lens than the side of the LEDs), which refracts the optical center axis of the LED light beam in a certain direction so that the areas illuminated by the LEDs do not overlap or overlap only slightly, and because the power of the LEDs can be controlled individually or in groups so that each LED illuminates the target with the same or substantially the same intensity.

[0055] It is obvious that the invention is not limited solely to the embodiments described above, but it can be modified within the scope of the appended claims.

Claims

1. An LED matrix lighting device (20) for illuminating a lighting pattern with uniform intensity, the LED matrix lighting device (20) comprising: A plurality of LEDs (22); a collimating lens (23) in front of each LED (22) for collimating the light of the LED (22); and a light refracting element (24) in front of the collimating lens (23), arranged to refract light from at least a first portion of the LEDs (22) at a different refraction angle (39) than from at least a second portion of the LEDs (22), and wherein a current provided to at least one LED (22) can be adjusted based on a detected intensity deviation in a captured image, and a FWHM viewing angle (26) of the collimated light from the LEDs (22) is substantially as large as the difference between the refraction angles (39) such that a portion of the illumination pattern illuminated by the first portion of the LEDs is different from a portion of the illumination pattern illuminated by the second portion of the LEDs.

2. The LED matrix lighting device (20) according to claim 1, wherein the LED matrix lighting device (20) further comprises at least one power supply circuit (35) for the LEDs (22), and the amount of current provided to the first part of the LEDs (22) is different from the amount of current provided to at least the second part of the LEDs (22).

3. The LED matrix lighting device (20) according to claim 1 or 2, wherein the first part of LEDs (22) includes one LED (22), a row of LEDs (22) of the LED matrix, or a column of LEDs (22) of the LED matrix.

4. The LED matrix lighting device (20) according to claim 1 or 2, wherein the refraction angle (39) is determined based on the position of the LED (22) in the LED matrix lighting device (20).

5. The LED matrix lighting device (20) according to claim 1 or 2, wherein The refraction angle (39) is the angle between the optical center axis of the collimated light of the LED (22) and the optical center axis of the refracted light (38) of the same LED (22).

6. The LED matrix lighting device (20) according to claim 1 or 2, wherein a current provided to at least one LED is adjustable.

7. A machine vision system (40) for detecting deviations from a wood fiber web, wherein the machine vision system (40) comprises: The LED matrix lighting device (20) according to any one of claims 1 to 6; at least one imaging device (41) for capturing an image of the illuminated area; and Data processing device (42).

8. A machine vision system (40) according to claim 7, wherein the data processing means (42) is arranged to analyse the image data to detect intensity deviations in the captured images.

9. A method for illuminating a lighting pattern, comprising: Obtaining image data; Analyze image data; detecting, in the captured image, intensity deviations in a lighting pattern provided by the LED matrix lighting device (20) according to any one of claims 1 to 6; as well as A current provided to at least one LED (22) of the LED matrix lighting device (20) is adjusted based on intensity deviations detected in the captured image.

10. A computer program product implemented on a non-transitory computer readable medium, comprising computer program code, the computer program code being configured to, when executed on at least one processor, cause a system to perform a method comprising: Obtaining image data; Analyze image data; detecting, in the captured image, intensity deviations in a lighting pattern provided by the LED matrix lighting device (20) according to any one of claims 1 to 6; and A current provided to at least one LED (22) of the LED matrix lighting device (20) is adjusted based on intensity deviations detected in the captured image.

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