Patent Description:
The invention also relates to a system and a computer program product causing the system to carry out the method.

In continuous manufacturing processes, there are materials or products constantly running through the machine. In such processes, materials and products must be monitored in order to detect possible deviations or web breaks. Furthermore, condition of fabrics under materials or products is checked during scheduled or planned downtimes of a machine/machinery in order to detect possible deviations that may cause those above-mentioned deviations to materials or products or web breaks, but which could also cause unscheduled or planned downtimes of a machine/machinery. The product, machine or process may be monitored, for example, by machine vision systems such as camera systems. The captured images are analysed by a processing unit.

<CIT> discloses a method and an apparatus in which a cyclic pattern is inspected from a continuous cyclic pattern product. The apparatus comprises a line sensor camera, a light source which is arranged to face the camera, an upstream-side belt conveyor and a downstream-side belt conveyor by which an object to be inspected is moved between the camera and the light source. In addition, an image processor is provided. When the product is absent, the scan rate is set lower.

<CIT> discloses a fully automated method maintaining runnability in a paper or board machine, including detecting a web break, cleaning, checking of the cleanness level using machine vision, tail threading and (re)start-up or production. The detection of a web break is made using the machine's measuring or sensor systems. When the automation system detects and concludes the absence of the first object by the, a signal of this is transmitted and cameras are used to monitor the underlying second object to estimate its cleaning requirements.

<CIT> discloses a system for monitoring a paper web using cameras. In case of a web break, image storing is terminated. The imaging system detects both defects and web breaks. Cameras operate at maximum frequently or less frequently. The same cameras are used to find small defects and to cover the whole web, when the smallest defects cannot be found.

<CIT> discloses that it is advantageous to use a single machine vision system to monitor both defects and web breaks in a paper web.

<CIT> discloses a method for detecting a tear in a fibrous web in a drying section of a machine for producing the fibrous web. The method comprises the steps of: detecting the tear in the fibrous web passing through the drying section of at least one web tear detection device, and activating a cut-off apparatus dependant upon a signal from the web tear detection device.

<CIT> discloses a cutting-off device and tear detector are provided for cutting a web of paper in a press end of a paper machine, in response to a tear in the web of paper in a single-tier dryer end, the tear of the web of paper being recognized via a tear signal and transmitted to the cutting-off device.

Now there has been invented a method, a machine vision system with two different operating modes for two different objects, and a computer readable medium comprising a computer program stored therein.

In the following, various embodiments of the invention will be described in more detail with reference to the appended drawings, in which.

The present invention relates to a machine vision system according to example embodiments having two different operating modes for two different objects and comprising at least one image sensor used for imaging a web product and machine clothing and at least one lighting device for illuminating the web product and the machine clothing. The web product is a first object and it is imaged and illuminated in the first operating mode of the machine vision system. The machine clothing is the second object and it is imaged and illuminated in the second operating mode of the machine vision system.

The term "web product" refers in this context to any type of a wood fibre web. The term "wood fibre" refers in this context to any suitable wood fibre webs, for example, paper, cellulose or cardboard webs. The term "machine clothing" refers in this context to any type of fabric used, for example, in a paper, cardboard of cellulose machine/machinery for dewatering and/or transporting the web product. It may be, for example, a woven textile belt of felt. The web product and the machine clothing is illuminated and imaged in order to find web deviations from the web product and clothing deviations from the machine clothing. The term "web deviation" includes in this context any deviation detectable from the web product, for example, a defect, a hole, a stain, a definite change, a grey or dark spot, a streak, a wrinkle, an air bubble or a pattern in a web. The term "clothing deviation" includes in this context any deviation detectable from the machine clothing, for example, a defect, a hole, or a risen yarn etc. that may possibly cause machine clothing-related web defect(s). Machine clothing contributes to product quality, fibre and chemical conversion efficiency, and production speed.

As stated above, a machine vision system may comprise at least one image sensor, at least one lighting device and data processing device. The image sensor is used for capturing images of at least two different kinds of objects, for example, a web and machine clothing and the lighting device is used for lighting the objects arranged to be imaged. The machine vision system may have at least two different operating modes, wherein each mode is arranged to be suitable for a certain target: a first operating mode for the web product and the second operating mode for the machine clothing. Different operating modes may have different lighting and also the imaging frequency may be different. The operating mode may be selected on basis of the imaging target for enabling effective detecting of errors from both objects.

As discussed, the operating mode being used depends on the object. In the first operating mode the first object, the web product, is illuminated by a first type of illumination and images of the first object is captured at a first imaging frequency and in the second operating mode the second object, the machine clothing, are illuminated by a second type of illumination and images of the first object are continued to be captured at the first imaging frequency but possibly it is changed to the second imaging frequency. When at least one camera of the machine vision system is imaging and at least one lighting device is used for illuminating the web product in the first operating mode and the web product ends, for example, in a case of a web break, a camera sensor of the machine vision system detects the absence of the web or an external indication signal about the web break is transmitted to the machine vision system, for example, from a paper machine control system, the first operating mode of the machine vision system used for imaging and illuminating the web product is arranged to be changed to the second operating mode for imaging and illuminating the machine clothing. A second mode reconfiguration signal is at least transmitted to at least one lighting device for reconfiguring the at least one lighting device to the second operating mode. It is also possibly that a second mode reconfiguration signal is also transmitted to at least one camera sensor for reconfiguring the at least one camera sensor.

Respectively, when in the second operating mode the machine vision system detects that the web product is on the machine clothing or an external indication signal indicates to the machine vision system that the web product is on the machine clothing, the second operating mode of the machine vision system is changed to the first operating mode for imaging and lighting the web product until the next web break results in changing to the second operating mode.

When operating mode changes, also the illumination changes, for example, the type of lights, the number of lights, the direction of lights, the operation of lights or lights being used may change to be more suitable for imaging the object in question. In other words, illumination changes when imaging object changes so that illumination depends on the object to be illuminated. When operating mode changes, the reconfiguration signal may also determine for the image sensor(s) a resolution of images to be captured or how the images should overlap. However, in addition to changing illumination and possibly also imaging frequency, it is possible that when operating mode changes also image analysing parameters of the data processing device are reconfigured to be more suitable for current object. For example, in the first operating mode image analysing parameters are suitable for detecting deviations in a web product and in the second operating mode image analysing parameters are suitable for detecting deviations in machine clothing. There may be a need for different analysing parameters in different operating modes, because the type of deviations may be different in the web product and in the machine clothing. The colour of the web product and the machine clothing may be different, which may also cause a need for different image analysing parameters.

An image sensor of the machine vision system may be, for example, a camera, for example, a c-mos or ccd camera, a matrix or line scan camera, a black and white or colour camera, a regular or smart camera, or any suitable camera. Targets arranged to be monitored may be illuminated for imaging by at least one lighting device and a lighting device of the machine vision system may be, for example, a LED or one lighting device may comprise two, three, four or a plurality of LEDs.

The present invention further relates to a method according to example embodiments of the invention, wherein in a so called first operating mode one or more images of a web product are captured by one or more image sensors when illuminated by one or more lighting device. When the web product ends, for example, in a case of a web brake, or is no more in the process, the machine vision system detects the situation from images captured by one or more image sensor(s) or it receives an external indication signal about the web brake, the machine vision system is changed to the second operating mode for imaging and illuminating the machine clothing. The type of illumination and possibly also the image capturing frequency in the first and second operating mode may be different.

In the second operating mode at least one camera sensor image may capture images and at least one lighting device may illuminate the second type of illumination a predetermined time. In other words, it is possible that they do not continue capturing of images and illuminating until the second operating mode changes to the first operating mode. The machine clothing may comprise a seam or a kind of marking. The imaging and the second type of illumination may be continued at least until the seam or the some kind of marking in the web is detected from the machine clothing at least twice. This way it is ensured that the whole web product is imaged, but unnecessary imaging is avoided.

Image data of captured images is analysed by a data processing device of each image sensor of a machine vision system and/or image data of captured images is transmitted to an external data processing device of the machine vision system for analysis. The external data processing device is a data processing device that is not an integrated part of a camera. The data processing device may monitor the data in order to find deviation(s) in image data of a web product and/or image data of machine clothing.

<FIG> shows an embodiment of the invention, in which a machine vision system <NUM> is disclosed in conjunction with two objects, a web 17a and machine clothing 17b. The machine vision system <NUM> comprises two lighting devices <NUM>, <NUM> and two smart cameras <NUM>, <NUM> comprising an image sensor <NUM>, <NUM> and a data processing device <NUM>, <NUM>. Lighting devices <NUM>, <NUM> illuminates the movable web 17a and the machine clothing 17b when the web 17a is not available. The image sensors <NUM>, <NUM> are arranged to capture images from the movable web 17a and from the machine clothing 17b when the web 17a is not available and to transmit image data to the data processing device <NUM>, <NUM> of the smart camera <NUM>, <NUM>.

The data processing devices <NUM>, <NUM> comprise at least one processor, at least one memory including computer program code for one or more program units, and means for receiving image data wirelessly or via wired connection from the image sensor <NUM>, <NUM>, for example, a receiver or a transceiver, and means for transmitting trigger signals wirelessly or via wired connection, for example, a transmitter or a transceiver. There may be multiple processors e.g. a general purpose processor and a graphics processor and a DSP processor and/or multiple different memories e.g. volatile memory for storing data and programs at run-time and nonvolatile memory such as a hard disk for permanently storing data and programs. The data processing device <NUM> of the smart camera <NUM> and the data processing device <NUM> of the smart camera <NUM> may be any computing device suitable for handling image data such as a computer. The data processing device <NUM> is in electronic communication with the image sensor <NUM> and the lighting device <NUM> via signal lines and the data processing device <NUM> is in electronic communication with the image sensor <NUM> and the lighting device <NUM> via signal lines. The lighting devices <NUM>, <NUM> may also be integrated parts of the smart cameras <NUM>, <NUM>. The smart cameras <NUM>, <NUM> may also include a video controller and an audio controller for generating signals that can be produced for the user with computer accessories. The smart cameras <NUM>, <NUM> produce output to the user through output means. The video controller may be connected to a display. The display may be e.g. a flat panel display or a projector for producing a larger image. The audio controller may be connected to a sound source, such as loudspeakers or earphones. The smart cameras <NUM>, <NUM> may also include an acoustic sensor such as a microphone.

When the web 17a is on the machine clothing 17b as in <FIG>, the image sensors <NUM>, <NUM> are arranged to capture images of the web 17a and the lighting devices <NUM>, <NUM> are illuminating the web 17a in the first operating mode. The data processing devices <NUM>, <NUM> are configured to receive captured images as image data and analyse the image data in order to find deviations in the web 17a. The data processing devices <NUM>, <NUM> analyse the image data. If the data processing device <NUM> detects from the image data that the web 17a is not on the machine clothing 17b, it may reconfigure the image sensors <NUM>, <NUM> and the machine vision system <NUM> to a second operating mode. The data processing devices <NUM>, <NUM> are still configured to receive images captured in the second operating mode as image data and analyse the image data in order to find deviations in the machine clothing 17b.

As mentioned above, after reconfiguration the image sensors <NUM>, <NUM> continue to capture images of the machine clothing 17b in the second operating mode. In the second operating mode the image capturing frequency may be different or it may remain the same. The second image capturing frequency of the second operating mode may be, for example, higher than the first image capturing frequency of the first operating mode so that deviations in the machine clothing 17b can be more accurately imaged and detected. Deviations in the machine clothing 17b may be more difficult to detect, so there is a need to capture more images of the machine clothing 17b in order to enable more efficient monitoring of deviations in the machine clothing 17b. In the second operating mode, the lighting devices <NUM>, <NUM> are arranged to illuminate the machine clothing 17b in the second operating mode, wherein the type of illumination of the second operating mode is different than the type of illumination of the first operating mode. There may be a need, for example, for more efficient lighting when imaging the machine clothing 17b in the second operating mode, therefore the intensity of light of lighting devices <NUM>, <NUM> may be increased or there may be a need for less efficient lighting when imaging the machine clothing 17b in the second operating mode, therefore the intensity of light of lighting devices <NUM>, <NUM> may be decreased. Imaging of the machine clothing 17b in the second operating mode at the second image capturing frequency is shown in <FIG>. The need of the intensity of light of lighting devices <NUM>, <NUM> may depend, for example, on the colour of the machine clothing 17b compared to the web 17a.

In the second operating mode, the image sensors <NUM>, <NUM> capture images from at least the whole machine clothing cycle, for example, at least from a marking <NUM> to the marking <NUM> i.e. until the marking <NUM> is detected twice in the images captured by image sensors <NUM>, <NUM> by the data processing devices <NUM>, <NUM>.

<FIG> shows an embodiment of the invention, in which a machine vision system <NUM> is disclosed in conjunction with two objects, a web 23a and machine clothing 23b. The machine vision system <NUM> comprises at least two image sensors <NUM>, <NUM>, at least two lighting devices <NUM>, <NUM> and a data processing device <NUM> for analysing image data captured by the at least two image sensors <NUM>, <NUM>. The image sensors <NUM>, <NUM> are arranged to capture images from the moving object 23a that is a material web in a first operating mode and arranged to capture images from the second moving object 23b that is a machine clothing in a second operating mode and to transmit data of each image to the data processing device <NUM>. The lighting devices <NUM>, <NUM> are arranged to illuminate the moving objects 23a, 23b while imaging so that in both operating modes the illumination type being used is different.

The data processing device <NUM> comprises at least one processor, at least one memory including computer program code for one or more program units, and means for receiving image data wirelessly or via a wired connection, for example, a receiver or a transceiver, and means for transmitting configurations by reconfiguration signals wirelessly or via a wired connection, for example, a transmitter or a transceiver, to the lighting devices <NUM>, <NUM> and also possibly to the image sensors <NUM>, <NUM>. There may be multiple processors e.g. a general purpose processor and a graphics processor and a DSP processor, and/or multiple different memories e.g. volatile memory for storing data and programs at run-time, and nonvolatile memory such as a hard disk for permanently storing data and programs. The data processing device <NUM> may be any computing device suitable for handling image data, such as a computer. The data processing device <NUM> is in electronic communication with the image sensors <NUM>, <NUM> and the lighting devices <NUM>, <NUM> via signal lines. For handling the signals to/from the signal lines, the data processing device <NUM> comprises I/O circuitry. The connection between the lighting devices <NUM>, <NUM> and the data processing device <NUM> and the image sensors <NUM>, <NUM> and the data processing device <NUM> is a wired or wireless network. The data processing device <NUM> may also include a video controller and an audio controller for generating signals that can be produced to the user with computer accessories. The video controller may be connected to a display. The display may be e.g. a flat panel display or a projector for producing a larger image. The audio controller may be connected to a sound source, such as loudspeakers or earphones. The data processing device <NUM> may also include an acoustic sensor, such as a microphone. The lighting devices <NUM>, <NUM> may also be integrated parts of the camera sensors <NUM>, <NUM>.

The data processing device <NUM> is configured to analyse the received images captured by the image sensors <NUM>, <NUM> and if the data processing device <NUM> detects a deviation or a web break in the first operating mode or presence of a web in the second operating mode, it may indicate it for the process operator and/or transmit reconfiguration signals to at least one lighting device and possibly also to the image sensors.

When the web 23a is on the machine clothing 23b as in <FIG>, the image sensors <NUM>, <NUM> are arranged to capture images of the web 23a and the lighting devices <NUM>, <NUM> are illuminated the web 23a in the first operating mode. The data processing device <NUM> is configured to receive captured image as image data. The data processing device <NUM> is arranged to analyse the image data. If the data processing device <NUM> detects from the image data that the web 23a is not on the machine clothing 23b, it may reconfigure the image sensors <NUM>, <NUM> and the lighting devices <NUM>, <NUM> to a second operating mode for capturing images of the machine clothing 23b and illuminating the web machine clothing 23b. The data processing device <NUM> is configured to receive images captured in the second operating mode as image data and analyse the image data in order to find deviations in the machine clothing 23b.

As mentioned above, after reconfiguration to the second operating mode, the image sensors <NUM>, <NUM> are arranged to capture images of the machine clothing 23b in the second operating mode. In the second operating mode, the image capturing frequency may be different or it may remain the same compared to the first operating mode. The second image capturing frequency of the second operating mode may be, for example, higher than the first image capturing frequency of the first operating mode so that deviations in the machine clothing 23b can be more accurately imaged and detected or the second image capturing frequency may be the same in the first and in the second operating mode. The lighting devices <NUM>, <NUM> may be arranged to illuminate the machine clothing 23b in the second operating mode, for example, more efficiently or less efficiently than in the first operating mode depending on the configurations. Imaging of the machine clothing 23b in the second operating mode at the second image capturing frequency is shown in <FIG>.

The image sensors <NUM>, <NUM> capture images from at least the whole machine clothing cycle of the machine clothing 23b, for example, at least from a seam <NUM> of the machine clothing 23b to seam <NUM> i.e. until the seam <NUM> is detected twice in the images captured by image sensors from the seam <NUM> by the data processing device <NUM>.

<FIG> shows an embodiment of the invention, in which a machine vision system <NUM> is disclosed in conjunction with a machine clothing <NUM> as a moving object. The machine vision system <NUM> comprises an image sensor <NUM>, a lighting device <NUM> and a data processing device <NUM> for analysing image data captured by the image sensor <NUM>. The image sensor <NUM> is arranged to capture images from a material web (currently not on the machine clothing <NUM>) in a first operating mode and arranged to capture images from the machine clothing <NUM> in a second operating mode and to transmit data of each image to the data processing device <NUM>. The lighting device <NUM> is arranged to illuminate the machine clothing <NUM> (or the material web when available) while imaging so that in both operating modes the illumination type being used is different. The lighting device <NUM> may also be integrated parts of the camera sensor <NUM>. The data processing device <NUM> is configured to analyse the received images captured by the image sensor <NUM>.

<FIG> shows an embodiment of the invention, in which a machine vision system <NUM> is disclosed in conjunction with a machine clothing <NUM> as a moving object. The machine vision system <NUM> comprises three image sensors 31a, 31b, 31c, a lighting device <NUM> and a data processing device <NUM> for analysing image data captured by the image sensors 31a, 31b, 31c arranged in parallel for imaging the whole width of the machine clothing <NUM> (and a material web when on the machine clothing <NUM>). The image sensors 31a, 31b, 31c are arranged to capture images from the material web in a first operating mode and arranged to capture images from the machine clothing <NUM> in a second operating mode and to transmit data of each image to the data processing device <NUM>. The lighting device <NUM> is arranged to illuminate the machine clothing <NUM> (or the material web when available) while imaging so that in both operating modes the illumination type being used is different. The lighting device <NUM> may also be an integrated part of a camera sensor.

<FIG> shows a monitoring method <NUM> of a machine vision system according to an example embodiment. The machine vision system comprises at least one lighting device, at least one image sensor and a data processing device. In step <NUM>, the machine vision system is monitoring a first object, for example, a material web in a first operating mode. In a first operating mode the first object is illuminated by said at least one lighting device using a first type of illumination and images of the first object are captured by said at least one image sensor at a first imaging frequency, and wherein the first object is arranged at least partly on a second object. The second object may be, for example, a machine clothing. In step <NUM>, the captured image data of the captured images is transmitted to the data processing device for analysis. In step <NUM>, the machine vision system changes to monitor the second object in a second operating mode, if absence of the first object on the second object is detected by the data processing device in step <NUM>.

In many cases, in the second operating mode the second object is illuminated by said at least one lighting device using a second type of illumination and images of the second object are captured by said at least one image sensor at a second imaging frequency, wherein the first type of illumination is different that the second type of illumination and the second imaging frequency is different than the first imaging frequency. However, in the second operating mode, it may be possible, that the first type of illumination is the same than the second type of illumination or that the second imaging frequency is the same than the first imaging frequency.

The various embodiments of the invention set out in the appended set of claims can be implemented with the help of computer program code that resides in a memory and causes an apparatus to carry out the embodiments of the invention set out in the appended set of claims. For example, the apparatus that is a computing device, for example, a data processing device may comprise circuitry and electronics for analysing, receiving and transmitting data, a computer program code in a memory, and a processor which, when running the computer program code, causes the apparatus to carry out the features of an embodiment set out in the appended set of claims. The processor, when running the computer program code, may carry out the steps of the following method: capturing image(s) of a first object by an image sensor, for example, a camera sensor, a first illumination in a first operating mode and capturing image(s) of a second object by the image sensor in a second illumination in a second operating mode, when absence of the first object is detected.

Claim 1:
A method, comprising:
monitoring a moving web (17a) in a first operating mode of a machine vision system (<NUM>) comprising at least one lighting device (<NUM>, <NUM>), at least one image sensor (<NUM>, <NUM>) and a data processing device (<NUM>, <NUM>), wherein the monitoring in the first operating mode comprises illuminating the web (17a) arranged at least partly on a moving machine clothing (17b) by said at least one lighting device (<NUM>, <NUM>) in a first operating mode and capturing images of the web (17a) by said at least one image sensor (<NUM>, <NUM>) at an image capturing frequency;
transmitting the captured image data to the data processing device (<NUM>, <NUM>) for analysis; and
changing the machine vision system (<NUM>) to a second operating mode, if absence of the web (17a) on the machine clothing (17b) is detected, wherein in the second operating mode images of machine clothing (17b) are captured by said at least one image sensor (<NUM>, <NUM>) at the same or different image capturing frequency than in the first operating mode, characterized in that the lighting devices (<NUM>, <NUM>) are arranged to illuminate the machine clothing (17b) in the second operating mode, wherein intensity of light is increased or decreased for enabling effective detecting of deviations from the machine clothing (17b).