Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B07—SEPARATING SOLIDS FROM SOLIDS; SORTING
  • B07C—POSTAL SORTING; SORTING INDIVIDUAL ARTICLES, OR BULK MATERIAL FIT TO BE SORTED PIECE-MEAL, e.g. BY PICKING
  • B07C5/00—Sorting according to a characteristic or feature of the articles or material being sorted, e.g. by control effected by devices which detect or measure such characteristic or feature; Sorting by manually actuated devices, e.g. switches
  • B07C5/34—Sorting according to other particular properties
  • B07C5/342—Sorting according to other particular properties according to optical properties, e.g. colour

Definitions

• the invention relates to a method and an apparatus for sorting objects using a moving conveyor belt and a vision system.
• the invention particularly provides a method and apparatus for sorting first and second mutually differing types of object which have similar physical characteristics but differing visual characteristics.
• a sieve can be used to separate a first type of object from a second type.
• a magnet can be used.
• a problem occurs when objects have similar physical characteristics, such as two types of wood material, for instance MDF and wood, or such as two types of stone
• Such apparatuses are known from US 5,305,894 (McGarvey, 1994).
• the apparatuses described here comprise a conveyor belt device with a conveyor belt which typically moves with sufficient speed to propel objects reaching the end of the conveyor belt a distance away from the belt and
• a bank of nozzles is disposed above the ejection path of the objects propelled from the conveyor belt, which nozzles deflect objects downward in forced manner (i.e.
• a separation of the objects can in this way be obtained by targeted actuation of the nozzles, wherein a first type is deflected in forced manner by the nozzles and comes to lie close to the conveyor belt, and a second type comes to lie in unforced manner further away from the conveyor belt. Selection of objects which have a defect further takes place in said publication on the basis of colour using a graphics processor, and on the basis of this selection an ejection pattern is placed in a memory queue.
• This queue is advanced pulse by pulse in the memory on the basis of the pulses from an incremental shaft counter connected to the conveyor belt and, at the end of the queue, sent to a processor which actuates an ejector mechanism in order to eject the objects which have a defect. There is therefore a direct link between the advance of the queue in the memory and the incremental shaft counter.
• a drawback of the apparatuses for separating objects via a prior art camera is that only simple graphic analyses can be made of the image because the computation time for the image processing has to be constant and predictable.
• the method for sorting first and second mutually differing types of object using a moving conveyor belt comprises for this purpose the following successive steps of:
• step (j) position information (X and Y coordinates) obtained from step (j) to position information (X and Y coordinates) of each of said selected objects on the conveyor belt at the moment said position information (X and Y
• step (k) selecting and actuating with said controller, on the basis of position information (X and Y coordinates) of each of said selected objects on the conveyor belt from step (k), one or more nozzles of an array of nozzles placed at the end and transversely over the width of said conveyor belt at the moment the selected object comes within range of said one or more nozzles so that the direction of movement of the selected object can be changed by escape of a fluid from the one or more nozzles.
• the image processing unit can however be designed such that it is able to separate
• the speed of the conveyor belt is preferably set such that a speed is obtained whereby the objects placed on the conveyor belt no longer overlap each other .
• the pulse in step (c) is an electrical pulse.
• This pulse can however also be an optical pulse which is transmitted via for instance a glass fibre cable.
• the position information in step (i) is a set of X and Y coordinates for each of said selected objects related to the formed image.
• the position information in step (i) is a set of X and Y coordinates for each of said selected objects related to the conveyor belt. In this latter case the X-coordinates are related to the recorded image, corrected for the fixed distance - in pulses - between the beginning of the recorded image and the end of the conveyor belt.
• Beginning of the recorded image is understood to mean the position of the first scan line of the camera or the position of that side of the recorded image situated closest to the end of the conveyor belt.
• End of the conveyor belt is understood to mean that part of the conveyor belt where the belt returns to its starting position and/or where the objects are propelled from the conveyor belt and/or where the array of nozzles is located. The skilled person is free to choose this value as a function of the best operation of the sorting apparatus, and this value can thus be chosen with some margin.
• step (k) of said position information (X and Y coordinates) with the controller particularly comprises correcting by said controller the X-coordinate for the processing time of said imaging system and said
• said moment of actuation of the selected one or more nozzles by said controller in step (1) is the moment at which the number of pulses generated in said counter as of the X-coordinate being received by said controller in step (k) is equal to the X-coordinate of step (k); and wherein the selected one or more nozzles are those nozzles whose position at the end of said conveyor belt corresponds to the Y-coordinate of the selected object.
• the synchronization between the passage of an object close to the array of nozzles and the actuation of the nozzles is position-controlled and not time-controlled, and does not depend on the processing speed of the respective processors or even on the position of an object in the image. This is because the ejection of objects by one or more nozzles takes place on the basis of a counter reading which measures a position of the conveyor belt, wherein a predetermined number of pulses is first added in the method in order to correct for the relative distance between conveyor belt and array of nozzles.
• predetermined number of pulses defines a distance in that the quantity of pulses is directly proportional to the displacement of the conveyor belt. Determining of the moment of ejection is hereby separated from the computation time of the image processing. Earlier or later arrival of the results of the image processing will thus have no effect on the X-coordinate which determines the moment of ejection.
• the actuation of the one or more nozzles is even independent of the sequence of the position of a selected object in the image, this in contrast to the prior art, where the sequence of a selected object in a queue corresponds to the sequence of actuation of the one or more nozzles.
• An additional advantage of the invention is that the speed of the conveyor belt, if it is located high enough for objects to be propelled therefrom, can also vary
• said first type of object is Medium- Density Fibreboard (MDF) and said second type of object is wood.
• MDF Medium-Density Fibreboard
• Wood is understood here to mean wood from a natural source, for instance pinewood, oak, cedar, fir, ash and so on. The visual difference between MDF and wood is more complex than merely a colour difference. Surface texture and/or shape have to be analysed via
• the shape filter is for instance based on one or more of anisometry, strucfactor and circularity.
• the structure filter is based for instance on a region growing algorithm.
• Line scan cameras are known from the prior art and are known for their high operating speed.
• the recording of an image also becomes position-controlled by coupling this camera to the pulse generator. Changing the speed of the conveyor belt will hereby have no effect on the image.
• each image line represents a pulse, it will further be easy to express the distance of an object on the image in number of pulses.
• a further advantage is that, because each line is recorded at one and the same position on the conveyor belt, the image will be very homogenous, whereby less account need be taken of ambient factors in the image processing.
• a lighting unit is disposed for the purpose of illuminating said predetermined zone at an angle which differs at least 25° from the viewing angle of the camera, so that the surface relief of objects is more readily visible.
• Surface texture is an important element particularly for the purpose of distinguishing MDF and wood. Placing the light source at an angle relative to the camera allows the camera to observe shadows where there are height differences in the surface. These shadows can assist the image processing in obtaining a better defined view of the surface texture.
• the conveyor belt has a length between said predetermined zone and said end of the conveyor belt which amounts to at least three times Z times N mm.
• Z is the number of mm per pulse, while N represents the number of pulses per image.
• Z times N is thus the distance visible in one camera image.
• the invention further relates to a sorting apparatus for sorting first and second types of object using a moving conveyor belt, comprising:
• a feed unit provided for placing objects spaced apart on the conveyor belt
• a motor for driving the conveyor belt;
• a pulse generator coupled to the conveyor belt in order to measure the displacement of the conveyor belt and to transmit a pulse to a controller every Z mm, wherein Z is a real number between 0.1 and 50;
• a camera placed above a predetermined zone of the conveyor belt and provided to form an image of said zone, and wherein the camera is operatively coupled to the pulse generator in order to transmit an image to an image processing unit after a determined number N of pulses, wherein N is a natural number between 20 and 1000;
• an image processing unit provided for receiving and analysing images from the camera in order to select objects of the first type in the images and determine position information (X and Y coordinates) of each of the selected objects of the first type;
• controller provided for receiving pulses from a pulse generator, wherein the controller comprises a counter for the purpose of counting the pulses, provided for the purpose of conversion by said controller of said position information (X and Y coordinates) obtained from step (j) to position information (X and Y
• step (j) has reached the controller; and provided for the purpose of selecting and actuating said array of nozzles on the basis of position information received from the image processing unit.
• Figure la is a top view of a sorting apparatus
• Figure la is a side view of a sorting apparatus
• Figure 2 is an overview of the computation of the X and
• Figure 1 shows the sorting apparatus according to the invention for separating two types of object 4, in
• a conveyor belt device comprising a conveyor belt 1 running over at least a starting roller 2a and an end roller 2b, is driven by a drive motor 3 which is connected here to the starting roller in order to minimize slippage.
• a drive motor 3 which is connected here to the starting roller in order to minimize slippage.
• Present on the conveyor belt are objects of a first type and a second type to be separated.
• the end roller is preferably as small as possible in order to improve the ejection of the objects. This is because it has been
• Conveyor belt 1 is further connected via the end roller to a pulse generator 10 which measures the displacement of conveyor belt 1. Pulse
• Objects are laid on the conveyor belt using a feed device 8.
• This can be a manual feed, but is preferably a mechanical feed device; connected for instance to a container with objects, or a feed device connected for instance to a wood chipper.
• a vibrating chute is preferably used in order to ensure that the objects are separated and come to lie adjacently of each other and not on top of each other on the conveyor belt. This latter is also realized by maintaining a sufficiently high speed of the conveyor belt, for instance 3 m/sec.
• a camera 6 is placed above conveyor belt 1, over a predetermined zone thereof.
• This camera 6 is provided for the purpose of forming an image of said zone.
• the camera is a line scan camera.
• the placing of the camera can be determined experimentally. It is important that the camera can form an image of the full width of the conveyor belt.
• the camera hangs for instance about 1 metre above the conveyor belt and makes a recording of a narrow strip of the conveyor belt, the scan line 7.
• the line scan camera is connected to an image processing unit 13.
• Placed adjacently of the camera is a lighting unit 9. This consists in this exemplary embodiment of an LED bar extending over the whole width of the conveyor belt. The lighting ensures that the shapes and colours to be distinguished are
• halogen lamps depending on the application and the filters used to analyse the objects.
• the image processing unit transmits the position information of each object to a controller 14, which in turn actuates the array of nozzles but also receives pulse information from pulse generator 10.
• a controller 14 which in turn actuates the array of nozzles but also receives pulse information from pulse generator 10.
• the array of nozzles 5 is arranged above the ejection path of the objects propelled from the conveyor belt, wherein each nozzle can be separately activated.
• a fluid here air
• ejection a fluid, here air
• the pulse generator begins to generate pulses.
• the belt passes under the line camera and the forming of an image begins by the line camera, which
• the image line length is then preferably equal to a displacement of Z mm so as to be able to form a complete image without gaps.
• a typical image line length is for instance 1 mm, which then corresponds - at a conveyor belt speed of 3 m/sec - to a pulse frequency and to the recording speed of a single image line of 1/3000 sec. This lies well within the capabilities of a typical image line camera.
• the complete image is formed and transmitted to the image processing device.
• the size of the image thus amounts to 100 image lines. This transmission may require a determined amount of time.
• the conveyor belt in the example has already advanced 40 pulses and the selected object is located 597 pulses from the nozzles.
• the image processing unit determines the X and Y coordinates of each object on the basis of their position in the image and - via appropriate filters - it is determined for each object whether or not it has to be selected and ejected by one or more nozzles.
• the X and Y coordinates of each object to be ejected are stored in a table in the image processing system. Shown in the example is an object with the X-coordinate 37. This object is located during the forming of the image at a distance of 637 pulses from the nozzles, i.e. at a distance (X-coordinate) which is determined by an X-coordinate of the image plus a fixed number of pulses, here 600, this being the offset value which indicates the distance in pulses between the first image line and the array of nozzles.
• this table is transmitted to the controller, in this case a PLC (Programmable Logical
• the conveyor belt has again advanced a number of pulses further, i.e. 20 pulses in the example, this corresponding to a processing time of the image processing unit of 20/3000 sec.
• the table is then transmitted to the controller, which may also take a determined amount of time, in the example 20 pulses.
• the calculated X-position (637) is then corrected for the processing times (20 + 20 pulses) for respectively the image processing unit and the transmission to the controller, which can compare the position of the first image line in the recorded image, in the example at pulse P 0 , to the actual counter reading in the controller Pi at which the X-position is received by said controller, wherein the overall
• the controller then monitors the X-coordinate of each object in the table until the number of pulses generated in the counter from the moment the controller receives the X- position is equal to the corrected X-position of the object in question.
• a nozzle is activated in order to eject the selected object.
• the duration of the activation i.e. the period of time for which a fluid escapes, can be determined, for instance as being directly proportional to the size of the selected object and
• the counter can optionally be reset to zero.
• a particular case is an object present in two adjacent images. This object also has to be recognized with the same filters and if these filters select, among other criteria, according to shape, the shape recognition would not be correct (e.g. recognition of round shapes between angular shapes, wherein a round shape over two images would be recognized in a single image as an angular shape) .
• Known in the prior art is a method for dealing with such a case by forming two images overlapping each other in a zone, superimposing the images and calculating the position of each object from the superimposed images.
• this object is selected from the image and combined to form a single object having a shape corresponding to the actual shape of the object on the conveyor belt.
• the object is then processed by the image processing unit and the position information is determined .
• a sorting apparatus for the purpose of separating wood and MDF was constructed with the following components.
• Siemens box PC Siemens box PC

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Cited By (5)

Citations (6)

• 2011
  • 2011-11-16 BE BE2011/0663A patent/BE1020295A3/nl active
• 2012
  • 2012-11-16 WO PCT/BE2012/000050 patent/WO2013071375A1/en active Application Filing

Patent Citations (6)

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