Roller screen and method

Abstract

A roller screen for screening wood-based material and a method for controlling the operation of a roller screen. The roller screen (1) comprises a roller bed (2) having several rotating rollers (3) separated by screen openings ( 4 ). The material is fed by a feeding device (5) onto the roller bed as a material layer (7). One or more detection devices (S) determine a profile (P) of an upper surface of the material layer traveling on the roller bed. The detection data is provided to a control unit (CU) controlling the operation of the feeding device according to a selected control strategy and to provide a desired profile of the upper surface.

Description

[0001] Roller screen and method

[0002] Background of the invention

[0003] The invention relates to a roller screen for screening wood-based material into fractions o f di f ferent particle si zes when manufacturing wood-based panels .

[0004] Further, the invention relates to a method for controlling a roller screen of a panel manufacture plant .

[0005] The obj ect of the invention is described in more detail in the preambles of independent claims of the application .

[0006] Various wood-based panels such as chipboard, MDF, OSB and corresponding wood fibre boards are widely used in construction and furniture manufacturing . Wood chips or corresponding crushed or ground wood-based material used as one raw material component in these panels need to be screened into fractions of di f ferent particle si zes before they may be fed to a panel manufacturing press and used in panel manufacturing . One known device for screening such material is a roller screen having a roller bed comprising several parallel rotating rollers separated by screen openings . However, some drawbacks have been identi fied with the current roller screens and their control .

[0007] Short description of the invention

[0008] The inventive idea is to provide a novel and improved roller screen and a method of controlling its operation .

[0009] The features characteri zing the roller screen according to the invention are speci fied in the characteri zing part of the independent device claim .

[0010] The features characteri zing the method according to the invention are speci fied in the characteri zing part of the independent method claim .

[0011] The idea of the proposed solution is that a feeding device of a roller screen i s actively controlled during operation in response to measurement or detection data on a profile of an upper surface of a material layer traveling on a roller bed of the roller screen .

[0012] The roller screen comprises several one or several detection devices for determining a profile of an upper surface o f the material layer fed onto the roller bed in a widthwise direction of the material layer . The detection data is transmitted to a control unit of the roller screen . The control unit compares the obtained profi le data of the material layer and detects profile di f ferences in the widthwise direction of the material layer . Thereby the control unit may control the feeding device in response to the detected profile data of the material layer .

[0013] In other words , real-time detection data on the profile of the upper surface of the material layer, or so- called material mat , at its di f ferent widthwise points is produced by the detection devices during use of the roller screen . This gives a possibility to influence the profile of the upper surface of the material layer and distribution of the material layer on the roller bed by actively controlling the operation of the feeding device during use .

[0014] In the solution, a height of the upper surface is thus measured or determined by detectors at di f ferent width positions and on this basis a shape of the upper surface of the material mat may be determined at the control unit . Based on the profile data of the upper surface , a thickness distribution of the material mat in a transverse direction of the roller screen may also be determined, because thickness is directly proportional to the height of the upper surface . The profile data produced in real time provides good and rapid feedback on the success of feeding of the material and enables active and accurate control of the feeding .

[0015] Further, an advantage of the proposed solution is that it may be easily retrofitted to existing roller screens . This enables improvement of the ef f iciency of existing devices , a quicker response to the control of the feeding and reduction of wearing of the rollers .

[0016] According to one embodiment , the wood-based panel being manufactured is a chipboard, an OSB or a corresponding wood fibre board .

[0017] According to one embodiment , the control unit i s configured to control the feeding device to feed wood-based material onto the roller bed as a material layer having an even upper surface . In other words , a profile of the upper surface of the material layer that is as even as possible is used as a control parameter of the feeding device .

[0018] One advantage of the solution is that the material layer may be fed onto the roller bed as a layer having a thickness that is as uni form as possible . In addition, the material layer can be spread as a layer that is as wide as possible so that the full widthwise screening capacity of the roller bed may be better utili zed .

[0019] The goal is thus a uni formly thick and wide material layer, whereby the material being screened is well spread out on the roller bed .

[0020] Thereby the material being screened accumulating in a thick layer in a centre of the screen bed, leaving only thin layers at edges , or no material layer forming at all at the edges may be avoided . Such uneven distribution of the material being screened on the roller bed may have a strong wearing ef fect on a centre part of the rollers , or at that point of the rollers where the thickness of the material layer is greater than in other portions . Such uneven wearing of the rollers may be avoided by the proposed solution . When the rollers wear evenly across their entire length, the wearing and increasing of the screen openings may be compensated for by adj usting a distance between the rollers . The service li fe of the rollers may thus be extended . In addition, ef ficiency of the screening may be improved when the material being screened can be fed in a layer that is as even as poss ible and thus also as thin as possible . In the solution, the full width of the roller bed may be better utili zed .

[0021] According to one embodiment , the control unit i s configured to form the material layer having an even prof ile of the upper surface independently of absolute thickness , i . e . , a target thickness of the material layer is not used as a control parameter, but the control of the feeding device simply tends to continuously di stribute the available material flow evenly across the entire width of the roller bed .

[0022] According to one embodiment , the control unit i s configured to control the feeding device to feed a higher profile of the wood-based material onto both longitudinal edge portions of the roller bed than onto a centre portion between the edge portions in response to data provided to the control unit on a need to reduce wearing of the rollers in said centre portion . In other words , the control principle of the system may be , instead of an even upper surface of the material layer, to intentionally feed more woodbased material onto the edges than the centre part , such that the edges have a higher profile to compensate for the wearing ef fect . The rollers typically wear in their centre portion more than at the edges , and thus the rollers o ften have to be replaced speci fically due to the wearing of their centre parts . The wearing of the rollers is found to be proportional to , among other things , the thickness and mass of the material layer and the forces caused thereby, which are exerted on the rollers . When, according to the control principle of this embodiment, a higher material layer is fed onto the edges than the centre , the edges will be subj ect to a greater wearing ef fect and wearing at the edges may be increased, so to speak, intentionally and the wearing at the centre may be reduced . The solution thus evens out the wearing of the rollers at their di f ferent longitudinal points . This way, the service li fe of the rollers may be extended and production interruptions caused by replacement of the rollers may be reduced .

[0023] According to one embodiment , wear data on the degree of wearing of the rollers at their di f ferent longitudinal points is provided to the control unit . Based on the wear data, the control unit may create the shape of the upper profile used in the control of the feeding device and generate control commands for controlling the feeding device .

[0024] According to one embodiment , the control unit i s configured to estimate the progress of wearing of the rollers and is , based on this estimate , configured to control the feeding device to form an uneven upper profile and actively influence and control the wearing of the rollers . To estimate the progress of the wearing, data on the progress of wearing of the rollers of other corresponding roller screens may be provided to the control unit or the estimation may be based on history data of the roller screen in question . The rollers may be checked and the wearing measured in conj unction with condition monitoring . Further, the wearing may also be estimated by calculation when the roller screen operating data, conditions , properties of the material being screened and operating hours are known .

[0025] According to one embodiment , the control unit i s configured to feed material onto the roller bed to form any shape of the upper profile , i f that is for some reason necessary . The reason may be related to , for example , the operation of the roller screen or condition of the rollers . This profile may also be asymmetrical , i . e . the solution enables feeding o f a higher profile to the area o f a first edge and a lower profile to the area of an opposite second edge of the roller bed . The profile may be linear or follow some curve shape between the edges .

[0026] According to one embodiment , the control unit may be configured to implement , during the operation of the roller screen, di f ferent profile shapes of the upper sur- face , whether predetermined or conf igured during the operation . In other words , the control unit does not have one single profile of the upper surface , but the control unit may select or generate , based on the situation and the provided data and commands , the profile shape used in the control . Further , the control unit may adj ust the absolute height position of the profile to be implemented based on the situation and the provided control parameters .

[0027] According to one embodiment , the control unit i s configured to determine the shape o f advance of the material layer based on the detection data . When detectors of the upper surface o f the material layer are arranged in two or more transverse rows at a distance from each other, the control unit may detect , based on the detection data, how wide the material layer is at each detector row and what the shape of the upper profile is at each detector row . The shape of the advance can thereby be discovered and the feeding and operation of the entire roller screen may be adj usted on that basis .

[0028] According to one embodiment , the roller screen comprises several detection devices for determining the profile of the upper surface of the material layer fed onto the roller bed at several detection points , which detection points are arranged at di f ferent points in the widthwise direction of the material layer . The detection data of the detection devices is transmitted to the control unit comparing the obtained profile data of the material layer at said detection points and detecting the profile di f ferences as viewed in the widthwise direction of the material layer .

[0029] According to one embodiment , there are at least three detection devices . The advantage of this solution i s that with three detection devices , a suf ficiently wide observation width and a suf ficient number o f measurement results to generate reliable control data may be obtained .

[0030] According to one embodiment , two detection devices are arranged at di fferent widthwise detection points . In some cases , even j ust two detection devices may be suf ficient to obtain the necessary control data for controlling the feeding device .

[0031] According to one embodiment, there are 4 - 8 detection devices arranged at several di f ferent detection points in the widthwise direction . There i s typically a good amount of space above the roller bed to mount even a larger number of detection devices . The thickness detection accuracy and coverage of the detection in the widthwise direction of the material layer may be improved by increasing the number of detection devices .

[0032] According to one embodiment , the detection device is a contactless detection device mounted above the roller bed .

[0033] According to one embodiment , the detection device is an optical measuring device , a laser sensor, a ToF sensor, an ultrasound sensor or a corresponding distance measuring device that sends and receives measurement signals .

[0034] According to one embodiment , the detection device comprises a camera providing data configured to be processed by a machine vision program or a corresponding image processing program . By means of image processing, the thickness data may be determined from image data provided by the camera for example based on the colour of the material layer . There may be several cameras or one camera may cover the entire widthwise direction of the roller screen .

[0035] According to one embodiment , the detection device is a 3D profile scanner having a detection range in the widthwise direction of the material layer . With one prof ile scanner, it is possible to cover the entire widthwise direction of the roller screen . I f necessary, there may be several profile scanners .

[0036] According to one embodiment , the detection device comprises a physical detector element arranged above the roller bed and configured to be either continuously in contact with the upper surface of the material layer moving in the feeding direction of the roller bed, or alternatively arranged at a predetermined height position and configured to be af fected by the material layer only when the thickness of the material layer exceeds a predetermined thickness . The physical detector element may be for example a roll or a drag, whose movement is monitored by means of a sensor or measuring device .

[0037] According to one embodiment , the detectors are arranged in one transverse row .

[0038] According to one embodiment , the detectors are arranged as close to the feeding device as possible as viewed in the feeding direction . The detectors may be mounted for example at the first or the second roller . When distance from the feeding device is small , measurement data is quickly obtained for controlling the feeding device .

[0039] According to one embodiment , detectors are arranged in the feeding direction in several transverse rows at a distance from the feeding device and each other . Thereby, by comparing the measurement results of the detectors in di f ferent rows , data is obtained on how the profi le of the upper surface changes when the material moves forward along the roller bed while also being screened . The measurement results may be used for controlling the operation of the feeding device and the entire roller screen .

[0040] According to one embodiment , the feeding device comprises at least one feeding conveyor arranged transversely at a feeding end of the roller bed and configured to transfer material to be screened it receives in the transverse direction of the roller bed . The feeding device is provided with several adj usting elements for controlling the material flow being fed from the feeding conveyor to the roller bed . Further, the feeding device comprises actuators for adj usting the adj usting elements under control o f the control unit . According to one embodiment , the actuator for moving the adj usting elements may be a hydraulic cylinder, pneumatic cylinder, hydraulic motor, linear motor or electric motor .

[0041] According to one embodiment , the feeding conveyor is a feed screw which comprises a conveyor screw at least partially surrounded by a j acket having several feed openings for feeding the material to be screened onto the roller bed . The adj usting elements of the feed conveyor are adj usting plates supported movably relative to the feed openings to control the si ze of the free flow opening of the feed openings .

[0042] According to one embodiment , the conveyor screw is a two-headed screw configured, while rotating, to trans fer the material to be screened from the portions of both ends of the conveyor screw toward the centre part of the conveyor screw . In this case, there are at least three adj usting plates , one adj usting plate in the centre and one on each side of the centre adj usting plate .

[0043] According to one embodiment , the conveyor screw is a two-headed screw configured, while rotating, to trans fer the material to be screened from the centre part of the conveyor screw toward the edges , i . e . to the portions of both ends of the conveyor screw . In other words , the material being processed is fed to the centre part of the feeding device and the screw conveyor distributes the material from the centre part to the edges . Falling of the material from the feed openings onto the roller bed is adj usted by means of the adj usting plates so as to obtain a desired profile of the upper surface for the material layer being fed to the roller bed . When using one two-headed screw, only one rotating apparatus is needed and the structure may be , due to the unitary structure , simple , inexpensive to manufacture , and durable . According to one embodiment , the adj usting plates of the feeding conveyor comprise an oblique adj ustment surface as viewed in their direction of movement . Thereby, the oblique front edge of the adj usting plates constricts the free flow opening of the feed opening so that the amount of material being fed may be controlled at di f ferent width positions of the roller bed .

[0044] According to one embodiment , the conveyor screw may compri se a first and a second screw component arranged one after the other in the axial direction and rotated by their own rotating apparatuses . The solutions according to the above described embodiments , such as adj ustment of the feed openings and the oblique shape of the adj usting plates , may be applied in this embodiment .

[0045] According to one embodiment , the feeding conveyor is alternatively a drag conveyor . The drag conveyor may comprise a conveyor chain or belt driven as an endless loop, which is mounted in the conveyor channel and which is provided with flights or corresponding proj ections that are transverse relative to the direction of movement and move the wood fibre material forward in the feeding direction .

[0046] According to one embodiment , the roller screen comprises a feeding channel for supplying the wood-based material to the feeding device . In connection with the feeding channel there is at least one detector for determining the capacity of a material flow being supplied to the feeding device . Thereby, the control unit is conf igured to control the capacity of the feeding device based on the determined capacity data of the material flow .

[0047] In other words , the material flow fed to the feeding device is monitored and the feeding device is adj usted on that basis . The capacity of the material flow may vary greatly depending on, e . g . , the process equipment and conveyor systems upstream of the roller screen . Thanks to this embodiment the control unit may quickly react to changes in the capacity, such that the profile of the upper surface of the material layer traveling on the roller screen remains desirable . For example , when the material flow is low, the control unit adj usts down the capacity of the feeding device , such that enough material to be fed as a wide material mat can be supplied from the available low material flow . Without such control based on the capacity o f the material flow, the material could j ust spread into a narrow, thicker material layer at the feeding channel . Correspondingly, when the material flow i s high and steady, the control unit may control the feeding device to maximi ze the amount of material being fed to provide a profile of the upper surface that i s as even as poss ible , whereby the entire roller bed of the roller screen is maximally utili zed .

[0048] According to one embodiment , the amount of woodbased material that is feedable by the feeding device varies during operation, i . e . the feeding device does not continuously have an unlimited capacity of the material flow, but the material flow to the feeding device varies independently of the roller screen itsel f . Changes in the material flow may, however, be quickly reacted to by detection of the material flow and active control of the feeding device . The capacity of the material flow input to the roller screen may be detected, instead of detectors in the feeding channel , from control data of an upstream process device or from detection data of associated measuring devices .

[0049] According to one embodiment , the solution relates to a method for controlling a roller screen of a panel manufacture plant . The method comprises the following steps : wood-based material to be screened is fed to a feeding device ; a material layer is fed by the feeding device onto a roller bed of the roller screen, the material layer having a width and a thickness ; the material layer fed onto the roller bed is screened by means of several rotating rollers and screen openings between them; material having passed through the screen openings is sorted into sorting stations below the roller bed; and operation of the roller screen is controlled by means of at least one control unit . Further, the method comprises : a profile of an upper surface of the material layer fed onto the roller bed is detected by one or more detection devices as viewed in a widthwise direction of the roller screen; detection data generated by the detection device is transmitted to the control unit ; di f ferences in the profile o f the upper surface in the widthwise direction of the material layer are detected, based on the detection data, in the control unit ; and the feeding device is controlled under control of the control unit in response to the detected data on the profile of the upper surface .

[0050] According to one embodiment , the solution relates to a method wherein the feeding device is controlled to form an even profile of the upper surface of the material layer in response to the data on the profile of the upper surface . In other words , the feeding device is controlled based on the detection data to form an upper profile that is as even as possible across the entire width of the roller bed .

[0051] According to one embodiment , the solution relates to a method wherein wear data on the rollers is used in the control unit as at least one control parameter of the feeding device . Thereby, the feeding device is controlled to form portions having di f ferent heights in the profile of the upper surface of the material layer at widthwise points of the roller bed in response to the wear data on the rollers .

[0052] According to one embodiment , the solution relates to a method wherein a material flow of the wood-based material being fed to the feeding device is determined and the feeding device is controlled using the determined material flow as at least one control parameter .

[0053] The embodiments described above and the features disclosed therein may be combined to provide desired solutions . Brief description of the figures

[0054] Some embodiments of the proposed solution are shown in more detail in the following figures , in which

[0055] Fig . 1 shows schematically a side view of one roller screen and some features related to its control ,

[0056] Fig . 2 shows schematically a top view of one roller screen,

[0057] Fig . 3 shows schematically adj ustment of feed openings in connection with one feeding device by means o f adj usting plates ,

[0058] Fig . 4 and 5 show schematically adj usting plates of one feeding device with oblique adj ustment surfaces in two di f ferent operating positions , and

[0059] Fig . 6 shows schematically one arrangement wherein a feeding device of a roller screen is controlled by taking roller wear data into account .

[0060] For clarity, some embodiments of the proposed solutions are shown in the figures in a simpli fied form . The same reference numbers are used in the figures to refer to the same elements and features .

[0061] Detailed description of some embodiments

[0062] Fig . 1 shows a simpli fied representation of a roller screen 1 compri sing a roller bed 2 having several parallel rollers 3 rotated during operation about their rotation axes . The rollers 3 are arranged at a distance from each other in a transverse direction relative to their rotation axes , whereby adj acent rollers 3 are separated by screen openings 4 . Wood-based material to be screened is fed by a feeding device 5 located at a first end, i . e . feeding end, of the roller screen 1 onto the roller bed 2 on top of which it moves towards a second end of the roller screen 1 in a moving direction D of the roller screen 1 . Below the roller bed 2 there are sorting stations 6 into which material being screened falls through the screen openings 4 . As can be seen from Fig . 1 , the screen openings 4 are smaller at the first end of the screen than at its second end . The si ze of the screen openings 4 may also be adj usted, thereby af fecting the screening result .

[0063] The feeding device 5 feeds the material to be screened on top of the roller bed 2 as a material layer 7 that has a width W in a longitudinal direction of the rollers 3 , a thickness T in a transverse direction of the rollers 3 , and a profile P of an upper surface . The feeding device 5 may be a feeding conveyor 8 trans ferring material to be screened in the widthwise direction W . The feeding device 5 also comprises adj usting elements 9 by means of which the material flow being fed from the feeding conveyor 8 to the roller bed 2 may be adj usted by means of actuators A. The material to be screened is fed into a feeding channel 10 of the feeding device 5 that may have a detector 11 for detecting a material f low Q being fed . The material flow Q or capacity may vary to a great extent as a function of time t , as shown by graph 12 . Variation in the material flow Q may be caused by e . g . an upstream process device 13 or transporting device 14 . Data on the available material flow Q is provided to a control unit CU of the roller screen 1 that may adj ust the operation of the feeding device 5 based on the obtained data .

[0064] Further, several detection devices S are arranged above the roller bed 2 to determine the profile P of the upper surface of the material layer 7 fed onto the roller bed 2 at several di f ferent detection points in the widthwise direction W . The detection devices S may be contactless sensors or measuring devices , and they are arranged in a transverse row . Each detector device S determines a height H of the material layer 7 . Alternatively, the profile of the material layer 7 is determined by means of a 3D profile scanner Sp, or for example by a machine vision application having a widthwise W detection range Ta that may cover the entire width of the roller bed 2 . The detection data is transmitted to the control unit CU processing the detection data, detecting profile di f ferences , and generating control commands for the actuators A of the feeding device 5 to control the feeding of material . The control unit CU comprises a processor that may execute a computer program or an algorithm for processing the detection data and controlling the rol ler screen 1 and its devices . A control parameter or control principle may be provided to the control unit CU, according to which the control unit CU controls the actuators A by taking the detection data into account . The control parameter may be to form a profile P of the upper surface that is as even as possible for the material layer 7 . This is illustrated in Fig . 1 by graph 15, showing two alternative horizontal target graphs 16a, 16b . The profile of the upper surface is even in the target graphs 16a, 16b, i . e . the height H is constant as a function of the width W . The target graphs 16a, 16b are shown at di f ferent height positions , which demonstrates that the target of the control parameter is an even profile of the upper surface and the absolute height position and the thickness T of the material layer have no substantial importance . Graph 17 shows a situation where the operation of the feeding device 5 is not actively adj usted during operation of the rol ler screen 1 . In this case , the height of the upper surface is typically greater at the centre than the edges of the roller bed, whereby the profile is a curve as shown in the figure, where the height H varies as a function of the width W .

[0065] Fig . 2 shows the structure of the roller screen 1 from above . Several detection devices S are supported on a transverse support 18 above the roller bed 2 , which form a row 19 of the detection devices S close to the feeding device 5 . There may be two or more of such rows of detection devices . The feeding device 5 is a feeding conveyor 8 , to a centre part of which the material flow Q of wood-based material is supplied from the feeding channel 10 . The feeding conveyor 8 is a feed screw 20 comprising a conveyor screw 21 , which is rotated by a rotating motor 22 . The feed screw 20 is surrounded by a jacket 23 having several feed openings 24 for feeding the material to be screened through them to the roller bed 2. For clarity, Fig. 2 does not show the adjusting elements by which the size of the feed openings 24 may be adjusted. As shown by arrows in Fig. 2, the feed screw 20 transfers material in a transverse direction from the centre towards the edges, i.e. from the feeding channel 10 towards both edges of the roller bed 2. Due to this transverse transport and active adjustment of the feed openings 24, the type of profile of the upper surface formed on the roller bed 2 of the material being fed from the feeding device 5 may be influenced. By means of the detection devices S the control of the feeding device 5 has feedback and adjustment of the feed openings 24 may be carried out as a continuous adjustment process, in case the control unit detects a need to control the profile of the upper surface taking the received control principle into account .

[0066] Fig. 3 shows a heavily simplified view of one solution for adjusting the feed openings 24 of the feeding device 5. For clarity, the feeding conveyor is not shown. The feed openings 24 are typically located at the base or side of the feeding device 5 and they may be openings formed in the jacket 23 and may be rectangular in shape. Adjusting plates 25 are provided in conjunction with the feed openings 24 and may be moved by means of the actuators A relative to the feed openings 24. The actuator A may comprise a motor M and a gear V. The motor M may be for example an electric motor or a hydraulic motor. In some cases the motor M may be configured to drive the adjusting plate 25 directly without the gear V. Fig. 3 shows different positions of the adjusting plates 25 in an operating situation by dashed lines 26a - 26c.

[0067] Fig. 4 and 5 show the feeding device 5 in which the adjusting plates 25 are moved along guides 27 by the actuators A that may be pressure-medium actuators 28, such as pneumatic or hydraulic cylinders . The front edges of the adj usting plates 25 have oblique adj ustment surfaces 29. When the material flow Q i s directed to the centre of the feeding device 5 , the oblique adj ustment surfaces 29 are arranged so as to constrict , during the adj usting movement , the free opening o f the adj ustment openings 24 more in the centre part than the edges of the feeding device 5 . This may be clearly seen in Fig . 5 . Thereby, the material directed to the centre part of the feeding device 5 can be transported, as indicated by arrows 30 , in a transverse direction toward the edges . Thus the distribution of the material layer on the roller bed may be influenced . For clarity, Fig . 4 and 5 do not show the feeding conveyor .

[0068] Fig . 6 illustrates one control principle in which the feeding device 5 of the roller screen 1 is controlled by taking wearing of the rollers 3 into account . Wear data 31 may be fed into the control unit CU, including actual wear data 32 from measurements of the rollers 3 , a wear estimate 33 and control parameters 34 given by the operator of the roller screen related to the control of wearing of the rollers 3 . The control unit CU may control the actuators A of the feeding device 5 such that the even profile of the upper surface as shown in Fig . 1 is not to be formed, but a profile comprising di f ferent heights of the upper surface is intentionally formed . Thereby, a thicker material layer may be directed to the edges of the roller bed 2 than the centre . This is illustrated in graph 35 by curve 36 . Because detection data is provided to the control unit CU from the detection devices S , the control unit CU is able to continuously monitor whether the actual shape of the upper surface profile corresponds to the profile shape of the upper surface used as the control parameter .

[0069] Fig . 6 further illustrates by dashed lines 37 the typical wearing of the rollers 3 at their centre part . Thereby the screen opening 4 a at the ends of the rollers 3 is smaller than the screen opening 4b at the centre . When feeding is controlled by taking the wear data into account , uneven wearing on the rollers 3 may be avoided . The surfaces of the rollers 3 may comprise desired surface patterns , such as diamond patterns 38 illustrated in Fig . 2 and 6 . The figures and their description are intended to only illustrate the idea of the invention . However, the scope of protection of the invention is defined in the claims of the application .

Claims

Claims1. A roller screen (1) for screening wood-based material into fractions of different particle sizes when manufacturing wood-based panels, and which roller screen (1) comprises: a roller bed (2) having several parallel rollers(3) configured to rotate about their rotation axes, wherein the rollers (3) are spaced at a distance from each other in a transverse direction relative to their rotation axes, whereby adjacent rollers are separated by screen openings(4) through which material being screened is arranged to move from top of the roller bed (2) to at least one sorting station (6) below the roller bed (2) while the material being screened travels in a direction of movement (D) of the roller screen; a feeding device (5) for feeding material to be screened on top of the roller bed (2) as a material layer (7) that has a width (W) in a longitudinal direction of the rollers (3) and a thickness (T) in a transverse direction of the rollers (3) ; and at least one control unit (CU) for controlling operation of the roller screen (1) ; char ac t e r i z e d in that the roller screen (1) comprises at least one detection device (S) for determining a profile (P) of an upper surface of the material layer (7) fed onto the roller bed (2) ; the detection data of the detection device (S) is configured to be transmitted to the control unit (CU) configured to detect profile differences as viewed in a widthwise direction of the material layer; and the control unit (CU) is configured to control the feeding device (5) in response to the detected profile differences of the material layer.

2. The roller screen according to claim 1, c h a r a c t e r i z e d in that the control unit (CU) is configured to control the feeding device (5) to feed wood-based material onto the roller bed (2) as a material layer having an even upper surface .

3. The roller screen according to claim 1, c h a r a c t e r i z e d in that the control unit (CU) is configured to control the feeding device (5) to feed a higher profile of the woodbased material onto both longitudinal edge portions of the roller bed (2) than onto a centre portion between the edge portions in response to data provided to the control unit (CU) on a need to reduce wearing of the rollers (3) in said centre portion.

4. The roller screen according to any preceding claim 1 - 3, c h a r a c t e r i z e d in that the roller screen (1) comprises several detection devices (S) for determining the profile (P) of the upper surface of the material layer (7) fed onto the roller bed (2) at several detection points, which detection points are arranged at different points in the widthwise direction of the material layer (7) ; and wherein the detection data of the detection devices (S) is configured to be transmitted to the control unit (CU) configured to compare the obtained profile data of the material layer at said detection points and configured to detect profile differences as viewed in the widthwise direction of the material layer.

5. The roller screen according to claim 4, c h a r - a c t e r i z e d in that there are at least three detection devices (S) .

6. The roller screen according to any preceding claim 1 - 5, c h a r a c t e r i z e d in that the detection device (S) is a contactless detection device mounted above the roller bed (2) .

7. The roller screen according to any preceding claim 1 - 6, c h a r a c t e r i z e d in that the detection device (S) is a 3D profile scanner (Sp) having a detection range (Ta) in the widthwise direction (W) of the material layer.

8. The roller screen according to any preceding claim 1 - 7, c h a r a c t e r i z e d in that the feeding device (5) comprises at least one feeding conveyor (8) arranged transversely at a feeding end of the roller bed (2) and configured to transfer material to be screened it receives in the transverse direction of the roller bed ( 2 ) ; the feeding device (5) is provided with several adjusting elements (9) for controlling the material flow being fed from the feeding conveyor (8) to the roller bed (2) ; and which feeding device (5) comprises actuators (A) for adjusting the adjusting elements (9) by remote control under control of the control unit (CU) .

9. The roller screen according to claim 8, c h a r a c t e r i z e d in that the feeding conveyor (8) is a feed screw (20) which comprises a conveyor screw (21) at least partially surrounded by a jacket (23) having several feed openings (24) for feeding the material to be screened onto the roller bedand wherein the adjusting elements (9) are adjusting plates (25) supported movably relative to the feed openings (24) to control the size of the free flow opening of the feed openings (24) .

10. The roller screen according to any preceding claim 1 - 9, c h a r a c t e r i z e d in that the roller screen (1) comprises a feeding channel (10) for supplying the wood-based material to the feeding device ( 5 ) ; in connection with the feeding channel (5) there is at least one detector (11) for determining the capacity of a material flow (Q) being supplied to the feeding device ( 5 ) ; and the control unit (CU) is configured to control the capacity of the feeding device (5) based on the determined capacity data of the material flow (Q) .

11. A method for controlling a roller screen (1) of a panel manufacture plant, in which method: wood-based material to be screened is fed to a feeding device ( 5 ) ; a material layer (7) is fed by the feeding device (5) onto a roller bed (2) of the roller screen (1) , the material layer having a width (W) and a thickness (T) ; the material layer (7) fed onto the roller bed (2) is screened by means of several rotating rollers (3) and screen openings (4) between them; material having passed through the screen openings (4) is sorted into sorting stations (6) below the roller bed; and operation of the roller screen (1) is controlled by means of at least one control unit (CU) ; char ac t e r i z e d in thata profile (P) of an upper surface of the material layer (7) fed onto the roller bed (7) is detected by at least one detection device (S) as viewed in a widthwise direction of the material layer (7) ; the detection data of the detection device (S) is transmitted to the control unit (CU) ; profile differences as viewed in the widthwise di- rection of the material layer are detected, based on the detection data, in the control unit (CU) ; and the feeding device (5) is controlled under con- trol of the control unit (CU) in response to the detected data on the profile (P) of the upper surface.

12. The method according to claim 11, c h a r a c t e r i z e d in that the feeding device (5) is controlled to form an even profile (P) of the upper surface of the material layer (7) in response to the data on the profile of the upper surface.

13. The method according to claim 11, c h a r a c t e r i z e d in that wear data (31) on the rollers (3) is used in the control unit (CU) as at least one control parameter of the feeding device (5) ; and the feeding device (5) is controlled to form portions having different heights (H) in the profile (P) of the upper surface of the material layer (7) at widthwise points of the roller bed (2) in response to the wear data (31) on the rollers.

14. The method according to any preceding claim 11- 13, c h a r a c t e r i z e d in that a material flow (Q) of the wood-based material being fed to the feeding device (5) is determined and the feeding device (5) is controlled using the determined material flow (Q) as at least one control parameter.

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