WO2025133275A1 - Corrugated board production line with video cameras for detecting a stock of corrugated board, and method - Google Patents

Abstract

A corrugated board production line is described, comprising at least one corrugator and a double facer. A feeding bridge of single faced corrugated board from the corrugator towards the double facer is arranged between the corrugator and the double facer. A video camera frames at least one portion of the bridge. A stock of single faced corrugated board forms on the bridge, in the form of festoons, which move along the bridge. The amount of stock of corrugated board is a function of the number of festoons on the bridge, and hence of the location of the festoon in the most advanced position along the bridge, in the direction of feed from the corrugator to the double facer. Through images captured by the video camera it is possible to obtain information on the location of the most advanced front of the stock and hence on the amount of single faced corrugated board found on the bridge.

Description

CORRUGATED BOARD PRODUCTION LINE WITH VIDEO CAMERAS FOR DETECTING A STOCK OF CORRUGATED BOARD, AND METHOD

DESCRIPTION

TECHNICAL FIELD

[0001] The present description relates to corrugated board production plants.

BACKGROUND ART

[0002] Corrugated board is produced starting from smooth paper webs fed from respective parent reels. Corrugated board usually comprises at least one sheet of corrugated paper and two sheets of smooth paper, also called liners, between which the sheet of corrugated paper is placed. The liners are glued to the sheet of corrugated paper at the crests of the corrugations. In general, corrugated board can comprise more than one sheet of corrugated paper. Usually, a separation sheet of smooth paper is interposed between each pair of sheets of corrugated paper.

[0003] A plant or line for the production of sheets of corrugated board generally comprises one or more unwinders of reels of continuous webs of smooth paper and one or more corrugators. Each corrugator converts a continuous web of smooth paper into a continuous web of corrugated paper and joins the continuous web of corrugated paper to a continuous web of smooth paper, or liner. The composite continuous web thus obtained at the output of the corrugator is fed to double facer, where it is joined to a second liner. In general, the line can comprise one or more corrugators to feed one or more webs composed of a continuous corrugated web and a liner to the double facer. The line further comprises a section for converting the corrugated board coming from the double facer, commonly known as dry-end, to distinguish it from the section including the machines from the unwinders to the double facer (wet-end). The dry-end section usually comprises a longitudinal slitting and scoring station, which cuts the corrugated board web into continuous longitudinal strips.

[0004] The continuous longitudinal strips are then further processed to produce a series of separate sheets, or a fanfold, i.e., a strip folded in a zigzag manner according to transverse score and fold lines. [0005] WO2017/036685 discloses a corrugated board production plant with a plurality of video cameras adapted to detect defects on the corrugated board during production.

[0006] JP2019188501 discloses a further corrugated board production plant, with a video camera along the final portion of the line, in which single sheets of corrugated board cut crosswise are advanced.

[0007] US2004/089394 disclsoes a plant for the production of corrugated board. This known plant includes a complicated system for calculating the corrugated board stock on a bridge, between a corrugator and a double facer. The system includes nozzles to spray water at predetermined spots on the corrugated board and moisture sensors to detect where moisture is present in the corrugated board. The moisture sensors, in combination with photoelectric detectors, are used to calculate the stock of corrugated board on the bridge. This system for determining the stock is complex and inaccurate.

[0008] Another system for detecting the stock of corrugated board on a bridge of a corrugated board plant is disclosed in US576663. This system is also based on the use of photoelectric detectors, and is complicated and inaccurate.

[0009] In a different technical field, US2016/018544 and in US5970274 describe machines in which individual sheets are transported along a path within which devices are provided that control the proper feeding of the sheets based on the transition of the leading or trailing edges of the individual sheets. Failure to pass the leading or trailing edges of sheets is interpreted as an indication that sheets have been jammed along the feed path.

[0010] US2005/073082 discloses, in a different technical field, a machine that processes individual printed sheets, which includes a waste accumulation system with a sensor to detect the presence of waste.

[0011] Notwithstanding numerous improvements made to plants for the production of corrugated board, to improve their performance and reduce production defects, or shutdowns or slowdowns of the line, there are still some critical aspects, which can cause production losses. SUMMARY

[0012] According to a first aspect, disclosed herein is a corrugated board production line, comprising in combination: a corrugator, comprising: a first corrugating roller and a second corrugating roller cooperating with each other to corrugate a first paper web; a pressure member to glue the first paper web, corrugated by the first corrugating roller and by the second corrugating roller, to a second smooth paper web and form a single faced corrugated board; a first unwinder to feed the first paper web to the corrugator; a second unwinder to feed the second paper web to the corrugator; a double facer; a third unwinder to feed a third smooth paper web to the double facer, the third paper web being glued to the single faced corrugated board on said double facer; a feeding bridge extending between the corrugator and the double facer; a first video camera located above the bridge and framing a feed path of a continuous web of single faced corrugated board along said bridge; an image processing unit, adapted to process images captured by the video camera located above the bridge and to calculate, based on the content of said images, an amount of stock of single faced corrugated board on the bridge.

[0013] The production line thus configured allows the amount of stock on the bridge to be continuously checked. Having established an admissible maximum value and minimum value of stock, as a function of the amount of stock obtainable by processing the image captured by the video camera, it is possible to modulate the speed of the machines upstream and downstream of the bridge, so as to decrease or increase the stock. For example, if the stock drops below an admissible minimum value, the speed of the corrugator can be increased, and/or the feed speed of the board along the double facer and in the machinery downstream thereof can be decreased.

[0014] According to a further aspect, disclosed herein is a method for controlling a stock of single faced corrugated board on a feeding bridge of single faced corrugated board to a double facer in a corrugated board production line, wherein at least one video camera connected to an image processing unit is associated with the bridge. The method comprises the following steps: supplying a single faced corrugated board from a corrugator to the feeding bridge; forming a stock of single faced corrugated board on the bridge; framing with the video camera a portion of the bridge in which the stock of single faced corrugated board is located; from successive images captured by the video camera, obtaining information on the amount of stock on the bridge.

[0015] According to a further aspect, disclosed herein is a corrugated board production line, comprising in combination: a corrugator, comprising: a first corrugating roller and a second corrugating roller cooperating with each other to corrugate a first paper web; a pressure member to glue the first paper web, corrugated by the first corrugating roller and by the second corrugating roller, to a second smooth paper web and form a single faced corrugated board; a first unwinder to feed the first paper web to the corrugator; a second unwinder to feed the second paper web to the corrugator; a double facer; a third unwinder to feed a third smooth paper web to the double facer, the third paper web being glued to the single faced corrugated board on said double facer; a bridge extending between the corrugator and the double facer; a cross cutter; a basket, which can be positioned downstream of the cross cutter and adapted to collect trimmings removed from the corrugated board through cross cutting performed by the cross cutter; a video camera positioned to frame at least one portion of the basket located downstream of the cross cutter; and an image processing unit, adapted to process images captured by the video camera and to determine, based on said images, a level of filling of the basket with trimmings of corrugated board accumulated in the basket.

[0016] By analysing the images captured by the video camera it is possible to verify when the basket requires to be emptied or replaced. For this purpose, a control unit can generate an alarm and/or information sent to an operator, via a suitable interface, which may consist of, or comprise, for example, a mobile device, such as a smartphone or a tablet.

[0017] This interface can also be used to provide information and/or an alarm in case of an excessive decrease or excessive increase of the stock of board on the bridge, which can be determined as mentioned above through a video camera provided for this purpose.

[0018] According to yet another aspect, described herein is a method for detecting a level of filling of a basket for accumulating trimmings of corrugated board downstream of a cross cutter in a corrugated board production line; wherein the method comprises the following steps: capturing images of the basket through a video camera; and obtaining, from an image captured by the video camera, a matrix in which the vertical edges of objects contained in the image are highlighted.

[0019] According to yet another aspect, described herein is a corrugated board production line, comprising in combination: a corrugator, comprising: a first corrugating roller and a second corrugating roller cooperating with each other to corrugate a first paper web; a pressure member to glue the first paper web, corrugated by the first corrugating roller and by the second corrugating roller, to a second smooth paper web and form a single faced corrugated board; a first unwinder to feed the first paper web to the corrugator; a second unwinder to feed the second paper web to the corrugator; a double facer; a third unwinder to feed a third smooth paper web to the double facer, the third paper web being glued to the single faced corrugated board on said double facer; a bridge extending between the corrugator and the double facer; a first video camera located in a critical position for the formation of jamming of corrugated board, and configured to capture images of the corrugated board passing through; and an image processing unit, adapted to process images captured by the video camera located in said critical position, and adapted to determine, based on the content of said images, the onset of a condition of jamming, along a path along which a continuous corrugated board web advances. As will become clear later, the system described herein allows the detection of the onset of a jamming condition in an area where there is a continuous corrugated board web, which may be either a continuous single faced corrugated board web (i.e. comprising a single smooth liner glued to a single corrugated paper web), or a continuous composite corrugated board web (i.e. comprising two smooth outer liners and at least one corrugated paper web between the outer liners).

[0020] By processing the images captured by one or more video cameras located in one or more critical positions, it is possible to promptly identify the onset of a condition of jamming and consequently provide an operator with information and/or an alarm. This can take place with an interface, that can be the same one mentioned above for indicating anomalies in the basket for collecting trimmings and/or anomalies in the stock of board on the bridge. [0021] According to yet another aspect, described herein is a method for detecting a condition of jamming in a corrugated board production line, the method comprising the following steps: capturing an image of the corrugated board passing along the line; and processing the image to extract therefrom information indicative of the onset of a condition of jamming of the corrugated board.

[0022] Further advantageous embodiments and features of the methods and of the lines described herein are illustrated below and defined in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The invention will be better understood by following the description and the accompanying drawings, which illustrate a non-limiting exemplary embodiment of the invention. More in particular, in the drawing:

Figs. 1A, IB, 1C and ID illustrate successive portions of a corrugated board plant or production line, arranged in sequence along the feed path of the board;

Fig.2 illustrates an enlargement of the feeding bridge of the single faced corrugated board to the double facer of the production line of Figs. 1 A-1D;

Figs. 3, 4, 5, 6, 7 and 8 show images illustrating the process for determining the stock of single faced corrugated board on the bridge feeding the double facer;

Figs. 9 to 19 show images illustrating the process for controlling jamming; and Figs. 20 to 28 show images illustrating the process for controlling the level of filling of a basket to collect trimmings.

DETAILED DESCRIPTION

[0024] The detailed description of exemplary embodiments set forth below refers to the accompanying drawings. The same reference numbers in different drawings identify identical or similar elements. Moreover, the drawings are not necessarily to scale. The detailed description set forth below does not limit the invention. Rather, the scope of the invention is defined by the appended claims.

[0025] The reference in the description to “an embodiment” or “the embodiment” or “some embodiments” means that a particular feature, structure or element described in relation to an embodiment is included in at least one embodiment of the subject described. Therefore, the phrase “in an embodiment” or “in the embodiment” or “in some embodiments” used in the description does not necessarily refer to the same embodiment or embodiments. Moreover, the particular features, structures or elements can be combined in any suitable way in one or more embodiments.

[0026] The embodiment illustrated describes a plant or line for the production of sheets of double corrugated board, i.e., with two corrugated paper webs interposed between two smooth paper webs, or liners, and a smooth paper web interposed between the two corrugated paper webs. Moreover, the line is configured to produced two stacks of sheets on two adjacent stackers.

[0027] However, it must be understood that the features described below can equally be used in plants with a different number of corrugators and hence adapted to produce a corrugated board web comprising a different number of webs or sheets. The stacking systems can also differ, for example to form a single stack or more than two stacks of board sheets.

[0028] Similarly, the double facer and the longitudinal slitting and scoring station, described below by way of example, can be configured in a different manner from that described and illustrated herein.

[0029] With reference to the accompanying drawings, the line comprises a first section 3 for producing a first web of single faced corrugated board , a second section 5 for producing a second web of single faced corrugated board, a third section 7 for feeding the two single faced corrugated board webs and a smooth paper web to a double facer8 of a section 9 comprising said double facer8 and related accessories. A composite corrugated board formed by the assembly of the single faced corrugated board webs and of the further smooth paper web glued thereto and which forms a second liner of the composite corrugated board web, is delivered from the section 9.

[0030] Downstream of the section 9 a section 11 is provided, in which devices for removing trimmings are located and, downstream thereof, a section 13 is provided for longitudinal slitting and longitudinal scoring of the continuous corrugated board web coming from the section 9 containing the double facer 8, to divide the corrugated board web into a plurality of longitudinal strips of corrugated board and to form score lines along the longitudinal extension of the single longitudinal strips of continuous corrugated board. The section 13 is also indicated below as slitter-scorer 13.

[0031] The slitting and scoring section 13 can comprise slitting tools 13 A and scoring tools 13B, illustrated briefly and schematically in Fig. lC. The slitting tools 13 A can comprise one or more assemblies of rotating blades cooperating with fixed counterblades or rotating counter-blades, the blades and the counter-blades being positioned respectively above and below the path of the composite corrugated board web CC. The blades and counter-blades can be adjustable in cross direction trasnverse to the direction of feed F of the composite corrugated board web CC, to divide the latter into two or more longitudinal strips SI, S2 which will then be cut into single sheets by cross cutting. Besides dividing the composite corrugated board web CC into single longitudinal strips, the slitting tools are also used to generate side trimmings, which normally contain defective edge areas of the composite corrugated board web and which are discarded.

[0032] The scoring tools can comprise rotating scoring tools positioned above and below the path of the composite corrugated board web CC and generate thereon longitudinal score lines, which form fold lines of the sheets of composite corrugated board that are produced by cross cutting the strips of composite corrugated board CC formed by the slitting tools.

[0033] Located downstream of the slitting blades are suction nozzles 14 for removing the lateral trimmings generated by the slitting tools.

[0034] In the illustrated embodiment, the line or plant 1 further comprises, by way of example: a cross cutting section 15 for cutting the strips di corrugated board SI, S2 coming from the section 13; a double conveyor 17 with two series 17 A, 17B of conveyors that convey sheets Fc of board towards respective stackers; and finally two stackers or stacking areas, indicated with 19A and 19B, to form stacks Pl, P2 of sheets of board cut in the section 15 and fed by the double conveyor 17 (17A, 17B).

[0035] In some embodiments, a single conveyor 17 and a single stacker 19 can be provided.

[0036] A first corrugator 21 is arranged in the section 3. Corrugators which can be used to produce a web of single faced corrugated board are known. Only the main elements of the corrugator, which can, for example, be produced as described in US 78714223 or in EP 1362691, will be described below.

[0037] In brief, the corrugator 21 can comprise a first corrugating roller 23 cooperating with a second corrugating roller 25 and with a pressure roller 27, or other pressure member, to join a smooth paper web and a corrugated paper web to each other, as described below. A first smooth paper web N1 is fed to the corrugator 21 from a first unwinder 29. The unwinder 29 can be produced in a known way and is not described in detail. The unwinder 29 can comprise two positions for a first reel Bl being unwound, from which the first smooth paper web N1 is delivered, and a second reel BIX standing by, which will be unwound when the reel Bl is depleted.

[0038] A second smooth paper web N2 is unwound from a second unwinder 31, which can be substantially the same as the unwinder 29, and on which there can be arranged a first reel B2, from which the paper web N2 is unwound, and a second reel B2X standing by, which will start to be unwound when the reel B2 is depleted.

[0039] The first smooth paper web N1 is fed to the corrugating roller 23 after passing around a heating roller 33. The winding arc of the smooth paper web N1 around the heating roller 33 can be modified to transfer to the smooth paper web N1 a larger or smaller amount of heat coming from the inside of the heating roller 33, for example heated with steam circulating therein.

[0040] The first smooth paper web N1 is corrugated by passing through the nip formed by the corrugating rollers 23 and 25. A corrugated paper web N1 is thus obtained at the outlet of the nip between the corrugating rollers 23 and 25. By means of a gluing assembly 35, a suitable glue is applied to the flutes formed on the corrugated paper web thus obtained, so that the corrugated paper web N1 can be glued on the smooth paper web N2 fed, together with the corrugated paper web Nl, through the nip formed between the second corrugating roller 25 and the pressure roller 27.

[0041] The gluing assembly 35 can comprise an applicator roller 36, in contact with the flutes of the corrugated paper web N 1 driven around the second corrugating roller 25. The applicator roller 36 receives the glue from a distributor roller or anilox roller 38, which picks up glue from a tank 40 or other glue source. The distance between the rollers 36 and 38 can be adjusted to adjust the amount of glue applied to the corrugated paper web N 1.

[0042] In some embodiments, the second smooth paper web N2 can be fed around one or more rollers 37, 39 arranged between the unwinder 31 and the corrugator 21, to be heated. The contact arc between the smooth paper web N2 and one, the other, or both the rollers 37, 39 can be modified to vary the amount of heat transferred from the roller or rollers 37, 39 to the smooth paper web N2 before this comes into contact with the pressure roller 27. The pressure roller 27 can also be heated internally to perform gluing between the paper webs N1 and N2 in conditions of high pressure and high temperature.

[0043] At the outlet of the corrugator 21 a single faced corrugated board web NS, formed by the first corrugated paper web N 1 and by the second smooth paper web N2, is obtained, as shown in the enlargement of Fig. 2. The flutes or crests O formed on the first paper web N1 are glued by means of a glue C, applied by the gluing assembly 35 on the flutes O, to the surface of the smooth paper web N2 facing the corrugated paper web N 1.

[0044] Positioned downstream of the corrugator 21 is abridge 41, extending towards the section 5 and the successive sections 7 and 9 of the line 1. A stock S of single faced corrugated board web NS can be formed on the bridge 41, with the formation of suitable accumulated loops or festoons, so that the operating speed of the corrugator 21 can be at least partly independent from the operating speed of the sections downstream.

[0045] The single faced corrugated board web NS is then fed along a first path that extends above the bridge 41 to a heating roller 43, around which the single faced corrugated board web NS can be wound for an adjustable arc, to be suitably heated before reaching double facer 8 of the section 9.

[0046] In the illustrated embodiment, the line 1 comprises a second section 5 substantially the same as the section 3, in which, through a further pair of paper webs N4, N5 coming from unwinders the same as the unwinders 29 and 31 and a corrugator the same as the corrugator 21, a second single faced corrugated board web, once again indicated with NS, is formed. This is fed to the bridge 41 to form a stock S and to be fed towards the double facer 8 of the section 9 winding around a heating roller 45, substantially the same as the heating roller 43.

[0047] In other embodiments, the section 5 and the respective corrugator can be omitted. Vice versa, in yet further embodiments more than two sections 3, 5 can be provided, with relevant corrugator and unwinder of the paper webs to form respective single faced corrugated board webs NS which are then joined to each other by gluing by means of the double facer 8 of section 9.

[0048] A smooth paper web N3 is unwound from a further unwinder 47 and fed, preferably passing around a heating roller 49, to the double facer section 9. In a known way, gluing assemblies 51, 53 apply a glue to the flutes of the respective corrugated paper web of the two single faced corrugated board web NS, to glue these to each other and to the smooth paper web N3, which will form the second outer liner of the composite corrugated board CC delivered from the section 9, the first outer liner being formed by the smooth paper web N2.

[0049] The section 9 containing the double facercan be produced in a known way and will not be described in detail herein. Examples of embodiments of double facers are disclosed in US 7.291.243 and in US 2012/0193026, to which reference can be made for further details of the production of this section of the line.

[0050] Arranged in the section 11 is a cross cutter 61, which can perform cross cutting to sever, completely or only partially, the composite corrugated board CC fed from the section 9. The cross cutter 61 can, for example, be produced as described in US 6,722,243. As will be described in more detail hereunder, the cross cutter 61 can be used in particular to discard portions of corrugated board CC in which gluing defects or other defects are present.

[0051] The composite corrugated board CC fed through the slitting and scoring section 13 is divided into longitudinal strips SI, S2, which can be diverted along two paths defined by the two conveyors 17A, 17B of the section 17. The section 13 can be produced in a known way, for example as described in US 5.951.454, US 6.165.117, US 6.092.452, US 6.684.749, US 8.342.068 or in other prior art document cited in the aforementioned patent documents.

[0052] The two conveyors 17 A, 17B convey sheets of corrugated board Fc, obtained in the section 15 by cross cutting the continuous strips SI, S2 of composite corrugated board CC. The conveyors 17 A, 17B unload the sheets onto the stackers 19 A, 19B to form stacks Pl, P2 on stacking tables 63, 65, known and which can be produced, for example, as described in EP 1710183, US 5,829,951, or other patent documents cited therein.

[0053] The reference number 62 indicates a cross cutting station of the continuous strips SI, S2 of composite corrugated board CC coming from the longitudinal slitting and scoring section 13. In the illustrated embodiment, the station 62 comprises superimposed cross cutters 62A, 62B, which divide each continuous strip coming from the section 13 into single sheets of a given length. In this exemplary embodiment, two cross cutters 62A, 62B are provided, placed at two different levels, as the line 1 operates on two levels on which the two conveyors 17A, 17B, which feed the sheets Fc to the two stackers 19A, 19B, are positioned. If a single stacker 19 is provided, a single cross cutter may suffice.

[0054] Positioned between each cross cutter 62A, 62B and the relevant conveyor 17A, 17B are shingling members 64A, 64B, adapted to arrange the single sheets Fc of composite corrugated board CC in a shingled arrangement, i.e., with the sheets Fc partially overlapping one another, on the conveyors 17 A, 17B, as shown in particular in Fig.1(D). The shingling members 64 A, 64B can comprise a conveyor that slows the feed of the sheets Fc and overhead brushes which, in combination with the underlying conveyors, causes partial overlapping of the sheets Fc of composite corrugated board obtained by cross cutting the single longitudinal strips SI, S2.

[0055] The shingled sheets Fc are fed by the two conveyors 17A, 17B (each of the which can be formed by a series of single belt conveyors in series) to the stackers 19 A, 19B. Arranged at the outlet end of the conveyors 17A and 17B are unloading members 20A, 20B, which can each comprise a respective upper roller cooperating with the corresponding underlying end of the conveyor 17 A, 17B.

[0056] In the production line or plant 1 described above, there are some critical aspects for controlling correct operation of the line.

[0057] A first critical aspect concerns the formation and maintenance of a correct stock of single faced corrugated board NS on the bridge 41, or on each bridge 41, if the line 1 has more than one. The stock of single faced corrugated board NS on the or on each bridge 41 of the line can be used, for example, in the step of splicing a paper web from a depleted reel to a paper web from a new reel standing by. To ensure correct operation of the whole line, it is in fact advantageous during this transitory splicing step for the speed of the web material, downstream of the point in which splicing takes place, to remain approximately constant, while in the splicing area the feed speed of the paper web to be spliced is temporarily halted.

[0058] Maintaining a substantial uniformity of feed of the single faced corrugated board and of the composite corrugated board along the double facer and downstream thereof is important, for example, to guarantee uniform heating of the paper webs around the rollers or other heating members and along the double facer 8. For example, a slowing of the paper webs on the double facer 8 can cause overheating and hence gluing defects or damage to the paper webs. This is because the thermal inertia of the double facer 8 and of the heating rollers (e.g. rollers 43, 45, 49) does not allow a sufficiently fast modulation of their temperature to adapt to a variation in the amount of corrugated board passing through per unit of time.

[0059] Therefore, in some cases and in some circumstances, it is important to verify that there is a sufficient amount of stock of single faced corrugated board NS on the bridge 41 before staring the operation of splicing a paper web coming from a depleted reel to a paper web of a new reel. This stock can vary over time and be gradually increased, for example, as the splicing step draws near. The need to perform splicing can be predicted as a function of the diameter of the reel or reels of paper, or in some cases also by continuously measuring the length of paper web that has been unwound since the last splicing operation.

[0060] To determine (at least at the level of percentage of filling of the bridge 41) the amount of single faced corrugated board NS present on the bridge 41, or on each bridge 41, a system of video cameras can be used, comprising one or more video cameras located above each bridge 41. In the illustrated embodiment, Figs.1(A) and 1(B) indicate a video camera 101 located in an intermediate position along each bridge 41. The video camera 101 can be single. In some cases, a plurality of video cameras can be provided, arranged side by side in a direction transverse to the direction of feed (arrow F) of the single faced corrugated board NS on the bridge 41.

[0061] As shown in the drawing, in particular in Fig.2, the video camera is oriented backwards, i.e. it frames the corrugated board web which advances along the bridge 41, approaching the video camera 101. The video camera has an inclined optical axis forming with the direction of advance of the corrugated board, an angle less than 90°, for example less than 45°.

[0062] In some embodiments, a system with several video cameras can be provided, distributed along the longitudinal extension of the bridge 41, i.e., along the direction F, or with several assemblies of video cameras aligned with one another in transverse direction and the single assemblies distanced from one another in the direction F.

[0063] The video camera 101, or each video camera associated with the bridge 41 can be connected to a control unit 100 (Fig.1(B)) which can be programmed to perform the image processing process described below. Alternatively, the or each video camera 101 can be equipped with its own calculation resources that process the images captured by the video camera, and send the control unit 100 the data relating to the result of processing.

[0064] Therefore, in general, each video camera is associated with an image processing unit. This can be the control unit 100, which receives the images captured by the video camera or cameras 101 and processes them. In this case, the control unit represents an image processing unit for one or more video cameras of the line. Alternatively, the or each video camera 101 is provided with its own image processing unit, which processes the images captured by the video camera. In this case, data, signals or commands obtained by processing the images on the video camera can be sent to the control unit 100.

[0065] In other embodiments, it would be possible to have intermediate solutions, for example in which one or more processing units of images captured by one or more video cameras process the images to output data that are conveyed to the control unit 100. If necessary, these data can be further processed by the control unit 100. Therefore, in this case, processing of the images can take place in different steps by means of different processing units that can perform processing in series.

[0066] The indications provided here with reference to the video camera or cameras 101 associated with the bridge 41 and with reference to the way in which the calculation resources for processing the respective images captured by the video cameras are distributed, also applies for the remaining video cameras with which the production line 1 can be provided and which will be described in greater detail below.

[0067] The control unit 100 can be connected to one or more human-machine interfaces (HMI). Fig. 1(B) shows two interfaces 102 and 104, for example for entering data and instructions and for displaying information or notifications. In some embodiments, the control unit 100 can be connected to a mobile unit, such as a smartphone, a portable computer, a tablet or other peripheral, generically indicated with 106, which can be provided to personnel in charge of supervising and managing the production line 1.

[0068] In general, the stock S is formed on the bridge 41 starting from the point in which the single faced corrugated board NS is unloaded onto the bridge 41 from the guide roller 103 or other feed member of the single faced corrugated board NS coming from the respective corrugator 21. The stock S moves in the direction of feed F and occupies a length Ls of the bridge 41. The stock S is formed by superimposed loops or festoons of single faced corrugated board NS. The various loops or festoons are approximately the same as one another. Therefore, the length Ls of the section of bridge 41 occupied by the stock S of single faced corrugated board NS provides a quantitative datum on the length of single faced corrugated board web NS available in the stock S. The longer the length Ls is, the greater the stock will be. This can be expressed in percentage with respect to the total length between a position of minimum stock and a position of maximum stock.

[0069] Fig.2 shows an enlarged side view of the portion of bridge 41 on which the stock S forms. MAX and MIN indicate the points of maximum stock and minimum stock, i.e., the maximum and minimum stocks admissible on the bridge. The MIN point can represent a point in which the stock is at a minimum admissible value (which can be equal to zero). The video camera 101 is located above a bridge 41 so as to frame the whole length of the bridge between the MAX and MIN points. Fig.3 shows an image framed by the video camera 101 in a condition of stock S between the MAX and MIN points.

[0070] To determine the amount of single faced corrugated board NS available in the stock S in percentage with respect to a corresponding minimum amount and maximum amount, it is possible to process the images framed by the video camera 101, or by each video camera 101, with a process described below with specific reference to Figs.3 to 9.

[0071] With initial reference to Fig.3, the process firstly captures successive images of the area framed by the video camera 101, on which four points defining the line of minimum accumulation, i.e., minimum stock and of maximum accumulation, i.e., maximum stock, are identified.

[0072] Each captured image is converted into a grayscale image, so that a level of luminosity, i.e., an intensity of the pixel, will be associated with each pixel.

[0073] As the single faced corrugated board web NS is moving, by obtaining the difference between successive images, i.e., successive frames captured by the video camera 101 and converted into grayscale, it is possible to identify the area in which the single faced corrugated board NS stretches, i.e., the area in which the loops or festoons forming the stock S stretch forming a portion of stretched single faced corrugated board NS. The area of stretched corrugated board appears essentially the same in successive images, while in the area where the loops or festoons of the stock are present, successive images are different from one another due to the feed movement of said loops or festoons.

[0074] Consequently, by subtracting two successive frames or images, previously converted to grayscale, the area of stretched single faced corrugated board NS will become black, as each pixel in this area has, in the two images subtracted from each other, the same intensity. Vice versa, the area in which the loops or festoons of stock NS are present will appear light, as the intensity of the single pixels varies over time as a result of movement. This also applies for the edges of the single faced corrugated board NS downstream of the stock S, as the single faced corrugated board NS has irregularities along the edges, and this means that corresponding pixels in two successive frames will not have the same luminosity.

[0075] It must be noted that the two frames that are subtracted from each other are not necessarily immediately successive, but could be spaced in time by an interval higher than the acquisition interval. Each frame is considered as a matrix of pixels. The images obtained from the difference is illustrated in Fig.4. In substance, it has light pixels, tending towards white, in the areas in which the single faced corrugated board NS passes from being in accumulated form (loops of stock S) to stretched form, and along the edges, i.e., in the areas in which the board oscillates.

[0076] The image of Fig.4 is further processed to identify the line along which the farthest forward loop of corrugated board, i.e., the loop farthest downstream in the direction of feed of the board, is arranged, as this line is the one that delimits the area of the stock S along the bridge.

[0077] For this purpose, according to embodiments described herein, it is possible to proceed as follows.

[0078] In a subsequent processing step a threshold is applied to all the values of the matrix represented by the pixels of the image, so as to pass from a matrix of integer values (grayscale) to a binary matrix, i.e., consisting of black and white pixels. This black and white image is shown in Fig.5. Subsequently, the area of the matrix with the greatest density of white pixels is searched for.

[0079] For this purpose, elementary operators that process the matrix can be applied to the black and white binary matrix. A first applicable operator is the “dilation” operator, the effect of which is to gradually enlarge (dilate) the white areas. This operator makes it possible to expand the objects of an image, fill small gaps and connect objects separated by a distance smaller than the size of the structuring element being used by the operator. In the example illustrated herein, application of the dilation operator with a structuring operator of suitable size in terms of pixels provides (starting from the image of Fig.5) the result shown in Fig.6.

[0080] An erosion operator, the function of which on a binary image is to erode the contours of the white regions, is applied to this new image. The operation is repeated several times maintaining the size of the matrix of the structuring element of this operator. The result obtained, starting from the image of Fig.6, is shown in Fig.7. In practice, an image (Fig.7) in which a single white line, positioned at the boundary area between the stretched single faced corrugated board NS downstream of the stock S and the stock S itself appears, has been obtained from a grayscale image (Fig.4), where the areas of oscillation of the single faced corrugated board NS are identified by gray pixels. In substance, the white line of Fig.7 is the beginning of the stock S.

[0081] The amount in percentage of stock on the bridge 41 is determined by the relative position between the white line obtained from processing as described above with respect to the position of maximum and minimum stock, as clearly illustrated in Fig.8.

[0082] In brief, by processing the image obtained by the video camera 101 the amount of stock S in percentage with respect to the values of minimum stock and maximum stock is obtained.

[0083] If a single video camera 101 is not sufficient to generate an image of the whole area between minimum value and maximum value of the stock S, it is possible to use a pair of video cameras arranged in sequence along the bridge and to combine the images of the two video cameras, producing a single matrix of pixels that is the sum of the two matrices of pixels representing two images that are temporally simultaneous in time but spatially distanced along the longitudinal extension of the bridge 41 (extension in the direction of feed of the single faced corrugated board NS). The maximum stock line and the minimum stock line will be found in the image obtained from the sum of the two partial images captured by the two successive video cameras, one of these images containing the minimum stock line and the other the maximum stock line.

[0084] A further critical aspect in the management of the line 1 described above is the possibility of jamming (or jam-ups) of paper in various points of the production line. For this purpose, it is possible to use one or more video cameras arranged so as to frame critical areas of the path of the paper webs, or of the single faced corrugated board NS or composite corrugated board CC, continuous or divided into sheets. [0085] Typically, one or more video cameras can be provided in the following areas or positions of the line 1 :

- at the inlet and/or at the outlet of the cross cutter 61, where video cameras 103 and 105 are respectively indicated, see Fig.lC;

- at the suction nozzles 14, where one video camera 107 is indicated, see Fig.1(C);

- at the inlet and at the outlet of the slitter-scorer assembly 13, see video cameras 109, 111 in Fig.1(C);

- at the shingling members 64A, 64B, see video cameras 113A, 113B in Fig.1(D); and

- at the stackers 19A, 19B, see video cameras 115A, 115B in Fig.1(D).

[0086] Further video cameras, not shown, can, for example, be positioned in intermediate areas or positions along the slitting-scoring assembly, for example between pairs of tools arranged in sequence along the direction of feed of the corrugated board.

[0087] It must be understood that the list indicated above is an example and that further video cameras can be arranged in other critical points of the line 1. In some embodiments, fewer video cameras than those listed can also be provided.

[0088] These video cameras can also be connected to the control unit 100, which can be programmed to perform the image processing described below. Alternatively, one, some or each video camera can be provided with its own calculation resources that process the images captured by the video camera, and send data relating to the result of processing to the control unit 100.

[0089] The images captured by these video cameras are processed so as to detect the possible onset of jamming of the paper or board in the area framed by the video camera. Analysis of the images captured by the video camera has the aim of detecting whether and where the paper (in the form of paper web, or of single faced NS or composite CC corrugated board) has a different behaviour from the normal movement, corresponding to a condition of jamming.

[0090] The image processing method is configured such that by examining the images (frames), captured in succession by the respective video camera, it is possible to verify whether the web material (paper or board) is undergoing deformations or alterations which could result in jamming.

[0091] An embodiment of the algorithm is described below with reference to Figs. 9 to 19. Each image captured by the video camera, for example the video camera 105 installed downstream of the cross cutter 61, is converted into grayscale and is considered as a matrix of lines and columns, where each element of the matrix is represented by the intensity of a respective pixel of the image.

[0092] M lines equidistant from one another and N columns equidistant from one another are chosen on the matrix. Fig.9 schematically represents a matrix (with a much smaller number of exemplary elements than the pixels that actually form in image, for reasons of representation) highlighting three (M=3) lines Rl, R2, R3, of elements of the matrix that will be taken into consideration for the subsequent processing operations. Fig.10 schematically represents the same matrix, highlighting four (N=4) columns Cl, C2, C3, C4 of elements of the matrix that will be taken into consideration for the subsequent processing operations.

[0093] The first step of the processing method consists in generating, for each line, a vector V_M of a length m-p, where m is the number of elements of the line and p is an integer chosen at will and typically between 1 and 20, for example between 2 and 10, preferably between 4 and 6. The i^th element of the vector F_Mis given by the absolute value of the difference between the value of the i^th element and the value of the element (i+p)^th of the starting line Rj, as schematically indicated in Fig.l l. The method is repeated for the M lines chosen in the initial matrix, thereby obtaining for each of the M lines chosen a vector of a length (m-p), whose elements are given by absolute values of the differences in intensity of the starting pixels.

[0094] Each vector V_M is then reordered in decreasing order of the values of each element belonging to it. The reordered vector is indicated herein as V_M. The first element of the vector is the element with the highest value, the last is the element with the lowest value. For each vector V_M the value in T^th position starting from the highest value is extracted, where T is an integer chosen in a suitable manner, for example between 5 and 30, preferably between 8 and 15, for example between 9 and 11. The value of the T^th element of the reordered vector V_M is compared with a threshold value ThM.

[0095] The same process is used on the N columns chosen, obtaining a vector V_N that is then transformed into a vector reordered according to decreasing values of its elements, indicated with V_N. Each element in S^th position (where S can be equal to T or different from T, but chosen with analogous criterion) is compared with a threshold value ThN that can be equal to or different from the threshold value ThM.

[0096] In brief, in a nutshell the process generates for each image a series of M+N values, each of which is compared with a threshold value (equal or different for the M values obtained from the M lines and for the N values obtained from the N columns).

[0097] In substance, the criterion described above highlights a variation of the image framed by the video camera, which occurs in the case of a deformation of the corrugated board which can precede jamming. The algorithm described prevents generating false jamming alarms in the case of isolated defects, such as splice lines, a mark or other artifact that is not symptomatic of the start of jamming of the corrugated board, passing in front of the video cameras. Vice versa, a gradual deformation on a relatively large surface of corrugated board, which typically results in jamming, is identified by the algorithm as it is reflected in a plurality of above-threshold values of the reordered vectors V_M and V_N .

[0098] A jamming alarm is generated based on how many of the N+M values exceed the respective threshold. For a greater robustness of the process in relation to false alarms, advantageously a jamming signal is generated only if a certain number of (or all of) the M values calculated for the M lines exceed the respective threshold ThM, and if a certain number of (or all of) the N values calculated for the N columns exceed the respective threshold ThN.

[0099] For a better understanding of the process, Figs. 12 to 19 show two real situations in which the video camera frames an area of the production line 1, for example upstream of the cross cutter 61. Fig. 12 shows an image captured by the video camera 103 in a condition of normal operation, i.e., without jamming. The image, already converted into grayscale, shows two areas of different intensity of the pixels that form it, due to the presence of a shadow projected onto the corrugated board. Fig.13 shows, on the same image, a grid formed of three lines and seven columns of pixels. Fig.12 shows one of these columns, to which the processing illustrated in Fig.14 refers by way of example. It must be understood that analogous processing is performed on the pixels of the remaining lines and columns represented by the grid shown in Fig.13.

[0100] Fig.14 shows the steps A, B, C of generating the vector V_N starting from the column of pixels chosen and the step of generating the vector V_N (located in position D in Fig.14). For reasons of practical representation, Fig.14 only illustrates a portion of the column of pixels and hence of the respective vectors V_N and V_N.

[0101] More specifically, in Fig.14 the position A indicates a portion of the column of pixels considered. The position B indicates the same portion of column offset by four positions (in this case the value “p” indicated above is p = 4). The figures indicated in the single elements of the vector are the intensity of the single pixels. The position C indicates the (partial) vector V_N formed by the difference of the intensity values. Therefore, the first element of the (partial) vector V_N is equal to 80-40=40. The vector in position D is the reordered vector V_N. The first element has the value 120, which is the maximum value contained in V_N. The last element has the value 0, which is the minimum value contained in V_N. The value in the S^th position is the value that is compared with the threshold Th\. In this case the value is 40.

[0102] The sequence of Figs. 16 to 19 illustrates the same images as the sequence in Figs. 12 to 15, but in a condition in which the captured image shows jamming of the board. As can be observed from Fig. 19, the S^th position of the vector V_N. (vector in D) has the value 80 rather than 40. The threshold with which the value in S^th position is compared is chosen so as not to raise an alarm in the situation in Figs.12 to 15 and to raise an alarm in the situation in Figs. 16 to 19.

[0103] From the images in Figs. 12 to 19 it is clear that the process described above allows the generation of an alarm signal for jamming by processing the image captured by the video camera. As mentioned, for a greater robustness and insensitivity to noise, the alarm signal can be generated when a number greater than one of the line or column vectors considered generates a reordered vector with a value in T^th or S^th position greater than the threshold value.

[0104] A further critical aspect of the operation of the line 1 is represented by the need to accumulate and remove portions of composite corrugated board CC which are cross cut and discarded, for example upstream of the slitting and scoring section 13. More precisely, trimmings of this type are formed by the cross cutter 61. The trimmings can be collected by providing a basket 93 in which trimmings CD generated by cross cuts performed by the cross cutter 61 are accumulated.

[0105] To ensure correct operation of the whole line or plant 1, it is advisable firstly to check that the basket 93 is present and correctly position at the outlet of the cross cutter 61. Moreover, it is advisable to check the level of filling of the basket 93, i.e., the amount of discarded sheets of board accumulated in the basket 93, to ensure that the trimmings CD are collected correctly preventing subsequent trimmings from falling to the ground, should the basket be completely filled. By detecting the level of filling of the basket 93 it is possible to provide the operator with a notification, for example, to empty the basket or replace it with an empty one.

[0106] For this purpose, a video camera 120 that frames the basket 93 frontally or laterally can be provided in the area of the basket 93. The images captured by the video camera 120 can be processed to: (a) detect the presence or absence of the basket 93; and (b) to detect the amount of trimmings of corrugated board CD accumulated and hence the level of filling of the basket.

[0107] In particularly efficient embodiments, the video camera 120 is positioned laterally with respect to the basket 93, although in the drawing it is shown in a frontal position simply for clarity of representation.

[0108] Lateral framing of the basket 93, i.e., the view corresponding to the one shown in Fig.1(C) allows more efficient viewing, as will be clear from the following description of the method for processing the captured images.

[0109] The captured images are converted into grayscale. Fig.12 shows an image converted into grayscale of a basket 93 partially filled with trimmings of board, lying on the bottom of the basket. The image can be cropped to a size suitable to contain the side area of the cart, on which the following processing method is then performed. [0110] A vertical Gaussian blur filter is applied to the captured image. This filter acts on each pixel of the image, setting its value to the mean of all the values of the pixels present in a defined neighbourhood of the pixel considered. The filter is defined “vertical” as the size of the neighbourhood of the pixel considered has a size much larger in vertical direction than in horizontal direction.

[oni] An edge detection filter is applied to the image obtained by applying the vertical Gaussian blur filter, through which a new black and white image is obtained, in substance forming a binary matrix, where each pixel represents an element of the matrix and each element can take two values corresponding to the black and to the white in the image obtained. In other words, the result of applying the two filters is a black and white image, i.e., a binary matrix, in which vertical edges of the objects visible in the image are highlighted. Figs. 21, 22 and 23 show three of these images obtained for three different levels of filling of the basket 93. The image of Fig.21 corresponds to a practically empty basket, the image of Fig.22 corresponds to intermediate filling and the image of Fig.23 corresponds to a practically full basket.

[0112] The subsequent step consists in applying a “dilation” operator followed by an “erosion” operator to the binary matrix obtained, so as to join the dashed lines to each other, reduce the noise and increase the definition of the edges. Figs. 24, 25 and 26 show the result obtained by applying the dilation and erosion operators to the images of Figs. 21, 22 and 23.

[0113] To estimate the level of filling of the basket 93 the method can at this point include a further image processing step, from which a single column vector, containing a number of elements equal to the number of rows of the image previously processed is obtained. Each element of the column vector is obtained by calculating the mean of each line of the image. In other words, the j^th element of the column vector has a value that is the mean of the values of the N elements of the j^th line of the image. By scrolling the column vector thus obtained from top to bottom the first values corresponding to black pixels are discarded. The first white pixel that is encountered indicates the upper part of the basket 93. The last white pixel of the series indicates the level of board in the basket. The last element of the column vector, i.e., the lowest one, indicates the bottom of the basket. Based on these data the percentage of filling of the basket is calculated.

[0114] Figs. 27 and 28 indicate, respectively: a binary image or matrix obtained after applying the dilation and erosion operators in a condition with the basket filled to 20%; and the respective column vector.

[0115] With the same video camera 120 the presence or absence of the basket 93 can be detected. For this purpose, the basket can be provided with a marking, framed by the video camera 120 when the basket 93 is correctly in position. The image captured by the video camera 120 can be processed so as to verify the presence or absence of the marking in the position in which it should be when the basket 93 is in the correct position.

[0116] A system of the type described can be interfaced with a local IT network, which allows one or more lines inside the same plant or several plants to be monitored. A production line equipped with the aforesaid system of video cameras can also be connected to a remote control unit, for example via a communication portal. It would also be possible for alarm signals, diagnostic messages or other information, obtainable from the data processed as described above, to be transmitted via email, text message or other messaging systems on local or remote computers, or on mobile devices such as mobile phones or tablets.

[0117] Having described various aspects of the corrugated board production line, the innovative aspects of the present description are summarized below:

Clause 1. A corrugated board production line, comprising in combination: a corrugator, comprising: a first corrugating roller and a second corrugating roller cooperating with each other to corrugate a first paper web; a pressure member to glue the first paper web, corrugated by the first corrugating roller and by the second corrugating roller, to a second smooth paper web and form a single faced corrugated board; a first unwinder to feed the first paper web to the corrugator; a second unwinder to feed the second paper web to the corrugator; double facer; a third unwinder to feed a third smooth paper web to the double facer, the third paper web being glued to the single faced corrugated board on said double facer; a feeding bridge extending between the corrugator and the double facer; a first video camera located above the bridge and framing a feed path of single faced corrugated board along said bridge; and an image processing unit, adapted to process images captured by the video camera located above the bridge and to calculate, based on the content of said images, an amount of stock of single faced corrugated board on the bridge.

Clause 2. The line of clause 1, wherein the image processing unit is configured to identify, on images captured by the video camera, the location of a stock of single faced corrugated board in the form of festoons moving along the bridge.

Clause 3. The line of clause 2, wherein the image processing unit is configured to determine the location of the stock on the bridge in the images captured by the video camera through subtraction of successive images obtaining difference images, and through identifying on the difference image a line corresponding to the front of the stock of single faced corrugated board.

Clause 4. A method for controlling a stock of single faced corrugated board on a feeding bridge of single faced corrugated board to a double facer in a corrugated board production line, wherein at least one video camera connected to an image processing unit is associated with said bridge; wherein the method comprises the following steps: supplying a single faced corrugated board from a corrugator to the feeding bridge; forming a stock of single faced corrugated board on the bridge; framing with the video camera a portion of the bridge in which the stock of single faced corrugated board is located; from successive images captured by the video camera, obtaining information on the amount of stock on the bridge.

Clause 5. The method of clause 4, wherein the step of forming the stock of single faced corrugated board on the bridge comprises the step of forming a series of accumulated festoons of single faced corrugated board from an inlet of the bridge toward an outlet of the bridge.

Clause 6. The method of clause 5, wherein the step of obtaining information on the amount of stock on the bridge comprises the step of identifying the position of a front of the series of accumulated festoons on the bridge.

Clause 7. The method of clause 6, wherein the step of identifying the position of the front of the series of accumulated festoons comprises the step of converting successive images captured by the video camera into binary matrices and of subtracting two binary matrices corresponding to two successive images captured by the video camera from one another to obtain a difference matrix.

Clause 8. The method of clause 7, further comprising the step of applying one or more operators to the difference matrix to identify on the difference matrix a line corresponding to the position of the front of the series of festoons accumulated on the bridge.

Clause 9. The method of clause 8, wherein said operators comprise a dilation operator and an erosion operator.

Clause 10. A corrugated board production line, comprising in combination: a corrugator, comprising: a first corrugating roller and a second corrugating roller cooperating with each other to corrugate a first paper web; a pressure member to glue the first paper web, corrugated by the first corrugating roller and by the second corrugating roller, to a second smooth paper web and form a single faced corrugated board; a first unwinder to feed the first paper web to the corrugator; a second unwinder to feed the second paper web to the corrugator; a double facer; a third unwinder to feed a third smooth paper web to the double facer, the third paper web being glued to the single faced corrugated board on said double facer; a bridge extending between the corrugator and the double facer; a cross cutter; a basket, which can be positioned downstream of the cross cutter and adapted to collect trimmings removed from the corrugated board through cross cutting performed by the cross cutter; a video camera positioned to frame at least a portion of the basket located downstream of the cross cutter; and an image processing unit, adapted to process images captured by the video camera and to determine, based on said images, a level of filling of the basket with trimmings of corrugated board accumulated in the basket.

Clause 11. The line of clause 10, wherein the image processing unit is configured to obtain, from an image captured by the video camera, a matrix in which vertical edges of objects contained in the image are highlighted.

Clause 12. The line of clause 11, wherein the image processing unit is configured to convert the image captured by the video camera into a grayscale image, from which to obtain said matrix.

Clause 13. The line of clause 10 or 11, wherein the matrix is a binary matrix.

Clause 14. The line of clause 11 or 12 or 13, wherein the image processing unit is configured to obtain, from the matrix, a vector whose values are indicative of the level of filling of the basket.

Clause 15. The line of any one of clauses 10 to 14, wherein the video camera is positioned to frame the basket laterally, according to a line of view orthogonal to the direction of feed of the corrugated board along the line.

Clause 16. A method for detecting a level of filling of a basket for accumulating trimmings of corrugated board downstream of a cross cutter in a corrugated board production line; wherein the method comprises the following steps: capturing images of the basket through a video camera; and obtaining, from an image captured by the video camera, a matrix in which the vertical edges of objects contained in the image are highlighted.

Clause 17. The method of clause 16, comprising the step of converting the image captured by the video camera into a grayscale image before obtaining said matrix therefrom.

Clause 18. The method of clause 16 or 17, wherein the matrix is a binary matrix

Clause 19. The method of clause 16 or 17 or 18, wherein the step of obtaining the matrix comprises the steps of: applying a vertical Gaussian blur filter to the image detected by the video camera, if necessary previously converted into a grayscale image; and subsequently applying an edge detection filter to the image.

Clause 20. The method of clause 19, further comprising the following steps subsequent to application of the edge detection filter: applying a dilation operator to the matrix; and subsequently applying an erosion operator to the matrix.

Clause 21. The method of any one of clauses 16 to 20, comprising the step of obtaining, from the matrix, a vector, whose values are indicative of the level of filling of the basket.

Clause 22. The method of any one of clauses 16 to 21, comprising the step of verifying the presence of a basket based on images captured by the video camera.

Clause 23. The method of clause 22, wherein the presence of the basket is verified based on the presence of a marking applied to the basket.

Clause 24. The method of any one of clauses 16 to 23, wherein the video camera is positioned to frame the basket laterally, according to a line of view orthogonal to the direction of feed of the corrugated board along the line.

Clause 25. The method of any one of clauses 16 to 24, comprising the step of generating a request for replacement or emptying of the basket when through processing of the images captured by the video camera it is detected that the level of filling of the basket has reached a limit value.

Clause 26. A corrugated board production line, comprising in combination: a corrugator, comprising: a first corrugating roller and a second corrugating roller cooperating with each other to corrugate a first paper web; a pressure member to glue the first paper web, corrugated by the first corrugating roller and by the second corrugating roller, to a second smooth paper web and form a single faced corrugated board; a first unwinder to feed the first paper web to the corrugator; a second unwinder to feed the second paper web to the corrugator; a double facer; a third unwinder to feed a third smooth paper web to the double facer, the third paper web being glued to the single faced corrugated board on said double facer; a bridge extending between the corrugator and the double facer; a first video camera located in a critical position for the formation of jamming of corrugated board, and configured to capture images of the corrugated board passing through; and an image processing unit, adapted to process images captured by the video camera located in said critical position, and adapted to determine, based on the content of said images, the onset of a condition of jamming.

Clause 27. The line of clause 26, wherein the critical position is one or more of the following: the inlet of a cross cutter; the outlet of the cross cutter; the inlet of suction nozzles for longitudinal trimmings of the corrugated board; a position upstream or a position downstream of scoring tools; a position upstream or a position downstream of slitting tools; a position adjacent to shingling members; a position adjacent to a stacker.

Clause 28. The line of clauses 26 or 27, wherein the processing unit is configured to: extract, from a matrix whose elements consist of pixel intensities of the image captured by the video camera or of a portion thereof, a plurality of vectors corresponding to a series of lines and to a series of columns of the matrix; process the values of the single vectors to extract therefrom information indicative of an abnormal variation of intensity of the pixels along the respective vector.

Clause 29. The line of clause 28, wherein the processing unit is configured to: obtain, for each vector, a difference vector, whose elements consist of the difference, in absolute value, of the intensities of two successive, but not contiguous, pixels of the vector; order each difference vector in increasing order of the values of the elements thereof and obtain an ordered difference vector; compare an element in a predefined position of each ordered difference vector with a threshold value; generate a jamming notification if, for a predefined number of said ordered difference vectors, the element compared with the threshold value exceeds the threshold value.

Clause 30. A method of detecting a condition of jamming in a corrugated board production line, the method comprising the following steps: capturing an image of the corrugated board passing along the line; processing the image to extract therefrom information indicative of the onset of a condition of jamming of the corrugated board.

Clause 31. The method of clause 30, wherein the step of processing the image comprises the following steps: extracting, from a matrix whose elements consist of pixel intensities of the image captured by the video camera or of a portion thereof, a plurality of vectors corresponding to a series of lines and to a series of columns of the matrix; and processing the values of the single vectors to extract therefrom information indicative of an abnormal variation of intensity of the pixels along the respective vector.

Clause 32. The method of clause 31, wherein the step of processing the values of the single vectors comprises the following steps: obtaining, for each vector, a difference vector, whose elements consist of the difference, in absolute value, of the intensities of two successive, but not contiguous, pixels of the vector; ordering each difference vector in increasing order of the values of its elements and obtaining an ordered difference vector; comparing an element in a predefined position of each ordered difference vector with a threshold value; and generating a jamming notification if, for a predefined number of said ordered difference vectors, the element compared with the threshold value exceeds the threshold value.

Clause 33. The method of any one of clauses 30 to 32, wherein the images are captured in one or more of the following positions: upstream of a cross cutter; downstream of the cross cutter; close to suction nozzles of longitudinal trimmings of the corrugated board; upstream of scoring tools; downstream of scoring tools; upstream of slitting tools; downstream of slitting tools; at shingling members; and at a stacker.

Claims

1. A corrugated board production line, comprising in combination: a corrugator, comprising: a first corrugating roller and a second corrugating roller cooperating with each other to corrugate a first paper web; a pressure member to glue the first paper web, corrugated by the first corrugating roller and by the second corrugating roller, to a second smooth paper web and form a single faced corrugated board; a first unwinder to feed the first paper web to the corrugator; a second unwinder to feed the second paper web to the corrugator; a double facer; a third unwinder to feed a third smooth paper web to the double facer, the third paper web being glued to the single faced corrugated board on said double facer; a feeding bridge extending between the corrugator and the double facer; a first video camera located above the bridge and framing a feed path of single faced corrugated board along said bridge; and an image processing unit, adapted to process images captured by the video camera located above the bridge and to calculate, based on the content of said images, an amount of stock of single faced corrugated board on the bridge.

2. The line of claim 1, wherein the image processing unit is configured to identify, on images captured by the video camera, the location of a stock of single faced corrugated board in the form of festoons or loops moving along the bridge.

3. The line of claim 2, wherein the image processing unit is configured to locate the position of a leading loop or festoon, in the direction of advancement of the corrugated board on the bridge, between a minimum stock position and a minimum stock position.

4. The line of claim 2 or 3, wherein the image processing unit is configured to determine the location of the stock on the bridge in the images captured by the video camera through subtraction of successive images obtaining difference images, and through identifying on the difference image a line corresponding to the front of the stock of single faced corrugated board.

5. A method for controlling a stock of single faced corrugated board on a feeding bridge of single faced corrugated board to a double facer in a corrugated board production line, wherein at least one video camera connected to an image processing unit is associated with said bridge; wherein the method comprises the following steps: supplying a single faced corrugated board from a corrugator to the feeding bridge; forming a stock of single faced corrugated board on the bridge; framing with the video camera a portion of the bridge in which the stock of single faced corrugated board is located; and from successive images captured by the video camera, obtaining information on the amount of stock on the bridge.

6. The method of claim 5, wherein the step of forming the stock of single faced corrugated board on the bridge comprises the step of forming a series of accumulated loops or festoons of single faced corrugated board from an inlet of the bridge toward an outlet of the bridge.

7. The method of claim 6, wherein the step of obtaining information on the amount of stock on the bridge comprises the step of identifying the position of a front of the series of accumulated festoons or loops on the bridge.

8. 8. The method of claim 7, wherein the step of identifying the position of a front of the series of accumulated festoons on the bridge comprises the step of locating the most advanced festoon or loop in the direction of advancement of the corrugated board on the bridge, between a minimum stock position and a maximum stock position.

9. The method of claim 7 or 8, wherein the step of identifying the position of the front of the series of accumulated festoons or loops comprises the step of converting successive images captured by the video camera into binary matrices and of subtracting two binary matrices corresponding to two successive images captured by the video camera from one another to obtain a difference matrix.

10. The method of claim 9, further comprising the step of applying one or more operators to the difference matrix to identify on the difference matrix a line corresponding to the position of the front of the series of festoons or loop accumulated on the bridge.

11. The method of claim 10, wherein said operators comprise a dilation operator and an erosion operator.