Method for positioning and calibrating functional rollers relative to embossing rollers , an embossing unit or embossing-laminating unit

Abstract

By means of a first actuator and a second actuator, respectively associated with opposite axial ends of the functional roller, the functional roller and the embossing roller are moved toward each other, and are pressed against each other with an equal thrust by means of the first actuator and the second actuator. Then, the embossing roller and the functional roller are rotated while they are in contact with each other and pressed against each other. Then, the functional roller and the embossing roller are moved away from each other by means of the first actuator and the second actuator, and the functional roller and the embossing roller are brought to a spaced position, performing an equal stroke with the first actuator and the second actuator, so as to keep the functional roller and the embossing roller parallel to each other. Then, the functional roller and the embossing roller are moved again toward each other, and the position of first mutual contact between the functional roller and the embossing roller is detected and stored.

Description

METHOD FOR POSITIONING AND CALIBRATING FUNCTIONAL ROLLERSRELATIVE TO EMBOSSING ROLLERS, AN EMBOSSING UNIT OREMBOSSING-LAMINATING UNITDESCRIPTIONTECHNICAL FIELD

[0001] The present invention relates to the field of machines for converting web materials. Embodiments described herein particularly relate to converting machines for paper, particularly tissue paper, for the production of toilet paper, kitchen towels, handkerchiefs, napkins, and similar products.

[0002] Specifically, improvements to embossing units or embossing-laminating units for converting a multi-ply web material, especially tissue paper, are disclosed herein.BACKGROUND ART0

[0003] Cellulose products, for example toilet paper rolls, kitchen towel rolls, handkerchiefs, and paper napkins, are produced using a cellulose web material, typically tissue paper, fed from one or more parent reels coming from a continuous paper-making machine.

[0004] In some cases, the parent reels are unwound and rewound into reels or rolls of smaller diameter and smaller axial dimensions in so-called slitter-rewinders or rewinders.

[0005] The reels, coming from the continuous machine, or from the slitter-rewinder, feed converting lines for the production of consumer products, for example napkins, handkerchiefs, toilet paper rolls, kitchen towels and the like.

[0006] The converting line usually comprises an unwinding station, adapted to unwind one or more reels of cellulose web material. One or more plies of cellulose web material are fed, either along the same path or along separate paths, to machines positioned along the converting line downstream of the unwinding station, to undergo one or more processing operations, to finally obtain products intended for sale andconsumption.

[0007] Typically, a converting line comprises, downstream of the unwinding station, at least one embossing unit, which performs an embossing operation on one or more plies constituting the continuous cellulose web material. Embossing consists in permanently deforming the cellulose web material by making the cellulose web material pass in an embossing nip defined between an embossing roller, provided with embossing protuberances, and a pressure roller. The embossing roller is usually a roller integrally made of steel or having at least one outer sleeve made of steel, or other hard material, provided with the embossing protuberances. The pressure roller may have a hard outer surface, engraved with engravings complementary to the embossing protuberances of the embossing roller. In more widely used embodiments, the pressure roller has a smooth outer surface, i.e. a surface generally free of engravings or protuberances, formed by a yielding layer, preferably an elastically yielding layer.

[0008] In use, the pressure roller and the embossing roller are pressed against each other in the embossing nip. If the pressure roller is coated with a yielding material, the pressure between the embossing roller and the pressure roller is such that the embossing protuberances of the embossing roller penetrate at least partially into the yielding coating of the pressure roller, while the embossing roller and the pressure roller rotate in opposite directions at substantially equal peripheral speed. This results in permanent deformation of the web material that is fed through the embossing nip at a feed speed substantially equal to the peripheral speed of the embossing roller and the pressure roller.

[0009] In some cases, the converting line comprises an embossing unit having a single embossing roller and a single pressure roller, which form a nip through which the web material, that may consist of one or more plies of cellulose fibers, passes.

[0010] More often, the converting line comprises an embossing unit with more than one embossing roller, each co-acting with a respective pressure roller, so as to emboss separately two plies of cellulose fibers, each of which may consist of one or more layers of cellulose fibers. An embossing unit of this type is more specifically called "embossing-laminating unit," as it comprises a laminating system, where the two (or more) separately embossed plies are bonded together by application of a functionalfluid, by mechanical ply-bonding, or in other manner. The laminating system may comprise, for example, a nip defined between two opposite and counter-rotating embossing rollers, or between an embossing roller and a laminating roller. The result is a multi-ply embossed cellulose web material.

[0011] In some embodiments, the plies are bonded in the embossing-laminating unit using a glue, which may be in an aqueous suspension. More generally, a functional fluid can be used, typically a functional liquid. In some cases, the functional fluid is simply water, with no added adhesive substance. The function of the functional fluid is to promote the formation of hydrogen bonds between the fibers of the cellulose webs. Therefore, in this document, the term "functional fluid" refers to a generic fluid that, applied as described below, promotes the bonding of the plies. In this sense, the functional fluid is a glue; therefore (unless otherwise indicated) in the present description and in the claims the term “glue” refers to a fluid, typically in a liquid state, that acts as a functional fluid adapted to obtain, to facilitate, or to promote the bonding of cellulose plies.

[0012] The embossed cellulose web material coming from the embossing unit is further processed in converting stations downstream of the embossing unit, for example, it is wound in logs, i.e. rolls with a diameter equal to the diameter of the finished rolls and an axial length multiple of the axial dimension of the finished rolls. The logs are then cut into individual rolls, which are then packaged for transportation and distribution. In this case, a rewinder is provided in the converting station.

[0013] In other converting lines, downstream of the embossing unit there is arranged a converting station comprising an interfolding machine, or a cutting and folding machine, for producing tissue paper napkins or handkerchiefs or logs of napkins or handkerchiefs, which, if necessary, may be interfolded (in the case of interfolding machines). Also the logs of napkins or handkerchiefs are then cut into individual packets, which are then packaged for being marketed.

[0014] One of the critical aspects in managing the embossing unit is the control of the co-action between the embossing roller and the pressure roller, i.e. the roller pressing against the embossing roller to generate the protuberances in the ply of web material passing through the nip between the embossing roller and the pressure roller.The embossing depth, i.e. the height of the embossed protuberances generated in the ply of cellulose material, shall be properly set to achieve the required characteristics in the finished web material. In particular, the embossing depth must be sufficient to obtain a product of adequate apparent thickness and optimal appearance, characterized by the embossing patterns. The softness and absorbency features can also be affected by the embossing depth, which must therefore be controlled and correspond to the desired value.

[0015] The embossing depth must also be sufficiently uniform along the width of the web material so as not to have portions with higher protuberances and portions with lower protuberances. This drawback can cause serious consequences in downstream machines, particularly in rewinders and interfolding machines that, if processing a web material of non-uniform height, produce non-conforming products. For example, in the case of a rewinder, lack of uniformity in apparent thickness of the web material, due to a lack of uniformity in the height of the protuberances, can lead to the production of rolls with a non-constant diameter. These dissimilarities in winding or interfolding can also cause jams.

[0016] As mentioned above, in some embossing machines two or more pairs of rollers are provided, each pair consisting of an embossing roller and a corresponding pressure roller. Each embossing roller / pressure roller pair embosses a respective ply of web material. The two embossed plies must then be bonded together. Bonding is achieved by applying, to the tops of one of the embossed plies, a functional liquid, for example a glue. In some cases, the two embossed plies are then put over each other and laminated, so as to apply pressure between the two plies at the areas where the functional fluid has been applied.

[0017] In some embossing machines of this type, also known as embossinglaminating units as they perform an embossing operation and a laminating operation, the two embossed plies are laminated in a nip defined between one of the two embossing rollers and a laminating roller.

[0018] In some cases, one of the two plies is not embossed and is bonded by lamination to an embossed ply.

[0019] In any case, when a laminating roller is provided, the laminating pressuremust be correct to have a high-quality finished product.

[0020] For example, an insufficient laminating pressure, even if only onto a portion of the width of the web material, may cause the plies not to be bonded together, or to be bonded very weakly with easy delamination. Conversely, an excessive laminating pressure may cause unwanted further embossing of the bonded plies. In both cases, production defects occur, and the products must be discarded.

[0021] In general, the pressure rollers are coated with an elastically yielding material, such as natural or synthetic rubber. Similarly, in some cases, also the laminating rollers are coated with an elastically yielding material, such as natural or synthetic rubber, usually of higher hardness than the elastically yielding material used for the coatings of the pressure rollers.

[0022] In the present document, the term "elastically yielding material" refers to a material that elastically deforms under the operating conditions of the embossing unit. Therefore, a steel roller does not have an elastically yielding lateral surface, in the meaning explained above, because it does not deform perceptibly or appreciably when subjected to the normal pressure stresses during operation. Conversely, a rubber coating of a pressure roller is elastically yielding, because, during operation, the mutual pressure between the embossing roller and the pressure roller causes an elastic deformation of the rubber coating of the pressure roller.

[0023] The coatings made of yielding material are subject to wear due to the pressure against the embossing roller. This causes a gradual change in the diameter of the pressure rollers and the laminating rollers.

[0024] It is therefore necessary to precisely adjust the position of the pressure roller and / or the laminating roller relative to the corresponding embossing roller in order to achieve proper embossing and lamination.

[0025] The adjustment of the mutual position is also necessary when, for example, the embossing roller and / or the pressure roller shall be replaced.

[0026] In general, at the startup of each production cycle, it is necessary to set correctly the position of the embossing roller and the pressure roller or laminating roller relative to each other.

[0027] According to one aspect, a method is disclosed herein that solves the problem of an easy, accurate and correct positioning of a pressure roller and / or a laminating roller relative to a corresponding embossing roller. Specifically, the correct positioning typically occurs prior to the start-up of the converting line in which the embossing unit is located, for example and in particular before initiating the feeding of the web-like material.SUMMARY

[0028] According to an aspect, a method is disclosed herein for adjusting, in an embossing unit, the relative position between an embossing roller, carried by a stationary bearing structure, and a functional roller, movable relative to the stationary bearing structure and adapted to define, with the embossing roller, a nip through which a continuous ply of web material passes. The method comprises a first step of moving the functional roller and the embossing roller toward each other by means of a first actuator and a second actuator associated respectively with a first axial end and a second axial end of the functional roller, and of pressing the functional roller against the embossing roller with an equal thrust by means of the first actuator and the second actuator. Then, a step is performed of rotating, for an interval of time, the embossing roller and the functional roller while they are in contact with each other and pressed against each other. Then, a step is carried out of moving the functional roller and the embossing roller away from each other by means of the first actuator and the second actuator, and bringing the functional roller and the embossing roller to a spaced position, performing an equal stroke with the first actuator and the second actuator, so as to keep the functional roller and the embossing roller parallel to each other. Then, a step is performed of moving again the functional roller and the embossing roller toward each other by means of the first actuator and the second actuator, while keeping the functional roller and the embossing roller parallel to each other, and of detecting an storing the position of first mutual contact between the functional roller and the embossing roller.

[0029] The adjustment takes place in a preliminary phase with respect to production. It is therefore a procedure for calibrating the relative position of the embossing roller and the functional roller.

[0030] The position of first mutual contact is a reference position, or zero position. Then, at any appropriate time, even after the above procedure is finished, a further step can be performed of bringing the functional roller from the position of first mutual contact, as defined above, to a position closer to the embossing roller, up to a working position defined by a physical parameter of interaction between the embossing roller and the functional roller. This step can be carried out immediately after the step of detecting the first mutual contact position, or at a different time, even long after the conclusion of the procedure described above. In this case, the functional roller is returned to the (stored) position of first mutual contact, and, from this position, a step is performed of continuing to move the functional roller and the embossing roller toward each other while keeping the functional roller and the embossing roller parallel to each other.

[0031] The working position can be identified based to a stroke made by the functional roller toward the embossing roller, measured from the first contact position. In this case, the physical parameter of interaction between the embossing roller and the functional roller is a distance.

[0032] Therefore, in this case, the embossing unit is controlled in position. What is sought and maintained is the mutual position between the embossing roller and the pressure roller. This mutual position can correspond to a precise mutual penetration of the protuberances of the embossing roller into the yielding coating of the pressure roller. The embossing depth is thus defined, and can be kept constant, regardless of changes in other physical parameters, for example the temperature, which can expand the rollers and / or change the softness / hardness of the elastically yielding coating.

[0033] In other embodiments, the physical interaction parameter is a force (equal at the two ends of the functional roller) with which the functional roller and the embossing roller are pressed against each other.

[0034] An embossing unit is also disclosed herein, which comprises one or more embossing assemblies, each of which comprises an embossing roller and at least one functional roller, in which a control unit is also provided that is configured, i.e. programmed, to perform the method defined above. In practice, a program is stored in the control unit, which, when executed, carries out the steps of the method definedabove.

[0035] Further characteristics and embodiments of the method and the embossing unit, or embossing-laminating unit, of the present invention are described below and defined in the attached claims.BRIEF DESCRIPTION OF THE DRAWING

[0036] Embodiments of the invention are illustrated in the attached drawing, where: Fig. 1 shows an embossing-laminating unit;Fig. 1A shows a schematized enlargement of the detail indicated with A in Fig. 1;Fig. IB shows a schematized enlargement of the detail indicated with B in Fig. 1 ;Fig. 2 shows a detail of a pressure roller and the respective embossing roller;Fig. 3 shows a view according to III-III of Fig. 2; andFig. 4 shows a block diagram of the method for adjusting the position of a functional roller relative to the respective embossing roller according to the invention.DETAILED DESCRIPTION

[0037] In the following description, reference will be made to an embossinglaminating unit, comprising two assemblies, each of which consists of a pressure roller and a respective embossing roller, for separately embossing two plies of cellulose web material. The embossing-laminating unit described herein also comprises a laminating roller to facilitate the bonding of the plies that have been separately embossed by the two assemblies comprising the embossing roller and the pressure roller.

[0038] However, as it will be clearly apparent to those skilled in the art from reading the following description, the innovative aspects described herein can also be used in simple embossing units, which comprise a single pair consisting of one embossing roller and one respective pressure roller.

[0039] It is also possible to use the innovative elements described herein in an embossing-laminating unit with no laminating roller, in which the lamination of separately embossed plies occurs between two opposite embossing rollers, between which a laminating nip is defined. This occurs, for example, in the so-called point-to- point embossing-laminating units.

[0040] The embossing unit may also comprise more than two embossing rollers with the respective pressure rollers, or embossing rollers with which more than one pressure roller co-act.

[0041] When multiple pressure rollers are provided, it is advantageous for each of them to have systems for adjusting the position relative to the respective embossing roller, even if this is not strictly necessary.

[0042] With reference to the attached drawing, in the embodiment shown in Fig. l, an embossing-laminating unit 5 (herein also simply "embossing unit") is shown, comprising a first embossing roller 21 provided with embossing protuberances 2 IP (Fig. 1A) and co-acting with a first pressure roller 23 that has an outer surface 23A consisting of a coating made of a yielding material, especially an elastically yielding material, for example rubber. The embossing-laminating unit 5 also comprises a second embossing roller 25 provided with embossing protuberances 25P (Fig. IB) and co-acting with a second pressure roller 27 that has an outer surface 27A consisting of a coating made of a yielding material, especially an elastically yielding material, for example rubber.

[0043] The first pressure roller 23 is supported by a pair of movable bearing members. In the illustrated embodiment, the movable bearing members comprise swinging arms 24, hinged to a stationary structure 45 around an axis 24A. The two swinging arms 24 are positioned at the two opposite axial ends of the first pressure roller 23. The axis 24A is preferably parallel to the rotation axis 21A of the first embossing roller 21 and to the rotation axis 25 A of the second embossing roller 25. When properly positioned and in use, also the rotation axis 23A of the first pressure roller 23 is parallel to the axis 24A and the axis 21 A.

[0044] To press the first pressure roller 23 against the first embossing roller 21, two approach actuators are provided moving the first embossing roller 21 toward the first pressure roller 23. The two approach actuators are indicated with the reference number 26; each of them is hinged to one of the two swinging arms 24 and to the stationary bearing structure 45. The reference numbers 26 A and 26B indicate the hinges connecting each actuator 26 to the respective swinging arm 24 and the stationary bearing structure 45, respectively. Here below, the approach actuators will be alsobriefly referred to as "actuators.

[0045] The second pressure roller 27 is supported on a pair of movable bearing members. In the illustrated embodiment, the movable bearing members comprise swinging arms 28, hinged to the stationary structure 45 around an axis 28A. The two swinging arms 28 are positioned at the two opposite axial ends of the second pressure roller 27. The axis 28A is preferably parallel to the rotation axis 21A of the first embossing roller 21 and to the rotation axis 25 A of the second embossing roller 25. When properly positioned and in use, also the rotation axis 27A of the second pressure roller 27 is parallel to the axis 28A and the axis 21 A.

[0046] Two approach actuators 30 (here below, simply “actuators”) are provided to press the second pressure roller 27 against the second embossing roller 25; each actuator is hinged to one of the two swinging arms 28 and to the stationary bearing structure 45. The reference numbers 30A and 30B indicate the hinges connecting each actuator 30 to the respective swinging arm 28 and the stationary bearing structure 45, respectively.

[0047] Between the first embossing roller 21 and the first pressure roller 23 a first embossing nip 31 is formed, to which the first ply VI is fed. Between the second embossing roller 25 and the second pressure roller 27 a second embossing nip 33 is formed, to which the second ply V2 is fed.

[0048] The two embossed plies are bonded together in a laminating nip that may be formed between the first embossing roller 21 and the second embossing roller 25, for example in the case of a point-to-point embossing unit. Alternatively, as shown in Fig. 1, the embossed ply V2 can be detached from the second embossing roller 25 and driven around the first embossing roller 21, to pass, together with the ply VI, through a laminating nip 36 formed between the first embossing roller 21 and a laminating roller 35.

[0049] The laminating roller 35 may be supported by a pair of movable bearing members. In the illustrated embodiment, the movable bearing members comprise swinging arms 38, hinged to the stationary structure 45 around an axis 38 A. The two swinging arms 38 are positioned at the two opposite axial ends of the laminating roller 38. The axis 38A is preferably parallel to the rotation axis 21A of the first embossingroller 21 and to the rotation axis 25 A of the second embossing roller 25. When properly positioned and in use, also the rotation axis 35A of the laminating roller 35 is parallel to the axis 24 A and the axis 21 A.

[0050] Two approach actuators 40 (here below, simply “actuators”) are provided to press the laminating roller 35 against the first embossing roller 21; each actuator is hinged to one of the two swinging arms 38 and to the stationary bearing structure 45. The reference numbers 40A and 40B indicate the hinges connecting each actuator 40 to the respective swinging arm 38 and the stationary bearing structure 45, respectively.

[0051] The laminating roller 35 may have an outer surface made of an elastically yielding material, typically of higher hardness than the outer surface 23 A, 27A of the pressure rollers 23, 27. In other cases, the outer surface of the laminating roller 35 is made of steel or other material of such hardness that it does not deform significantly under the load determined by the pressure with which the laminating roller is pressed against the embossing roller. In both cases, whether the outer surface of the laminating roller 35 is elastically yielding or not, the position adjustment procedure described below is the same.

[0052] Each actuator 26, 30, 40 may comprise, or consist of, a cylinder-piston actuator. In some embodiments, each actuator 26, 30, 40 comprises, or consists of, a pneumatic or hydraulic cylinder-piston actuator. The use of pneumatic actuators has significant advantages, for example if compared to a hydraulic system, because it uses simple air as working fluid, rather than oil or other liquid. The use of air eliminates all problems related to any leakages of the working fluid.

[0053] In the diagram of Fig. 1, the reference numbers 26X, 30X and 40X indicate pressure switches associated with each actuator, 26, 30 and 40, respectively. The pressure switches 26X, 3 OX, and 40X are adapted to detect the value of the working fluid pressure in each actuator. In some embodiments, the two actuators associated with the two ends of a same roller are associated with a single pressure switch that reads the working fluid pressure of both actuators acting on the same roller. In other embodiments, each actuator has an own independent pressure switch. The pressure switches 26X, 3 OX, and 40X are connected to a control unit 42, described in more detail below. The data connections between the pressure switches and the control unit42 are indicated with P26, P30 and P40.

[0054] To bond the two plies VI, V2, a functional liquid, such as glue, can be used, applied to the ply VI when the ply is guided around the first embossing roller 21 and engaged thereto after having being permanently deformed in the embossing nip 31, so that embossed protuberances have been formed in the ply VI and are adhering to the embossing protuberances 21P of the first embossing roller 21.

[0055] To apply a functional liquid, a dispensing unit is, for example, provided for dispensing glue or other functional liquid, for example simply water. In the following, the dispensing unit for dispensing glue or other functional fluid, indicated with the reference number 37 in Fig. 1, can be referred to also simply as "dispenser".

[0056] In embodiments described herein, the dispenser 37 comprises a slide 41 guided along guides 43 integral with the stationary bearing structure 45 that supports the embossing-laminating unit 5. The slide 41 is engaged to the guides 43 through shoes 47. In other embodiments, the dispensing unit 37 is constrained to the stationary bearing structure 45 by means of a rotoidal joint so as to rotate around a rotation axis and to move toward, or away from, the first embossing roller 21.

[0057] The dispenser 37 may comprise a dosing roller, here below referred to as “screened roller”, indicated with the reference number 57, which takes functional liquid, for example glue, from a tank or other functional liquid source 59. The screened roller 57 transfers the functional liquid to a dispensing roller 61, which can be provided with an interchangeable plate, not shown in detail. The dispensing roller, or plate roller, 61 is configured to transfer functional liquid, received from the screened roller 57, to the embossed ply VI, and more precisely to at least some of the embossed protuberances of the ply VI that are engaged to the embossing protuberances 2 IP of the first embossing roller 21. To this end, the outer surface of the dispensing roller 61, onto which the screened roller 57 doses the functional liquid, is spaced from the heads of the embossing protuberances 2 IP by a distance that is equal to, or preferably less than, the thickness of the ply VI at the embossing protuberances 2 IP.

[0058] The pressure rollers 23, 27 and the laminating roller 35 constitute functional rollers co-acting with a respective embossing roller 21, 25. As mentioned in the introductory section of this document, the correct positioning of each functional rollerrelative to the embossing roller is an important aspect in the operation of the embossing unit 5. In general, each of the pressure rollers 23, 27 and the laminating roller 35 can be properly positioned relative to the corresponding embossing roller in the manner described below. In other embodiments, the position adjustment described below applies to only one, or to each, of the pressure rollers and not to the laminating roller, for example if the laminating roller is not provided or if it has a very high hardness. In other embodiments, the position adjustment is carried out only for the laminating roller and not for the pressure rollers, or for only one of them.

[0059] The actuators 26, 30, 40 interface with the control unit 42 mentioned above. The connections between the actuators and the control unit are schematically indicated by the references Cl, C3, C5.

[0060] With reference again to Fig. 1, the members and the operations for adjusting the position of either functional roller relative to the corresponding embossing roller are described below with reference to Figs. 2 and 3. In these figures, one generic functional roller 100 is shown. The functional roller 100 can be either of the above described first pressure roller 23, second pressure roller 27, laminating roller 35. Therefore, the members and the functions described with reference to Figs. 2 and 3 may be those of one or more of the three functional rollers 23, 27, 35. The reference 100A indicates the rotation axis of the functional roller 100. The first axial end and the second axial end of the functional roller 100 comprise respective journals that engage in end supports. The axial ends are indicated with 100B in Fig. 3, and the journals of the two axial ends are indicated with 100C.

[0061] The reference number 102 indicates the movable bearing members of the functional roller 100. In the illustrated embodiment, the movable bearing members comprise swinging arms, supporting the generic functional roller 100, which may represent the swinging arms 24 and / or the swinging arms 28 and / or the swinging arms 38. The pivoting axis of the swinging arms 102 is indicated with 102A. The reference number 104 indicates the two approach actuators (briefly "actuators") that press the generic functional roller 100 against the respective embossing roller, which may be either the first embossing roller 21 or the second embossing roller 25. Each actuator is hinged, at 104 A, to the respective swinging arm 102 and, at 104B, to the stationary bearing structure 45.

[0062] The reference number 105 indicates generic pressure switches for each generic actuator 104. The letter P indicates the connection of the pressure switch with the control unit 42. The generic pressure switch 105 may represent either of the previously mentioned pressure switches 26X, 3 OX, 40X.

[0063] To each swinging arm 102 (and thus to each arm of one or more pairs of arms 24, 28, 38), a position transducer is associated, whose function is to detect a position of the respective functional roller 102 (i.e. 23, 25, 35).

[0064] In the illustrated embodiment, each position transducer comprises, for example, an encoder 108 associated with, or embedded in, the respective actuator. The reference CIO indicates a connection of the encoders 108 and the actuators 104 to the control unit 42. Thus, the connection CIO in Fig. 2 corresponds to each of the connections indicated with Cl, C3, C5 in Fig. 1.

[0065] In some embodiments, to each actuator 104 a force transducer is also associated, configured to detect a force generated by the mutual contact between the generic functional roller 100 and the corresponding embossing roller 21, 25. In the illustrated embodiment, a force transducer is provided, embedded in the hinge 104 A that connects each swinging arm 102 to the respective actuator 104. Each force transducer may comprise one or more load cells, for example associated with a pin of the respective hinge. The force transducers are generically indicated in Figs. 2 and 3 with the reference number 110. Each force transducer 110 can represent a force transducer associated with either end of the first pressure roller 23, a force transducer associated with either end of the second pressure roller 27, and a force transducer associated with either end of the laminating roller 35.

[0066] Even if, in Fig. 2, the force transducers 110 are inserted into the hinges connecting the swinging arms 102 to the respective actuators 104, this is not the only possible arrangement. For example, the force transducers can be inserted into the end supports of the functional roller 100. The supports are indicated with the reference number 103 in Fig. 3. In other embodiments, the force transducers can be inserted into the hinges connecting the swinging arms 102 to the stationary structure, i.e. the hinges that define the axes 24 A, 28 A, and 38 A. It should be understood that the force transducers can be arranged differently for the three functional rollers 23, 25, 35.Preferably, the force transducers are mounted on the swinging arms, i.e. at the above- mentioned hinges and / or the roller carried by the swinging arms.

[0067] In some embodiments, it is also possible to insert the force transducers into the supports of the respective embossing roller 21, 25. In the case of the second embossing roller 25, the force transducers inserted into the supports of the embossing roller detect the force exchanged between the second embossing roller 25 and the second pressure roller 27. In the case of the embossing roller 21, the force transducers detect the force exchanged between the first pressure roller 25 and the first embossing roller 21 and / or the force exchanged between the first embossing roller 21 and the laminating roller 35. To this end, it is possible to use transducers adapted to detect the force in a given direction, or to perform the detection of the force exchanged between embossing roller and functional rollers (pressure roller 25 and laminating roller 35) in different and sequential steps of an adjustment procedure, described below.

[0068] A connection C20 between the respective force transducer and the control unit 42 is shown in Fig. 2. The connection C20 corresponds to one or the other of the connections indicated with C2, C4, C6 in Fig. 1.

[0069] In other embodiments, the force transducers are omitted and, instead of them, only the pressure switches are used to perform the position adjustment procedure, as it will be explained below.

[0070] In some embodiments, the adjustment procedure also uses other parameters, for example one or more electrical parameters of an actuation motor 21M or 25M driving the respective embossing roller 21 or 25 in rotation. The motor is schematically shown in Fig. 2. The reference C7 indicates the data connection between the motor 25M or 2 IM and the control unit 42. The detected electrical parameter can be the current absorbed by the motor in various operating steps, or the power absorbed, or the transmitted torque, measured, for example, by a torque meter.

[0071] With the members shown in Figs. 2 and 3, it is possible to perform, on the generic functional roller 100, a position adjustment step at the beginning of a production cycle. This position adjustment step, described below with reference to the functional roller 100, can be performed on one or both of the two pressure rollers 23, 27 and / or the laminating roller 35 of Fig. 1. In the case of the pressure roller 23 andthe laminating roller 35, if the adjustment cycle is performed on both the rollers, it is possible to run the cycle successively, firstly on one and then on the other of the two rollers co-acting with the embossing roller 21. In other cases, the position adjustment cycle on the pressure roller 23 and the laminating roller 35 can be performed simultaneously.

[0072] The purpose of the position adjustment cycle is to bring the functional roller and the embossing roller parallel to each other and to position the functional roller in the desired position relative to the embossing roller.

[0073] The first step of the cycle of adjusting the position of the functional roller 100 relative to the embossing roller 21, 25 consists in moving the functional roller 100 toward the respective embossing roller by means of the two actuators 104. The approach movement continues until an equal force, i.e. a thrust, is achieved for the two actuators 104, i.e. for the two ends of the functional roller 100. In practice, in this step the two actuators 104 press the functional roller 104 against the embossing roller with equal force.

[0074] This thrust can be measured by a force sensor or transducer, for example by the load cells defined above. In other embodiments, the thrust is determined by a pressure signal generated by the pressure switch(es) 105 associated with the actuators 104. This approach can be advantageous because the pressure switches reading the working fluid pressure of the actuators 104 are, in any case, present in the embossinglaminating unit. Thus, in this case, no specific additional sensor or transducer shall be added to what is already provided on the embossing-laminating unit, to perform this step of the cycle of adjusting the mutual position between the embossing roller and the functional roller. In practice, when the pressure switches are used as transducers to detect the force by which the pressure roller and the embossing roller are pushed against each other, a functional roller 100 is controlled to move toward the embossing roller 21, 25 at a predetermined pressure, i.e. both actuators 104 are controlled to move the rollers toward each other by a predetermined fluid pressure, to which a predetermined force corresponds. Preferably, the predetermined pressure is less than the operating pressure. This pressure is detected through the respective pressure switches associated with each actuator or pair of actuators.

[0075] This step of moving the rollers toward each other can be performed with the embossing roller 21 or 25, and thus the functional roller 104, stationary, i.e. not rotating. Furthermore, in this step, the web material VI or V2 can be present around the embossing roller 21, 25, or not.

[0076] Once the contact position and the required thrust value have been reached, the embossing roller 21, 25 is driven in rotation by the motor 2 IM, 25M. In some cases, the rotation of the embossing roller can start before reaching the preset mutual thrust between the functional roller 100 and the embossing roller 21, 25.

[0077] The functional roller 100 is driven in rotation by friction by the embossing roller 21, 25, which penetrates with its embossing protuberances 21P, 25P into the elastically yielding coating of the functional roller 100. It is also possible to drive also the functional 100 roller in rotation by means of an autonomous motor or of the same motor 2 IM, 25M, for example, with an adequate transmission, like a chain transmission, a gear transmission, a belt transmission, or the like.

[0078] The system consisting of the functional roller 100 and the embossing roller 21, 25 is kept rotating for a given time interval, which can be, for example, several seconds or tens of seconds, or longer, for example several minutes or tens of minutes. It should be understood that the indicated values are neither binding nor limiting, but merely illustrative.

[0079] The rotation (in opposite directions) of the functional roller 100 and the respective embossing roller 21, 25 for a given time interval causes the adjustment of the mutual positions of these rollers, that are positioned parallel to each other, thanks to the uniform, i.e. equal, thrust on the two ends of the functional roller 100, applied by the actuators 104.

[0080] After the time interval required for adjusting the mutual position of the two rollers 104 and 21, or 25, has finished, the next step of the position adjustment cycle is performed. This step consists in moving the functional roller 100 and the embossing roller 21, 25 away from each other by means of the actuators 104. This movement is performed in such a way that in the final position reached by the functional roller 100, it is parallel to itself, that is, parallel to the position in which it was in the previous step, in contact with, and pushed against, the respective embossing roller 21, 25. Thiscondition can be achieved by acting on the two actuators 104 so that they move back to the same extent, i.e. they cause the two ends of the functional roller 100 to perform an equal stroke.

[0081] The stroke performed by the two actuators 104 is detected by the encoders, or other position or displacement sensors, 108. The movement is controlled by the control unit 42, which stops the back movement (i.e. the movement away) of the two ends of the functional roller 100 when the two encoders, or other position or displacement sensors, 108 give an equal signal corresponding to the desired displacement.

[0082] Once the functional roller 100 has reached the pre-set position spaced from the embossing roller 21, 25, the next step is performed, which consists in moving again the functional roller 100 toward the embossing roller 21, 25 by means of the actuators 104. In this step, the embossing roller 21, 25 can be stationary or rotating. The stroke performed by the two actuators is detected by the encoders 108, or other sensors or transducers. Adequately, in this step the stroke of the two actuators 104 is synchronous, i.e. the two actuators move the two ends of the functional roller 104 equally and synchronously toward the embossing roller 21, 25, so that during this movement the functional roller 104 remains parallel to itself. This synchronism is not strictly necessary in the previous step, as in that step what is important is the final spaced position, where the functional roller 100 must be parallel to itself, i.e. parallel to the position taken in the previous step where the rollers 21, 25 and 100 rotate in mutual contact.

[0083] During the synchronous forward movement of the two actuators 104 and the consequent gradual movement of the functional roller 100 toward the embossing roller 21, 25, the position where the functional roller 100 touches the embossing roller 21, 25, i.e. the position of first mutual contact between the functional roller 100 and the embossing roller 21 25, is detected (by the encoders 108).

[0084] The first mutual contact can be detected in several ways. In some embodiments, the pressure switch(es) 105 can be used for this purpose. In fact, the working fluid pressure of the two actuators 104 increases suddenly when, due to the gradual movement of the functional roller 100 toward the embossing roller 21, 25, thefirst mutual contact between the rollers occurs. The pressure signal detected by the pressure switch(es) 105 is transmitted to the control unit 42, which also receives the signals from the encoders 108. Therefore, the control unit 42 can identify the instant when the first contact occurs and know the relative position between the functional roller 100 and the embossing roller 21, 25.

[0085] In other embodiments, the condition of first contact (and therefore the position taken by the functional roller 100 at the time of first contact) can be detected using load cells or other force sensors, indicated above. In fact, these sensors detect a peak of thrust or force when the mutual contact occurs between the embossing roller 21, 25 and the functional roller 100. The signal from the force sensors is sent to the control unit 42, which also knows the corresponding position of the functional roller 100 through the signals from the encoders 108.

[0086] In other embodiments, the first mutual contact between the functional roller 100 and the embossing roller 21, 25 can be detected by an electrical signal from the motor 2 IM, 25M that drives the embossing roller 21, 25 in rotation, the signal being a function of an electrical parameter, for example the current or power absorbed by the motor. The detected electrical parameter increases suddenly, i.e. shows a peak, when the embossing roller 21, 25 is touched by the functional roller 100. In fact, at that instant there is a sudden increase in the resistant torque that the motor must overcome to keep the embossing roller 21, 25 rotating. In other embodiments, the peak of the resistant torque (therefore, of the torque delivered by the motor) can be detected by a torque sensor positioned on the shaft connecting the electric motor to the roller.

[0087] The various methods for detecting the instant of first mutual contact between the functional roller 100 and the embossing roller 21, 25 can be combined with one another, or they can be used alternately, or even differently for the different functional rollers.

[0088] Once the first contact position, where the functional roller 100 is parallel to, and touches, the embossing roller 21, 25, has been reached, this position is stored as the reference position, or first contact position, so that an optional last step of the procedure can be carried out, which involves bringing the functional roller 100 to the working position. This further step can be performed in different ways depending onthe type of control applied to the working position. In any case, the zeroing procedure, i.e. the adjustment procedure, can be considered finished when the reference position, or first contact position, of the functional roller 100 has been stored. The subsequent step of bringing the functional roller 100 to the working position can be performed immediately after the previous ones, or at a different time, even many hours or days after the reference position has been stored.

[0089] In some embodiments, the relative position between the functional roller 100 and the embossing roller 21, 25 is controlled. In other words, the working position is defined as a position that maintains a certain degree of penetration of the embossing protuberances 2 IP, 25P into the elastically yielding coating of the functional roller. This mode of control is based on the concept that the embossing-laminating unit must keep a geometric condition of co-action between the embossing roller 21, 25 and the functional roller 100, a geometric condition to which corresponds a given embossing depth of the ply VI or V2.

[0090] In this case, the step following the detection of the first contact position (which may be the final step of the position adjustment method) brings the functional roller 100 and the embossing roller 21, 25 into a working position defined by the relative position between them. The working position is defined by a predetermined stroke of movement of the functional roller 100 and the embossing roller 21, 25 toward each other, starting from the first contact position. Therefore, in this case the final step of the adjustment method comprises an additional movement of the functional roller 100 and the respective embossing roller 21, 25 toward each other. The stroke is read by the encoders or other equivalent sensors 108, and is the same for the two actuators 104, so that the functional roller 100 remains parallel to itself.

[0091] In other embodiments, if the final working position is set according to a mutual pressure between the functional roller 100 and the embossing roller 21, 25, the final step of adjusting the working position (following the detection of the first contact position) is performed on the basis of a thrust exerted by the two actuators 104. The thrust can be read by the pressure switches 105 or the load sensors or load cells, if present. The final position is the position where the mutual thrust between the rollers 21, 25, and 100 reaches a preset value, which is the same for both ends of the functional roller 100.

[0092] In some cases, to move the functional roller 100 relative to the respective embossing roller 21, 25, it is possible to have a motorized mechanical stop co-acting with a respective swinging arm 102. In practice, the actuators 104 of a functional roller push the respective swinging arm 102 against the respective motorized mechanical stop. This latter, actuated by the respective actuator, moves the swinging arms 102 of the functional roller 100, so as to move the functional roller toward, or away from, the respective embossing roller 21, 25 depending on the height, or distance, detected by the encoders 108. In the controlled approach movement, after a functional roller 100 has been positioned parallel to the respective embossing roller 21, 25, the motorized mechanical stops are actuated to move each swinging arm 102, and therefore the functional roller 100 toward, or away from, the respective embossing roller 21, 25, to the same extent.

Claims

Claims1. A method for adjusting, before starting production, in an embossing unit, the relative position between an embossing roller, carried by a stationary bearing structure, and a functional roller, movable relative to the stationary bearing structure and adapted to define, with the embossing roller, a nip through which a continuous ply of web material passes; wherein the method comprises the following steps:(a) by means of a first actuator and a second actuator, respectively associated with a first axial end and a second axial end of the functional roller, moving the functional roller and the embossing roller toward each other, and pressing the functional roller against the embossing roller with an equal thrust by means of the first actuator and the second actuator;(b) rotating, for an interval of time, the embossing roller and the functional roller while they are in contact with each other and pressed against each other;(c) moving the functional roller and the embossing roller away from each other by means of the first actuator and the second actuator, and bringing the functional roller and the embossing roller to a spaced position, performing an equal stroke with the first actuator and the second actuator, so as to keep the functional roller and the embossing roller parallel to each other;(d) moving again the functional roller and the embossing roller toward each other by means of the first actuator and the second actuator, while keeping the functional roller and the embossing roller parallel to each other;(e) detecting and storing the position of first mutual contact between the functional roller and the embossing roller.

2. The method of claim 1, further comprising the following step: from the position of first mutual contact, continuing to move the functional roller and the embossing roller toward each other while keeping the functional roller and the embossing roller parallel to each other, to a working position defined by a physical parameter of interaction between the embossing roller and the functional roller.

3. The method of claim 2, wherein the physical parameter defining the working position is a forward stroke of the first actuator and the second actuator from the position of first mutual contact.

4. The method of claim 2, wherein the physical parameter defining the working position is a thrust with which the functional roller and the working roller are pressed against each other.

5. The method of any one of the preceding claims, comprising the step of detecting the mutual thrust between the functional roller and the embossing roller by means of an arrangement of load sensors.

6. The method of any one of the preceding claims, wherein: the first actuator comprises a first cylinder-piston actuator driven by a working fluid; and the second actuator comprises a second cylinder-piston actuator driven by a working fluid.

7. The method of claim 6, wherein the mutual thrust between the functional roller and the embossing roller is determined by the pressure of the working fluid in the first cylinder-piston actuator and in the second cylinder-piston actuator.

8. The method of any one of the preceding claims, wherein the step of detecting the position of first mutual contact between the functional roller and the embossing roller comprises one or more of the following steps: detecting an increase in a load applied to the functional roller by the first actuator and the second actuator; detecting an increase in an electrical parameter of a motor driving the embossing roller in rotation; a combination thereof; detecting an increase in a torque transmitted by an actuator driving the embossing roller in rotation.

9. The method of claim 8, when dependent on at least claim 6, wherein the step of detecting an increase in a load applied to the functional roller by the first actuator and the second actuator comprises the step of detecting an increase in the pressure of the working fluid driving the first cylinder-piston actuator and the second cylinder-piston actuator.

10. The method of any one of the preceding claims, wherein thefunctional roller has an elastically yielding coating and defines, with the embossing roller, an embossing nip; wherein, in the working position, embossing protuberances of the embossing roller penetrate the elastically yielding coating of the functional roller; and wherein the method comprises the step of feeding a ply into the embossing nip.

11. The method of any one of claims 1 to 10, wherein the functional roller has a smooth surface and defines, with the embossing roller, a laminating nip; wherein the method also comprises the step of feeding a first ply and a second ply into the laminating nip.

12. An embossing unit, comprising: a first embossing roller, carried by a stationary bearing structure; a first functional roller, co-acting with the first embossing roller and defining, with the first embossing roller, a first nip, through which a feed path for a first ply of web material extends; wherein the first functional roller is supported on the stationary bearing structure at a first axial end by a first movable bearing member, and at a second axial end by a second movable bearing member; a first approach actuator for moving the first functional roller toward the first embossing roller, the first approach actuator being associated with the first movable bearing member; a second approach actuator for moving the first functional roller toward the first embossing roller, the second approach actuator being associated with the second movable bearing member; a system for detecting the thrust exerted by the first approach actuator and the second approach actuator; a system for detecting the relative position between the functional roller and the embossing roller; a control unit, configured to implement the method of one or more of the preceding claims.

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