Method and apparatus for curling sheet material

Abstract

The present invention relates to a method for curling a sheet (2), the sheet having a thickness (11), moisture, composition and width before curling, the method comprising: - obtaining one of the following sheet (2) characteristics before curling: o the thickness (11) of the sheet; o the moisture of the sheet; o the composition of the sheet; o the width of the sheet; - curling the sheet (2) to form a plurality of corrugations on the sheet (10), the curling comprising: o providing a pair of curling rollers (4, 5) defining a roller gap (6) therebetween, the roller gap (6) having a roller gap size (14); o inserting the sheet (2) into the roller gap (6); - evaluating the post-curling characteristics of the sheet (10) after curling; and - changing the roller gap size (14) based on one of the obtained pre-curling sheet (2) characteristics and based on the evaluated post-curling sheet (10) characteristics. The present invention also relates to an apparatus (1) for curling a sheet (2).

Description

Technical Field

[0001] The present invention relates to a method and an apparatus for curling a sheet material. Background Art

[0002] In the manufacture of aerosol generating articles such as heat not burn products, components in the form of strips are often used. The components may include an aerosol forming substrate and a filter element. One or both of the filter element and the aerosol forming substrate may include a plurality of channels to provide an air flow through the strip. The plurality of channels may be provided by curling a sheet of material and thereby gathering the material within the strip to form the channels. In such examples, the curled sheet is typically formed by curling a substantially continuous sheet.

[0003] In the field of aerosol-generating articles, the material to be rolled (ie, the continuous sheet) may be, for example, homogenized tobacco (eg, reconstituted tobacco or cast leaf), a sheet made of polylactic acid, or a cotton sheet.

[0004] Methods and apparatus for making curled sheets for use in aerosol-generating articles are known in the art. Known methods for making curled sheets generally involve feeding a substantially continuous sheet between a pair of staggered rollers to apply a plurality of curled corrugations to the continuous sheet. The curled sheet is then gathered to form a continuous strip having a plurality of axial channels. The strip is then wrapped and cut into smaller segments to form an aerosol-forming substrate or filter for an aerosol-generating article.

[0005] The crimping process is important for an efficient manufacturing process of aerosol-generating articles. Summary of the invention

[0006] The present invention relates to a method for curling a sheet, the sheet having a thickness, moisture, composition and width before curling, the method comprising: obtaining one of the following pre-curling sheet characteristics: the thickness of the sheet; the moisture of the sheet; the composition of the sheet; the width of the sheet. The method may also include curling the sheet to form a plurality of corrugations on the sheet, the curling comprising: providing a pair of curling rollers defining a nip therebetween, the nip having a nip size; and inserting the sheet into the nip. The method may also include evaluating a post-curling characteristic of the sheet after curling. The method may also include changing the nip size based on one of the obtained pre-curling sheet characteristics and based on the evaluated post-curling sheet characteristics.

[0007] The present invention also relates to an apparatus for curling a sheet material, the sheet material having a pre-curling characteristic of one of the following before curling: thickness, moisture, composition and width. The apparatus comprises: a conveying device, the conveying device being suitable for conveying the sheet material along a conveying direction; a pair of curling rollers, the pair of curling rollers being used for curling the sheet material to form a plurality of corrugations on the sheet material, the pair of curling rollers defining a roller gap therebetween, the roller gap having a roller gap size. The apparatus may also comprise a sensor suitable for evaluating the post-curling characteristic of the sheet material, the sensor being located downstream of the pair of curling rollers in the conveying direction. The apparatus may also comprise one of the following: a sensor, the sensor being suitable for evaluating one of the pre-curling characteristics of the sheet material, and transmitting a signal function of one of the pre-curling characteristics evaluated, the sensor being located upstream of the pair of curling rollers in the conveying direction; a memory, the memory containing data related to one of the pre-curling characteristics of the sheet material. The apparatus may further comprise a control unit adapted to receive a signal function of one of the evaluated pre-curling characteristics or adapted to retrieve data related to the one of the pre-curling characteristics. The method may further comprise a first actuator for changing the roller gap size; and a feedback control loop system adapted to activate the first actuator based on one of the evaluated pre-curling characteristics of the sheet material or based on the data retrieved with respect to one of the pre-curling characteristics and based on the evaluated post-curling characteristics of the sheet material.

[0008] A sheet of material is curled between two curling rollers, between which a nip is formed. Due to the curling, a plurality of corrugations are formed on the sheet. A first evaluation of the pre-curling properties of the sheet is performed upstream of the curling rollers. A second evaluation of the post-curling properties of the sheet is performed downstream of the curling rollers. The first upstream evaluation relates to one of the following: the thickness of the sheet, the humidity of the sheet; the composition of the sheet; the width of the sheet. The second downstream evaluation relates to the properties of the sheet imparted by the corrugations, such as the properties of the plurality of corrugations on the sheet. If desired, the nip size may be varied based on the post-curling properties of the sheet evaluated and the pre-curling properties of the sheet obtained. In this way, a continuous feedback loop for optimal curling can be achieved, since the nip size depends on the properties of the sheet present before and after curling. The effect of curling on the sheet can be monitored, and the nip size can be adapted to the specific conditions of curling the sheet.

[0009] As used herein, the term "sheet" refers to a sheet-like element whose width and length are substantially greater than its thickness. The width of the sheet is preferably greater than 10 mm, more preferably greater than about 20 mm or about 30 mm. Even more preferably, the width of the sheet is between about 60 mm and about 300 mm. The thickness of the sheet can be between about 50 microns and 300 microns, it can be between about 100 microns and about 250 microns, it can be between about 175 microns and about 250 microns, it can be between about 130 microns and about 220 microns.

[0010] As used herein, the term "rod" refers to a cylindrical element of substantially cylindrical, oval or elliptical cross-section comprising two or more components of an aerosol-generating article.

[0011] An "aerosol generating article" according to the invention may be in the form of an article in which an alkaloid-containing material, such as a tobacco material, is heated to form an aerosol, rather than being burned. An aerosol generating article is an article in which an alkaloid-containing aerosol is generated from an alkaloid-containing material, for example from a tobacco extract or other nicotine source, without burning or heating. An aerosol generating article according to the invention may be an integrally assembled aerosol-forming article. An aerosol generating article according to the invention may be a component of an aerosol generating article, which is combined with one or more other components to provide an assembled article for generating an aerosol. An example is a consumable part of a heated smoking device.

[0012] "Alkaloid-containing material" is a material containing one or more alkaloids. The alkaloids may include nicotine. Nicotine may be present in, for example, tobacco.

[0013] Alkaloids are a group of naturally occurring compounds that contain mainly basic nitrogen atoms. The group also includes some related compounds that have neutral or even weakly acidic properties. Some synthetic compounds with similar structures are also called alkaloids. In addition to carbon, hydrogen, and nitrogen, alkaloids can also contain oxygen, sulfur, and, more rarely, other elements such as chlorine, bromine, and phosphorus.

[0014] Alkaloids are produced by a variety of organisms including plants. They can be purified from crude extracts of these organisms by acid-base extraction. Caffeine, nicotine, theobromine, atropine, tubocurarine are examples of alkaloids.

[0015] As used herein, the term "homogenized tobacco material" refers to a material formed by agglomerating particulate tobacco, which contains the alkaloid nicotine. Thus, the alkaloid-containing material may be a homogenized tobacco material.

[0016] The most commonly used form of homogenized tobacco material is regenerated tobacco sheet and cast leaf.The method for forming homogenized tobacco material sheet generally comprises the step of mixing tobacco powder and binding agent to form slurry.Slurry is then used to produce tobacco web.For example, so-called cast leaf is produced by casting viscous slurry onto a moving metal belt.Alternatively, regenerated tobacco can be formed in a process similar to papermaking using slurry with low viscosity and high water content.

[0017] Other forms of manufacturing the sheets are possible.

[0018] Sheets of homogenized tobacco material A tobacco composition can be formed using particulate tobacco (eg, reconstituted tobacco) or a blend of tobacco particulates, a humectant, and an aqueous solvent.

[0019] In addition to tobacco, the homogenized tobacco sheet may also contain a binder.The homogenized tobacco sheet may contain an aerosol former, such as guar gum and glycerol.

[0020] As used herein, the term "curled sheet" refers to a sheet having a plurality of corrugations. The term "curling" refers to the process of forming a plurality of corrugations on a sheet of material. Preferably, the sheet of material is a substantially flat sheet of material or a previously untreated sheet of material with respect to producing a structured surface. However, the curling of a sheet that already includes corrugations is also conceivable. The corrugations on the sheet may be formed by a curling roller. The curling roller may include the corrugations on its surface.

[0021] As used herein, the term "corrugation" means a plurality of ridges formed by alternating peaks and valleys connected by the sides of the corrugation. This includes, but is not limited to, corrugations having a square wave profile, a sine wave profile, a triangular profile, a sawtooth profile, or any combination thereof. The corrugations may be defined on a roller, such as a curved roller, or defined on a sheet. The corrugations on a roller refer to a plurality of ridges formed on the outer surface of the roller. The corrugations on a sheet refer to a plurality of ridges when the sheet is placed on a flat surface without stretching the sheet itself.

[0022] As used herein, when referring to a pair of rollers formed by a first and a second curling roller, the term "substantially staggered" means that the corrugations of the first and second curling rollers are at least partially meshed. This includes symmetrical or asymmetrical arrangements of the corrugations of one or both of the rollers. The corrugations of the curling rollers may be substantially aligned, or at least partially offset. The peaks of one or more corrugations of the first or second curling roller may be staggered with the valleys of a single corrugation of the other of the first and second curling rollers. Preferably, the corrugations of the first and second curling rollers are staggered so that substantially all of the valleys of the corrugations of one of the first and second curling rollers each partially receive a single corrugation peak of the other of the first and second curling rollers.

[0023] A "curling roller" is a roller for curling a sheet. The curling roller defines an outer surface and an axis of rotation. The outer surface includes a plurality of corrugations. Preferably, the corrugations extend radially around the outer surface. Preferably, the corrugations define a circumference on the surface of the curving roller. As used herein, the "diameter of the curling roller" is considered to be the largest diameter among the diameters defined by a cross section along a plane perpendicular to the axis of rotation of the curling roller.

[0024] As used herein, "a distance between a first take-up roller having a first rotation axis and a second take-up roller having a second rotation axis" refers to a distance between their respective first rotation axes and second rotation axes.

[0025] As used herein, the term "longitudinal direction" refers to a direction extending along or parallel to the length of a sheet.

[0026] As used herein, the term "width" refers to the direction perpendicular to the conveying direction of the sheet when processed.

[0027] As used herein, the term "pitch value" of a corrugation refers to the lateral distance between valleys at either side of the peak of a particular corrugation or the lateral distance between two adjacent peaks of two adjacent corrugations. In the case of corrugations on a sheet, the pitch value is calculated in a configuration where the sheet lies on a flat surface without stretching the sheet itself.

[0028] As used herein, the term "amplitude value" of a corrugation refers to the height of the corrugation from the peak of the corrugation to the deepest point of the deepest directly adjacent valley. For example, in the case of corrugations in a roller, the amplitude of the corrugation can be measured in the radial direction. The radial direction is the direction along the radius connecting the rotation axis of the roller and the peak or valley. The radius is perpendicular to the rotation axis. The height of the valley is measured as the distance in the radial direction between the rotation axis and the deepest point of the valley. The height of the peak is measured as the distance in the radial direction between the rotation axis and the highest point of the peak. Therefore, the "amplitude value" is the difference between the height of the peak and the height of the valley. In the case of corrugations in a sheet, the amplitude value is calculated in a configuration where the sheet is located on a plane and the sheet itself is not stretched. The amplitude of the sheet corrugation is calculated as the distance between a first plane and a second plane, the first plane being parallel to the second plane. The first plane is in contact with the peak of the corrugation, and the second plane is in contact with the deepest point of the adjacent valley of the peak.

[0029] When corrugations are formed on the sheet, the ridges may be parallel to each other. The ridges may be parallel to the conveying direction of the sheet when curled. The ridges may form an angle between 0 and 45 degrees with the conveying direction of the sheet when curled.

[0030] As used herein, the term "flank angle" refers to the angle between the corrugation sides of a particular corrugation. The flank angle may be the same for all corrugations. In addition, one or more corrugations may be asymmetric about the radial direction.

[0031] As used herein, the term "nip" refers to the gap between the first and second curling rollers forming the pair of curling rollers. During operation, the sheet to be curled passes through the nip. The first and second curling rollers define a first rotation axis and a second rotation axis, respectively. In addition, the first curling roller defines a first outer surface, and the second curling roller defines a second outer surface. The nip defines a nip size. The size of the nip is defined along a plane perpendicular to the first or second rotation axis for each cross section of the first and second curling rollers. In each cross section, the nip size is the minimum Euclidean distance between the first and second outer surfaces for a given relative position between the first and second curling rollers. During the relative rotation of the first and second curling rollers, the size of the nip may vary. In the case where the surfaces of the first and second curling rollers are rotationally invariant to the rotation around the first and second rotation axes, the nip size may be constant, or the nip size may vary. In addition, the nip size may be constant along the width of the rollers, or it may also vary. Preferably, for each cross section, there are two nip sizes. The nip size may also vary along the width of the roll. Two cross sections taken at two different locations along the axis of rotation of the crimping roll may show different nip sizes.

[0032] Preferably, the nip size is constant per cross section. Preferably, the nip size is constant in all cross sections. A constant nip size allows to obtain a constant treatment of the material over the entire width of the sheet.

[0033] However, the present invention also contemplates that the roller may flex slightly during use, so that a constant curl profile in the sheet requires the nip size to be slightly larger towards the center of the roller.

[0034] The term "stickiness" refers to the adhesive or cohesive properties of a sheet. Adhesion is the tendency of dissimilar particles or surfaces to adhere to each other, while cohesion refers to the tendency of similar or identical particles or surfaces to stick to each other. The stickiness of a sheet can be measured using a LIDAR (Laser Imaging Detection and Ranging) adapted to measure the distance between the device and the sheet unrolled from a roll. The LIDAR is positioned in a manner facing the unrolled portion of the sheet. The "non-sticky" sheet has the closest distance to the LIDAR, as the unrolled portion of the sheet immediately separates from the roll. The distance between the LIDAR and the unrolled portion of the sheet increases as the stickiness increases.

[0035] Hereinafter, the terms "upstream" or "downstream" refer to the direction of movement or conveyance of the sheet material.

[0036] As used herein, the term "gathered" or "gathered" when referring to a sheet of material means that the sheet of material is rolled or otherwise compressed or contracted into a strip form substantially transverse to the direction of transport of the sheet of material.

[0037] As used herein, the terms "horizontal" and "vertical" have their standard meanings.

[0038] In the apparatus of the present invention, a sheet having the following characteristics is provided: a given thickness, moisture, composition and width. The above characteristics are collectively referred to as the "pre-curl characteristics" of the sheet. The pre-curl characteristics may be substantially uniform within the sheet, or may vary at different locations of the sheet. The thickness, moisture, composition and width of the sheet may be within given ranges, with the ranges for each characteristic being included.

[0039] The sheet defines two opposing surfaces, and the opposing surfaces define opposite sides of the sheet.

[0040] Preferably, the sheet material is provided by unwinding a bobbin.

[0041] At least one of the pre-curl characteristics of the sheet is obtained. One of the pre-curl characteristics obtained may be the thickness of the sheet. One of the pre-curl characteristics obtained may be the humidity of the sheet. One of the pre-curl characteristics obtained may be the width of the sheet. One of the pre-curl characteristics obtained may be the composition of the sheet.

[0042] The composition can refer to the chemical composition of the sheet material, such as the ingredients of the sheet material. For example, the composition can include a blend of the sheet material. If the sheet material is a sheet material containing alkaloids, the blend of the sheet material is applicable. In this case, the sheet material is prepared by blending the material containing alkaloids to obtain a predetermined blend. The alkaloid-containing material can be a tobacco material. Preferably, more than one tobacco type is blended together. For example, at least two different tobacco types are blended together. The term "tobacco type" means one of different tobacco varieties. For the present invention, these different tobacco types can be distinguished into three main groups: flue-cured tobacco, sun-cured tobacco and spice tobacco. The difference between these three groups is based on the tobacco baking process carried out before further processing into tobacco products.

[0043] Flue-cured tobacco is tobacco with generally large light-colored leaves. Throughout this specification, the term "flue-cured tobacco" is used for tobacco that has been smoked. Examples of flue-cured tobacco are Chinese flue-cured tobacco, Brazilian flue-cured tobacco, American flue-cured tobacco, such as Virginia tobacco, Indian flue-cured tobacco, Tanzanian flue-cured tobacco or other African flue-cured tobacco. Flue-cured tobacco is characterized by a high sugar-nitrogen ratio. From a sensory perspective, flue-cured tobacco is a type of tobacco that is accompanied by a spicy and refreshing sensation after curing. According to the present invention, flue-cured tobacco is a tobacco having a reducing sugar content of about 2.5% to about 20% based on the dry weight of the tobacco leaf and a total ammonia content of less than about 0.12% based on the dry weight of the tobacco leaf. Reducing sugars include, for example, glucose or fructose. Total ammonia includes, for example, ammonia and ammonia salts.

[0044] Sun-cured tobacco is tobacco with generally large dark leaves. Throughout this specification, the term "sun-cured tobacco" is used for tobacco that has been air-dried. In addition, sun-cured tobacco can be fermented. Tobacco that is mainly used for chewing, snuff, cigars and pipe blends is also included in this category. From a sensory perspective, sun-cured tobacco is a type of tobacco that is accompanied by a dark cigar-type feeling of smoky flavor after baking. Sun-cured tobacco is characterized by a low sugar-nitrogen ratio. Examples of sun-cured tobacco are Malawi white burley or other African white burley, dark-cured Brazilian Galpao, sun-cured or air-cured Indonesian Kasturi. According to the present invention, sun-cured tobacco is a tobacco having a reducing sugar content of less than about 5% by tobacco leaf dry weight and a total ammonia content of at most about 0.5% by tobacco leaf dry weight.

[0045] Oriental tobacco is tobacco that often has small light-colored leaves. Throughout this specification, the term "Oriental tobacco" is used for other tobaccos with high aromatic content, such as high-content essential oils. From a sensory perspective, Oriental tobacco is a tobacco type that is accompanied by a spicy and aromatic sensation after baking. Examples of Oriental tobacco are Greek Oriental, Oriental Turkey, Semi-Oriental tobacco, and baked American Burley, such as Perique, Rustica, American Burley, or Meriland.

[0046] In addition, the blend may include so-called filler tobacco. Filler tobacco is not a specific tobacco type, but it includes tobacco types that are primarily used to supplement other tobacco types used in the blend and do not bring specific characteristic aromas to the final product. Examples of filler tobacco are stems, midribs or stems of other tobacco types. A specific example may be the flue-cured stems of flue-cured Brazilian lower stems.

[0047] In every type of tobacco, tobacco leaves are for example further graded according to the position, color, surface texture, size and shape in the source, plant.The tobacco leaves of these and other characteristics are used to form tobacco blends.Tobacco blends are mixtures belonging to the same or different types of tobacco, so that tobacco blends have the specific characteristics of agglomeration.This feature can be for example unique taste or specific aerosol composition when heating or burning.Blends comprise specific tobacco types and grades with a given ratio relative to another.

[0048] According to the present invention, different grades within the same tobacco type can be cross-blended to reduce the variability of each blend component. According to the present invention, different tobacco grades are selected to obtain a desired blend with a predetermined specific characteristic. For example, the blend can have a target value of reducing sugar, total ammonia and total alkaloids by dry weight of homogenized tobacco material. Total alkaloids are, for example, nicotine and minor alkaloids, including nornicotine, anatabine, anabasine and myosmine.

[0049] For example, bright tobacco can include A-grade tobacco, B-grade tobacco and C-grade tobacco. A-grade bright tobacco has a slightly different chemical characteristic from B-grade and C-grade bright tobacco. Spicy tobacco can comprise D-grade tobacco and E-grade tobacco, and wherein D-grade spicy tobacco has a slightly different chemical characteristic from E-grade spicy tobacco. For illustration, the possible target value of tobacco blend can be, for example, a reducing sugar content of about 10% by dry weight of total tobacco blend. In order to realize selected target value, 70% bright tobacco and 30% spicy tobacco can be selected to form tobacco blend. 70% bright tobacco is selected from A-grade tobacco, B-grade tobacco and C-grade tobacco, and 30% aromatic tobacco is selected from D-grade tobacco and E-grade tobacco, and the amount of A, B, C, D, E-grade tobacco included in the blend depends on each chemical composition in A, B, C, D, E-grade tobacco, to meet the target value of tobacco blend.

[0050] Various tobacco types have different chemical properties. It is believed that there are more than 300 kinds of chemical compositions in tobacco leaves. In the tobacco of the same type, different grades also can have the difference of chemical composition. The chemical composition of tobacco may be affected by heredity, agricultural practice, soil type and nutrients, weather conditions, plant diseases, leaf position, gathering and sun-drying procedure.

[0051] For example, a suitable sensor may be used to measure the obtained one pre-curl property. Preferably, the sensor measures the pre-curl property in real time, i.e. preferably measures the pre-curl property of the sheet during processing of the sheet. Measuring the pre-property of the sheet means measuring the property of the sheet at least at a predetermined position, i.e. measuring the pre-curl property of at least a first portion of the sheet. Any sensor measuring one pre-curl property is preferably positioned upstream of the curling roller.

[0052] One or more sensors for measuring the same pre-curl characteristic can be used to measure the pre-curl characteristic of the sheet. The same pre-curl characteristic of the sheet can be measured in one position or in multiple positions. If measured in more than one position, each measurement generates data and the data is collected. The data collected from different measurements can be statistically combined. The average of all pre-curl measurements of the same characteristic can be performed.

[0053] In case of measuring thickness, a thickness sensor may be used.

[0054] The thickness sensor may include a mechanical sensor. The thickness sensor may include an optical sensor. The thickness sensor may include a mechanical sensor and an optical sensor.

[0055] In the case of measuring humidity, a humidity sensor may be used. The humidity sensor may include a grammage sensor.

[0056] In case of measuring width, a distance sensor may be used.

[0057] The pre-curling properties may be obtained from a database. The method of the present invention preferably includes accessing a database and retrieving data about one of the pre-curling properties of the sheet from the database. The database may include one or more of the pre-curling properties: thickness, moisture, composition or width of the sheet before curling. Data related to one or more pre-curling properties may be stored in an accessible memory stored in the database.

[0058] The pre-curling characteristic may be obtained by a user's input. A sheet or other input device may be provided, and a user, such as an operator, may input a value of the pre-curling characteristic of the sheet. In addition, data related to one of the pre-curling characteristics may be scanned data provided on a bobbin made of the sheet, such as a representative code.

[0059] The pre-curling characteristics can be obtained by remote signal. Wireless or wired data transmission can be performed to input the pre-curling characteristics.

[0060] Preferably, more than one pre-curling property of the sheet is obtained. Preferably, the moisture content of the sheet is obtained. Preferably, the thickness of the sheet is obtained. Preferably, the moisture content and thickness of the sheet are obtained.

[0061] The sheet is transported along a transport direction. The transport may be performed by any suitable means, for example by traction via rollers. Preferably, the transport is performed at a sheet speed comprised between about 50 meters per minute and about 400 meters per minute.

[0062] In addition, the sheet is curled. Curling is performed using a pair of curling rollers, which are represented as a first curling roller and a second curling roller. The first crimp roller and the second crimp roller are positioned adjacent to each other and form a nip between the first crimp roller and the second crimp roller. The first curling roller defines a first rotation shaft and a first outer surface. The second bending roller defines a second rotation shaft and a second outer surface. The first rotation shaft and the second rotation shaft are preferably parallel to each other. The first rotation shaft and the second rotation shaft are preferably horizontal. Preferably, the first crimping roller and the second crimping roller have a width equal to or greater than the sheet so that the entire sheet can be curled between the first crimping roller and the second crimping roller. Preferably, the cross-section of the first outer surface along a plane perpendicular to the first rotation axis is a circumference. Preferably, the cross-section of the second outer surface along a plane perpendicular to the second rotation axis is a circumference. At least one of the first curling roller or the second curling roller comprises a corrugation. Preferably, the corrugated is formed on the first outer surface or on the second outer surface. Preferably, corrugations are formed in the first outer surface and the second outer surface. When the sheet is inserted into the nip between the first curling roller and the second curling roller, corrugations on the first curling roller or on the second curling roller or both are in contact with the sheet. Due to the corrugation on the sheet, corresponding corrugation is formed on the sheet as the sheet passes through the nip. In the case where both the first and second curling rollers include corrugations, the first and second curling rollers may be designed and arranged in a generally staggered manner at least some of their corrugations.

[0063] Alternatively, only one of the first crimping roller and the second crimping roller may include corrugations, and the other of the first crimping roller and the second crimping roller may have a substantially smooth outer surface. The smooth outer surface may be cylindrical.

[0064] Alternatively, both the first curling roller and the second curling roller may include corrugations in the non-corresponding section. The first curling roller may include a section with corrugated and a section without corrugated. Preferably, on the first outer surface, the segment with corrugated and the segment without corrugated are adjacent. The second bending roller may include a section with corrugated and a section without corrugated. Preferably, on the second outer surface, the segment with corrugated is adjacent to the segment without corrugated. In this configuration, when the first curling roller and the second curling roller face each other, the section with corrugated ripple of the first curling roller faces the section without corrugation of the second curling roller. For each portion of the material sheet in contact with the first and second curling rollers, only one of the first curling rollers and the second curling rollers forms curling corrugations on that portion of the material sheet.

[0065] The corrugations on the first or second crimping roller preferably have all the same pitch. More preferably, if the corrugations are present in both the first and second crimping rollers, they all have the same pitch. Furthermore, preferably, all the corrugations in the first or second crimping roller have the same amplitude.

[0066] Preferably, the nip size between the first crimping roller and the second crimping roller is comprised between about 100 microns and about 300 microns. Too small a nip size, i.e., a nip size less than 100 microns, may damage the sheet. Too large a nip size may not allow the sheet to be crimped enough to further process the sheet appropriately, such as gathering it in strips.

[0067] Preferably, the pitch of the ridges in the first take-up roller or in the second take-up roller or in both is comprised between 200 and 1500 microns. More preferably, said pitch is comprised between 800 and 1200 microns.

[0068] Embodiments of crimping rollers that can be used for the present invention are described in WO 2018 / 189325 of the same applicant. Preferably, all corrugations in the first crimping roller or the second crimping roller have the same side angle. Preferably, all corrugations in the first crimping roller or the second crimping roller have the same amplitude. Preferably, all corrugations in the first crimping roller or the second crimping roller have the same pitch.

[0069] The corrugations in the first crimping roller or the second crimping roller may have an amplitude comprised between about 0.1 millimeters and about 1.5 millimeters.

[0070] The nip between the first and second take-up rollers has a given nip size. Preferably, for a given cross section taken along a plane perpendicular to the first or second rotation axis, the nip size changes during rotation of the first and second take-up rollers. The nip size is preferably a step function between a first value and a second value. Before and after the "jump" between the first and second values, the nip size is preferably constant.

[0071] The roll gap size is determined by the distance between the first crimping roller and the second crimping roller and the diameters of the first crimping roller and the second crimping roller.

[0072] During the curling process, the sheet passes through a roller gap formed between a first curling roller and a second curling roller. The first curling roller and the second curling roller form curling corrugations having a given pattern on the sheet. The corrugations on the sheet have a pattern determined by the pattern of the corrugations on the first curling roller and the second curling roller. The corrugations on the sheet also define a pitch and an amplitude. Due to the flexibility and elasticity of the sheet, the amplitude and pitch of the corrugations on the sheet may be different from the amplitude and pitch of the corrugations on the first curling roller or the second curling roller.

[0073] For example, by means of a first actuator, the gap size can be changed. The first actuator can change the gap size by changing the distance between the first curling roller and the second curling roller. For example, there can be a linear drive. The linear drive can change the position of the rotation axis of the first curling roller, or the position of the rotation axis of the second bending roller, or the position of the rotation axis of both. The eccentric mechanism can rotate and change the position of the rotation axis of the first curling roller or the second curling roller or both in the rotational movement. The change in the gap size can be within the range of ±50 microns of the gap size. The gap size can vary between 20% and 50% of the original gap size, and even more preferably between 20% and 30%.

[0074] Downstream of the first curling roller and the second bending roller in the conveying direction, a characteristic of the sheet is evaluated, for example a characteristic of the corrugations formed on the sheet. To this end, the apparatus may include a sensor to detect one of the characteristics of the corrugations formed on the sheet by the bending roller. The sensor may be an optical sensor, such as an infrared or laser sensor. The optical sensor may include a light emitter on one side of the sheet and a light receiver on the other side of the sheet. The optical sensor may include a laser profiler.

[0075] For the "post-curling property" of the sheet, at least the property of the sheet after curling is meant. The post-curling property may be a property of the corrugations formed on the sheet. It is also possible to evaluate the properties of more than one corrugation. The characteristic of the corrugation refers to any characteristic of the pattern formed by the curling rollers on the sheet. The characteristic may be, for example, the number of corrugations formed on the sheet, the pitch of the corrugations formed on the sheet, the amplitude of the corrugations formed on the sheet, the side angle of the corrugations formed on the sheet, the stability of the corrugations formed on the sheet, etc. The corrugations on the sheet have a given geometric pattern, which defines the spacing, amplitude, side angle and other geometric parameters. For the "stability of the corrugations", the stability of these geometric properties over time means, that is, if after a given amount of time, the value of the property remains essentially unchanged or the property changes within a given interval, then the property is stable. The post-curling property may be the diameter of the strip formed by gathering the curled sheet. The diameter of the strip depends on the properties of the sheet, such as the depth of the curl, that is, the amplitude of the corrugations formed on the sheet. The post-crimping property may be the resistance to draw of the shaped strip obtained by gathering the crimped sheet. Among other factors, the resistance to draw depends on the waves formed in the sheet, which form "air channels" in the strip.

[0076] The evaluation of the post-curling characteristics of the sheet is performed after the sheet is curled. The evaluation of the post-curling characteristics of the sheet means evaluating the post-curling characteristics of the sheet at least at one position.

[0077] Preferably, the evaluation of the post-curling property of the sheet is performed in real time. Preferably, the post-curling property is evaluated at different time points. Preferably, the evaluation of the post-curling property is checked at a given frequency while the sheet is moving. Statistics can be calculated based on all evaluations of the same post-curling property at different times.

[0078] Preferably, evaluating the post-curling characteristics of the sheet includes measuring the post-curling characteristics of the sheet. More preferably, evaluating the post-curling characteristics of the sheet includes evaluating the characteristics of the corrugations formed on the sheet. Preferably, evaluating the characteristics of the corrugations formed on the sheet includes measuring the characteristics of the corrugations. More preferably, measuring the characteristics of the corrugations includes measuring the characteristics of the corrugations by a sensor.

[0079] One sensor can be used to measure the post-curling properties of the curled sheet.Several sensors can be used to measure the post-curling properties of the curled sheet.

[0080] The post-curl property of the sheet may be evaluated at one location of the curled sheet. The post-curl property of the sheet may be evaluated at several locations of the curled sheet. If the evaluation is performed in more than one location, each determination generates data and the data is collected. The data collected from the different determinations may be statistically combined, for example, a statistic may be calculated based on all determinations of the same post-curl property at different locations on the sheet. An average of all determinations of the same post-curl property of the sheet may be performed.

[0081] The evaluation of the post-curling characteristic of the sheet is used to adjust the roll gap size. According to the value of the post-curling characteristic of the sheet, it can be determined that the roll gap size is not optimal. Determining whether the roll gap size is optimal also depends on one of the pre-curling characteristics of the sheet obtained. For each value of one pre-curling characteristic obtained, a given value of the post-curling characteristic of the sheet can be expected. Therefore, the expected value of this post-curling characteristic of the sheet depends on the pre-curling characteristic of the sheet. If the evaluation value of the post-curling characteristic of the sheet is different from the expected value, the roll gap size is preferably changed. "Expected value" also means a range of expected values.

[0082] For example, for a given obtained thickness of the sheet before curling, a certain roller gap size is pre-set. However, after evaluating the post-curling characteristics of the curled sheet, it can be seen that the preliminarily set roller gap size is not optimal because the post-curling characteristic values ​​of the sheet, such as the characteristics of the corrugations on the sheet, are outside the desired range. According to the present invention, after the preliminary setting based on the pre-curling thickness, the roller gap size is adjusted based on the evaluated post-curling characteristics of the sheet.

[0083] The step of changing the nip size based on one of the obtained pre-curling characteristics of the sheet and based on the evaluated post-curling characteristics of the sheet may include one of the following steps. A single changing step based on the pre-curling and post-curling characteristics may be implemented. It is also possible to implement a changing step that occurs in two sub-steps: a first sub-step in which the changing is performed based on the pre-curling characteristics and a second sub-step in which the changing is performed based on the post-curling characteristics. The first sub-step and the second sub-step may be reversed: it is also possible to perform a first sub-step in which the changing is performed based on the post-curling characteristics and a second sub-step in which the changing is performed based on the pre-curling characteristics.

[0084] Preferably, the rolled sheet material is used in an aerosol-generating article. Preferably, the rolled sheet material is used to form a component of an aerosol-generating article.

[0085] The crimping process produces various effects related to the material forming the sheet that is squeezed between the crimping rollers.

[0086] The effects of the first range occur during the subsequent manufacturing process, for example, a curled sheet of material can be compressed into a strip more easily than a sheet without curling. In addition, a more predictable result is obtained.

[0087] Once the rolled sheet of material is compressed into a strip and added to an aerosol-generating article, the second range of effects is related to the rolling, such as the user's smoking experience. More specifically, the rolling process affects the contact between the air penetrating the aerosol-generating article and the rolled sheet of material, and affects the resistance to draw (RTD).

[0088] However, a non-optimal or sub-optimal curling process may excessively weaken the curled web of material. A non-optimal or sub-optimal process may hinder the release of substances from the curled sheet of material into the permeating air in the strip and adversely affect the RTD value.

[0089] The correct roller gap size is related to the correct curling of the sheet. Among other parameters, the roller gap size can be the reason whether the curled sheet has the correct "degree of curl". The correct "degree of curl" is important in the subsequent processing steps of the sheet. For example, the correct amount of curling can make the sheet "foldable" enough to gather into strips without breaking. The correct degree of curling can avoid the "foldable" sheet from including structural damage. For example, when wrapping the sheet, if the sheet curling degree is less than the correct degree of curling, the material forming the sheet may show that it can resist the expansion force of the wrapping material after being gathered into strips and wrapped in the wrapping material. This prevents the sheet from forming strips correctly. In addition, a low degree of curling can also affect the ability of the sheet to bend. On the other hand, if the sheet is curled beyond the correct degree of curling, the sheet may have structural damage. A small part of the material forming the sheet may break away from the formed strip. The small part may travel inside the aerosol generating article. Small parts may also travel in the machine that processes the strip. This may increase the downtime for machine cleaning. The correct degree of curl is therefore a balance between the folding properties of the sheet and the absence or minimization of damage.

[0090] The correct degree of curling relates to the post-curling properties of the sheet. Preferably, the correct degree of curling relates to the properties of the sheet caused by the corrugations formed during the curling process. The correct degree of curling may be related to the properties of the corrugations on the sheet. For example, to determine the degree of curling, the amplitude of the corrugations formed on the sheet by the curling roller is evaluated. Preferably, the property of the corrugations evaluated after curling is the amplitude of at least one corrugation formed on the sheet.

[0091] Therefore, according to the present invention, a feedback loop control system of the curling process is preferably implemented, which receives data related to the characteristics of the sheet before and after the curling process. For example, the feedback loop control system may include sensors located upstream and downstream of the first curling roller and the second bending roller. The feedback loop system is preferably connected to the first actuator to command the first actuator. The feedback loop control system is capable of adjusting the roll gap size so that the roll gap size can be continuously optimized during the process.

[0092] For example, for each obtained pre-curling characteristic, a given post-curling characteristic is expected due to empirical data. A range of values ​​of the post-curling characteristic can be expected. A lookup table or database can be formed so that for a given pre-curling characteristic, the expected value of the post-curling characteristic is retrieved. A range of expected values ​​of such a post-curling characteristic can be retrieved. Preferably, according to the empirical data, a roller gap size value is associated according to the expected value or value range of the post-curling characteristic. Then, the first curling roller and the second curling roller are arranged so that there is an associated roller gap size between them. The sheet is then curled using the associated roller gap size. The desired post-curling characteristic is then evaluated. If the evaluated post-curling characteristic is different from the expected post-curling characteristic, the roller gap size is changed. This also applies to several pre-curling characteristics as input: there can be a multidimensional table so that for a selected plurality of pre-curling characteristics, the value of a given post-curling characteristic is first retrieved and then evaluated.

[0093] The post-curling property may be the amplitude of the ripples formed on the sheet. Therefore, for a given thickness or sheet moisture before curling, the corresponding expected value of the ripple amplitude is retrieved from the database. From empirical data, it is known that the expected amplitude value can be obtained with the relevant roll gap size. The relevant roll gap size is set and the sheet is curled. The amplitude of the ripples formed on the sheet is then measured. If the measured amplitude value differs "too much" from the expected value, i.e., if the difference between the expected amplitude value and the measured amplitude value is above a given threshold in absolute value, the roll gap size is changed.

[0094] Preferably, the method includes changing the gap size while curling. The evaluations performed upstream and downstream of the curling roller may preferably be performed at a certain frequency during the manufacturing process. For example, the evaluation may be performed several times per minute. The evaluation may be performed between 1 minute and 30 minutes. Preferably, the evaluation is performed every 1 minute to 15 minutes. Preferably, the pre-curling data and the post-curling data are continuously collected and evaluated. The gap size may be changed while the sheet is being curled without stopping the manufacturing process. The process may be adapted to changing environmental conditions. The method may adapt to changes in the pre-curling characteristics of the sheet.

[0095] Preferably, the sheet is a sheet of alkaloid-containing material. Preferably, the sheet is a plastic sheet. The curling method or device can be used for sheets of alkaloid-containing material, such as homogenized tobacco sheets, which are "sticky" and relatively brittle. The curling method or device can be used for plastic sheets, such as polylactic acid (PLA) sheets, which are elastic.

[0096] Preferably, the sheet has mechanical properties, viscosity, and temperature. The method preferably includes determining an additional pre-curling property of the sheet. The additional pre-curling property of the sheet may be a mechanical property of the sheet. "Mechanical properties" may include one or more of the following: tensile strength, elastic modulus, elastic limit, maximum elongation, hardness, melting temperature, glass transition, etc. The additional pre-curling property of the sheet may be the temperature of the sheet. The additional pre-curling property of the sheet may be the viscosity of the sheet. The method may include changing the roller gap size based on one of the additional pre-curling properties of the sheet determined. The method may include changing the roller gap size based on the mechanical properties of the sheet. The method may include changing the roller gap size based on the temperature of the sheet. The method may include changing the roller gap size based on the viscosity of the sheet. The method may include changing the roller gap size based on a combination of two parameters in the additional pre-curling properties. The method may include changing the roller gap size based on a combination of three parameters in the additional pre-curling properties. "Mechanical properties, viscosity, temperature of the sheet" are collectively referred to as additional pre-curling properties of the sheet. Furthermore, in addition to or as an alternative to the listed parameters, other parameters of the sheet can be determined. These additional parameters can be used as a basis for varying the nip size in the method of the present invention.

[0097] It will be appreciated that the sheet has additional pre-curling properties at a given position. This means that, depending on the position of the sheet considered for determination, the sheet may have different additional pre-curling properties. For example, different parts of the sheet may have different viscosities, temperatures, mechanical properties. Preferably, at least one additional pre-curling property is determined at a given position of the sheet. For example, the determination is made using a suitable sensor. The determination may be made by measurement. Alternatively, one of the pre-curling properties may be input by a user. Alternatively, one of the additional pre-curling properties of the sheet may be retrieved from a memory. For example, the mechanical properties of the sheet may already be known from a previous processing step and data relating to the mechanical properties may be retrieved. In this case, no measurement is required. The additional pre-curling properties may be read by scanning a bar code located on a bobbin formed by the sheet.

[0098] A single additional pre-curl characteristic may be determined. Multiple additional pre-curl characteristics may be determined. A combination of measured additional pre-curl characteristics and pre-curl characteristics determined in other ways (e.g., input by a user or retrieved from a memory) may be used as a basis for changing the roll gap size. The type and number of additional pre-curl characteristics determined may depend on the type and number of sensors available. In addition, a single determination may be made for the same additional pre-curl characteristic. Multiple determinations may be made for the same additional pre-curl characteristic. The final determination may be a statistical combination of all determinations. The statistical combination may include an average value (mean) of the determinations of the same additional pre-curl characteristic. The roll gap size may vary based on one or more of these additional pre-curl characteristic determination results. The effect of the roll gap size on the sheet may be related to the additional pre-curl characteristics described above. For example, depending on the properties of the material being curled, such as its mechanical properties, viscosity, composition, temperature or other parameters, the roll gap size may have different "curling effects". Therefore, these additional pre-curl characteristics may also be related to determining the optimal roll gap size. Furthermore, additional pre-curling characteristics may vary depending on process conditions, for example, additional pre-curling characteristics may vary depending on the temperature or humidity of the environment in which the sheet is located. Additional pre-curling characteristics may change during the curling process, and thus it is preferred to adjust the nip size based on one or more of the additional pre-curling characteristics. As an example, the temperature or humidity of the environment may change the brittleness of the sheet and, in turn, its behavior during curling. Thus, changes in humidity or temperature during the process may trigger changes in the nip size to maintain optimal curling results.

[0099] The method preferably includes: measuring the temperature of the environment in which the sheet is located during curling. The method preferably includes: measuring the humidity of the environment in which the sheet is located during curling. The method preferably includes: measuring the device temperature of a part of the device used to curl the sheet. The method preferably includes: changing the roller gap size according to the ambient temperature, or the ambient humidity, or the device temperature. In the following, "ambient temperature, ambient humidity, device temperature" are collectively referred to as environmental parameters. Other parameters may be included in "environmental parameters". Preferably, at least one environmental parameter is measured by a suitable sensor. Environmental parameters, i.e., parameters of the environment in which the sheet is located, may affect the sheet parameters and therefore the effect of the roller gap size on the curling effect of the sheet. One of the environmental parameters depending on the available sensors can be measured. More than one environmental parameter can be measured. The roller gap size can vary according to these environmental parameters.

[0100] Preferably, evaluating the post-curling properties of the sheet after curling includes evaluating properties of a plurality of corrugations formed on the sheet after curling.

[0101] The curling process forms corrugations on the sheet, in particular a plurality of corrugations, and these corrugations have a given amplitude and pitch. Preferably, the step of evaluating the characteristics of the plurality of corrugations formed on the sheet comprises evaluating the pitch or amplitude of at least one of the plurality of corrugations. The characteristic of the plurality of corrugations preferably used to determine whether the correct degree of curling has been achieved is the pitch or amplitude of at least one of the plurality of corrugations. More preferably, the pitch or amplitude of the plurality of corrugations is determined. The average of the pitch values ​​or amplitude values ​​determined for several corrugations can be calculated. The pitch and amplitude of at least one of the plurality of corrugations can be evaluated. "Evaluating the pitch or amplitude of the corrugations" means evaluating a value as a function of the pitch or amplitude of the corrugations.

[0102] Preferably, the evaluated pitch or the evaluated amplitude of the corrugations is compared with an expected pitch range or an expected amplitude range, respectively. If the evaluated amplitude or the evaluated pitch is outside the expected amplitude range or the expected pitch range, respectively, the nip size is changed. Preferably, the average pitch over several corrugations or the average amplitude over several corrugations is compared with an expected pitch range or an expected amplitude range, respectively.

[0103] Preferably, evaluating the pitch or amplitude of at least one of the plurality of corrugations comprises determining the profile of the at least one corrugation. More preferably, evaluating the pitch or amplitude of the at least one corrugation comprises determining the profile of several of the plurality of corrugations. Preferably, the profile of the corrugation is perpendicular to the conveying direction of the sheet material. The profile of the corrugation is substantially the profile defined by a cross section of the sheet material taken at a given position by a plane perpendicular to the conveying direction. Preferably, the profile defines alternating peaks and valleys. Preferably, the amplitude of the peaks of the profile is evaluated. Preferably, the average amplitude is calculated by calculating the average of the different amplitudes between different corrugations. The average amplitude may be a characteristic of the corrugation.

[0104] Preferably, evaluating the characteristics of the plurality of corrugations comprises: aggregating the pitch or amplitude of at least one of the plurality of corrugations at different positions along the sheet or at subsequent time intervals; and comparing the pitch or amplitude of at least one corrugation aggregated at different positions along the sheet or at subsequent time intervals. More preferably, the method further comprises changing the roll gap size based on the comparison. A parameter that can change the effect of curling on the sheet is the "stability" of the corrugations produced on the sheet. "Stability" means that the characteristics of the corrugations, such as the pitch or amplitude of the corrugations formed on the sheet, remain substantially the same from the moment of formation by the curling roller. The first curling roller and the second curling roller form the corrugations on the sheet with an amplitude and a pitch. It is preferred to check whether the characteristics of the corrugations remain stable on the sheet, for example, whether the amplitude or pitch changes, or whether the amplitude and pitch change. The amplitude or pitch of the corrugations can change over time, that is, at a given point in time, they can have a specific value, and after a time interval, the specific value can change. The amplitude or pitch of the corrugations may vary depending on the position of the sheet at which the measurement is made, i.e., at a given position, the pitch or amplitude may have a certain value, while at another position, the pitch or amplitude may have a different value. If the difference is above a threshold, i.e., if the amplitude value or pitch value varies by more than a certain percentage of its value, the nip size may be changed, for example to a smaller nip size, thereby forming more stable corrugations.

[0105] Preferably, the method comprises: removing at least a portion of the sheet based on the evaluated post-curling characteristic of the sheet. The method preferably comprises the step of removing a portion of the sheet based on the evaluated post-curling characteristic of the sheet and one of the pre-curling characteristics of the sheet obtained. The sheet may be removed as a whole, or only a portion of the sheet may be removed, and the remainder of the sheet without the removed portion may be further processed. The remaining portion of the sheet that is further processed has a post-curling characteristic of the sheet within a desired tolerance, such as a post-curling characteristic of the corrugation. For example, in the case where the value of the post-curling characteristic of the sheet is outside a given range in a given portion of the sheet, the curled sheet is rejected and not further processed for the pre-curling sheet characteristic. Alternatively, only the portion of the sheet having the post-curling characteristic of the sheet outside the given range is cut or otherwise removed. In this way, a portion of the outer tolerance of the curled sheet is removed from the processing line as quickly as possible.

[0106] The method preferably comprises creating a database comprising one of the obtained pre-curling properties of the sheet material in relation to any of: the manufacturing date of the sheet material, the ambient temperature of the environment in which the sheet material is during curling, the length of fibres present in the sheet material, the humidity of the environment in which the sheet material is during curling, the processability of the sheet material. The database may be used for traceability purposes of the curled sheet material or of a component of a manufactured aerosol-generating article comprising the curled sheet material. The database may be used to create correlations between different parameters. In this way, in the absence of some sensor of the pre-curling property or the ambient parameter in the device, the value of the desired sheet parameter (i.e. the pre-curling property of the sheet material) or the ambient parameter may be predicted from this database.

[0107] Preferably, the method includes setting a first gap size based on a pre-curling characteristic of the sheet obtained. The method may also include adjusting the first gap size to set a second gap size based on the evaluated post-curling characteristic of the sheet. Preferably, the adjustment of the gap size is performed in two steps. First, the gap size is set to a first value based on the pre-curling characteristic of the sheet. Then the post-curling characteristic is evaluated. If the post-curling characteristic is not the expected characteristic of the obtained pre-curling characteristic, the first gap size is adjusted. The first gap size becomes the second gap size. The second gap size is determined based on the post-curling characteristic. Typically, given the pre-curling characteristic, the gap size is correctly set, that is, the first gap size is usually the gap size that gives the sheet the correct degree of curl. However, in those cases where the first gap size does not give the correct degree of curl, the gap size may change after evaluating the post-curling characteristic.

[0108] Preferably, the sensor suitable for evaluating one of the pre-curling properties of the sheet material comprises a sensor suitable for measuring the thickness of the sheet material. More preferably, the sensor measuring the thickness of the sheet material comprises a mechanical sensor comprising a wheel or a slide in contact with the sheet material. Preferably, the sensor measuring the thickness of the sheet material comprises an optical sensor irradiating an electromagnetic beam onto the sheet material. Preferably, the sensor measuring the thickness of the sheet material comprises an interferometer. More than one sensor may be used to measure the thickness of the sheet material, such as two or more sensors of the same type, such as two optical sensors, or two or more sensors of different types, such as an optical sensor and a mechanical sensor.

[0109] The mechanical sensor may include a wheel that rolls on the top surface of the sheet. The mechanical sensor may include a slide that contacts the top surface of the sheet. The height of the wheel or the height of the slide and its variation are preferably checked and compared to the expected thickness of the sheet. The comparison is within a preset tolerance.

[0110] The interferometer may include an optical light emitter to shine a light beam, such as an infrared beam, onto a sheet of material and an additional surface, such as a highly reflective metal surface, located below the sheet. When the light beam shines onto the sheet, some of the light is reflected back by the top surface of the sheet, and some of the light passes through the sheet and is reflected by the metal sheet. The reflected light may form an interference pattern that may be detected. According to interferometry, the thickness of the sheet may be calculated based on the optical path difference between the light reflected at the top surface of the sheet and the light reflected on the metal surface below the sheet, which produces an interference difference or phase difference.

[0111] The optical sensor may include an LED transmitter and receiver located on two opposite sides of the sheet. The LED may emit a diffuse beam of LED light in a parallel, uniform manner on one side of the sheet, and the light is detected by a receiver located on the other side of the sheet, such as at a reference roller on which the sheet runs. Since the reference roller position is known, the material thickness is calculated as the difference between the roller position and the optical sensor measurement.

[0112] Preferably, the sensor for evaluating the post-curling properties of the sheet comprises a sensor adapted to measure the properties of a plurality of corrugations. Preferably, the sensor for evaluating the properties of the corrugations on the sheet comprises a laser profiler. The laser profiler emits a laser radiation beam having a substantially linear shape. The laser profiler is adapted to determine the profile of the object hit by the laser line. Preferably, the laser profiler emits a laser line substantially perpendicular to the conveying direction of the sheet. Preferably, the laser line is long (wide) enough to hit several corrugations. The laser profiler is adapted to determine the profile of the cross section of the sheet on a plane perpendicular to the conveying direction. Preferably, the laser profiler acquires the profile at a given frequency. During the curling of the sheet, the laser profiler is adapted to form an image. The image is formed by a series of acquisitions of the laser profiler, each acquisition of the laser line being irradiated on the sheet. The laser profiler used in the present invention is, for example, a Keyence LJV7020 using a controller XG-X2800. For the profile obtained by each laser line, the laser profiler is adapted to obtain an average amplitude. The profile obtained by each laser line includes the profiles of several corrugations.

[0113] Preferably, the control unit is connected to the laser profiler, the control unit being adapted to determine the amplitude or pitch of the profile obtained by the laser profiler.Based on the profile of the sheet, the pitch and amplitude of the corrugations formed on the sheet by the first and second crimping rollers can be determined.

[0114] Preferably, the device comprises an ambient temperature sensor, which is suitable for measuring the temperature of the environment in which the sheet is located and is suitable for emitting a signal representing the measured ambient temperature. Preferably, the device comprises an ambient humidity sensor, which is suitable for measuring the relative humidity of the environment in which the sheet is located and is suitable for emitting a signal representing the measured relative humidity of the environment. Preferably, the device comprises a viscosity sensor, which is suitable for measuring the viscosity of the sheet at a given position and emitting a signal representing the measured viscosity. The feedback control loop may be suitable for activating the first actuator based on the signal emitted by the ambient temperature sensor. The feedback control loop may be suitable for activating the first actuator based on the signal emitted by the ambient humidity sensor. The feedback control loop may be suitable for activating the first actuator based on the signal emitted by the viscosity sensor. The advantages of having an additional sensor have been outlined with reference to the method.

[0115] Preferably, the apparatus comprises: a second actuator for discarding at least a portion of the sheet; a feedback control loop system adapted to activate the second actuator based on the measured pre-curl characteristic of the sheet or based on the data retrieved with respect to one of the pre-curl characteristics or based on the evaluated post-curl characteristic. The second actuator may comprise a reject gate. The second actuator is preferably activated when the sheet or a portion of the sheet needs to be discarded because the post-curl characteristic of the sheet is not within a prescribed range in view of the pre-curl characteristic.

[0116] Preferably, the control unit communicates with a sensor adapted to measure the pre-curling characteristic of the sheet, the laser profiler and one of the first actuators. Furthermore, the control unit may be adapted to receive input from a user. The control unit is able to access a memory storing the pre-curling characteristic of the sheet. The control unit may be a microprocessor, a microcontroller or a computer. The control unit preferably communicates with all pre-curling sensors and post-curling sensors present in the device so that the signals from the sensors can be processed centrally. Preferably, the control unit comprises a memory in which the measured values ​​can be stored. The control unit may also receive input from a user, for example via a keyboard, a touch screen, an indicating device or a button.

[0117] Preferably, the feedback loop system is adapted to activate the second actuator based on a signal related to the ambient temperature. Preferably, the feedback loop system is adapted to activate the second actuator based on a signal related to the ambient relative humidity. Preferably, the feedback loop system is adapted to activate the second actuator based on a signal related to the stickiness of the sheet material. Preferably, the feedback loop system is adapted to activate the second actuator based on a plurality of signals from different sensors. BRIEF DESCRIPTION OF THE DRAWINGS

[0118] Other advantages of the present invention will become apparent from its detailed description with non-limiting reference to the accompanying drawings:

[0119] - Figure 1 is a schematic side view of an apparatus for making curled sheet material;

[0120] - Figure 2 As Figure 1 A schematic perspective view of a portion of a crimping roller of an apparatus;

[0121] - Figure 3 yes Figure 1 a schematic side view of an apparatus of with a sheet of material removed and showing further details;

[0122] - Figure 4 is used Figure 1-3 A schematic enlarged front view of a cross section of a sheet of material being curled by the apparatus;

[0123] - Figure 5 yes Figure 1 a more detailed schematic side view of a portion of a device;

[0124] - Figure 6 is a schematic top view of a curled sheet according to the present invention; and

[0125] - Figure 7 It is a diagram showing the stages of the method of the present invention. DETAILED DESCRIPTION

[0126] exist Figure 1 In FIG. 1 , the basic layout of an apparatus 1 for producing a sheet of crimped material 10 for use in an aerosol-generating article (not shown) is shown in schematic side view.

[0127] The sheet of material is fed by a feed bobbin 3. On the feed bobbin 3, a "ring-shaped" sheet of a flat and thin layer of material 2 to be crimped using the device 1 is provided. The material 2 may be a homogenized tobacco sheet. It will be appreciated that the sheet 2 wound on the feed bobbin 3 is not strictly speaking ring-shaped, however, the total length of the sheet may be several hundred meters and therefore much longer than its width. Furthermore, a switching mechanism may be provided between two consecutive feed bobbins 3 (not shown), so that a continuous crimping process is possible.

[0128] The apparatus 1 comprises a first crimping roller 4 and a second crimping roller 5. Between the first crimping roller and the second crimping roller, a roll gap 6 is formed. The roll gap defines a roll gap size 14. The first crimping roller 4 defines a first rotation axis 24. The second crimping roller 5 defines a second rotation axis 25. The first rotation axis 24 and the second rotation axis 25 are located at Figure 1 and 3 Each is represented by a cross, and Figure 2 The first rotation axis 24 and the second rotation axis 25 are preferably parallel and horizontal. Preferably, during operation, one of the first crimping roller 4 or the second crimping roller 5 rotates clockwise, while the other of the first crimping roller or the second crimping roller rotates counterclockwise.

[0129] The first crimping roller 4 and the second crimping roller 5 show a structured outer surface comprising a plurality of ridges or corrugations. The corrugations are not visible in the drawings. A different arrangement may also be chosen, in particular only one of the first crimping roller 4 or the second crimping roller 5 shows a structured surface.

[0130] The sheet 2 is inserted between the first crimping roller 4 and the second crimping roller 5 in the nip 6 so as to be crimped. Downstream of the first crimping roller 4 and the second crimping roller 5, a crimped sheet 10 is formed in which the corrugations are generated by the pressure applied by the crimping rollers 4,5.

[0131] The sheet 2 is conveyed toward the first winding roller 4 and the second winding roller 5 by the conveying device 7. The conveying device 7 defines a conveying direction of the sheet 2. Figure 1 , 2 , 5 and 6 are indicated by arrow 8.

[0132] Upstream of the first curling roller 4 and the second curling roller 5, the pre-curling properties of the sheet 2 are measured. For example, the thickness 11 of the sheet 2 is measured. The apparatus 1 comprises a thickness sensor 9 adapted to measure the thickness 11 of the sheet 2 in one or more portions of the sheet itself before curling. Alternatively or in addition, the apparatus 1 comprises a moisture sensor 90 adapted to measure the moisture of the sheet 2 in one or more portions of the sheet itself before curling.

[0133] Furthermore, the device 1 comprises a control unit 100 in communication with the thickness sensor 9 and the moisture sensor 90. The thickness sensor 9 and the moisture sensor 90 are adapted to send to the control unit 100 one or more signals representative of the thickness 11 and the moisture in one or more portions of the sheet 2, respectively.

[0134] Downstream of the first and second curling rollers 4, 5, a sensor is positioned for detecting the characteristics of the corrugations, such as a laser profiler 12. The sensor 12 is adapted to determine the characteristics of the corrugations, in this example, it is adapted to detect the profile of the corrugations formed in one or more portions of the corrugated sheet 10. The laser profiler 12 is in communication with the control unit 100 and is adapted to send one or more signals representative of the profile of the curled sheet 10 in one or more portions thereof to the control unit 100.

[0135] As in Figure 3As can be seen better in the figure, in which the material sheet is not depicted for the sake of clarity, the nip 6 between the first crimping roller 4 and the second crimping roller 5 is adjustable. The apparatus 1 comprises a first actuator, Figure 3 The first actuator 13 can change the distance between the first and second rotation axes 24, 25. The first actuator 13 is actuated by a signal sent by the control unit 100.

[0136] The device 1 also includes only Figure 3 , which is suitable for discarding the curled sheet 10 based on a signal generated by the control unit 100 after having received a signal from the laser profiler 12. The second actuator 15 is connected to the control unit 100, which sends a signal to the second actuator 15 in case the laser profiler 12 detects a corrugation profile having characteristics outside a given interval on the curled sheet 10.

[0137] The device 1 may also include a temperature sensor 16 to measure the temperature of the environment in which the sheet 2, the curled sheet 10 and the device 1 are located; a humidity sensor 17, which is suitable for measuring the relative humidity of the environment in which the sheet 2, the curled sheet 10 and the device 1 are located; a temperature sensor 19, which is suitable for measuring the temperature of the sheet 2 or the curled sheet 10 at a given position. All sensors 16, 17, 19 (in Figure 3 ) are connected to the control unit 100. Other sensors may also be present. Furthermore, the control unit 100 comprises a memory 18 in which a database is present. In the database, there are data such as the composition of the sheet material.

[0138] In addition, other data are stored in the memory 18, such as expected values ​​of the characteristics of the corrugations formed on the sheet by the bending rollers 4, 5, expected values ​​based on the pre-bending characteristics of the sheet. Figure 7 As shown, three expected amplitudes of the corrugations are shown, each expected amplitude of the corrugations corresponding to a pre-curling moisture value of the sheet 2. Depending on the moisture measurement value of the sensor 90, different expected values ​​of the curl amplitude are predicted.

[0139] exist Figure 4 In FIG. 1 , an enlarged view of a curled sheet 10 is depicted in a front cross-sectional view. The curled sheet 10 comprises a plurality of corrugations, all of which are indicated at 20 , which form a “wavy” pattern. The corrugations 20 define a given amplitude 23 and a given pitch 26 .

[0140] The device 1 operates according to the method of the invention.

[0141] The sheet 2 is unwound from a supply bobbin 3 and enters the nip 6 between a first take-up roller 4 and a second take-up roller 5 of the apparatus 1 as a single flat material layer 2. The processing of the sheet 2 is completed in the nip 6, which is formed between the take-up rollers 4, 5 by appropriately placing the two take-up rollers 4, 5 at a certain distance by means of a first actuator 13. The size 14 of the nip 6 is usually smaller than the thickness 11 of the incoming sheet 2, so that the sheet 2 is slightly compressed in the nip 6.

[0142] The nip size 14 is selected based on the signals sent by the thickness sensor 9 and the moisture sensor 90 to the control unit 100, which in turn controls the first actuator 13. Using the memory 18 and the data stored therein and the thickness or moisture measurement data, the control unit 100 receives the data from the control unit 100 and the first actuator 13. Figure 7 Expected values ​​of the characteristics of the waves to be formed on the curled sheet 10 are retrieved from a graph similar to the graph shown in for the measured values ​​of thickness or moisture. Figure 7 The diagram is a representation of a lookup table, which for the sake of clarity is represented as a diagram. For example, the control unit 100 retrieves the expected value of the corrugation amplitude 23 for the sheet moisture measurement value. Therefore, the roller gap size 14 is set to move the actuator 13 accordingly so that the expected characteristics of the corrugation may be obtained.

[0143] Due to the design of the first crimping roller 4 and the second crimping roller 5, in particular due to the design of the outer surfaces of the crimping rollers 4, 5, the sheet 2 passing through the roller gap 6 has the corrugations 20 formed thereon. Figure 6 A top view of corrugations 20 on a portion of a sheet 10 is depicted in FIG.

[0144] The laser profiler 12 detects the profile of the curled sheet 10 at a given point. To detect the profile, the laser line 21 strikes and irradiates the Figure 6 The curled sheet 10 shown. Preferably, the laser line 21 is substantially perpendicular to the conveying direction 8. The laser profiler 12 irradiates the sheet 10 preferably when the curled sheet 10 is on the idle roller 70 (see Figure 5 ) while rotating. The laser line 21 is preferably several millimeters long to illuminate more than one corrugation 20. The profile obtained by the laser profiler 12 is similar to Figure 4 The laser profiler 12 irradiates the sheet 10 at a given frequency in order to retrieve several profiles when the curled sheet 10 moves along the conveying direction 8 .

[0145] for Figure 4For each profile shown, the laser profiler 12 or the control unit 100 calculates the amplitude 23 of the ripples. Then, for each profile, the average amplitude is calculated. The average amplitude is characteristic of a plurality of ripples 20 of interest. If the average amplitude is outside a given first range for a given measured humidity, the sensor 12 sends a signal to the control unit 100, which in turn sends a signal to the first actuator 13 to change the nip size 14. Alternatively, the average amplitude can be calculated directly in the control unit 100.

[0146] In case the average amplitude 23 is outside the second range, the sensor 12 sends a signal to the control unit 100, which in turn sends a signal to the second actuator 15 to discard the curled sheet 10. In case the average amplitude is directly calculated in the control unit 100, the sensor 12 does not send a signal.

[0147] The first actuator 13 is also operable to change the nip size 14 based on a signal from any one of the sensors 16, 17, 19. The second actuator 15 is also operable to discard the curled sheet 10 based on a signal from any one of the sensors 16, 17, 19.

[0148] The signals from the sensors 9, 12, 16, 17, 19, 90 are preferably sent to the control unit 100 at a given frequency and during the entire crimping process. Thus, a continuous adjustment of the nip size 14 is possible. The control unit 100 together with the sensors 9, 12, 16, 17, 19, 90 defines a feedback control loop.

[0149] If the sheet 10 is not discarded, the rolled sheet 10 is fed to a product bobbin 27 on which the rolled sheet 10 is wound.

Claims

1. A method for curling a sheet material, the sheet material having thickness, moisture, composition and width before curling, the method include: - Obtain the value of one of the following pre-curling sheet properties: o the thickness of the sheet; o humidity of the sheet; o the composition of the sheet; o the width of the sheet; - curling the sheet to form a plurality of corrugations on the sheet, the curling comprising: o providing a pair of crimping rollers defining a nip therebetween, the nip having a nip size; o inserting the sheet into the nip; - evaluating the value of the post-curling sheet property of the sheet after curling; and - obtaining an expected value of the post-curling sheet property of the sheet for the obtained value of the one pre-curling sheet property, and changing the roller gap size while curling if the evaluated value of the post-curling sheet property is different from the expected value of the post-curling sheet property of the sheet.

2. The method according to claim 1, wherein the sheet is a sheet of a material containing an alkaloid or a plastic sheet.

3. The method according to claim 1 or 2, wherein the sheet has mechanical properties, viscosity, temperature before curling, and the method include: - Determine one of the following additional pre-curling sheet properties: o Mechanical properties of the sheet; o the temperature of the sheet; o the stickiness of the sheet; as well as - varying the nip size based on one of the additional pre-curling sheet properties determined.

4. The method according to claim 1 or 2, wherein evaluating the post-curling sheet properties of the sheet after curling comprises evaluating properties of the plurality of corrugations formed on the sheet after curling.

5. The method of claim 4, wherein the plurality of corrugations have a pitch and an amplitude, and wherein a characteristic of the plurality of corrugations is evaluated include: - evaluating said pitch or said amplitude of at least one corrugation of said plurality of corrugations. 6 . The method of claim 5 , wherein evaluating the pitch or the amplitude of at least one corrugation of the plurality of corrugations comprises determining a profile of the at least one corrugation.

7. The method according to claim 1 or 2, wherein include: - removing at least a portion of the sheet based on the evaluated post-curling sheet properties of the sheet.

8. The method according to claim 1 or 2, wherein include: - setting a first nip size based on one of the obtained pre-curling sheet characteristics; - adjusting the first nip size to set a second nip size based on the evaluated post-curling sheet properties of the sheet.

9. An apparatus for curling a sheet material, the sheet material having the following pre-curling characteristics before curling: ·thickness, ·humidity, Composition, and ·width, The device include: - a conveying device adapted to convey the sheet along a conveying direction; - a pair of crimping rollers for crimping the sheet to form a plurality of corrugations on the sheet, the pair of crimping rollers defining a nip therebetween, the nip having a nip size; a sensor adapted to evaluate a value of a post-curling characteristic of the sheet, the sensor adapted to evaluate a post-curling characteristic of the sheet being located downstream of the pair of curling rollers in the conveying direction; - One of the following: o a sensor adapted to evaluate the value of one of the pre-curling characteristics of the sheet, the sensor adapted to evaluate the value of one of the pre-curling characteristics of the sheet and to transmit a signal function of the evaluated one of the pre-curling characteristics, the sensor adapted to evaluate the value of one of the pre-curling characteristics of the sheet being located upstream of the pair of curling rollers in the conveying direction; o a memory containing data relating to one of the pre-curl properties of the sheet material; - a control unit adapted to receive said signal function of one of the evaluated pre-curl characteristics or to retrieve data related to said one pre-curl characteristic; - a first actuator, which changes the roller gap size; as well as - A feedback control loop system, which is suitable for starting the first actuator if the expected value of the post-curl characteristic of the sheet material obtained based on the value of one of the pre-curl characteristics of the sheet material evaluated or based on the data retrieved relative to one of the pre-curl characteristics is different from the value of the post-curl characteristic of the sheet material evaluated.

10. The apparatus of claim 9, wherein the sensor adapted to evaluate one of the pre-curl properties of the sheet material comprises a sensor adapted to measure the thickness of the sheet material, the sensor adapted to measure the thickness of the sheet material comprising one of: - a mechanical sensor comprising a wheel or a slide in contact with the sheet; - an optical sensor for radiating an electromagnetic beam onto the sheet; -Interferometer.

11. Apparatus according to claim 9 or 10, wherein the sensor adapted to assess one of the post-curling properties of the sheet comprises a sensor adapted to assess a property of the plurality of corrugations.

12. The apparatus of claim 11, wherein the sensor adapted to evaluate the characteristics of the plurality of ripples include: -Laser profiler.

13. Apparatus according to claim 12, wherein the control unit is connected to the laser profiler, the control unit being adapted to determine the amplitude or pitch of the profile obtained by the laser profiler.

14. The apparatus according to claim 9 or 10, comprising one of the following: - an ambient temperature sensor adapted to measure the temperature of the environment in which the sheet is located and to emit a signal representative of the measured ambient temperature; - an ambient humidity sensor adapted to measure the relative humidity of the environment in which the sheet is located and to emit a signal representative of the measured relative humidity of the environment; - a viscosity sensor adapted to measure the viscosity of the sheet at a given location and to emit a signal representative of the measured viscosity; - a transparency sensor adapted to measure the transparency of the sheet and to emit a signal representative of the measured transparency, the transparency sensor being located downstream of the pair of crimping rollers.

15. The device according to claim 9 or 10, wherein include: a second actuator for discarding at least a portion of the sheet; The feedback control loop system is adapted to activate the second actuator based on the evaluated pre-curl property of the sheet material or based on the data retrieved with respect to one of the pre-curl properties or based on the evaluated post-curl property.

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