The invention relates to a method and an apparatus to crimp a sheet.

In the manufacture of aerosol-generating articles, such as for example heat-not-burn products, often components which are in rod format are 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 comprise a plurality of channels to provide air-flow through the rod. The plurality of channels may be provided by crimping a sheet of material and consequently gathering the material within the rod to form the channels. In such examples, the crimped sheet is generally formed by crimping a substantially continuous sheet.

This material to be crimped, that is the continuous sheet, in the field of aerosol-generating articles, may be for example homogenized tobacco, such as reconstituted tobacco or cast leaf, a sheet made by polylactic acid, or a sheet of cotton.

Methods and apparatuses for manufacturing a crimped sheet for use in an aerosol-generating article are known in the art. Known methods of manufacturing a crimped sheet generally involve feeding a substantially continuous sheet between a pair of interleaved rollers to apply a plurality of crimp corrugations to the continuous sheet. The crimped sheet is subsequently gathered to form a continuous rod having a plurality of axial channels. The rod is then wrapped and cut into smaller segments to form an aerosol-generating substrate or filter for an aerosol generating article.

The crimping process is important for an effective manufacturing process of the aerosol-generating article.

The invention relates to a method to crimp a sheet having, before crimping, a thickness, a moisture, a composition and a width, the method comprising: obtaining one pre-crimping sheet characteristic among the thickness of the sheet; the moisture of the sheet; the composition of the sheet; the width of the sheet. The method may further comprise crimping the sheet to form a plurality of corrugations on the sheet, the crimping including: providing a pair of crimping rollers defining a nip therebetween, the nip having a nip size; and inserting the sheet in the nip. The method may further include evaluating a post-crimping characteristic of the sheet after crimping. The method may also include varying the nip size on the basis of the obtained one of the pre crimping sheet characteristics, and on the basis of the evaluated post-crimping sheet characteristic.

The invention also relates to an apparatus to crimp a sheet having, before crimping, a pre-crimping characteristic among: a thickness, a moisture, a composition, and a width. The apparatus comprises: a transport device adapted to transport the sheet along a transport direction; a pair of crimping rollers to crimp the sheet forming a plurality of corrugations on the sheet, the pair of crimping rollers defining a nip therebetween, said nip having a nip size. The apparatus may also comprise a sensor adapted to evaluate a post-crimping characteristic of the sheet, the sensor being located downstream the pair of crimping rollers in the transport direction. The apparatus may also comprise one of the following: a sensor adapted to evaluate one of the pre-crimping characteristics of the sheet, and send a signal function of the evaluated one of the pre-crimping characteristics, the sensor being located upstream the pair of crimping rollers in the transport direction; a memory containing data relative to one of the pre-crimping characteristics of the sheet. The apparatus may further comprise a control unit adapted to received said signal function of the evaluated one of the pre-crimping characteristics or to retrieve the data relative to one of pre crimping characteristics. The method may also comprise a first actuator to vary the nip size; and a feedback control loop system adapted to activate the first actuator on the basis of the evaluated one of the pre-crimping characteristic of the sheet or on the basis of the data retrieved relative to one of the pre-crimping characteristics, and on the basis of the evaluated post-crimping characteristic of the sheet.

A sheet of material is crimped between two crimping rollers forming a nip therebetween. Due to the crimping, a plurality of corrugations is formed on the sheet. A first evaluation of a pre-crimping characteristic of the sheet is performed upstream the crimping rollers. A second evaluation of a post-crimping characteristic of the sheet is performed downstream the crimping rollers. The first upstream evaluation relates to one of: the thickness of the sheet, the moisture of the sheet; the composition of the sheet; the width of the sheet. The second downstream evaluation relates to a characteristic of the sheet imparted by the corrugations, for example a characteristic of the plurality of corrugations on the sheet. If needed, the nip size may varied on the basis of the evaluated post crimping characteristic of the sheet and the obtained pre-crimping characteristic of the sheet. In this way, a continuous feedback loop for an optimal crimping may be implemented, because the nip size depends on characteristics of the sheet present both before and after crimping. The effect of the crimping on the sheet may be monitored and the nip size may be adapted to the specific conditions of the crimped sheet.

As used herein, the term “sheet” denotes a laminar element having a width and length substantially greater than the thickness thereof. The width of the sheet is preferably greater than 10 millimeters, more preferably greater than about 20 millimeters or about 30 millimeters. Even more preferably, the width of the sheet is comprised between about 60 millimeters and about 300 millimeters. The thickness of the sheet may be comprised between about 50 micrometers and 300 micrometers, it may be comprised between about 100 micrometers and about 250 micrometers, it may be comprised between about 175 micrometers and about 250 micrometers, it may be comprised between about 130 micrometers and about 220 micrometers.

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

“Aerosol-generating articles” according to the present invention may be in the form of articles in which an alkaloids containing material, such as a tobacco material, is heated to form an aerosol, rather than combusted. Aerosol generating articles are articles in which an alkaloids-containing aerosol is generated from an alkaloids-containing material, for example from a tobacco extract, or other nicotine source, without combustion or heating. Aerosol-generating articles according to the invention may be whole, assembled aerosol forming articles. Aerosol-generating articles according to the invention may be components of aerosol-generating articles that are combined with one or more other components in order to provide an assembled article for producing an aerosol. An example is the consumable part of a heated smoking device.

A “material containing alkaloids” is a material which contains one or more alkaloids. The alkaloids may comprise nicotine. The nicotine may be found, for example, in tobacco.

Alkaloids are a group of naturally occurring chemical compounds that mostly contain basic nitrogen atoms. This group also includes some related compounds with neutral and even weakly acidic properties. Some synthetic compounds of similar structure are also termed alkaloids. In addition to carbon, hydrogen and nitrogen, alkaloids may also contain oxygen, sulfur and, more rarely, other elements such as chlorine, bromine, and phosphorus.

Alkaloids are produced by a large 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.

As used herein, the term “homogenized tobacco material” denotes material formed by agglomerating particulate tobacco, which contains the alkaloid nicotine. The material containing alkaloids can thus be a homogenized tobacco material.

The most commonly used forms of homogenized tobacco material is reconstituted tobacco sheet and cast leaf. The process to form homogenized tobacco material sheets commonly comprises a step in which tobacco powder and a binder, are mixed to form a slurry. The slurry is then used to create a tobacco web. For example by casting a viscous slurry onto a moving metal belt to produce so called cast leaf. Alternatively, a slurry with low viscosity and high water content can be used to create reconstituted tobacco in a process that resembles paper-making.

Other forms of makings a sheet are possible. The sheet of homogenized tobacco material may be formed using particulate tobacco (for example, reconstituted tobacco) or a tobacco particulate blend, a humectant and an aqueous solvent to form the tobacco composition.

The homogenized tobacco sheet may include, in addition to the tobacco, a binder. The homogenized tobacco sheet may include an aerosol-former, such as guar and glycerin.

As used herein, the term “crimped sheet” denotes a sheet with a plurality of corrugations. The term “crimping” denotes the process of formation of a plurality of corrugations on a sheet of material. Preferably, the sheet of material is an essentially flat sheet of material or a previously untreated sheet of material with respect of generating a structured surface. However, crimping of a sheet already including corrugations can be envisaged as well. Corrugations on a sheet may be formed by crimping rollers. Crimping rollers may include corrugations on their surface.

As used herein, the term “corrugations” denotes a plurality of ridges formed from alternating peaks and troughs joined by corrugation flanks. This includes, but is not limited to, corrugations having a square wave profile, sinusoidal wave profile, triangular profile, sawtooth profile, or any combination thereof. Corrugations can be defined on rollers, such as crimping rollers, or on a sheet. Corrugations on a roller denote a plurality of ridges formed on an outer surface of the roller. Corrugations on a sheet refer to a plurality of ridges when the sheet is laid on a planar surface without stretching the sheet itself.

As used herein, the term “substantially interleave”, when referred to a pair of rollers formed by a first crimping roller and a second crimping roller, denotes that the corrugations of the first crimping roller and second crimping roller at least partially mesh. This includes arrangements in which the corrugations of one or both of the rollers are symmetrical or asymmetrical. The corrugations of the crimping rollers may be substantially aligned, or at least partially offset. The peak of one or more corrugations of the first crimping roller or second crimping roller may interleave with the trough of a single corrugation of the other of the first crimping roller and second crimping roller. Preferably, the corrugations of the first crimping roller and second crimping roller interleave such that substantially all of the corrugation troughs of one of the first crimping roller and second crimping roller each partially receive a single corrugation peak of the other of the first crimping roller and second crimping roller.

A “crimping roller” is a roller used for crimping a sheet. The crimping roller defines an outer surface and a rotational axis. The outer surface comprises a plurality of corrugations. Preferably, the corrugations are radially extending around the outer surface. Preferably the corrugations define circumferences on the surface of the crimping roller. As used therein, the “diameter of the crimping roller” is considered the largest diameter among the diameters defined by cross sections along a plane perpendicular to the rotational axis of the crimping roller.

As used therein, the “distance between a first crimping roller having a first rotational axis and a second crimping roller having a second rotational axis” refers to the distance between their respective first rotational axis and second rotational axis.

As used herein, the term “longitudinal direction” refers to a direction extending along, or parallel to, the length of the sheet.

As used herein, the term “width” refers to a direction perpendicular to the transport direction of the sheet while processed.

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

As used herein, the term “amplitude value” of corrugations refers to the height of a corrugation from its peak to the deepest point of the deepest directly adjacent trough. For example, in case of corrugations in rollers, the amplitude of the corrugation may be measured along a radial direction. The radial direction is the direction along a radius connecting the rotational axis of the roller and the peak or the trough. The radius is perpendicular to the rotational axis. The height of the trough is measured as the distance along the radial direction between the rotational axis and the deepest point of the trough. The height of the peak is measured as the distance along the radial direction between the rotational axis and the highest point of the peak. The “amplitude value” is thus the difference between the height of the peak and the height of the trough. In case of corrugations in a sheet, the amplitude value is calculated in a configuration where the sheet lies on a plane without stretching the sheet itself. The amplitude of a 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 in contact with the peak of the corrugation and the second plane is in contact with the deepest point of the adjacent trough to the peak.

When the corrugations are formed on a sheet, the ridges may be parallel to each other. The ridges may be parallel to the direction in which the sheet is transported while crimped. The ridges may form an angle between 0 degrees and 45 degrees with the direction in which the sheet is transported while crimped.

As used herein, the term "flank angle" refers to the angle between the corrugation flanks of a particular corrugation. The flank angle may be the same for all corrugations. Further, one or more of the corrugations may be asymmetrical about the radial direction. As used herein, the term “nip” refers to a gap present between a first crimping roller and a second crimping roller forming the pair of crimping rollers. The sheet to be crimped passes through the nip during operation. The first crimping roller and second crimping roller define a first rotational axis and a second rotational axis, respectively. Further, the first crimping roller defines a first outer surface and the second crimping roller defines a second outer surface. The nip defines a nip size. The size of the nip is defined for each cross section of the first and second crimping rollers along a plane perpendicular to the first rotational axis or to the second rotational axis. In each cross section, the nip size is the smallest Euclidean distance between the first outer surface and the second outer surface for a given relative position between the first crimping roller and the second crimping roller. The nip may vary in size during the relative rotation of the first crimping roller and second crimping roller. The nip size might be constant in case the surface of both first and second crimping rollers is rotationally invariant for rotations around the first and second rotational axis, or it may change. Further, the nip size might be constant along the width of the roller, or it may change as well. Preferably, for each cross section, there are two nip sizes. The nip size may also vary along the width of the roller. Two cross sections taken at two different locations along the rotational axis of the crimping roller may show different nip sizes.

Preferably, the nip size for each cross section is constant. Preferably, the nip size is constant among all of the cross sections. A constant nip size allows to obtain a constant treatment of the material across the width of the sheet.

However, the invention also contemplates that the roller may bend slightly during use such that a constant crimping profile in the sheet material requires that the nip size is slightly larger towards the center of the roller.

With the term “stickiness”, reference is made to the adhesive properties or cohesive properties of the sheet. Adhesion is the tendency of dissimilar particles or surfaces to cling to one another, while cohesion refers to the tendency of similar or identical particles or surfaces to cling to one another. The stickiness of a sheet may be measured using a LIDAR (Laser Imaging Detection and Ranging) adapted to measure a distance between the measuring apparatus and a sheet which is unwounded from a roller. The LIDAR is positioned in such a way to face the unwound portion of the sheet. A “not-sticky” sheet has the closest distance to the LIDAR, because the unwound portion of the sheet immediately detaches from the roller. The distance between LIDAR and unwound portion of the sheet increases with increasing stickiness.

In the following, with the term “upstream” or “downstream”, reference is made to the direction of motion or transport of the sheet.

As used herein, the terms “gathered” or “gathering” when referred to a sheet denote that a sheet is convoluted, or otherwise compressed or constricted substantially transversely to the transport direction of the sheet into rod form.

As used herein, the terms “horizontal” and “vertical” have their standard meaning.

A sheet having the following characteristic: a given thickness, moisture, composition and width is provided in the apparatus of the invention. The above characteristics are called globally as “pre crimping characteristics” of the sheet. The pre-crimping characteristics may be substantially uniform within the sheet or may vary in different locations of the sheet. The thickness, moisture, composition and width of the sheet may be comprised within given ranges, a range for each characteristic.

The sheet defines two opposite surfaces, and the opposite surfaces defines opposite sides of the sheet.

Preferably, the sheet is provided by unwinding a bobbin.

At least one of the pre-crimping characteristics of the sheet is obtained. The obtained one of the pre-crimping characteristics may be the thickness of the sheet. The obtained one of the pre crimping characteristics may be the moisture of the sheet. The obtained one of the pre-crimping characteristics may be the width of the sheet. The obtained one of the pre-crimping characteristics may be the composition of the sheet.

The composition may refer to the chemical composition of the sheet, such as the constituents of the sheet. For example, the composition may include the blend of the sheet. The blend of the sheet is applicable if the sheet is a sheet of material containing alkaloids. In this case, the sheet is made blending the material containing alkaloids in order to obtain a pre-determined blend. The material containing alkaloids may be tobacco material. Preferably, more than one tobacco type is blended together. For example, at least two different tobacco types are blended together. With the term “tobacco type” one of the different varieties of tobacco is meant. With respect to the present invention, these different tobacco types are distinguished in three main groups of bright tobacco, dark tobacco and aromatic tobacco. The distinction between these three groups is based on the curing process the tobacco undergoes before it is further processed in a tobacco product.

Bright tobaccos are tobaccos with a generally large, light coloured leaves. Throughout the specification, the term “bright tobacco” is used for tobaccos that have been flue cured. Examples for bright tobaccos are Chinese Flue-Cured, Flue-Cured Brazil, US Flue-Cured such as Virginia tobacco, Indian Flue-Cured, Flue-Cured from Tanzania or other African Flue Cured. Bright tobacco is characterized by a high sugar to nitrogen ratio. From a sensorial perspective, bright tobacco is a tobacco type which, after curing, is associated with a spicy and lively sensation. According to the invention, bright tobaccos are tobaccos with a content of reducing sugars of between about 2.5 percent and about 20 percent on dry weight basis of the leaf and a total ammonia content of less than about 0.12 percent on dry weight basis of the leaf. Reducing sugars comprise for example glucose or fructose. Total ammonia comprises for example ammonia and ammonia salts.

Dark tobaccos are tobaccos with a generally large, dark coloured leaves. Throughout the specification, the term “dark tobacco” is used for tobaccos that have been air cured. Additionally, dark tobaccos may be fermented. Tobaccos that are used mainly for chewing, snuff, cigar, and pipe blends are also included in this category. From a sensorial perspective, dark tobacco is a tobacco type which, after curing, is associated with a smoky, dark cigar type sensation. Dark tobacco is characterized by a low sugar to nitrogen ratio. Examples for dark tobacco are Burley Malawi or other African Burley, Dark Cured Brazil Galpao, Sun Cured or Air Cured Indonesian Kasturi. According to the invention, dark tobaccos are tobaccos with a content of reducing sugars of less than about 5 percent of dry weight base of the leaf and a total ammonia content of up to about 0.5 percent of dry weight base of the leaf.

Aromatic tobaccos are tobaccos that often have small, light coloured leaves. Throughout the specification, the term “aromatic tobacco” is used for other tobaccos that have a high aromatic content, for example a high content of essential oils. From a sensorial perspective, aromatic tobacco is a tobacco type which, after curing, is associated with spicy and aromatic sensation. Example for aromatic tobaccos are Greek Oriental, Oriental Turkey, semi-oriental tobacco but also Fire Cured, US Burley, such as Perique, Rustica, US Burley or Meriland.

Additionally, a blend may comprise so called filler tobaccos. Filler tobacco is not a specific tobacco type, but it includes tobacco types which are mostly used to complement the other tobacco types used in the blend and do not bring a specific characteristic aroma direction to the final product. Examples for filler tobaccos are stems, midrib or stalks of other tobacco types. A specific example may be flue cured stems of Flue Cured Brazil lower stalk.

Within each type of tobaccos, the tobacco leaves are further graded for example with respect to origin, position in the plant, colour, surface texture, size and shape. These and other characteristics of the tobacco leaves are used to form a tobacco blend. A blend of tobacco is a mixture of tobaccos belonging to the same or different types such that the tobacco blend has an agglomerated specific characteristic. This characteristic can be for example a unique taste or a specific aerosol composition when heated or burned. A blend comprises specific tobacco types and grades in a given proportion one with respect to the other.

According to the invention, different grades within the same tobacco type may be cross-blended to reduce the variability of each blend component. According to the invention, the different tobacco grades are selected in order to realize a desired blend having specific predetermined characteristics. For example, the blend may have a target value of the reducing sugars, total ammonia and total alkaloids per dry weight base of the homogenized tobacco material. Total alkaloids are for example nicotine and the minor alkaloids including nornicotine, anatabine, anabasine and myosmine.

For example, bright tobacco may comprise tobacco of grade A, tobacco of grade B and tobacco of grade C. Bright tobacco of grade A has slightly different chemical characteristics to bright tobacco of grade B and grade C. Aromatic tobacco may include tobacco of grade D and tobacco of grade E, where aromatic tobacco of grade D has slightly different chemical characteristics to aromatic tobacco of grade E. A possible target value for the tobacco blend, for the sake of exemplification, can be for example a content of reducing sugars of about 10 percent in dry weight basis of the total tobacco blend. In order to achieve the selected target value, a 70 percent bright tobacco and a 30 percent aromatic tobacco may be selected in order to form the tobacco blend. The 70 percent of the bright tobacco is selected among tobacco of grade A, tobacco of grade B and tobacco of grade C, while the 30 percent of aromatic tobacco is selected among tobacco of grade D and tobacco of grade E. The amounts of tobaccos of grade A, B, C, D, E which are included in the blend depend on the chemical composition of each of the tobaccos of grades A, B, C, D, E so as to meet the target value for the tobacco blend.

The various tobacco types have different chemical characteristics. It is believed that more than 300 chemical constituents are present in tobacco leaves. Within the same type of tobacco, different grades may also have differences in chemical composition. The chemical constituents of tobacco may be influenced by genetics, agricultural practice, soil type and nutrients, weather conditions, plant disease, stalk position, harvesting and curing procedures.

The obtained one of the pre-crimping characteristics may be measured, for example using a suitable sensor. Preferably, the sensor measures the pre-crimping characteristic real-time, that is, the pre-crimping characteristic of the sheet is preferably measured during processing of the sheet. Measuring the pre-characteristic of the sheet means measuring the characteristic of the sheet at least in a predetermined location, that is, at least the pre-crimping characteristic of a first portion of the sheet is measured. Any sensor to measure one of the pre-crimping characteristics is preferably positioned upstream the crimping rollers.

One sensor or more sensors for measuring the same pre-crimping characteristic could be used to measure the pre-crimping characteristic of the sheet. The same pre-crimping characteristic of the sheet may be measured in one location or in more locations. If measured in more than one location, each measurement produces a data and the data are gathered. The gathered data from the different measurements may be statistically combined. A mean of all pre-crimping measurements of the same characteristic may be performed.

In case the thickness is measured, a thickness sensor may be used.

The thickness sensor may comprise a mechanical sensor. The thickness sensor may comprise an optical sensor. The thickness sensor may comprise a mechanical sensor and an optical sensor.

In case the moisture is measured, a moisture sensor may be used. The moisture sensor may comprise a Grammage sensor.

In case the width is measured, a distance sensor may be used.

The pre-crimping characteristic may be obtained by means of a database. The method of the invention preferably includes accessing a database and retrieving from the database data relative to one of the pre-crimping characteristics of the sheet. The database may include one or more of the pre-crimping characteristics: thickness, moisture, composition or width of the sheet before crimping. The data relative to one or more pre-crimping characteristics may be stored in an accessible memory where the database is present.

The pre-crimping characteristic may be obtained by user’s input. A panel or other input device may be provided and an user, for example an operator, may enter the value of a pre-crimping characteristic of the sheet. Further, data relating to one of the pre-crimping characteristics may be obtained scanning data provided on bobbins made of the sheet, for example a representative code.

The pre-crimping characteristic may be obtained by a remote signal. A wireless or cabled data transmission may take place to input the pre-crimping characteristic.

Preferably, more than one pre-crimping characteristic of the sheet is obtained. Preferably, the moisture of the sheet is obtained. Preferably, the thickness of the sheet is obtained. Preferably, the moisture and the thickness of the sheet are obtained.

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

Further, the sheet is crimped. Crimping is performed using a pair of crimping rollers, denoted as first crimping roller and second crimping roller. The first crimping roller and second crimping roller are positioned one adjacent to the other and a nip is formed between the first crimping roller and the second crimping roller. The first crimping roller defines a first rotational axis and a first outer surface. The second crimping roller defines a second rotational axis and a second outer surface. The first rotational axis and the second rotational axis are preferably parallel to each other. The first rotational axis and second rotational axis are preferably horizontal. Preferably, the first crimping roller and second crimping roller have a width which is equal to or larger than the width of the sheet so that the whole sheet can be crimped between the first crimping roller and the second crimping roller. Preferably, cross sections of the first outer surface along a plane perpendicular to the first rotational axis are circumferences. Preferably, cross sections of the second outer surface along a plane perpendicular to the second rotational axis are circumferences. At least one of the first crimping roller or second crimping roller includes corrugations. Preferably, the corrugations are formed on the first outer surface or on the second outer surface. Preferably, the corrugations are formed in both the first outer surface and in the second outer surface. The corrugations on the first crimping roller or on the second crimping roller, or on both, come into contact with the sheet when the sheet is inserted into the nip between the first crimping roller and second crimping roller. Due to the corrugations’ action on the sheet, corresponding corrugations are formed on the sheet when it passes through the nip. In case both first crimping roller and second crimping roller include corrugations, the first crimping roller and second crimping roller may be designed and arranged in a way that at least some of their corrugations substantially interleave.

Alternatively, only one of the first crimping roller and second crimping roller may include corrugations, the other of the first crimping roller and second crimping roller may have an essentially smooth outer surface. This smooth outer surface may be cylindrical.

Alternatively, both the first crimping roller and second crimping roller may include corrugations, in non-corresponding sections. The first crimping roller may comprise sections having corrugations and sections without corrugations. Preferably, a section with corrugation is adjacent to a section without corrugation on the first outer surface. The second crimping roller may comprise sections having corrugations and sections without corrugations. Preferably, a section with corrugation is adjacent to a section without corrugation on the second outer surface. In such a configuration, when the first crimping roller and the second crimping roller face each other, the sections with corrugations of the first crimping roller face sections without corrugations of the second crimping roller. For each portion of the sheet of material which comes into contact with the first crimping roller and the second crimping roller, only one of the first crimping roller and second crimping roller forms crimp corrugations on that portion of the sheet of material.

The corrugations on the first crimping roller or on the second crimping roller have preferably all the same pitch. More preferably, if corrugations are present both in the first crimping roller and in the second crimping roller, they all have the same pitch. Further, preferably, all corrugations in the first crimping roller or in the second crimping roller have the same amplitude. Preferably, the nip size between the first crimping roller and the second crimping roller is comprised between about 100 micrometres and about 300 micrometres. A too small nip size, that is, a nip size smaller than 100 micrometres, may damage the sheet. A too large nip size may not crimp the sheet enough to properly further process the sheet, for example to gather it in a rod.

Preferably, the pitch of the ridges in either the first crimping roller, or in the second crimping roller, or in both, is comprised between 200 micrometres and 1500 micrometres. More preferably, the pitch is comprised between 800 micrometres and 1200 micrometres.

An embodiment of crimping rollers which can be used in the present invention is described in WO 2018/189325 by the same Applicant. Preferably, all corrugations in the first crimping roller or in the second crimping roller have the same flank angle. Preferably, all corrugations in the first crimping roller or in the second crimping roller have the same amplitude. Preferably, all corrugations in the first crimping roller or in the second crimping roller have the same pitch.

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

The nip between the first crimping roller and the second crimping roller has a given nip size. Preferably, the nip size changes during the rotation of the first crimping roller and second crimping roller for a given cross section taken along a plane perpendicular to the first rotational axis or the second rotational axis. The nip size is preferably a step function between a first value and a second value. Before and after the “jump” between the first value and the second value, the nip size is preferably constant.

The nip size is determined, among others, by the distance between the first crimping roller and second crimping roller, and by the diameter of the first crimping roller and second crimping roller.

During the crimping process, the sheet passes through the nip that is formed between the first crimping roller and the second crimping roller. The first crimping roller and second crimping roller form crimp corrugations on the sheet material with a given pattern. The corrugations on the sheet have a pattern which is determined by the pattern of the corrugations on the first crimping roller and second crimping roller. The corrugations on the sheet also define a pitch and amplitude. The amplitude and pitch of the corrugations on the sheet may be different from the amplitude and pitch of corrugations on the first crimping roller or on the second crimping roller due to the flexibility and elasticity of the sheet.

The nip size can be varied, for example by means of a first actuator. The first actuator may vary the nip size by varying the distance between the first crimping roller and the second crimping roller. For example, a linear drive may be present. The linear drive may change the position of the rotational axis of the first crimping roller, or of the second crimping roller, or of both. An excenter mechanism may rotate and, in the rotational movement, change the position of the rotational axis of the first crimping roller or of the second crimping roller, or of both. The variation of the nip size may be in a range of nip size ± 50 micrometres. The nip size may vary between 20 percent and 50 percent of the original nip size, even more preferably between 20 percent and 30 percent.

Downstream the first crimping roller and the second crimping roller in the transport direction, a characteristic of the sheet is evaluated, for example a characteristic of the corrugations formed on the sheet is evaluated. For this purpose, the apparatus may comprise a sensor to detect one of the characteristics of the corrugations formed in the sheet by the crimping rollers. The sensor may be an optical sensor, for example 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.

With “post-crimping characteristic” of the sheet, at least a characteristic of the sheet after crimping is meant. The post crimping characteristic may be a characteristic of the corrugations formed on the sheet. A characteristic of more than a corrugation can be evaluated as well. With characteristic of a corrugation, any characteristic of the pattern formed by the crimping rollers on the sheet is meant. 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 flank angle of the corrugations formed on the sheet, the stability of the corrugations formed on the sheet and others. The corrugations on the sheet have a given geometrical pattern defining, among others a pitch, amplitude, flank angle and other geometrical parameters. With “stability of the corrugations” the stability in time of these geometrical characteristics is meant, that is, a characteristic is stable if after a given amount of time its value remains substantially unchanged or it varies within a given interval. A post-crimping characteristic may be a diameter of the rod formed gathering the crimped sheet. The diameter of the rod depends on the characteristic of the sheet, such as the depth of the crimping, that is, the amplitude of the corrugations formed on the sheet. A post-crimping characteristic may be the resistance to draw of the formed rod obtained by gathering the crimped sheet. Among other factors, the resistance to draw depends on the corrugations formed in the sheet, which form “air channels” in the rod.

The evaluation of a post-crimping characteristic of the sheet is performed after the sheet has been crimped. Evaluating the post-crimping characteristic of the sheet means evaluating the post crimping characteristic of the sheet at least in a location.

Preferably, the evaluation of a post-crimping characteristic of the sheet is performed real-time. The post-crimping characteristic is preferably evaluated at different points in time. Preferably, the evaluation of a post-crimping characteristic is preferably checked at a given frequency while the sheet moves. A statistical quantity can be calculated on the basis of all evaluations of the same post-crimping characteristic at different times.

Preferably, evaluating the post-crimping characteristic of the sheet includes measuring the post crimping characteristic of the sheet. More preferably, evaluating a post-crimping characteristic of the sheet includes evaluating a characteristic of the corrugations formed on the sheet. Preferably, evaluating a characteristic of the corrugations formed on the sheet includes measuring a characteristic of the corrugations. More preferably, measuring the characteristic of the corrugation includes measuring the characteristic of the corrugations by means of a sensor.

One sensor may be used to measure the post-crimping characteristic of the crimped sheet. Several sensors may be used to measure the post-crimping characteristic of the crimped sheet.

The post-crimping characteristic of the sheet may be evaluated in one location of the crimped sheet. The post-crimping characteristic of the sheet may be evaluated in several locations of the crimped sheet. If evaluated in more than one location, each determination produces a data and the data are gathered. The gathered data from the different determinations may be statistically combined, for example a statistical quantity can be calculated on the basis of all determination of the same post-crimping characteristic in different locations on the sheet. A mean of all determinations of the same post-crimping characteristic of the sheet may be performed.

The evaluation of a post-crimping characteristic of the sheet is used to adapt the nip size. Depending on the value of the post-crimping characteristic of the sheet, it may be determined that the nip size is not optimal. The determination whether the nip size is optimal depends also on the obtained one of the pre-crimping characteristic of the sheet. For each value of the obtained one of the pre-crimping characteristics, a given value of the post-crimping characteristic of the sheet may be expected. This expected value of the post-crimping characteristic of the sheet therefore depends on the pre-crimping characteristic of the sheet. If the evaluated value of the post-crimping characteristic of the sheet is different from the expected value, then the nip size is preferably varied. With “expected value” also a range of expected values is meant.

For example, for a given obtained pre-crimping sheet thickness, a certain nip size is preliminary set. After the evaluation of the post-crimping characteristic of the sheet after crimping, however, it may be seen that the preliminary set nip size is not optimal because the post-crimping characteristic value of the sheet, for example a characteristic of the corrugations on the sheet, is outside a desired range. According to the invention, the nip size is therefore adjusted on the basis of the evaluated post-crimping characteristic of the sheet after the preliminary setting based on the pre-crimping thickness. The step of varying the nip size on the basis of the obtained one of the pre-crimping characteristics and on the basis of the evaluated post-crimping characteristic of the sheet may include one of the following. A single variation step based on both pre-crimping and post-crimping characteristics can be implemented. A variation step which takes place in two sub-steps may be implemented as well: a first sub-step in which the variation is made on the basis of the pre-crimping characteristic and a second sub-step in which the variation is made on the basis of the post-crimping characteristic. The first sub-step and second sub-steps may be reversed: a first sub-step in which the variation is made on the basis of the post-crimping characteristic and a second sub-step in which the variation is made on the basis of the pre-crimping characteristic may be performed as well.

Preferably, the crimped sheet is used in an aerosol-generating article. Preferably, the crimped sheet is used to form a component of the aerosol-generating article.

The crimping process creates various effects related to the material forming the sheet which is pressed between the crimping rollers.

A first range of effects occurs during the subsequent manufacturing processes, such as for example the fact that a crimped sheet of material can be more easily compressed into a rod than a sheet which has not been crimped. In addition, a more predictable outcome is obtained.

Once the crimped sheet of material is compressed into a rod and added to the aerosol-generating article, a second range of effects is related to the crimping, such as the users’ smoking experience. More specifically, the crimping process affects the contact between the air, penetrating the aerosol generating article, and the crimped sheet of material, and the resistance to draw (RTD).

However, a non-optimal or sub-optimal crimping process may excessively weaken the crimped web of material. A non-optimal or sub-optimal process may hinder the release of substances from the crimped sheet of material to the penetrating air in the rod, as well as adversely affect the RTD value.

The correct nip size is relevant for the correct crimping of the sheet. The nip size may be responsible, among other parameters, whether the crimped sheet has a correct “crimp level”. The correct “crimp level” is important in the subsequent processing steps of the sheet. For example, the correct amount of crimping may cause the sheet to become “foldable” enough to be gathered into a rod form without breaking. The correct crimp level may avoid that the “foldable” sheet includes structural damage. For example, when wrapping the sheet, if the latter is crimped less than the correct crimp level, the material forming the sheet, after being gathered into a rod and wrapped inside a wrapper, may display an expansion force that can resist the wrapper. This prevent the sheet to form rods properly. Further, low crimp level may also affect the ability of the sheet to bend. On the other hand, if the sheet is crimped more than the correct crimp level, the sheet may present structural damage. Small parts of the material forming the sheet may get detached from the formed rod. The small parts may travel inside the aerosol-generating article. The small parts may also travel within the machines processing the rods. This may increase the machine cleaning downtime. The correct crimping level is thus a balance between the folding characteristics of the sheet and the absence or minimization of damages.

The correct crimp level relates to the post-crimping characteristic of the sheet. Preferably, the correct crimp level relates to the characteristic of the sheet which are caused by the corrugations formed by the crimping process. The correct crimp level may relate to the characteristic of the corrugations on the sheet. For example, the crimp level is determined evaluating the amplitude of the corrugations formed on the sheet by the crimping rollers. Preferably, the characteristic of the corrugations evaluated after crimping is the amplitude of at least a corrugation formed on the sheet.

A feedback loop control system of the crimping process is thus preferably implemented according to the invention, receiving data relating to the sheet’s characteristics before the crimping process and after the crimping process. For example, the feedback loop control system may include sensors located upstream and downstream of the first crimping roller and the second crimping 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 nip size, so that it can be constantly optimized during the process.

For example, for each obtained pre-crimping characteristic, thanks to empirical data, a given post crimping characteristic is expected. A range of values of the post-crimping characteristic may be expected. A look-up table or a database may be formed so that for a given pre-crimping characteristic, the expected value of a post-crimping characteristic is retrieved. A range of expected values of such post-crimping characteristic may be retrieved. Preferably from empirical data, from this expected value or value range of the post-crimping characteristic, a nip size value is associated. The first crimping roller and the second crimping roller are then arranged so that the associated nip size is present between them. The sheet is then crimped using the associated nip size. The post-crimping characteristic which is expected is then evaluated. If the evaluated post crimping characteristic is different from the expected one, then the nip size is varied. This applies also with several pre-crimping characteristics as input: a multi-dimensional table may be present so that for the selected multiple pre-crimping characteristics, a value of a given post-crimping characteristic is first retrieved and then evaluated.

The post-crimping characteristic may be the amplitude of the corrugations formed on the sheet. Therefore, for a given thickness or moisture of the sheet before crimping, in a database, a corresponding expected value for the corrugations’ amplitude is retrieved. It is known from empirical data that the expected amplitude value can be obtained with an associated nip size. The associated nip size is set and the sheet crimped. The amplitude of the corrugations formed on the sheet is then measured. If the measured amplitude value differs “too much” from the expected value, that is, if the difference between the expected amplitude value and the measured amplitude value is - in absolute value - above a given threshold, the nip size is varied.

Preferably, the method comprises varying the nip size while crimping. The evaluations made upstream and downstream the crimping rollers can be preferably made at a certain frequency during the manufacturing process. For example, the evaluation can be made several times per minute. It may be made once between 1 minute and 30 minutes. Preferably, the evaluation is made every between 1 minute and 15 minutes. Preferably, the pre-crimping and post-crimping data are continuously gathered and evaluated. The nip size may be varied while the sheet is crimped without need to stop the manufacturing process. The process may adapt to changing ambient conditions. The process may adapt to changes in the pre-crimping characteristics of the sheet.

Preferably, the sheet is a sheet of a material containing alkaloids. Preferably, the sheet is a plastic sheet. The crimping method or apparatus can be used for sheets of a material containing alkaloids, for example homogenized tobacco sheets, which are “sticky” and relatively fragile. The crimping method or apparatus may be used for plastic sheets, such as polylactic acid (PLA) sheet, which is elastic.

Preferably, the sheet has a mechanical characteristic, a stickiness, a temperature. The method preferably includes determining one additional pre-crimping characteristic of the sheet. The additional pre-crimping characteristic of the sheet may be the mechanical characteristic of the sheet. “Mechanical characteristic” may include one or more of: tensile strength, elastic modulus, elastic limit, maximum elongation, hardness, melting temperature, glass transition and others. The additional pre-crimping characteristic of the sheet may be the temperature of the sheet. The additional pre-crimping characteristic of the sheet may be the stickiness of the sheet. The method may comprise varying the nip size on the basis of the determined one of the additional sheet pre crimping characteristics. The method may comprise varying the nip size on the basis of the mechanical characteristic of the sheet. The method may comprise varying the nip size on the basis of the temperature of the sheet. The method may comprise varying the nip size on the basis of the stickiness of the sheet. The method may comprise varying the nip size on the basis of a combination of two parameters among the additional pre-crimping characteristics. The method may comprise varying the nip size on the basis of a combination of three parameters among the additional pre-crimping characteristics. “Mechanical characteristic, a stickiness, a temperature, of the sheet” are collectively called additional pre-crimping characteristics of the sheet. Further, other parameters of the sheet may be determined in addition or in substitution to those listed. These further parameters may be used in the method of the invention as a basis to vary the nip size.

It is to be understood that the sheet has an additional pre-crimping characteristic at a given location. This means that the sheet may have different additional pre-crimping characteristics depending on the location of the sheet which is considered for the determination. For example, different portions of the sheet may have different stickiness, temperatures, mechanical characteristics. Preferably, at least one of the additional pre-crimping characteristics is determined at a given location of the sheet. The determination is made for example using suitable sensors. The determination may be made by means of a measurement. Alternatively, the one of the pre crimping characteristics may be entered by the user. Alternatively, the one of the additional pre crimping characteristics of the sheet may be retrieved from a memory. For example, the mechanical characteristic of the sheet may be already known from a previous process step and the data relative to the mechanical characteristic is retrieved. In this case, no measurement is needed. The additional pre-crimping characteristic may be read scanning a barcode positioned on a bobbin formed by the sheet.

A single additional pre-crimping characteristic may be determined. A plurality of additional pre crimping characteristics may be determined. A combination of measured additional pre-crimping characteristics and otherwise determined (for example, entered by the user or retrieved in a memory) pre-crimping characteristics may be used as a basis to vary the nip size. The type and number of additional pre-crimping characteristics determined may depend on the type and number of sensors available. Further, for the same additional pre-crimping characteristic, a single determination may be made. For the same additional pre-crimping characteristic, a plurality of determination may be made. The final determination may be a statistical combination of all the determinations made. The statistical combination may include an average (mean) of the determinations of the same additional pre-crimping characteristic. The nip size may be varied on the basis of one or more of these additional pre-crimping characteristic determinations. The effect that the nip size has on the sheet may be related to the above mentioned additional pre-crimping characteristics. For example, the nip size may have a different “crimping effect” depending on the properties of material that is crimped, such as its mechanical characteristics, stickiness, composition, temperature or other parameters. Thus, also these additional pre-crimping characteristics may be relevant for the determination of the optimal nip size. Further, the additional pre-crimping characteristics may vary depending on the process conditions, for example the additional pre-crimping characteristics may vary depending on the temperature or humidity of the environment where the sheet is located. The additional pre-crimping characteristics may change during the crimping process and therefore adjustment of the nip size as a function of one or more of the additional pre-crimping characteristics is preferred. As an example, temperature or humidity of the environment may vary the fragility of the sheet, and in turn its behaviour during crimping. Therefore, a change in humidity or temperature during the process may trigger a change in nip size to keep an optimal crimping result.

The method preferably includes: measuring an ambient temperature of an environment where the sheet is located during crimping. The method preferably includes: measuring an ambient humidity of an environment where the sheet is located during crimping. The method preferably includes: measuring an apparatus temperature of a portion of an apparatus for crimping the sheet. The method preferably includes: varying the nip size on the basis of the ambient temperature, or the ambient humidity, or the apparatus temperature. In the following “an ambient temperature, an ambient humidity, an apparatus temperature” are collectively called ambient parameters. Other parameters may be included in the “ambient parameters”. Preferably, at least one of the ambient parameters is measured by suitable sensors. The ambient parameters, that is, the parameters of the environment where the sheet is located, may influence the sheet parameters and thus the crimping effect that the nip size has on the sheet. One of the ambient parameters, depending on the available sensors, may be measured. More than one ambient parameters may be measured. The nip size may be varied depending on these ambient parameters.

Preferably, evaluating a post-crimping characteristic of the sheet after crimping includes evaluating a characteristic of the plurality of corrugations formed on the sheet after crimping.

The crimping process forms corrugations on the sheet, in particular a plurality of corrugations, and the corrugations have a given amplitude and pitch. Preferably, the step of evaluating a characteristic of the plurality of corrugations formed on the sheet includes evaluating the pitch or the amplitude of at least one corrugation of the plurality. The characteristic of the plurality of corrugations which is preferred to determine whether a correct crimp level is reached is the pitch or the amplitude of at least one corrugation of the plurality. More preferably, the pitch or the amplitude of several corrugations of the plurality is determined. A mean value of the pitches values or of the amplitudes values determined for several corrugations may be calculated. Both pitch and amplitude of at least one corrugation of the plurality may be evaluated. “Evaluating the pitch or the amplitude of the corrugation” means evaluating a value which is function of the pitch or amplitude of the corrugations.

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 varied. Preferably, the mean pitch over several corrugations or the mean amplitude over several corrugations is compared with the expected pitch range or the expected amplitude range, respectively.

Preferably, evaluating the pitch or the amplitude of at least one corrugation of the plurality includes determining a profile of at least one corrugation. More preferably, evaluating the pitch or the amplitude of at least one corrugation includes determining a profile of several corrugations of the plurality. Preferably, the profile of the corrugations is taken perpendicularly to the transport direction of the sheet. The profile of corrugation is substantially the profile defined by a cross section of the sheet taken at a given location by a plane perpendicular to the transport direction. Preferably, the profiles defines alternating peaks and troughs. Preferably, the amplitude of the peaks of the profile is evaluated. Preferably, the mean amplitude is calculated, by calculating the mean of different amplitude among different corrugations. The mean amplitude may be the characteristic of the corrugations.

Preferably, evaluating a characteristic of the plurality of corrugations includes: gathering at different locations along the sheet or at subsequent time intervals the pitch or the amplitude of at least one corrugation of the plurality; and comparing the pitch or the amplitude of the at least one corrugation gathered at different locations along the sheet or at subsequent time intervals. More preferably, the method also comprises varying the nip size on the basis of the comparison. A parameter which may vary the effect that the crimping has on the sheet is the “stability” of the created corrugations on the sheet. “Stability” means that the characteristic of the corrugations, such as the pitch or the amplitude of the corrugations formed on the sheet, remains substantially the same from the moment of formation by the crimping rollers onwards. The first crimping roller and second crimping roller from corrugations on the sheet having an amplitude and a pitch. It is preferred to check whether the characteristic of the corrugation remains stable on the sheet, for example, whether the amplitude or pitch change, or the amplitude and the pitch change. The amplitude or pitch of the corrugations may change over time, that is, at a given point in time they may have a certain value and, after a time interval, the certain value may vary. The amplitude or pitch of the corrugations may vary depending on the sheet location in which the measurement is made, that is, at a given location the pitch or amplitude may have a certain value and in another location the pitch or amplitude may have a different value. If this difference is above a threshold, that is, if the amplitude value or pitch value varies more than a certain percentage of its value, then the nip size may be varied, for example to a smaller nip size, so that more stable corrugations are formed.

Preferably, the method includes: removing at least a portion of the sheet on the basis of the evaluated post-crimping characteristic of the sheet. The method preferably includes the step of removing a portion the sheet on the basis of the evaluated post-crimping characteristic of the sheet and the obtained one of the pre-crimping characteristic of the sheet. The sheet can be removed as a whole, or only a portion of the sheet can be removed and the rest of the sheet, without the removed portion, may be further processed. The remaining portion of the sheet, which is further processed, has the post-crimping characteristic of the sheet, such as the post-crimping characteristic of the corrugations, within the desired tolerances. For example, in case the value of the post-crimping characteristic of the sheet is outside a given range in a given portion of the sheet, for a pre-crimping sheet characteristic, the crimped sheet is rejected and not further processed. Alternatively, only the portion of the sheet having a post-crimping characteristic of the sheet outside a given range is cut or otherwise removed. In this way, a portion of crimped sheet outside tolerances is removed from the processing line as soon as possible.

The method preferably includes creating a database comprising the obtained one of the pre crimping characteristic of the sheet in relation to any of: the date of manufacturing of the sheet, an ambient temperature of an environment where the sheet is located during crimping, length of fibers present in the sheet, a humidity of an environment where the sheet is located during crimping, a machinability of the sheet. This database may be used for traceability purpose of the crimped sheet or of the component of the aerosol-generating article manufactured including the crimped sheet. The database may be used to create a correlation between different parameters. In this way, in case some sensors of pre-crimping characteristics or of ambient parameters are not present in the apparatus, from such a database the value of a desired sheet parameter (that is, a pre-crimping characteristic of the sheet) or ambient parameter can be predicted.

Preferably, the method comprises setting a first nip size on the basis of the obtained one of the pre-crimping characteristics of the sheet. The method may further comprise adjusting the first nip size to set a second nip size on the basis of the evaluated post-crimping characteristic of the sheet. Preferably, the adjustment of the nip size is performed in two steps. The nip size is first set at a first value on the basis of pre-crimping characteristics of the sheet. The post-crimping characteristic is then evaluated. If the post-crimping characteristic is not the expected one for the obtained pre crimping characteristic, then the first nip size is adjusted. The first nip size becomes a second nip size. The second nip size is determined on the basis of the post-crimping characteristic. Generally, given the pre-crimping characteristics, the nip size is correctly set, that is, the first nip size is generally a nip size giving a correct crimp level to the sheet. However, in those occasions where the first nip size does not give the correct crimp level, the nip size can be varied after the evaluation of the post-crimping characteristics.

Preferably, the sensor adapted to evaluate one of the pre-crimping characteristics of the sheet includes a sensor adapted to measure the thickness of the sheet. More preferably, the sensor to measure the thickness of the sheet includes a mechanical sensor including a wheel or a skate in contact to the sheet. Preferably, the sensor to measure the thickness of the sheet includes an optical sensor to impinge an electromagnetic beam onto the sheet. Preferably, the sensor to measure the thickness of the sheet includes an interferometer. More than a sensor can be used to measure the thickness of the sheet, for example two or more sensors of the same type, for example two optical sensors, or two or more sensors of different types, for example an optical sensor and a mechanical sensor.

The mechanical sensor may include a wheel rolling on a top surface of the sheet. The mechanical sensor may include a skate in contact with the top surface of the sheet. The height of the wheel or the height of the skate and its variations are preferably checked and compared with the expected thickness of the sheet. The comparison is made within a pre-set tolerance.

The interferometer may include an optical light emitter to impinge a light beam, such as an infrared light beam, onto the sheet of material and onto an additional surface, such as a highly reflective metal surface, placed below the sheet. As the light beam impinges onto the sheet, some of the light is reflected back by the top surface of the sheet, and some light passes through the sheet, and it is reflected by the metal sheet. The reflected light may form an interference pattern, which may be detected. From interferometry, the sheet thickness can be calculated, from the differences in optical path between the light reflected at the top surface of the sheet and the light reflected on the metal surface below the sheet which create interference or phase differences.

The optical sensor may include a LED emitter and a receiver located at the two opposite side of the sheet. The LED may emit a beam of diffused LED light in a parallel, uniform manner on one side of the sheet and the light is detected by the receiver located on the other side of the sheet, for example at a reference roller on which the sheet runs. As the reference roller position is known, the material thickness is computed as the difference between the roll position and the optical sensor measurements.

Preferably, the sensor to evaluate a post-crimping characteristic of the sheet includes a sensor adapted to measure a characteristic of the plurality of corrugations. Preferably, the sensor to evaluate the characteristic of the corrugations on the sheet includes a laser profiler. A laser profiler emits a beam of laser radiation having substantially the shape of a line. The laser profiler is adapted to determine the profile of an object on which the laser line impinges. Preferably, the laser profiler emits a laser line substantially perpendicular to the transport direction of the sheet. Preferably the laser line is long (wide) enough to impinge on several corrugations. The laser profiler is adapted to determine the profile of a cross section of the sheet on a plane perpendicular to the transport direction. Preferably, the laser profile acquires profiles at a given frequency. During the crimping of the sheet, the laser profiler is adapted to form images. The images are formed by sequences of acquisitions by the laser profiler, an acquisition for each laser line impinging the sheet. A laser profiler used in the present invention is for example Keyence LJV7020 using the controller XG-X2800. For the profile obtained by each laser line, the laser profiler is adapted to obtain the mean amplitude. The profile obtained by each laser line includes the profile of several corrugations.

Preferably, the control unit is connected to the laser profiler, the control unit being adapted to determine the amplitude, or the pitch of the profiles obtained by the laser profiler. From the profile of the sheet, the pitch and amplitude of the corrugations formed on the sheet by the first crimping roller and second crimping roller may be determined.

Preferably, the apparatus includes an ambient temperature sensor adapted to measure the ambient temperature of the environment where the sheet is located and to emit a signal representative of the measured ambient temperature. Preferably, the apparatus includes an ambient humidity sensor adapted to measure the ambient relative humidity of the environment where the sheet is located and to emit a signal representative of the measured ambient relative humidity. Preferably, the apparatus includes a stickiness sensor adapted to measure a stickiness of the sheet at a given location and to emit a signal representative of the measured stickiness. The feedback control loop may be adapted to activate the first actuator on the basis of the signal emitted by the ambient temperature sensor. The feedback control loop may be adapted to activate the first actuator on the basis of the signal emitted by the ambient humidity sensor. The feedback control loop may be adapted to activate the first actuator on the basis of the signal emitted by the stickiness sensor. The advantages of having additional sensors has been outlined with reference to the method.

Preferably, the apparatus includes a second actuator to discard at least a portion of the sheet, the feedback control loop system being adapted to activate the second actuator on the basis of the measured pre-crimping characteristic of the sheet or on the basis of the data retrieved relative to one of the pre-crimping characteristics or on the basis of the evaluated post-crimping characteristic. The second actuator may include a reject gate. The second actuator is preferably activated when a sheet or a portion of the sheet needs to be discarded because the post-crimping characteristic of the sheet is not within the prescribed range, given the pre-crimping characteristic.

Preferably, the control unit is in communication with the sensor adapted to measure one of the pre crimping characteristics of the sheet, the laser profiler and the first actuator. Further, the control unit may be adapted to receive input from a user. The control unit may be capable of accessing a memory where the pre-crimping characteristics of the sheet are stored. The control unit may be a microprocessor, a microcontroller or a computer. The control unit preferably is in communication with all pre-crimping sensors and post-crimping sensors present in the apparatus, so that the signals from the sensors can be elaborated centrally. Preferably, the control unit includes a memory where measurements values can be stored. The control unit may also receive inputs from a user, for example via a keyboard, a touchscreen, a pointing device, or buttons.

Preferably, the feedback loop system is adapted to activate the second actuator on the basis of a signal relative to the ambient temperature. Preferably, the feedback loop system is adapted to activate the second actuator on the basis of a signal relative to the ambient relative humidity. Preferably, the feedback loop system is adapted to activate the second actuator on the basis of a signal relative to the stickiness of the sheet. Preferably, the feedback loop system is adapted to activate the second actuator on the basis of a plurality of signals coming from different sensors.

Further advantages of the invention will become apparent from the detailed description thereof with non-limiting reference to the appended drawings:

- Fig. 1 is in a schematic lateral view of an apparatus for the manufacturing of a crimped sheet of material;

- Fig. 2 is a schematic perspective view of the crimping pair of rollers, part of the apparatus of figure 1 ;

- Fig. 3 is a schematic lateral view of the apparatus of figure 1 where the sheet of material has been removed and further details are shown;

- Fig. 4 is a schematic enlarged front view in section of a sheet of material crimped using the apparatus of figures 1 - 3;

- Fig. 5 is a schematic lateral view of a portion of the apparatus of figure 1 with more details;

- Fig. 6 is a schematic top view of a crimped sheet according to the invention; and

- Fig 7 is a graph representing a phase of the method of the invention.

In Fig. 1, the basic layout for an apparatus 1 for manufacturing a crimped sheet of material 10 for an aerosol-generating article (not shown in the drawings) is shown in a schematic lateral view.

The sheet of material is supplied by means of a supply bobbin 3. On the supply bobbin 3, an “endless” sheet of a flat and thin layer of material 2 to be crimped using the apparatus 1 is provided. The material 2 can be a homogenised tobacco sheet. It is to be understood that the sheet of material 2 that is wound up on supply bobbin 3 is strictly speaking not endless, however, the overall length of the sheet of material can be several hundred metres and is therefore much longer than its width. Furthermore, a handover mechanism between two consecutive supply bobbins 3 (not shown) may be provided so that a continuous crimping process is possible.

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 nip 6 is formed. The nip defines a nip size 14. First crimping roller 4 defines a first rotational axis 24. Second crimping roller 5 defines a second rotational axis 25. The first rotational axis 24 and the second rotational axis 25 are each indicated by a cross in figures 1 and 3 and visible in their extension in figure 2. First rotational axis 24 and second rotational axis 25 are preferably parallel and horizontal. Preferably, one of the first crimping roller 4 or second crimping roller 5 rotates clockwise while the other of the first crimping roller or second crimping roller rotates counter-clockwise during operation.

The first crimping roller 4 and second crimping roller 5 show a structured outer surface, including a plurality of ridges or corrugations. The corrugations are not visible in the drawings. It is also possible that a different arrangement is chosen, in particular that only one of the first crimping roller 4 or second crimping roller 5 shows a structured surface.

The sheet 2 is inserted between first crimping roller 4 and second crimping roller 5, in the nip 6, in order to be crimped. Downstream the first crimping roller 4 and second crimping roller 5, a crimped sheet 10 is formed, in which corrugations are created by the pressure applied by the crimping rollers 4, 5.

The sheet 2 is transported towards the first crimping roller 4 and second crimping roller 5 by means of a transport device 7. The transport device 7 defines a transport direction for the sheet 2 which is indicated by arrow 8 in figures 1, 2, 5 and 6.

Upstream of the first crimping roller 4 and second crimping roller 5, a pre-crimping characteristic of the sheet 2 is measured. For example the thickness 11 of the sheet 2 is measured. Apparatus 1 includes a thickness sensor 9 adapted to measure the thickness 11 of sheet 2 in one or more portions of the sheet itself before crimping. Alternatively or in addition, apparatus 1 includes a moisture sensor 90 adapted to measure the moisture of sheet 2 in one or more portions of the sheet itself before crimping.

Further, apparatus 1 includes control unit 100 in communication with thickness sensor 9 and moisture sensor 90. Thickness sensor 9 and moisture sensor 90 are adapted to send one or more signals representative of the thickness 11 and of the moisture, respectively, of the sheet 2 in one or more of sheet’s portions to control unit 100.

Downstream of the first crimping roller 4 and the second crimping roller 5, a sensor to detect a characteristic of the corrugations, such as a laser profiler 12, is located. The sensor 12 is adapted to determine a characteristic of the corrugations, in the example it is adapted to detect the profile of the corrugations formed on the crimped sheet 10 in one or more of its portions. The laser profiler 12 is in communication with control unit 100 and is adapted to send one or more signals representative of the profile of the crimped sheet 10 in one or more of its portions to control unit 100.

As better visible in figure 3, where the sheet of material is not depicted for clarity purposes, the nip 6 between first crimping roller 4 and the second crimping roller 5 is adjustable. Apparatus 1 includes a first actuator, indicated by an arrow 13 in figure 3, which is used to change the nip size 14. The first actuator 13 might change the distance between the first and second rotational axis 24, 25. First actuator 13 is actuated by signals sent by control unit 100.

Apparatus 1 also comprises a second actuator 15, indicated by an arrow in figure 3 only, which is adapted to discard the crimped sheet 10 on the basis of signals produced by the control unit 100 after having received signals from the laser profiler 12. The second actuator 15 is connected to control unit 100, which sends to the second actuator 15 a signal in case the laser profiler 12 detects a profile of the corrugations on the crimped sheet 10 having characteristics outside a given interval.

Apparatus 1 may also comprise a temperature sensor 16 to measure the temperature of the environment where the sheet 2, crimped sheet 10 and apparatus 1 are located; a humidity sensor 17 adapted to measure the relative humidity of the environment where the sheet 2, crimped sheet 10 and apparatus 1 are located; a temperature sensor 19 adapted to measure a temperature of the sheet 2 or of the crimped sheet 10 at a given location. All sensors 16, 17, 19 (visible in figure 3) are connected to control unit 100. Further sensors might be present as well. Further, control unit 100 includes a memory 18 where a database is present. In the database, data such as the composition of the sheet are present.

Further, in the memory 18 other data, such as expected values of characteristics of the corrugations formed by the crimping rollers 4, 5 on the sheet, expected values based on pre crimping characteristics of the sheet, are stored. For example, as shown in fig. 7, three expected amplitudes of the corrugations are shown, each expected amplitude of the corrugations corresponding to a pre-crimping moisture value of the sheet 2. Depending on the measured value of the moisture by sensor 90, a different expected value of the crimping amplitude is expected.

In figure 4, an enlarged view of the crimped sheet 10 is depicted in a front sectional view. The crimped sheet 10 includes a plurality of corrugations, all indicated with 20, which form a “wavy” pattern. The corrugations 20 define a given amplitude 23 and a given pitch 26. The apparatus 1 works according to the method of the invention.

The sheet 2 unwinds from the supply bobbin 3 and enters the nip 6 between the first crimping roller 4 and second crimping roller 5 of the apparatus 1 as a single, flat layer of material 2. The processing of the sheet of material 2 is done in the nip 6 which is formed between the crimping rollers 4, 5 by an appropriate placement of the two crimping rollers 4, 5 at a certain distance by means of the first actuator 13. The size 14 of the nip 6 is typically smaller than the thickness 11 of the entering sheet 2, so that the sheet 2 is slightly compressed in the nip 6.

The nip size 14 is selected according to signals sent by thickness sensor 9 and moisture sensor 90 to control unit 100 which in turn controls the first actuator 13. Using the memory 18 and the data stored therein, and the measured data of thickness or moisture, the control unit 100 retrieves from graphs analogous to the one represented in figure 7 the expected value of the characteristic of the corrugations which are to be formed on the crimped sheet 10 for the measured value of thickness or moisture. The graph of figure 7 is a representation of a look-up table, represented as a graph for clarity purposes. For example, the control unit 100 retrieves the expected value of the amplitude 23 of the corrugations for the measured value of moisture of the sheet. The nip size 14 is thus set accordingly moving actuator 13 so that the expected characteristic of the corrugations is possibly obtained.

Due to the design of the first crimping roller 4 and the second crimping rollers 5, in particular due to the design of the outer surfaces of the crimping rollers 4, 5, the sheet of material 2 that passes through the nip 6 has corrugations formed on it 20. A top view of the corrugations 20 on a portion of the sheet 10 is depicted in figure 6.

The laser profiler 12 detects the profile of the crimped sheet 10 at a given point. In order to detect the profile, a laser line 21 impinges and illuminate the crimped sheet 10 as shown in figure 6. Preferably, the laser line 21 is substantially perpendicular to the transport direction 8. The illumination of the sheet 10 by the laser profiler 12 preferably takes place while the crimped sheet 10 rotates on an idle roller 70 (see figure 5). The laser line 21 is preferably several millimetres long to illuminate more than a corrugation 20. The profile obtained by the laser profiler 12 is similar to the curve depicted in figure 4. The laser profiler 12 illuminates the sheet 10 at a given frequency so as to retrieve several profiles while the crimped sheet 10 moves along the transport direction 8.

For each profile as shown in figure 4, the laser profiler 12 or the control unit 100 calculates the amplitude 23 of the corrugations. Then for each profile, a mean amplitude is calculated. The mean amplitude is the characteristic of the plurality of corrugations 20 of interest. If the mean amplitude is outside a given first range for the given measured moisture, the sensor 12 sends a signal to control unit 100 which in turn sends a signal to the first actuator 13 to change the nip size 14. The mean amplitude may be alternatively calculated directly in the control unit 100.

In case the mean amplitude 23 is outside a second range, the sensor 12 sends a signal to control unit 100 which in turn sends a signal to the second actuator 15 to discard the crimped sheet 10. In case the mean amplitude is calculated directly in the control unit 100, no signal is sent by the sensor 12.

The first actuator 13 may also be operated in order to vary the nip size 14 also on the basis of signals coming from any of sensors 16, 17, 19. The second actuator 15 may also be operated in order to discard the crimped sheet 10 also on the basis of signals coming from any of sensors 16, 17, 19. The signals from sensors 9, 12, 16, 17, 19, 90 are preferably sent to the control unit 100 at a given frequency and during the whole crimping process. Continuous adjustments of the nip size 14 are therefore possible. The control unit 100 defines, together with the sensors 9, 12, 16, 17, 19, 90 a feedback control loop.

If the sheet 10 is not discarded, the crimped sheet 10 is fed to a product bobbin 27, on which the crimped sheet 10 of material is wound up.