A method and unit for laminating a continuous plant- based layer

Abstract

A method for laminating a continuous plant-based layer (S), in particular for the industry of smokers' articles, performed by means of a laminating unit (1) comprising at least one pair of opposite laminating rollers (101, 102, 201, 202) defining between them a passage gap (103, 203). The method comprises a step of detecting at least one actual thickness value of the continuous layer (S) at the outlet from the gap (103, 203) in at least one measurement point (Pa, P2) by means of at least one measurement device (104, 204), and a step of adjusting the amplitude (A) of the gap (103, 203) as a function of the at least one measured actual thickness value: the adjustment being made by means of reciprocal movement between the rollers (101, 102, 201, 202) of the respective pair of rollers.

Description

[0001] DESCRIPTION

[0002] A METHOD AND UNIT FOR LAMINATING A CONTINUOUS PLANTBASED LAYER

[0003] Technical field

[0004] The present invention relates to a method and a unit for laminating a continuous plant-based layer, in particular for the industry of smokers’ articles.

[0005] Background art

[0006] In the relevant field of the present invention, laminating a continuous plantbased layer is known, where the expression "plant-based" is intended to mean a material (tobacco or non-tobacco) obtained by grinding or other similar procedure to modify the grain size thereof so as to promote subsequent mixing treatments. In particular, it is intended that the continuous layer is a semi-finished product obtained from the mixture and processing of at least one dry plant-based component made of fibers and / or powder, such as, for example, tobacco or non-tobacco (cellulose or cellulose derivatives, rapeseed, hemp, straw or other varieties, hemp, aromatic leaves or others) with a moist component, such as, for example, water and one or more additives, according to the generality of the invention. In particular, lamination is a fundamental process for producing continuous layers. This process takes place through a unit comprising at least one pair of opposite laminating rollers, defining between them a passage gap, through which the material is passed for processing into a continuous layer having a calibrated thickness (laminate).

[0007] Typically, the pair of rollers consists of a fixed upper roller and an adjustable lower roller: the lower roller may be moved closer towards or further away from the upper roller to vary the amplitude of the gap between the two rollers. This adjustment is vital for controlling the thickness of the laminated material. The adjustment of the amplitude of the gap is performed as a function of the format or one or more measurements performed on the thickness of the laminated material at the outlet from the respective pair of rollers.

[0008] As is known, the measurement of the thickness of the continuous layer occurs offline. In other words, the operators of the laminating process stop the laminating apparatus to take a sample of the laminated material and measure it. Based on the results of these measurements, the operators adjust the amplitude of the gap to obtain the desired thickness of the laminated material.

[0009] The Applicant has observed that, although widely used, the aforesaid adjustment system has disadvantages, which make the use thereof not without drawbacks.

[0010] Firstly, the offline measurements require the suspension of the laminating apparatus to take and measure the continuous layer sample. This results in interruptions in production and reduced process efficiency. Indeed, each time the apparatus is shut down and restarted, there are production delays and additional resources are consumed. Furthermore, restarting the apparatus may be complicated and require complex procedures, further increasing the production downtime.

[0011] Secondly, since the measurements are performed offline, the adjustment of the amplitude of the lamination gap cannot be performed continuously and systematically. This leads to a lack of real-time control over the thickness of the laminated material. Variations in the supply material or in the operating conditions may influence the thickness of the continuous layer without the operators noticing until the next offline measurement. Consequently, discrepancies may arise in the quality of the product, as well as an increase in waste.

[0012] Again, interruptions in production, the need for offline measurements, and the production of waste as a result of material damage contribute to additional costs and material waste. This may reduce the overall profitability of the laminating process and influence the competitiveness of the product on the market.

[0013] Disclosure of the invention

[0014] In said context, the technical task of the present invention is therefore to provide a method and a unit for laminating a continuous plant-based layer, specifically for the industry of smokers’ articles, which are without the drawbacks present in the prior art.

[0015] It is therefore the object of the present invention to provide a method and a unit for laminating a continuous plant-based layer, specifically for the industry of smokers’ articles, which are capable of obtaining a qualitatively satisfactory finished product.

[0016] It is a further object of the present invention to provide a method and a unit for laminating a continuous plant-based layer, specifically for the industry of smokers’ articles, which are capable of ensuring an efficient and less costly process.

[0017] The specified technical task and the specified objects are substantially achieved by a method for laminating a continuous plant-based layer, specifically for the industry of smokers’ articles, performed by a laminating unit comprising at least one pair of opposite laminating rollers defining between them a passage gap. The method comprises a step of measuring at least one actual thickness value of the continuous layer at the outlet from the gap in at least one measurement point by means of at least one measurement device, and a subsequent step of adjusting the amplitude of the gap as a function of the at least one measured actual thickness value: the adjustment is thus performed by reciprocal movement between the rollers of the pair of rollers. Said measurement of the at least one actual thickness value of the continuous layer is performed in-line on the continuous web, thus on the continuous web during the processing step. In particular, said measurement step is performed whilst the web advances along the advancement plane thereof at the outlet from the gap and preferably within a maximum distance of 50 cm from the outlet of the gap.

[0018] The Applicant has observed that the aforesaid laminating system is more efficient, precise, and reliable, whilst simultaneously ensuring a reduction in operating costs. In fact, said system eliminates the need for interruptions in production to collect material samples, allowing continuous operation of the laminating unit and increasing the efficiency of the production process. This results in greater production and reduced downtime, improving the overall profitability of the operation.

[0019] Furthermore, by virtue of the real-time measurement of the thickness of the continuous layer, it is possible to monitor and control the laminating process with greater precision and reactivity. In fact, it is possible to immediately adjust the amplitude of the lamination gap to compensate for any variations in the supply material or operating conditions, ensuring the consistency of the thickness of the laminated material and the quality of the final product.

[0020] Again, said system ensures the option of collecting and analyzing data in real time, providing detailed information on process performance and trends over time. This allows continuously improving the process through data-based optimizations and adjustments, contributing to maximizing operational efficiency and product quality in the long term.

[0021] The method according to the present invention may also comprise one or more of the technical aspects, outlined below.

[0022] According to an aspect, the method may be performed in a fully automated manner or only in a partially automated manner.

[0023] According to a first example, the laminating unit operates in a fully automated manner and may comprise:

[0024] - a movement device connected to the pair of rollers and configured to vary the amplitude of the passage gap in such a way as to modify the thickness of the continuous layer at the outlet from the pair of rollers, in particular by reciprocal movement towards and away from each other between the rollers of the pair of rollers; - at least one measurement device positioned downstream of the pair of rollers and configured to measure an actual thickness value of the continuous layer at the outlet from the gap at a respective measurement point and to generate at least one corresponding measurement signal; and

[0025] - a control unit, connected to the movement device and the measurement device, and configured to receive the measurement signal and to control the movement device as a function of the received measurement signal. According to a second example, the laminating unit operates only in a partially automated manner. According to said example, the actuation of the movement device is carried out manually by one or more operators.

[0026] The fully automated embodiments will be described below in the present description.

[0027] According to an aspect, the measurement of the actual thickness value may be performed at a plurality of measurement points of the continuous layer, distributed transversely relative to the advancement direction of the continuous layer.

[0028] In other words, the unit may comprise two or more measurement devices distributed transversely relative to the advancement direction of the continuous layer at the outlet from the respective pair of rollers, in such a way as to measure a plurality of actual thickness values at respective measurement points of the continuous layer and to generate respective measurement signals: the control unit is configured to control the movement device as a function of said received measurement signals.

[0029] Advantageously, said technical feature offers the advantage of a more complete and accurate assessment of the thickness of the laminated material. In fact, by distributing the measurement points transversely relative to the advancement direction of the layer, it is possible to detect localized variations in thickness, contributing to ensuring greater consistency and uniformity of the thickness of the laminated material across the entire amplitude, and thus improving the quality of the final product. According to an embodiment, the measurement of the actual thickness value may be performed at two measurement points, positioned symmetrically relative to a longitudinal mid-plane of the continuous layer and in particular positioned close to the lateral edges of the continuous layer. Preferably, the measurement of the actual thickness value is performed at two measurement points, positioned symmetrically relative to a longitudinal mid-plane of the continuous layer and in particular at a distance comprised between 5 mm and 800 mm, preferably comprised between 10 mm and 600 mm, from the lateral edges of the continuous layer. In other words, the unit may comprise two measurement devices positioned symmetrically relative to a longitudinal mid-plane of the continuous layer and preferably close to opposite lateral edges of the continuous layer, in particular at a distance comprised between 5 mm and 800 mm, preferably comprised between 10 mm and 600 mm from the lateral edges of the continuous layer.

[0030] According to alternative embodiments, the measurement of the actual thickness value is performed at three or more measurement points, preferably mutually equidistant and distributed transversely relative to the advancement direction of the continuous layer.

[0031] According to alternative embodiments, the detection of the actual thickness value is performed at a single measurement point.

[0032] In general, increasing the number of measurement points on the web makes the measurement more accurate to the benefit of the final product quality, but necessarily increases the costs of the system.

[0033] According to an aspect, independently of the number of measurement points used for measuring the actual thickness value of the continuous layer, the measurement of the actual thickness value may be performed by a single measurement sensor or, preferably, by a respective pair of measurement sensors for each measurement point.

[0034] In other words, preferably, each measurement device of the laminating unit comprises a pair of measurement sensors for each measurement point, each configured to generate a respective measurement signal: the control unit is thus configured to receive and process said measurement signals, obtaining an actual thickness value of the continuous layer at the measurement point.

[0035] If the detection of the actual thickness value is performed by a respective pair of measurement sensors for each measurement point, it may be performed while the continuous layer is adhered to one of the rollers of the pair of rollers, or it may be performed while the continuous layer is moving in suspension at the outlet from the pair of rollers.

[0036] Regarding the first type of measurement, i.e. when the continuous layer is adhered to one of the rollers of the pair of rollers, the at least one measurement device may comprise a differential measurement device equipped with a first measurement sensor and a second measurement sensor. The first measurement sensor, preferably an optical and / or laser sensor, faces a roller of the pair of rollers in such a way as to optically detect a first surface of the continuous layer positioned with the second surface thereof, opposite the first surface, adhering to said roller so as to detect the position of said first surface of the continuous layer, whilst the second measurement sensor, preferably by penetrating radiation and / or an eddy current sensor, instead faces said roller of the pair of rollers and is configured to detect the outer surface of said roller in such a way as to detect the position of said outer surface of the roller: the step of detecting the actual thickness value comprises a step of processing respective measurement signals received from the first and second measurement sensors to obtain the instantaneous thickness value.

[0037] In other words, by measuring the distance between these two surfaces, the system calculates the instantaneous value of the thickness of the continuous layer. This approach allows obtaining an accurate and reliable measurement of the thickness, reducing the effects of any variations or defects in the surface of the roller or of the laminated layer. In short, the measurement occurs by the difference of the two measurements, allowing obtaining a more precise and consistent thickness value.

[0038] Regarding the second type of measurement, that is when the continuous layer is moved in suspension at the outlet from the pair of rollers, the at least one measuring device may comprise an opposing measuring device equipped with a first measuring sensor and a second measuring sensor.

[0039] The first measuring sensor, preferably an optical and / or laser sensor, is configured and / or positioned to face a first surface of the continuous layer, whilst the second measuring sensor, preferably an optical and / or laser sensor, configured and / or positioned to face a second surface of the continuous layer, opposite the first surface: the step of measuring the actual thickness value comprises a step of processing respective measurement signals received from said first and second measurement sensors to obtain the instantaneous thickness value.

[0040] Preferably, the first and second sensors are operational on the same point (but on opposite surfaces). Furthermore, preferably, the laser is of the triangulation type for determining a position of the point on the surface (distance in a direction perpendicular to the plane of the continuous layer). According to an aspect, the method may comprise a step of processing a plurality of measurement signals emitted by the at least one measurement device to obtain a temporal trend of the actual thickness value.

[0041] Advantageously, by tracking the temporal trend of the thickness value, it is possible to prevent the formation of product defects due to uncontrolled variations in the thickness of the continuous layer. For example, a progressive increase in thickness could indicate malfunctioning of the rollers (caused, for example, by the progressive deformation of the rollers or by distancing due to the roller fastening system), allowing operators to intervene before significant defects arise.

[0042] Preferably, the step of processing the plurality of measurement signals may further comprise a sub-step of filtering the measurement signals for eliminating outlier events and / or surface roughness components of the continuous layer. In other words, the sub-step of filtering the signals measured by the sensors serves to eliminate undesired or non-representative information from the measurement data. This may include the elimination of anomalous signals (outliers), which could be caused by measurement errors or sudden variations in the thickness of the continuous layer. Additionally, it may also include the removal of surface roughness components, i.e., variations in the surface profile of the continuous layer, which might not be relevant for measuring the actual thickness of the material. Advantageously, said technical feature contributes to improving the reliability and accuracy of the thickness measurements, reducing the risk of errors or distortions caused by anomalous signals.

[0043] According to an aspect, independently of how the step of measuring the actual value of the continuous layer is performed, the step of adjusting the gap may be actuated when the actual thickness measured is external to a predetermined reference range and / or is kept externally at the range for a predetermined time interval. In other words, if the measured actual thickness of the continuous layer significantly deviates from the desired thickness for a certain period of time, the system may automatically activate the adjustment of the amplitude of the gap to correct the discrepancy. This helps to maintain the thickness of the laminated material within the desired limits and to ensure a more uniform and consistent production.

[0044] Functionally, according to an aspect, at least one of the rollers of the at least one pair of rollers is an adjustable roller supported by end supports, and the adjustment of the amplitude of the gap as a function of the processed signal is performed by independently moving the end supports of the adjustable roller.

[0045] In other words, at least one of the rollers of the at least one pair of rollers may be an adjustable roller supported by end supports, whilst the movement device comprises a first actuator connected to a first of the end supports and a second actuator connected to the other end support: the control unit is thus configured to independently control the first actuator and the second actuator.

[0046] Advantageously, the use of independent actuators allows for an accurate and targeted adjustment of the amplitude of the passage gap along the amplitude of the continuous layer. This means that it is possible to compensate for localized variations in the thickness of the material or in the profile of the roller, ensuring a uniform and consistent thickness of the laminated material. This technical feature is particularly advantageous when combined with the use of at least two measurement points distributed along an amplitude of the continuous layer. In fact, the use of multiple sensors distributed along the amplitude of the continuous layer allows the system to detect localized variations in the thickness of the material more accurately. These sensors provide detailed information on any irregularities along the amplitude of the material, allowing the actuators to compensate for and correct these variations in real time.

[0047] According to an embodiment, each actuator is a linear actuator, preferably of the worm screw type or male-and-female type.

[0048] According to an aspect, the adjustment of the amplitude of the passage gap may be used to ensure the desired thickness during the operational steps when the format has been previously set. However, advantageously, the method may comprise a format adjustment step performed by simultaneously moving the end supports of the adjustable roller to set a nominal amplitude suitable for a different format. Said format adjustment step may be performed before starting the laminating process or during the laminating process.

[0049] According to an aspect, the laminating may be performed through a single laminating stage or, preferably, the laminating may be performed by a plurality of laminating stages, each comprising a respective pair of opposed laminating rollers defining a respective passage gap.

[0050] According to the second case, namely with the presence of multiple laminating stages in series, the adjustment of the amplitude of the gap in each laminating stage may be performed as a function of the actual thickness of the web at the outlet from the respective gap. Preferably, the adjustment in each step may be made independently with respect to the other steps.

[0051] According to an exemplary embodiment, the adjustment of the amplitude of the gap in the final laminating stage, positioned further downstream, is performed as a function of the actual thickness value of the web at the outlet from the final laminating stage and measured by the aforesaid opposing measurement device, in which the adjustment of the amplitude of the gap in each preceding laminating stage is performed as a function of the actual thickness value of the web at the outlet from the preceding laminating stage and measured by the aforesaid differential measurement device.

[0052] The specified technical task and the specified objects are further substantially achieved by a unit for laminating a continuous plant-based layer, in particular for the industry of smokers’ articles.

[0053] Preferably, the unit is suitable for carrying out the aforesaid method according to the description.

[0054] According to an aspect, the unit may comprise at least one accessory distance sensor, connected to the control unit and configured to detect the actual distance between the rollers of at least one pair of rollers. In particular, said at least one accessory distance sensor is configured to measure an absolute displacement of the adjustable roller with respect to a reference position. Preferably, said reference position corresponds to the mechanical contact state between the cylindrical surfaces of the lower roller and the upper roller, defining a nominal zero gap.

[0055] Preferably, the unit comprises at least one pair of accessory distance sensors.

[0056] Preferably, the at least one accessory distance sensor is of the indirect contact probe, linear or optical encoder type.

[0057] Functionally, the at least one accessory distance sensor generates positional feedback signals proportional to the actual distance measured between the instantaneous position of the adjustable roller and the aforesaid zero position. This configuration allows for a direct and continuous measurement of the actual amplitude of the gap with micrometric resolution.

[0058] According to said embodiment, the control unit may therefore be configured to receive, as input, the measurements performed by the at least one accessory distance sensor and compare said measurement with the displacement commanded to the actuators.

[0059] The control unit may therefore be configured to determine any discrepancies due to mechanical play, slippage, or wear of the transmission members and implement a closed-loop control cycle, which integrates the thickness data detected by the aforesaid measuring devices with the positional data detected by the at least one accessory distance sensor, ensuring that the adjustment of the gap corresponds to the calculated theoretical variation.

[0060] Advantageously, the adoption of the at least one accessory distance sensor dedicated to the direct measurement of the amplitude of the gap introduces significant systemic improvements. Said devices, coupled to the adjustment actuators, enable a closed feedback control, which verifies, in real-time, the correspondence between the commanded displacement and the actual position taken by the movable roller with respect to the zero contact reference. This eliminates cumulative errors resulting from mechanical clearances, hysteresis of the transmission members, or thermal slippage, increasing the repeatability of the adjustment. The synergy between indirect measurement of the laminate thickness and direct verification of the mechanical geometry reduces dimensional waste, identifies phenomena of early wear in the actuators, decreasing unplanned downtime for corrective maintenance.

[0061] Further features and advantages of the present invention will become clearer from the indicative, and therefore non-limiting, description of an embodiment of a method and a unit for laminating a continuous plantbased layer, particularly for the industry of smokers’ articles.

[0062] Brief description of drawings

[0063] Said description will be presented below with reference to the attached drawings provided purely for indicative purposes and, therefore, nonlimiting, in which:

[0064] - figure 1 shows a diagrammatic side view of a laminating unit in an operational step according to the present invention;

[0065] - figure 2 shows a diagrammatic top view of a detail (first laminating stage) of the laminating unit in figure 1 in an operational step;

[0066] - figure 3 shows a diagrammatic front view of a detail (first laminating stage) of the laminating unit in figure 1 in a non-operational step.

[0067] Detailed description of preferred embodiments of the invention

[0068] The method for laminating a continuous plant-based layer, in particular of the smoking articles industry, will now be described in an embodiment thereof with reference to the laminating unit 1 used to implement it.

[0069] The continuous layer "S" according to the present invention is a layer based on material of plant origin. In the present description, the expression "plant origin" is intended to mean a plant-based material (tobacco or non-tobacco) processed by grinding or other similar procedure to modify the granularity thereof so as to promote subsequent mixture treatments. In particular, it is intended to mean that the continuous layer is a semi-finished product obtained from the mixture and processing of at least one dry plant component, such as, for example tobacco or nontobacco (rapeseed, hemp, straw or other varieties, cellulose or cellulose derivatives, hemp, aromatic leaves or others) with a wet component, such as, for example, water and one or more additives, according to the generality of the invention.

[0070] In the embodiment illustrated for exemplary and therefore non-limiting purposes, unit 1 comprises a first laminating stage 100 and a second laminating stage 200: the first laminating stage 100 comprises a respective upper roller 101 and a respective lower roller 102, whilst the second laminating stage 200 comprises a respective upper roller 201 and a respective lower roller 202.

[0071] The rollers 101 , 102 of the first laminating stage 100 are opposed to each other and define between them a passage gap 103, and are configured to perform a lamination of a material "M" obtaining a continuous layer "S".

[0072] The term "material" is intended to mean a generic semi-finished product, which may be in the form of a slurry, in the form of a continuous layer, or in the form of discrete portions. In the illustrated embodiment, the material "M" is a continuous layer carried by a conveyor belt 300.

[0073] The upper roller 101 is a fixed roller, while the lower roller 102 is an adjustable roller. In particular, unit 1 comprises a movement device 10 connected to the pair of rollers 101 , 102 of the first lamination step 100 and configured to vary the amplitude "A" of the passage gap 103 so as to modify the thickness of the continuous layer "S" at the outlet from the pair of rollers 101 , 102, in particular by reciprocal movement towards and away from each other between the rollers 101 , 102.

[0074] The first lamination step 100 is associated with at least one measurement device 104 arranged downstream of the pair of rollers 101 , 102 and configured to detect an actual thickness value of the continuous layer "S" at the outlet from the gap 103 at a respective measurement point "P1" and to generate at least one corresponding measurement signal.

[0075] Unit 1 comprises a control unit "U", connected to the movement device 10 and the measurement device 104, and configured to receive the measurement signal and to control the movement device 10 as a function of the received measurement signal.

[0076] As shown in figure 2, the measurement of the actual thickness value is performed at two measurement points "P1" of the continuous layer "S", distributed transversely relative to the advancement direction of the continuous layer "S". For this purpose, unit 1 comprises two measurement devices 104 distributed transversely relative to the feeding direction of the continuous layer "S" at the outlet from the respective pair of rollers 101 , 102, so as to detect a plurality of actual thickness values at respective measurement points "P1" of the continuous layer "S" and to generate respective measurement signals. The control unit "U" is configured to control the movement device 10 as a function of the received measurement signals.

[0077] Preferably, the measurement of the actual thickness value is performed at two measurement points "P1" positioned symmetrically relative to a longitudinal mid-plane of the continuous layer "S" and in particular positioned close to the lateral edges of the continuous layer "S", preferably at a distance comprised between 5 mm and 800 mm, preferably comprised between 10 mm and 600 mm, from the lateral edges of the continuous layer "S". For this purpose, the two measurement devices 104 are positioned symmetrically relative to the longitudinal mid-plane of the continuous layer "S" and preferably close to opposite lateral edges of the continuous layer "S", in particular at a distance comprised between 5 mm and 800 mm, preferably comprised between 10 mm and 600 mm, from the lateral edges of the continuous layer "S".

[0078] Furthermore, preferably, the measurement of the actual thickness value in at least one measurement point "P1" is performed by means of a respective pair of measurement sensors 104a, 104b for each measurement point "P1". For this purpose, each measurement device 104 comprises a pair of measurement sensors 104a, 104b for each measurement point "P1", each configured to generate a respective measurement signal: the control unit "U" is configured to receive and process the measurement signals, obtaining an actual thickness value of the continuous layer "S" at the respective measurement point "P1 ".

[0079] Preferably, downstream of the first laminating stage 100, the measurement of the actual thickness value at the two measurement points "P1" is performed whilst the continuous layer "S" is adhered to the lower roller 102 of the respective pair of rollers 101 , 102.

[0080] For this purpose, each measurement device 104 is a differential measurement device equipped with a respective first measurement sensor 104a and a respective second measurement sensor 104b.

[0081] The first measurement sensor 104a, preferably an optical and / or laser sensor, faces the lower roller 102 in such a way as to optically detect a first surface of the continuous layer "S" positioned with the relative second surface, opposite the first surface, adhering to the lower roller 102 in such a way as to detect the position of the first surface of the continuous layer "S" whilst the second measurement sensor 104b, preferably by penetrating radiation and / or an eddy current sensor, faces the lower roller 102 and is configured to detect the outer surface of the lower roller 102 in such a way as to detect the position of the outer surface of the lower roller 102.

[0082] As shown in figure 3, in relation to the adjustment of the amplitude "A" of the gap 103, the movement device 10 comprises a first actuator 10a connected to a first end support 102a of the lower roller 102 and a second actuator 10b connected to a second end support 102b of the lower roller 102. The two actuators 10a, 10b can be independently controlled by the control unit "U" as a function of the measurement signals. Preferably, each actuator 10a, 10b is a linear actuator, preferably of the worm screw type or male-and-female type.

[0083] Downstream of the first laminating stage 100, the continuous layer "S" produced is supported by a conveyor belt 400 configured to carry the continuous layer "S" from the first laminating stage 100 to the second laminating stage 200.

[0084] The rollers 201 , 202 of the second laminating stage 200 are opposed to each other and define between them a passage gap 203, and are configured to perform a lamination of the continuous layer "S" deriving from the first laminating stage 100. The upper roller 201 is a fixed roller, whilst the lower roller 202 is an adjustable roller. In particular, the unit 1 comprises a movement device 10 connected to the pair of rollers 201 , 202 of the second laminating stage 200 and configured to vary the amplitude "A" of the passage gap 203, thereby modifying the thickness of the continuous layer "S" at the outlet from the pair of rollers 201 , 202, in particular by reciprocal movement towards and away from each other between the rollers 201 , 202.

[0085] The second laminating stage 200 is associated with at least one measurement device 204 positioned downstream of the pair of rollers 201 , 202 and configured to measure an actual thickness value of the continuous layer "S" at the outlet from the gap 203 at a respective measurement point "P2" and to generate at least one corresponding measurement signal.

[0086] The control unit "U" is connected to the movement device 10 and to the at least one measurement device 204 and configured to receive the measurement signal and control the movement device 10 as a function of the received measurement signal.

[0087] Preferably, the measurement of the actual thickness value is performed at two measurement points "P2" positioned symmetrically relative to a longitudinal mid-plane of the continuous layer "S" and, specifically, positioned close to the lateral edges of the continuous layer "S", preferably at a distance comprised between 5 mm and 800 mm, preferably comprised between 10 mm and 600 mm from the lateral edges of the continuous layer "S". For this purpose, the two measurement devices 204 are positioned symmetrically relative to the longitudinal mid-plane of the continuous layer "S" and preferably close to opposite lateral edges of the continuous layer "S", in particular at a distance comprised between 5 mm and 800 mm, preferably comprised between 10 mm and 600 mm from the lateral edges of the continuous layer "S".

[0088] Alternatively, the measurement of the actual thickness value may be performed at a single measurement point. Preferably, said measurement point is positioned close to the longitudinal mid-plane line of the continuous layer "S".

[0089] Furthermore, preferably, the measurement of the actual thickness value in at least one measurement point "P2" is performed by a respective pair of measurement sensors 204a, 204b for each measurement point "P2". For this purpose, each measurement device 204 comprises a pair of measurement sensors 204a, 204b for each measurement point "P2", each configured to generate a respective measurement signal: the control unit "U" is configured to receive and process the measurement signals, obtaining an actual thickness value of the continuous layer "S" at the respective measurement point "P2".

[0090] Preferably, downstream of the second laminating stage 200, the measurement of at least one actual thickness value at the two measurement points "P2" is performed whilst the continuous layer "S" is moving in suspension at the outlet from the pair of rollers 201 , 202.

[0091] For this purpose, each measurement device 204 is an opposing measurement device equipped with a respective first measurement sensor 204a and a respective second measurement sensor 204b.

[0092] The first measurement sensor 204a, preferably an optical and / or laser sensor, is configured and / or positioned to face a first surface of the continuous layer "S" whilst the second measurement sensor 204b, preferably an optical and / or laser sensor, is configured and / or positioned to face a second surface of the continuous layer "S", opposite the first surface. The step of measuring the actual thickness value therefore comprises a step of processing respective measurement signals received from the first and second measurement sensors 204a, 204b to obtain the instantaneous thickness value.

[0093] With regard to the adjustment of the amplitude "A" of the gap 203 of the second laminating stage 200, the movement device 10 substantially has the same structure already described with reference to the first laminating stage 100. In particular, the movement device comprises a first actuator connected to a first end support of the lower roller and a second actuator connected to a second end support of the lower roller. The two actuators can be independently controlled by the control unit "U" as a function of the measurement signals. Preferably, each actuator is a linear actuator preferably of the worm screw type or male-and-female type. Downstream of the second laminating stage 200, the continuous layer "S" is supported and conveyed to the outlet by a conveyor 500.

[0094] Preferably, the adjustment of the two laminating stages 100, 200 takes place independently. At a functional level, for each laminating stage 100, 200, a thickness value may be set at the outlet of the respective pair of laminating rollers 101 , 102, 201 , 202.

[0095] For the first laminating stage 100, the movement device 10 therefore adjusts the amplitude "A" of the gap 103 by moving the lower roller 102 with respect to the upper roller 101 based on the actual thickness value of the continuous layer "S" measured by means of the measurement devices 104 at the respective measurement points "P1 ".

[0096] For the second laminating stage 200, the movement device 10 therefore adjusts the amplitude "A" of the gap 203 by moving the lower roller 202 with respect to the upper roller 201 based on the actual thickness value of the continuous layer "S" measured by means of the measurement devices 204 at the respective measurement points "P2".

[0097] Preferably, there is provided a step of storing a plurality of actual thickness values measured in sequence at a determined measurement point "P1", "P2" and a subsequent step of determining, by means of the control unit "U", a trend of the actual thickness value at the determined measurement point "P1", "P2" for a predetermined observation period.

[0098] Preferably, the method further comprises a step of processing a plurality of measurement signals emitted by the at least one measurement device 104, 204 to obtain a temporal trend of the actual thickness value. Preferably, the step of processing the plurality of measurement signals comprises filtering the measurement signals for eliminating outlier events and / or surface roughness components of the continuous layer "S". Finally, according to an aspect, a step of adjusting the format may be involved, actuated by simultaneously moving the end supports of the adjustable roller for setting a nominal amplitude "A" suitable for a different format. According to this step, the format adjustment may be performed for one or both laminating stages by means of the aforesaid moving device. Said format adjustment step may be performed before starting the system or when the system is operational.

Claims

CLAIMS1. A method for laminating a continuous plant-based layer (S), in particular for the industry of smokers’ articles, carried out by a laminating unit (1 ) comprising at least one pair of opposing laminating rollers (101 , 102, 201 , 202) defining between them a passage gap (103, 203), comprising the following steps:- measuring in line at least one actual thickness value of said continuous layer (S) at the outlet from said gap (103, 203) at least at one measurement point (P1 , P2) using at least one measurement device (104, 204);- adjusting the amplitude (A) of said gap (103, 203) as a function of said at least one actual thickness value measured, said adjustment being performed by reciprocal movement between the rollers (101 , 102, 201 ,202) of said pair of rollers (101 , 102, 201 , 202).

2. The method according to claim 1 , wherein said measurement of the actual thickness value is performed at a plurality of measurement points (P1 , P2) of said continuous layer (S), distributed transversely relative to the advancement direction of said continuous layer (S).

3. The method according to claim 2, wherein said measurement of the actual thickness value is performed at two measurement points (P1 , P2), positioned symmetrically relative to a longitudinal mid-plane of said continuous layer (S) and in particular positioned close to the lateral edges of the continuous layer (S), preferably at a distance of between 5 mm and 800 mm from the lateral edges of the continuous layer (S).

4. The method according to any one of the preceding claims, wherein at least one of the rollers (102, 202) of said at least one pair of rollers (101 , 102, 201 , 202) is an adjustable roller supported by end supports (102a, 102b) and wherein said adjustment of the amplitude (A) of the gap (103,203) as a function of said processed signal is performed by independently moving said end supports (102a, 102b) of the adjustable roller (102, 202).

5. The method according to claim 4, also comprising a step of adjustingthe format actuated by simultaneously moving said end supports (102a, 102b) of the adjustable roller (102, 202) for setting a nominal amplitude (A) suitable for a different format.

6. The method according to any one of the preceding claims, wherein said measurement of the actual thickness value at least at one measurement point (P1 , P2) is performed by means of a respective pair of measurement sensors (104a, 104b, 204a, 204b) for each measurement point (P1 , P2).

7. The method according to any one of the preceding claims, wherein said measurement of at least one actual thickness value at least at one measurement point (P1 ) is performed whilst the continuous layer (S) is adhered to one of the rollers (102, 202) of said pair of rollers (101 , 102, 201 , 202).

8. The method according to claim 7, wherein said at least one measurement device (104) comprises a differential measurement device equipped with:- a first measurement sensor (104a), preferably an optical and / or laser sensor, facing a roller (102) of the pair of rollers (101 , 102) in such a way as to optically detect a first surface of the continuous layer (S) positioned with the relative second surface, opposite the first surface, adhering to said roller (102) in such a way as to detect the position of said first surface of the continuous layer (S);- a second measurement sensor (104b), preferably by penetrating radiation and / or an eddy current sensor, facing said roller (102) of the pair of rollers (101 , 102) and configured for detecting the outer surface of said roller (102) in such a way as to detect the position of said outer surface of the roller (102); and wherein the step of measuring the actual thickness value comprises a step of processing respective measurement signals received from said first and second measurement sensors (104a, 104b) to obtain the instantaneous thickness value.

9. The method according to any one of the preceding claims, wherein saidmeasurement of at least one actual thickness value at least at one measurement point (P2) is performed whilst said continuous layer (S) is moved in suspension at the outfeed from said pair of rollers (201 , 202)10. The method according to claim 9, wherein said at least one measurement device (204) comprises an opposing measurement device equipped with:- a first measurement sensor (204a), preferably an optical and / or laser sensor, configured and / or positioned to face a first surface of the continuous layer (S);- a second measurement sensor (204b), preferably an optical and / or laser sensor, configured and / or positioned to face a second surface of said continuous layer (S), opposite said first surface; and wherein the step of measuring the actual thickness value comprises a step of processing respective measurement signals received from said first and second measurement sensors (204a, 204b) to obtain the instantaneous thickness value.11 . The method according to any one of the preceding claims, also comprising a step of storing a plurality of actual thickness values measured in succession at a predetermined measurement point (P1 , P2) and a subsequent step of determining, using the control unit (U), a trend of said actual thickness value at said predetermined measurement point (P1 , P2) for a predetermined observation period.

12. The method according to any one of the preceding claims, also comprising a step of processing a plurality of measurement signals emitted by said at least one measurement device (104, 204) to obtain a time trend of said actual thickness value.

13. The method according to claim 12, wherein said step of processing the plurality of measurement signals comprises filtering said measurement signals for eliminating outlier events and / or surface roughness components of the continuous layer (S).

14. The method according to any one of the preceding claims, wherein thelaminating is performed by means of a plurality of laminating stages (100, 200), each comprising a respective pair of opposite laminating rollers (101 , 102, 201 , 202) defining a respective passage gap (103, 203); and wherein said adjustment of the amplitude of the gap (103, 203) in each laminating stage (100, 200) is performed as a function of the actual thickness of the continuous layer (S) at the outlet from the respective gap (103, 203), preferably the adjustment in each laminating stage (100, 200) being performed independently with respect to the other laminating stages (100, 200).

15. The method according to claims 8, 10 and 14, wherein the adjustment of the amplitude (A) of the gap (203) in the final laminating stage (200), positioned further downstream, is performed according to the actual thickness value of the continuous layer (S) at the outlet from the final laminating stage (200) and measured by means of said opposing measurement device (204), and wherein the adjustment of the amplitude (A) of the gap (103) in each previous laminating stage (100) is performed according to the actual thickness value of the continuous layer (S) at the outlet from said previous laminating stage (100) and measured by means of said differential measurement device (104).

16. A unit (1 ) for laminating a continuous plant-based layer (S), in particular for the industry of smokers’ articles, comprising:- at least one pair of opposite laminating rollers (101 , 102, 201 , 202) defining between them a passage gap (103, 203) and configured for laminating a material to obtain a continuous layer (S);- a movement device (10) connected to said pair of rollers (101 , 102, 201 , 202) and configured for varying the amplitude (A) of said passage gap (103, 203) so as to modify the thickness of said continuous layer (S) at the outfeed from the pair of rollers (101 , 102, 201 , 202), in particular by reciprocal movement towards and away from each other between the rollers (101 , 102, 201 , 202) of said pair of rollers (101 , 102, 201 , 202);- at least one measurement device (104, 204) positioned downstream ofsaid pair of rollers (101 , 102, 201 , 202) and configured for measuring in line an actual thickness value of said continuous layer (S) coming out from the gap (103, 203) at a respective measurement point (P1 , P2) and for generating at least one corresponding measurement signal;- a control unit (U), connected to said movement device (10) and to said measurement device (104, 204) and configured to receive said measurement signal and to control said movement device (10) as a function of said measurement signal received.

17. The unit (1 ) according to claim 16, comprising two or more measurement devices (104, 204) distributed transversally relative to the advancement direction of said continuous layer (S) at the outlet from said pair of rollers (101 , 102, 201 , 202) so as to measure a plurality of actual thickness values at respective measurement points (P1 , P2) of said continuous layer (S) and to generate respective measurement signals; and wherein the control unit (U) is configured to control said movement device (10) as a function of said measurement signals received.

18. The unit (1 ) according to claim 17, comprising two measurement devices (104, 204) positioned symmetrically relative to a longitudinal midplane of said continuous layer (S) and preferably close to opposite lateral edges of the continuous layer (S), in particular at a distance of between 5 mm and 800 mm from the lateral edges of the continuous layer (S).

19. The unit (1 ) according to any one of claims 16 to 18, wherein at least one of the rollers (102, 202) of said at least one pair of rollers (101 , 102, 201 , 202) is a roller which can be adjusted supported by end supports (102a, 102b) and wherein the movement device (10) comprises a first actuator (10a) connected to a first of said end supports (102a) and a second actuator (10b) connected to the other end support (10b), said control unit (U) being configured to independently control said first actuator (10a) and said second actuator (10b).

20. The unit (1 ) according to claim 19, wherein each actuator (10a, 10b) is a linear actuator preferably of the worm screw or male-and-female screwtype.

21. The unit (1 ) according to any one of claims 16 to 20, wherein each measurement device (104, 204) comprises a pair of measurement sensors (104a, 104b, 204a, 204b) for each measurement point (P1 , P2), each configured to generate a respective measurement signal, and wherein the control unit (U) is configured to receive and process said measurement signals obtaining an actual thickness value of the continuous layer (S) at the measurement point (P1 , P2)22. The unit (1 ) according to claim 21 , wherein said at least one measurement device (104) comprises a differential measurement device equipped with:- a first measurement sensor (104a), preferably an optical and / or laser sensor, facing a roller (102) of the pair of rollers (101 , 102) in such a way as to optically detect a first surface of the continuous layer (S) positioned with the relative second surface, opposite the first surface, adhering to said roller (102) in such a way as to detect the position of said first surface of the continuous layer (S);- a second measurement sensor (104b), preferably by penetrating radiation and / or an eddy current sensor, facing said roller (102) of the pair of rollers (101 , 102) and configured for detecting the outer surface of said roller (102) in such a way as to detect the position of said outer surface of the roller (102).

23. The unit (1 ) according to claim 21 , wherein said at least one measurement device (204) is an opposing measurement device equipped with:- a first measurement sensor (204a), preferably an optical and / or laser sensor, configured and / or positioned to face a first surface of the continuous layer (S);- a second measurement sensor (204b), preferably an optical and / or laser sensor, configured and / or positioned to face a second surface of said continuous layer (S), opposite said first surface.

24. The unit (1 ) according to any one of claims 16 to 23, comprising a plurality of laminating stages (100, 200), each comprising a respective pair of laminating rollers (101 , 102, 201 , 202), and at least one measurement device (104, 204) for each laminating stage (100, 200), configured for measuring the actual thickness of the continuous layer (S) coming out from the respective gap (102, 203) at least at one measurement point (P1 , P2).

25. The unit (1 ) according to claim 22, 23 or 24, wherein the measurement device (204) associated with the final laminating stage (200), positioned further downstream, is configured as an opposing measurement device, and wherein the measurement device (104) associated with each previous laminating stage (100) is configured as a differential measurement device.

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