WO2020114766A1

WO2020114766A1 - Labelling machine, method for handling a web-like labelling material in an automated labelling process and label

Info

Publication number: WO2020114766A1
Application number: PCT/EP2019/081831
Authority: WO
Inventors: Michele GUGOLE
Original assignee: Sidel Participations SAS
Current assignee: Sidel Participations SAS
Priority date: 2018-12-07
Filing date: 2019-11-19
Publication date: 2020-06-11
Anticipated expiration: 2021-06-07

Abstract

The invention relates to a labelling machine (1) configured to apply labels (2) onto articles (3) destined to contain a pourable product; the machine (1) comprises: a conveyor (6) configured to advance a plurality of articles (3) along a transfer path (P); a transfer device (13) configured to receive a succession of labels (2) in a receiving station (B), and to feed them to an application station (A), at which they are applied onto respective articles (3); at least one position sensor (15), configured to sequentially detect the position of reference elements (16), each provided on a respective label (2), and to generate a corresponding first information correlated to the current position (R) of each reference element (16); and a control unit (17) configured to receive the first information generated by said position sensor (15), so as to compare it sequentially with a second information correlated to a pre-set nominal position (N) of the reference element (16), and calculating a position error (E) between the current position (R) and the nominal position (N); the control unit (17) is furthermore configured to: control a discard of the articles (3) onto which a corresponding label (2) has been applied for which the control unit (17) has calculated a non-zero position error (E), when the position error (E) is higher than a pre-set first threshold value (Es1) and lower than a preset second threshold value (Es2) higher than the first threshold value (Es1); and to control a stop of the machine (1) when the position error (E) is higher than the second threshold value (Es2) for a pre-set number of labels (2).

Description

TITLE: "LABELLING MACHINE, METHOD FOR HANDLING A WEB-LIKE

LABELLING MATERIAL IN AN AUTOMATED LABELLING PROCESS AND LABEL"

* * *

TECHNICAL SECTOR

The present invention relates to a labelling machine for handling a labelling material in an automated labelling process, in particular a labelling machine configured for applying labels onto articles, preferably articles configured to contain a pourable product, for example bottles, containers, or the like.

The present invention likewise relates to a method for handling a labelling material in an automated labelling process during which labels are applied onto articles, in particular articles configured to contain a pourable product, for example bottles, containers, or the like.

The present invention moreover relates to a label that is designed to be applied, by means of a labelling process, to articles adapted to contain a pourable product, for example bottles, containers, or the like.

PRIOR ART

Known to the art are labelling machines that are commonly used for preparing, conveying, and applying labels onto articles, in particular bottles, containers or the like, which are destined to be filled with pourable products, preferably purable food products.

Particularly widespread is the use of glued labels, obtained starting from a web of a web-like labelling material wound on one or more reels.

In detail, said web is cut into portions of equal size, to which glue is applied. The glue is applied via gluing means, for example rollers, spraying systems, injection systems, or the like. The labels thus obtained are then transferred and glued on the outer side surface of respective articles.

Another particularly widespread type of labelling contemplates the realization of tubular labels, known as "sleeve labels", obtained starting from a web of heat- shrink film wound on one or more reels. These sleeve labels are applied with a certain degree of play on the respective articles and then heated in an oven to obtain their shrinkage and perfect adhesion to the side surfaces of the articles themselves. This type of labels does not involve the use of glue.

Irrespective of the type of label used, a labelling machine typically comprises:

- a carousel rotatable about a vertical axis and configured to convey a plurality of successive articles along a horizontal path having the shape of an arc of a circle ; - an input station, at which the articles to be labelled are fed to the carousel;

- an output station, at which the labelled articles leave the carousel; and

- one or more labelling modules arranged peripherally with respect to the carousel and configured to feed respective pluralities of labels to the carousel itself at an application station, in order to apply said labels onto the respective articles.

Generally, the labelling module comprises:

- one or more storage units, normally rotary rollers around which corresponding reels of labelling material in the configuration of a continuous web are wound;

- a plurality of unwinding rollers, which support, in use, the web wound off the reel and guide it along a feed path;

- a knife configured to cut, at a cutting station, a sequence of individual labels having the same length from the web of labelling material; and

- a vacuum drum for transferring the labels, which is configured to receive, hold, and advance each previously cut label and feed said label to the carousel at the application station.

In case the glued labels are used, the labelling module further comprises at least one gluing roller arranged substantially tangential to the vacuum drum for spreading glue on at least the ends of each individual label .

In the case of sleeve type labels, these are wound in a tube around respective forming spindles, which are fed by the carousel and carry the articles to be labelled thereon. The labels are then welded at their overlapping ends. At this point, the spindles are retracted into the base of the carousel so as to enable the insertion with play of the articles into the respective sleeve labels. Subsequently, the articles with the slack labels are sent to the heating oven to obtain heat-shrinking of the labels and perfect adhesion of the latter to the articles themselves.

Typically, the drum has a lobed cylindrical or toroidal shape, and is mounted, rotatably about its own axis, on a stationary distributing element of the labelling module .

In detail, the drum is configured to receive the previously cut labels at a receiving station and, after a rotation of a given angle about its own axis, to release said labels at the application station, so that they will be applied onto the respective articles or onto the forming spindles .

The stationary distributing element comprises first ducts for the passage of air, connected to a vacuum source (or aspirator) . The drum is in turn provided with second ducts for the passage of air, configured to communicate with the first ducts in given angular positions of the drum itself, according to the rotation of the latter about its own axis. These second ducts terminate in a plurality of respective ports made through and on an outer side surface of the drum, adapted to receive and support the labels.

In practice, according to the angular position assumed by the drum about its own axis, with respect to the distributing element, the ports are set in communication, through the first and the second ducts, with the vacuum source. When this occurs, a suction force is set up on the outer side surface of the drum, capable of supporting and holding each label, when it is advanced from the receiving station to the application station.

Conveniently, the carousel, the drum, the gluing roller, and the unwinding rollers are synchronised in phase so as to carry out the entire labelling process properly.

In the field of labelling machines of the type mentioned above, it is well known that it may happen that one or more successive labels, which form the web of labelling material and are still to be separated, are not positioned properly (i.e., in a nominal way) relative to the cutting station.

More precisely, the cutting section of each label, i.e., the section where a label is separated from the web of labelling material, is considered as not being properly positioned when it is located downstream or upstream of the cutting station at the moment of cutting. Instead, in correct operating conditions, the cutting section coincides with the cutting station at the moment of cutting.

Erroneous positioning leads to a non-nominal separation of the labels from the web of labelling material, i.e. to a non-nominal cut of the labels by the knife .

The erroneous positioning causes a necessary discard of the labels cut in a non-nominal way, with consequent waste of labelling material.

Generally, the problem illustrated above is more likely to arise during the so-called "splicing", i.e., the joining of one final end of a reel of labelling material to the starting end of the next reel, which is carried out in order not to have to stop the labelling machine whenever one reel runs out, thus rendering it necessary to join the previous reel to the subsequent one.

In order to overcome the technical drawback referred to above, according to a solution known in the sector, labelling machines comprise a position sensor, for example a photoelectric cell, capable of detecting the instantaneous position of a mark or reference band, placed on each label and typically made in a colouring with a dark shade, for example black.

In detail, according to this configuration, the sensor detects, in use, the instantaneous position of the band of each label, in succession and prior to cutting the latter, and sends the detected position to a control unit.

The control unit compares the detected position with a pre-set nominal (or reference) position of the band.

The control unit is generally programmed for "accepting" a pre-set threshold positioning error, for example +/- 5 mm of difference of the detected position with respect to the pre-set nominal position.

If, from the comparison performed by the control unit, it follows that the detected position of a given band does not coincide with the nominal position and the value is within the difference range between the nominal position and the threshold error, the control unit controls a rephasing (deceleration or acceleration) of the unwinding rollers, so as to determine a progressive compensation of the positioning error and to bring the subsequent labels back into position, so that such error will tend to zero and the corresponding bands will return to the nominal position .

Normally, the above compensation is made in successive steps, for example, 2 mm of compensation for each label fed to the drum.

In the case where, from the comparison made by the control unit, it follows that the detected position of the band does not coincide with the nominal position and the positioning error is higher than the threshold error, and hence is outside of the aforesaid difference range, said label is discarded.

After a certain number of discarded labels, for example 5 labels, the machine is stopped in order to prevent excessive waste of labelling material, and a rephasing of the unwinding rollers of the labelling module is carried out while the machine is stopped.

The Applicant has noted that labelling machines operating according to the configuration described above, although being functionally valid, may undergo further improvements .

In particular, a need is felt in the industry to limit as much as possible the stoppage of the machine in order not to penalize the productivity thereof.

AIM AND SUMMARY OF THE INVENTION

The aim of the present invention is to provide a labelling machine that will present a high reliability and limited cost and will make it possible to meet the need specified above connected to the labelling machines of the known type. According to the invention, the above aim is achieved by a labelling machine as claimed in claim 1.

The aim of the present invention is likewise to provide a method for handling labelling material which will make it possible to meet, with a high reliability and limited cost, the need specified above connected with the labelling machines of the known type.

According to the invention, the above aim is achieved by a method for handling labelling material as claimed in claim 6.

A further aim of the present invention is to provide a label which will present high reliability and limited cost, and will make it possible to meet the need specified above connected to the labelling machines of the known type.

According to the invention, the above aim is achieved by a label as claimed in claim 10.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, a preferred non-limiting embodiment thereof is described in what follows, purely by way of example and with the aid of the attached drawings, wherein:

- Figure 1 is a simplified schematic top plan view of a labelling machine provided according to the present invention; and

- Figures 2 to 5 illustrate, in a larger-scale schematic front view and during different operating conditions, a label obtained from a web of labelling material, which can be fed to the labelling machine of Figure 1.

DETAILED DESCRIPTION

With reference to Figure 1, number 1 indicates as a whole a labelling machine configured to apply labels 2 onto articles 3, in particular bottles, containers or the like, destined to be filled with pourable products.

Preferably, the labels 2 applied by the machine 1 are of the type known as "glued labels", i.e., portions of labelling material of pre-set length, cut starting from a web 4 of labelling material wound on one or more reels 5 and spread with glue. Said labels 2 are subsequently transferred and applied onto the outer surface of the respective articles 3.

According to an alternative embodiment not shown, the labelling machine could also operate with labels of the type commonly known as "sleeve labels", i.e., tubular labels obtained starting from a web of heat-shrink film wound on one or more reels (not illustrated) ; these sleeve labels are applied with a certain degree of play onto the respective articles 3 and then heated in an oven to obtain shrinkage thereof and perfect adhesion to the lateral surfaces of the articles 3 themselves. The machine 1 basically comprises:

- a carousel 6 rotatable about a vertical axis Z, configured to convey a plurality of successive articles 3 along a horizontal path P having the shape of an arc of a circle ;

- an input station I, through which the articles 3 are fed to the carousel 6;

- an output station 0, which receives the labelled articles 3 from the carousel 6;

- an output conveyor, for example an output star wheel 7, configured to receive from the carousel 6 the articles 3 labelled at the output station 0 and feed them towards a final conveyor (not illustrated) ; and

- at least one labelling module 8 (schematically illustrated only in part) arranged peripherally with respect to the carousel 6 and configured to feed a plurality of labels 2 to the carousel 6 itself, and apply them onto the respective articles 3, at an application station A.

In detail, the labelling module 8 comprises:

- at least one shaft 9 configured to rotatably support at least one reel 5 from which the web 4 of labelling material is wound off;

- a plurality of unwinding rollers 10, which, in use, support the web 4 wound off the reel 5 and guide it along an advancement path Q;

- a cutting device, for example a knife 11, configured to separate, in particular to sequentially cut, each label 2 from said web 4 of labelling material at a cutting station T, thus obtaining labels 2 having the same length;

- at least one gluing roller 12 apt to sequentially spread glue on each individual label 2, previously cut by the knife 11;

- a transfer device, in particular a vacuum drum 13 for transferring the labels 2, rotatable about an axis X, positioned peripherally to the carousel 6, and configured to receive and advance each label 2 previously cut from the web 4, and apply said label 2 onto the respective article 3, at the application station A; and

- a feeding device, preferably a feed roller 14, rotatable about an axis Y and configured to receive the web 4 of labelling material from the reels 5 and feed it to the unwinding rollers 10 and, hence, towards the cutting station T.

Preferably, the drum 13 has a substantially cylindrical-toroidal lobed shape.

In greater detail, the drum 13 sequentially receives, in use, the labels 2 previously cut by the knife 11 in a receiving station B arranged downstream of the cutting station T, holds the labels 2 on a lateral surface 13a thereof, and, after a rotation of a given angle about the axis X, releases said labels 2 at the application station A, so that they will be applied onto the respective articles 3, according to a manner known and not described in detail.

In practice, the drum 13 is rotatably mounted on a distributing element (not illustrated) comprising first ducts (not illustrated) for the passage of air, which are connected to a vacuum source, for example an aspirator (not illustrated in detail) . The drum 13 is in turn provided with second ducts (also not illustrated) for the passage of air, configured to communicate with the first ducts of the distributing element, at given angular positions assumed by the drum 13, according to the rotation about the axis X, with respect to the distributing element itself.

The second ducts terminate in a plurality of respective ports (not visible in the attached figures) , obtained through and on the lateral surface 13a of the drum 13, which is configured to receive and support the labels 2.

In practice, depending on the angular position assumed by the drum 13 about the axis X, with respect to the distributing element, the ports are set in communication, through the first and the second ducts, with the vacuum source. When this occurs, a suction force is set up on the lateral surface 13a, which is in this way able to support and hold each label 2 by means of suction, when the latter is advanced from the receiving station B to the application station A.

The machine 1 further comprises at least one position sensor 15 configured to sequentially detect the position of reference elements, in the specific example reference bands 16 (Figures 2-5), each provided on a respective label 2 of the web 4 of labelling material.

In detail, the position sensor 15 detects, in use, the position of each band 16 before the separation of the corresponding labels 2 from the web 4 of labelling material takes place.

Hence, the position sensor 15 is arranged upstream of the cutting station T, relative to the advancement path Q and, preferably, is arranged peripherally with respect to an unwinding roller 10 positioned upstream of the cutting station T and downstream of the feed roller 14.

As visible in Figures 2 to 5, each label 2 has a substantially rectangular shape and comprises:

- an outer surface defining the visible part of the label 2;

- an inner surface, which faces on the opposite side with respect to the outer surface and is destined to co operate in contact with a lateral surface of a respective article 3; and

- at least one band 16, which is provided on one of the outer surface and the inner surface and is destined to be detected by the position sensor 15 during the labelling process .

According to this preferred and non-limiting embodiment, each band 16 is defined by a mark obtained with a colouring having a dark shade compared to the shade of colouring of the rest of the respective label 2.

However, in order to prevent the position sensor 15 from detecting the position of other feutures of the label that might be confused with the band 16, the sensor is only activated for a detection interval having an extension smaller than the total extension of the individual label 2.

According to another embodiment (not illustrated) , each band 16 could be made of a material capable of reflecting ultraviolet radiation and capable of transmitting and/or absorbing visible light.

In this way, it is not necessary to restrict the detection interval of the position sensor 15, the extension of which may hence coincide with the entire extension of the label. In other words, the position sensor 15 may be kept active for the entire duration of the labelling process, without incurring in detection errors.

The position sensor 15 is further configured to generate a corresponding first information correlated to the current position R (Figures 2-5) of the band 16 of each label 2 detected by the position sensor 15 itself.

As visible in Figure 1, the machine 1 further comprises a control unit 17 configured to receive the series of first informations generated by the position sensor 15, to sequentially compare each first information with a second information correlated to a pre-set nominal position N (Figures 2-5) of the bands 16, and to calculate a position difference value between the current position R and the nominal position N based on the comparison between the first and second informations.

In other words, the control unit 17 sequentially compares, in use, the current position R of each band 16, detected by the position sensor 15, with the pre-set nominal reference position N (implemented in the control unit 17) and calculates a position error E, in particular an absolute position error E, corresponding to the aforesaid position difference value between the current position R and the nominal position N.

In light of the above, the position error E may be defined by the formula E = |R - N|, where E, R, and N are values of length or arcs of circumference.

Each label 2 for which the control unit 17 has calculated a non-zero position error E will be separated from the web 4 by the knife 11 in a non-nominal position.

More precisely, said label 2 will not be cut at its own respective pre-set nominal cutting sections 18 (Figures 2- 5) .

Furthermore, the control unit 17 is configured to record the labels with a non-zero position error E, so as to be able to automatically identify the corresponding articles 3 advanced by the carousel 6 onto which said labels 2 will be applied, according to a manner known and not described in detail.

Advantageously, the control unit 17 is further configured to control a discard of the articles 3 onto which a label 2 has been applied for which the control unit 17 has calculated a non-zero position error E, when this position error E is higher than a first threshold value of difference of position, corresponding to a pre-set first threshold error Esl, and is lower than a second threshold value of difference of position, corresponding to a pre-set second threshold error Es2 and higher than the first threshold error Esl.

Conveniently, both the first threshold error Esl and the second threshold error Es2 are defined both in terms of positive deviation from the nominal position N (i.e., a deviation in the direction of the carousel 6) and in terms of negative deviation from the nominal position N (i.e., a deviation in the direction of the feed roller 14) . It is pointed out that in the present description reference is made to absolute values of the position error E and of the first and second threshold errors Esl and Es2. The same concepts may in fact be applied in the case where these errors are to be understood in a positive or negative sense with respect to the nominal position N.

According to a further aspect of the present invention, the control unit 17 is configured to control a stop of the machine 1 when the position error E is higher than the second threshold error Esl for a pre-set number of labels 2 for which a non-zero position error E has been calculated, for example five consecutive labels 2 having a non-zero position error E.

According to another aspect of the present invention, the control unit 17 is configured to control an advancement of a given quantity, in this specific case a relative rotation of a given angle (not illustrated) of the drum 13 with respect to the feed roller 14 (or of the feed roller 14 with respect to the drum 13) , when the position error E is smaller than the first threshold error Esl and as long as said position error E is non-zero, so as to cause a progressive reduction of the position error E.

In practice, if the control unit 17 calculates a position error E other than zero and lower than the first threshold error Esl, it controls (according to a manner known and not described in detail) the aforesaid relative rotation between the drum 13 and the feed roller 14.

Preferably, said relative rotation is performed in successive steps; i.e., a determined quantity, for example 2 mm, is compensated for each label 2 fed to the drum 13.

In this way, a progressive compensation of the position error E is obtained, which continues until said position error E is equal to zero.

In light of the above, it is possible to identify four operating conditions:

- if the control unit 17 calculates a zero position error E, the labelling process continues without any action or variation (Figure 2);

- if the control unit 17 calculates a non-zero position error E and lower than the first threshold error Esl, it controls the aforesaid compensation by means of relative rotation between the drum 13 and the feed roller 14 (Figure 3) ;

- if the control unit 17 calculates a non-zero position error E, higher than the first threshold error Esl and lower than the second threshold error Es2, it controls the discard of the corresponding articles 3, i.e., the articles 3 onto which a label 2 separated in a non-nominal position has been applied (Figure 4); and if the control unit 17 calculates a non-zero position error E higher than the second threshold error Es2, it is configured to control a stop of the machine 1 when the position error E is higher than the second threshold error Esl for a pre-set number of labels 2 for which a non-zero position error E has been calculated, for example five consecutive labels 2 having a non-zero position error E (Figure 5) .

As visible in Figure 1, the machine 1 further comprises discard means, preferably an expeller 20 configured to eject the articles 3 onto which an aforesaid label 2 non-nominally separated, i.e. a label 2 for which the control unit 17 has calculated a non-zero position error E.

Preferably, the expeller 20 is of a pneumatic type. According to this configuration, when the control unit 17 controls the activation of the expeller 20, the latter emits a jet of compressed air that pushes the corresponding article 3 out of the star wheel 7 towards a container 21.

According to an alternative embodiment (not illustrated) , the expeller 20 is of the mechanical or hydraulic type.

The operation of the labelling machine 1 according to the present invention will be described in the following, with particular reference to an initial condition in which a band 16 of a respective label 2 still not separated from the web 4 advances along the advancement path Q and arrives at the position sensor 15.

In this condition, the position sensor 15 detects the current position R of the band 16 and generates the first information .

The control unit 17 receives the first information and compares the current position R with the pre-set nominal position N, calculating the position error E (positive or negative, according to the direction of the deviation with respect to the nominal position N) .

This is followed by one of the operations referred to above in the aforesaid four operating conditions, according to the value of the position error E.

The process is repeated for each label 2 to be applied and for each reel 5 to be unwound.

The advantages of labelling machine 1, label 2 and the method according to the present invention will be clear from the foregoing description.

In particular, thanks to the aforesaid configuration of the machine 1, it is possible to prevent frequent stops of the machine 1 in the case in which the control unit 17 calculates a non-zero position error E for one or more labels 2.

In this way, the labelling process is more efficient, faster, and more linear.

It is clear that modifications and variations may be made to the machine 1, the method, and the label 2 described and illustrated herein, without thereby departing from the scope of protection defined by the appended claims .

Claims

1.- A labelling machine (1) configured to apply labels (2), obtained from a web (4) of labelling material, onto articles (3) destined to contain a pourable product; said machine (1) comprising:

- a conveyor (6) configured to advance a plurality of said articles (3) along a transfer path (P) ;

- a transfer device (13) arranged peripherally with respect to said conveyor (6) and configured to receive a succession of said labels (2), one after another, at a receiving station (B) , and to advance said labels (2) towards an application station (A) , at which said labels (2) are fed to said conveyor (6) for being applied onto respective said articles (3) ;

- at least one position sensor (15) configured to sequentially detect the position of reference elements (16) each provided on a respective label (2) of said web (4) and to generate a corresponding first information correlated to the current position (R) of each said reference element (16) detected by said position sensor (15); and

- a control unit (17) configured to receive said first information generated by said position sensor (15), to sequentially compare said first information with a second information correlated to a pre-set nominal position (N) of said reference element (16), and to calculate a position difference value (E) between said current position (R) and said nominal position (N) based on the comparison between said first and second information;

characterized in that said control unit (17) is further configured to:

- control the discard of the articles (3) onto which a corresponding label (2) has been applied for which said control unit (17) has calculated a non-zero position difference value (E) , when said position difference value (E) is higher than a first pre-set threshold value (Esl) of difference of position and lower than a second pre-set threshold value (Es2) of difference of position higher than said first threshold value (Esl); and to

- control a stop of said machine (1) when said position difference value (E) is higher than said second threshold value (Es2) for a pre-set number of labels (2) for which said control unit (17) has calculated a non-zero position difference value (E) .

2.- The machine according to Claim 1, further comprising a cutting device (11) configured to sequentially separate each label (2) from said web (4) of labelling material at a cutting station (T) arranged upstream of said receiving station (B) relative to an advancement path (Q) of said labels (2);

wherein said position sensor (15) is arranged upstream of said cutting station (T) , relative to said advancement path (Q) .

3.- The machine according to Claim 2, further comprising a feeding device (14) configured to feed said web (4) of labelling material towards said cutting device (11) ;

wherein said position sensor (15) is arranged downstream of said feeding device (14) .

4.- The machine according to Claim 3, wherein said control unit (17) is further configured to control an advancement by a given quantity of one (13, 14) of said transfer device (13) and feeding device (14) relative to the other (14, 13) of said transfer device (13) and feeding device (14), when said position difference value (E) is lower than said first threshold value (Esl) and as long as said position difference value (E) is non-zero, so as to cause a progressive reduction of said position difference value (E) .

5.- The machine according to any one of the preceding claims, further comprising discard means (20) configured to discard said articles (3) onto which a corresponding label (2) has been applied for which said control unit (17) has calculated a non-zero position difference value (E) ;

said control unit (17) being further configured to activate said discard means (20) when said position difference value (E) is higher than said first threshold value (Esl) and lower than said second threshold value (Es2 ) .

6.- A method for labelling articles (3) destined to contain a pourable product; the method comprising the steps of :

- advancing a plurality of said articles (3) along a transfer path (P) ;

- conveying a succession of individual labels (2), one after another, from a receiving station (B) to an application station (A), at which said labels (2) are applied onto respective articles (3) ;

- sequentially detecting the position of at least one reference element (16) provided on each label (2);

- generating a first information correlated to the current position (R) detected during the step of detecting;

- comparing said first information with a second information correlated to a pre-set nominal position (N) of said reference element (16); and

- calculating a position difference value (E) between said current position (R) and said nominal position (N) based on the comparison made during the step of comparing; characterized by further comprising the steps of:

- discarding the articles (3) onto which a corresponding label (2) has been applied for which a non- zero position difference value (E) has been calculated during the step of calculating, when said position difference value (E) is higher than a first pre-set threshold value (Esl) of difference of position and lower than a second pre-set threshold value (Es2) of difference of position higher than said first threshold value (Esl); and

- stopping the labelling process when said position difference value (E) is higher than said second threshold value (Es2) for a pre-set number of labels (2) for which a non-zero position difference value (E) has been calculated, during the step of calculating.

7.- The method according to Claim 6, wherein said labels (2) are obtained from a web (4) of labelling material; the method further comprising the step of:

- sequentially separating each label (2) from said web (4) of labelling material at a cutting station (T) arranged upstream of said receiving station (B) relative to an advancement path (Q) of said labels (2);

wherein the step of detecting is performed prior to the step of separating.

8.- The method according to Claim 7, further comprising the step of:

- feeding said web (4) of labelling material towards said cutting station (T) by means of a feeding device (14); wherein the step of detecting is performed downstream of said feeding device (14) .

9.- The method according to Claim 8, further comprising the steps of:

- providing a transfer device (13) configured to carry out the step of conveying; and

- controlling a displacement by a given quantity of one (13, 14) of said transfer device (13) and feeding device (14) relative to the other of said transfer device (13) and feeding device, when said position difference value (E) is lower than said first threshold value (Esl) and as long as said position difference value (E) is non zero, so as to cause a progressive reduction of said position difference value (E) .

10.- A label (2) designed to be applied, by means of a labelling process, onto articles (3) apt to contain a pourable product; said label (2) having a substantially two-dimensional configuration and comprising:

- an outer surface defining the visible part of the label (2);

- an inner surface, which faces on the opposite side with respect to said outer surface and is destined to co operate in contact with a lateral surface of a respective article (3) ; and

- at least one reference element (16), provided on one of said outer surface and inner surface and destined to be detected, in use, by a position sensor (15) during said labelling process;

characterized in that said reference element (16) is made of a material capable of reflecting ultraviolet radiation and capable of transmitting and/or absorbing visible light.