WO2006061775A2

WO2006061775A2 - Control method for the feed of label tapes in labelling devices

Info

Publication number: WO2006061775A2
Application number: PCT/IB2005/054062
Authority: WO
Inventors: Damiano Fabbri
Original assignee: Damiano Fabbri
Priority date: 2004-12-06
Filing date: 2005-12-05
Publication date: 2006-06-15
Also published as: WO2006061775A3; ITMN20040037A1

Abstract

A method for controlling the feed of tape (1) in a label device provides the adjustment of the feed speed of a tape (1) according to a value of maximum correlation (pm) between a reference vector and between second vectors (Sj) related to images (2) existing on the tape (1), so as to perform, with a determined frequency, the feeding of a tape portion (10) with length (It) so that the images (2) tend to be arranged in a centered position or at a wished distance from respective edges (12, 13) of said portion (10) .

Description

CONTROL METHOD FOR THE FEED OF LABEL TAPES IN LABELLING DEVICES

DESCRIPTION The present invention relates to a method for controlling the feed of label tapes in labelling devices. As it is known, a label is substantially a recognizing member, generally formed by a tag, having inscriptions or images, which allows to detect or classify an object or the content of a phial, bottle or other container.

Currently, in particular, labels printed on film or paper tape are placed on bottles or phials by means of appropriate label devices, which have the task of unwinding a tape, generally in the form of a reel, so as to provide, with a precise rate, portions of tape with a length so as to form labels wherein the printing is centered or however positioned in the desired way.

Such aspect is particularly important as whatever operation is performed on the tape, both printing or cutting, it has to take place with sufficient precision, and above all coordinated with the devices which perform the specific operations on the tape.

In greater detail, the operation which reveals to be more critical is the cutting of the label, wherein the tape is divided into portions with a length so as to be able to be placed on the bottle or other container thereto the label is destined.

Firstly, in fact, it must be understood that the tape cutting takes place by means of a knife whose cyclic motion cannot be connected directly with the tape feed and therefore, in order to have centered labels, it is necessary that the tape feed is so that upon each cycle of the knife a portion is unwound with a length corresponding to the label.

The labelling system, then, has to take into account the speed of the knife and each time it has to unwind the same quantity of film so that upon each cutting always a label with the same length is generated.

Furthermore, the label system has to be able to cut the tape in a well precise position so that the formed label has a centered printing.

In fact, a cutting in a wrong position, repeated cyclically during the production cycle, would lead in short to obtain not usable labels, wherein the printing is not centered or, even, it is cut. Such result is aesthetically and functionally not acceptable with the risk of having to discard the bottle and the relative content with consequent wastes of material, time and huge production costs.

A main problem of this type of devices is that the printing on the film is never constant, but it tends to vary its own length. This variation in the length is caused by a bad quality of the printing on the tape or by elongations of the tape during the tape transport, in particular in the cases wherein such tape is made of easily deformable plastic materials.

It has been found that the length of the printing can vary between the beginning and the end of the film reel even by 5mm. Due to such length variation, the control of the tape feed in the labelling devices must adapt dynamically the speed of the unwinder to continue to produce labels of the same size of the printing.

In order to be able to cut the labels correctly, the reel producers insert in the printing drawing a black rectangle with small sizes, called "spot", or notch which is utilized to synchronize the unwinder.

In fact, a specific sensor reads the spot and upon each new spot the system calculates the distance of the unwound film with respect to the previous one, thus by obtaining the label length. In greater detail, in order to implement the reading of the first spot, an operator places manually the tape with the notch just before the reading position of the sensor so that the latter can detect the notch as first read signal as soon as the unwinder starts to move.

Furthermore, in order to read the subsequent spot, the label length is pre-set, so that the device control allows to search for the subsequent spot in a tape space with the length approximately corresponding to the length of the pre-set label.

In particular, in the notch area there is a reading space which does not show inscriptions or other images, so that the sensor is helped in the task of finding the subsequent notch in a so-called "notch reading window".

The use of the spot, even if it helps considerably the printing centering and, consequently, the correct cutting of the label, has underlined a plurality of drawbacks.

A first drawback existing in the current labelling devices derives from the fact that in the reels of low quality (but not only them) , wherein the length variation of the printing onto the film is particularly underlined (therefore the distance between the subsequent spots is greatly variable) , the system fails to find the notch and, in jargon, "it looses the notch".

Consequently, an instruction for locking the device is given which stops the- production to avoid unuseful product wastes by involving time losses to restore the productivity with consequent costs.

Furthermore, it happens that, if the sensor initially reads the signal, as referring signal, that is as notch, different from the one which represents the notch, the system will continue to look for and read that wrong reference by consequently producing wrong labels, with the shifted printing. Therefore, all bottles with such labels will have to be eliminated with consequent damages both in terms of waste of time and wasted material.

Another detected drawback arises from the fact that the spot and "the notch-reading window" occupy a label -A- portion, this film portion being substantially wasted since it cannot be used for any other purpose. It has been found that in the very large label formats wherein the relationship between the length of the "notch-reading window" and the label length is small, even 3% of the whole reel is wasted and up to 5% in the smaller label formats.

An additional detected drawback arises when the cutting phase is not precise, therefore the spot or the notch-reading window are not covered by the label closing overlapping part, thus jeopardizing the bottle appearance.

In addition to the problems underlined sofar, another detected problem arises for the fact that the spot needs a manual operation of positioning the film, in a well precise position, to allow then the automatic start of the production. Such operation slows down the hourly productivity of the labelling device, since it requires the presence of a specialized operator. Therefore, the technical problem underlying the present invention is to provide a labelling device able to obviate the drawbacks mentioned above by referring to the known art.

Such problem is solved by a method for controlling the feed of label tapes in labelling devices according to claim 1 and by label devices according to claim 11.

The present invention has some important advantages. The main advantage lies in the fact that it allows a control of the tape feed without using any notch or other reference sign, even if it guarantees high precision in the tape feed, so as to maximally reduce the tape wastes.

An additional advantage relates the fact that it allows a high reliability in controlling the feed so as to avoid the risk of producing labels out of control and the consequent material waste. At last, it requires very simple and quick manual operations, thus by reducing the use of manpower .in the label production.

Other advantages, features and application modes of the present invention will be evident from the following detailed description of some embodiments, shown by way of example and not for limitative purposes.

The figures of the enclosed drawings will be referred to, wherein: figure 1 is a perspective view of a container comprising a label; figure 2 is a front view of a label; figure 3 is a schematic illustration showing a feeding and cutting section of a label device according to the present invention; figure 4 is a schematic illustration showing an acquisition phase of the signals related to a label to be moved; figures 5A, 5B, 5C are front views showing labels of different length after errors during a printing phase; figure 6 is a graph illustrating the application of a correlation operation between two vectors; figures 7A, 7B and 7C are schematic illustrations showing the course of a correlation index for respective phase displacements between two vectors; figure 8 is a front view of a not centered reference image; and figure 9 is a schematic illustration showing the phase correction in a label device according to the present invention.

By firstly referring to figure 1, a label 100 is placed at a bottle 101, or any other container, so that an image 2 is able to be seen, printed on the same to show the product features or to provide any other information type.

It is evident that the image 2 can be constituted by any type of figure or inscription, or still by the combination thereof. In the present embodiment, for the maximum illustrating clarity, the image is represented by a letter A, the sizes thereof occupy almost the whole extension of the label 100.

In order to allow a complete reading of the image, the label is cut so that the image 2 is in a substantially centered position.

Alternatively, for example in case of labels used on other containers, preferably the image will be at a determined distance from respective ends 12 and 13, illustrated in figure 2. Furthermore, as it will be seen hereinafter, the control method according to the present invention could be used also for other operations on the labels which, still by way of example, are performed at constant distance from one of the ends.

By referring again to figure 2 and to the present embodiment, the label 1 has a length 1 so as to be wholly wound around a bottle 101 or, in case, by allowing a small overlapping of the ends mentioned above.

In this latter case, the overlapping will be kept conveniently at the minimum, to reduce the length necessary to the label and, consequently, the costs of the same. It is also evident that in case the label is destined to other purposes its length will be connected to other features, such as, for example, the longitudinal extension of the cover of a container.

Analogously to the known art, the label is implemented by cutting a continuous tape 1, illustrated in the figure 4, above thereof the image 2 is printed, repeated cyclically for the whole length of the tape 1.

The printing phase takes place according to the known art during which errors are possible, such as, for example, the dilatation or the change in the printing length.

By still referring to figure 4, the tape 1, gathered under the form of reel, is unwound through appropriate feeding means 3, which allow to make the tape 1 to feed toward cutting means 4.

After the cutting operation of the tape, the label 100 which is implemented in this way, can be sent to a fastening section, not illustrated in figure, wherein the label 100 is placed on the bottle 101 or on any other container.

However, it must be comprised that such section, or in case other sections implementing different operations, forexample, the packing process of the containers, are implemented according to known art and therefore they are within the range of any person skilled in the art. For this reason they will not be described hereinafter in greater detail.

In the present embodiment, the feeding means 3 are formed by rollers 31, actuated by electric motors not illustrated in figure, thereamong the tape 1 is placed and fed by means of the rotation of the same.

In order to control the rotation of the rollers and, consequently, the feeding speed of the tape, the electric motors are controlled by specific control means 5, the operation and control logic thereof will be described hereinafter.

The cutting means 4, instead, are implemented by a rotating knife which, upon each complete rotation, carries out a cutting of the tape 1 so as to produce a label. The length of such label will be connected to the feeding speed of the tape 1, since the faster the tape runs, the greater is the length of the label which will pass under the knife during the rotation thereof.

In fact, it is to be meant that the knife does not obstruct the tape feed, but simply it implements the cut thereof upon each complete rotation.

For a better illustrating clarity, hereinafter the rotation direction of the knife will be designated with θ, whereas the feeding direction of the tape with x.

Still by referring to figure 4, between the feeding section and the cutting section there is a sensor 6 which allows acquiring signals related to the image 2 during the unwinding of the tape.

It is to be noted that such components generally are present in the known label devices and, consequently, the method according to the present invention could be adapted also to the existing label devices without requiring particular costs for the changes which, as it will be illustrated hereinafter, mainly relate to the feed control.

In fact, the method for controlling the tape feed according to the present invention, initially comprises an initialization phase of the system which will be repeated once only for each type of label which has to be produced.

In such phase the tape is made to feed for a length equal to the one of the label which one wants to utilize.

As mentioned, such length could not remain constant for all the labels which will be produced, due to the printing errors and therefore, in this initialization phase, the tape 1 is being fed for the length which theoretically the label should have in case there are no printing errors.

During feeding, the sensor 6, which is kept fixed above the tape, acquires first signals, related to the image present in the tape. As it will be seen hereinafter, such image will be compared to what acquired during the production of labels and consequently having a reference function, it will be designated as reference image 21 hereinafter.

It must be meant, however, that such image 21 has no particular feature with respect to the other images 2 existing on the tape and, in such acquisition phase, anyone of such images can be used. As it will be explained hereinafter, it is not necessary that the image be centered during the acquisition, but it will be sufficient to acquire a length 1 of the tape in any position it is with respect to the sensor 6. Furthermore, in case of more complex labels, wherein several images are present, preferably all these images will be acquired, even if such feature does not reveal necessary, as it will be seen hereinafter.

In particular, then, the signals are acquired under the form of a reference vector S_ref. Such vector is represented by a sequence of values ai _ret:

^ref ⁼ \^airef'^a2ref f ^• " ^anref)

According to the present embodiment, in fact, and by referring to figure 3, the sensor 6 acquires a plurality of distinct values referring to the reference image 21.

For example, such values can correspond to the ones acquired by dividing the tape length 1, used in such initialization phase, into n equal intervals.

In this way, upon each n-th of interval, the sensor 6 will acquire an instantaneous value a± _rβf and the sequence of these n acquisitions will constitute the vector S_ref of the reference image 21. The sequence of values ai _ref depends, apart upon the properties of the image impressed onto the printing, also upon other factors such as the features of the sensor and the distance thereof from the tape.

The signal will be related to gradation, colours, threshold values, distance from the film o any other feature of the image. Furthermore, it could be digital or analogic, in the latter case the vector S_ref is obtained substantially by means of a sampling of the acquired signal.

As far as what just said, the vector S_ref does not depend upon time, but only upon the position of the tape with respect to the sensor and, consequently, the initialization and acquisition process of the signal is independent from the kinematic state of the labelling device.

Such feature allows the operation independently from the speed or accelerations or decelerations necessary for the productive chain. After such initialization phase, the production of labels starts, which are being fed by means of feeding means and cut by the knives in order to be then sent to the subsequent label stations.

As mentioned, the labels could not be cut with constant length due to the printing errors which, even if small, during the production would accumulate, making the labels unusable since, for example, the image 2 would result to be cut.

Therefore, the control method according to the present invention allows to correct such errors, so that the label cut takes place always in a controlled way.

By referring to figure 5A, an example is shown wherein the printing takes place in a constant way and the labels can be cut with constant length 1. Actually, the situations illustrated in figures 5B and 5C alternatively occurs instead, wherein respectively the printing is not centered or, more generally, it is out of phase with respect to the usual tape feed, and the printing has a distortion, in other words the image 2 is lengthened or shortened with respect to the reference image 21.

In both cases, such printing errors involve the need of implementing tape cuts with different sizes with respect to the length 1, with a variable quantity l_c defined hereinafter as correction length.

In order to obtain a label with the image 2 positioned in the correct position, when they contain the errors mentioned above, the tape is being fed so as to adjust the feeding by summing (or in case subtracting) the correction length l_c.

In order to explain in detail the operation of the method according to the present invention, firstly it is to be noted that the motion of the cutting means is not controlled by the control means, but simply it takes place at constant speed or however at variable speed in a not controlled way. Nevertheless, in each case, the feature which adjusts the frequency therewith the cut takes place is the cyclic rotation of the cutting means, in particular the rotation of 360 degrees of the knife.

At each cycle, the knife produces a label, the length thereof is equal to the quantity of the tape which passes through the cutting means during a complete rotation. Such length will be designated hereinafter as cutting length l_t which, in order to produce labels with the image centered or however in the wished position, will be equal to the sum (or difference) of the reference length 1 and of the correction length l_c.

The control means have then the task of feeding the tape 1 in a such way that the knife carries out the cutting of a tape portion with a length equal to l_t, each time corrected depending upon the image 2.

Such action takes place by means of the variation in the feeding speed of the tape 1, by operating on the feeding means, so that on each complete revolution of the cutting means, easily detectable by means of an encoder or other detecting means, the correct feeding is achieved, corresponding in other words to the cutting length l_t.

In order to implement such action, the method according to the present invention provides the acquisition, by means of the sensor 6, of the signals related to the images on the tape 1, in particular related to the image corresponding to the label which will have to be cut.

Also such signals are acquired under the form of a vector S, which, analogously to the vector S_r8f, acquired during the initialization phase, will be constituted by a sequence of values ai, acquired in subsequent instances, referred to the particular features of the image 2.

However, by dividing such length into n parts to obtain the acquisition intervals, equal parts would not be obtained or, as alternative, the whole length would not be covered as, in this case, the cutting length I_t is not constant, due to the errors illustrated sofar.

As explained previously, the feature adjusting the cutting frequency and, consequently, also the interval between a reading of the vector S and the subsequent one, is given by the whole rotation of the cutting means.

Consequently, upon each cutting cycle n acquisitions of signals related to the image 2 which is feeding under the sensor 6 will be carried out.

It is to be noted that, also in this case, the acquisition is not always related to one single image 2, but, during one cycle of the cutting means, two adjacent images can partially pass below the sensor.

Examples of possible acquisitions are reported in figures 7A, 7B and 1C. As alternative to such acquisition mode, or in case in combination, it is possible using however as reference the tape feeding, regulated by the feeding means 3. This alternative can be useful in the cases wherein it is necessary to adjust the tape feeding when the knife is not operating, as in the adjusting procedure of the phase, which will be described hereinafter. In particular, it results particularly advantageous the use of the two acquisition modes in combination, according to the ongoing procedure. In each case, whatever the acquisition may be, the sensor 6 provides a vector S containing the same number n of values existing in the reference vectors S_ref.

Therefore, the vector S is created by means of the state of the sensor 6 upon each n-th knife revolution, so as to define a vector S=(ai,a₂, ..a_n) independent from time and instead associated to the knife position.

On the contrary, in case the tape feeding is utilized as tape reference, an acquisition will be performed upon each n-th of cutting length I_t/ even if a certain error is accepted for the reasons explained above. For this reason, whatever operation may be performed on such vector it will be valid both during the acceleration phase and the deceleration phase of the label device.

It is to be noted that in the initialization procedure the value of the vector S_ref has been associated to the quantity of tape unwound below the sensor, whereas now the vector S is associated to the knife position.

This choice derives from the fact that during the initialization procedure, in general, the device and the knife are not operating, by allowing to consider only the tape position as reference. During the production phase it is possible to have a constant and pre-established number n of samples of the vector S, by using the knife position as reference. If during the production phase the vector S had been associated to the tape position, a variable number of samples would be obtained, since the length l_t varies according to the printing.

After the acquisition of the vector S, the similarity degree between the latter and the reference vector S_ref is evaluated.

Such operation is carried out by applying a correlation operator between the two vectors and, in particular, by means of a cross correlation. The expression of cross correlation applied to the vectors S_rβf and S is expressed in the following form, wherein S designates the transposed vector S: p

wherein p is a characterizing value of the correlation degree, called correlation index.

In order to perform such operation, the control means comprises a correlator 51, illustrated in figure 4 which, by applying the preceding formula, carries out the scalar product between S_ref and S, thus obtaining the cosine of the angle δ between the two vectors. A simplified example of this operation is illustrated in figure 6.

Therefore, the correlation index p=f(S_Eβf,S) is a measure of the similarity between the two sequences of acquired signals. In fact, when S is similar to S_ref, the cosine of such angle is proximate the unity whereas when S is different from S_ref, the cosine tends to zero. Therefore, the more the two vectors are different, the more p is proximate zero.

Furthermore, the correlation index p has a particular invariance peculiarity with respect to the scale changes of both vectors.

The just described feature results particularly useful when analogic sensors are used, since in this way signal gain changes of the sensor 6 or changes in the sensor distance from the tape induce however very small variations in the value p.

When S_ref is equal to S, the index p reaches its maximum value corresponding to 1. Therefore, for values very near to 1, the two sequences of samples are very similar and they are strictly correlated.

In fact, p can also be meant as an index which provides a similarity measure between two vectors.

In addition to what described sofar, the sequence of samples S can be equal to S_ref but it gives a low correlation index p.

This happens when the vectors have the same values, but translated of a certain number of indexes, in other words there is a phase displacement between the image actual position and the one taken as reference. The correlator 51 is able to detect such phase displacement and to recognize the wave forms translated with respect to the reference one S_rβf. In particular, the correlation operator is not applied only between S_Eef and the acquired vector S, but between a series of second vectors obtained by means of n rotations of the indexes of the values of the vector S. By designating the vector S_j the circularly translated vector S (on the left) of j values, the n possible rotations of S are:

S = S₀ = (a_ira₂, ...,a_n)

S₁ = (a₂,a₃, ...a_n,a,)

"^2 ⁼ \^a3r^a4r "^{• a}n' ^a\' ^aϊ)

S_j = [a_j+l,a_j+2r ... a_n, a_u ... , a^)

S_n-I ⁼ \^an ' ^a\ l ^{• • ■} ' ^an-\ )

S = S_n = (a_ira₂, ... , aj

Therefore, it will be possible to calculate the relationship Pj=f(S_rβf,S_j) for each generic vector Sj, thus constructing a graph of the course of the correlation index p_j .

The graph which is going to be implemented represents the course of the correlation indexes P_j and identifies in its maximum p_m of index m, the phase displacement existing between the image at the current pitch and the reference one.

By referring to figures 7A, 7B and 7C, the graphs of the correlation indexes p_j for different acquisitions of the vector S are shown, corresponding to images in different position.

Different indexes m correspond to different phase displacements between the images, which require respective correction lengths l_c. Therefore, it is possible to create a relationship between the index m, corresponding to the maximum correlation degree, and the correction length which has to be added to the length 1 in order to obtain the correct cutting length l_t. By referring to what previously said, the maximum p_m is not sure to be proximate the unity as theoretically should result from the equation

S_m) since the vector S is subjected to different forms of noise which attenuate the similarity with the reference sequence S_ref. In the maximum p_m the correlator finds the strongest similarity between the sequences of samples S_ref and S. Therefore, among the possible phases n, m is the one which, with greater probability, better represents the phase displacement of the current image with respect to the reference one. Greater in detail, the values a^ (with k varying from 1 to n) which constitute the vector S are conditioned by different factors: sampling troubles, in other words the sensor value is not always associated in a precise way to the same knife position, some pulses can be dilated by one sample, others can be reduced by one sample, troubles which overlay onto the sensor signal since there could be external causes such as the tape lightening, the sensor position or its quality and, at last, troubles due to the printing when it is of low quality or the tape is dirty or it moves during the production.

In addition to what has been said sofar, P_m can be seen also as a measure of the quality of the tape which is going to be cut. In fact, it is even possible to detect errors of format change in the label device, since in this case, S_rβf and S will be wholly not correlated and P_m will have values very proximate the zero.

In general, in case of using other correlation functions, the maximum point as index of maximum correlation could be not indicative, on the contrary being indicative the minimum or other singular points.

Once performed all steps previously illustrated, at this point the phase displacement lying between the vector S and the reference one S_ref is known, therefore it would suffice to send m (changed in sign) to a standard regulator PI, illustrated in figure 4, to reach the phase between the two vectors S and S_rβf.

Having S and S_ref iⁿ phase, however, not necessarily means producing correct labels, that is with the centered printing, since in order to obtain the printing centering it is necessary to take into account, apart from the label length l_t, also the distance existing between the sensor 6 and the cutting means 4, and the positioning of the image used as reference.

In fact, firstly it has be understood that the distance between the sensor 6 and the cutting means 4 not necessarily is equal to a multiple of the cutting length of the labels. On the contrary, as it is variable, it will be surely different.

Furthermore, as already mentioned previously, it is not requested the reference image be centered but a partial image or parts of two adjacent images can be equally used, as illustrated for example in figure 9.

Such feature reveals particularly advantageous since it allows limiting the time of the initialization phase, by requiring a reduced use of specialized manpower, which on the contrary would be necessary if it had been essential to have a correct centering of the reference image.

Exactly for this reason, the position of the sensor 6 with respect to the cutting means 4 has no involvement to obtain the cutting of labels with the image in the wished position.

In fact, the important feature for the purpose of the operation of a label device is that of obtaining labels wherein the image is located in controlled position, that is centered or at a desired distance from the ends 12 and 13. The control method of the tape feed according to the present invention allows controlling the tape speed, so that upon each knife cutting a length of tape l_t has been fed so as to obtain labels with images in correct positions, by compensating the printing errors. Therefore, in order to make such operation independent from the acquisition of the reference image and from the distance between the sensor and the cutting means, a constant parameter is introduced during the label production phase, which allows, once having corrected the length based upon the printing errors, to implement labels with the image in the wished position, independently from initialization and distance between sensors and cutting means. Practically, by referring to figure 9, once having carried out the initialization phase, the tape position is adjusted by introducing a. reference phase P_ref, so that, after having considered the correction by means of correlation, the knife cuts in the wished position, whatever the tape initial position may be.

Such parameter "reference phase" P_Eef can be adjusted manually from an operator which follows the start of the cutting phases until obtaining the correct parameter.

This possibility reveals particularly advantageous, since it allows using the same reference vector S_rΘf also for different tapes, on condition that they utilize the same image. In fact, by replacing the tape, for example because the reel wherein is it gathered is ended, after having inserted the new tape it will not be necessary to repeat the acquisition phase nor to set the reference phase, since they remain constant.

In each case, as the new tape will be inserted in a wholly casual way, it is preferable to wait that the device returns in the correct phase, which as already explained is connected to the correlation value and to the reference phase, before starting again the labelling procedures.

This automatic procedure of putting in phase the tape can be started by the operator according to need and it allows a label production with correct printing as from the first bottle.

In general, however, and by referring again to figure 9, the quantity P_e=P_ref-:m, which hereinafter will be designated as phase error, is processed by a standard regulator PI 52 to produce the control action onto the motor so that the label device produces labels with centered printing or however positioned at the wished distance from the ends 12 and 13.

When this condition is obtained, the value of m tends towards P_rβf/ since the errors due to the printing will be correct, while remaining different the positioning parameter, adjusted indeed by means of the parameter P_ref.

The use of the regulator PI 52 reveals particularly advantageous since it allows, by adjusting the tape feeding speed, to correct gradually both the printing errors connected to the phase displacement, for example due to a printing delay, and those due to the distortion of the same.

Whereas in the first case the correction possibility is quite evident, since it is question of translating the printing phase error directly into a tape feeding correction by means of the action of respective means 3, in the second case the applicant has experimented that the application of the operator of cross correlation between a dilated image and the reference one, provides an index m of maximum correlation, which, once introduced in the standard regulator PI, according to the modes shown above, causes the system to unwind, in a knife rotation cycle, a tape quantity equal to the length of the distorted printing. This optimal behaviour of the system is kept until distortions in the order of 5% on the printing length, value which is more than sufficient to cover the applications inherent the labelling devices.

In case, however, other types of regulators can be used to obtain the correction with the features illustrated above.

Furthermore, it is to be noted that during its unwinding, sometimes the tape moves, by slightly translating in the width sense. Such situation does not create problems since, with an appropriate choice of the reading position of the sensor, the continuity of the design on the printing guarantees a good correlation degree between sensor pulse sequences derived from adjacent film positions.

Such possibility can be further limited by using band sensors instead of usual sensors which allow only a point reading of the tape.

Furthermore, it is to be noted that the more the number n of samples is high, the more the image represented by the pulse sequence is accurate and method precision increases. More precisely, the number of the required processings grows in quadratic way and then the upper limit for the value of n is determined by the processing speed of the control means and of the correlator speed, once established the parameters of production speed and precision in the positioning of the image onto the label.

Still according to the present invention, it is possible not taking the whole sequence of n pulses to create the vector S_ref but to use only a sub-part ni<n thereof. Therefore, a quantity of tape l_p lower than 1 will be unwound and, consequently, a sequence of samples S_ref with sizes nχ<n will be obtained which will allow an increase in the processing speed of the system and higher production speeds.

At last, several variants in the implementation of the described method can be provided, in particular in the using of the feeding correction which, for example, can be used to bring the tape in the correct position so that the product expiring date be printed on the image or which also can control the exact point wherein the junction of two tapes has to take place.

In general, in fact, the control of the tape feeding can be used to implement, in cyclical way and according to a determined frequency, a plurality of specific operations on the tape, such as cutting, printing or the junction.

Furthermore, even the cross correlation operator can be replaced by any other operator, which provides characterizing values of the correlation or similarity degree of the same, by basing upon the acquired vectors.

The present invention has been described sofar by referring to preferred embodiments. It is to be meant that other embodiments belonging to the same inventive core may exist, all within the protective scope of the claims reported herebelow.

Claims

1. Method for controlling the feed of tapes (1) in labelling devices, so as to implement, in a cyclic way and according to a determined frequency, specific operations, such as cutting, printing or junction, on said tape (1) to implement labels (100) , characterized in that it comprises:

D a first initialization step, consisting in acquiring first signals, related to reference images (21) , said signals being acquired in form of a reference vector (S_rβf) ; and the cyclic repetition of the steps of: D providing a plurality of second vectors (S_j) by acquiring signals related to images (2) existing on said tape and related to said labels (100);

D applying a correlation operator between said reference vector (S_ref) and said plurality of second vectors (Sj), apt to provide a set of respective values (Pj)_/ characterizing the correlation degree between said reference vector and said plurality of second vectors; D identifying a value of maximum correlation (ρ_m) inside said set;

D adjusting the feeding speed of said tape (1) according to said value of maximum correlation (Pm) r by means of specific control means (5), so as to implement, at said determined frequency, the feeding of a tape portion (10) with length (l_t) so that said second images

(2) tend to be arranged in a centered position with respect to said tape portion, or however at a wished distance from respective edges (12, 13) of said portion, in order to carry out said specific operation in a fixed relative position with respect to said portion (10) .

2. Method for controlling the feed of label tapes according to the preceding claim, comprising additional steps of identifying a reference phase

(P_re_f) apt to define the phase displacement between said reference image (21) and said second images (2) and to adjust the tape feeding (1) so as to bring back in phase said second images (2) with said reference image (21) .

3. Method for controlling the feed of label tapes according to one of the preceding claims, wherein said second vectors (Sj) are obtained by means of the combination, according to a cyclic rotation, of values (a_±) of a single vector (S), said values (a*) being obtained by means of said signals acquired by said sensor (6) and being related to said images (2) .

4. Method for controlling the feed of label tapes according to one of the preceding claims, wherein said correlation operation takes place by means of a cross correlation function, so as to obtain cosine of an angle δ between said reference value (S_ref) and each one of said second vectors (S_j) .

5. Method for controlling the feed of label tapes according to one of the preceding claims, wherein said specific operations comprise the cutting of said tape, and said frequency is determined by the cyclic motion of cutting means (4) .

6. Method for controlling the feed of label tapes according to the preceding claim, wherein said sensor (6) is apt to acquire a number n of values upon each motion cycle of said cutting means (4), said n values being apt to form said vectors (S_ref, S)

7. Method for controlling the feed of label tapes according to claim 5 or 6, wherein said frequency is determined alternatively by the cyclic motion of said cutting means (4) or by the feeding of a determined length of said tape (1) .

8. Method for controlling the feed of label tapes according to claim 5 or 6 or 7, wherein upon each cycle of said cutting means said tape is made to feed for a quantity equal to the cutting length (It) •

9. Method for controlling the feed of label tapes according to one of the preceding claims, wherein said signals apt to provide said vectors (S_ref, S) are acquired during the feeding of said tape (1) .

10. Method for controlling the feed of label tapes according to one of the preceding claims, wherein said control means (5) comprises a correlator

(51) apt to implement said correlation operation, a regulator (52) apt to provide a feeding correction of said tape (1) implemented by specific feeding means (3) , basing upon said value of maximum correlation, so as to obtain the desired feeding.

11. Labelling device, apt to implement specific operations on a tape (1) at single portions (10) apt to form a label (100), characterized in that it comprises control means (5) of the feeding speed of said tape (1) , said control means being apt to implement the control method according to one or more of the claims 1 to 10.