Abstract:
A machine to realise articles ( 10 ) including a set of elements localised in determined positions (F 1 , . . . F 5 ) includes respective treatment units S 1,  . . . , S K ) capable of being selectively regulated (M 1,  . . . , M K   ; 104 ). The regulation system of the machine also includes a memory ( 112 ) to store ( 112 ) reference values for the above-said positions (F 1,  . . . , F 5 ) and a visual inspection station ( 106 ) to detect ( 1000, 1002 ) the position (F 1,  . . . , F 5 ) of the various elements ( 14  to  24 ) in at least one article ( 10 ) realised through the above-said respective treatment units (S 1,  . . . , S K ). A processing module ( 104 ) compares ( 1006 ) the position (F 1,  . . . , F 5 ) detected through the visual inspection station ( 106 ) with the stored ( 112 ) reference values ( 112 ), and, when the position (F 1,  . . . , F 5 ) as detected through the visual inspection station ( 106 ) does not correspond to the respective reference value ( 112 ), regulates ( 1010 ) the corresponding treatment unit (S 1,  . . . , S K ) to restore the position (F 1,  . . . , F 5 ) to the reference value ( 112 ).

Description:
FIELD OF THE INVENTION  
       [0001]    The present invention relates to techniques for the automatic regulation of production lines. 
         [0002]    The invention was developed with specific attention to its possible use in production lines for the manufacturing of hygienic-sanitary products. Reference to this possible field of application is not intended as limiting of the scope of the invention. 
       DESCRIPTION OF THE RELATED ART  
       [0003]      FIG. 1  schematically illustrates a hygienic-sanitary article, such as, for example, a pull-up/diaper for babies. 
         [0004]    Reference to this type of article is by way of example only: in fact, as will be evident in the following, the solution described herein is adapted for being applied to the production of any article manufactured by advancing base elements (possibly still connected in a chain) though a cascade of work stations realizing additional characteristics (or features) of the article, for example, through the application of additional elements to the base element of the article. All of this also foreseeing the possibility that, when the base elements are connected in a chain, once the manufacturing of articles is completed or almost completed, an additional work station (typically a cutting station) provides for the segmentation of the chain therefore providing single independent articles. 
         [0005]    This operating mode is broadly documented in the art, as demonstrated—by way of example only—by the document EP-A-1 523 968. 
         [0006]    The article illustrated in  FIG. 1  (which, remember, refers to a possible exemplary embodiment) is indicated in its entirety with  10  and it includes a base element or chassis  12  on which additional elements are successively applied such as:
       an absorbing nucleus or core  14 ,   an elasticized front-tape  16 ,   a pair of posterior side-panels  18  provided with closing elements  20  at their extremities, and   a pair of front wings  22  destined to cooperate with the side panels  18  to insure closing of the pull-up/diaper around the waist, once it is put on.       
 
         [0011]    Naturally, what was said above and repeated once more here, is by way of illustration only: for example, even within the field of the same type of article considered (pull-up/diaper) there are possible variants of embodiment of a practically infinite number. For example (this listing not intended as limiting) the chassis  12  and the absorbing nucleus or core  14  can possibly be integrated in a single element from the beginning; the front wings  22  may not be present, etc. 
         [0012]    Furthermore, as is well known to one skilled in the art, a product such as a pull-up/diaper as exemplified with  10  in  FIG. 1  usually includes numerous other elements (for example, elastic located longitudinally and surrounding the leg openings, the so-called lateral containing cuffs, etc.) which were neither mentioned, nor illustrated herein since they are not relevant to the purposes of describing and understanding the invention. 
         [0013]    What is relevant herein is the fact that for the purpose of insuring the quality of the final product, each of the elements or features previously mentioned is to be located in a precise position and, in particular, at a distance F 1 , F 2 , F 3 , F 4 , F 5  well determined with respect to a reference position. This reference position in susceptible of being identified, for example, as is schematically illustrated in  FIG. 1 , with the position of the front edge  24  of the article  10  (that is, the extremity edge in proximity of which the front tape  16  is located). Naturally, the above-said reference position is susceptible of being identified based on any other characteristic or feature of the article  10 . 
         [0014]    In fact, the same position of the above-said front edge  24  (deriving from a transversal segmentation of the chain of product blanks used in the working phase—so that the front edge  24  of an article  10  corresponds to the posterior edge of the previous article in the exiting sequence of the article from the machine) is itself realised in correspondence to the desired position and therefore can be considered equivalent to one of the above-said features of the product. 
         [0015]    By adopting a terminology in current use in fields such as the automatic packaging field or the field of manufacturing of products such as hygienic-sanitary products, the fact that various elements are located at the desired distance F 1 , . . . , F 5  corresponds to the fact that the respective application and/or work stations operate under exact “phasing” conditions with respect to a reference or “master” timing, which in the illustrated example can be identified with the timing of the cutting station destined to separate the single articles  10  operates cyclically. 
         [0016]    In the production lines used to realise article according to the previously described criteria, the need frequently arises for proceeding to the so-called “format change” that is, to a set of operations directed at enabling the realisation of articles which, though presenting the same structure, have different dimensions (and therefore relative distances between the various elements). 
         [0017]    Currently, when in a system or machine of this type, there is a change of format, it is provided for an operator to act on the machine so that the various stations or working units are correctly “phased” with the reference or master timing. This is possible because the various units are usually actuated by servomotors over which it is possible to have practically total control through a motion control system. 
         [0018]    To align all of the servomotors to a relative position or reference phase, the operator simply chooses a reference point for the product (for example, the final cut, that is, the anterior edge  24  of the article  10  in  FIG. 1 ) from which to initiate a position shift or offset with respect to the master and to the various servomotors moving the working unit. The operation is concluded when the position of the various elements of the article have the desired values. 
         [0019]    This operation is repeated for each working unit. 
         [0020]    The execution modes of such “re-phasing” process are essentially delegated to the operator, who observes the products in exit and over time increments or decrements the phase of the single working unit until the application position of the element in question (or, more generally, the realisation position of the desired feature) falls into the desired range, usually defined by a nominal value and a corresponding tolerance window to be respected. 
         [0021]    In any case, this is a demanding operation in terms of time (with consequent penaltsation of the working cycle), which requires that the operator have a certain experience. 
         [0022]    Within the context considered in the foregoing, certain operating conditions may arise where the “feature” to be realised correctly is the alignment with the body of the article of a layer (for instance a polyethylene film) having matter printed thereon. This printed matter may include drawing or graphic decoration, which must evidently be applied onto the final article with a correct phase. This by also taking into account that the film in question may be subject to variations in length, depending on factors such as, e.g. temperature or productions drifts. 
         [0023]    For that reason, it is known that reference signs may be applied onto such films, such as e.g. reference marks, which can be detected optically (in the visible or infrared range, so that these marks are not visible to the human eye) localized at determined positions, at a notionally constant distance. By detecting any “swerving” of the distance between such consecutive marks and the expected, constant reference value, it is possible to intervene on a respective processing unit (one usually has to do with a metering group from which the film unwinds to be applied onto the product) by varying the degree of longitudinal tension applied to the film to bring back to the expected reference value the distance between the determined positions where the marks are located. All this by further ensuring a orrect “phasing” in applying the film onto the article. 
         [0024]    The provision, in systems or machines for the realisation of article of the type described, of visual systems for final product quality control is already known. These visual systems are capable of providing information in merit to waste, by detecting, without requiring the intervention of an operator, for example, the fact that one or more article exiting from the machine are defective, requiring the discarding of the same and, possibly, the arrest of the machine to proceed with the appropriate interventions. 
       OBJECT AND SUMMARY OF THE INVENTION  
       [0025]    The invention is based on the recognition of the fact that, in view of the way in which the “re-phasing” sequences are set up and manually carried out by an operator and since each unit of the machine involved is independent from the others since each is managed by a corresponding servomotor, it could be useful to automate the entire procedure, reducing the realignment times of the various units and reducing the error to a minimum. All of this with the further possibility of introducing a monitoring during the normal functioning of the machine so to be able to immediately detect and correct a loss of correct phasing condition. 
         [0026]    The present invention has the object of providing a perfected solution capable of fully satisfying the above-presented needs. 
         [0027]    According to the present invention, such an object is achieved by means of a method having the features specifically recalled in the claims that follow. 
         [0028]    The invention also refers to a corresponding system, as well as a computer program product, loadable in the memory of at least one computer, and including the software code portions for performing the steps of the method of the invention when the product is run on at least one computer. 
         [0029]    As used herein, reference to such a computer program product is intended to be equivalent to reference to a computer-readable medium containing instructions for controlling a system to coordinate the performance of the method according to the invention. The reference to “at least one computer” is evidently intended to highlight the possibility of the present invention being implemented in a modular and/or distributed fashion. 
         [0030]    The claims form an integral part of the technical disclosure of the invention provided herein. 
         [0031]    In an embodiment, the solution described herein foresees that the invention provided by the visual inspection station is used to precisely calculate the distances between the different parts to be inspected of the article in production. 
         [0032]    Starting from such data, information is sent to the controller of the movement system so that, extrapolating from the basal information, the controller can appropriately move the servomotor of each unit, putting their functioning “in phase”. 
         [0033]    With respect to a traditional manual re-phasing system, which requires the intervention of an expert operator, the solution described herein allows the automatic acquisition and processing of the re-phasing data. 
         [0034]    Certain embodiments of the arrangement described herein provide for the action of detecting the position of one or more elements on the article realised being performed after the element has been applied onto the article. 
         [0035]    Certain embodiments of the arrangement described herein provide for the action of detecting the position of one or more elements on the article realised being performed before the element (e.g. a film more or less tensioned) has been applied onto the article. 
         [0036]    Certain embodiments of the arrangement described herein provide for the action of detecting the position of one or more elements on the article realised being performed, dendoing on the element considered, before and/or after the element has been applied onto the article. 
     
    
     
       BRIEF DESCRIPTION OF THE ANNEXED DRAWINGS  
         [0037]    The invention will now be described, by way of non-limiting example only, with reference to the enclosed drawings wherein: 
           [0038]      FIG. 1  was discussed previously, 
           [0039]      FIG. 2  is a functional block schema of a system or machine usable for realising the solution described herein, 
           [0040]      FIG. 3  illustrates some elements of  FIG. 2  in more detail, and 
           [0041]      FIG. 4  is a flow diagram representative of the functioning of the solution described herein. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0042]    In the following description, various specific details are given to provide a thorough understanding of embodiments. The embodiments can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, known structures, materials or operations, are not shown or described in detail to avoid obscuring various aspects of the embodiments. 
         [0043]    Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular configuration, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of phrases such as “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular configurations, structures or characteristics may be combined in any suitable manner in one or more embodiments. The references provided herein are for convenience only and do not define the scope of protection or of the embodiments. 
         [0044]    In  FIG. 2 , the numeric reference  100  illustrates in its entirety a system (“machine”) usable to realise articles, such as, for example, hygiene-sanitary articles  10  illustrated in  FIG. 1  and previously described. 
         [0045]    According to a configuration, itself known, the system  100  includes a motorised conveyor  102  (for example, including one or more motorised loop belt conveyor (of known type) allowing advancement from right to left, with reference to the point of observation in FIG.  2 —a chain of base elements (for example, the chassis  12  in  FIG. 1 ) for the realisation of the article  10 . 
         [0046]    Traversing in succession a plurality of work stations S 1 , . . . , S k-2 , S k-1  such base elements are completed with the application of the various other elements  14 ,  16 ,  18 ,  22  completing the article  10 . Finally, traversing a additional work station S k  (substantially configured as a cutting station, for example, with counter rotating knives) the chain of article blanks advancing on the conveyor  102  is finally segmented into the single articles  10 , forming the front edge  24 . 
         [0047]    As was already said several times in the introductory part of the present description, the nature and characteristics of the article  10  are not determining for the purpose of comprehending the realisation of the invention, whose field of application is absolutely general. Analogously, the characteristics—and the number—of the various stations S 1 , . . . , S k  are determining factors of the characteristics of article  10  realised from time to time, and once again, they are not themselves essential features for comprehending and realising the inventions. 
         [0048]    For such purpose, it will be sufficient to remind that the various stations S 1  . . . , S k  act because they are activated by a corresponding motor/actuator M 1 , . . . , M k  subjected to control by a control module  104 . 
         [0049]    The numeric reference  106  then indicates a visual inspection station (for example, a video camera) that can frame the articles  10  at the exit from the cascade of work stations S 1  . . . , S k  and detect the position of the various elements  12  to  22 , in the context of a single article. For such purpose, the functioning of the visual inspection station  106  can be synchronised with the transit in front of the visual inspection station itself of a reference element present in each article  10 ; for example, as shown in  FIG. 1 , the reference element in question can be the extremity edge  24  and in such case the functioning of the visual inspection station  106  is actually synchronised with the functioning of the cutting station S k . 
         [0050]      FIG. 2  refers to a positioning of the visual inspection station  106  down stream from the cutting station S k . It will also be appreciated that the act of detecting the position of the various elements of the article  10  can also be performed upstream of the cutting station S k , therefore before the articles  10  are separated. Also, those skilled in the art will note that the act of the detecting the various elements  12  to  22  of the single article  10 , represented herein as being performed by a single visual inspection station or video camera  106  could, at least in principle, be realised through a plurality of visual systems (therefore a plurality of video cameras) placed along the cascade of work stations S 1 , . . . , S k . The solution of performing the detection with a single visual inspection station has the advantage of greater overall simplicity of the system. 
         [0051]    Specifically, in those applications where the “feature” to be realised correctly is the alignment with the body of the article of a layer (for instance a polyethylene film) having matter printed thereon, the visual inspection station or video camera  106  intended to detect the positions of the reference signs (marks) may be located in correspondence with the metering unit from which the film unwinds to be applied onto the product. The visual inspection station or video camera  106  “reads” in real time the distance between two subsequent marks, thus the position that these marks will have on at least one article realised with the respective portion of film. This even if, of course, the reading action is performed before such a film portion is actually applied onto the article. 
         [0052]    The output signal of the video camera  106  is sent to the input of the control module  104 . As schematically illustrated in  FIG. 3 , in the exemplary embodiment illustrated herein, the module  104  includes two computer systems  108  and  110  located in cascade. 
         [0053]    The main function delegated to the system  108  is that of analysing the image output from the video camera  106  so to detect the position (that is, the distances F 1  to F 5  in  FIG. 1 ) of the various elements of an article  10  exiting from the system. This occurs through processing performed on the visual detection data from the video cameral  106 , better described in the following. 
         [0054]    Instead, the task delegated to system  110  is that of comparing the positional data elaborated by the system  108  starting from the image output of the video camera  106  with the reference values stored in a memory  112  (represented as a separate entity in  FIG. 3 , but usually integrated into one of the systems  108  or  110 ) to then provide the regulation function of the work “phase” of the various units S 1 , . . . , S k , that is, in practice, the control of the work phase of the various servomotors/actuators M 1 , . . . , M k . 
         [0055]    In an exemplary embodiment, the position reference values (F 1 , . . . , F 5 ) stored in the memory  112  are determined in the form of a nominal position value with an acceptable variation range with respect to said nominal value. 
         [0056]    In an exemplary embodiment, the visual inspection station can be constituted by a matrix video camera, for example a CCD video camera with a resolution of 1024×768 pixels such as, for example, the XCL-X700 video camera made by Sony. 
         [0057]    The part of the module  104  indicated by  108  in  FIG. 3  can be configured around a personal computed (PC) of current production equipped with an acquisition and image analysis module (for example the card Cognx VPM-8602X). 
         [0058]    In substance, the function delegated to the PC  108  (in addition to the general one of system management) is that of detecting from the video camera  106  images corresponding to the single articles  10  exiting from the system or machine  100  to analyse such images (according to known criteria) so to allow detection of the distances F 1 , . . . , F 5  to which, by way of example, reference is made in  FIG. 1 . 
         [0059]    Below in the present description, it is assumed that each of such distances is linked in a univocal way to the functioning “phase” of a corresponding station between the stations S 1 , . . . , S k  included in the system  100 . 
         [0060]    In the example illustrated herein, the distances F 1 , . . . , F 5  are all distances detected in the general advancing direction of the articles  10  through the system  100 . It will also be appreciated that the same general criteria described in the following concerning the regulation of the intervention phase of the servomotor/actuator M 1 , . . . , M k  could also extend to a regulation function of application distances/positions of various elements of the article  10  detected not in the advancing direction (that is, according to the terminology common in the art, “machine direction”), but also in a direction transverse to the advancing direction (that is, “cross direction”). As was already said, the numeric reference  112  also indicates the presence of a card or, in general, a memory area in which the nominal values of the distances F 1 , . . . , F 5  together with the corresponding tolerance ranges for each type of article  10  intended to be realised with the illustrated system, are stored. 
         [0061]    Therefore, the function of the modules  104  is that of detecting on a single article  10  (or, better yet, on a sample lot of n successive articles  10  exiting from the system  100 ) the actual values of the distances F 1 , . . . , F 5  and to act on the control of the servomotors/actuators M 1 , . . . , M k  when and each time it is necessary, modifying the “phase” of the work cycle of the corresponding work stations to restore (and maintain) the values of the distances F 1 , . . . , F 5  to within the tolerance ranges provided. 
         [0062]    In an exemplary embodiment, the complex of control elements indicated in its entirety with  110  is centred on a PLC (Programmable Logic Control) Siemens S400 with a Profibus interface associated with a servomotor control unit such as, for example, a PPC R02 servomotor control unit made by Rexroth Indramat. 
         [0063]    The set indicated with  104  may contain accessory elements of current use destined to allow the correct interfacing between groups  108  and  100 . Among such elements a Cognex distribution block for I/O exchange (synchronisation trigger) of PC-video camera, that is, a Profibus CP5611 card to allow exchange of data between personal computer and PLC can be cited as an example. 
         [0064]    The possibility of controlling the various servomotors/actuators Mi, . . . , M k  by the module  110  is represented in  FIG. 3  showing the connection in exit between the module  100  and a generic servomotor/actuator Mj. 
         [0065]    In an exemplary embodiment, the module  104  acquires the images to be inspected from the video camera  106 , converting the signal into Camera Link video format. The signal can be acquired by the personal computer  108  through an acquisition card (for example, VPM-8602X-000 made by Cognex). This can be provided with an auxiliary connecter for connection to a distribution block (VPM-8600 Cognex, for example) to which a servomotor encoder is also connected (in the case in which a linear video camera is used) and/or an external trigger signal providing the synchronisatton to the image acquisition. Such synchronising signal can be referred, at least roughly, to the “master” timing of intervention, for example that of the cutting unit S K  (see  FIG. 1 ). 
         [0066]    The signal from the video camera  106  can be elaborated by inspection software such as, for example, the ProInspect 3.1 software by Univision susceptible of being supported by a personal computer such as the personal computer  108 . By using such inspection software, it is possible to create a function that in fact permits the measurement of the values of the distances F 1 , . . . , F 5  starting from the images received from the video camera  106 . In the flow diagram in  FIG. 4 , the block  1000  represents the zeroing of the index of the n features measured by the system (in the example in  FIG. 1 , the features from F 1  to F 5 ), while the blocks  1002  and  1004  actually represent the functions of image acquisition and of the determination of the values of the distances F 1  to F 5 . In a preferred way, the distances in question are detected as the arithmetic average of the measurements made on k articles  10  in sequence (where k is a settable parameter in the visual system). 
         [0067]    The detected value is sent to the PLC of module  110  (for example, through a Profibus card) and elaborated. In an exemplary embodiment, the input data expected by the relative function consists of two values, one constituted by the actual measurement and the other by a code defining the object (that is, the element or feature from 14 to 22) for which the distance with respect to the reference point (for example, the anterior edge  24  in  FIG. 1 )  1 s being calculated. The measured value is compared with the reference value stored in memory  112  and, if the difference between the two falls outside of the tolerance window, a signal is sent to the control function of the servomotor that is representative of the quantity of re-phasing to apply to the servomotor/actuator, which moves the handling unit responsible for the location of the element/realisation of the feature considered. 
         [0068]    In those applications where the “feature” to be realised correctly is the alignment with the body of the article of a layer (for instance a polyethylene film) having matter printed thereon, the visual inspection station or video camera  106  “reads” in real time the distance between two subsequent marks, thus the position that these marks will have on at least one article realised with the respective portion of film. The value of the distance between two subsequent marks read by the visual inspection station or video camera  106  is compared with the reference value stored in the memory  112  and, if the difference between the two falls outside the tolerance window, a signal is sent to the control function of the servomotor/actuator of the metering unit for the film which is representative of the amount of which operation of such servomotor/actuator is to be re-phased in order to change the degree of longitudinal tension applied to the film in order to bring the distance between the determined positions where the marks are located back to the desired reference value; this by also ensuring the correct phasing in applying the film onto the article. 
         [0069]    The step  1006  corresponds to the verification of the fact that the correct positioning of the single feature F j  that is being measured in the specific step of the flow diagram has been verified. Reference  1012  simply corresponds to the verification of the fact that the correct positioning of all of the characteristics/features of the product has been verified. In the illustrated exemplary embodiment, the verification of the correct realisation of the single characteristics or features is performed in a pre-established sequence according to an order given by a priority index determined for each article in function of the specificity of the same: it will be appreciated in fact that errors in the positioning of a specific element can be more serious, less tolerable with respect to others and therefore such to require a higher priority regulation/correction intervention. Also, keeping in consideration that some of the required interventions may be conditioned by the execution of others on which they might be constrained. Assuming that step  1006  provided a positive output, then in step  1012  it is determined whether all of the features of the product  10  are correctly positioned. 
         [0070]    Assuming for now that step  1012  provided a negative output, in a step  1008  the index j relative to the characteristic/feature, that is, to the servomotor/actuator object of the phasing regulation action is incremented and then returning upstream of step  1002 , the control cycle of the single feature begins again through the steps  1002 ,  1004  and  1006  providing for the verification of whether the F j  distance data considered from time to time falls within the range of acceptable values stored in memory  112 . If that is the case, with a positive output in steps  1006  and  1012 , the system evolves again upstream of step  1000  which zeros the index of the features to be controlled, restoring it to 1 and therefore starting a new complete cycle in which it periodically verifies the fact that the system has maintained the desired regulation conditions providing for the performance of the correction interventions possibly needed, running again the sequence of operations previously described (or even only a subset of the same). If instead step  1006  indicates that an error exists in the realisation of the feature, then the desired correction action is realised in a step  1010  and the system evolves again upstream of step  1002  to verify whether the correction intervention has been sufficient or whether a new correction cycle is required. 
         [0071]    It will be appreciated that the flow diagram in  FIG. 4  in general presents the concept according to which the regulation operation is performed in sequence on the various features/distances considered, moving to a successive feature only after the previous feature/distance in the priority order has been correctly adjusted to the acceptable tolerance values. 
         [0072]    The experiments performed so far by the Applicant show that this mode of operation is preferable in terms of global results of accuracy and rapidity of execution of the regulation and control operation. 
         [0073]    Naturally, without prejudice to the underlying principle of the invention, the details of realisation and the embodiments may vary with respect to what has been described herein as non-limiting, without departing from the scope of the invention as defined by the annexed claims.