Abstract:
The present invention concerns the field of graphic apparatuses and in particular its object is an apparatus for the so-called “weeding” of plastic or paper films having or more self-adhesive, double sided adhesive or electrostatic layers coupled with a support liner treated with a non-stick agent. The apparatus comprises a gripper ( 3 ) with a pinching head ( 8 ) comprising a plurality of self-centering jaws ( 16 ).

Description:
TECHNICAL FIELD OF THE INVENTION 
       [0001]    The present invention concerns the field of graphic apparatuses and in particular its object is an apparatus and a relative method for the so-called “weeding” of plastic or paper films having or more self-adhesive, double sided adhesive or electrostatic layers coupled with a support liner treated with a non-stick agent. 
       BACKGROUND OF THE INVENTION 
       [0002]    In the preparation of adhesive graphics, simply decorative or also having a protective function, obtained through various printing or through simple engraving processes, a distribution of single graphics is obtained on a single sheet comprising films of the type indicated above, printed and/or cut, coupled with a supporting silicone release paper, or liner. A cutting machine thus has the function of cutting the fringes of the various programmed drawings or writings only on the film, without however cutting also the support/release paper. At this stage there is the need of removing the “weeds”, that is, the parts of adhesive film which are not processed and are therefore outside the graphics. In fact, the subsequent user, for his production requirements, needs to have a sheet in which there are only the graphics on the support paper, so that the same graphics can be easily removed and applied as desired. 
         [0003]    Such a removal operation of the superfluous film, on the whole also called “weed” for the sake of simplicity, is in fact called weeding. This is a very onerous operation and at the same time delicate since, especially when the contours of the graphics have irregular shapes, or in any case they have indentations or acute curves or undercuts (situation which occurs even with simple alphanumerical characters), the film of weed to be removed tends to tear, leaving residues, or to pull away also the graphical part that should instead be left unaltered. There are also often small parts, typically the internal hollows of characters and writings in general, which require operations that are accurate, precise and repeated. 
         [0004]    Such an operation is currently carried out in a completely manual manner, with serious affection of the production time and on labor costs. Automation of the weeding process, despite the attempts made, has been found to be problematic, indeed for the difficulties mentioned above, furthermore enhanced by the fact that the different graphics to be treated and their distribution demand requirements that are always different. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention, on the other hand, provides a response to this strongly felt need, by providing a series of surprisingly effective technical expedients that make possible to achieve a weeding system that obtains a fully effective result, capable of replacing the manual methods currently in use, with consequent remarkable advantages. 
         [0006]    The essential features of a fine weeding device according to the invention are defined in annexed claim  1 . Other advantageous features, in connection with preferred or in any case effective embodiments, are the subject of the different dependent claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    Characteristics and advantages of the fine weeding device according to the present invention will become apparent from the following description of embodiments thereof, made purely by way of example and not limitative, with reference to the attached drawings in which: 
           [0008]      FIG. 1  is a schematic axonometric view of an automatic weeding apparatus; 
           [0009]      FIG. 2  is a top plan view of the apparatus; 
           [0010]      FIG. 3  is an axonometric view from below of a gripper of a fine weeding device that according to the invention is included in the apparatus; 
           [0011]      FIGS. 4 and 5  are axonometric exploded views of respective parts of the gripper of  FIG. 3 , in particular a damper and a pinching head; 
           [0012]      FIG. 6  is an exploded view of a radial jaw of the pinching head of  FIG. 5 ; 
           [0013]      FIGS. 7   a  and  7   b  show respectively from a side and from above a pinching block of the jaw of  FIG. 6 ; 
           [0014]      FIG. 7   c  is an enlarged detail of the inside of circle C of  FIG. 7   a;    
           [0015]      FIG. 8  and  FIG. 9  schematically depict, respectively in an axonometric view and in front view, a fine weeding device according to a different embodiment of the invention; 
           [0016]      FIG. 10  is a sectional view taken along a longitudinal plane of the apparatus of a seizing head of a rough weeding device; 
           [0017]      FIGS. 11 and 12  are, respectively, a front view and a top plan view of a blower of the rough weeding head of  FIG. 10 ; 
           [0018]      FIGS. 13 to 15  are cross-section views of the blower in the previous figures, taken respectively along the lines XIII, XIV e XV of  FIG. 11 ; 
           [0019]      FIG. 17  is a further representation, in this case partial, schematic, broken and axonometric, of the rough weeding head; and 
           [0020]      FIGS. 17   a  to  17   l  represent schematically respective subsequent stages of the rough weeding process. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]    With reference to said figures, an apparatus according to the invention is intended to automatically remove the weed, which advantageously undergoes a pre-emptive cutting operation, with suitably positioned assisting cuts that are added to the conventional ones that define the periphery/outline of the various graphic elements. The cuts, carried out with conventional plotters, in turn have the characteristic of cutting the self-adhesive, adhesive or electrostatic, plastic or paper film, without affecting the support paper or liner. The present invention concerns the actual weeding apparatus, per se provided with novel and advantageous structural and functional characteristics. 
         [0022]    The apparatus comprises a frame  1  equipped with a top plane  1   a  on which through known pneumatic systems the sheets of material to be weeded are fed and moved forward. Upstream of the plane there is arranged a feeder  2 , advantageously having a lifting surface, with a motorised control, on which to position the sheets with dimensions that can vary from 200×300 mm to 1000×1400 mm or also reels having corresponding size. The plane  2   a  of the feeder can comprise, along two consecutive sides, mechanical abutments that are suitable for allowing a reference of the sides of the sheet, the so-called “print register” sides. This, along with the control of the height of the plane, ensures that when a stack of sheets is arranged on the plane, the sheet on top, intended to be processed, is always positioned perfectly with respect to the work plane  1   a  of the frame  1 . 
         [0023]    A first part of the plane  1   a,  taking as a reference the advancement direction of the material indicated with the arrow X of  FIG. 2 , represents a fine weeding station m, that is a station of fine removal of small parts of weed, including those parts that are generated by a plurality of weeding assisting cuts. Once the fine weeding has been carried out, the main body of the weed (through a rough weeding station/process M which will be described in greater detail hereafter) can be detached completely and effectively, without leaving residues, without tearing material or removing undesired parts. 
         [0024]    A fine weeding device operates at the fine weeding station m ( FIG. 2 ), with a gripper  3  that a portal  4  supports in a vertical arrangement, allowing the gripper to move along the three coordinates XYZ, in which the plane XY is the one parallel to the plane  1   a  and the axis Z is the direction along which the gripper  3  extends. 
         [0025]    To such a purpose the portal  4  has a crosspiece  5  which can be displaced along the advancement direction X and along which a carriage  6  moves, in accordance with the direction Y, and in turn supports the fine weeding gripper  3  through a linear actuation system along the direction Z. All such movements, just like those that are not specified otherwise, are controlled by motorizations implemented as obvious to a person skilled in the art. It is in any case worth noting how the movement along Z of the gripper  3  is advantageously carried out by means of a recirculating ball system driven by a direct brushless motor that ensures speed and precision with a repeatability in the order of a hundredth of a millimetre. 
         [0026]    The portal  4  also has a suction rod, which is not visible in the figures, which through a suction pad system feeds the sheet and arranges it so as to align the front left corner (imagining an observer which is standing looking towards the same direction as the advance movement direction) with a suitably pre-set reference. During transport the sheet remains lifted in the front part that is gripped by the suction pads but is progressively made to adhere to the plane  1   a  in the remaining part towards the tail. The plane  1   a  is indeed connected to a vacuum pump system and the friction of the sheet created by the suction during movement ensures a perfect flatness preventing air bubbles or creases from forming on the sheet itself. 
         [0027]    Once the sheet has been positioned on the suction work plane at the fine weeding station m, the gripper  3  can carry out the fine removal of the various (small) weed parts, including those created by the plurality of weeding assisting cuts, according to the instructions from the control system, in turn processed on the basis of technical criteria that shall be further explained hereafter. 
         [0028]    The gripper  3  is represented in particular in  FIGS. 3 to 7   c  and includes from top to bottom (the reference is at the work position in alignment with the axis Z) a damper  7  ( FIG. 4 ) and a pinching or gripping head  8  ( FIG. 5 ) adapted to come into contact with the adhesive film and to remove it through pinching and lifting, without of course affecting the liner support underneath. The damper  7  has the function of ensuring that the head  8  exerts a pressure with constant intensity on the material to be worked, compensating for possible non-homogeneity in shape of the suction plane, and makes use of a pre-loaded spring  9  that elastically opposes the movement of a stem  10 , through which the damper is connected to the head  8 , the stem being slidingly supported inside a base cylinder  11 . 
         [0029]    The head  8  moreover comprises an annular tool-holding flange  12  that can be coaxially connected in a reversible manner, with a quick fit system that can be driven pneumatically, at the aforementioned stem  10  of the damper  7 . Once the flange is removed, it can be supported in a suitable manner on a tool changing station (replacement of jaws  16  and/or blocks  17  as detailed further on) through four pins  13  projecting radially from the flange itself. A support disc  14  is connected to the flange  12 , again coaxially, on the opposite side of the stem  10 , said support disc being in turn the support for a pneumatically driven self-centring chuck  15  equipped with three radial jaws  16  provided with respective pinching blocks  17  which represent the actual manipulation element of the film/weed to be removed. 
         [0030]    The jaws  16  are thus driven by the self-centring chuck  15  that, when considered as such, has known mechanical characteristics. Through a base  16   a  of each jaw  16  the same jaws are linked with the chuck ( FIG. 6 ); from the base  16   a  a strut  16   b  projects, and at the free end of the strut  16   b  a relative pinching block  17  is supported, preferably obtained through electric discharge so as to ensure a perfect mutual adherence of the three blocks when the self-centring chuck, and therefore the jaws, take up a radially locked end stop position (closed position). 
         [0031]    The block  17  is kept aligned by two pins  18  that prevent the sliding along the axis X and Y, whereas the sliding along the axis Z is prevented by a plate  19  held by a screw  20 . 
         [0032]    Entering in greater detail as far as the shape of the pinching blocks  17  is concerned, said shape being particularly meaningful for one aspect of the invention, each block has two front facets  17   a  that extend parallel with respect to the axis Z, separated by an edge  17   b,  forming an angle, measured on the plane XY, of 120°. Those are indeed the faces that, by projecting frontally with respect to the strut  16   a  of the jaw  16 , come into contact with one another causing the stop in the aforementioned closed position (shown in  FIG. 3 ). The front facets  17   a  extend further in the direction Z at the lower side (the free one or pinching one) defining, in cooperation with an inclined wall  17   c,  a pyramid shaped projection at the top of which a contoured prism-like tip  17   d  forms the “finger” for gripping the material. Such a tip has an elevation, measured along the axis Z and with respect to the inclined wall  17   c  from which it branches off, in the order of some tenths of a millimetre, for example five, enabling it to sink into the adhesive plastic material without damaging the liner of silicone release paper underneath. 
         [0033]    According to an embodiment shown in  FIGS. 8 and 9 , the fine weeding device comprises two or more grippers  3 ′ that are supported in a carousel arrangement that allows for a greater work speed by hiding a discharge step of the weed pinched by a gripper, with respect to a fine weeding step carried out by another gripper. In the figures two grippers  3 ′ can be noticed, mounted on a revolving support plate  41  that is driven into rotation around the axis Z (that in this case is no longer the central axis of a single gripper, but the axis of the gripper system as a whole), by an actuator  42 . Moreover, the linear actuation system along Z is here indicated at  43 . A shelf  44  can be also noted, supported by the crosspiece  5  and offering to the grippers  3 ′, in their proximity, and in particular to the inactive gripper, the possibility to unload the weed previously pinched. Finally, a video-camera  45  and a lighting device  46  are represented, these additional components advantageously assisting the control of the fine weeding process, ensuring a correct centering of the sheet to be processed and a consequent high precision on the pinching points previously determined by the strategy set by the control software. Besides, the reference marks on the sheet can be focused and the conformity of the material to a standard quality evaluated, so that possible defective pieces are traced and do not proceed further to the weeding process. 
         [0034]    The operation of this embodiment can be easily appreciated in particular from  FIG. 9 , that shows how in this case the support of the grippers  3 ′ by the plate  41  is carried out with a further linear degree of freedom, according to directions Z′ parallel with the axis Z. Such further degree of freedom is related with the weed unload function that indeed requires a reciprocating motion of lifting and lowering the gripper so as to leave the weed over the shelf. An elastic pusher  47  is secured with the plate  41  and acts on the tail of the gripper  3 ′ in the pinching position to calibrate the force applied in the pinching step. Two springs  48  are associated with respective support guide for the reciprocating motion of the single grippers  3 ′, being urged between the same grippers and the plate  41  in order to compensate for the variations in height due to the elevation of the weed collection plane (defined by the shelf) and to the accumulation of removed weed. 
         [0035]    Particular self-adhesive materials may require, for a correct unloading, the provision of an air ejection through a nozzle (not shown) placed close to the jaws of the gripper and turned on as the weed is brought into contact with the unload surface, preventing that some parts may adhere to the surfaces of the gripper. 
         [0036]    In operation, each fine weeding step thus occurs, in brief, with the positioning of the gripper on the appropriate coordinates XY, the jaws being in the open configuration. The device then goes down along the axis Z closing the jaws in a synchronised manner in order to complete the run as they come into contact with the weed to be removed, which is thus gripped between the tips  17   d  that are mutually tightened. This action causes there to be a first detachment of the weed, the removal of which is completed with a new lifting, not necessarily exactly vertical, in some cases and preferably preceded by a displacement along XY. By using the embodiment with the carousel arrangement, a new step as the one here just described is carried out getting rid of the waiting step necessary to the unload of the pinched/removed material, because the rotation of the plate  1  makes a free and active gripper immediately available while the other one unloads the material on the shelf  44 , possibly provided with an adhesive, weed collection belt as indicated by the reference numeral  44   a.  In the absence of a carousel system the single gripper can carry out the unloading or discharge over a sliding belt made from consumable plastic or paper material, with an obvious configuration which is not shown. 
         [0037]    Once the fine weeding phase is over, the sheet proceeds over the plane  1   a  and thus enters the already mentioned rough weeding station M in which a weed seizing head  21  of a rough weeding device operates ( FIGS. 10 to 16 ), cooperating in an initial phase with a cutting system. The rough weeding device has the configuration of a crosspiece arranged along the axis Y above the plane  1   a  and it is supported in a mobile manner along the axis X by a lateral guide system  1   c  of the plane itself. An adjustment of the position along the axis Z can be also provided, through for example abutment screws to be actuated manually. 
         [0038]    The head  21  comprises a front suction rod  23  that takes hold of the sheet and positions it above the cutting device, embedded in the plane  1   a  in an inlet position of the rough weeding station M. In this phase, the suction system of the rough weeding head  21  carries out an opposing effect to the action of a blade that moves along the axis Y, controlled by a pneumatic piston, through a recirculating ball slide on the entire length of a linear guide. The liner of silicone release paper placed under the self-adhesive plastic material is cut for its entire width at a distance of around 2.5 cm from the front edge of the sheet, so as to define a flap or edge that can be easily folded upwards, with the consequence and the aim that shall soon become clear. The precision with which the blade sinks into the liner is ensured by a micrometer screw, whereas the stop abutment of the knife is ensured by a pneumatic piston that brings a support disk of the blade in contact with the supporting plane of the sheet. The gap on the axis Z between the knife and the disk thus defines the depth of the cut. 
         [0039]    Once the liner has been cut, the sheet still held by the suction rod  23  is brought inside the actual rough weeding station M, making the cutting line of the liner coincide with a reference mark of a device for lifting the head flap of the liner. Such a device is schematically represented and indicated with reference numeral  36  in  FIGS. 17   b  to  17   l,  and it consists substantially of a bar that can be lifted along the axis Z through linear pneumatic actuators that are not represented, between a lowered position in which it is concealingly integrated inside the plane  1   a  and a raised position in which it is capable of folding upwards by 90° the front flap or edge of the sheet, defined by the cutting means indicated above. 
         [0040]    The lifting strip is preferably shaped with a staggered or comb-shaped edge that engages with a matching shape of the rough weeding plane, so as to lift the flap or edge at the end margin of the suction area, i.e. with the suction that is in any case active between the teeth of the staggering/comb and assists a lift precisely by 90° of the flap or edge. 
         [0041]    A further component of the weed seizing head is a blower  28  that, on a plane that is parallel and adjacent to the plane  1   a,  produces an ejection of pressurised air that is capable of covering the entire width (direction Y) and is directed according to X, in a direction that is in accordance with that along which the sheet advances forward. Advantageously, the blower  28 , shown in particular in  FIGS. 11 to 14 , takes the shape of an elongated blade extending along the axis Y with a plurality of adjacent and independent sectors, for example ten, that are driven by respective solenoid valves  29  in order to dispense air, through suitable channels  28   b,  during the movement of the sheet only where actually required. 
         [0042]    The pressurised air comes out from a system of front slits  28   a  of the blower, to which a pair of rollers  30 ,  31  are associated, spaced along the direction X and arranged so that the blade is substantially tangent with respect to them. More precisely, a rear roller  30  is made from silicone material, whereas a front roller  31  is preferably made from aluminium with a non-stick coating and is mobile towards and away from the rear roller  30 . The rotation of such rollers is controlled by, and is synchronised with, the forward movement of the whole head, through a pinion and rack transmission (the pitch of the rack being in particular the same as the diameter of the two rollers). 
         [0043]    In an upper area of the group, and therefore above the components described above, there are a pull drum  33  with an incomplete development (that is, without a circular sector preferably having an angle that is equal or slightly lower than 90°) and above the drum  33 , a shaft  32  for collecting the weed in a reel (around a core of disposable cardboard), both motorized and arranged with their rotation axis extending along the axis Y. The motorisation of the roller and the shaft is mutually independent, with a torque limiter that can be set in order to ensure the correct tension of the weed, thus avoiding ripping or accumulation thereof. The shaft  32  can moreover translate towards and away from the pull drum  33 . 
         [0044]    The incomplete pull roll, indeed thanks to its C-shaped section, defines a radial face  33   a  that cooperates with a clamp member  35  so as to be able to lock the weed and pull it. 
         [0045]    Entering into greater detail as far as the work sequence of the rough weeding process is concerned, and with particular reference to  FIGS. 17   a  to  17   l , the blower blade  28  is positioned at the front edge of the sheet, indicated with F. In  FIG. 17   a  it can be noted also the folding flap Ft indeed generated frontally as a result of the half-cut previously mentioned (cutting line indicated with L). Initially, the radial face  33   a  of the C-shaped drum  33  is arranged perpendicular with the plane  1   a,  tangent to the back roller  30  and substantially aligned with the cutting line L. Also the front margin of the blower blade is positioned precisely in a way such as to coincide with the cutting line L. The clamp member  35  is open and the front roller  31  is in a forward displaced position ( FIGS. 17   a  and  17   b ). 
         [0046]    As a result of the lifting of the folder  36 , the folding flap Ft, including both the weed Fs and the liner Fl joined to one another, is folded upwards ( FIG. 17   c ). At this stage the front roller  31  retracts ( FIG. 17   d ) and in cooperation with the rear roller  30  seizes the material, in contact with the adhesive side and directs it upward, whereas, at the same time, the head retracts in direction X, in opposite fashion to the advancement motion of the sheet ( FIGS. 17   d  and  17   e ). While this occurs the weed Fs starts becoming detached from the liner of silicone release paper Fl, with the latter kept in contact with the plane  1   a  thanks to the suction exerted by it and to the jet of the blower  28  which is responsible for the function, useful in some cases, of preventing the lifting of small parts belonging to the graphics and that must indeed stay placed on the liner. 
         [0047]    As visible from  FIG. 17   f , the weed Fs has been fed onto the radial face  33   a  of the pull drum  33  and the clamp member  35  can close to lock it. A rotation of the drum  33  at this stage continues the removal of the weed Fs which is circumferentially wound around the roll, while in a coordinated manner, the head unit continues to move rearwards. The rotation also brings the weed to the shaft  32  bearing the winding core. In order to start collecting, the shaft  32  moves tangentially alongside the drum  33  ( FIG. 17   h ) so as to be, in turn, wrapped up by the same weed ( FIG. 17   i ). Once the winding has been triggered, the winder can lift up so as to allow it to freely expand its diameter ( FIG. 17   l ). Of course, for each treated sheet, the aforementioned sequence is repeated and the reel of collected weed continues to grow. Once the diameter of such a reel has reached a set size, a sensor detects it, and stops the apparatus so as to allow the reel itself to be extracted and replaced with an empty cardboard core. 
         [0048]    The present invention provides therefore a device capable of making the fine weeding process effectively automatic, remarkably reducing the production times and significantly improving the productive results as far as costs and reliability are concerned. 
         [0049]    The present invention has been here described with reference to its preferred embodiment. It should be understood that that there may be other embodiments within the same inventive concept, as defined by the scope of protection of the following claims.