Abstract:
A process for pallet packaging includes steps of maintaining the pallet stationary, and subjecting a spool supplying the packing film to a movement around the pallet of rectangular trajectory, whereby in each cycle or turn of the spool four segments of rectilinear displacement are defined therefor related one to another through orthogonal inflections, and whereby the pressure of the film is maintained constant throughout the wrapping, avoiding risks of the same being torn. The spool is mounted on a headstock in association directly or indirectly with the free extremity of the multiple articulated arm of a robot, with an operating program developed for the aforementioned movements.

Description:
[0001]    This application is a continuation of PCT/ES00/00103 filed Mar. 23, 2002. 
     
    
     
       OBJECT OF THE INVENTION  
         [0002]    The present invention relates to a new packing procedure, with the clear objective of providing a pallet with its load with a wrapping based on plastic foil or film, which suitably stabilises said load during subsequent handling of the pallet and/or protects it from dust and water, procedure which has been specially conceived in order to improve the packing conditions, specifically by avoiding tears in the plastic film and permitting a higher operational speed, with the consequent enhancement in the performance of the packing machine, with considerable stretching of the film and consequent saving therein.  
           [0003]    The new procedure permits the wrapping of four or five faces indifferently, utilising a single spool of film.  
           [0004]    The invention concerns also the machine for putting the procedure mentioned into practice.  
         BACKGROUND OF THE INVENTION  
         [0005]    At the present time there are two basic solutions for the packing of a pallet with its load, both of which are based on winding over said assembly an adequately tightened plastic foil or film, in such a manner that the pallet&#39;s load, generally made up of separate elements, is perfectly bound in itself and to the actual pallet, in order to ensure the stability of the assembly in subsequent handling during transport.  
           [0006]    One such solution consists in mounting the pallet with its load on a rotating platform, whilst the film-feeding spool is arranged laterally with respect to the pallet and is subjected to a vertical displacement movement, so that the plastic foil is wound helicoidally over the outside surface of the load whilst the pallet turns.  
           [0007]    The fundamental problem with this solution lies in that, in the initial phase of packing, that is when the load is not secured, the centrifugal force produced by the rotary movement of the pallet causes the same to tend to be displaced in a radial direction and to fall, which substantially limits the speed at which the pallet is turned and consequently the working rate of the machine.  
           [0008]    Machines of this type are reflected, for example, in the European Patents with application number 91401689.4 and 92401863.3.  
           [0009]    The other solution consists in maintaining the pallet stationary during packing, in order to avoid the problems with centrifugal force of which mention was made above, it being the film-feeding spool which describes a planetary movement around the pallet, at the same time as it simultaneously undergoes an alternating motion in the vertical direction, as for example occurs in the machines reflected in the European Patent with application number 90402027.8 or the PCT with publication number WO 90/06261.  
           [0010]    This second type of machine, structurally much more complex than the first type, and consequently much more expensive, and which due to its large turning circle produces high inertial forces because of the weight of the moving elements, which make necessary a large reinforced framework. It also presents as a fundamental problem, which is also applicable to the case of the machines of the first type, a serious risk of tearing the film as the pulling motion of said film is in both cases circular and constant, meaning that “tugging” occurs is said film in correspondence with the folding the latter undergoes on reaching the corners or upright edges of the load, in such a manner that in correspondence with said edges extra straining and stretching are produced which are the effects that produce the risk of tearing which has just been mentioned.  
         DESCRIPTION OF THE INVENTION  
         [0011]    The packing procedure which the invention proposes, applicable to a packing machine of the second type of those mentioned above, that is of those in which the pallet with its load is maintained steady during the packing, resolves in a fully satisfactory manner the aforementioned problems in the different aspects stated.  
           [0012]    To this end and in more specific terms, the procedure of the invention consists in subjecting the headstock of the film spool to a cyclic motion around the pallet with its load, but with the special particularity that said headstock describes a trajectory always parallel to the outline of the pallet. More specifically, in each cycle or turn of the spool around the pallet, four segments of perfectly rectilinear displacement are defined, parallel to the four faces of the pallet, related to each other through orthogonal inflections, in correspondence with the upright edges of said pallet, that is, in contrast to the circumferential trajectory of the headstock in the classic procedure, with the procedure of the invention said headstock describes a rectangular trajectory, all of this such that the exit tension on the film from the aforementioned headstock remains constant during the entire packing and the tension is also constant with which said film is applied both to the faces and to the edges of the pallet-load assembly, there being no uniform stretching and tensions in the film tending to provoke tears therein.  
           [0013]    Complementarily, both for achieving the putting into practice of the procedure mentioned, and for avoiding the problems of conventional packing machines, inherent in the high inertia produced by the motion thereof, the machine on which the object of the invention is also centred, incorporates, in a lateral disposition with respect to the zone of stationary positioning of the pallet, a robot provided with an articulated arm to which is directly or indirectly joined the headstock carrying the film-feeding spool, said robot coming with a program which permits it to describe the cyclic movement of rectangular trajectory at constant speed of which mention has been made above.  
           [0014]    The robot itself can also supply the spool-bearing headstock with the necessary movement of vertical displacement, in order that the wrapping of the film take place helicoidally, or this vertical movement can be achieved by the coupling to the extremity of the articulated arm of the robot of a vertical guide rail on which the spool-bearing headstock in turn shall be displaced. The employment of one system or another, or the combination of both, depends on the maximum height of the pallet to be wrapped.  
           [0015]    Provision has also been made for the spool-bearing headstock to include a means of tilting which permits it to adopt an inclined position, in the uppermost location, for the wrapping of the top face of the load formed on the pallet, that is for what is commonly termed as wrapping of the “fifth face”.  
           [0016]    Finally and in accordance with another of the characteristics of the invention, it has also been foreseen that between the film-feeding spool and the guide roller through which said film is channelled to the pallet, two rollers are mounted for pre-stretching the film, both motor-driven, in such a manner that the stretching is produced by means of different velocities in one and the other roller and over a very short segment or path, it being moreover possible to graduate or vary at will the desired degree of stretching by means of the appropriate relative velocity between the two rollers, adapting it specifically to the quality or characteristics of the film with which one is working. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0017]    To complete the description being made and for the purpose of assisting in a better understanding of the characteristics of the invention, in accordance with a preferred practical embodiment thereof, attached hereto as an integral part of said description, is a set of drawings in which, by way of illustration and not restrictively, the following is shown:  
         [0018]    [0018]FIG. 1.- Shows a schematic top plan representation of a packing machine, in which, through the presentation of various positions for the headstock supplying the plastic film, the essential nature of the procedure of the invention can be appreciated.  
         [0019]    [0019]FIG. 2.- Shows, according to a general perspective, a specific practical embodiment of the schematic machine of the previous figure. 
     
    
     PREFERRED EMBODIMENT OF THE INVENTION  
       [0020]    In the light of the foregoing figures, and more specifically FIG. 1 it can be seen how, in accordance with the procedure of the invention, the pallet ( 1 ), with its load is maintained stationary, whilst the spool ( 2 ) furnishing the film is the element which is displaced around the pallet ( 1 ), but doing so with a rectangular trajectory ( 3 ) according to the section of the pallet ( 1 ), in such a manner that the headstock ( 4 ) bearing the aforementioned spool ( 2 ) describes around the pallet ( 1 ) a trajectory in which four rectilinear segments are described, parallel and close to the respective faces of the pallet ( 1 ), related to each other through orthogonal folds in correspondence with the upright edges of the pallet ( 1 ), and more specifically with the load positioned thereon.  
         [0021]    In this manner it is achieved that the instantaneous velocity of the spool ( 2 ) is constant over the entire surface of the pallet ( 1 ), with the exception of the very short spans corresponding to the inflections of said trajectory in correspondence with the upright edges of the pallet, whereby the tension in the plastic film ( 5 ) is likewise constant and uniform, permitting a higher working speed, without the risk of tearing the film ( 5 ) in question.  
         [0022]    This special mobility of the spool ( 2 ), and more specifically of the headstock ( 4 ) upon which the spool ( 2 ) is mounted, is achieved with the collaboration of a robot ( 6 ) provided with a multiple and articulated arm ( 7 ), to the free extremity ( 8 ) of which is fastened the headstock ( 4 ), in such a manner that with the assistance of a duly developed program for said robot ( 6 ), the aforementioned movements of the headstock ( 4 ) are achieved around the pallet ( 1 ).  
         [0023]    The robot ( 6 ) can produce exclusively the circumferential movement of the headstock ( 4 ) around the pallet ( 1 ), following the rectangular trajectory of which mention has been made previously, in such a manner that said headstock ( 4 ) is not directly mounted on the extremity of the multiple arm ( 7 ) of the robot, but instead said headstock ( 4 ) is mounted on vertical guide rails ( 9 ), as can be seen in FIG. 2, which are in association with the extremity of the multiple arm ( 7 ) of the robot, in a such a manner that the necessary motion of the spool ( 2 ), for the helical wrapping of the film ( 5 ) is produced by means of displacement of the headstock ( 4 ) on the guide rails ( 9 ), whilst the latter, driven by the robot ( 6 ), describe the rectangular trajectory ( 3 ) or, as in the case of FIG. 1 the headstock ( 4 ) can be directly fastened to the free extremity ( 8 ) of the multiple arm ( 7 ) of the robot, in which case said robot ( 6 ) must provide simultaneously the headstock with both movements, the annular movement ( 3 ) around the pallet ( 1 ) and the parallel and complementary vertical displacement of said headstock ( 4 ).  
         [0024]    In any case, provision has been made so that the spool ( 2 ) may be mounted on the headstock ( 4 ) with interposition of a gyratory disc ( 10 ) which permits the spool ( 2 ) to take up a vertical disposition, corresponding to the lateral wrapping of the pallet ( 1 ) with its load, that shown in FIG. 1, or to adopt a suitably inclined disposition, as shown in FIG. 2, for the wrapping of the top base defined by the load of the pallet ( 1 ).  
         [0025]    In both cases provision is also made between the spool ( 2 ) that feeds the film and the delivery roller ( 11 ), that is the piece which suitably channels it towards the pallet ( 1 ), for a pair of stretching drums or rollers ( 12 ) to be fitted, both motor-driven, substantially close to one another, as is shown in FIG. 1 and having distinct and adjustable speeds, in order to permit, in turn, the degree of stretching in the film to be regulated as a function of the characteristics thereof. In this sense and for example when the film is of poor quality, provided in origin with some small hole, when the stretching takes place said hole logically grows, it being possible that it extend in an uncontrolled manner with the conventional systems to the point where the film tears, whilst the rollers ( 12 ) of the invention, by determining a very short stretching space, do not grant sufficient time for the “expansion” of said holes, thereby limiting considerably the risk of tearing.