Abstract:
An apparatus for wrapping a film around each of a sequence of objects passing sequentially through a wrapping station has a supply of the film adjacent the station, a feed head at the station having a base, a support carried on the base and rotatable relative thereto about a vertical axis, and a feeder on the base for pulling the film off the supply and feeding it to the support. A film storer carried on the support is operable to take in and store a length of film fed to the support by the feeder. A pull-down device in the station is vertically displaceable below the feed head.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a system for wrapping a stack of objects. More particularly this invention concerns a packaging apparatus and method for palletized goods moving on a conveyor. 
     BACKGROUND OF THE INVENTION 
     A typical production-packaging apparatus for wrapping a stack of objects with a film has at least one film supply for the film, a film-feed head for feeding the film, and a device for pulling the film down over the stack of objects. The invention further relates to a method of wrapping a stack of objects with a film. Within the scope of the invention, “film” means in particular a plastic film, preferably an elastic thermoplastic film. It is within the scope of the invention that the stack of objects to be wrapped is a stack of products. The stack may also be a single object or whiteware, for example refrigerators or the like. The stack of objects to be wrapped is advantageously accommodated on a pallet. 
     In practice, it is not uncommon for stacks of objects or pallets carrying these stacks of objects having different orientations to be consecutively supplied to a wrapping station of an apparatus for wrapping the stack of objects. Thus, a stack of objects that in top view are not square or a pallet that in top view is not square having the length/width dimensions L/W is initially supplied and wrapped, and subsequently another stack of objects that has the dimensions W/L and that is rotated by 90° about a vertical axis with respect to the first stack of objects must be supplied and wrapped. Additional measures are necessary here in order to obtain a film or film sheet that in such a case is also optimally adapted to the dimensions of the stack of objects or of the pallet. 
     In practice it is known, among other things, to lift the stack of objects using the elevator of a shrink-wrapping device and to rotate the stack of objects by 90° for the covering operation. However, this often results the stack of objects falling over, together with product losses and facility down times. It is also known to provide in the conveyor a rotatable table underneath the film-feed head so that the stack of objects may be appropriately rotated. However, constrictions result in the transition regions between the rotatable table and the conveyor edge due to the fact that the pallets associated with the stacks of objects often become stuck at the transitions, and the stacks of objects then frequently fall over. It is also known in practice to design the entire film-feed head to be rotatable by 90° so that the film can always be fed in the desired direction. This approach is relatively complicated, and the process is also too slow, in particular because of the large mass that has to be moved. 
     It is further known in practice for the film initially to be completely provided in the feed head and welded, and then transferred to a roller and rolled up by the roller. This roller is then rotated by 90° with respect to the direction of transport, and the film is transferred from the roller to the pull-down device. These measures known in practice are also relatively complicated. The multiple transfers of the film result in a relatively high susceptibility to malfunctions. 
     OBJECTS OF THE INVENTION 
     It is therefore an object of the present invention to is provide an improved method and apparatus for wrapping a foil around an object or stack of objects. 
     Another object is the provision of such an improved method and apparatus for wrapping that overcomes the above-given disadvantages, in particular by means of which differently oriented stacks of objects, in particular non-square stacks of objects that are rotated by 90° with respect to one another, may be consecutively wrapped in a simple, less complicated, rapid, and operationally reliable manner. 
     A further object of the invention is to provide a corresponding method of wrapping stacks of objects. 
     SUMMARY OF THE INVENTION 
     An apparatus for wrapping a film around each of a sequence of objects passing sequentially through a wrapping station has according to the invention a supply of the film adjacent the station, a feed head at the station having a base, a support carried on the base and rotatable relative thereto about a vertical axis, and a feeder on the base for pulling the film off the supply and feeding it to the support. A film storer carried on the support is operable to take in and store a length of film fed to the support by the feeder. A pull-down device in the station is vertically displaceable below the feed head. 
     It is within the scope of the invention that the rotatable support is turned when, after a first stack of objects having a first orientation is wrapped, a second stack of objects having a second orientation different from the orientation of the first stack of objects is to be wrapped, and/or when stacks of objects having different dimensions are to be consecutively wrapped. The rotatable support is turned in particular after a first stack of objects that in top view is not square and that has the dimensions L·W is wrapped, and before a second stack of objects that in top view is not square, and that has the dimensions W·L, and that is rotated by 90° about a vertical axis with respect to the first stack of objects is wrapped. In this regard, L stands in particular for the length of the stack of objects that here is the longer horizontal dimension, and W stands in particular for the width of the stack of objects that here is the shorter horizontal dimension. It is therefore within the scope of the invention that the stacks of objects to be consecutively wrapped may have the same dimensions but are rotated with respect to one another only by 90°. In principle, however, the stacks of objects to be consecutively wrapped may also have different dimensions. 
     It is also within the scope of the invention that a film section for a subsequent covering operation may be stored in the film storer of the rotatable support. Thus, the film section stored in the film storer should advantageously have a sufficient length for covering a stack of objects. Within the scope of the invention, “covering a stack of objects with the film” in particular also generally means wrapping a stack of objects with a film. 
     According to the invention, the base of the film-feed head has at least one film feeder for advancing and transporting the film. The base advantageously includes guide rollers and/or deflection rollers for the film, i.e. for the film fed to the film-feed head from the film supply. It is within the scope of the invention that the base of the film-feed head is not rotatable, or is not rotatable relative to the rotatable support. 
     The rotatable support is advantageously rotatable on the nonrotatable base by at least 90°, i.e. rotatable by 90° relative to the base. It is within the scope of the invention that the rotatable support is rotatable about an axis extending parallel to the covering direction of the film, and is preferably rotatable about a vertical axis. “Covering direction of the film” means the direction in which the film is pulled over the stack of objects using the pull-down device, normally downward. 
     According to one particularly preferred embodiment of the invention, the rotatable support has a film cutter for separating the film section stored in the film storer. It is within the scope of the invention that the film cutter, as a component of the rotatable support, rotates together with the rotatable support relative to the base. The film cutter is is advantageously designed as a blade. 
     According to one very preferred embodiment of the invention, the film is designed as a tubular film; i.e. the film may be fed as a tubular film. It is recommended that the tubular film is designed as a side-gusseted tube. In this case, in addition to two superposed film layers the tubular film advantageously has a fold inset on each side. In one preferred embodiment of the invention, a tubular film or a side-gusseted tube in the form of a film sheet is drawn over the stack of objects. To this end, it is recommended that the tubular film be welded in a manner known per se. 
     The rotatable support preferably has a film welder by means of which one end of the film section stored in the film storer may be welded closed. It is within the scope of the invention that the film welder, as a component of the rotatable support, together with the rotatable support is rotatable relative to the base. It is also within the scope of the invention that the end of the film section stored in the film storer is welded such that a hood-shaped film section, i.e. a film sheet, is formed. The film welder advantageously includes two welding bars that may be moved relative to one another. 
     It is recommended that the rotatable support has an opener for opening the film section or tubular film section stored in the film storer. It is understood that the film section or tubular film section is opened before covering the stack of objects. The opener, as a component of the rotatable support, together with the rotatable support is rotatable relative to the base. It is recommended that the opener is designed as a suction opener having a plurality of suction side plates. 
     It is within the scope of the invention that the film storer has at least one driving element movable transverse to the covering direction U of the film, for entraining the film transverse to the covering direction U of the film. In this manner the partial film sections entrained by the driving element are stored or temporarily stored in the film storer. The at least one driving element is preferably a looping roller. 
     One particularly preferred embodiment of the invention is characterized in that at least one driving element is movable in a first direction transverse to the covering direction U of the film, so that two first oppositely situated partial film sections of the film entrained by the driving element may be stored in the film storer, the driving element being deflectable and movable in a second direction opposite the first direction and transverse to the covering direction U of the film, so that further partial film sections of the film entrained by the driving element may be stored in the film storer. The partial film sections, i.e. the deflected partial sections of the film, also complement the film section stored in the film storer. At least two driving elements, i.e. two driving elements according to the very preferred embodiment of the invention described above, are provided. 
     According to one recommended embodiment of the invention, the film storer has at least one continuous belt, at least one driving element for the film being fixed to the continuous belt, and the driving element entraining the film transverse to the covering direction U of the film when the continuous belt moves. The above-described storage of partial film sections or of the film section is carried out in this manner. The continuous belt may be a chain, a toothed belt, or the like. It is within the scope of the invention that the continuous belt be guided over two deflection rollers or cylinders, at least one deflection roller or cylinder being driven and thus functioning as a drive roller or cylinder for the continuous belt. 
     One very recommended embodiment is characterized in that at least one first driving element is on the upper stretch of the continuous belt and at least one second driving element is on the lower stretch of the continuous belt, and when the continuous belt moves, the first driving element for entraining the film transverse to the covering direction U of the film is movable to the right, and the second driving element for entraining the film transverse to the covering direction U of the film is movable to the left. In this manner, each of the two driving elements causes two oppositely situated partial film sections to be stored. As described above, the driving elements are preferably looping rollers. It is within the scope of the is invention that the above-mentioned partial film sections and the partial film sections deflected at the driving elements are complementary to the film section stored in the film storer. One particularly preferred embodiment of the invention is characterized in that the driving element initially moved to the right passes around the first deflection roller of the continuous belt and is then preferably moved to the left, transverse to the covering direction U of the film, and the driving element initially moved to the left passes around the second deflection roller of the continuous belt and is then preferably moved to the right, transverse to the covering direction U of the film. The first driving element previously on the upper stretch moves to the lower stretch of the continuous belt, and the second driving element previously on the lower stretch moves to the upper stretch of the continuous belt. In this embodiment, each driving element produces two additional oppositely situated partial film sections. A relatively long film section is thus stored in the film storer. In principle, the embodiments explained above with regard to the continuous belt also function without a continuous belt when in these embodiments the driving elements are moved in the described manner by other means, i.e. means known to one skilled in the art. 
     At least one guide roller, preferably a plurality of guide rollers, for the film is preferably on the upper stretch of the continuous belt, and/or at least one guide roller, preferably a plurality of guide rollers, for the film is preferably on the lower stretch of the continuous belt. It is within the scope of the invention that the guide rollers are fixed to the continuous belt and are moved with the continuous belt. The purpose of the guide rollers is to prevent the partial film sections from lying directly on top of one another after the deflection operation or deflection operations, since otherwise they would interfere with one another or would interfere with the film storer. 
     It is recommended that the film-feed head is movable in the covering direction U of the film and opposite the covering direction U of the film. The base and the rotatable support, as components of the film-feed head, are then movable together with the film-feed head. The film-feed head is advantageously vertically movable. It is recommended that the film-feed head as well as the pull-down device are movable on vertical posts, preferably on only two vertical posts. At least one film storer is preferably between the film supply and the film-feed head. The film storer is used for accommodating or for storing film when the film-feed head moves in the covering direction U, and for dispensing film when the film-feed head moves opposite the covering direction U. 
     To achieve the object, the invention also teaches a method of wrapping stacks of objects with film. This method comprises the steps of pulling a tube of the film from a supply to a feed head above a stationary wrapping station and displacing the objects one after the other into and out of the wrapping station in a conveying direction with a long longitudinal dimension of some of the objects forming a first group generally parallel to the direction and the long longitudinal dimension of others of the objects forming a second group transverse to the direction. For each of the objects of one of the groups, a leading end section of the film is pulled straight through the feed head and then down over the object and the leading section is cut off. For each of the objects of the other of the groups, a leading end section of the film is looped in a storer in the film head and the looped leading end section is cut off. Then the storer and the looped and cut-off leading end section are rotated through at least 90° about a vertical axis, and the looped and cut-off leading end section is pulled down out of the storer over the object. 
     It is within the scope of the invention that one end, i.e. the upper or trailing end, of the film section stored in the film storer is welded while the rotatable support is rotated. The weld seam formed in this manner is advantageously cooled during rotation of the rotatable support. It is recommended that for the subsequent covering operation, the film section or tubular film section is opened during or after the rotation of the rotatable support. In addition, it is understood that the rotatable support may be rotated back, in particular rotated back by 90°, when a stack of objects that is in turn rotated by 90° is to be wrapped. 
     The invention is based on the discovery that by using the apparatus according to the invention and the method according to the invention, consecutively supplied stacks of objects having different orientations may be wrapped in a simple, less complicated, and operationally reliable manner. It is emphasized in particular that a change from a wrapping of a first stack of objects to a wrapping of a second, differently oriented stack of objects is possible in a rapid, less complicated, and operationally reliable manner. The apparatus according to the invention is characterized by a relatively simple and less complex design. It is also emphasized that existing devices may be retrofitted with the components according to the invention in a relatively simple and economical manner. The apparatus according to the invention is also characterized by extremely low susceptibility to malfunctions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The above and other objects, features, and advantages will become more readily apparent from the following description, reference being made to the accompanying drawing in which: 
         FIG. 1  is a perspective view of an apparatus according to the invention for wrapping a stack of objects; 
         FIG. 2  is a perspective view of the film-feed head of the apparatus according to the invention; 
         FIG. 3  is a cross-sectional side view of the film-feed head in a first position; 
         FIG. 4  is the structure of  FIG. 3  in a second position; 
         FIG. 5  is the structure of  FIG. 3  in a third position; and 
         FIG. 6  is the structure of  FIG. 3  in a fourth position. 
     
    
    
     DETAILED DESCRIPTION 
     As seen in  FIG. 1 , an apparatus for wrapping a stack  1  of objects with a film  2  has a film-feed head  3  for feeding the film  2  and a pull-down device  4  for subsequently covering the stack  1  with the film  2 , typically by pulling it down over the stack  1 . The device  4  can be moved up and down on vertical posts or columns  25  by an unillustrated actuator, and the head  3  is mounted at the tops of the posts  25 . The apparatus also has a film supply in the form of a film coil  5  from which the film  2  is fed to the film-feed head  3 . The stacks  1  are moved horizontally past a wrapping station  27  formed by the apparatus according to the invention in a transport direction D by a conveyor shown schematically at  26 . 
     According to the invention as also shown in  FIG. 2 , the film-feed head  3  has a base  6  and a support  7  rotatable about a vertical axis relative to the base  6 . Here the rotatable support  7  is underneath the base  6 . The base  6  includes a film feeder  8  for pulling the film  2  off the spool  5  and advancing it to the rotatable support  7 . The base  6  also has guide rollers or deflection rollers  9  for the film  2 . Preferably the film  2  is a tube, in particular with side gussets. 
     The rotatable support  7  has a guide ring  10  connected to the base  6  and a film storer  11  carried on the rotatable support  7  underneath the guide ring  10  and whose function according to the invention is described in more detail below. The rotatable support  7  is also equipped with a film cutter in the form of a blade  12  that can cut a section  13  that may be tubular from the film  2 . The rotatable support  7  also has a film welder in the form of two welding bars  14 . Using this film welder or these welding bars  14 , an upper end of the film section  13  may be welded together, to form a hood-shaped film section  13 , or for a simple flat film  2  a simple sheet. This hood-shaped film section  13  or this film sheet is then pulled down over the stack  1  by the device  4 . To this end, the rotatable support  7  also has an opener  15  for spreading the film section  13  or the tubular film section. Preferably and here the opener  15  includes suction side plates  16  known per se for opening the tubular film. 
     The apparatus according to the invention is used for wrapping stacks of objects  1  that in cross section or top view are not square, that is that are of different horizontal width W and length L dimensions where W≠L, and that are usually carried on pallets  17  that likewise in cross section or top view are not square. The instant invention is particularly applicable to a situation where as illustrated a nonsquare stack  1  or a nonsquare pallet  17  having for instance its width dimension W extending parallel to the conveying direction  26  is followed by a stack  1  having its length direction L parallel to the transport direction  26 , that is they are rotated relative to one another about respective vertical axes by 90°. In principle, the two consecutively supplied stacks  1  and the respective pallets  17  described above may thus have the same dimensions or sizes. Here they are rotated with respect to one another only by 90°. To allow the film  2  or the tubular film to then be fed without constraint, according to the invention the rotatable support  7  is rotatable relative to the base  6  of the film-feed head  3 , here by 90° so that it can align with the workpiece stack  1 . 
     The film storer  11  has two endless belts  19  carried on respective horizontally confronting end walls  18  of the support  7  and supporting two looping rollers  20  for the film  2  that extend between the continuous belts  19  and between the end walls  18  of the rotatable support  7 . In addition, guide rollers  21  for the film  2  are fixed to the continuous belts  19 , and likewise extend parallel to the rollers  20  between the end walls  18  of the rotatable support  7 . The continuous belts  19  are themselves spanned over two deflection rollers  22 , at least one of which is is driven by an unillustrated motor carried on the support  7 , and both of which are journaled permanently in the two end walls  18 . Here the continuous belts  19  are chains, and the drive deflection roller  22  carries sprockets that mesh with the chains. Only one end wall  18  and only one continuous belt  19  are visible in  FIGS. 3 through 6 . 
     Thus the system operates as follows: 
     The film  2  here is of the side-gusset type comprising a tube with two folded-in side gussets so that the tube as shown in  FIG. 1  has a width equal to somewhat more than the long dimension or length L of the stacks or packages being wrapped, and the gussets, open up to a dimension equal to the short dimension or width L of the stacks or packages being wrapped. 
     Thus for wrapping a package  1  whose length L is parallel to the conveyor direction  2 , the film  2  is fed from the feeder  8  to the base  6  of the rotatable support  7 , and specifically, past the film blade  12  and the welding bars  14 , and through the film storer  11  until reaching the opener  15 . The end of the film  2  is advantageously conveyed to the lower edges of the suction side plates  16 . The suction side plates  16 , which in  FIG. 3  are separated, are then brought together so that the film  2  is gripped and cannot advance between them. Then the device  4 , which has gripped the leading end of the cut-off film section  13 , is pulled down on the columns  25  so that the spread tube section  13  is fitted over the package  1 . When a section of the film tube  2  sufficient to cover the entire package  1  has passed through the cutter  12 , the bars  14  are closed and the cutter  12  is operated to weld closed the upper end of the section and cut the section off the tube  2 . Typically after being pulled over the stack or package  1 , the tube section  2  is heat shrunk either in the wrapping station  27  or downstream, or the tube section may be elastically stretched as it is pulled down and released to engage tightly around the package  1 . This is all generally standard. 
     When, however, a package arrives at the wrapping station  27  offset by 90° the film  2  is fed through the storer  11  to the suction side plates  16  that are then closed. The film storer  11  is then started by moving the belts  19  such the looping roller  20  on the upper stretches of the continuous belts  19  carries the film  2  along to the right, and the looping roller  20  on the lower stretches of the continuous belts  19  carries the film  2  along to the left ( FIG. 4 ). In the lower region of the film storer  11 , the film  2  passes over a film-guide roller  23  movable transverse to a covering direction U of the film  2 . In the position of  FIG. 4 , two opposite film sections  24  are engaged around the looping rollers  20  and are stored in the film storer  11 . 
     The looping rollers  20  continue to move around the deflection rollers  22  of the continuous belts  19  so that the looping roller  20  previously on the upper stretches moves to the lower stretches, and the looping roller  20  previously on the lower stretches moves to the upper stretches ( FIG. 5 ). The looping rollers  20  are moved further along the upper stretches and the lower stretches toward the center of the film storer by corresponding movement of the continuous belts  19 , resulting in the position illustrated in  FIG. 6 . The partial film sections  24  situated or stored in this manner in the film storer  11  have a total length that is considerable, and easily enough to reach from the top to the bottom of a relatively tall object or stack  1 . 
     After the desired length of film has been stored ( FIG. 6 ), the film feeder  8  and the continuous belts  19  are stopped. The bars  14  for welding the film section  13  are then closed, and the film section  13  is separated from the remaining film  2  by the film blade  12 . This is followed by rotation of the rotatable support  7  or the rotation of the guide ring  10  of the rotatable support  7 . The rotatable support  7  is advantageously rotated by 90° during the welding process and during cooling of the produced weld seam. Rotation of the support  7  with the storer  11  therefore aligns the stored tube  2  with the crosswise workpiece  1  as shown in  FIGS. 1 and 2 . 
     For the covering operation, the film section  13  is opened by the opener  15  or by the suction side plates  16 , and, as the result of reverse movement of the continuous belts  19 , the film storer  11  releases the film section  13 , and, the pull-down device  4  draws the film section  13  down over the stack  1 . This is not illustrated in greater detail in the figures.