Abstract:
Apparatus for forming a top film sheet from a film web wound upon a roll of film and for setting it onto an object to be packaged. A free end portion of the film depends downwardly from a pair of holding jaws, and a pair of pulling jaws is movable between an EXTENDED position at which the pair of pulling jaws will be disposed beneath the pair of holding jaws so as to grasp the free end portion depending downwardly from the pair of holding jaws, and a RETRACTED position at which the pair of pulling jaws will cause a portion of the film to be withdrawn from the roll of film so as to form the top film sheet after the portion of the film, withdrawn from the roll of film, is severed by a cutting blade.

Description:
FIELD OF THE INVENTION 
   The present invention relates to an apparatus for forming a top film sheet from a film web wound upon a roll of film and for setting it onto an object to be packaged. A free end portion of the film depends downwardly from a pair of holding jaws, and a pair of pulling jaws is movable between an EXTENDED position at which the pair of pulling jaws will be disposed beneath the pair of holding jaws so as to grasp the free end portion depending downwardly from the pair of holding jaws, and a RETRACTED position at which the pair of pulling jaws will cause a portion of the film to be withdrawn from the roll of film so as to form the top film sheet after the portion of the film, withdrawn from the roll of film, is severed by a cutting blade. 
   BACKGROUND OF THE INVENTION 
   Referring to FIGS.  1  and  1 A- 1 E, a prior-art device for forming a top film sheet  1  from a film web  3  wound on a roll  2  and setting it onto an object to be packaged (not shown) is known from specification EP 0 336 517 B1 and from a prior-art wrapping machine marketed under the trademark “Octopus”. This prior-art device for setting a sheet comprises a machine frame  4  supported on a fixed base. The machine frame  4  comprises vertical upright columns  5 , which are outlined in  FIG. 1  in dotted broken lines. 
   The device further comprises a frame  6 , which comprises two parallel guide beams  7  disposed at a distance from each other and secured by their ends to each other with transverse bars  8  to form a rectangular horizontal frame structure. The frame  6 , guided by the upright columns  5 , is arranged to be movable upwards and downwards in the vertical direction. 
   Such a device is normally used in conjunction with a prior-art wrapping machine, where a top film sheet is first set onto an object to be wrapped, usually a loaded pallet, whereupon the object is wrapped around with film web in a spiralling fashion. For this purpose, a wrapping frame may be attached to the aforesaid frame  6  to guide a film dispenser delivering the film (as in  FIG. 2 ). Alternatively, the film dispenser may be connected to a crank that turns about a vertical axis, as in specification EP 0 336 517 B1. 
   The device further comprises a holding device fixedly mounted on the guide beams  7  and extending transversely between them. The holding device  9  comprises a pair of holding jaws  10 ,  11 , which are movable relative to each other between a closed position I and an opened position II. In the closed position I (see  FIGS. 1A ,  1 B,  1 D and  1 E), the holding jaws  10  and  11  are pressed together from opposite sides of the film web to grip the film web between the holding jaws  10  and  11 . In the opened position II (see  FIG. 1C ), the holding jaws  10  and  11  have a first gap  12  between them to allow the film web  3  to move between the holding jaws. 
   The device further comprises a cutting device  13 , which is disposed in the vicinity of the holding device  9  for severing the film web  3 . 
   The device additionally comprises a pulling device  14 , which extends transversely between the guide beams  7  and is mounted on the guide beams so as to be movable between a first position A (see  FIG. 1B ) located near the holding device  9  and a second position B located at a distance from the holding device  9  (see  FIGS. 1A ,  1 C- 1 E). 
   As shown in  FIG. 1A , the pulling device  14  comprises a pair of pulling jaws  15 ,  16 , which are movable relative to each other between a closed position III and an opened position IV. In the closed position III (see  FIGS. 1A ,  1 C and  1 D), the pulling jaws  15 ,  16  are pressed together from opposite sides of the film web to grip the film web between the pulling jaws. In the opened position IV (see  FIGS. 1B and 1F ), the pulling jaws  15 ,  16  have a second gap  17  between them to release the film web  3  from the grip of the pulling jaws. 
   As can be seen from  FIG. 1 , the pulling jaws  15  and  16  are claws which have a point-like grip on the film. ‘Point-like grip’ here means a grip over a very small surface area. The claws  15 ,  16  hold the film web with a point-like grip. The device has several pairs of claws  15 ,  16  at a distance from each other over the width of the film web. Several pairs of claws  15 ,  16  are provided to enable the pulling device to pull webs of different widths so that the claws always engage the film by its edges and additionally between the edges. The thinner the film used, the more pairs of claws  15 ,  16  are needed in the pulling device to distribute the pulling force over the film. For the claws  15 ,  16  to be able to grip the end of the film web, the support  19  included in the holding device  9  and serving as a counter-element for the cutting blade must be provided with notches  34  corresponding to the claws to receive the claws when the pulling device  14  fetches the end of the film web from the holding device  9 . 
   Referring to  FIGS. 1A-1E , the device in  FIG. 1  is operated according to the prior-art method in the following steps. 
     FIG. 1A  visualizes that, at the beginning of the cycle, the holding device  9  engages the film web  3  with a first grip near its free end on a first side of the object to be packaged. 
   As shown in  FIG. 1B , the pulling device  14  engages the free end of the film web with a second grip. 
   As shown in  FIG. 1C , the first grip of the holding device  9  is released and, maintaining the second grip of the pulling device  14  on the end of the film web, the free end of the film web is pulled horizontally to a distance from the point of the first grip onto the object to be packaged, to its second side, said distance corresponding to the length of the top film sheet to be formed. 
   As shown in  FIG. 1D , the film web is held fast with a third grip by the holding device  9  on the first side of the object to be packaged. 
   As shown in  FIG. 1E , the film web is severed by means of a cutting device  13  along a cutting line near the third grip to form a top film sheet  1  and the second grip on the end of the film web is released, thus allowing the top film sheet  1  to fall freely onto the object to be packaged. The third grip taken by the holding device  9  constitutes the first grip on the end of the film web for a new sheet forming cycle. To form the next sheet, the steps of  FIGS. 1A-1E  are performed again. 
   A problem with the prior-art device and method is that all the pairs of claws  15 ,  16  must be made to grip the film web with equal force and that a sufficient pressing power must be available to allow the film web to be pulled from the roll  2 , which does not necessarily always turn very easily and therefore pulling the film requires the use of force. In the case of thin film, a large number of claw pairs  15 ,  16  must be available and the claws and notches  34  have to be fitted to the width of the film to be used. In accordance with the positions of the claw pairs, the counter-support  19  has to be provided with many different arrays of notches  34  because, depending on the user&#39;s needs, it may sometimes be necessary to use a narrow film and sometimes a wide film. These have to be fitted in such a way that the device will work properly. The outermost notch and claw pair have to be very close to the side edge of the film web. Such individual fitting work is time-consuming and difficult. Due to the notches  34  in the cutting counter-support  19 , problems also appear when the film is being severed, because in the area of the notch  34  the film web may not be severed completely because in the region of the notch the film can withdraw before the cutting blade. In the prior-art device, problems occur especially when the film is very thin, e.g. of the order of 15 μm. 
   OBJECT OF THE INVENTION 
   The object of the present invention is to overcome the above-mentioned drawbacks. 
   A specific object of the invention is to disclose a method and a device that will make it possible to use in the device a very thin film, even of a thickness of the order of 15 μm, to form a top film sheet. A further object is to disclose a device in which the width of the film web to be used is not limited but may be a freely selectable width narrower than a predetermined maximum width in the device. A further object is to disclose a device and a method that will always guarantee complete severing of the film web. An additional object is to disclose a device that is simpler, more reliable and cheaper than earlier devices. Yet another object is to disclose a device the manufacture of which requires no customer-specific fitting and is therefore cheaper than before. 
   BRIEF DESCRIPTION OF THE INVENTION 
   The present invention is directed toward an apparatus for forming a top film sheet from a film web wound upon a roll of film and for setting it onto an object to be packaged. A free end portion of the film depends downwardly from a pair of holding jaws, and a pair of pulling jaws is movable between an EXTENDED position at which the pair of pulling jaws will be disposed beneath the pair of holding jaws so as to grasp the free end portion depending downwardly from the pair of holding jaws, and a RETRACTED position at which the pair of pulling jaws will cause a portion of the film to be withdrawn from the roll of film so as to form the top film sheet after the portion of the film, withdrawn from the roll of film, is severed by a cutting blade. 
   In the method according to the invention, the end of the film web is gripped by a second grip over the entire width of the film web. The film web is gripped by a first grip and a third grip at a point located at a distance from the cutting line such that near the free end there remains a length of film web hanging freely downwards so that this length of film web can be gripped by the second grip. 
   In an embodiment of the method, the film web is supported in the area near the cutting line from the top side of the film web over the entire width of the film web on the other side of the cutting line in relation to the third grip. 
   In an embodiment of the method, the second grip is formed as a substantially continuous unbroken grip extending over the entire width of the film web. 
   In an embodiment of the method, the film web is severed by slitting. 
   In an embodiment of the method, the film web is gripped by the first and third grips over the entire width of the film web. 
   In an embodiment of the method, the first and the third grips are formed as substantially continuous unbroken grips extending over the entire width of the film web. A substantially continuous unbroken grip may be e.g. a line-like grip or a succession of point-like gripping points very close to each other, which in practice correspond to a line-like grip. 
   In an embodiment of the method, the first, the second and the third grips are formed by pressing the film web between two jaws. 
   According to the invention, in the device the motion of the pulling jaws between the closed position and the open position takes place in a substantially horizontal direction. The pulling jaws have been arranged to grip the end of the film web over the entire width of the film web. The gripping line of the holding jaws is at a distance from the cutting line of the cutting device, so that near the free end of the film web there remains a length of film web hanging freely downwards that can be gripped by the pulling jaws. 
   In an embodiment of the device, the device comprises a support arranged near the cutting device to support the film web from the top side over the entire width of the film web along a supporting line located on the other side relative to the cutting line of the cutting device than the gripping line of the holding jaws. 
   In an embodiment of the device, the cutting device comprises a slitting blade controlled to be movable in the transverse direction of the film web to slit the film web so as to sever it, and a first power means for moving the slitting blade. 
   In an embodiment of the device, the pulling device comprises a first frame, which extends between the guide beams and is controlled to be movable on the guide beams so that it is guided and supported by these. Further, the pulling device comprises a first pulling jaw, which is secured to the first frame. Further, the pulling device comprises a second frame, which is movable in relation to the first frame. Further, the pulling device comprises substantially horizontal guide bars for controlling the mutual motion of the first frame and the second frame. Further, the pulling device comprises a second pulling jaw, which is secured to the second frame. In addition, the pulling device comprises a second power means for moving the second frame with respect to the first frame to move the first and the second pulling jaws between a closed position and an opened position. 
   In an embodiment of the device, the device has a first elastic element connected to at least one of the pulling jaws to achieve an elastic grip when the pulling jaws are pressed against each other. 
   In an embodiment of the device, a second elastic element is connected to at least one of the holding jaws to achieve an elastic grip when the holding jaws are pressed against each other. 
   In an embodiment of the device, the pulling jaw and/or the holding jaw is an elongated profiled bar. 
   In an embodiment of the device, the profiled bar forming the pulling jaw and/or the holding jaw has a longitudinal mounting slot. The first elastic element and/or the second elastic element is an elongated profiled strip formed from elastic material and provided with fastening elements for fastening to the mounting slot. 
   In an embodiment of the device, the second power means is a compression cylinder or the like, arranged to act in a point-like manner on the middle part of the first frame and the second frame. The profiled bar forming the second pulling jaw is secured to the second frame in a curved shape such that, when being moved from the opened position to the closed position, both ends of the profiled bar of the second pulling jaw touch the first pulling jaw first and in the closed position the middle part of the profiled bar of the second pulling jaw also touches the first pulling jaw, a constant compression force thus acting between the pulling jaws over the entire width of the film web. 
   In an embodiment of the device, the holding device comprises a third frame, which extends between the guide beams and is connected to the guide beams. Further, the holding device comprises a first holding jaw, which is secured to the third frame. Further, the holding device comprises a fourth frame, which is pivotally connected to the third frame. Further, the holding device comprises a second holding jaw, which is secured to the fourth frame. In addition, the holding device comprises a third power means for turning the fourth frame in relation to the third frame to move the first and the second holding jaws between the closed position and the opened position. 
   In an embodiment of the device, the cutting device is secured to the third frame. 
   In an embodiment of the device, the third frame is pivotally mounted so as to be turnable in relation to the guide beams. The device comprises a fourth power means for tilting the third frame. 

   
     LIST OF FIGURES 
     In the following, the invention will be described in detail with reference to embodiment examples and the attached drawing, wherein 
       FIG. 1  presents a diagrammatic axonometric oblique top view of a prior-art apparatus for setting a top film sheet, 
       FIGS. 1A-1E  present diagrammatic side views of the holding device, pulling device and cutting device of the prior-art apparatus at different stages of the prior-art method, 
       FIG. 2  presents a diagrammatic axonometric oblique top view of an embodiment of the apparatus of the invention, 
       FIG. 3  presents a diagrammatic axonometric oblique top view of the holding device and pulling device of the apparatus in  FIG. 2 , separated from the rest of the apparatus, and 
       FIGS. 4-11  present diagrammatic side views of the holding and pulling devices of  FIG. 3  at different stages of the method of the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 2  presents a device which can be used to form a top film sheet  1  from a film web  3  wound on a roll  2  and to set it onto an object P to be packaged (presented diagrammatically in dotted broken lines). The object P to be packaged may be e.g. a loaded pallet. The device comprises a machine frame  4  supported on a solid floor base. The machine frame  4  comprises vertical upright columns  5 , depicted in dotted broken lines in the figure. The device further comprises a frame  6 . The frame  6  comprises two parallel guide beams  7  disposed at a distance from each other and secured by their ends to each other with transverse bars  8  to form a rectangular horizontal frame structure. The frame  6 , guided by the upright columns  5 , has been arranged to be movable upwards and downwards in the vertical direction using known arrangements not shown. If the device is connected to a conventional wrapping machine, a wrapping frame  35  may be connected to the frame  6  to guide a film dispenser  36  from which a wrapping film web is delivered to wrap the sides of the object to be packaged in a spiralling or collar-like fashion or in some other conventional manner. Alternatively, the film dispenser may be connected in a second conventional manner to a crank revolving about a vertical axis. 
   The device comprises a holding device  9  fixedly mounted on the guide beams  7  and extending transversely between them. As shown in  FIGS. 4-10 , the holding device comprises a pair of holding jaws  10 , 11  which are movable relative to each other between a closed position I (see  FIGS. 4   5 , and  7 ) and an opened position II (see  FIG. 6 ). In the closed position I, the holding jaws  10  and  11  are pressed together from opposite sides of the film web to grip the film web between the holding jaws. In the opened position II, the holding jaws  10 , 11  have a first gap  12  between them to allow the film web to move between the holding jaws  10 ,  11 . 
   As can best be seen from  FIGS. 4-10 , the holding device  9  comprises a third frame  30 , which extends between the guide beams  7  and is connected to the guide beams  7 . A first holding jaw  10  is secured to the third frame  30 . A fourth frame  31  is pivotally connected to the third frame  30 . A second holding jaw  11  is secured to the fourth frame  31 . A third power means  32  is arranged for pivotally moving the fourth frame  31  in relation to the third frame  30  so as to move the first and the second holding jaws  10 , 11  between the closed position I and the opened position II. The third frame  30  is pivotally mounted so as to be pivoted in relation to the guide beams  7 . The device comprises a fourth power means  33  for tilting the third frame  30 . 
   A cutting device  13 , secured to the third frame  30 , is provided near the holding device  9  for severing the film web  3 . The cutting device  13  comprises a slitting blade  20 , which is guided to be movable in the transverse direction of the film web  3  from one longitudinal edge of the film web to the other to slit the film web apart. The blade  20  is moved by a first power means  21 . 
   The gripping line of the holding jaws  10 ,  11  is at a distance from the cutting line of the cutting device  13  so that near the free end of the film web  3  there remains a length  18  of film web hanging freely downwards that can be gripped by the pulling jaws  15 ,  16  of the pulling device  14  (see  FIGS. 4 ,  5 ,  8 - 10 ). 
   The holding jaws  10 ,  11  are elongated profiled bars, which are preferably formed from aluminum profiles of identical cross-section. Connected to holding jaw  10  is a second elastic element  27  to achieve an elastic grip when the holding jaws  10  and  11  are pressed against each other. The profiled bar forming holding jaw  10  is provided with a longitudinal mounting slot  28 . The second elastic element  27  is an elongated profiled strip formed from an elastic material, such as rubber or elastic plastic, and provided with fastening elements  29  for fastening to the mounting slot  28 . 
   Further referring to  FIGS. 3 and 4 , the device comprises a pulling device  14 , which extends transversely between the guide beams  7  and is mounted on the guide beams  7  so as to be movable between a first position A located near the holding device  9  and a second position B located at a distance from the holding device  9 . The pulling device  14  comprises a pair of pulling jaws  15 , 16  which are movable relative to each other between a closed position III (see FIGS.  5 - 8 , 11 ) and an opened position IV (see FIGS.  4 , 9 , 10 ). In the closed position III, the pulling jaws  15 , 16  are pressed together from opposite sides of the film web so as to grip the film web between the pulling jaws  15 , 16 . In the opened position IV, the pulling jaws  15 , 16  have a second gap  17  between them so as to release the film web from the grip of the pulling jaws  15 , 16 . The pulling jaws  15 , 16  have been arranged so as to grip the end of the film web over the entire width of the film web, and the motion of the pulling jaws  15 , 16  between the closed position III and the opened position IV takes place horizontally so that the pulling jaws can grip the downwardly hanging part  18  of the film web disposed below the holding jaws  10 , 11  (see  FIGS. 4 and 5 ). 
   As shown in  FIGS. 3 ,  4 - 11 , the pulling device  14  comprises a first frame  22 , which extends between the guide beams  7  and is controlled to be movable on the guide beams so that it is guided and supported by these. The first pulling jaw  15  is secured to the first frame  22 . A second frame  23  is movable in relation to the first frame  22 . Two horizontal guide bars  24  are arranged for controlling the mutual motion of the first frame  22  and the second frame  23 . The second pulling jaw  16  is secured to the movable second frame  23 . A second power means  25  is arranged for moving the second frame  23  with respect to the first frame  22  to move the first and the second pulling jaws  15 ,  16  between the closed position III and the opened position IV. 
   The pulling jaws  15 , 16  are elongated profiled bars which are preferably formed from aluminum profiles of identical cross-section. Connected to pulling jaw  15  is a first elastic element  26  to achieve an elastic grip when the pulling jaws  15 , 16  are pressed against each other. The profiled bar forming the pulling jaw  15  has a longitudinal mounting slot  28 . The first elastic element  26  is an elongated profiled strip formed from an elastic material, such as rubber or elastic plastic, and is provided with fastening elements  29  for fastening to the mounting slot  28 . 
   As can be seen from  FIG. 3 , the second power means  25  in the pulling device  14  is a power cylinder or the like, arranged to act in a point-like manner on the middle part of the first frame  22  and the second frame  23 . The profiled bar forming the second pulling jaw  16  is secured to the second frame  23  in a curved shape in a horizontal plane so that, when being moved from the opened position IV to the closed position III, both ends of the profiled bar of the second pulling jaw  16  touch the first pulling jaw  15  first and in the closed position the middle part of the profiled bar of the second pulling jaw  16  also touches the first pulling jaw  15 , a constant compression force thus acting between the pulling jaws  15 ,  16  over the entire width of the film web. 
   As the third power means  32  of the holding device  9  acts on the end of the fourth frame  31 , the profiled bar forming the second holding jaw  11  in the holding device  9  is secured to the fourth frame  31  in a curved shape such that, when being moved from the opened position II to the closed position I, the middle part of the profiled bar of the first holding jaw  11  touches the first holding jaw  10  first and in the closed position I the ends of the profiled bar of the second holding jaw  11  also touch the first holding jaw  10 , a constant compression force thus acting between the holding jaws  10 ,  11  over the entire width of the film web. 
   As shown in FIGS.  3  and  4 - 11 , the device further comprises a support  19  secured to the third frame  30  near the cutting device  13  to support the film web from the top side over the entire width of the film web  3  along a supporting line located on the other side relative to the cutting line of the cutting device  13  than the gripping line of the holding jaws  10 ,  11 . 
   In the following, the operation of the device will be described with reference to  FIGS. 4-11 . 
   In  FIG. 4 , the holding jaws  10  and  11  of the holding device  9  are in the closed position I, pressed together so that the film web  3  is in their grip, which is here referred to as a first grip. At the free end of the film web  3  drawn from the roll  2 , a length  18  of film web hangs freely downwards below the holding jaws  10 ,  11 . In  FIG. 4 , the pulling device  14  is in the opened position IV and moved to the first position A near the holding device  9 , in which position its pulling jaws  15  and  16  are below the holding jaws  10 ,  11 . A second gap  17  remains between the pulling jaws  15 ,  16 , and the length  18  of film web hangs down into this gap  17 . 
   In  FIG. 5 , the holding device  9  is still in the position of  FIG. 4 , but the pulling jaws  15 ,  16  of the pulling device  14  engage the aforesaid downwards hanging length  18  of film web by a grip which is here referred to as a second grip, in other words, the pulling device  14  is in the closed position III. 
   In  FIG. 6 , the holding jaws  10 , 11  of the holding device  9  are in the opened position II so that they have a first gap  12  between them, the aforesaid first grip being thus released, whereby the film web  3  can run between the holding jaws  10 , 11 . The pulling jaws  15 , 16  of the pulling device  14  continue to hold the end of the film web  3  when the pulling device  14  has been moved, over the object P to be packaged, to the second position B, in which it is at a distance from the holding line of the holding device  9  and the cutting line of the cutting device  13  that substantially corresponds to the length of the top film sheet to be formed. 
   In  FIG. 7 , the pulling device  14  is still in the same position as in  FIG. 6 . The holding device  9  again engages the film web  3  by a grip which is here referred to as a third grip. The support  19  supports the film web in the area near the cutting device  13  from the top side of the film web over the entire width of the film web. 
   In  FIG. 8 , the slitting blade  10  of the cutting device  13  has slit the film web  3  apart, leaving on the side of the roll  2  a length  18  of film web hanging below the holding jaws  10 ,  11  so that it can be gripped by the pulling device  14 , i.e. engaged again by a first grip to form the next top film sheet  1 . A top film sheet  1  has now been formed. Immediately after the cutting, the pulling jaws  15 ,  16  of the pulling device  14  are opened into the opened position IV, in other words, the second grip is released, thereby releasing the top film sheet  1  so that it will fall down onto the object to be packaged below, as illustrated in  FIG. 10 . 
     FIG. 11  additionally presents an alternative for the stage shown in  FIG. 7  when a presser  37  is used to press the film web  3  against the upper surface of the object to be packaged. The presser  37  is used to ensure that the top film sheet will be set in a controlled manner on the object P. The presser  37  can be used e.g. when the upper surface of the object P to be packaged is at a very low level. In that case, the film web is at an angle α relative to the horizontal direction. In this situation, to bring the holding device  9 , support  19 , cutting blade  20  and film web  3  to an advantageous position where the web will be reliably severed, in respect of the direction of the film web, the entire holding device  9  is tilted by the fourth power means  33 . 
   The invention is not limited to the embodiment examples described above; instead, many variations are possible within the scope of the inventive concept defined in the claims.