Abstract:
The invention concerns an improved retainer system allowing reliably strapping a package while incurring only minimized wear. This problem is solved by using an additional retainer device ( 17 ) placed in front of the inner side of the strap guide frame ( 11 ) and comprising an elastic, longitudinally stretched element ( 18, 19 ) and a mating support ( 30 ), said element and mating support being made of a low-wear material relative to the strap and being mutually parallel and parallel to the strap outlet aperture ( 23 ). The elastic element and the mating support subtend thereby a gap to pull the strap consecutively through it.

Description:
BACKGROUND 
       [0001]    The present invention relates to package-strapping apparatus, of which the strap in particular is a thermoplastic tape that is fed from a conveyor by means of a cross-sectionally U-shaped strap guide frame to a locking unit, a strap outlet apeture of said frame being at least partly closed by a first strap retainer device in order to preclude premature strap issuance from said frame, said retention device opening when the strap is pulled back to be tensioned around the package and to allow drawing the strap out of its outlet aperture. 
         [0002]    Such strapping apparatus are pertinently known already in the state of the art and illustratively include the German patent documents 199 12 940 A1 and 25 07 717 C3 and the European patent document EP 0 738 658 B1. 
         [0003]    The strap guide frame of such strapping apparatus typically comprises several legs associated with the said strap retainer device. The state of the art essentially discloses two designs of said retainer devices. In a first design the said retainer device is constituted by several cross-sectionally L-shaped flaps or lids bilaterally configured on at least one guide frame leg. Such lids are displaceably mounted at said guide legs and are approximately as long as the associated legs. In their rest position, they are biased toward said frame by retaining springs and they cover the strap outlet aperture. When the strap is pulled back in order to be tensioned around the package, said lids either are opened in automatic manner or by an external control, and thereby in their open position will impulsively make available the strap segment corresponding to their length. 
         [0004]    In a further design of the state of the art, the strapping retainer device is constituted by lip-shaped flexible or plastic elements of defined cross-sectional shape which also are configured bilaterally in the region of the strap outlet aperture and which close said aperture. As described in the German patent document DE 199 12 940 A1, when being pulled back to be tensioned around the package, the strap displaces the zones of said cross-sectionally shaped elements only in its discharge zone, said zone during said process migrating around the strap guide frame. 
         [0005]    The strap retainer device meets several purposes. On one hand it is meant to preclude premature and uncontrollable strap issuance from said outlet aperture when the strap is inserted into the said guide frame. As regards vertical strap guide frames, moreover, said retainer device supports the strap inside the guide frame against gravity. 
         [0006]    Another significant function of the retainer device is to guide the strap when being pulled out of the strap outlet aperture during pull-back and tensioning around the package. Ideally the strap should be precisely situated within an accurately defined strapping plane on the package. In principle too the lids and the flexible, cross-sectionally shaped strips adequately assure such positioning, however various details are disadvantageous. 
         [0007]    As already mentioned above, the said lids always uncover a relatively large portion of the strap outlet aperture, as a result of which strap issues from said zone in uncontrolled manner. When said lids are very long, the strap may come to rest on the package outside the strapping plane, and strapping of the package will be oblique and inadequate to keep said package together. The state of the art furthermore includes a procedure using several short lids, in fact minimizing the above problem, though the strap still may occasionally exit in uncontrollable manner the various zones of its outlet aperture and moreover it tends to twisting whereby it will not always come to rest flat on the package surface. When stacking packages, twisted straps can entail stacking instability. A plurality of small lids also incurs the drawback of requiring substantial maintenance. Each of such small lids is connected by an articulating fastener to said frame and comprises wear-susceptible retaining springs that must be changed frequently. Another drawback is the substantial noise generated by each lid hitting the strap guide frame when said strap outlet aperture is closed again. 
         [0008]    The problem of uncontrolled strap pull-out from said strap&#39;s aperture does not arise when using the above cited textile lips or plastic, cross-sectionally well defined elements. In fact only the zone from which the strap is being removed will open the cross-sectionally well defined elements resting under tension against the strap applying a force directed in the direction of pulling on said strap and hence allowing removing the strap in controlled manner from the strap outlet apertures. Considering the present-day strap pull-back and pull-out rates occurring when the strap is tensioned around the package, said elastic, cross-sectionally well defined strips wear comparatively fast, again entailing higher costs of maintenance. 
       SUMMARY 
       [0009]    Accordingly it is the objective of the present invention to create an improved package strapping apparatus, in particular an improved retainer device offering reliable package strapping at and wear as low as possible. 
         [0010]    This problem is solved by an apparatus in which a second strap retainer device comprising an elastic, longitudinally stretching and a mating support, is placed in front of the side of the strap guide frame which is associated to at least one zone of the strap outlet aperture, the said elastic, longitudinally stretching element and mating support, which are constituted at least in one zone forming a strap contact area, being made of a low-wear material such as a metal and configured parallel to one another and the strapping central aperture, the longitudinally stretching element and the mating support subtending a gap narrower than the central strapping width, the strap, namely at least the elastic, stretching element, being consecutively pulled through said gap, deviating away from the said mating support, when being tensioned around said package. 
         [0011]    The apparatus of the present invention assures in advantageous manner that the package shall be strapped reliably within the strapping plane. For that purpose the present invention makes use of two strap retainer devices, a first retainer device reliably closing the strap outlet aperture and the second one assuring pulling the strap in controlled manner out of said strap outlet aperture. Because of the said contact areas of the present invention, the second retainer device will be wear-resistant. 
         [0012]    To simplify the manufacture of the elastic, longitudinally stretching element and of the mating support, they may be wholly made of a low-wear material such as a metal, and in particular of steel. 
         [0013]    Advantageously the first strap retainer device is constituted by spring-loaded lids movably mounted on said frame, in particular when the lid length of the multi-leg guide frame each time corresponds to the length of the associated guide frame leg. The lids reliably preclude premature strap issuance through the strap guide frame and so to speak incur no wear when compared to flexible cross-sectional defined strips which in principle also may be used in this case. 
         [0014]    When the mating support also is designed as an elastic, longitudinally stretching element, this feature does advantageously simplify the design of the second strap retainer device. 
         [0015]    When at least one elastic, longitudinally stretching element is associated to a multi-leg strap guide frame, replacement costs due to possible damage can be reduced compared to the design having a single elastic element. 
         [0016]    The elastic, longitudinally stretching element may be a simple wire, a rope, a tape or the like. The essential factor is the element&#39;s low wear feature. Such standard components allow economically manufacturing the second strap retainer device. 
         [0017]    Moreover, in the case of a multi-leg frame, the elastic, longitudinally stretching element should be longitudinally tensioned along the strap guide frame at least along one guide frame leg in order to attain a constant gap while being longitudinally tensioned, as a result of which the strap shall be pulled through said gap against the retaining force exerted by the said tensioned element on said strap. 
         [0018]    Advantageously the said elastic, longitudinally stretched element is configured by its end area above a tensioner at the strap guide frame, the tension of said element being regulated by said tensioner. In this manner, even if there were an elongation of said element during operation of the apparatus of the present invention, a constant tension would be assured by readjustment. 
         [0019]    When the elastic, longitudinally stretched element is guided in at least one end zone of the strap guide frame using a course-changing means, this feature makes possible on one hand using an endless elastic element running within said strap guide frame. On the other hand such course-changing allows configuring the tensioner on the outside face of the strap guide frame while maintaining a constant gap width between the elastic elements. Moreover other advantageous fasteners of which the shape would preclude their configuration in the gap zone may be used in the present invention. 
         [0020]    In an especially preferred embodiment mode of the present invention, the course-changing element is a roller fitted with a circumferential groove guiding the elastic, longitudinally stretched element and comprising a conical zone facing the strap outlet aperture. This circumferential groove assure reliable guidance of the said elastic element on the course changing element. The area of the course-changing means tapering conically toward the strap outlet aperture constitutes a strap slide surface, and consequently the strap is virtually safeguarded against impediments when being pulled out. 
         [0021]    If the tensioner and/or the course-changing means are mounted displaceably on the strap guide frame, both elements may be displaced by the strap being pulled through said gap, thereby reducing the danger that said strap might snag in this region. 
         [0022]    If the mating support also is designed as an elastic, longitudinal stretching element and is configured above tensioners in at least one end area of the strap guide frame and/or is guided over a course-changing means, then both elastic, stretching elements may be widened by the said strap in gap-enlarging manner. 
         [0023]    In a further embodiment mode of the present invention, at least one holder component is configured in displaceable and spring-loaded manner substantially perpendicularly to a strapping plane subtended by the strap guide frame, said holder component comprising at least one leg which is situated in the area of the elastic, longitudinally stretching element and to which is affixed the course-changing means and/or tensioner for at least one elastic, longitudinally stretching element. 
         [0024]    This holder component allows advantageously avoiding affixing the course-changing means and/or the tensioner at the guide frame itself, as a result of which strap guidance cannot be hampered by individual guide or affixation components. As already mentioned above, in particular the tensioner may be configured by changing the course of said elastic element outside the gap zone. In this manner constant gap width will be assured. On account of the displaceable holder component, the strap when being pulled out of its guide frame is able to force the tensioner and/or the course-changing means out of their gap-defined path, as a result of which the holder component shall not hamper the strap&#39;s retraction or pull-out. 
         [0025]    If the holder component is fitted with an adjustment means allowing adjusting a separation between the mating support and the holder component legs, then the gap width defined between the elastic, longitudinally stretching element may be adjusted and the gap of the second retainer device can be matched to various strap widths. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0026]    Further advantages of the package strapping apparatus of the present invention are elucidated in its following description in relation to an illustrative embodiment mode shown in the appended drawings. 
           [0027]      FIG. 1  is a perspective overview of the apparatus of the invention,  FIG. 2  is a cross-section of the strap guide frame along the sectional line II-II of  FIG. 1 , 
           [0028]      FIG. 3  is a sectional view in the manner of  FIG. 2  showing the strap when being pulled back and tensioned, 
           [0029]      FIG. 4  is a perspective of a portion of the strap guide frame of  FIG. 3 , 
           [0030]      FIG. 5  is a sectional view of the strap guide frame along the sectional line II-II of  FIG. 1 , 
           [0031]      FIG. 6  is a sectional view according to  FIG. 5  showing the strap during the pull-back and tensioning procedure, 
           [0032]      FIG. 7  is a perspective of a portion of the strap guide frame of  FIG. 6 , 
           [0033]      FIG. 8  is a perspective of a strap guide frame zone including the holder component, and 
           [0034]      FIG. 9  is a sectional view of the holder component along the sectional line IX-IX of  FIG. 8 . 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0035]      FIG. 1  shows a package strapping apparatus denoted overall by the reference  10 . Said apparatus shows a strap guide frame  11  mounted on a base S. A number of different and omitted units are housed within the base S, one of said units being a strap locking system. A packing bench supporting the package to be strapped and conventionally transverse to said frame  11  also is omitted. 
         [0036]    The strap guide frame  11  is constituted by four frame legs  12  joined to each other by corner parts  13 . Said frame furthermore comprises a first retainer device  14  consisting of flaps or lids  15  and  16  and enclosing strap outlet aperture  23  omitted from this Figure but shown in  FIG. 2 . In this Figure a pair of lids  15 ,  16  is displaceably supported on each frame leg  12 , the lengths of said lids  15  and  16  in each case substantially corresponding to the length of a frame leg  12 , as a result of which said lids  15  and  16  completely close the strap outlet aperture  23 . 
         [0037]    Be it noted in this respect that instead of comprising the shown long lids  15  and  16 , a frame leg  12  also may comprise several shorter lids and that in particular the lids  15  and  16 —namely as a first retainer device—need not mandatorily be configured in the region of the base S. 
         [0038]    A second retainer device  17  is associated with at least one side of the strap guide frame  11 , in this instance therefore the inside, of a segment of the strap outlet aperture  23 , and said second device here comprises elastic elements in the form of prestressed and hence energetically elastic (non dissipative of energy) wire cables  18  and  19  subtending between them a gap  24 . In this instance each pair of wire cables  18  and  19  is respectively associated to a frame leg  12 . Accordingly the second retainer device  17  shown in  FIG. 1  comprises four pairs of wire cables  18  and  19 . Obviously a circumferential pair of wire cables  18  and  19  also may be used as energy-conserving cable elements. 
         [0039]    Two holder components  20  and  21  being part of the retainer device  17  are displaceably mounted on each corner part  13 . The strap  22  (omitted from  FIG. 1 ) is shot in the direction of the arrow “a” by means of an omitted but well known strap mover at high speed into the strap guide frame  11  until the leading strap end, having completed one lap through said frame, has reached the locking unit. Once there, the end of the strap  22  is held in place and the free length of said strap  22  will be pulled back in the arrow direction “b”. In the process, the pairs of lids  15  and  16  open up and uncover the strap outlet aperture  23 , as a result of which the tape can be pulled out of the strap guide frame  11  and be pulled farther through the gap  24  subtended between the cables  18  and  19  until the constituted strap loop around the package has been tautened. 
         [0040]      FIG. 2  is a sectional view along line II-II of  FIG. 1  of a frame leg  12 . The lids  15  and  16  are displaceably suspended from a C-shaped clearance  25  of the frame leg  12  to allow them to tip open in the directions “c” and “d” away from said leg  12 . By means of fasteners  27 , a helical spring  26  connects the pair of lids  15 ,  16  to each other and keeps them in a rest position closing the tape (strap) duct  23 . A strap guide part  28  is replaceably configured in the strap guide frame  11  and subtends a glide surface  29  on which said strap  22  is inserted without significant friction into the strap guide frame  11 . The pair of wire cables  18 ,  19  is configured a space before the strap outlet aperture  23  and subtends the gap  24  of a width “w” less than the strap width W. 
         [0041]      FIG. 3  is a sectional view corresponding to  FIG. 2 , the strap  22  in this instance being partly pulled out of the strap guide frame  11  and through the gap  24  of the second retainer device  17 . When pulling the strap  22  out of its guide frame  11 , the lids  15  and  16  of the first retainer device  14  are opened in the displacement directions “c” and “d” by the strap  22  or by extraneous control and in this manner they uncover the strap outlet aperture  23 . Next the strap  22  dips into the gap  24  subtended by the wire cables  18  and  19  of the second retainer device  17  and in this manners said strap expands the gap  24 . 
         [0042]      FIG. 4  is a partial, perspective view of a frame leg  12  and shows that the wire cables  18  and  19  will be forced apart only in that zone where the strap  22  is being pulled out at the time. Accordingly the wire cables  18  and  19  are consecutively forced apart by the strap  11  and then will immediately close thereafter. They restore automatically the gap which is less than the strap width W. This process may be construed as being a consecutive peeling of the strap  22  out of the second strap retainer device. 
         [0043]    Like  FIG. 2 ,  FIG. 5  shows a section of a leg  12  of the strap guide frame  11 , the second retainer device  17  in this instance being of a different design. 
         [0044]    Instead of the two wire cables  18  and  19  that heretofore combined the mating support and the elastic element into each other, this new design associates a substantially rigid mating support  30  with the wire cable  18 . The mating support  30  is mounted by means of a cross-sectionally C-shaped bar  31  to the frame leg  12 , whereby its strap guide surface  32  is situated approximately in the area of present left outer edge  33  of  FIG. 5  of the strap  22 . If the strap guide surface  32  were situated too far in the zone of strap width W, said strap  23  when being pulled through the gap  24  would be undesirably twisted by the mating support  30 , possibly entailing defective package strapping. 
         [0045]    On the other hand the longitudinally stretched wire cable  18  can be forced away from the mating support and is situated in the zone of the strapping width W, and, as already discussed above and as shown in  FIG. 6 , is forced apart in gap-widening manner by the strap  22 . 
         [0046]      FIG. 6  is a section corresponding to  FIG. 5 , and, similarly to the embodiment of  FIG. 3 , in this instance the strap  22  is pulled out its guide frame  11  and through the gap  24  of the second retainer device  17 . The strap  22  again opens the lids  15  and  16  which uncover the strap outlet aperture  23  and it glides along the strap contact surface  32  of the mating support  30 , the wire cable  18  in the process being forced in gap-widening manner away from the rigid mating support  30 . Said mating support  30  remains in its position in the process. 
         [0047]    The above described process is also described in  FIG. 7  which shows a partial perspective of the frame leg  12 . Again it shows that the strap  22  when being pulled through the gap  24  consecutively widens it in the pull-out direction “x”, the wire cable  18  resuming its rest position behind the strap  22  (as seen in the x-direction) at a gap  24  less than the strap width W between the mating support  30  the wire cable  18 . The wire cable segment  18  is identical with the wire cable segment  19  and in this instance too resets itself free of hysteresis. 
         [0048]      FIG. 8  shows a corner zone of the strap guide frame  11 . This view shows the first retainer device  14  with its lids  15  and  16  sealing the strap guide frame  11 . The view is of the first retainer device  14  with its lids  15  and  16  sealing the strap guide frame  11 , said lids being shown in cutaway form in the zones denoted by B. Said zones show a tape-like strap  22  inserted in the strap guide frame  11 . Within the corner zones of the strap guide frame  11 , the lids  15  and  16  comprise sheetmetal guides  35  which converge conically in a direction away from the corner part  13 . Two holder components  36  are present at the corner part itself and receive course-changing means, in this instance rollers  37 , further tensioning parts  38  in the form of helical screws which are displaceably mounted by means of hinges  39  to the corner part  13  (also see  FIG. 9 ). The rollers  37  are fitted with a circumferential groove  40  receiving the elastic elements, in this case the wire cables  18  and  19 . 
         [0049]    The segments of the rollers  37  facing the strap outlet aperture  32  or the frame  4  leg  12  are designed as cones  41 . The circumferential surfaces of the cone  41  which tapers toward the strap outlet aperture offer guide, respectively glide, surfaces to the strap  22 . In the present embodiment mode, one pair of wire cables  18 ,  19  is associated with each frame leg  12 . Accordingly always one end of the wire cable  18  or  19  is affixed in affixation aperture  42 , whereas the other end of said particular wire cable  18  or  19  is affixed by means of a tensioner  38  to the holder component  36 . 
         [0050]    The design of the holder components  36  is shown once more in  FIG. 9 . The holder component  36  consists of the holder component legs  43 ,  44  and  45 , the holder component legs  43 ,  44  holding the course-changing rollers  37  for the wire cables  18  and  19 . The holder component  36  is linked by the holder component leg  45  to the hinges  39  of the corner parts  13  by means of screw bolts  46 . These screw bolts  46  anchor the tensioners  38  in the holder component leg  45 , the cable tension transmitted from the tensioners  38  to the wire cables  18  and  19  being adjustable by turning said screw bolts in or out. The holder component legs  44  moreover each bear an adjustment component in the form of an adjustment screw  47  resting on the corner part  13 . The spacing between the mating support  30  and the holder component leg  43  may be varied by turning in or out the adjustment screws  47 . In this manner the gap  24  can be matched by being widened or narrowed to the particular strap  22  being used. Not only variously wide or narrow tape-like straps are applicable, but also string, wires or similar elastic, longitudinally stretchable components. In the embodiment modes shown in  FIGS. 1 through 4 ,  8  and  9 , the wire cables  18  and  19  each time constitute the mating support to the other wire cable, as a result of which the gap  24  between the wire cables  18  and  19  is variable each time. 
         [0051]    As regards the embodiment mode illustrated in  FIGS. 5 through 7 , the mating support  30  preferably should be rigidly mounted to the strap guide frame in the absence of a holder component  36 . The gap between the rigid mating support  30  and a displaceable holder component  36  associated with one of the elastic elements—in this instance the wire cable  18 —could be matched by resetting the adjustment screw  47 . In order to keep the holder components  36  in a gap-subtending rest position, said holder components shall be pulled by helical springs  48  in the “y” or “z” directions toward the said strap guide frame. 
         [0052]    The interaction between the first and second retainer devices  14  respectively  17 , when pulling back the strap  22  and tensioning it around the package is best illustrated and elucidated in relation to  FIGS. 1 ,  3 ,  4  and  8 . 
         [0053]    Initially the strap  22  of  FIG. 1  is moved in the input shot direction “a” into the strap guide frame  11  and guided along consecutive frame legs  12  to the locking unit housed in the base S. In the process a strap loop of a length corresponding to the frame periphery has been formed. In order to now tension the strap  22  about the omitted package, said strap is pulled back in the direction “b”. Being kept in place in the region of the base whereas its length has been shortened, the strap first passes at one end zone through its outlet aperture  23  to exit its guide frame  11 . In the process said strap first slides along the on-edge sheetmetal structures  35  of the pairs of lids  15  and  16  to enter the still closed strap outlet aperture  23  and next forces apart said lids respectively in the directions “c” and “d” as shown in  FIG. 3 . The lids  15  and  16  uncover said outlet aperture  23  over the entire length of a guide frame leg  12 . 
         [0054]    Thereupon the strap  22  glides along the circumferential surface of the cones  41  of the course-changing rollers  37  and in this manner it forces apart the holder components  36  against the force of the helical spring  48  until the gap in this zone corresponds to the strap width. This process takes place at every corner zone. 
         [0055]    By further retracting the strap  22 , the strap loop length is further reduced and the strap is pulled through the gap  24 . In the process said strap exits the region of the holder components  36  shown in  FIG. 8  and follows the gap  24 , henceforth acting as a guiding gap in the strapping plane, constituted by the wire cables  18  and  19 . In the process the strap  22  in its outlet zone consecutively widens the gap  24  that shall close again beyond said strap&#39;s rear. The pressure laterally applied by the wire cable tension against the strap  22  entails frictional impedance against pull-back, as a result of which the strap  22  shall be tensioned between two points of the second retainer device  17  during the entire pull-back procedure. The strap  22  is guided in this manner in the strapping plane subtended by its guide frame  11  and is snugly applied against the package. 
         [0056]    In summary, the present invention is characterized by the following advantages. By using two strap retainer devices, each of these devices can be designed optimally with respect to its function. Lids of which the lengths approximately correspond to the lengths of the associated guide frame legs have been found appropriate in the state of the art for application to an uncontrolled strap outlet during the input shot intake implemented from the strap guide duct. The elastic, longitudinally stretching elements are preferably energy conserving (non-dissipating) cables which can consist entirely of metal. In the process the sharp (tape) edge of said strap comes into contact only with a minute contact surface of said elastic element, whereby, besides using a low-wear material, wear is reduced further. 
         [0057]    Moreover the second strap retainer device substantially assumes the function of stabilizing said tape when latter is ejected in order to attain snug strap apposition to the package within the strapping plane. 
         [0058]    A second strap retainer device constituted by two longitudinally stretching energy-conserving elements will not require special width-matching when changing straps because following gap spreading said elements reset themselves automatically in hysteresis free manner whereby constant gap width is maintained.