Abstract:
A strap driving device for a strapping machine comprises
       an insertion-return unit;   a tensioning unit; and   guide channel portions for the strap which lead toward the device for inserting, returning and tensioning the strap and away from said device, with the guide channel portions being provided with cheeks guiding the strap along both sides of its flat sides, wherein   rollers on one side of the insertion, return and tensioning unit and the cheeks of the guide channel portions are mounted preferably stationarily on the same side while the cheeks of the guide channel portions on the other side are mounted on a movable carrier which is displaceable, by means of an actuation device, between a working position with closed pairs of rollers and guide channel portions and a service position with open pairs of rollers and guide channel portions.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to a strap driving device for a strapping machine comprising a device for inserting, returning and tensioning a strap, the device having at least one pair of rollers through which the strap is drivably guided in and opposite to the insertion direction and is tensionable around the object in the strapping machine opposite to the insertion direction, and guide channel portions for the strap which lead toward the device for inserting, returning and tensioning the strap and away from said device, with the guide channel portions being provided with cheeks guiding the strap along both sides of its flat sides. 
         [0003]    2. Background Art 
         [0004]    A strapping machine is for example disclosed in DE 196 02 579 A1. Along with the components which are usually present in such machines such as machine frame, work table, and strap guide frame for guiding the strap around the object to be strapped in the form of a loose loop, the strapping machine comprises a strap driving device disposed underneath the work table. Said strap driving device comprises a combined device for inserting, returning and tensioning the strap. 
         [0005]    Practically speaking, an insertion-return unit for inserting the strap into the strap guide frame and for returning the strap from the strap guide frame until the strap is disposed around the object to be strapped as well as a tensioning unit for tautening the strap around the object are provided to achieve this purpose, with the tensioning unit being in many cases dependent on the stack height. 
         [0006]    The insertion-return unit comprises a pair of rollers, with the strap being guided through the roller gap thereof in such a way as to be drivable by one of the rollers in the insertion and return directions. The tensioning unit comprises another pair of rollers, with the strap also being guided through the roller gap of which so as to be tensionable, by means of at least one of the rollers, in the return direction about the object to be strapped in the strapping machine. 
         [0007]    For guiding the strap through the strap driving device, there are finally provided guide channel portions which guide the strap supplied by a supply roller or an intermediate storage device to the tensioning unit, between the tensioning unit and the insertion-return unit and from the insertion-return unit in the direction of the strap guide frame on the work table. The guide channel portions are in each case formed by cheeks guiding the strap along both sides of the flat sides, the cheeks being embodied as webs or lateral surfaces of larger prismatic bodies. 
         [0008]    A major problem in the operation of strapping machines is the trouble-free handling of the strap which, in order to achieve high cycle times for the strapping process, needs to be guided through the strapping machine at high speeds before it is suddenly reversed in its direction of movement so as to come to a stop. Owing to the flexible nature of the strap or due to a wear of the machine or of the strap along the transport path, the strap may get stuck or tangled up along the transport path. The strap driving device is particularly susceptible to this kind of problem due to the fact that the drive rollers of the insertion-return unit and of the tensioning unit directly act on the strap in the strap driving device. The problem in this regard is that the various driving components of the strap driving device are arranged in a closely nested manner, making the strap very hard to access. In the event of heavy problems such as a so-called “Z-folding” of the strap where three strap layers are disposed on top of one another over a short distance, the strap may become “jammed” in the guide channel portions in such a way that it can no longer be pulled out. In order to resolve this problem in known strap driving devices, one or several cheeks of the guide channel portions or even rollers of the various driving units need to be dismounted. This, of course, results in a high machine downtime which may not only affect the strapping machine but, in the worst case, also an entire production line for print media, for example. 
       SUMMARY OF THE INVENTION 
       [0009]    It is therefore the object of the invention to improve a strap driving device in such a way as to allow transport problems caused in the event the strap gets stuck to be resolved quickly and easily. 
         [0010]    This object is achieved by a strap driving device for a strapping machine wherein the at least one roller on one side of the device for inserting, returning and tensioning the strap and the cheeks of the guide channel portions are mounted preferably stationarily on the same side while the at least one roller on the other side of said device and the cheeks of the guide channel portions on said other side are mounted on a movable carrier which is displaceable by means of an actuation device between a working position with closed pairs of rollers and guide channel portions and a service position with open pairs of rollers and guide channel portions. With respect thereto, it is provided according to the invention that the rollers on one side of the insertion, return and tensioning device as well as the cheeks of the guide channel portions are mounted preferably stationarily on the same side while the rollers on the other side of said device as well as the cheeks of the guide channel portions of said other side are mounted on a movable carrier which is displaceable, by means of an actuation device, between a working position with closed pairs of rollers and guide channel portions and a service position with open pairs of rollers and guide channel portions. 
         [0011]    It is obvious that when the strap gets stuck in the actuation device, said actuation device can be opened by a simple action of the actuation device by displacing the movable carrier. The rollers and guide channel portions on one side of the transport path of the strap thus move away from the opposite machine elements into a service position where the strap can be tension-relieved and removed easily or reinserted in the correct position. Afterwards, it is sufficient to move the carrier back into the working position by means of the actuation device so that the transport path of the strap through the strap driving device is closed and the machine is operational again. There is no need for time-consuming assembly works, allowing malfunctions to be repaired extremely quickly. 
         [0012]    Features, details and advantages of the strap driving device according to the invention will become apparent from the ensuing description of an embodiment by means of the drawing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0013]      FIG. 1  shows a schematic side view of a strapping machine; and 
           [0014]      FIGS. 2 and 3  show a side view of a strap driving device of said strapping machine in the working position and in the service position. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0015]    As shown in  FIG. 1 , the strapping machine comprises a machine frame  1  mounted on rollers, with a work table  2  being mounted on the machine frame  1 . The work table  2  comprises conveyor belts (not shown) by means of which the object  4  to be strapped such as a stack of magazines according to  FIG. 1  are transported to the strapping position on the work table  2 . For so-called cross-strappings, the work table  2  may additionally be provided with an integrated turntable as disclosed in EP 0 445 429 B1 . 
         [0016]    On the work table  2  is arranged a vertical strap guide frame  6  by means of which the strap  7  may be guided around the object  4  on the work table  2  so as to form a loose loop. To this end, the strap  7 , which is stored on a supply spool (not shown in more detail) on the side of the machine frame  1 , is inserted into the strap guide frame  6  through the strap driving device  5  (only illustrated schematically in  FIG. 5 ) underneath the work table  2  and through the welding head  3  of the strapping machine and is guided around said strap guide frame  6  until it arrives at the welding head  3  again. The strap end is fixed there, and the strap  7  is returned by means of the strap driving device  5 , with the strap  7  passing out of the strap guide frame  6  so as to be disposed around the object  4  in the form of a still non-tensioned loop. Afterwards, the strap is tensioned by means of the strap driving device  5  so as to be tightly disposed around the object  4 . The overlapping strap layers in the welding head  3  are for example thermally welded so that the thus formed strapping is separated from the strap. The object  4  is thus strapped and ready for transport. 
         [0017]    The design of the strap driving device  5  is to be explained by means of  FIG. 2 . The main assemblies are the insertion-return unit  8  on the one hand and the tensioning unit  9  on the other hand which perform the above-explained manipulations of the strap  7  according to their designation. 
         [0018]    Guide channel portions  10 ,  11 ,  12  are provided for forming a defined transport path for the strap  7  through the strap driving device  5 . A first guide channel portion  10  guides the strap  7  arriving from the supply spool or the intermediate storage (neither of which is shown) to the tensioning unit  9 . A second guide channel portion  11  connects the tensioning unit  9  and the insertion-return unit  8 . A last guide channel portion  12  leads away from the insertion-return unit  8  in the direction of the welding head  3  and to the entrance point of the strap  7  into the strap guide frame  6 . 
         [0019]    The insertion-return unit  8  comprises a pair  13  of drive rollers with a roller  14  which is driven by a motor (not shown) and a pressure roller  15  which is not driven. The latter is coupled with an incremental encoder  16  for detecting the angular rotation performed by the roller  15 . Said angular rotation is a measure for the length of strap  7  transported by the pair  13  of drive rollers. 
         [0020]    For inserting the strap  7 , the roller  14  of the pair  13  of drive rollers is set in rotation in the corresponding direction by actuation of the drive motor via a control unit (not shown), and the strap  7  is guided around the strap guide frame  6  until the free end thereof comes to rest in the region of the welding head  3  where it is fixed. Afterwards, the pair  13  of drive rollers is activated in the opposite direction, causing the strap  7  to be returned in the manner described above. 
         [0021]    The tensioning unit  9  comprises a rubberized pair  17  of tensioning rollers with rollers  18 ,  19  which are adapted to be coupled with each other, the pair  17  of tensioning rollers applying a high tensile force owing to its drive motor (not shown) for tensioning the strap  7  around the object  4  to be strapped. 
         [0022]    The guide channel portions  10 ,  11  are formed by web-shaped cheeks  20 ,  21  which are guided across the rollers  18 ,  19  and are fixed in the strap driving device  5  by means of projecting retaining feet  22 ,  23  in a manner yet to be explained. The rollers  18 ,  19  penetrate through recesses in the cheeks  20 ,  21 , the recesses not being shown in more detail in the drawing. Likewise, the guide channel portion  12  is also formed by cheeks  24 ,  25  on both sides, with the one cheek  24  being formed by the lateral surface of a prismatic body  24  which is approximately T-shaped in a plan view. The other cheek  25  has a curved portion which is bent across a looping angle U for the strap  7  corresponding to the outer periphery of the roller  14  and continues in a straight portion. The cheek  25  is formed as a lateral surface at a corresponding longitudinal prismatic body  27 . 
         [0023]    The components of the strap driving device  5  adjoining the left-hand side—relative to the insertion direction E—of the strap  7 , in other words the cheek  20 , the rollers  14  and  18  as well as the cheek  24  are mounted stationarily on a mounting member  28  of the strap driving device  5 . The components disposed on the right-hand side—relative to the insertion direction E—of the strap  7 , in other words the cheek  21 , the roller  19 , the pressure roller  15  and the cheek  25  on the other hand are mounted on a movable slide  29  serving as carrier which is mounted for displacement in the opening direction O. To this end, said slide  29  is mounted on two bars  30  serving as linear guides running parallel to the opening direction O, with the ends of the bars  30  being mounted in a socket member  31  designed as a vertically arranged cross-bar. 
         [0024]    Instead of the linear opening assembly, there may also be provided a corresponding pivoting mechanism allowing the carrier to be pivoted away over a large radius. 
         [0025]    In order to move the slide  29  from the working position shown in  FIG. 2  into the service position shown in  FIG. 3 , an actuation device in the form of a hand-operable, single-arm pivot lever  32  is provided the fixed end of which is pivot-mounted in the socket member  31  via a shaft  33 . The pivot lever  32  is disposed in front of the strap driving device  5  in a well-accessible manner and protrudes horizontally beyond the pair  17  of rollers in the working position shown in  FIG. 2 . 
         [0026]    The pivot lever  32  could also be actuated automatically, for instance when opening the door of the machine. 
         [0027]    On the rear side of the socket member  31  not visible in  FIGS. 2 and 3 , a much shorter auxiliary lever  34  is also mounted to the shaft  33  and therefore coupled with the pivot lever  32 . The auxiliary lever  34  is a single-arm lever as well, comprising a pressure roller  35  on its free end which acts on the outside  36  of the slide  29  in a direction opposite to the opening direction O. 
         [0028]    It is conceivable as well to use an eccentric or an articulated lever according to the knee lever principle instead of the auxiliary lever  34 . 
         [0029]    The auxiliary lever  34  can be moved away from the slide  29 , causing the latter to be pulled outward in the opening direction O, by pivoting the pivot lever  32  from the pressure position of the pivot lever  32  shown in  FIG. 2  where the slide  29  is acted upon by the auxiliary lever  34  in the working position, in other words transport path for the strap  7  is closed and operational, into the release position of the auxiliary lever  34  shown in  FIG. 3 . In the service position thus assumed according to  FIG. 3 , the cheeks  25 ,  21 , the rollers  19  and the pressure roller  15  are positioned at a significant distance from the opposite components of the guide rail of the strap  7 , allowing a piece of strap  7  which is stuck there to be easily removed or aligned. 
         [0030]    The arrangement of the various angles of the guide channel portions  10 ,  11 ,  12  relative to the opening direction O deserves particular attention. The strap driving device  5  generally opens from the working position into the service position if the external angles A 21  and A 25  of the cheeks  21 ,  25  amount to approximately 10° to 170° relative to the opening direction O. In the illustrated embodiment, the external angle A 21  is up to approx. 115° while the external angle A 25  is at 167°. Another basic principle for arranging the guide channel portions  10 ,  11 ,  12  in order to ensure a functional opening of the strap driving device  5  in the event of a looping angle U of the strap  7  around the roller  14  of the pair  13  of drive rollers is that the internal angle I between the stationary cheeks  20  and  24  of the guide channel portions  10  or  11 / 12 , respectively, opens in the direction opposite to the opening direction O of the slide  29 . In this case, the displaceable cheeks  21 ,  25  as well as the pressure roller  15  and roller  19  can be pulled away from the corresponding opposite components in the opening direction O.