Abstract:
An apparatus for tensioning and closing of a tightening strap for package tightenings. The apparatus comprising a closing device for connecting two ends of the strap and a tensioning device having a tensioning wheel that can be driven, a pressure plate which can be moved against the tensioning wheel or lifted from the tensioning wheel, and a self-adjusting separating element which is arranged between the tensioning wheel and the pressure plate, whereby one end of the strap is taken up between said tensioning wheel and the separating element, and the other end of the strap is taken up between the separating element and said pressure plate, the apparatus further including an unblocking element which displaces the separating element during the lifting of the pressure plate from the tensioning wheel. The displacement being approximately parallel to the two ends of the strap.

Description:
This application claims priority based upon German Application Ser. No. DE 199 09 620 1, filed Mar. 5, 1999, and PCT/EP00/00807, filed Feb. 1, 2000. 
     BACKGROUND OF THE INVENTION 
     This invention relates to an apparatus for tensioning and closing tightening straps, in particular made of plastics, for tightening packages. This apparatus further includes a closing device for connecting the two ends of the tightening strap and a tensioning device which consists essentially of a tensioning wheel, which can be driven, a pressure plate, which can be moved against the tensioning wheel or lifted therefrom, and a self adjusting separating element, which is arranged between these two parts, whereby one end of the strap is received between the tensioning wheel and the separating element, and the other end of the strap is received between this and the pressure plate. 
     Such an apparatus serves to provide a package as for example a packed pallet or a large carton with a tightening, and to hold together the goods which are stacked on the pallet or packed into the carton and to secure them for transport. For the production of the tightening, a rigid strap, usually of plastics, is placed around the package, and then the ends of the strap are tensioned against one another with the help of the apparatus and are connected to one another when the desired tension is reached. The connection takes place with the help of the closing device, which consists generally of a friction welding device for plastic straps. The ends of the strap are threaded laterally into the tensioning device for tensioning, whereby the lower end of the strap lies between the pressure plate and the separating element, and the upper second end of the strap lies between the separating element and the tensioning wheel. The tensioning wheel, which is usually provided with barbs at its peripheral surface, or which is roughened in another way, is rotated by means of a suitable drive and draws the upper end of the strap through the apparatus into the closing device which is arranged behind the tensioning device, while the lower end of the strap is held in a clamping manner between the pressure plate and the separating element. The separating element is mounted in the tensioning device in a self-adjusting manner, that is, it can move within certain limits during the tensioning process, and so take up an optimal position relative to the tensioning wheel, so that the friction closure between the tensioning wheel and the upper end of the strap, which is necessary for the tension, is always ensured by means of the automatically resulting best position of the separating element relative to the tensioning wheel. The tightening strap can be pretensioned with a very strong force by means of the self-adjusting “flying” arrangement of the separating element, which is sometimes also called high tension wedge, and it can thereby ensure a very rigid tightening of the package, which is required in particular when transporting heavy packed goods over longer distances. 
     After the two ends of the strap are tensioned against one another with the desired tensioning force in the described manner, the closing device is actuated, whereby the two ends of the strap are pressed rigidly on top of one another by means of a pressure or a friction plate before they are connected to one another. With plastic straps, the connection usually takes place by means of friction welding, as mentioned, whereby the friction plate moves the upper end of the strap with a high speed transversely to the longitudinal direction of the strap over the lower end of the strap to and fro, and the friction heat resulting therefrom melts the ends of the strap at their surface and welds them to one another in this way. Subsequently, the drive for the to and fro movement of the friction plate is shut down, but this is kept in its lowered position which presses the two ends of the strap together, in which it presses together the ends of the strap, which are under tension, and therewith their load capacity, until the weld connection has cooled down. 
     After the completion of the tightening in the described manner, the apparatus has to be removed from the package or from the tightening strap. For this, it is necessary to lift not only the pressure plate and the separating element far enough from the tensioning wheel, so as to be able to thread the ends of the strap lying there between laterally out of the apparatus, but first the pressure or the friction plate of the closing device has to be lifted from the two ends of the strap which are connected to one another, as otherwise a lateral threading of the ends of the strap from the apparatus is not possible. In particular with an apparatus, in which the tightening straps are pretensioned with a very strong pretension force, for example with an apparatus which comprises a hydraulic or pneumatic drive for the tensioning wheel, the pressure or friction plate is under a large tension after the connecting or welding of the two ends of the strap, which tension is exerted thereon from the upper end of the strap, which is pretensioned with regard to the lower end of the strap. That is, the pressure or the friction plate is held under tension by the upper end of the strap in the longitudinal direction of the apparatus, which results in that venting or lifting of the friction plate after connecting the ends of the strap is only possible with a large force. It has indeed already occurred with an apparatus, in which the closing device is opened (vented) manually by means of a manual lever, that the force necessary for lifting the pressure plate was so large that the manual lever did not withstand the loads and broke. 
     So as to ease the opening or venting of the closing device, the tensioning device is usually vented first, that is, the pressure plate and the separating element are lifted a little from the tensioning wheel, with the aim that the two ends of the strap which pass between these three parts will be disengaged from the tensioning wheel, the separating element and the pressure plate, so that the upper end of the strap is no longer under tension, and thereby the pressure or friction plate of the closing device is also relieved. It has been shown that with such an apparatus, in which the ends of the strap are tensioned against one another with a strong force, these do not disengage safely from the tensioning wheel and the pressure plate when venting, but stay at the rough or toothed surface and retain their mutual pretension, so that the pressure or friction plate of the closing device stays under tension and can only be lifted with difficulty, despite prior venting. The reason for this is that the pressure plate of the tensioning device can only be lifted a limited distance from the tensioning wheel, as the entire apparatus is pressed with a strong force against the package by the completed tightening. As the venting path of the tensioning device is limited, the separating element, which has moved during the tensioning under the tensioning wheel in the direction of the tip of the approximately wedge-shaped opening between the upper and lower ends of the strap, does not disengage or disengage completely from the ends of the strap, that is, it ensures that these cannot disengage from the surfaces of the tensioning wheel or the pressure plate which are roughened by means of teeth or barbs. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, provided is a device for tensioning and closing tightening straps which avoids these disadvantages and ensures a relaxation of the tightening straps relative to one another after producing a connection laterally next to these, even when only a limited venting path is available between the pressure plate and the tensioning wheel in the tensioning device. 
     This is accomplished by a tensioning device according to the present invention which includes an unblocking element which displaces the separating element during the lifting of the pressure plate from its relative position to the tensioning roller or to the pressure plate approximately parallel to the two ends of the strap. With the help of such an unblocking element, the separating element is necessarily displaced during the venting of the tensioning device and is moved from the position which it has taken during the tensioning of the two ends of the strap against each other. The displacement of the separating element parallel to the longitudinal direction of the tightening results in that a relatively small opening width between the tensioning wheel and the pressure plate during the venting of the tensioning device between the tensioning wheel and the separating element on the one hand, and this and the pressure plate on the other hand, produces sufficiently large gaps, and the ends of the straps leave their frictional connection to the tensioning wheel or the pressure plate. In a particularly advantageous manner, the separating element can be displaced from the unblocking element in the approximately wedge-shaped gap which forms during lifting of the pressure plate in a direction pointing away from the tip of the wedge gap or the connecting point of the ends of the strap, that is in a region, in which the ends of the strap have a greater distance from one another. 
     A tensioning device according to one aspect of the present invention can include an unblocking element which essentially consists of a spring element engaging the separating element, which spring element is under a spring pretension and which also draws or presses the separating element, which is also called hold-up wedge, during the venting of the pressure plate from the wedge-shaped gap between the ends of the strap away from the tip of the wedge gap or the weld seam between the ends of the strap. An embodiment of the invention, in which the unblocking element consists essentially of a release wedge cooperating with a gliding surface of the separating element is of particular advantage. During the lifting of the pressure plate the gliding surface of the separating element reaches the oblique part of the release wedge and displaces thereby the separating element automatically forward out of the approximately wedge-shaped gap between the ends of the strap when the tensioning device is vented. The separating element is advantageously arranged at a carrier shoe carrying the pressure plate, which is moved transversely to the longitudinal direction of the tightening strap during the venting of the tensioning device and thereby lifts the pressure plate and the separating element simultaneously from the tensioning roller. 
     In accordance with another aspect of the present invention, the tensioning device includes a separating element which is conveniently designed as a separating plate with a curved surface which is adapted to the radius of the tensioning roller, whereby a safe hold of the upper end of the strap between the tensioning wheel and the separating element is effected and correspondingly high tensioning forces can be achieved. The pressure plate is preferably arranged in a fixed manner at the carrier shoe, while the separating element is mounted approximately parallel to the ends of the strap at the carrier shoe in a moveable manner. For this, it can engage a longitudinal hole with play, which is formed at the carrier shoe with a lateral mounting end, and can be secured therein by at least one securing bolt engaging an arresting opening in the securing end. 
     In accordance to yet another aspect of the present invention, the tensioning device includes an unblocking element which is preferably adjustable by means of an adjusting device, whereby the adjusting device can for example consist essentially of a set screw with which the relative position of the release wedge can be changed, or the pretension of a spring element serving as the unblocking element can be changed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing characteristics and advantages of the invention will in part be obvious and in part be pointed out more fully hereinafter in connection with the following description of preferred embodiments and the accompanying drawings, in which: 
     FIG. 1 is a partially sectioned elevational view of the side of a tensioning device according to the present invention for tensioning and closing of plastic tightening straps after welding the two ends of the strap; 
     FIG. 2 is a partially sectioned elevational view of the side of the tensioning device shown in FIG. 1 with the handle in the forward position for venting of the tensioning device; 
     FIG. 3 is an enlarged partially sectioned elevational view of the tension device as is shown in FIG. 2; 
     FIG. 4 a  is a principal diagram for illustrating the mode of operation the state of the art; and 
     FIG. 4 b  is a principal diagram for illustrating the mode of operation for the invention of this application. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now in greater detail to the drawings wherein the showings are for the purpose of illustrating preferred embodiments of the invention only, and not for the purpose of limiting the invention, FIGS. 1-3 illustrate a tensioning and closing device  10  for the tensioning and closing of plastic tightening straps for producing package tightenings which can for example serve for securing the transport of packed pallets or the like. Tensioning device  10  comprises a closing device  11  and a tensioning device  12  which lies in front thereof in the longitudinal direction of the strap, which essentially consists of a tensioning wheel  13 , which can be driven by means of a pneumatic drive, not shown in detail, a pressure plate  14 , which can be moved against the tensioning wheel or can be lifted therefrom, and a separating element  15 , which is arranged between these two parts, which is formed as a separating plate  16 , and which comprises a curved surface  17 , the curvature of which is adapted to the radius r of the tensioning wheel. 
     Closing device  11  essentially consists, in a known manner, of a lower abutment plate  18  and a friction plate  19 , which is arranged above this in the housing and can be lowered, which can be moved to and fro along a vertical axis by means of a suitable drive in a way not shown and described in detail. 
     The two ends  20 ,  21  of the strap of a tightening strap  22  are inserted laterally into device  10  for producing a tightening. For this, the friction plate  19  is in its raised position, in which it forms a sufficiently large gap  23  with the abutment plate  18 , so that the two overlapping ends  20 ,  21  of the strap can be inserted laterally between the friction plate and the abutment plate without being hampered. The pressure plate  14  and the separating element  15  are lifted from the tensioning wheel  13  for threading the ends of the strap into the tensioning device  12 . The pressure plate is arranged in one piece at a carrier shoe  24 , which is lowered at its upper end by means of an eccentric drive  25  by an actuating lever  26  when pivoting the lever forward, that is in the drawing anti-lockwise to the left relative to the axis  27  of the tensioning wheel  13 , and which is lifted again when the actuating lever  26  is pivoted in the opposite direction, that is, clockwise. The pressure plate  14  arranged at the lower end of the carrier shoe  24  is moved thereby approximately transversely to the traversing direction of the ends  20 ,  21  of the strap, which are guided through the apparatus. 
     Separating plate  16  is also arranged at carrier shoe  24  and can be moved together with pressure plate  14  approximately transversely to the traversing direction  28  of the ends of the strap. A slot-shaped opening  29  is provided in the carrier shoe  24  for receiving the separating plate  16 , the length L of which is larger than the length  1  of the separating plate. The separating plate is provided with a lateral projection, not seen in the drawing, which has a longitudinal hole, through which is inserted a securing bolt  30  projecting laterally through the slot-shaped opening  29 . Thereby, the separating plate  16  cannot fall out of the slot-shaped opening  29  at the side, but it is arranged therein with play and can displace itself parallel to the traversing direction  28  as well as along an axis approximately parallel to the axis  27  of the tensioning wheel, and can adjust itself largely freely in its relative position to the tensioning wheel. 
     Lower abutment plate  18  of the closing device  11  is provided with an unblocking element  32  for separating plate  16  at its front face  31 , which essentially consists of a release wedge  33 , which is secured to the abutment plate  18  by means of a set screw  35 , which is screwed into the front face  31  by means of a thread bore  34 . The arrangement is in such a way that the oblique release surface  36  of the release wedge from the tip  37  of the wedge lying approximately under the tensioning wheel axis  27  increases obliquely upwards in the traversing direction  28  of the upper end of the strap  20  toward the closing device  11  which lies behind. The oblique release surface  36  cooperates with the rear edge of the separating plate  16 , which forms a gliding surface  38 , as can best be seen in FIG.  3 . This results in that the separating plate is not only lifted radially from the tensioning wheel  13  by the carrier shoe  24 , which is then moved downwards, as is usual in the state of the art according to FIG. 4 b , but that is also additionally released from the release wedge approximately in the tangential direction of the tensioning wheel forward out of the wedge-shaped gap  39  formed by the ends  20 ,  21  of the strap against the traversing direction  28  of the upper end  20  of the strap. 
     For inserting the ends  20 ,  21  of the strap when producing a tightening, the pressure plate  14  and the separating plate  16  are lifted from the tensioning wheel  13  with the help of an actuating lever  26 , which displaces the carrier shoe  24 , into a position as seen in FIGS. 2 and 3. Therewith, the friction plate  19  has—as mentioned—a distance from the abutment plate  18  lying below, so that the ends of the strap can easily be inserted from the side of the apparatus. Subsequently, the actuating lever is pivoted into the position shown in FIG.  1  and lifts the carrier shoe  24  thereby, the upper end of the strap is clamped between the tensioning wheel  13  and the underlying separating plate  16 , and the lower end of the strap is clamped between this and the pressure plate  14 . Subsequently, the drive (not shown) for the tensioning wheel  13  is switched on, which rotates anti-clockwise in the direction of the arrow  40  and inserts the upper end  20  of the strap in the traversing direction  28  further into the closing device, while the lower end of the strap is held simultaneously by clamping it between the pressure plate  14  and the separating element  15 . The separating plate  16  is also displaced during this tensioning process due to its floating mounting at the carrier shoe  24  in the traversing direction  28 , and reaches the position shown in FIG. 1, in which it lies approximately under the axis  27  of the tensioning wheel  13 , and with its curved upper surface  17  at the surface of the tensioning wheel periphery, with the upper end  20  of the strap in the intermediate position. As can easily be seen, the upper end of the strap lies over a relatively large region at the outer periphery of the tensioning wheel, so that large tension forces are exerted on the strap and this can be placed under a large tension, due to the large roughness of the tensioning wheel at its periphery and the large contact surface. 
     When the desired tension is reached, the drive for the tensioning wheel switches off and the friction plate  19  is lowered in a known manner onto the upper end  20  of the strap and moves this transversely to the traversing direction  28  with a high speed to and fro over the lower end  21  of the strap, so that the two ends of the strap fuse and are welded to one another, as is shown at  41 . 
     After the hardening of the welding point  41  apparatus  10  has to be taken out from the finished tightening at the side. For this, it is necessary to lift the friction plate  19  on the one hand from the underlying ends of the strap, so as to release the gap  23  again, and on the other hand, to vent the tensioning device  12  in the manner described. Due to the high tension introduced into the strap by means of the tensioning wheel  13 , the friction plate  19  is kept drawn after the welding in the direction of the tensioning wheel against the traversing direction  28  by the upper end  20  of the strap. This tension has such a magnitude that friction plate  19  can only be brought from its shown position into the lifted position by using a very large force. So as to decrease the force for lifting the friction plate, the tensioning device is first vented, with the aim to disengage the upper end of the strap from the tensioning wheel and thereby to decrease the forces exerted between the friction plate and the tensioning wheel by the upper end of the strap. 
     FIG. 4 a  shows the arrangement of the individual parts in a very simplified manner, as they are arranged to one another in the state of the art. It can be seen easily that the separating plate  16  is lifted a little from the tensioning wheel  13 , but that the upper end  20  of the strap is still engaged with the tensioning wheel by means of a smaller radian measure, and will not be released sufficiently from the separating plate  16 , so as to disengage from the rough surface of the tensioning wheel. The desired effect, that is the removal of the force acting on the friction plate  19  by means of the upper end of the strap, will not be achieved without the unblocking element  32  with an arrangement according to FIG. 4 b.    
     With the invention however, the separating plate  16  is, when the closing device  11  is ventilated, not only lifted radially from the tensioning wheel, but is also simultaneously displaced to the front with the help of the unblocking element  32  into the increasing wedge-shaped gap  39  between the ends of the strap, where it presses the upper end of the strap no longer against the tensioning wheel  13 , so that it can disengage from the peripheral surface of the tensioning wheel and effect a relaxation of the friction plate  19 . The friction plate can then easily be lifted in an essentially known manner with the help of a toggle gear, not shown, and a tappet  42  actuating this, and release the slot  23 . The unblocking element  32  is shown in FIG. 4 b  as a screw tension spring  43  which draws the separating element  15  out of its effective engagement region below the tensioning wheel, when the wedge-shaped gap  39  is opened far enough by the lifting of the pressure plate  14  so as to release the separating plate. 
     While considerable emphasis has been placed on the preferred embodiments of the invention illustrated and described herein, it will be appreciated that other embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the invention. Accordingly, it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.