Abstract:
A welding head for looping machine is provided with a strap guide ( 7 ) for passing the looping strap ( 5 ) through the welding head ( 1 ), a strap fixing element ( 14 ) for holding the lapping strap sections ( 3, 4 ) which are to be welded together, a welding set ( 17 ) for melting the looping strap sections ( 3, 4 ) which are to be welded together, a pressing arrangement for joining the melted strap sections ( 3, 4 ) which are to be welded together, and a mechanically operating ejector ( 30 ) which is integrated in the welding head ( 1 ) for lifting the welded looping strap ( 5 ) out of the welding head ( 1 ).

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a welding head for a looping machine. 
     2. Background Art 
     Welding heads of the generic type come in various designs. Parts common to these welding heads are a strap guide passing the looping strap through the welding head, a strap fixing element holding the lapping strap sections which are to be welded together, a welding set melting the strap sections to be welded together, and a pressing arrangement joining the melted strap sections which are to be welded together. Examples of welding heads of the species are illustrated in German utility models DE 297 16 896 U1, DE 297 16 897 U1 and DE 297 16 898 U1. 
     When thin unstable stacks of, for instance, printed matters are looped, loading the product stack is possible only to a very restricted extent—if possible at all—because otherwise the stack would wave or fold. In this regard, the looping machine can operate only at a very restricted loop tensioning force. Since, owing to its instability, the product to be looped hardly offers any resistance to the tensioning of the strap, there is no stretching of the looping strap itself. This means that no contraction forces are inherently available in the strap, as a result of which the lapping and welded strap sections in the welding head will not come out of the welding head by themselves by the portion of the strap where the loop is closed. The noose of the strap possesses too low an elasticity of its own to enable the closed portion of the strap to come out of the welding head. 
     To solve these problems, actuation of the looping strap by compressed air has been proposed, the strap thus being blown out of the welding head. The air jets needed to this end are disposed beside the welding head or incorporated therein, which is accompanied with considerable constructional requirements. 
     The compressed air supply means necessary in this design causes additional expenditure for the supply infrastructure of a looping machine equipped with such a welding head. Very often, compressed air supply is not even available. 
     SUMMARY OF THE INVENTION 
     Proceeding from these problems, it is an object of the invention to embody a welding head for a looping,machine which can be employed universally and without compressed air supply means and which reliably enables the welded strap sections to come out of the welding head. 
     This object is attained by an ejector of mechanical operation which is integrated into the welding head, lifting the welded looping strap out of the welding head. 
     Because of the mechanical characteristics of the ejector, compressed air supply means can be omitted. This also implies reduced noise pollution during operation of the machine, because a mechanical ejector can work by far more quietly than hissing compressed air jets. Finally, from aspects of construction and control technique, a mechanical ejector is by far more easily to be put into practice and works more reliably. 
     Preferred embodiments of the looping machine and details of an exemplary embodiment of the invention will become apparent from the ensuing description, taken in conjunction with the annexed drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a diagrammatic lateral view of a welding head with the ejector in its normal position; 
     FIG. 2 is a section through the welding head on the line II—II of FIG. 1; and 
     FIGS. 3 and 4, respectively, are illustrations by analogy to FIGS. 1 and 2, respectively, with the ejector in the position of ejection. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The annexed FIGS. 1 to  4  illustrate only those components of the welding head  1  which are relevant to the present invention. Fundamentally, it is provided with a casing  2  (only roughly outlined), in which structural parts of functional relevance are lodged and guided in known manner. Ranking among these are in particular the clamping jaws  14 ,  15  (seen only partially) for actuation of the looping strap sections  3 ,  4 , led through the welding head  1 , of the looping strap designated in its entirety by  5 . The looping strap  5  is delivered via an insertion arrangement (not shown) from a strap supply and led through the welding head  1  into a strap guiding frame (not shown) where the looping strap  5  is guided in the form of a loose loop  6  around the stack to be looped until the leading end of the strap section  3  again arrives in the welding head  1 . In this regard, the structure of the welding head  1  constitutes prior art as described for instance in DE 297 16 896 U1 mentioned at the outset. 
     A strap guide  7  is primarily responsible for the passage of the looping strap  5  through the welding head  1 , its head  9  extending in the direction of passage  8  and having a laterally open guiding slot  10  for the looping strap  5 . Upon insertion through the welding head  1 , the looping strap  5  runs in this guiding slot  10 . A guiding finger  11  (FIG. 2) before the open side of the guiding slot  10  in the head  9  of the strap guide  7  works as a safeguard against the looping strap  5  coming out laterally. For the support of the head  9 , the strap guide  7  has a flat shank  12  which is displaceably guided in a guide groove (not shown) in the casing  2  transversely of the looping plane  13 . A cutting jaw  16  is provided in addition to the clamping jaws  14 ,  15 , by means of which the strap loop  6  can be severed from the inserted supply of strap after the strap sections  3 ,  4  have been welded together. 
     The actual welding set consists in a welding tongue  17  to be slipped laterally in between the two looping strap sections  3 ,  4 . This takes place after the loop  6  has been formed and tautened, the strap guide  7  being pushed out in the opposite direction synchronously of the insertion of the welding tongue  17  between the looping strap sections  3 ,  4 . In this way the strap section  4  which runs in the guiding slot  10  is released and can be pressed by the clamping jaw  15  against the upper strap section  3  with the welding tongue  17  lying in between. The pressure plate  18 , which constitutes the upper end of the welding head  1 , serves as an opposite bearing; it is displaceably supported on the casing  2  in parallel to the strap guide  7 . 
     Time-controlled actuation of the individual functional components of the welding head  1  takes place via a cam control  19 , only the cam shaft  19  and a cam disk  21  of which being illustrated in FIGS. 2 and 4. The cam disk  21  serves for actuation of the strap guide  7  and the pressure plate  18  during the lateral swing-out motion in the welding process and thereafter. The cam disk  21  faces a one-armed transmission lever  25  which, by means of a cam roller  23 , follows the curve of the cam disk  21  and is mounted pivotally about an axis  22 . Via an intermediate connecting rod  26 , the free end  24  of the transmission lever  25  is articulated to a fishplate  27  on the rear end of the shank  12  of the strap guide  7 . The cam control  19  and the transmission lever  25  serve for direct actuation of the strap guide  7  and indirect actuation of the pressure plate  18 . For the pressure plate  18 , after passing through a basic deflection length  28  of the strap guide  7 , is taken along in the direction of deflection, and thus also moved out laterally, by the head  9  of the strap guide  7  stopping on a shoulder  29  on the underside of the pressure plate  18 . 
     Gist of the present invention is an ejection lever  30  which is disposed underneath, and flanking, the strap guide  7  and which is double-armed and pivotal about a pivot axis  31  which is parallel to the direction of passage  8  of the looping strap  5  and laterally displaced therefrom. The free end  37  of the arm  32 , which is directed towards the looping plane  13 , is the actual ejector, the normal position of which (FIGS. 1,  2 ) is substantially horizontal. The driving end  34  of the second arm  33  of the ejection lever  30  is bent in the shape of a hook into the motion travel of the strap guide  7 , thus being actuated by the strap guide  7  during the motion of disengagement thereof. Thus, also the ejection lever  30  is indirectly drivable via the cam control  19  in a manner still to be described. As seen in FIG. 1, the ejection lever  30  is located by the side of the guide finger  11  referred to the direction of passage  8 . 
     The mode of operation of the welding head  1  during the welding process and afterwards is explained as follows: 
     In the normal position, seen in FIGS. 1 and 2, of the welding head  1 , the looping strap  5  is inserted through the guiding slot  10  of the strap guide  7  and again returned into the welding head  1 , forming a loose loop  6  around the product to be looped. The strap sections  3 ,  4  are fixed by the clamping jaws  14 ,  15 , after which the strap guide  7 , by the aid of the cam control  19 , is deflected by the basic deflection length  28  to the right referred to FIG.  2 . The pressure plate  18  and the ejection lever  30  remain in the normal position seen in FIGS. 1 and 2. The welding tongue  17 —also driven via a cam control  19 —moves between the two strap sections  3 ,  4 , melts them and is then retracted into the normal position seen in FIG.  2 . Directly afterwards, the strap sections  3 ,  4  are pressed one upon the other and from below against the pressure plate  18  by the aid of the clamping jaw  15 . Thus the closed loop is formed and fixed between the strap sections  3 ,  4 . Upon further rotation of the cam disk  21 , the cam roller  23  arrives on the nose  35  of the cam disk  21 , whereby the transmission lever  25  is further pivoted clockwise referred to FIGS. 2 and 4. Thus, the strap guide  7  is moved out beyond the basic deflection length  28 , taking along the pressure plate  18  into its position of disengagement laterally outside the looping plane  13 . In this case, the lower rear edge  36  of the head  9  of the strap guide  7  stops on the driving end  34 , bent inwards, of the ejection lever  30 , whereby the ejection lever  30  is pivoted clockwise about its pivot axis  31 . Thus, the ejection lever  30  lifts the welded strap  5  upwards out of the welding head  1 , whereby the looped package can be carried off the work table of the looping machine without any problems. 
     The release of the looping strap  5  is still further supported by the fact that the free end  37  of the arm  32  as well as the front end  38 , directed towards the looping plane  13 , of the pressure plate  18  are provided with an upward stripping slope  39 ,  40 . During the lifting motion, the looping strap  5  will slide off the stripping slope  39  of the ejection lever  30  and place itself on the stripping slope  40  of the pressure plate  18 , as seen in FIG.  4 . Upon return of the ejection lever  30  and the pressure plate  18  into their normal position, the stripping slope  40  the pressure plate  18  backs up the looping strap  5  and lifts the portion where the loop is closed over the pressure plate  18 . 
     Concluding it can be said that the ejection lever  40  together with its indirect pivot drive via the cam control  19  forms an ejector of mechanical operation which is integrated into the welding head  1 , lifting the welded looping strap  5  out of the welding head  1 .