Method and apparatus for positioning a welding jaw

Abstract

To be able to weld together layers of film ( 23, 24 ) lying one on top of the other with improved sealing seam quality, a distance (a) between sealing surfaces ( 30 ) of welding jaws ( 30 ) moved toward each other or between a sealing surface and a resistance is prescribed within a sealing duration by a control device ( 27 ) of a drive ( 8 ) configured as an electromagnetic linear drive (linear motor), the value for the distance (a) always being less than or equal to the value for the thickness (d) for the two layers of film ( 23, 24 ) lying one on top of the other.

1 . Method for positioning a welding jaw during a welding operation, in particular a welding jaw of a transverse sealing station of a vertical tubular bag machine, the welding jaw being moved in a circulating manner along a closed path or back and forth along a linear path, to be set against a resistance, in particular a second, oppositely running welding jaw, two layers of film lying one on top of the other, with a total thickness (d) for both layers of film together, of a film tube being pressed together between the resistance and the sealing surface of the welding jaw, in particular between the sealing surfaces of two welding jaws, in order to weld the film tube by means of heat introduced into the film tube via the sealing surface of the welding jaw or the sealing surfaces of the welding jaws, with an exerted pressure in a sealing plane (S) under a sealing force within a sealing time, and a drive being provided for the purpose of moving the welding jaw in a direction normal to a surface of the resistance or an oppositely running welding jaw, in order in this way to carry out the welding operation in a fixed location or along a sealing path within the sealing time, wherein a distance (a) between the sealing surface and the resistance or between the two sealing surfaces of the welding jaws during the welding operation is prescribed by a control device of the drive, and in that the value for the distance (a) is always less than or equal to the value for the thickness (d) for the two layers of film lying one on top of the other.  
     
     
         2 . Method according to  claim 1 , wherein the welding jaw is moved along the linear path, and, with the film at a standstill and the welding jaw lying against the film tube during the sealing time, values for the distance (a) are prescribed by the control device.  
     
     
         3 . Method according to  claim 1 , wherein the welding jaw is moved along the closed path, which has a straight portion, along which, while the film tube is being moved, the welding jaw moved with it welds the film tube values for the distance (a) being prescribed by the control device during the sealing time.  
     
     
         4 . Method according to  claim 1 , wherein the distance (a) is kept constant during the duration of the sealing time.  
     
     
         5 . Method according to  claim 1 , wherein the distance (a) is changed during the duration of the sealing time.  
     
     
         6 . Method according to  claim 4 , wherein, before the beginning of the welding operation, a distance (a) that is greater than or equal to the thickness (d) of the sum of the thickness of the two layers of film lying one on top of the other is prescribed, in order initially to preheat the layers of film before the welding operation is performed while exerting the sealing force with a reduced distance (a).  
     
     
         7 . Method according to  claim 1 , wherein the prescribed values for the distance (a) are compared with a sealing force to be achieved for these values or this value, and in that, if there is excessive sealing force for a specific distance (a), it is concluded that there is a product inclusion between the resistance and a sealing surface or between the sealing surfaces.  
     
     
         8 . Apparatus for performing the method according to  claim 1 , wherein the apparatus is a packaging machine, in particular a vertical tubular bag machine, which has for moving the welding jaw a drive which is designed as an electromagnetic linear drive operating on the suspension railway principle, has a part and a part, which is movable in relation to this part, and the movable part can perform a movement changing the distance (a), the respective value of the distance (a) being prescribed by the respective position of the movable part in relation to the part.  
     
     
         9 . Apparatus according to  claim 8 , wherein the movable part is connected directly to the welding jaw without any gear mechanism.  
     
     
         10 . Apparatus according to  claim 8 , wherein the movable part is directly connected to a cam plate, which has a cam line or two cam lines for changing the location of a cam connected to a jaw carrier of a welding jaw.