Embossing unit

Abstract

An embossing unit, wherein sheet material is fed between a first and a second embossing roller counter-rotating respectively about a first and a second axis of rotation defining a plane, one of the embossing rollers being subjected, in use, to a compression force towards the other embossing roller; and wherein at least one of the axes of rotation oscillates about a virtual hinge or instantaneous centre of rotation, which is movable, in the plane defined by the axes of rotation, in response to displacement, along a pitch line of tangency between the embossing rollers, of a point of application of a reaction force.

1 . An embossing unit comprising a first and a second embossing roller ( 3 ,  4 ) counter-rotating respectively about a first and a second axis ( 6 ,  7 ) of rotation defining a plane, the embossing rollers ( 3 ,  4 ) being tangent to each other along a pitch line ( 8 ) lying in said plane; and a push assembly ( 16 ) for pressing the embossing rollers ( 3 ,  4 ) against each other to grip, in use, sheet material ( 2 ) for embossing between the embossing rollers ( 3 ,  4 ) with a given compression force (F); at least one of the axes ( 6 ,  7 ) of rotation being an oscillating axis ( 7 ) oscillating about a third axis ( 15 ) perpendicular to said plane and defining, in said plane, a centre of rotation (C); characterized in that the centre of rotation (C) is an instantaneous centre of rotation (C), which is movable in said plane in response to displacement, along the pitch line ( 8 ) of tangency between the embossing rollers ( 3 ,  4 ), of a point (A) of application of a reaction force (R) to the compression force (F).  
   
   
       2 . An embossing unit as claimed in  claim 1 , wherein said first embossing roller ( 3 ) is a drive embossing roller, and said second embossing roller ( 4 ) is a driven embossing roller.  
   
   
       3 . An embossing unit as claimed in  claim 1 , wherein said oscillating axis ( 7 ) is the second axis ( 7 ); the first axis ( 6 ) is a fixed axis; and the push assembly ( 16 ) is connected to the second embossing roller ( 4 ).  
   
   
       4 . An embossing unit as claimed in  claim 1 , wherein, of the embossing rollers ( 3 ,  4 ), the one coaxial with said oscillating axis ( 7 ) is an oscillating embossing roller ( 4 ) oscillating about the third axis ( 15 ); a supporting unit ( 12 ) being provided to support the oscillating embossing roller ( 4 ); and said supporting unit ( 12 ) being interposed between the oscillating embossing roller ( 4 ) and the push assembly ( 16 ).  
   
   
       5 . An embossing unit as claimed in  claim 4 , wherein the supporting unit ( 12 ) is an articulated unit.  
   
   
       6 . An embossing unit as claimed in  claim 5 , wherein the supporting unit ( 12 ) comprises an articulated quadrilateral.  
   
   
       7 . An embossing unit as claimed in  claim 6 , wherein said articulated quadrilateral comprises a frame ( 18 ) movable parallel to said compression force (F) by the push assembly ( 16 ); a cross member defined by a shaft ( 11 ) coaxial with said oscillating axis ( 7 ) and supporting for rotation said oscillating embossing roller ( 4 ); and two connecting rods ( 21 ) perpendicular to the third axis ( 15 ) and having respective lines of action intersecting at said instantaneous centre of rotation (C).  
   
   
       8 . An embossing unit as claimed in  claim 7 , wherein each connecting rod ( 21 ) is a tie.  
   
   
       9 . An embossing unit as claimed in  claim 4 , wherein the supporting unit ( 12 ) is an articulated “rocking” unit.  
   
   
       10 . An embossing unit as claimed in  claim 9 , wherein the supporting unit ( 12 ) comprises a base ( 26 ) having a first surface ( 25 ); a fork ( 18 ) comprising a cross member ( 19 ) and two arms ( 20 ), the cross member ( 19 ) having a second surface ( 24 ); and a shaft ( 11 ) coaxial with said oscillating axis ( 7 ) and supporting said oscillating embossing roller ( 4 ); at least one of said first and said second surface ( 25 ,  24 ) being a curved surface ( 24 ) contacting the other of said first and said second surface ( 25 ,  24 ) at a point defining the instantaneous centre of rotation (C).  
   
   
       11 . An embossing unit as claimed in  claim 10 , wherein said push assembly ( 16 ) is connected to the base ( 26 ).  
   
   
       12 . An embossing unit as claimed in  claim 11 , wherein said curved surface ( 24 ) has a radius of curvature equal to at least twice the distance between the instantaneous centre of rotation (C) and the pitch line ( 8 ).  
   
   
       13 . An embossing unit as claimed in  claim 1 , the embossing unit ( 1 ) having, at any instant and in use, an instantaneous centre of stability (SC) defined as the point which lies in said plane, is integral with said oscillating axis ( 7 ), and, following infinitesimal oscillation of said oscillating axis ( 7 ), moves, in said plane and parallel to the pitch line ( 8 ), by the same amount as the instantaneous centre of rotation (C); the pitch line ( 8 ) being located, in use, between the instantaneous centre of stability (SC) and the oscillating axis ( 7 ).