Feed unit for feeding sheets to a packing line

Abstract

A feed unit for feeding sheets to a packing line, wherein a pickup device engages a withdrawal opening, formed in a vertical hopper housing a stack of sheets, to withdraw a single sheet from the stack and feed the sheet to the packing line; two rollers are located on opposite sides of the stack at the withdrawal opening in the hopper, and each has a lateral surface, on which rests a bottom portion of the stack, and rotates continuously about a respective longitudinal axis of symmetry in such a direction as to push the sheets in the stack upwards.

1 ) A feed unit for feeding sheets to a packing line; the feed unit ( 1 ) comprising a hopper ( 3 ) housing a stack ( 4 ) of sheets ( 2 ) and having a withdrawal opening ( 5 ); and a pickup device ( 6 ) which engages the withdrawal opening ( 5 ) in the hopper ( 3 ) to withdraw a single sheet ( 2 ) from the stack ( 4 ) and feed the sheet ( 2 ) to the packing line; the feed unit ( 1 ) being characterized by comprising, at the withdrawal opening ( 5 ) in the hopper ( 3 ), at least one roller ( 11 ) having a lateral surface ( 12 ) on which a portion of the stack ( 4 ) rests; and actuating means ( 13 ) for rotating the roller ( 11 ) about a respective longitudinal axis ( 14 ) of symmetry in such a direction as to push the sheets ( 2 ) in the stack ( 4 ) away from the withdrawal opening ( 5 ).  
   
   
       2 ) A feed unit as claimed in  claim 1 , wherein the actuating means ( 13 ) rotate the roller ( 11 ) at a given constant speed.  
   
   
       3 ) A feed unit as claimed in  claim 2 , wherein the actuating means ( 13 ) provide for adjusting the rotation speed of the roller ( 11 ).  
   
   
       4 ) A feed unit as claimed in  claim 3 , wherein the actuating means ( 13 ) provide for adjusting the rotation speed of the roller ( 11 ) as a function of the withdrawal rate of the sheets ( 2 ) from the withdrawal opening ( 5 ) in the hopper ( 3 ).  
   
   
       5 ) A feed unit as claimed in  claim 3 , wherein the actuating means ( 13 ) provide for adjusting the rotation speed of the roller ( 11 ) as a function of the number of sheets ( 2 ) in the stack ( 4 ).  
   
   
       6 ) A feed unit as claimed in  claim 1 , wherein the portion of the lateral surface ( 12 ) of the roller ( 11 ) contacting the stack ( 4 ) has a high friction coefficient.  
   
   
       7 ) A feed unit as claimed in  claim 6 , wherein the portion of the lateral surface ( 12 ) of the roller ( 11 ) contacting the stack ( 4 ) has a covering of elastic material.  
   
   
       8 ) A feed unit as claimed in  claim 7 , wherein the portion of the lateral surface ( 12 ) of the roller ( 11 ) contacting the stack ( 4 ) has knurling.  
   
   
       9 ) A feed unit as claimed in  claim 8 , wherein the knurling comprises a series of grooves parallel to the longitudinal axis ( 14 ) of symmetry.  
   
   
       10 ) A feed unit as claimed in  claim 1 , wherein an edge of the stack ( 4 ) rests on the lateral surface ( 12 ) of the roller ( 11 ).  
   
   
       11 ) A feed unit as claimed in  claim 1 , wherein the roller ( 11 ) is so formed that its lateral surface ( 12 ) only contacts part of the stack ( 4 ).  
   
   
       12 ) A feed unit as claimed in  claim 11 , wherein the roller ( 11 ) is so formed that two separate portions ( 15 ) of its lateral surface ( 12 ) contact the stack ( 4 ).  
   
   
       13 ) A feed unit as claimed in  claim 1 , wherein two parallel rollers ( 11 ) are provided, are located on opposite sides of the stack ( 4 ), and each comprise a lateral surface ( 12 ) on which a portion of the stack ( 4 ) rests; the actuating means ( 13 ) rotating each roller ( 11 ) about a respective longitudinal axis ( 14 ) of symmetry in such a direction as to push the sheets ( 2 ) in the stack ( 4 ) away from the withdrawal opening ( 5 ).  
   
   
       14 ) A feed unit as claimed in  claim 13 , wherein two parallel opposite bottom edges of the stack ( 4 ) rest on the two rollers ( 11 ).  
   
   
       15 ) A feed unit as claimed in  claim 13 , wherein a window for the passage of each sheet ( 2 ) and defined between the two rollers ( 11 ) is smaller than each sheet ( 2 ).  
   
   
       16 ) A feed unit as claimed in  claim 15 , wherein the minimum distance between the lateral surfaces ( 12 ) of the two rollers ( 11 ), measured in a direction perpendicular to the longitudinal axes ( 14 ) of symmetry of the two rollers ( 11 ), is less than the corresponding dimension of each sheet ( 2 ) measured in the same direction.  
   
   
       17 ) A feed unit as claimed in  claim 1 , wherein the hopper ( 3 ) comprises a number of fixed sections ( 7 ) for laterally retaining the stack ( 4 ).  
   
   
       18 ) A feed unit as claimed in  claim 1 , wherein the hopper ( 3 ) comprises at least one fixed supporting member located at the withdrawal opening ( 5 ) and defining a support for the stack ( 4 ) to retain the stack ( 4 ) inside the hopper ( 3 ).  
   
   
       19 ) A feed unit as claimed in  claim 1 , wherein the hopper ( 3 ) is a vertical hopper ( 3 ); the actuating means ( 13 ) rotating the roller ( 11 ) about its longitudinal axis ( 14 ) of symmetry in such a direction as to push the sheets ( 2 ) in the stack ( 4 ) upwards.  
   
   
       20 ) A feed unit as claimed in  claim 1 , wherein the pickup device ( 6 ) comprises a wheel ( 8 ) rotating about a respective central axis ( 9 ); and at least one suction gripping head ( 10 ) supported by the wheel ( 8 ) to move cyclically along an endless path through a loading station, where the gripping head ( 10 ) engages the withdrawal opening ( 5 ) in the hopper ( 3 ) to withdraw a respective sheet ( 2 ), and through a follow-up unloading station, where the gripping head ( 10 ) feeds the sheet ( 2 ) to the packing line.