Roller conveying unit for conveying a sheet by means of aspiration

A roller conveying unit for conveying a sheet by means of aspiration, comprising:

• a frame;
• a roller which is activatable in rotation with respect to the axis thereof, which is internally hollow and which comprises a first through-hole which sets the outside of the roller in fluid communication with the inside of the roller;
• a cylindrical surface which is arranged internally of the roller and which is concentric to the roller;
• an annular chamber being thus defined between the cylindrical surface and the internal surface of the roller;
• aspirating means for creating a depression in the annular chamber;
• an insert;
• wherein the insert:
• is borne by the roller;
• is inserted in the first through-hole of the roller;
• is dimensioned so as to contact the cylindrical surface;
• and comprises a second through-hole which in turn is in communication with the outside of the roller and extends through the first through-hole and the annular chamber;
• and comprises an internal portion which crosses the annular chamber which is partly inserted in the first through-hole and which is mobile along the first through-hole and across the annular chamber in order to take up a first position, wherein it enters into contact with the cylindrical surface, thus preventing fluid communication between the outside of the roller and the annular chamber via the second through-hole, or a second position, wherein it is detached from the cylindrical surface, placing the outside of the roller in fluid communication with the annular chamber via the second through-hole;
• and in that the roller conveying unit comprises:
• a cam which is solidly constrained to the frame;
• a cam follower which is borne by the roller and which engages with the cam and which commands the movement of the internal portion of the insert;
• wherein the cam is configured in such a way that, when the roller rotates with respect to the axis thereof, the cam follower runs on the cam and thus moves the internal portion of the insert between the first position and the second position, so that a sheet located on the outside of the roller and at the first through-hole is aspirated against the external surface of the roller by action of the depression generated by the aspirating means, and is consequently conveyed.