Advancement unit of sheets of paper in a machine for paper converting and related advancement method

An advancement unit configured to cause a plurality of sheets of paper, or other material permeable to air, of a predetermined length, to move along a predetermined advancing direction in a machine for paper converting, each sheet of said plurality having a head edge and a tail edge, said advancement unit comprising:

• a cutting group configured to divide a web made of paper, or another material permeable to air, into said plurality of sheets;
• a transfer roll positioned downstream of said cutting group and having an external surface, said transfer roll being configured to rotate at a first predetermined angular velocity (ω1) about a longitudinal rotation axis and to hold, alternately, on a first and on a second predetermined portion of said external surface respectively said head edge and said tail edge of said plurality of sheets coming from said cutting group, in such a way to cause said sheets to be transferred at a first predetermined tangential speed (v1);
• wherein said advancement unit furthermore, provides:
• a displacement group positioned downstream of said transfer roll and configured to move a plurality of catching members along a movement trajectory comprising at least one curvilinear portion and at least one straight portion, each catching member being configured to hold a respective head edge of a sheet during the movement of the same along said predetermined movement trajectory, in such a way to move said plurality of sheets in a partly overlapped configuration along a predetermined advancement trajectory;
• wherein said curvilinear portion of said movement trajectory is positioned upstream of said straight portion;
• wherein said plurality of catching members are moved along said curvilinear portion at a second tangential speed (v2) less than or equal to said first tangential speed (v1);
• and wherein each catching member comprises a main body provided with at least a catching hole configured to suck said head edge of a respective sheet of said plurality and to hold the head edge on a predetermined advancement trajectory during said movement of said respective catching member along said movement trajectory.