Suction device for separating and/or transporting sheets in a sheet-handling machine

Claim 1

In a sheet-handling machine, a suction device for engaging and then holding sheets, comprising, in combination, a pneumatic cylinder; a hollow piston units in said cylinder movable between a retracted and a non-retracted position and comprised of axially adjacent first and second portion, at least a part of the circumferential periphery of each of said portions being spaced from and out of contact with the inner periphery of said cylinder to define therewith respective first and second spaces, said piston unit including a sheet-engaging portion having a suction opening which communicates with the ambient atmosphere and constitutes the end of the hollw interior of said piston unit, said hollow interior communicating with said second space via said first space, said cylinder being provided with a suction port opening into said second space to form a path for the flow of ambient air into said suction opening and out through said port, the flow cross section of said first space being smaller than that of said second space so that said first space constitutes a flow restriction in said path; and drive means for causing said piston unit to move from retracted to non-retracted position and then back to retracted position, in order to cause said sheet-engaging portion to move into engagement with a sheet located in the path of movement of the latter and then hold said sheet by suction during the movement of said piston unit back to said retracted position, said drive means comprising suction-generating means connected to said port and operative for establishing subambient pressure in said second space, whereby said piston moves from said retracted to said non-retracted position upon the establishment of such subambient pressure as a result of the initial difference in pressures upstream and downstream of said first space, and whereby said piston returns to said retracted position due to the pressure equalization resulting when the sheet engaged and held by said sheet-engaging portion blocks further entrance of ambient air into said suction opening of the said sheet-engaging portion, wherein said first portion of said piston unit is cylindrical and constitutes a hollow piston portion and wherein said second portion of said piston unit is cylindrical and constitutes a hollow piston rod portion, and wherein said hollow piston portion is spaced from and out of contact with the inner periphery of said cylinder all around the circumferential periphery of said hollow piston portion, whereby there is no frictional wear of the circumferential surface of said piston portion and the facing inner surface of said cylinder, and wherein said cylinder is further provided with an axially extending guide portion for guiding said piston Rod portion, said guide portion having an axial end portion facing said piston portion, and wherein said piston rod portion is further provided with a recess constituting a suction release passage having one end opening into the ambient atmosphere and having another end which terminates just past said axial end portion of said guide portion when said piston unit is in said retracted position.