Sheet grader

Claim 2

Grader apparatus for sheets comprising a conveyor, a pair of ducts having downwardly directed openings adjacent to the conveyor, said openings being spaced apart in the direction of travel of the conveyor, a downwardly open channel extending in the direction of travel of the conveyor and located between the duct openings, and means for inducing suction in the ducts tending to maintain maximum suction in the duct openings and lesser suction in the channel, said suction drawing sheets passing below the ducts and channel into contact with the underside of the conveyor, and said lesser suction in the channel being insufficient to retain a sheet against the conveyor which is not long enough in said direction of travel to be subjected to substantially maximum suction at both ducts at the same time.

Claim 3

Apparatus as claimed in claim 1 in which there are at least two pairs of said ducts spaced apart transversely of the conveyor.

Claim 4

Grader apparatus as claimed in claim 1 in which said channel interconnects the openings of said pair of ducts.

Claim 5

Apparatus as claimed in claim 3, in which there are at least two pairs of said ducts spaced apart transversely of the conveyor.

Claim 6

Grader apparatus as claimed in claim 1 including a mechanism operable to move into the path of sheets supported on the conveyor and to divert sheets from the conveyor, a control means associated with said mechanism and comprising size-detecting elements adapted to operate the mechanism to move it to its sheet-diverting position as a sheet which has a length only slightly less than long enough to be subjected to maximum suction at both ducts at the same time, is against the conveyor.

Claim 7

Apparatus for grading sheets into those above and those below a certain size comprising a conveyor, a pair of ducts having inlet openings which are spaced apart along the conveyor a distance related to the size to either side of which it is required to grade the sheets, a channel opening towards the conveyor and interconnecting the inlet openings, and means for inducing suction in the ducts tending to maintain maximum suction in the duct openings and lesser suction in the channel, said suction-drawing sheets passing below the ducts and channel into contact with the underside of the conveyor, and said lesser suction in the channel being insufficient to retain a sheet against the conveyor which is less than said size and not long enough in said direction of travel to be subjected to substantially maximum suction at both ducts at the same time.

Claim 8

Apparatus for grading sheets into those above and those below a certain size comprising a conveyor, a pair of ducts having inlet openings which are spaced apart along the conveyor a distance related to the size to either side of which it is required to grade the sheets, a channel opening towards the conveyor and interconnecting the inlet openings, and means for inducing suction in the ducts tending to maintain maximum suction in the duct openings and lesser suction in the channel, said suction-drawing sheets passing below the ducts and channel into contact with the underside of the conveyor, and said lesser suction in the channel being insufficient to retain a sheet against the conveyor which is less than said size and not long enough in said direction of travel to be subjected to substantially maximum suction at both ducts at the same time.

Claim 9

Apparatus as claimed in claim 6 in which there are at least two pairs of said ducts spaced apart transversely of the conveyor.

Claim 10

Apparatus for grading sheets according to size comprising a conveyor against the underside of which sheets to be graded can be supported by suction, a pair of ducts each having an inlet opening, the inlet openings being spaced apart along the conveyor and close to the conveyor and the ducts being connected to the low-pressure side of a fan, a channel interconnecting the inlet openings and opening downwardly towards and adjacent to the conveyor, said fan inducing maximum suction in the duct openings and lesser suction in the channel, said suction-drawing sheets passing below the ducts and channel into contact with the underside of the conveyor, and said lesser suction in the channel being insufficient to retain a sheet against the conveyor which is not long enough in said direction of travel to be subjected to substantially maximum suction at both ducts at the same time.

Claim 11

Apparatus for grading sheets according to size comprising a conveyor against the underside of which sheets to be graded can be supported by suction, a pair of ducts each having an inlet opening, the inlet openings being spaced apart along the conveyor and close to the conveyor and the ducts being connected to the low-pressure side of a fan, a channel interconnecting the inlet openings and opening downwardly towards and adjacent to the conveyor, said fan inducing maximum suction in the duct openings and lesser suction in the channel, said suction-drawing sheets passing below the ducts and channel into contact with the underside of the conveyor, and said lesser suction in the channel being insufficient to retain a sheet against the conveyor which is not long enough in said direction of travel to be subjected to substantially maximum suction at both ducts at the same time.

Claim 12

Apparatus as claimed in claim 8. in which there are at least two pairs of said ducts spaced apart transversely of the conveyor.