Method of and mechanism for feeding sheet

A method of feeding a sheet in an auxiliary scanning direction with a sheet feed mechanism while the sheet is being scanned by a one-dimensionally deflected light beam along a main scanning line in a main scanning direction substantially perpendicular to said auxiliary scanning direction, said feed mechanism having an auxiliary scanning feed belt having a plurality of holes, a first suction chamber positioned upstream of said main scanning line with respect to the auxiliary scanning direction, a second suction chamber positioned downstream of said main scanning line with respect to the auxiliary scanning direction, and first and second valve bodies operatively connected to each other through a mechanical linkage and communicating with said first and second suction chambers, respectively, said method comprising the steps of:

• operating said first and second valve bodies through said mechanical linkage in ganged relation to attract the sheet to said feed belt under an attractive force developed by only said first suction chamber while the sheet is being fed in the auxiliary scanning direction;
• operating said first and second valve bodies through said mechanical linkage in ganged relation when the sheet is progressively fed in the auxiliary scanning direction, to reduce the attractive force developed by said first suction chamber and increase an attractive force developed by said second suction chamber;
• operating said first and second valve bodies through said mechanical linkage in ganged relation when the sheet is further progressively fed in the auxiliary scanning direction, to attract the sheet to said feed belt under the attractive force developed by only said second suction chamber while the sheet is being fed in the auxiliary scanning direction.