Sheet feed device for sheet fed printing machine, with speed and rotation direction of rollers altered to control sheet distance from rollers

摘要

At least one of rollers (14) is driven with circumferential speed deviating from size and direction of transport speed of sheet to control repulsive or suction force on sheet using Magnus effect. Pressure increases on one side and lowers on other side of roller, which causes pressure increase or decrease in space (15) between sheet and roller. Sheet feed unit contains feed rollers (14) with rotational axis orthogonal to sheet feed direction, spaced apart with openings (15) between for air flow from unit switchable from blow to suction function (21). Two neighboring rollers are driven in same direction or opposing direction, at different revolution. When rollers are moved in same direction as sheet, sheet is sucked onto rollers, useful for first printing run. When roller surface runs in opposing direction to sheet movement, due to Magnus effect sheet is kept from contact with rollers, useful for first and perfecting printing runs. Zonal suction or repulsion on sheet is achieved by control of revolution of single rollers.