A machine for handling sheets on conveyors to form a stack thereof comprising:
- a first tiltably mounted flow control conveyor disposed to receive sheets from the discharge of a cutting knife of a sheet processing machine and to discharge said sheets onto,
- a second inclined belt conveyor positioned to receive said sheets from said first flow control conveyor and to discharge said sheets to,
- a pair of rotating pinch rollers positioned to grip said sheets therebetween and to discharge said sheets onto,
- a platform of a vertical elevator positioned against said rollers and disposed to receive said sheets successively from said rollers while descending from an initial elevated position opposite the discharge of said rollers to form a stack upon said platform;
- said first flow control conveyor being further equipped with a vacuum source positioned beneath its carrying surface to effect retention of sheets thereon;
- separate driving means for said first conveyor and said second conveyor;
- speed control means disposed for operating said driving means of both of said conveyors initially at a first speed lower than the linear velocity of said sheets discharging from said processing machine thereby causing overlapping of said sheets on said conveyor;
- said speed control means being disposed for increasing the speed of both of said conveyors to a second relatively high speed for a short interval of time after a predetermined number of sheets has been discharged from said processing machine;
- said speed control means being further disposed for decreasing the speed of said first control conveyor to a third relatively slow speed said tilting control means being disposed for simultaneously positioning said first conveyor to said second vertical angle thereby interrupting the discharge of said sheets onto said second conveyor and slowing the forward movement of said sheets on said first flow control conveyor thus causing them to accumulate thereon while continuing the operation of said second conveyor at said second relatively high speed;
- tilting control means for positioning said first flow control conveyor alternately from a first vertical angle to a second increased vertical angle;
- said speed control means being still further disposed for continuing the operation of said second conveyor at said relatively high speed until said predetermined number of sheets has been discharged onto said descending platform thereby completing said stack thereon;
- means for arresting the descent of said elevator platform and means for discharging said stack therefrom said speed control means being disposed for simultaneously changing the speeds of both of said conveyors back to the said first speed said tilting control means being further disposed for positioning said flow control conveyor back to said first vertical angle;
- means for returning said elevator platform back to said initial position.