Abstract: An apparatus and method for delivering sheet material, such as signatures, to a gatherer feed mechanism from a vertically stacked on-edge array. A hopper loader delivers signatures to a hopper feed conveyor which moves the signatures in a generally vertically stacked array to a discharge area. Side guides extend above the conveyor to the discharge area. The side guides are spaced apart a distance less than the width of the signatures so that each signature is bowed in the direction of movement of the conveyor. Solenoid-operated pins are provided at the ends of the side guides to alternately hold and release opposite vertical edges of each signature at a predetermined hold-release frequency. The pins maintain the bow and hold the signatures and then release each one to the discharge area in an unbowed condition. Photodetectors maintain the respective pins in the hold position in the event that the delivery area of the hopper becomes full or only one edge of a signature is released.