Signature stacker

Abstract

A signature stream is intercepted by a bucket unlatched from the intercept position. The buckets are moved by drive chains. A spring assembly maintains tension upon the drive chains and spring loads the bucket in the 'home' position, providing a detent action upon this bucket to accelerate the bucket and also provide a force for drop-out of the bucket. A bucket cam follower guides the bucket to move from a normal path to the 'home' position. A microprocessor selectively halts each bucket during downward movement to reduce free fall time of signatures. A zero force cam engaged by the bucket cam follower counteracts the force otherwise applied to the chains by variable weight signatures on the bucket to maintain uniform tension on the chains. Circular cams move the free ends of the tines increasingly faster to orient the signature stack horizontally before the bucket withdraws from beneath the batch. Oscillating paddles jog the sides and corners of the signatures during stacking to form a neat batch. A turntable is rotated 180.degree. after receiving each signature batch. Chain driven pusher rods mounted independently of the rotatable turntable pass through a gap in the turntable to remove the stack. The microprocessor initiates movement of the turntable and pusher rods an adjustable delay after delivery of each signature batch as a function of free fall time of each signature batch. Position sensors indicate bucket position. A top of batch sensor measures signature and batch thickness. A turntable sensor prevents erroneous operation of the pusher rods.