Abstract: A live roller zero pressure accumulation conveyor and trigger assembly for sensing the presence or absence of articles on the conveyor are described. The trigger assembly includes a cam which is mounted to the conveyor for pivotal movement about an axis at or above the axes of rotation of the conveyor rollers, a leg on the cam spaced from the pivotal mounting and extending upwardly between a pair of the conveyor rollers, and a cam roller rotatably mounted adjacent the end of the leg. The cam roller is rotatable about an axis which is substantially parallel to the axes of rotation of the conveyor rollers.