How to prevent floor eggs?

Besides causing serious back ache, floor eggs cut into farm profits as well. You cannot sell floor eggs as first grade eggs, so the return is lower. Dirty eggshells are not the only reason; the high percentage of floor eggs with hairline cracks is another factor. Preventing hens to lay on the floor is key, but there are no guarantees. Doing everything possible is not only a question of the timing of opening the nest boxes, it is also important to remove any floor eggs as soon as possible. Hence