I have a conveyor with several stations, items flow in a linear fashion, I placed photo eyes to limit the number of items at any given station, stations have different cycle times, the logic of the photo eyes works, but if a station completes its cycle before the next station, the flow item moves to the space in between subsequence photo eyes, how can I have a station to move the item only if the next station is empty? meaning that it is blocked until the next station is open