I will upload the file of a principle of the logic that I want to apply. The first photocell is occupied and the previous motor stopped that I have achieved it but later at the intersection I have put two photocells and in that section there can only be a single object. If an object reaches photocell P3, the next one if this intersection of two photocells if is occuped conveyor2 would stop until it leaves the P3. I upload the model to make it clearer