What is the easiest way to solve such a problem. The robot collects from the conveyor belt elements and then puts them into the container. I used the ready palletizing function. The problem that I would like to solve is that after laying the layer robot should provide a spacer. The problem is that sometimes the spacer drops and the program gets stop. While writing the program I used the function of remembering the last item position. However, when you restart the program (After he dropped the spacer and stopped) the robot takes the last product from the conveyor belt and puts it as the last layer product , and only then takes a separator. After switching it on again, the robot should lay only the seperator, not how so far, i.e. the last product per layer (which is already placed) and later a spacer.

I'm working on the latest update. Universal Robots UR5e.

Thanks for your answer

For now, we're testing the program. After laying the last element of the  layer, the robot should go for the spacer, and then start to lay the next layer. There was a situation when the robot dropped the spacer and then we discovered this problem, which we are trying to solve now. It's not about regulation we are trying to avoid this kind of situation in the future. At this moment, after placing the last element of layer, the robot puts the spacer down, but if we "take it" from him, a window is displayed saying that the spacer has been dropped. Then, after restarting the program, the robot does not pick the spacer as the first. The robot puts the last element on the layer, which is already laid, which causes a collision.

I thought there was a "built-in function" somewhere that avoids this situation and checks for such a case. I have to check when they change values ​​of variables responsible for palletizing and storing the spacer and based on this knowledge to develop a robot operation logic.