I’m new to UR Robots i have a situation where i have two robots one is a part loading robot into packaging and the other robot is the box handling palleting robot. Currently the part handing robot counts the parts into the box then sends an output to start the box handling robot to collect the box. I currently stop the part handling robot from cycling via sending an output from the box handling robot. occasionally if timing is not right in the program the par handle robot doesn’t recieve the signal in time and possible for them to collide.
What are you asking? 
For better ways to do it?
I don’t think there’s a better way to do it. Maybe use a combination of more signals, so it’s not possible to get “out of sync” per se. If one robot is working inside the collision area, then it will set an output high.
And when it’s out, it will disable the output and enable another one.
You can also directly tie them together with an ethernet cable and use MODBUS to send data back and forth. This can include each robot’s joint positions or TCP location.
You shouldn’t ever have a timing issue though. You should let threads monitor the states of the variables so they are always ready to respond.