Fascinating video. Youtube suggested as the next video https://www.youtube.com/watch?v=4DKrcpa8Z_E and that one has at 2:52 what seems to be a maintenance vehicle placed over the same rails as the robots, so that might explain how the maintenance crew can do its job (the one in the video is labeled "Recovery 04", so my guess is that the main purpose of this one is to allow maintenance workers to rescue stuck robots).