As we have learned a few things about packing electronics for travel, we were not very concerned about clearing customs until we saw the customs declaration form and realized this was our first time travelling to Japan on business and we had no idea how to declare our robot.
While we are not international trade lawyers, here is how we understand it;
Commercial samples need an invoice for the sample if you are leaving the sample with a customer.
Commercial equipment used for demonstrations and exhibitions that will be re-exported within 1 year will need an ATA Carnet (カルネ). More information on ATA Carnet usage in Japan is available here.
Hopefully this helps another international robotics entrepreneur make it through customs.