The arms themselves could have sensors on them. Inductive loops sensing the presence of the stainless steel structure?
Also, I doubt centimeter scale precision would be needed; the arms have some compliance in them, I'm sure, as well as the ability to control how far in they swing.
Also, I doubt centimeter scale precision would be needed; the arms have some compliance in them, I'm sure, as well as the ability to control how far in they swing.