Paul, in answer to your questions: I need a permanent, sturdy solution
All the wafer handling robots I worked on in the semiconductor industry used absolute encoders for most rotating
joints. It doesn't get more robust than that. Of course they are expensive. How solid the coupler is depends on
whether you choose the right one. Finding the right coupler could be a challenge but for accuracy it doesn't get
any better than absolute encoder. Some of the robots I worked with in the factory automation industry also used
/absolute encoders. As I am sure you are aware , the robots in the semiconductor industry work/ 24/7/365.