Thanks Robodoc,
We got the same answer from Yaskawa.
My customer already ordered 2 new Robots.
The system works 24/6, it is not practical/economical to dismantle and send the Robots to Germany or Sweden for a complete rebuilt. We guessed that the price for a full mechanical overhaul will be about half the price of a new system. (Plus production lost...)
Milling machines have a Backlash compensation, and I understand that because they have a mechanical load on the Tool, it is working.
Welding robots only have their own complex 3D Inertia load, but I wonder if no other robot manufacturer have some kind of Backlash compensation ?