Our robot ABB IRB 6400 pick up parts then swings out and places parts on four conveyor lanes. (pick from +Y to -Y direction) We recently noticed that the part placement is slightly shifted toward the -Y direction. Worse for the far conveyor that the robot travels the furthest. We never had this problem over the last three years I have been with the company so I assume the shifting happened over many years. And nobody modified the program ever since it was commissioned almost seven years ago. All moves have FINE termination option and v7000 for speed. I don't think it's the program problem since this problem happened over many years.
What could possibly cause this? Brake parts on the base joint motor wearing out?