[tjohn]

hi Sir , 
  trying to descripe my question in different way. I've successfully syncronized robot with linear rail(7th axis) and positioner(8th axis) , how do I add one more positioner(9th axis) to be syncronized with 8th axis? 

electrically couple. I've tried to bring 9th axis directly under 8th axis in tree structure, but seem not work in that way 

May I have your advise?

[Albert]

You can synchronize a robot arm with up to 2 additional mechanisms. Each of these mechanisms can have a combined number of 6 axes (12 in total).

Can you share your RoboDK project? We may be able to help you better.