yes exactly true .... for example : when move axis rapid ,230 mm then dro show true but encoder show 237,234,236 in fact random ...

Ok, in this case I would say yes. You said you get nice results at half rapid speed then reducing the encoder resolution ( PPR) should work.
But as TP said your system will have lot of work to read the inputs.
For that I would choose the lowest encoder resolution where you can live with lets say 400 PPR or lower.

Alex

thanks dear friend ,you kind of to me ,so your comment is my result ... after see your last reply, i searching at pdf of servo drive manual about    
decrease encoder pulse, and i find a parameter can change ratio pulse output i guess may can help me but i don't try yet... 

Elaborating on what TP said, I will give you a few more clues.  Rogers encoder board uses a plug-in.  Brains or VB/macropump just arent fast enough to monitor closed loop with much success.  The plug-in compares steps sent by Mach to counts sent back from encoders.  It doesnt use DROs at all, but rather the raw data behind the scenes in Mach.  The encoder board is the only way Mach can read and compare it all fast enough.

However, if you are having any sort of luck at all, I encourage you to keep pushing and see what you can get it to do! :-)

Bodini ,thanks for your support...

However, if you are having any sort of luck at all, I encourage you to keep pushing and see what you can get it to do! :-)

I assume you want it for a kind of safty, if something fails to e stop the system.
a kind of closed loop isn't possible with a brain ( or macro ) not even close to.

the brain runs fix at 10HZ  so 100ms for one run.

that means you have a lag of 1mm at 600mm feedrate or 10mm at 6000mm feedrate and so on.

plus the lag time of the incoming pulses what is small compared to the brain.

Alex

Alex ,you right... i tried with 0.1 mm lag error at 2000 mm feed rate the 9 mm !! so that is too big and i looking for less like( 0.2 or 0.3 mm) maximum  in this case i take my answer with your advise ,in fact can t do this just because brain & macro too slow...
anyway i want say thank you and other