Finding 15µ is a challenge. Every control manufacturer rejects tuning on the telephone. 15µ tuning in a forum is suicide. Well I have nothing to lose and I hope you will forgive me. First, how far can we trust this scope. I think we also have a latency period that leads to measurement errors. Second, how is your measurement system connected? I think servo -> amplifier and scale -> encoder card right?
With this arrangement it is very difficult to do better. There is no time for linuxcnc to control it better.
And we are not sure is the error real? The test could be milling a circle and checking it on the measuring machine. If you see peaks at the quatrant end, it is often a backlash or acceleration problem. And you can try to change the following parameters: acceleration, backlash, PID. But it takes time.
Perhaps you also have the option of connecting the scale directly to the amplifier. This is how we avoid the problem of latency. The internal control loop is faster than via linuxcnc.
Lastly, check again how it works without scale. And compare endor data with stepgen position. This is a good way of identifying mechanical problems.
Good luck Chris
