Hi,
OK, so using manufacturers recommendation is good practice, but that does mean large and expensive ballscrews which will in turn require large and expensive servos,
but that's the nature of CNC.
Yes I used Auto-tune and its pretty straight forward. I did tweak the parameters manually, but its dubious that I made any improvements over Auto-tune, having said that
I did not use the scope, so it probably it not surprising that I could not secure any noticeable improvement.
The inertia ratio in my machine is about 5:1, and is very much within the 'sweet spot' for Auto-tune. At inertia ratios of 10:1 manual retuning after Auto-tune
would be common. At 20:1 I think you can forget Auto-tune, manual tuning is probably your only choice.
Also, do u think an oscilloscope will be helpful for manually tuning the servos?
I didn't bother, my machine PC is to gutless to do a good job with the software scope. If I were to revisit it I would use a more powerful development PC to run the tuning and set-up software
that would allow me to use the software oscilloscope.
i still wanna use 11nm 130mm flange servo, its worst performance is still better than open loop stepper i guess. Can i tune it by seeing the signals on oscilloscope? i never used an oscilloscope before but is it useful for this purpose?
I am a relative newcomer to AC servos but my experience is they far FAR
FAR outperform steppers. They, in practice, seem to be rather more powerful than the specs suggest. I believe
that it because of the overload properties of servos. When a stepper overloads it stalls, no ifs or buts, it just stalls. A servo on the other hand just 'digs' in and does the job.
I you give me some numbers I will do the inertia calculation for you. I can tell you at a glance that the inertia is
DOMINATED by the huge ballscrews, the 250kg axis is nothing, likely less than
5% of overall inertia.
What I need is the diameter, length and pitch of the ballscrew, any gear/belt reduction if used, and the weight of the axis and associated linearly moving components. The inertia of the servo
would be helpful, but we can make a pretty good ballpark guess on that.
Once we have the inertia equation then equation then the questions about use of the scope can be answered. If the inertia ratio is moderate then you don't really need to manual
tune....although it is instructive to do so, particularly with a scope to observe the results rather than inferring from movement data.
Craig