System Identification for control

Well theoretically they are interchangeable via a Fourier transform

I suspect the main issue will be that the response to either
Step or Bode plot will be dominated by nonlinearities

How do you measure the response of your router?

I don't know router sorry,,, but I got data using ethercat. and so I can watch the data with halscope.

thank you for your reply
I got some data about step command already
but I think the data can't be used for bodeplot
because bode plot require dynamic command and response like sine wave(in various frequency)
If I get the bode plot then I can know resonance(?) frequency or response which reached at -3dB

I have dual servo gantry system
Can I use stepgen in my linuxcnc ?? Or can I give velocity command with siggen???

First, I'll try with sim.axis example

 

As for me you will never get resonance freaquency in gantry system.
With increasing of the freaquency change, you will get decay of responce of your motor, it will overheet and may be, will give some smell. It all depends on your persistence.
Resonanse freaquency could be only in systems that has big PID regulator gains. You can increase this values - and resive resonance. I had such things. But if your gains in safe zone, you will never had problems with your gantry system because it's very inertial and has counterforces, if we spoke about cnc.

About stepgen I think it's witten in manual.
linuxcnc.org/docs/html/man/man9/stepgen.9.html
You need siggen set to the input of te stepgen, possibly.

Just in case you are still working on this, you might be interested to look at external offsets. There is a simulation configuration called 'Dynamic External Offsets' under /configs/sim/axis/external_offsets that uses a sinus generation on the z axis.
Maybe this could be adapted to your needs.

Hello,

i don't think that trying this within linuxcnc will lead to an usable result...

Event with using an 2khz Servo thread, the resolution for getting an good result would be to low.

but you told that you are using ethercat, this drives are all from the "newer days"... all drives i know have internal functions to draw and record an bode plott.
Everytime we have done this, the controller runs on an 65us cycle time....