How can i exract transfer fuction of my nonlinear real system?

I am trying to do PID control for my electroservo motor system by using nichols ziegler tuning method. My system has SSI encoder output for motor feedback mechanism. I will use this knowledge for control. According to nichols ziegler method i must know transfer function of my system. But i can not find its equation exactly. So how can i extract its transfer function? I need a methodology for this. Can i extract T.F. by using Matlab/Simulink?

Answer 1

[Arkadiy Turevskiy]

Can you "break" the control system and put some test signals through your motor - steps, chirps, sine waves, etc?

If you can measure such input-output data you can follow the approach shown in this video .