PID Control and Integral Windup on 6-Foot Tall Robot
PID Control and Integral Windup on 6-Foot Tall Robot
(OP)
It's almost spooky what a robot will do with just a few simple rules, as with a PID controller. I use PID to keep this 6-foot tall Falling-Up Robot balanced using stepper motors. But I'm having trouble with Integral Windup. If I lift the robot, or if it gets stuck somewhere, it goes biserk. I'm researching the Back-Calculation method to help "unwind" the error. Look for a good book on this. Any recommendations on this? Thanks.
https://www.youtube.com/watch?v=QHb9eYAyGJc
https://www.youtube.com/watch?v=QHb9eYAyGJc
RE: PID Control and Integral Windup on 6-Foot Tall Robot
Keith Cress
kcress - http://www.flaminsystems.com
RE: PID Control and Integral Windup on 6-Foot Tall Robot
First calculate the control term from the P and D terms. Call this Upd.
Now when calculating the integrator term, Ui, limit like this
Ui(n)=max(min(Ui(n-1)+Ki*error(n)*Δt,100-Upd,-100)-Upd)
Now the total control output,U(n) will never exceed 100%
U(n)=Ui(n)+Upd
Notice that if Upd is big then Ui(n) may be pushed back into negative values.
That is OK if your system is tuned right.
See page 6 of 27 where this is applied. I didn't plot the integrator term but you can see
on the next page that implementing the integrator limit in this way allows the control output to saturate but still not cause over shoot. This is an old Mathcad worksheet where I was trying to impress the importance of the derivative term.
I was not trying to show how to limit the integrator or I would have plotted that too.
http://deltamotion.com/peter/Mathcad/Mathcad%20-%2...
This is gold
Peter Nachtwey
Delta Computer Systems
http://www.deltamotion.com
http://forum.deltamotion.com/
RE: PID Control and Integral Windup on 6-Foot Tall Robot
RE: PID Control and Integral Windup on 6-Foot Tall Robot
google Adaptive Cruise Control System by January Mahlalela, I have explained and implemented the back calculation method.
Regards