Peter Nachtwey
Member
The goal this week is to tune a very difficult system using both feedwords and a PID.
System requiring PID AND Feed Forward tuning
This system is too difficult to tune by just cranking up the gains. The feed forwards must be used too. Even with the feed forward the system still has some pretty big error. If you look through the spread sheet you will see the error often get to .125 inches which is too high for many purposes.
The system is like a motor system with a flexible coupling. The motor adds the time constant and the integrating the velocity to position. The flexible coupling adds the complex poles. If you remember, complex poles ring or oscillate. A springy coupler is detrimental to performance yet I see too many applications that use them just because it makes like easier for the mechanical 'engineers'.
A hydraulic system can be modeled like this with caution. The real pole is from the valve response and the complex pair of poles comes from the cylinder. A hydraulic cylinder is really a mass on a spring. The problem with hydraulics is that nothing is linear. A well designed hydraulic system will not be too non-linear.
If you can tune this system then you can tune just about any reasonable system. This is the last of the tuning exercises.
Hopefully you have modified or experimented with the spread sheets or look at the formulas that are used in them.
BTW, the ISE to beat is 268.79. If you have difficulty in tuning this system then reduce the frequency of the target at cell E5.
System requiring PID AND Feed Forward tuning
This system is too difficult to tune by just cranking up the gains. The feed forwards must be used too. Even with the feed forward the system still has some pretty big error. If you look through the spread sheet you will see the error often get to .125 inches which is too high for many purposes.
The system is like a motor system with a flexible coupling. The motor adds the time constant and the integrating the velocity to position. The flexible coupling adds the complex poles. If you remember, complex poles ring or oscillate. A springy coupler is detrimental to performance yet I see too many applications that use them just because it makes like easier for the mechanical 'engineers'.
A hydraulic system can be modeled like this with caution. The real pole is from the valve response and the complex pair of poles comes from the cylinder. A hydraulic cylinder is really a mass on a spring. The problem with hydraulics is that nothing is linear. A well designed hydraulic system will not be too non-linear.
If you can tune this system then you can tune just about any reasonable system. This is the last of the tuning exercises.
Hopefully you have modified or experimented with the spread sheets or look at the formulas that are used in them.
BTW, the ISE to beat is 268.79. If you have difficulty in tuning this system then reduce the frequency of the target at cell E5.