Igor Chudov wrote: > Guys, honest, I did look for explanations and did not find enough. > > Could someone explain what are FF0, FF1 and FF2 parameters pertaining > to tuning a servo loop? > > FF0 is a value added to the output proportional to position. It is not really useful, but there for pedantic reasons.
FF1 is a value added to the output proportional to commanded velocity (ie. derivative of position, hence why FF0 exists.) So, if you have a velocity of 1 user unit per second, and an FF1 value of 1.0, the output command to the DAC will get an additional 1.0 added to what comes from the PID. This is a feedforward, so it takes no notice of actual velocity or error, but is immediate as it doesn't have to wait for the machine's response. FF2 is a value added to the output proportional to commanded acceleration. So, leave FF0 at 0.0 Once you have the PID set as good as you can get it, FF1 can be adjusted to reduce the error when in the cruise (constant velocity) part of a move. You can usually set it so the error is within 1-2 encoder counts of zero over a wide range of velocities. Then, adjust FF2, using very small values, generally, to reduce the error spikes during acceleration and deceleration. It is very easy to overcorrect with this, so you can reduce the setting to zero every once in a while to make sure which direction the real error is in. Typically, numbers look like 0.001 to 0.08 Jon ------------------------------------------------------------------------------ Start uncovering the many advantages of virtual appliances and start using them to simplify application deployment and accelerate your shift to cloud computing. http://p.sf.net/sfu/novell-sfdev2dev _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
