Jon and Andy, thanks. I finally understood what it was. It does look useful for my application, as evidenced by my use of Halscope. I will try it soon.
Also, could it be that my "servos cannot calm down" issue is somehow caused by noise getting into the tachometer signal? I did install ferrite cores on the motor cables, and they are twisted at least going to the main terminal block of the mill. But perhaps I still missed something. - Igor On Tue, Sep 14, 2010 at 11:18 AM, Jon Elson <[email protected]> wrote: > 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 > ------------------------------------------------------------------------------ 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
