Pat Lyons wrote: > Hello- > > I'm having some difficulty tuning my P, I, and D variables. I've used PID > before in school, and understand how they are calculated, but I wanted to > ask about the three terms I don't really understand... > > I found in the wiki these explanations: > > *FF1 = 2.000 a velocity feedforward, helps reduce following error > proportional to velocity > * > * FF2 = 0.25 an acceleration feedforward, helps reduce foll. error when > accelerating* > > However I dont quite understand them- would someone be willing to maybe > define the math behind these concepts? > Commanded velocity is computed by differentiating position, multiplied by FF1 and then added to the PID routine's output.
Acceleration is then computed from commanded velocity, X FF2 and added to the PID output. > and also- is deadband the window over and under 0 volts that yields no > movement? does this mean that you can kill steady-state oscillations by > increasing deadband? > Yes, that is exactly it, measured in user units, not "volts". So, if actual position differs by up to 10 ^ -5 inch, and deadband is set to 10^-5 inch, then the P output will remain zero. Deadband doesn't COMPLETELY kill oscillation, but it does serve to reduce it and allow it to settle into the deadband. You usually set it to 1.5 X the dimension of an encoder count. Jon ------------------------------------------------------------------------------ Let Crystal Reports handle the reporting - Free Crystal Reports 2008 30-Day trial. Simplify your report design, integration and deployment - and focus on what you do best, core application coding. Discover what's new with Crystal Reports now. http://p.sf.net/sfu/bobj-july _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
