Peter C. Wallace wrote: > > > As you mentioned before, raising the sample rate alleviates some of these > problems. Especially for torque or voltage mode amps. 100 Hz might be OK for > a > velocity mode amplifier where most or all of the D term is handled in the > motor drive, but would create to much phase shift in the D term (where you > can > least afford it) with voltage or current mode amplifiers. > > I rank motor drive systems like this. simplest to most complex: > > 1. Voltage mode, bare HBridges. Our Hbridges are like this. > Voltage mode requires high sample rates, probably greater then 1 KHz > Voltage more also _requires_ FF1 to compensate for BEMF. The lower output > impedance of votage mode amplifiers means less D term is needed than > current mode amplifiers. The PID output controls acceleration, but > acceleration is not a linear function of PID output. > > Yes, that is what I'm doing. And, yes, FF1 helps a lot. And, yes, very little D is needed, too much makes it unstable. > 2. Current (torque) mode. Our 8I20 is like this. Like Voltage mode, a high > sample rate is needed. The PID output controls acceleration. > > 3. Velocity mode. These amplifiers have a built in velocity loop, so normally > very little D term is required. Properly tuned, a quite slow sample rate > will work. PID output controls Velocity. > Assuming steady-state ONLY, that is true. But, CNC programs are not steady-state, they change velocity all the time. So, you can't sample too slowly or there will be big excursions of following error on the discontinuities.
Jon ------------------------------------------------------------------------------ This SF.net email is sponsored by: High Quality Requirements in a Collaborative Environment. Download a free trial of Rational Requirements Composer Now! http://p.sf.net/sfu/www-ibm-com _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
