On Sun, 2011-06-05 at 20:53 -0500, Jon Elson wrote: > dave wrote: > > On Sun, 2011-06-05 at 10:39 -0500, Chris Radek wrote: > > > >> On Sun, Jun 05, 2011 at 07:58:52AM -0700, dave wrote: > >> > >>> Plan 1. go to velocity mode and add a tach. The tach is low output. > >>> only about 2.5 V/1000 rpm. For some reason I can't get the system > >>> stable. When enabled it oscillates for a few seconds and faults. > >>> That is with the analog input at zero (shorted). > >>> I've moved the tach gain all over the place with no luck so far. > >>> > >> Are you sure it's not hooked up backwards? > >> > > > > Yep! No control at all .... just takes off in one direction if I reverse > > the connections. > > > OK, that's a sign that the tach is doing the most basic function > properly. I built my own > velocity servo amps over a decade ago, and STILL end up tweaking the > performance every > once in a while, trying to eliminate the jitters that happen every now > and then. So, I sure > don't have a magic recipe for tuning a velocity servo.
Well, I do better with velocity amps than I do with torque mode. A good final tuning tool would be nice. I often think about an approach where one tunes manually to get close, which, depending on your definition is good or not so good, < 0.001 following error. Since I'm convinced but cannot prove that tuning parameters interact try fine tuning as follows: Apply a sine wave or sawtooth to the amp and randomly vary P, I, D, FF1, and FF2 within a small zone and select for the best following error. Unfortunately, I can think about it but don't have the skills to implement such an approach. > > But, if it oscillates with no input, that clearly means either there is > too much gain on the tach > input or it needs more compensation. Try turning down the tach gain or > velocity gain (they > label these differently on different makes). Oh, you said you did that, > already! Possibly, you > need a resistor attenuator to drop the tach feedback some more. Perhaps > try a 2:1 > divider, with 1 K Ohm resistors in series with the tach output and then > one across the > tach inputs of the servo amp. > > Well, what frequency of oscillation was it? Really fast buzzing or slow > rocking back and forth? > That might give some hints whether it is compensation or not. 1 sec period and about 180 degrees of shaft rotation; just an estimate not a quantitative measurement. > > Is there a velocity compensation pot, or do you have to solder caps onto > a header? (some amps > make you do this). > > And, finally, are you sure the tach is giving a clean output? It could > have brush noise causing > intermittent signals. Also, you need to be sure there is no slack > between the tach and the motor. > If there is a sloppy coupling or belt, it could allow the motor to rock > some amount before the > tach starts to move, that would guarantee oscillation. > > Jon Lots of good ideas above, for now I'm taking the easy way out. Swap out for a SEM MT30H44 since I have several just waiting for an application. Later I can setup the Keling on a test bench and hack away at it. A scope on the tach might reveal interesting things. I need to get the mill going quickly since I have several projects going including cnc on my Jet lathe. Looking back I really should have worked harder at getting a dead cnc lathe and gone from there but hindsight is good stuff. Of course living in neverneverland is a problem. Only HI or AK would be worse for shipping costs. Dave > ------------------------------------------------------------------------------ > Simplify data backup and recovery for your virtual environment with vRanger. > Installation's a snap, and flexible recovery options mean your data is safe, > secure and there when you need it. Discover what all the cheering's about. > Get your free trial download today. > http://p.sf.net/sfu/quest-dev2dev2 > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users ------------------------------------------------------------------------------ Simplify data backup and recovery for your virtual environment with vRanger. Installation's a snap, and flexible recovery options mean your data is safe, secure and there when you need it. Discover what all the cheering's about. Get your free trial download today. http://p.sf.net/sfu/quest-dev2dev2 _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
