Jon, I will try to switch my Y axis to torque mode to see if it helps with spurious oscillations.
The "bad brushes" may be a good explanation. But I feel like I should try torque mode for many reasons. - Igor On Tue, Sep 14, 2010 at 8:05 PM, Jon Elson <[email protected]> wrote: > Igor Chudov wrote: >> 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. >> > Yes, it is possible. It is also possible the brushes in your tach are > dirty or just plain > worn out. You could hook the tach to an oscilloscope and turn the motor > by hand > or with a battery. If you see a lot of spikes or discontinuities, that > is real bad for > a servo loop. I did some testing about a decade ago trying to figure > out how slow > an axis could move, and I got it down to where the tach would have been > producing > about 7 microvolts. This was however enough to keep the servo loop > closed, as if I > shorted the tach with a screwdriver, the servo amp would immediately > fault out. > If brush noise is the problem, you may be able to put a 0.1 uF capacitor > across the > tach inputs at the servo amp to suppress this, but it is likely to > slowly get worse. > Or, possibly, continued use will actually improve the problem, as the > tach's commutator > may have tarnished while the machine sat, before you bought it, now it > is getting cleaned. > I give the caution about not scoping the tach signal while the machine > is running, as > it may cause ground loop problems, depending how the tach connection to > the servo > amp is set up. > > I used 3 instrumentation amps in my own servo amp design, one for > command input, > one for tach input and one for current sensing. These eliminated all > ground loops > in the servo system. Many servo amps leave these out due to cost, and > therefor > suffer some ground loops between one servo amp, through the common grounds > and back to another servo amp. > > 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
