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
