Chris, would you care to hazard a guess at how much phase shift you see from the 7i48 input to the velocity input at the servo amp?
Neil On Tue, Aug 10, 2010 at 7:19 PM, Chris Radek <[email protected]> wrote: > Hi all, > > I have a VMC with low inertia servos and 25 amp 270 volt velocity mode > servo amps. It has tachometers and 1/25400 inch (micron) resolution > rotary encoders on the motors. > > I have been struggling with a bad tachometer on Y for a while now - it > would come and go - and when people started talking again about > generating tach signals for retrofitting Fanuc setups that don't have > real tachometers, I got interested. > > I was out of DAC outputs, so I got a second servo interface board > (7i48, which is a Mesa product that has six DACs and six differential > encoder inputs, and is newly supported in EMC2/git-master). > > The hostmot2 Mesa driver has a high quality encoder velocity output > that it generates based on high resolution timestamps on encoder > edges. > > In HAL, I hooked this velocity output directly to a new DAC and set > the DAC scaling so that rapid speed will give an output around 9 > volts. I wired the DAC output directly to the servo amp in place of > the tachometer. > > This voltage is a lot lower than the real tachometer generates, but > the servo amp has a gain control and it was very easy to set the amp > accordingly. > > I'm happy to report that the motion on Y is smoother than I have ever > heard it. This machine rapids (I have it set conservatively) at 7.5 > inch/sec and 30 inch/sec2 acceleration. > > Adjusting the tunings (amp and EMC) just a bit, I was quickly able to > get following errors within about 10 encoder counts (0.0005 inches) > during accelerations to rapid speed, and virtually nil (a count or > two) during cruises/cuts. > > I think this is awesome and send thanks to Peter W for his cool > products and hostmot2 work and Seb K for his hostmot2 driver work. I > have every reason to believe that machines with these generated > velocity signals and "missing" tachs are not a problem for EMC2 + > Mesa. > > Chris > > > ------------------------------------------------------------------------------ > This SF.net email is sponsored by > > Make an app they can't live without > Enter the BlackBerry Developer Challenge > http://p.sf.net/sfu/RIM-dev2dev > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users > -- http://www.pixpopuli.com ------------------------------------------------------------------------------ This SF.net email is sponsored by Make an app they can't live without Enter the BlackBerry Developer Challenge http://p.sf.net/sfu/RIM-dev2dev _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
