Hi Jon, I'm in way over my head here but I see a couple of issues. One being which method will track actual velocity best and the other is performance of the tach around zero crossing. It is an interesting problem. ;-)
Dave On Jul 11, 2008, at 9:48 PM, Jon Elson wrote: > I mentioned to some people at the CNC Workshop that I was > working on a resolver to quadrature converter board, and we > hooked one up to a servo motor to compare a real encoder against > the AB signals derived from the resolver. That all worked quite > well. > > Well, a customer also wanted a velocity signal from it to > simulate a DC tachometer. I said "Oh, simple, it has a digital > velocity output, I'll just hook that to a DAC and it is done!" > Ahh, not so fast. The AD2S1200 chip is designed to run up to > 1000 RPS = 60,000 RPM, so if full scale of 2047 (12-bit signed > binary value) is 60,000 RPM, then one bit = 29 RPM. Oh oh, that > is never going to work to close the loop of a positioning servo > like on a machine tool axis! I've confirmed by twirling the > resolver shaft that this appears to be the true scale factor for > the chip. > > So, I am going to have to develop the velocity value from the > quadrature signals. Since the chip interpolates the resolver to > 4096 counts/rev, I should be able to produce much better > resolution at reasonable speeds. For instance, at 60 RPM, you > get 4096 counts/second. At 100 counts/second, it would be > turning only ~1.5 RPM, so some really simple filtering should > work. I'm trying to decide if I should do this digitally or > have encoder counts produce fixed-width pulses on a pair of > charge pumps, one on each input to a differential amp. > Digital would get rid of all the adjustment pots, of course. > > Any thoughts? > > Jon > > ---------------------------------------------------------------------- > --- > Sponsored by: SourceForge.net Community Choice Awards: VOTE NOW! > Studies have shown that voting for your favorite open source project, > along with a healthy diet, reduces your potential for chronic lameness > and boredom. Vote Now at http://www.sourceforge.net/community/cca08 > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users ------------------------------------------------------------------------- Sponsored by: SourceForge.net Community Choice Awards: VOTE NOW! Studies have shown that voting for your favorite open source project, along with a healthy diet, reduces your potential for chronic lameness and boredom. Vote Now at http://www.sourceforge.net/community/cca08 _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
