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
