Chris Radek wrote: > On Wed, Aug 19, 2009 at 10:11:19PM -0500, Jon Elson wrote: > > >> you could put in a one-shot chip to stretch the index pulse >> > > I said it once already but I don't think everyone caught it: on a > spindle encoder used for threading and tapping, it doesn't matter > the slightest bit if you miss the index sometimes. > > You certainly must not stretch it longer than one count, whatever > you do. You would make the cure worse than the problem. > > Well, if somebody has a 1000 cycle/rev encoder on the spindle, and is using a PC that can only handle a 16 KHz base thread, then he has a severe mismatch already. Most lower-cost encoders have an index that is a couple counts wide, and not usually gated on one of the quadrature tracks. Gated index is a feature of some of the higher-priced encoders. With a 1000 cycle/rev encoder giving 4000 quadrature counts/rev, a jitter of a couple counts is not going to make much difference, amounting to a few tenths of a degree at most. In this particularly horrible case, at 1000 RPM he is getting 4 million counts/minute = 66667 counts/second. With a base thread of 16 ms, he can only pick up one in 4 quadrature counts, so he is totally sunk. So, fixing the index pulse to reliably sense that, and completely forgetting the quadrature counting is the only thing that would work. He would then only use the index pulse, once per rev. Not a very good solution at all. Might as well run Mach in that case.
Jon ------------------------------------------------------------------------------ Let Crystal Reports handle the reporting - Free Crystal Reports 2008 30-Day trial. Simplify your report design, integration and deployment - and focus on what you do best, core application coding. Discover what's new with Crystal Reports now. http://p.sf.net/sfu/bobj-july _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
