Neil Whelchel wrote: > > As far as your suggestion about losing track of position by switching > from/to the index pulse above/under certain speeds, you will have to build > a better case.. ;) Let's say that we can count individual pulses under > 3000 RPM, and our target speed is 10000 RPM. Then in this case, we could > use say 2000 RPM as a handoff, this way we still have 1000 RPM overhead, > and we know that in the time of one revolution it would be impossible to > go from 2000 RPM to over 3000. So far, as long as all of the hardware and > electrical stuff works fine, we would never lose count. Yes, but what if it is making the decision RIGHT as the index pulse appears? Is it possible that the logic would get confused as to whether to add one full turn or not? This will eventually happen, and it has to do it right, EVERY time. This is one of those clock domain issues, where there is a tiny interval where the logic could be confused, and you have to put in extra logic to prevent that from happening. So as the shaft > accelerates through the 2000 mark, we know exactly when the index will > come around, and what our count will be at that point, if all is as > expected, we simply ignore the quadrature, and look within a small > time window (just wide enough to account for possible > acceleration/deceleration) in for the next index pulse. Well, on my Bridgeport, the index is every .200", so when in the "high speed" mode, you effectively have an encoder with 5 counts/inch! And so, your mechanical position is known only to within 0.2 inches! I can't imagine machining anything like that.
This all seems unrelated to servo systems on machine tools, anyway. Turbine engines are something else. Jon ------------------------------------------------------------------------- Check out the new SourceForge.net Marketplace. It's the best place to buy or sell services for just about anything Open Source. http://ad.doubleclick.net/clk;164216239;13503038;w?http://sf.net/marketplace _______________________________________________ Emc-developers mailing list Emc-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-developers
