Chris Radek wrote: > On Fri, Oct 30, 2009 at 10:11:49PM -0500, Jon Elson wrote: > >> One thing that has been common in the Fanuc systems is they use servo >> amps that need velocity >> feedback from the motors, but they don't have tachs on them. The >> controller synthesizes an analog >> velocity signal from the encoder and sends that to the amps. >> > > That sounds odd and makes me wonder (again) about something on my > machine. > > I have tachs, but they were not wired to the amps. They went to "some > part" of the main computer of the Yasnac control [which was missing]. > Then "something else" came from the control board and went to the > velocity feedback input on the amps. > Yup, that was the way the old Fanuc controls worked. They used either the L290 or a similar quadrature to voltage converter chip. The L290 was a frequency to voltage converter specifically designed for this purpose. It used 2 identical sections feeding into a difference amp so encoder dither doesn't count as velocity. Unfortunately, it is no longer available. > I do not know what was there - it's possible they were just wired > together. I wired them straight through. > > Any guesses whether something was there? I had some trouble getting > stable velocity loops, and it makes me wonder. > The problem is the real Fanuc machines had no tachs, so it makes the retrofit harder. If you DO have tachs, then no problem.
One possible setup had a circuit that compared absolute velocity from the encoder to absolute velocity from the tachs. If the encoder velocity was 20% greater than the tach showed, it caused an E-stop. This was used in the days of encoders with incandescent light bulbs, where an encoder failure was a yearly ocurrence. The Allen-Bradley 7320 had this. Jon ------------------------------------------------------------------------------ Come build with us! The BlackBerry(R) Developer Conference in SF, CA is the only developer event you need to attend this year. Jumpstart your developing skills, take BlackBerry mobile applications to market and stay ahead of the curve. Join us from November 9 - 12, 2009. Register now! http://p.sf.net/sfu/devconference _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
