Chris Radek wrote: > On Fri, Jul 06, 2007 at 02:52:38PM -0500, Jon Elson wrote: > >>I was seeing it stopping in discrete quanta of .020", ie. 0.000, >>0.020, 0.040" etc. > > > How many counts is this for you? It must mean something. Yeah, it must, but I can't correlate it with anything sane. I believe this works out to 400 quadrature counts. The shielding problem mentioned below would lead to cross-coupling of the A and B signals into the Z, so it should maybe repeat every 4 quadrature counts. Maybe there are channel-channel timing variations that repeat 10 times on my encoder (1000 cycle/rev, 4000 count/rev) such that at those spots the A and B rise exactly in sync and the combined crosstalk makes the encoder logic see a rising edge.
Anyway, I noticed I had the shield of my encoder cable hanging, so I grounded it, and the problem has gone away. One of the side effects of the latest changes in the PPMC encoder FPGA config is that there is no filtering on the index pulse anymore. That may be a mistake, and I can see about putting additional filtering before the flip-flop that recognizes the index pulse. But, that signal should be pretty clean, anyway, especially if you have differential encoders. So, I believe that there must be a problem with Stuart's encoder signals. After grounding the shield, I was able to home 50 times, from a variety of positions, without a single observable variation in the home position. (My encoder here is single-ended.) So, the current CVS trunk and the FPGA configuration I brought to the Workshop, and what Stuart Stevenson has on his boards, should work with a clean index signal from the encoder. If it doesn't, then the encoder index signal at the PPMC encoder board has noise issues. If this needs further attention, it is definitely a hardware issue, and nothing that affects the ppmc driver. Jon ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
