On Wednesday 30 September 2009, Sven Wesley wrote: >Guys, > >I'm pretty convinced I've found the problem. >I believe the encoder/cable for Z is the problem, simply picking up noise. >When Z is run by itself there's no or very little offset. I noticed that >when I executed the EMC Axis logo the servo caused sudden jumps. So I made > a new test program where Y and Z was moving 10 mm back and forth at the > same time. I could actually hear the servo jumping. I think it's a TTL > encoder and they are really sensitive for noise, and quality cables > doesn't really help. >I've mounted a new CUI differential encoder and I'll make a new cable. If >that works I'll replace them all. > Aha! Clues. C.E.T.'s like me love them.
Based on the if it walks & quacks like a duck theory, do you have any idea what the pullup resistors are for that TTL circuitry? If there is any resistive load on those lines that goes back to ground instead of to VCC, it will play all sorts of tricks on you because the internal pullup of a TTL circuit is very weak. Often under 100 microamps. This means that you may not be getting a good logic one, and in that state, its very sensitive to induced noise. To check, try tying about a 4.7k to 10k 1/8 to 1/2 watt resistor from those data lines up to the 5 volt buss. The TTL circuitry can easily pull that down even if its only a few hundred ohms, but it might make all the difference in the noise immunity. The voltage at a logic 1 s/b higher than 3 volts, and 4 won't hurt a thing. A full 5 gets iffy again because there are TTL chips about that don't like an input at or above the VCC rail. This you can measure with a digital multimeter while everything is hot by turning the lathe spindle very slowly by hand, and you should see less than +0.150 volts when its low, and more than +3 volts when its high. This will give a noise margin of at least half a volt when low (and being low means the driver is turned on tight and it will gobble up most noises there that are not ground loop induced, and at 3 volts, a 0.6 volt noise margin since the guaranteed logic 1 to a TTL input is normally 2.4 volts. Check all 3 lines/ of all axis's circuits just for grins. I HTH Sven. >I really hope this will the end of the story. > >--S -- Cheers, Gene "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) The NRA is offering FREE Associate memberships to anyone who wants them. <https://www.nrahq.org/nrabonus/accept-membership.asp> Smoking is one of the leading causes of statistics. -- Fletcher Knebel ------------------------------------------------------------------------------ Come build with us! The BlackBerry® 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/devconf _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
