On Friday 13 July 2012 06:20:53 Viesturs Lācis did opine: > 2012/7/13 Hugh Wylie <[email protected]>: > > Having deleted MIN_VELOCITY parms and correcting the A-joint type to > > LINEAR, the time lag (having resulted from very different velocity > > vector commands to the 5i23) is eliminated. > > Glad to hear that. > > Could You, please, explain a little more about the relation between > racking and motor PSU? > > I am offered to retrofit a double-spindle wood milling machine to > LinuxCNC. The main problem currently is that one joint loses its > position over time, so parts get ruined. The solution they are using > is rehoming machine every 20-30 minutes. > > There are 4 stepper joints and only one of them is losing position. > Client says that there is no regularity for the amount of lost > position - sometimes they notice it on the parts very quickly, other > times parts are good for longer time (note that some low number of > lost steps is not that noticeable, so the quality is acceptable). > > I was trying to come up with all the possible causes for the situation: > 1) currently corresponding joints on both sides are hardwired together > - each step and dir line is connected to 2 drives in parallel, so each > drive gets only half of signal strength;
Those sorts of problems are generally viewable on a scope, but in any event should go away with a breakout board similar to a cnc4pc model C1G, which is not only opto isolated, but can drive or sink 24 mills per output, more than enough to drive 2 or 3 drivers of the 2M542 class. > I was thinking that this > might make those lines more sensitive to any noises; > 2) the power lines to motor that is losing position runs close to > power lines of spindle motor; > I was thinking that some noise could be induced in power line, but > power for another motor goes there as well, but that motor is not > losing position; > > What else could that be? A ground loop could be a possibility too. The star ground topology is a good one for us, and each drivers input ground reference should be on its own conductor, not shared with the driver's power ground, all the way back to the common point of the star. Same idea for the shielding on the motor and any encoder cables, all shielding should be connected only to this central common ground point bolt, a long one obviously. The far end of the shielding should stop near the motor without touching any may or may not be grounded portion of the machinery frame. The machine frame itself should be separately tied to this common bolt. And at some point, the static ground from the powerline should find its way to this bolt. For those of us in the US, and generally subject to the NEC, that is the longer round pin of a 120 volt plug, or the long blade in a 3 or 4 pin 240 volt plug. 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) My web page: <http://coyoteden.dyndns-free.com:85/gene> is up! "And remember: Evil will always prevail, because Good is dumb." -- Spaceballs ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
