On Sat, Oct 9, 2010 at 8:20 PM, Jon Elson <[email protected]> wrote:
> Stuart Stevenson wrote: > > > > in screenshots 1 2 and 3 notice the squared trace on the beginning of the > > accel and decel > > I get this on all axes including the spindle and am unable to tune it > away > > I have tried many different combinations of tuning values > > the best trace is the spindle with a max accel of 2 - this allowed a much > > higher Pgain and stiffened the spindle considerably > > the spindle has very little inertia as it drives only the gearbox and > > spindle > > I see the squared traces on the spindle > > the ending traces work smooth until I start getting the tuning a lot > tighter > > then the traces tend to even out on all axes > > do you believe this is a result of the marriage between the fanuc > hardware, > > ppmc and emc2? > > motion of the axes feels, looks and cuts smooth and accurate - the > following > > error spikes are the focus > > > Well, not sure exactly what you are seeing. The first traces have > ferror going up to .025", > which is huge. Maybe these are feedsrates too high for cutting, but it > seems like the servo > loop needs to be much stiffer. Possibly this is a mismatch between what > voltage is needed > to command the drive for some velocity, and the output EMC is giving for > that velocity. > That would be a change of P. > > But, those steps you are referring to, which are most obvious in the > expanded ferror > trace on screenshot 4 are something else. I MIGHT guess the drive is > having a delay > before responding to the change in velocity command. I haven't seen > anything quite > like that before. How are you getting the encoder info to EMC? Are you > using the > auxiliary encoder output from the servo drive? I wonder if this output > has some > extra delay - like the drive only updates position a couple hundred > times a second. > > Ohhhh! Are these Fanuc drives with the serial pulse coder? The ones > that have a > backup battery in the drive for the encoder? Those require the drive to > command the > encoder to send a new position report. I have no idea what the update > rate of these > is. Also, I think the whole idea of this scheme was that the CNC > control would send some > signal to the drive and ALL axes would sample the position > simultaneously. Maybe of you > don't provide this encoder "sync" signal, then the drives only > interrogate position at a lower > rate. I'm just guessing at this, I haven't been able to dig up more > than the most incredibly vague > info in the serial pulse coder protocol. > > For the XY and Z axes we pigtailed the connector so EMC2 gets the same signal the drive gets. At the same time and rate. For the spindle we used the encoder pulse out of the spindle drive as the spindle motor feedback is two sine waves. Friction sounds logical for the start of the accel but not for the start of the decel. I get the same distortion in both places. If you notice the trace is squared at the beginning of the accel and the beginning of the decel. I would like to feed an EMC2 generated proportional pulse (psuedo encoder) to the velocity feedback of the drive to see if that would not eliminate the drives tuning and let EMC2 handle closing the loop. > Jon > > > ------------------------------------------------------------------------------ > Beautiful is writing same markup. Internet Explorer 9 supports > standards for HTML5, CSS3, SVG 1.1, ECMAScript5, and DOM L2 & L3. > Spend less time writing and rewriting code and more time creating great > experiences on the web. Be a part of the beta today. > http://p.sf.net/sfu/beautyoftheweb > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users > thanks Stuart -- dos centavos ------------------------------------------------------------------------------ Beautiful is writing same markup. Internet Explorer 9 supports standards for HTML5, CSS3, SVG 1.1, ECMAScript5, and DOM L2 & L3. Spend less time writing and rewriting code and more time creating great experiences on the web. Be a part of the beta today. http://p.sf.net/sfu/beautyoftheweb _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
