On May 25 2013 12:21 PM, Jon Elson wrote: > Dave wrote: >> >> If you have a big gantry, you don't want to have to rotate the >> motors or >> encoders to get the index pulses aligned. >> >> Consider a gantry that has 1+ kw motors on each side of the gantry >> with >> gearboxes and encoders integral to the motors. >> >> That would not work. >> > So, your solution is to allow the motors to move, independently, to > their > index positions, which could randomly be up to 1/2 shaft rotation > apart, > and then move to the correct home offset for each side? Well, I > think that > won't work, either. The two sides of the gantry must always be kept > aligned within a small difference from the rest position at turn-on. > I am sure there are ways to align the two sides of the machine so > the index marks are nearly equal. Slipping the pinion a few teeth > (May require removing the pinion from the shaft) should be able > to get it close. Many encoders have slots to slip the encoder angle > for these adjustments, or to slip the shaft coupling at the encoder. > But, my guess is that the machine is ALREADY well-aligned, and > that only needs to be verified once before powering up.
I have not been keeping up with all the details of this one, but if you move both motors simultaneously in either direction and simply count the index marks, once you see both marks you can then calculate how far it should be adjusted to match up. Later in the year I hope to work on a retrofit that has a gantry setup like this. The gantry I am looking at has 2x 800w motors on it, and is 16' wide. If I calculate moving one motor a single rotation (say a circumference of 3.14" for a 1" pinion) this will rack the gantry by about 0.94 degrees and 0.016" loss of width. If turning half that you are looking at 0.47 deg and 0.008" respectively. All that being said, it is likely that you are already very close to being aligned, but there should be some way to calculate how far it is off based on your geometry and setup. My guess is that if you assume that you have a reasonably decent alignment to start with (or at least you are not twisting the gantry) and move it back and forth to find the actual position of the homes, then you can make an informed decision on how far it would be safe to adjust one side. EBo -- ------------------------------------------------------------------------------ Try New Relic Now & We'll Send You this Cool Shirt New Relic is the only SaaS-based application performance monitoring service that delivers powerful full stack analytics. Optimize and monitor your browser, app, & servers with just a few lines of code. Try New Relic and get this awesome Nerd Life shirt! http://p.sf.net/sfu/newrelic_d2d_may _______________________________________________ Emc-developers mailing list Emc-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-developers
