On Oct 28, 2011, at 10:49 AM, Dave wrote: > Tom, > > I've thought about doing the "reduced torque into a hard stop" also to > eliminate homing switches. That is very attractive. If you are > hitting a hard stop, then why do you think you need to look for an index > mark also?
You're right, I probably don't. We were just thinking for accuracy and repeatability it might be nice. On the other hand, if the pinion (we have rack and pinion) would move/slip for some reason then encoder position would move and that would cause a change in home position (from the last time, that is). So, perhaps it is better to just let the Granite home then have EMC come online and just set everything to home. > The idea of an index mark (that I have understood) is to get a more > repeatable homing indicator than a limit switch can provide. > I don't see how that is an improvement over running into a hard stop. > When torqued into a hard stop your gear train backlash is pushed into > one direction. > > I think it might be possible to set your drive torque to a reduced > value, have EMC2 do it's homing routine and let the machine hit the hard > stops, then when the following error hits a certain value (not the limit > - set that way up high), use that to trip the EMC2 "home switch > input". That would let you keep EMC2 in control at all times. I guess > you could also do a search for an index mark after hitting the following > error value also, but I am not sure that would be an improvement. > > Many Servo drives can be set to change the limit torque via a switch input. You are probably correct that EMC could be made to do this if the drive is capable of being told to reduce torque. The Granites don't have that as a feature (reducing torque on command), but do already have homing to hard stop (at reduced torque) as part of their Homing Controller code. We have a hammer and that looks like a nail! -Tom ------------------------------------------------------------------------------ The demand for IT networking professionals continues to grow, and the demand for specialized networking skills is growing even more rapidly. Take a complimentary Learning@Cisco Self-Assessment and learn about Cisco certifications, training, and career opportunities. http://p.sf.net/sfu/cisco-dev2dev _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
