On 10/28/2011 7:50 AM, Tom Easterday wrote: > On Oct 28, 2011, at 3:57 AM, Viesturs Lācis wrote: > >> 2011/10/28 andy pugh<bodge...@gmail.com>: >> >>> On 28 October 2011 01:20, Tom Easterday<tom-...@bgp.nu> wrote: >>> >>>> Is there a command or parameter that can be set while EMC/Axis is running >>>> that will make it ignore following error (and then after issuing again - >>>> pay attention to ferror)? I want to have my servo drive control an axis >>>> and I want EMC to ignore it while I do this, then take back over control. >>>> But I don't want to have to disable Axis. >>>> >>> You could latch the encoder feedback into a mux2. If you link the >>> output to the input then it acts like a sample-hold block (there is a >>> sample-hold, but that is s32 not float). If you wire the select pin to >>> the homing pin, and the other input to the encoder position, you can >>> freeze the feedback. >>> >> It is not clear to me, how exactly the "I want to take control of >> particular joint from EMC2 for a while and then give it back to EMC2" >> idea is meant to be used and if You want EMC2 to know the actual joint >> position even when You are controlling it. >> The thing I did for THC purposes - I modified kinematics so that >> joints[3] = tran.pos->z + offset and the offset value was set by THC >> module. That way Z height was adjusted by THC and EMC2 always knew the >> position of joint, displayed it in DRO and also did not allow to >> exceed soft limits. >> Depending on the way You want to take over control of particular joint >> and then then giving it back to EMC2 (does the switch of control >> happen in the same joint position, does EMC need to know exact joint >> position, when You are controlling it etc), You might do something >> similar. >> > This is for homing my gantry. It has two joints on one axis (the Y axis). > I want to have EMC ignore following error, and not control the motors while I > send a signal simultaneously to each of the two Granite Devices drive modules > which will then home both joints to a hard stop (and come off those hard > stops a small amount). The Granites ignore incoming signals while they are > doing this so I need EMC to be ok with the fact that it is not commanding the > motors and that there is huge following error. > > Once the Granite is done doing it's homing I want EMC to then search for > index on one of the two joints while moving the opposite joint in sync (so > the gantry doesn't rack) . > > By the way, ultimately once we get things working, we will have a THC enabled > and I like your idea of the offset. Can you post (or pastebin) your config > for how you do the z+offset? > > Thanks, > Tom > > PS: I found a thread in the mailing list archives talking about options for > gantry homing that sounded like there was some work being done in that area. > Did anything come of that? Is there anything new on that front in 2.5? >
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? 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. Dave ------------------------------------------------------------------------------ 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
