Hi Cliff I can short tell you how we do it on our waterjet cutting machines at work. I work for a waterjet cutting machine manufacturer, developing our own cnc software.
Each gantry axis has it's home switch. There is an adjustable configuration value for the offset distance between those 2 switches. Homing sequence: 1. Positioning speed until both of the 2 gantry axis home switches tripped (sequentially), then stop the gantry. 2. The gantry is now moved with homing speed in the other direction. 3. After the first switch (now in the other direction) trips again, the hardware is put in a homing state wich means after the next reference mark comes it will save the position into a register. 4. The machine still continues moving until the same happens on the second switch (on the other gantry axis). 5. Homing motion stops and the gantry is adjusted (deskewed?). This means one axis motor corrects it's position deviation in respect to the configured home switch offset. 6. Positoning move to home position Our motors are pretty strong and can offset the 2 gantry axis easily. If the correction would be more than 20mm we expect a unsers input to make the gantry adjustment to be sure it's really wanted (gantry length is 3500mm). On the other hand the strong mechanics can handle big position offsets between the 2 axes (see above, 20mm). I don't know whether or how this maps to emc2. Just wanted to give you an idea how others (we) do it. Our homing is not generic, since it's optimized for our machines only. Good luck with this, good you are taking initiative to improve that. Hope it helps. thanks. Marc Am Dienstag, den 20.04.2010, 02:07 -0700 schrieb Cliff Blackburn: > Thats one thing I'm not totally positive about yet, but from how it > looks in the source I can use home_offset on one the second joint to > correct skew, leaving the first at zero. > > For instance.. > > Distance between homes switches is 2in. > > INI Specifies > Joint0, home_offset = 0 > home = 0 > Joint1, home_offset = -2in > home = 0 > > Both linked joints will travel towards home switch. Joint0 trips first, > puts Joint1 in follow mode. After joint0 completes it's home it loads > its position with 0(home_offset) then it moves to home.. (which will > just be a bit of overshoot) > > After Joint0 stops, Joint1 starts homing and Joint0 goes into follow mode.. > They both travel towards joint1 home. After Joint1 completes its home > it's loaded with -2(home_offset). Because Joint0 was following it should > also be at -2 as well.. so they are now both loaded with -2 for position. > > On second thoughts It might be better to stop homing joint0 at the > HOME_FINAL_MOVE_START state instead of HOME_FINISHED.. Then start homing > joint1.. after they are both this far and loaded with their home_offset > values they stop following each other and both drive to their HOME > positions and at the end of the move any skew should be corrected? right? > > I guess I need to add another error check to make sure both joints HOME > value is the same. > > Thats what I was thinking about, I'm still new to EMC so not sure if > this will work the way I'm thinking. > > Alex Joni wrote: > > HI Cliff, > > > > looks good so far. > > What happens when both are homed, but the home position is different > > (slight > > skew). > > Does it get corrected? Does the offset get remembered? > > (At least that's what I think happens if one joint _always_ follows the > > other one during homing). > > > > Regards, > > Alex > > > > > > ----- Original Message ----- > > From: "Cliff Blackburn" <[email protected]> > > To: <[email protected]> > > Sent: Tuesday, April 20, 2010 10:11 AM > > Subject: [Emc-developers] Coordinated Gantry Homing by Linked Joints > > > > > > > >> I started working on a modification to homing.c so you can home a gantry > >> style machine properly I have started working on it but have more work > >> before i find how many bugs I created in the process. It adds a option > >> to link 2 joints together. The joints will home themselves one at a time > >> while maintaining the same velocities. Quite a few commercial machines > >> can do this out of the box and I think EMC should too. > >> > >> Ideally I don't want to touch what already works and think the best > >> solution is to introduce custom homing modules (simple, gantry, > >> crazymach) which can do coordinated motion if needed. Although this > >> seems like the most configurable + ideal way it's also is the most work > >> :( This way *seems* simple with minimal changes. > >> > >> This is the basic plan so far.....What do you think, good/bad idea? is > >> it useful to anyone? or should I go a completely different method. > >> > >> Plan > >> - Add a HOME_LINK_JOINT property to the joints. This property defines > >> which joint is linked linked to it. > >> - It will at all times will insure both joints move together. (Const vel > >> at least) > >> - The first joint to come into contact with it's switch will put the > >> second into a HOME_LINK_WAIT waiting state. > >> - While the second is in the waiting state the first will complete it's > >> home and follow all of it's moves. > >> - The move following is done in the home_start_move() funtion > >> - Once the first joint has come to a complete stop after homing it will > >> be sent to HOME_FINISHED state. > >> Now it will set the second joints state to HOME_START > >> - The second joint will now follow the first until it also hits the > >> HOME_FINISHED state > >> - The joints will check each other see they are both completed and sets > >> the HOMING flag off and HOMED true...etc... > >> > >> Error Checking > >> - Must check all velocities, accels, etc.. are equal between joints, if > >> not it's a warning and use the smallest values from the two. > >> - Joints which are linked must have the same home_sequence. If not it is > >> a critical error and quit > >> - Joints can only link to 1 other joint, and that joint can only link > >> back to the orig. (e.g. cannot link 3 or have some kinda chain.. > >> Simplicity) > >> > >> Requirements > >> - Make minimal changes to the homing configuration. > >> - Don't break working home procedures...! > >> - Allow all current home methods even if the 2 linked joints use a > >> different procedure. > >> - Up to user to specify home offset values to adjust for table skew and. > >> - Doesn't matter which joint homes first > >> - Always stay in sync. > >> - An error in one will trip the other > >> > >> ------------------------------------------------------------------------------ > >> Download Intel® Parallel Studio Eval > >> Try the new software tools for yourself. Speed compiling, find bugs > >> proactively, and fine-tune applications for parallel performance. > >> See why Intel Parallel Studio got high marks during beta. > >> http://p.sf.net/sfu/intel-sw-dev > >> _______________________________________________ > >> Emc-developers mailing list > >> [email protected] > >> https://lists.sourceforge.net/lists/listinfo/emc-developers > >> > >> > > > > > > ------------------------------------------------------------------------------ > > Download Intel® Parallel Studio Eval > > Try the new software tools for yourself. Speed compiling, find bugs > > proactively, and fine-tune applications for parallel performance. > > See why Intel Parallel Studio got high marks during beta. > > http://p.sf.net/sfu/intel-sw-dev > > _______________________________________________ > > Emc-developers mailing list > > [email protected] > > https://lists.sourceforge.net/lists/listinfo/emc-developers > > > > > ------------------------------------------------------------------------------ > Download Intel® Parallel Studio Eval > Try the new software tools for yourself. Speed compiling, find bugs > proactively, and fine-tune applications for parallel performance. > See why Intel Parallel Studio got high marks during beta. > http://p.sf.net/sfu/intel-sw-dev > _______________________________________________ > Emc-developers mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-developers ------------------------------------------------------------------------------ _______________________________________________ Emc-developers mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-developers
