At 10:13 PM 11/8/2008, you wrote: >Ron Ginger wrote: > >> I have some Gcodes where the I and J are in absolute > coordinates, EMC2 seems > >> to like I and J in incremental coordinates, is there a simple way, or > >> something that will enable EMC2 to read these Gcodes. > >> > >> Regards > >> > >> Dave > > > > Mach3 supports both, G90.1 sets to absolute mode, G91.1 sets to > > incremental mode. Its valid to change it on the fly within a program. > > > >That seems like it might be a useful feature. I've started implementing >it in EMC2, but as usual when you look at the details, some tricky cases >show up. > >Here is what I'm planning: > >Right now, IJ arcs require you to supply at least one of the >coordinates, otherwise it reports an error. Things like: > >G2 I1 > >are OK - that means make a complete circle that starts where you are >now, goes around a point 1 unit to the right, and return to the starting >point. > >In the default G91.1 incremental IJK mode, nothing at all will change. > >In the new G90.1 absolute IJK mode, that same line is ambiguous. Where >is the center of the circle? Is it at X=1, Y=(whatever the last J word >was)? That might be what you'd expect, since when you omit X, Y, or Z >from a move, it uses the current value. But for I and J the "current >value" isn't as well defined. Is it the center of the last arc? What >if I or J was used in a canned cycle a few lines up? Should it be that >value? > >The Mach manual says "In Absolute it will, of course usually be >necessary to use both I and J words unless by chance the arc's centre is >at the origin." So Mach is using zero if you don't specify I or J (or >K, depending on the plane). > >I don't see any clear reason for a user to expect one approach or the >other. Whichever I do, somebody is going to be unpleasantly surprised >when they leave out an I or J and the arc isn't where they want it. > >So, I'm going to require both coordinates when in G90.1 absolute mode. >I think it is better to stop and print an error (during the preview >phase if running Axis), than to make a cut somewhere it isn't expected. > >Comments and suggestions are welcome, but if you want to make I/J/K >optional in absolute mode, be prepared to define exactly what will >happen in all cases, and come up with very good reasons to justify the >additional complexity. > >Regards, > >John Kasunich
Absolute IJK mode is just the same as absolute mode for XYZ. The values in IJK are relative to the current work offset. The only question is are they modal or not, I have never seen a control that was setup to use absolute IJK words. I think the reasoning for absolute IJK was that when programming at the machine from a part drawing it is more likely you can just read the values off the drawing and avoid doing some math. Sounds like Mach is declaring IJK to be non modal, I would think they would be modal and so a line with just a G2 or G3 could be perfectly valid. I get the feeling that absolute mode IJK in arcs would require the interpreter to do more calculations then incremental IJK arcs resulting in slower block processing. Probably not a problem since block rates tend to only be a problem with cam generated programs that use many thousands of 0.0005 long G1 moves that you want to run at 200 IPM. NCPlot does have a tool that will convert a program from one to the other, also does many other conversions. It is a windows program but well worth the cost of the license if you do any amount of macro B programming. I think just leave EMC as it is and write a little app that does the conversion off line, most any CAM system should be able to output either format so we are only talking about a few existing old g code programs. In my opinion the user would be better off rewriting those programs anyway to take advantage of modern cutters anyway. ;) ______________ Andre' B. ------------------------------------------------------------------------- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK & win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100&url=/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
