On 10/26/15 10:00 AM, John Kasunich wrote: > On Mon, Oct 26, 2015, at 11:43 AM, Sebastian Kuzminsky wrote: >> On 10/26/15 8:50 AM, andy pugh wrote: >>> Some systems have many indexes and a way to distinguish between them. >>> Sometimes the indices are different distances apart (some linear scales) or >>> there may be a secodary feedback system (robots with encoder + index and a >>> potentiometer). >>> >>> I don't think that LinuxCNC can work with these systems at the moment as >>> the home_offset is a static value read from the INI. ... >> >> I don't understand what problem you're solving, or what your solution >> entails. Can you give more details? > > Imagine a lathe Z axis. The leadscrew has an encoder with an index pulse. > > It can be inconvenient to home to a fixed location. If you put the home > switch at the headstock end you might run into the chuck if a larger-than- > normal chuck is mounted. (Or the workpiece, if one is loaded). If you put > the switch at the other end you might run into the tailstock depending on > where it is located. > > Now imagine that you have some kind of coarse absolute position > measurement. Perhaps linear potentiometer connected to the carriage. > It can't measure position to 0.001", but it can do +/- 0.050". The screw > pitch is 0.200". So the pot can tell you where you are to within one turn > of the screw. > > In theory, it should be possible to home by moving the carriage approximately > one turn of the screw in either direction, to find an index pulse. The pot > tells > you what turn you are on, the index tells you exactly where you are in that > turn. > > But there needs to be a mechanism for LinuxCNC to use the info from the pot.
Thanks John, that example makes it clear. I now see the utility of having HOME_OFFSET settable from HAL, and I support Andy's suggestion of making it into a pin, to be driven by the pot or some other suitable sensor. -- Sebastian Kuzminsky ------------------------------------------------------------------------------ _______________________________________________ Emc-developers mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-developers
