On Sun, 2008-07-20 at 16:30 -0400, Kenneth Lerman wrote: > What do you mean by "encoder is in an invalid position". Every position > read from an absolute encoder is valid in the sense that it reflects the > actual position of the encoder within its tolerance.
I don't think it does. Every edge from on/off to off/on has an unstable region, which can be cleaned up with hysteresis, which requires motion (?). The only time the data is valid, is when all bits are cleanly within a stable area, off any edges. > If you used a 256 count encoder for your 24 positions, each tool > position would correspond to 256/24 = 10-2/3 counts. So if the encoder > read from 0-10, that would be position zero. 11-22 would be position > one, etc. > > On power up, you would read the encoder and that would tell you what > position you were at. Assuming that the tool positions corresponded to > the start of each range, 0 would correspond to position 0, 10 would > correspond to tool position 1. 21 would correspond to tool position 2, > etc. To allow for some "slop", you would probably set things up so that > 255, 0, 1 were tool position 0. 9, 10, 11 were tool position 1, etc. > > If you found that you were between positions, it wouldn't really matter. > The first time you seek to a tool, you would still know where you are > and where you have to go. Bingo. You need motion to do that, it just took me a while to realize I could deal with that on the first tool change. Or, use the spiffy magnetic sensor. > A true absolute encoder is a static device. You can read a value without > moving it. > > Ken Thanks for your help. That's why I posted the question. -- Kirk Wallace (California, USA http://www.wallacecompany.com/machine_shop/ Hardinge HNC/EMC CNC lathe, Bridgeport mill conversion, doing XY now, Zubal lathe conversion pending Craftsman AA 109 restoration Shizuoka ST-N/EMC CNC) ------------------------------------------------------------------------- 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
