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. > > 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. > > A true absolute encoder is a static device. You can read a value without > moving it. >
I wonder if Kirk is thinking of (or already has) something like the tool turret "encoder" on the Mazak at the CNC workshop? That machine has five prox switches that generate a 5 bit code to indicate which tool is selected. It is a simple absolute encoder, _except_ that the prox switches are "looking at" a series of drilled holes in the disk that forms the tool turret. When the turret is at an intermediate position, between two tools, none of the holes line up, and the prox switches report all zeros. There is an additional prox that says "you are in a valid position". In any case, Kirk may be over-worrying about this. Unless somebody kills the power in the middle of a tool-change, the machine will always power up in a valid position. You can't ignore that possible invalid situation, but it will by no means be a frequent problem. Regards, John Kasunich ------------------------------------------------------------------------- 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 [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
