Well, for the same cost, you can use the material differently and instead of having a half circle, have two quarter circles and get twice the resolution. Or, you could have four 1/8 circles ...
:-) Ken John Kasunich wrote: > Kenneth Lerman wrote: >> Jon Elson wrote: >>> Kirk Wallace wrote: >>>> On Mon, 2008-07-28 at 00:33 -0500, Jon Elson wrote: >>>> ... snip >>>> >>>>> you might be >>>>> able to cobble up a substitute by making a disc with a narrow >>>>> slot and one of those U-shaped optical sensors from a floppy drive. >>>> I have thought about this, but I wonder how accurate these are. If you >>>> want to resolve .0002", I think you typically need angular accuracy >>>> to .16 degrees. I guess I could try it to find out. >>>> >>> I came up with .36 degrees. A good-sized disc with a >>> narrow-enough slot should work. Basically, you are making a >>> 1000 line resolution encoder, but with only one line. >> Is that true? Since you always approach the home position in the same >> direction, the width of the slot shouldn't matter at all. You should >> just be looking at the leading edge. >> >> Ken >> > > Exactly - which leads to another interesting possibility. If you make a > disk that is as close as possible to 180 degrees "on" and 180 degrees > "off", you can mount two sensors at 90 degrees to each other. The > result is a quadrature signal, with four counts per rev. Since each > sensor still has only one rising edge per rotation, either sensor can be > used as the index. (You would only need two hardware inputs, one of > which would be split in HAL to drive both phase A and the index of the > encoder, the other would drive phase B). > > This would be a great candidate for a cheap lathe threading encoder. > The CVS version of EMC2 can use a single pulse per rev encoder for > threading, but this simple 4 count quadrature encoder would provide > about 16x better performance during load induced speed changes, for very > little extra cost. > > 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 -- Kenneth Lerman Mark Kenny Products Company, LLC 55 Main Street Newtown, CT 06470 888-ISO-SEVO 203-426-7166 ------------------------------------------------------------------------- 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
