Off-center encoder error
Posted by
Chris Stratton
on 2001-07-13 13:58:48 UTC
I'm wondering if anyone could comment on the relation between
centering error (runout) of encoder disk mounting and the resulting
measurement error. I'm sure I can figure it out myself, but if the
relationship is already known that would be helpfull.
My gut feeling is that it isn't too critical, especially for a large
diameter disk. The rounout would seem to directly translate to a
cyclic error of equal magnitude in the linear position of the edge of
the disk. But when you consider the measuring circle might be an inch
and a half in diameter (ie, nearly 5 inches in circumference) and the
screw is probably .2" pitch that means that the linear position error
is only a 25th of the centering error. If one can get the disk
centered to within 2.5 thou, the position error would be .0001, which
is probably less than the give in any ballscrew system I can afford.
Chris
--
Christopher C. Stratton, stratton@...
Instrument Maker, Horn Player & Engineer
22 Adrian Street, Somerville, MA 02143
http://www.mdc.net/~stratton
NEW PHONE NUMBER: (617) 628-1062 home, 253-2606 MIT
centering error (runout) of encoder disk mounting and the resulting
measurement error. I'm sure I can figure it out myself, but if the
relationship is already known that would be helpfull.
My gut feeling is that it isn't too critical, especially for a large
diameter disk. The rounout would seem to directly translate to a
cyclic error of equal magnitude in the linear position of the edge of
the disk. But when you consider the measuring circle might be an inch
and a half in diameter (ie, nearly 5 inches in circumference) and the
screw is probably .2" pitch that means that the linear position error
is only a 25th of the centering error. If one can get the disk
centered to within 2.5 thou, the position error would be .0001, which
is probably less than the give in any ballscrew system I can afford.
Chris
--
Christopher C. Stratton, stratton@...
Instrument Maker, Horn Player & Engineer
22 Adrian Street, Somerville, MA 02143
http://www.mdc.net/~stratton
NEW PHONE NUMBER: (617) 628-1062 home, 253-2606 MIT