"DoN. Nichols" wrote:

On 2012-02-14, Michael A. Terrell wrote:

jk wrote:

"Michael A. Terrell" ? wrote:

?
? Add an encoder on the spindle to read the actual speed and use that
?to set the timing, then the processor generates the drive in sync for
?whatever ratio you need. Not as ridgid as gears, but will let you do
?small jobs OK.
?
Well for threading
You also need to be able to sync not just to spindle speed, but to
spindle position, unless you are going to cut that thread in a single
pass. Thus you also need an index pulse.


It does need indexed but I was thinking of absolute position
encoding, which would take care of both.

Most encoders don't have absolute position encoding. That
requires multiple tracks to generate binary (or more likely, gray code,
which is designed so only one bit changes at a time, so it is harder to
miss something).

Most rotary encoders on spindles have only two tracks -- one has
only one hole, to show the index point, and the other has as many holes
as needed for the resolution. If you are counting pulses, reset to zero
every time the index passes. Yes, I have some encoders which give
binary data, but they are a bit fragile to use on a machine tool, and in
particular, they depend on a single long filament lamp to illuminate all
the tracks and sensors. Those lamps are made of unobtanium, so if you
design and build a tool using one, and the lamp dies, you have to re-do
the design. (Yes, you probably could do it using LEDs instead of a
lamp, but still getting that narrow line of illumination will be tricky,
especially inside the small housing provided.

Better to have the two track encoder (index and count), and set
up a quadrature detector, so you can count the counter up or down
depending on which direction the spindle moves in at the moment.


AVAGO makes a lot of solid state sensors. I think they are the old
semiconductor division of HP.
http://www.newark.com/jsp/search/browse.jsp?N=502+2203+202064&Ntk=brand&Ntt=AVAGO&N tx=

i had a pile of salvaged encoders from motors industrial high speed
printers ant mainframe tape drives, but I'd have to look for them. Some
used a lamp, while others were LED. Some end up on the surplus marked,
as well. I would pick one that I had extras of, if I use either used,
or surplus.


--
You can't have a sense of humor, if you have no sense.