On Mon, 03 Oct 2005 18:19:17 GMT, xray
wrote:

On Mon, 03 Oct 2005 10:33:39 -0700, Eric R Snow
wrote:

SNIP


If you've got an o'scope you can look directly at the
encoder channels to eliminate any possibility that it's the
readout, if that's what you mean by display error. Less
convenient, but workable, would be a voltmeter or two. Or
even an LED on each channel, as long as you're careful to
limit the current based on the encoder's drive capability.

Ned Simmons
Ned, I have a scope. I don't really know how to use it. I need to get
a book on oscilloscopes in general. The scope is a Tektronix 465B. The
only probe I have is one with a red and black wire terminating in
little hook shaped clamps. If this will work can you tell me how?
Thanks,
Eric

I was just thinking... Why not make a test setup to check the encoder
outside of your intended system?

Say you want to move the shaft 1/10000 rev with .01 inch applied. The
circumference required will be .01 * 10000 = 100". The radius for that
circle is about 15.9".

Why not attach a light, but firm, arm to your encoder, 16" long. To
remove as much load as possible, put the encoder so its shaft is
horizontal with the 16" arm hanging straight down. Clamp a micrometer so
it touches the rod near the end and put a light spring (rubber band?) to
pull the lever against the micrometer barrel. Now, moving the micrometer
.01 should move the encoder 1/10000 rev.

Obviously, you could shorten the lever by some factor and still get
decent measurements.

Just one other approach, if you feel so inclined.

-Rex
What I'm trying to do is move the encoder in the system and see what
happens. Since I have the laser, mirror, and some clay the setup will
be easy. I don't want the measuring to influence the encoder. So if
the carriage moves .0008 and the display doesn't I can't tell where
the problem is. If the carraige moves .0008 and the encoder shaft
turns the requisite amount, and the display doesn't change then it's
the encoder. But if the carriage moves .0008 and the encoder shaft
doesn't move, and the display doesn't change, then the error is in my
setup and I can look for it. I don't think it's the encoder, but it
seems to me that the mechanical setup is backlash free. So until I
eliminate something it won't be solved. And the encoder check is the
easiest so far.
Eric
Eric