Re: Bridgett update

Hi,

What I have seen happen is contamination of the encoder wheel,
especially the the high resolution ones, (1,000 lines). If the
optical radius is .25", the line and space dimensions are very small;
0.0007" each.

You have to be careful with modular encoders to never touch the
surface of the encoder wheel. A fingerprint is enough to obscure
several lines on a glass-chrome wheel or a plastic-film one. If it is
an etched metal wheel, then be careful to not bend it. They are VERY
delicate.

Same problem with sealed encoders. Avoid opening them, there is a
chance you will introduce something very small that will land on the
wheel.

Suspect contamination if the motor "jumps" in some locations but runs
smoothly elsewhere. The "jump" will usually be in the same radial
location.

Use a non-lint producing wipe wetted with a little bit of isopropyl
alcohol to clean an encoder wheel. Be very careful not to scratch it.
Do the same for the fixed grating located over the phototransistors.

Sometimes, if the wheel has been misaligned, it will bave rubbed off
the chrome or film, causing this problem. The only recourse then is
to replace the encoder.

If you have a dual channel o'scope, you can check the encoder
integrity by triggering off of encoder channel A while displaying
both channels. Spin the encoder at a constant rate and look for
cyclic errors and jitter. If there is crud on the wheel, this will
reveal it.

Hope that helps.

Mariss