Hey Eric,

I think you "typo-ed" two places. The first mention of the shaft
radius should be 0.159154943, rather than .19something; and later on
you effectively multiply 0.0001 X 10,000 and get 0.1 instead of a
whole number "1".

These didn't seem to affect the idea though, except what does
fastening a mirror onto the shaft do for you? Why not just fasten the
laser to the shaft, and measure the laser-beam movement at the
1591.54943" point as 1". If you don't have a 132 foot distant surface
available, then you might consider using mirrors to multiply/divide
that distance to something more practical, or better yet, make the 132
foot point right near where you are going to be working?. As his is a
"counting" discovery, you don't need much "wall" space. You can count
forward and backward 18 pulses in 3 feet of wall, or along a
yard-stick!!

Interesting. Let us know how you make out. I've had very little to
do with encoders except use in determining speed and the derived
acceleration and deceleration, and they were 1024 X 2 models. Any
chance that two encoders on the same shaft would help you? That's how
we determined direction.

Take care.

Brian Lawson,
Bothwell, Ontario






On Mon, 03 Oct 2005 07:50:45 -0700, Eric R Snow
wrote:

This may seem off topic but it's not really. Measuring is important to
machining. And I need to make a measurement without putting pressure
on the item being measured. Now, for the purists, I know that light
will put a little pressure on what I'm measuring, but this will have
way less effect than any kind thing I can measure. I have an encoder
that outputs 10,000 pulses per revolution. With a shaft measuring
.19515" (radius) each pulse equals .0001 on the circumference. So, if
the radius keeps multiplying by 10 then the amount traveled by the
circumference will increase by 10. Here's the plan:
Put a mirror on the shaft.
Shine a laser at the mirror.
Adjust the mirror until the laser is visible on a target 1591.5"
(132.625 feet) away.
This will increase the amount traveled to .1" for every pulse.
So, measuring the distance the spot travels will show how many pulses
should be generated.
The reason for this measurement is to rule out backlash in the
encoder. It appears that there is a 9 pulse error. In other words, if
the encoder shaft is turned one way and the count is noted, and then
turned the other way until the count changes, it appears that the
shaft turns an amount equal to 9 pulses. I need to rule this out
because this is the error I'm getting is a mechanical system and it
appears that all the mechanical lash has been reduced to less than
.0001". The last thing seems to be the encoder itself.
Thank You,
Eric R Snow,
E T Precision Machine