Ignoramus21167 wrote:

On 2010-06-04, Pete C. wrote:

Ignoramus21167 wrote:

On 2010-06-04, Pete C. wrote:

Ignoramus21167 wrote:

The servos on my mill have sinusoidal encoders which are not
compatible with most CNC control stuff.

I am looking at various options.

One is to make a converter to convert sinusoidal to quadrature. It is
a pain in the butt to do due to lack of documentation on what wire
does what.

Another one is to reuse a converter board from the existing Heidenhain
controller. Same issue as above. (and I do have documentation, it just
does not say what is what).

I have opened up one of my servos to see the shaft. It is a 10mm
shaft.

For that size, US Digital has suspiciously cheap encoders E7P:

http://usdigital.com/products/encode...otary/kit/e7p/

They seem like they will fit, however, I am slightly surprised at the
price.

I Wanted to know if anyone has any suggestions, as I do not want to go
a wrong way.

i

Those are pretty low resolution, only up to 720 CPR. The encoders on the
CNC machines I used to work on were all around 2,000 CPR. You have to do
the math with your ballscrew pitch to figure out what the final movement
resolution is, but I expect it will be far too low. Also since this is a
servo setup, the minimum servo error with such a low resolution encoder
could equate to an unacceptable position error at the cutter.

Well, on the back of the envlope calculation is: ball screw pitch 1/8"
(0.125"). Pulley ratio 1:2. So, 720 CPR results in

0.125"/2/720 = .0000868 inch per cycle
OR
0.002mm

That would be acceptable to me.

i

.0000868" per count * servo error tolerance of +/- 128 counts (256 count
window) = 0.0222208" error which is very significant and would not be
acceptable to me.

that sounds bad!

i

Bingo! That would be why the "big boys" use 2,000 CPR or better
encoders.

What is the CPR on your current encoders?