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Message ID: 397
Entry time: Tue Dec 16 16:34:11 2014
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| Author: |
Joe Strzalka |
| Type: |
8-ID-"G" |
| Category: |
Beamline Hardware |
| Subject: |
GIXS DIffractometer: Encoder calibration |
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Copying info from an email to Norman Huber (2010.06.29) describing our calibration of the encoders:
Thank you for your reply regarding the large tilt stage and the
encoders. Earlier, I didn't have time to test your expression with the
value you supplied for the radius using the encoder, but now I have. I think we will keep on using the expression we obtained from fitting the data measured using an optical interferometer (I sent you the data and our fits back on June 8). The attachment shows residuals (measured value - fit value) computed for three cases:
1. your expression for the upper segment using 602.7 mm for the encoder radius (red) -- this is not really a fit, as all the parameters are
fixed. It shows the residuals get systematically larger away from zero.
b = 630.16 mm
c = 602.7 mm
d = 184 mm
beta = 16.977 degrees
encoder resolution = 0.1 mm
offset = 3.1062 degrees (the value from our best cubic fit, this would be the wedge + an offset due to the table not being perfectly
level)
2. the best fit using your expression (black), letting everything
float. The values I obtained this way were:
b = 630.23 mm
c = 602.63 mm
d = 183.98 mm
beta = 16.975 degrees
encoder resolution = 0.09984 mm
offset = 3.1043 degrees
3. our cubic expression (blue)
I haven't made the comparison for the lower segment yet, but I expect
the results will be similar.
Attachments:
39277_57682.PDF -- Huber's drawing of the two-tilt stage indicating correct radii for the encoders.
Movement lower segment.pdf & Movement upper segment.pdf are information from Huber about the angular positioning of the arc segments. Ultimately, these are *not* the calibrations in use at 8-ID-E.
These expressions are valid for relating the motor steps to the worm gear advance. But the radii used are different from the radii where the encoders are mounted.
HuberTiltStageCalibration.pdf -- description of the encoder calibration in use at 8-ID-E. The data derive from measurements by the APS Survey Group.
CubicHuberResidualsComaprison.pdf -- the figure described in the email above, comparing residuals from different fits to the Survey Group data. |
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