Magnet Fiducialization with Coordinate Measuring Machines Page: 3 of 7
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Form fit quality checks are available, but the user is required to provide a global
"common sense" check.
On the other hand, CMMs are powerful, complex systems whose operators re-
quire extensive training. They are also quite costly. Hourly rates at local inspection
shops can be quite reasonable, however.
All three of these methods are used at SLAC. Optical tooling continues to
take most of the load with CMM measurements used only for special components.
The IMS systems are used for components which are too large for a CMM but
require the redundancy checks not provided by optical tooling. Two SLAC CMM
experiences are outlined below.
Experience With CM M Measurements
The Final Focus CQ-SQ Quad Pair
This magnet pair consisted of two 2001b solid steel cored magnets 5 inches
long with a width of 10 inches and a height of 12 inches. The bore diam-
eter was 3/ 4 - inch and four tooling balls at the top corners served as external
fiducials (Figure 2). The purpose of the CMM inspection was to check the op-
tical tooling measurements taken before installation. Beam steering studies
indicated possible errors in the original fiducials.
The inspected procedure consisted of scanning a sample of 180 points per pole
tip to determine the best fit circle for each pole tip surface. Another circle
was fitted to the centers of the four pole circles to find a best fit geometric
center. (Figure 2). This was repeated at both ends to set the X, Y and Z
origins as well as the yaw and pitch angles. Roll was to be defined by the
split plane.
The quality of the results were greatly diminished by the configuration of
the magnet. Roll could not be accurately set because the split plane was not
accessible. Attempts to use the centers of the pole tips to set the orientation
proved unsuccessful due to the extremely short lever arm (1.5 inch). Also,
tooling the CMM probe could not fully access all balls. The results which
could be compared to previous measurements showed discrepancies of up to
400ims. Since the CMM measurements did not repeat well and the geometry
was poor, the results were discarded. Repeated optical tooling inspection
showed changes in fiducial coordinates of up to 150im. This illustrates that
for this case neither method satisfied the 50pm inspection tolerance.
The conclusion is that magnets should be designed with CMM measurable
features. "After the fact" fiducialization may be difficult if not, impossible
for magnets without them. However, new video systems technology may
improve this situation.-208-
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Friedsam, H.; Oren, W. & Pietryka, M. Magnet Fiducialization with Coordinate Measuring Machines, article, August 12, 2005; [Menlo Park, California]. (https://digital.library.unt.edu/ark:/67531/metadc875985/m1/3/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.