Introduction to CMM
Global User Manual
10-19
Intro. to CMM
Qualifying Probe Tips
Probe Compensation
CMMs generally gather their data by touching the workpiece
with a probe (either a solid probe or an electronic touch trigger
probe) attached to the machine’s measuring axis. Although the
tip of the probe is very accurate, once the probe is attached to the
CMM, the location of the tip to the machine’s coordinate system
must be determined prior to measuring. Since it’s the tip’s
circumference that touches the part, the probe’s center and radius
are determined by measuring a very accurate sphere
(requalification sphere).
Once the center and radius of the tip are known, when the probe
contacts a workpiece, the coordinates of the tip are mathemati-
cally “offset” by the tip’s radius to the tip’s actual point of
contact. The direction of the offset is automatically determined
by the alignment procedure.
We do a similar procedure when we park a car. The better we can
estimate our offset from the exterior of the car, the closer we can
park it to the curb.
Figure 23 Qualifying Probe Tips
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