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Immersion's Tri-Test Calibration Method™ for
MicroScribe® MX Devices Calibration tests used in production
of the MicroScribe MX series devices are based on the draft specifications
produced by the B89.4.22 Committee of the American Society of Mechanical
Engineers (established October 1994). The committee is responsible for
setting standards for the performance evaluation of articulated arm coordinate
measuring machines (AACMMs).
Three tests are used in production of MicroScribe MX devices and are
detailed below.
Effective Diameter Performance Test
In this test, the diameter of a calibrated sphere is measured using nine
probing points. The diameter measurement is repeated three times, and
the largest deviation is reported.
Single Point Cone Test
The B89.4.22 draft document refers to this test as the “Single Point
Articulation Performance Test Using a Hard Probe.” This test is
intended to assess the arm's ability to provide similar values of a point
coordinate. In it the ball probe attached to the device is placed in a
conical hole, or kinematic seat, and ten values are taken while the arm
is articulated through a broad range of motion. The measurements are repeated
in ten different positions throughout the workspace. At each location
the following calculations are performed:
1. Average coordinate (sample mean) of the 10 measurements.
2. Distance from each measurement to the average coordinate.
3. Twice the standard deviation (2*sspat )
The SPAT performance reports the sspat at the location with the highest
result from calculation 3.
Volumetric Length Accuracy Test
In this test, the known positions of the points from the Single Point
Cone test are used. For every measurement, the distances between it and
all the measurements not taken in the same cone are calculated. The known
lengths between these points are compared to the lengths calculated by
the device calibration software. This approach mirrors the ASME B89.4.22
specification, but uses known points in the workspace rather than ball
bar gages. The results of this test are reported as the maximum deviation.
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