Appendix A Polaris Vicra Calibration Performance And Methodology; Polaris Vicra Performance; Calibration Method - Northern Digital Polaris Vicra User Manual

Appendix A Polaris Vicra Calibration Performance and Methodology

Standard industry practice dictates that all measurement and testing instruments should be
periodically calibrated to ensure they are operating within tolerances acceptable to the user and/or
the user's customers.
The user must establish a calibration procedure and interval that is appropriate for the accuracy
requirements of their application.
The Position Sensor is a highly specialized instrument developed exclusively by NDI. For all
calibration procedures, return the Position Sensor to NDI. This practice ensures that all calibrations
are conducted in accordance with procedures established specifically for the Polaris Vicra Position
Sensor.
Note
The NDI Accuracy Assessment Kit (AAK) can be used in the field as an aid to determine whether a Position
Sensor is performing acceptably for the user's application.
If, at any time, a concern should arise that the Position Sensor is not measuring accurately, it should
be returned to NDI.
Note
The calibration procedure at NDI applies to single markers and cannot be directly applied to an application that
uses tools with several markers.
A.1

Polaris Vicra Performance

The Polaris Vicra System performance is determined by a statistical analysis of the 3D Euclidean
distance error between the reported position of an NDI marker and its true position, based on
measurements taken throughout the entire Polaris Vicra System's measurement volume. Acceptance
criteria for the Polaris Vicra System's performance are based on the RMS values of the accuracy and
repeatability.
The 3D RMS volumetric accuracy acceptance criterion is less than or equal to 0.25 mm, based on
a single marker stepped through a statistically representative set of positions throughout the
measurement volume, using the mean of 30 samples at each position at 20°C.
The 3D RMS repeatability acceptance criterion is less than or equal to 0.20 mm, based on total
samples of a single marker stepped through a statistically representative set of positions throughout
the measurement volume, using 30 samples per position at 20°C.
A.2

Calibration Method

The following method is used to calculate the Polaris Vicra System's accuracy and repeatability:
An NDI marker is accurately moved to each of n locations (X
measurement volume. The mechanism that moves the marker is assumed to have an accuracy that is
at least 10 times better than the measured accuracy of the Polaris Vicra System. This assumption
allows the errors in the marker positioning to be ignored.
At each of the n locations, the Polaris Vicra System takes m readings of the marker's 3D position
(x , y , z ).
ij ij ij
Polaris Vicra User Guide - Revision 2
Polaris Vicra Calibration Performance and Methodology
, Y , Z ) spread throughout the
i i i
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