ORBIT FR Field Probes - Manual (Page 9)

Field Probes
Obtaining Best Results When Using An Aperture Field Probe
When scanning with an Aperture Field Probe, as the probe moves
along the linear axis, angular movement may occur in the carriage
roll axis due to gear compliance. The torque applied on the gear
increases as the load moves away from the center. This angular
deviation can be observed and read by the synchro or incremental
encoder of the positioner.
In order to obtain accurate positioning data, it is necessary to
monitor the roll angle Q, because it may change as the probe
moves away from the center (see drawing).
The probe position is given as (R,
 ) in polar coordinates, where
R is the probe distance from the center of rotation and  is the roll
angle. In Cartesian units the following transformation applies:
X = R Cos 
Y = R Sin 