Spatial Variance
Mechanical inaccuracies in the commanded versus actual location of a translation stage define the precision limits of an inspection system. This gap arises from friction, backlash in the lead screws, component fatigue or thermal deformation of the metal components.
Motion Uncertainty
Repeatability and accuracy represent the two primary components of the total displacement variance. A stage might return to the same location consistently while still remaining offset from the absolute coordinate required by the system. Lead screw pitch errors or non-linearities in the motor drive contribute to the positioner positioning error during multi-axis movements.
Because 3d imaging relies on precise alignment of dozens of individual frames, even small mechanical deviations degrade the quality of the final volumetric data.
Calibration Requirement
Laser interferometers or high-precision glass scales provide the data needed to map the stage movement and create a correction table. Compensation software uses this map to adjust the motor pulses and bring the physical carriage into alignment with the digital grid. If the positioner positioning error exceeds the pixel size of the detector, the resulting images lack the sharpness needed for solder joint analysis.
Frequent verification of the stage health maintains the integrity of the automated defect recognition software. While a controller may send a signal for a specific coordinate, positioner positioning error describes the physical distance between that requested point and the center of the x-ray beam.
