Positional uncertainty in optical-based metrology systems in large volume manufacturing

Modern manufacturing increasingly utilizes automated systems for component positioning and assembly and a vital aspect of autonomous precision manufacturing is large volume metrology. One popular approach uses light rays, which travel through the volume of air, to calculate the position of an object of interest. These optical-based metrology systems such as photogrammetry and laser tracking are crucial in improving the accuracy and quality associated with robotic assembly. However, in an industrial setting, these positional measurement systems give rise to uncertainties which can in many instances be greater than the required tolerances. One source of this uncertainty is light refraction due (in part) to temperature fluctuations in the air. This paper will describe how COMSOL Multiphysics can be used to create simulated data with complete ground truth on the refractive index field in the volume, and will discuss the measurement uncertainties associated with these simulations. Over industry relevant distances (tens of metres) the uncertainty in the position measurement due to light refraction is of the order of a millimetre.