Image processing for calibrating a coordinate measurement set-up

Image processing was used to efficiently calibrate a measurement set-up composed of multiple translation and rotation stages, and a sensing element fixed to a cantilever. Using the dimensions of individual devices to estimate the sensor position proved tedious: positioning and alignment errors between components accumulate and some physical dimensions are unknown or hard to measure. Defining a coordinate mapping via image processing seemed a convenient alternative and indeed typically yielded a measurement accuracy of less than 220 µm pixel width. The measurement rig was used to gather the magnetic field data of circular paths in a plane around electric conductors with a variety of cross-sections. To be of use in subsequent analysis steps, measurements had to be mapped by the calibration above onto both a cylinder and a Cartesian coordinate system. Additional error sources not accessible to visual inspection were identified when a calibration rod was measured. Correction of these errors completed the data preparation. As a proof of the concept, the centroid location and the integral current—two basic parameters of the current density which caused the magnetic field readings—were computed.