Measuring geometries with high aspect ratio and high accuracy: an investigation of 3D-printed micro-optics for optical coherence tomography fibre probes

The gap between the rotor and stator of an axial flux motor for electric vehicles must be measured extremely precisely in order to guarantee a specific distance when assembling the motor. In order to determine the distance of the gap, a freeform micro-optic was designed and printed by means of two-photon polymerization. The optic was printed onto the fibre of an Optical Coherent Tomography (OCT) device. The probe to be used for assembling the electric motors has a diameter of 200 micrometers and a length of 800 micrometers. The results show that when the probe is inserted into a gap, its distance can be determined with an accuracy of less than 1 micrometer. The depth at which the distance of the gap can be determined depends only on the length of the fibre used, so that the 3D-printed fibre probes enable the measurement of geometries with high aspect ratios.