Optical inspection of stator slots for electric motors

An optical non-contact inspection system was developed for measuring the slots in stator lamination stacks. To avoid passing go/no-go gage blocks through the slots, a machine vision system is instead used to measure the stator core slots and identify the presence of burrs within the slots. Utilizing telecentric optics along with an alignment monitoring system configured to monitor and orient the stator core, the core slots can be oriented relative to the imaging axis for further metrology measurements. Among these measurements, the smallest opening dimensions (slot width and depth) of each slot due to misalignment of laminations and the detection of burrs along the edges of the slots throughout the length of the lamination stack are critical for full stator assembly. Advanced image processing algorithms were developed to obtain sub-pixel accuracy which is required to measure the slots. This, used in conjunction with a robust vision calibration technique, increases the feasibility of building a device that can be implemented as a production inspection system. Experiments show the reliability of the computer vision approach and how it can be used in the inspection of slots in lamination stacks.