Automated magnetic inspection of permanent magnet rotors

We report on the development of a magnetic inspection station for permanent magnet rotors, based on the established magnetic field camera technology, which uses high density two-dimensional Hall sensor arrays for fast high-resolution measurements of magnetic field distributions. The high speed of the system allows measuring the radial field distribution of a rotor in a few seconds with high axial (0.1mm) and angular (0.1°) spatial resolutions. The resulting 2D field distribution contains a lot of information about different important magnetic properties of the rotor, which are extracted using proprietary data analysis software. This analysis results in quantitative values for properties such as polarity identification, statistical analysis of the field distribution, north-south pole asymmetry, pole size measurement and analysis, pole peak uniformity, total magnetic flux, localized magnetization defects and localized material defects. It is argued that modern permanent magnet machines need innovative magnetic inspection solutions such as that described in this paper.