Contactless In-Line Fan Quality Inspection by a mmWave FMCW Radar: Insights on the Use of Displacement Measurements

In-line quality inspection processes are of crucial importance in verifying and maintaining a production site's performance, both in terms of production conformity and timely delivery. During the fabrication process, defects and imperfections can occur, and the affected manufactured parts must be identified and discarded, if necessary. The method used to perform this operation must be both reliable and fast, so as not to add excessive delays in the production process. To improve the inspection speed, contactless methods are preferred by companies, as they do not involve the application and removal of probes on the device under test (DUT). In such an application context, this article explores the performance of a measurement method based on the use of a mmWave radar sensor for contactless quality inspection. The DUT is an industrial fan, and displacement measurements are used to derive its rotation speed and main vibration harmonics. The results are validated by comparison with reference rotation speed and vibration measurements. Experiments show that using the radar-based method, the measured displacement is representative of the vibrations occurring in the central part of the fan and provides a relative percent error in the evaluation of the rotation speed of 3%, compared to the 1.6% obtained using piezoelectric accelerometers. The influence of the radar's transmitting antenna radiation pattern on the displacement measurement is also experimentally demonstrated.