High-Resolution and Real-Time Embedded Ultrasonic Monitoring System for Lubricating Film Thickness in a Roller Bearing

The lubricating film provides both load support and friction resistance in roller bearings. Hence, thefilm property critically affects the reliability of the bearing,and monitoring the film thickness in real time is essential for proper operation. This is commonly approachedby employing ultrasonic systems that enable noninvasivemeasurements. However, the effectiveness of the measurement is limited by low signal resolution and computation efficiency. These constraints can be traced to theexcitation circuit design and the complicated data processing routines. To tackle these problems, an embeddedmeasurement system is developed in this work. First, thedependence between pulse parameters and piezoelectrictransducers is derived, and a customized circuit for ultrasonic pulse transmission/reception is designed. The relative computation errors caused by circuit interference aremaintained below 40.4 nm. Moreover, an in situ localizationalgorithm capable of extracting ultrasonic signal of contact regions (SCR) is proposed to improve the resolutionin measuring the dynamic lubricant distribution. Finally,a dedicated FPGA architecture is developed combiningboth asynchronous dataflows and multichannel pipelines,achieving microsecond-scale computation efficiency undera maximum pulse repetition frequency of 125 kHz, whichcan match a linear velocity of 13.7 m/s, correspondingto 6932.6 r/min of inner rings and a nominal diameter of450619 mm· r/min. Moreover, in situ experiments with aroller bearing demonstrate that SCR of 54.9 µm width canbe accurately captured. Furthermore, the lubricating filmthickness can be calculated within 7 µs. These resultsdemonstrate that the proposed system is able to providein situ monitoring of lubricating film thickness in rollerbearings.