PCIAS: Precise and Contactless Measurement of Instantaneous Angular Speed Using a Smartphone

Measuring Instantaneous Angular Speed (IAS) of rotating objects is ubiquitous in industry and our daily life. Engineers diagnose the operation condition of engines with IAS. Anemometers obtain instantaneous wind speed with the IAS of rotating cups. Traditional IAS measurement systems have their limitations in the aspects of installation, accuracy, and cost. In this paper, we propose PCIAS, a system that uses acoustic signals of a smartphone to measure IAS of rotating objects in a contactless manner. PCIAS covers a pretty large IAS measurement range (the numerical interval of IAS) from 10 Revolutions Per Minute (RPM) to 10000 RPM, which outperforms almost all existing Commercial-Off-The-Shelf (COTS) IAS meters. In PCIAS, we first choose an appropriate measurement range according to applications. We then use the smartphone to collect acoustic signals backscattered or generated by the object. Next, we extract acoustic features of the object to eliminate interferences from the environment. After that, we propose a robust tracking algorithm to estimate IAS by matching cycle time length of acoustic features adaptively. We build two testbeds to evaluate the accuracy and the robustness of our system in different IAS ranges. Our experiments show that PCIAS achieves a relative accuracy of more than 92% in the low IAS range, more than 94% in the middle IAS range, and more than 96% in the high IAS range. Finally, We exhibit two typical cases to demonstrate the practical use of our system.