LAUSR

Dynamic and accurate measurement of instantaneous rotational speed is desirable in many industrial processes for both condition monitoring and safety control purposes. This article presents a novel imaging-based system for instantaneous rotational speed measurement. The low-cost imaging device focuses on the side surface of a rotating shaft without the use of a marker, entailing benefits of noncontact measurement, low maintenance, and wide applicability. Meanwhile, new periodicity determination methods based on the Chirp-Z transform and parabolic interpolation-based autocorrelation algorithm are proposed to process the signal of similarity level reconstructed using an image correlation algorithm. Experimental investigations are conducted on a purpose-built test rig to quantify the effects of the periodicity determination algorithm, frame rate, image resolution, exposure time, illumination conditions, and photographic angle on the accuracy and reliability of the measurement system. Experimental results under steady and transient operating conditions demonstrate that the system is capable of providing measurements of a constant or gradually varying speed with a relative error not greater than ±0.6% over a speed range from 100 to 3000 revolutions per minute (r/min). Under step-change conditions, the proposed system can achieve valid speed measurement with a maximum error of 1.4%.