Non-Contact Ultralow Rotational Speed Measurement of Real Objects Based on Rotational Doppler Velocimetry

Rotational speed measurement has increasingly become an important requirement both in the industrial and aerospace fields. This article presents a technique for rotational speed measurement based on the non-contact optical method by using superposition vortex light. To the best of our knowledge, for the first time, we realized the ultralow rotational speed measurement as low as 0.001 r/s with high accuracy based on real rotating objects. By using an optical vortex (OV) with a large topological charge up to ±65, the rotational frequency is magnified significantly. The detection system proposed in this article has a simple structure and non-contact features, including a transmitter, a receiver end, and a control and signal processing unit. Depending on the rotational speed of the target, the different sampling time is used to achieve near real-time speed acquisition. The experimental results suggest that the measurement result of the rotational speed has nothing to do with the receive angle of the receiver, and different receive distances only affect the intensity of the signal. An autocorrelation algorithm is designed which can effectively improve the signal-to-noise ratio of the detection signal. At different rotation speeds, the experimental results are in good agreement with the theoretical value. Our work fills the margin of the ultralow rotational speed measurement of RDE, and the related technique in this article may be useful in the precision mechanical testing and spatial instability targets sensing.