Study Of Techniques Of Measuring The Diameter Of Rotating Object Using Laser Doppler Effect

The laser Doppler Effect (LDE) is extensively applied in the parameters measurements of gas, liquid and moving surface of solid, etc. and the LDE based measurements has been developed very rapidly in recent years. The diameter measurement accuracy of the rotating objects is not high enough at present, which can not meet the needs of the industry production. A LDE-based new method of measuring the diameter of rotating cylinder has been put forward in this thesis, and the signal demodulation has been performed by use of both the optical heterodyne detection and the frequency measurement with counter.First, according to the LDE principle, the theoretical expression of an optical system of dual-beam with dual-scattering (DBDS) is derived in this thesis. On the basis of the theoretical calculations, the optical system has been designed and the parameters of the optical components have also been determined. According to the principle of the optically heterodyne detection, the expression of phase conditions of optical heterodyne detection in the DBDS optical system has been derived, the optically heterodyne detection system has been set up, and a pin-hole has been chosen according to the calculation result.Secondly, the main circuits of the signal demodulation have been designed which include I/V conversion, amplification, waveform transformation, frequency division, frequency measurement and display units. The theoretically and experimentally obtained results have shown that the measuring system can be used to measure of the diameter of the rotating cylinder, with a measurement range is from 5mm to 800mm and an accuracy of approximately 0.08mm.Thirdly, the error analyse have been performed for the measuring results considering the various error sources. The influencing factor of Doppler broadening is discussed in detail when measuring the solid moving surface. A specific factor of Doppler broadening, namely, solid surface shape broadening factor, is introduced when the LDE is used to measure the moving non-planar surface. At last, an improvement scheme of the measuring system is given.