A high-accuracy non-contact online measurement method of the rotor-stator axial gap based on frequency scanning interferometry

Abstract

Rotor-stator axial gap is a key design parameter that directly affects the efficiency and safety of large rotating machines. With optimum axial clearance value determined, the rotating machine can work with the highest efficiency. To realize active clearance control (ACC) of rotating machinery, high-precision non-contact online measurement of the axial gap must be carried out. However, traditional measurement methods are challenged by the extreme working environment, such as extreme temperature, high rotating speed, and narrow space conditions; no mature measurement method was reported to realize the high accuracy, non-contact, and online performance required by the axial gap measurement. In this paper, a rotor-stator axial gap measurement method is proposed based on frequency scanning interferometry, and the mathematical model of axial clearance measurement is established. The weak reflection signal of lens and time delay estimation algorithm is employed to undermine the impact of probe pigtail length drift caused by the temperature change under extreme conditions. The axial gap measurement prototype based on sweep frequency ranging was developed, and the measurement and system calibration was carried out. The experimental results verify the effectiveness and accuracy of the method. The drift of the system was less than 20μm in 30 minutes with millimeter level pigtail drift, and the measurement accuracy was better than 50μm.