Study Of Tip-timing Method Vibration Monitoring Based On Fiber Bragg Grating Magnetic Coupling Sensor

Ventilator is one of the key equipment in coal production and has been vividly called "the lung of mine". The rotating blades are the core parts of the ventilator. Excessive blade vibration has serious impact on the safety and reliability of ventilator. Because the ventilator blades usually work in harsh environment with high dust, and greasy dirt, so the existing sensor is difficult to meet requirement of blade vibration real-time online monitoring. In this paper, a tip-timing method based on fiber Bragg grating magnetically coupling sensor is proposed to study and analyze the ventilator blade vibration, aiming at realizing long-distance and non-contact real-time online security monitoring of blade vibration. Compared to the electronic sensors and fiber intensity reflective sensor, fiber grating magnetic coupling sensors have advantages such as explosion-proof, able to work in harsh environment with humid air, full of dust and greasy dirt, capable of achieving long-distance signal transmission, joining together easily with other fiber Bragg grating sensors to form a network in order to achieve multi-parameter distributed online monitoring.Aiming at the approach proposed, confirmatory experimental study is carried out. The major work which has been done currently includes the following aspects:(1) Blade vibration mechanism and three main parameters, vibration stress, vibration mode and natural frequency, which reflect the blade vibration are studied. Take this as the foundation, the theoretical formula for calculating the static frequency and dynamic frequency are presented, which lay a theoretical foundation for successive research of sensors used to monitor blade vibration.(2) On the basis of the predecessors’ work, a kind of sensor combining fiber grating and magnet probe has been invented and is used as the tip-timing sensor. According to the synchronized conversion theory of tip timing sensor signal, the time signal corresponding to the maximum of the fiber Bragg grating center wavelength fiber grating is the time impulse signal demanded when blade reaches the tip-timing sensor. The maximum value of fiber Bragg grating center wavelength is only used as a threshold. This demonstrates the feasibility of using this sensor as the tip-timing sensor for mine explosion-proof ventilator blade vibration monitoring.(3) Modal analysis is carried out toward the structure of fiber Bragg grating magnetic coupling sensor and the first ten modes to which the theoretical natural frequency corresponding are obtained. The analysis of the each vibration mode of sensor is committed from the first mode. Then it can be found that the third-order modes diaphragm driven by a fiber Bragg grating along the axial vibration of magnet probe, corresponding to the theoretical natural frequency79.5Hz this article required parameters.(4) Through the actual vibration experiments, it’s found that natural frequency of the sensor is about85Hz. Through static displacement experiments and speed experiments, the appropriate distance range between the magnet probe and the measured blade is set as2.5mm～4mm when sensor is mounted. Normal blade vibration experiment and damaged blade vibration in which17mm by1mm crack exists are done respectively. The comparative analysis of two sets of blade vibration data under831r/min normal blade vibration experiments of four blade amplitude of0.339mm, the damaged blade vibration amplitude to1.372mm and its180-degree angle blade amplitude is0.339mm, the other two blades the amplitude is0.248mm. By comparing the results of data analysis, it can be found that using this approach to monitor blade vibration is feasible.