The Key Technology Research And Application Of Mechanical Equipment Dynamic Monitoring Based On Optical Fiber Sensing

The large mechanical equipment is stepping into large-scale, complication, high speed, high efficiency and automatization, which has made great social and economic benefits, but also brings some new issues, especially the change of mechanical equipment state physical quantity showing randomness, multi-dimensional, time-varying, coupling and nonlinear features, then making accidents more abrupt, catastrophic, and social. Therefore, it has been the hot topic and urgent technology to depth perception, intelligent monitoring and fault diagnosis for machinery equipment condition monitoring.Currently mechanical equipment condition monitoring mainly use conventional electromagnetic-type sensors, but such sensors have some limitations such as measuring parameters single, anti-electromagnetic interference capability weak, as well as long-distance signal transmission capacity poor, making application limited in the multi-parameters distributed dynamic monitoring of machinery equipment. Using optical fiber sensing technology for real-time monitoring of the mechanical equipment, there is increasing incomparable advantages than conventional sensors in explosion-proof, anti-electromagnetic interference, heat resistance and high pressure resistance, easier to multiplex network, and suitable for remote monitoring. The mechanical equipment condition monitoring has been studied by optical fiber sensing technology, but mostly in the stage of theory or focus on the static measurement, single content and not systematic. In view of this, this paper undoubtedly has a very important significance to study detection methods and diagnosis system and develop fiber optic sensor for mechanical equipment long-term, dynamic, multi-parameters monitoring.According to the main features of typical parts (bearings, shaft, blades, etc.) in mechanical equipment, on the basis of the analysis of the dynamic characteristics of the respective conditions, this paper systematically researched and proposed dynamic monitoring theory and detection methods based on optical fiber sensing technology; developed a variety of fiber Bragg grating vibration sensors, and then these sensors are applied to the state detection of the machinery.The main contents and conclusions of this paper are as follows:1. Systematically studied the dynamic monitoring theory of mechanical equipment, the dynamics characteristics of the typical components (bearings, rotor and blades) of the mechanical equipment and associated coupling system dynamics are analyzed; combined with the characteristics of dynamic online detection of mechanical equipment and the unique properties of optical fiber sensing technology, proposed a dynamic signal data measuring and processing method based on optical fiber sensor.2. According to the different needs of dynamic monitoring of machinical equipment, two different types fiber accelerometer were developed. The first one is "L" shaped cantilever beam, which belong to wavelength demodulation type high-sensitivity sensor, the frequency detection range of0-60Hz, sensitivity to60pm/m/s2, and acceleration measurement range greater than25m/s2, suitable for low speed heavy equipment; The second is intensity-demodulation high frequency acceleration sensor, which adopts double FBGs matching demodulation and light intensity ratio algorithm to solve problems about the detection frequency not high and the signal intensity instability. The frequency detection range of this sensor was greater than500Hz, so based on this principle, the three-dimensional integrated optical fiber accelerometer was designed, which can be used for vibration measurement of high speed equipment.3. Discusses the feasibility of simultaneous measurement of temperature and torque in a rorating shaft using a dual fiber grating sensor. It shows theoretically that torsion affects the differential-mode wavelength of the gratings in the proposed configuration, whereas temperature changes only the common-mode wavelength, allowing measurement of both torsion and temperature. Thus, the experimental system was set up to carry out static and dynamic experiments of shaft torque and temperature. For the particular system investigated experimentally, the differential wavelength change due to torque was12.88pm/Nm, and the corresponding temperature sensitivity was-1.28pm/℃. In contrast to these values, the temperature sensitivity of the common-mode wavelength change was18.5pm/℃, and its torque cross-sensitivity was-1.25pm/Nm. In the dynamic experiment, shaft torque was tested in different conditions, the results showed that:optical fiber sensing technology can reflect real-time shaft load state, and in-depth analysis of its signal, even analysis some equipment failure such as system imbalance and misalignment fault.4. Studied on-line detection method of crack propagation in the rotating components—a case study of rotating blades. The micro-cracks were processed on the blades using femtosecond laser micromachining technology in order to purpose of fault simulation of blade in the blade state detection, and validated by the finite element analysis and experiment on the authenticity of simulation. The blade-line state detection was taken by combining FBG sensor and fiber optic rorating joint (FORJ), FBG sensors pasted on sensitive parts of the blades detect strain and frequency variations, FORJ is responsible for transferring FBG signal to the demodulation system. The blade strain and frequency variations were used to judge the real time status of blades. Finally the blade crack was studied effects on fatigue fracture and failure rate.5. Discussed the key technologies of dynamic monitoring in engineering applications—taken petrochemical equipment condition monitoring as an example. In the petrochemical industry, the importance of the safe operation of mechanical equipment is particularly prominent. In this paper, the fiber Bragg grating vibration sensor and the condition monitoring system is applied to fault detection of petrochemical machinery equipment. Reciprocating hydrogen compressor as the monitoring object was taken for a long time online measurement and achieved good results on the equipment vibration of crankcase, cross head and cylinder head and temperature variation of valve position. Experimental results confirmed that the fiber optic sensing technology had broad application prospects in monitoring the safe operation of large machinical equipment.