Research On Sensing Principle And Key Technology Of Mechanical Vibration Based On Fiber Bragg Grating

Large rotating machinery equipment,such as aircraft engine,high precision machine tools and large-scale steam turbine,is the basic and strategic equipment in national economy and national defense construction.The national security and stable development of national economy are directly affected by them.Therefore,it's very important to real-time monitor mechanical equipment state by some effective detection technologies,which can improve safety and reliability of mechanical equipment and reduce the loss of national economy.Using the vibration signal to evaluate rotating machinery health,which is the most common and effective method.Compared with traditional vibration sensors,fiber Bragg grating(FBG)sensors are resistant to electromagnetic interference,corrosion and high temperature,small in size,light in weight and easy to conduct distributed dynamic measurement.So it develops two new research directions: multi-parameter distribution dynamic test for mechanical system,and offers a new method to measure the mechanical vibration.With the support under national high technology research and development program of China(863 Program)and others projects,it's mainly research on sensing principle and key technology of mechanical vibration based on FBG.The detection of mechanical vibration is considered as application background,it's mainly focus on solving two basic scientific problems: match model between the diversity of mechanical vibration information and distribution FBG sensing signal;relationship between vector characteristics of vibration and multi-dimensional perception mode of FBG sensing.The main work and research achievements are as following:(1)Based on sensing principle and mechanical properties of FBG,it ensures vibration sensing model of FBG.Vibration test methods are based on FBG paste type,FBG axial and transverse vibration sensing model are proposed.The pasted FBG processing criterions are regulated by theory and experiment analysis.Also the axial and transverse continuous vibration equations with concentrate mass are built;on the basis of the previous analysis,their sensing properties are analyzed through theory.It provides the basic guidance for the subsequent design of FBG vibration sensor.(2)Due to the pasted FBG vibration sensing characteristics are easily affectedby pasted processing,it proposes a pasted processing method to enhance the FBG vibration sensor sensitivity,which is validated by the theory,simulation and experiment.Based on medium and high frequency vibration signals testing requirements for rotating machinery,it develops a diaphragm FBG vibration sensor based on the axial vibration characteristic of optical fiber.The relationship between sensing properties and design parameters of sensor structure is set by numerical analysis method,and finall an experiment difference method is used to eliminate the thermal load effect for FBG.(3)For vibration properties of rotating machinery rotor,a non-contact FBG vibration testing method has presented,which is designed by magnetic coupling principle,diaphragm and FBG sensing.The sensing characteristics of sensor are studied by vibration experiment system.Theoretical model is optimized through theoretical-experimental-theoretical mutual correction method,as well as the sensing characteristics are estimated by the modified sensor model.It can be used to real-time monitor vibration of shaft in the harsh environment after dual differential temperature compensation.(4)Based on the horizontal and axial vibration properties of optical fiber,a two-dimensional decoupling method based on dual FBGs is proposed,which is considered as the basic principle to design the distributed two-dimensional FBG vibration sensor.The decoupling principle and theoretical model of sensor are verified by numerical simulation and experiment.Combing the previous decoupling principle and redesign the mechanical structure,a new detection method for three-dimensional vibration based on FBGs is presented,and the well decoupling results are ensured by some experiments.It develops the transverse vibration sensitivity optimized model through adjusting weight of mass and pre-stress.In order to measure high frequency vibration signal and come over overload damage,improved two-dimensional FBG vibration sensor is proposed through reinfored beam/string,which is parallel fixed with fiber.Finally its validity has proved by experiment.(5)The vibration measurement for the rotating machinery is conducted through the designed vibration sensors in the previous dissertation.First of all,the eddy current sensor is considered as the measurement reference,the measured signal'seffectiveness of non-contact FBG vibration sensor is esured by eddy current sensor,which is the measurement reference,and the extracted shaft critical speed of non-contact FBG vibration sensor is consistented with eddy current sensor.Secondly,constructed FBG vibration monitoring network based on the above designed FBG vibration sensors to measure vibration of rotating machinery through distributed characteristic of optical fiber.Finally a real-time vibration monitoring system based on non-contact FBG technology is set up for the low speed balance test platform in Yangtze River power Group Company.