Research On Plastic Optical Fiber Vibration Sensor For Helicopter Tail Shaft Health Monitoring

With the development of sensor detection technology and the enhancement of comprehensive processing power of computers,the greenization and intelligence of helicopter technology are constantly being improved.The helicopter health condition monitoring system is a remarkable symbol of its remarkable development,the transmission system is one of the main monitoring and management objects of the health condition monitoring system,the tail shaft is the main part of the transmission system,which is very important for its health monitoring.The main work of the tail shaft is high-torque rotating tail rotor with tail rotor.Vibration is the inevitable main feature in its working process,the application of optical fiber sensing technology in aircraft is more and more widely.In this paper,an intensity modulation type reflective optical fiber vibration sensor has been proposed for the vibration monitoring of the tail shaft.Due to its low cost,small size,flexible design,demodulation and other advantages of convenience,it is widely used in various fields.The main contents of this paper are as follows:(1)Based on the application and development of health monitoring system in helicopter technology and the research status of the working characteristics of this system and tail transmission shaft in China,combining with the analysis of the working characteristics of the helicopter and the tail shaft and the requirements of the environment measuring sensor,this paper has presented the sensor structure and research significance.(2)The tail shaft of the helicopter is made up of a couple of shafts connected by a coupling,which has been simplified into a rotating shaft composed of a plurality of two fixed fulcrums,and the vibration characteristic analysis has been carried out.The theoretical model of the intensity distribution of the outgoing light field at the fiber end face and the theoretical model of the coupling optical power of the receiving fiber have been established.The intensity distribution of optical fiber end face has been simulated and analyzed,and the received optical power of single fiber has been calculated.The influence of received fiber radius and numerical aperture on received optical power has been analysised.A simulation experiment has been carried out to simulate the vibration of tail shaft of helicopter with eccentric disc and the theoretical analysis and calculation have been carried out.(3)The sensor device for measuring the vibration of the tail shaft have been designed and manufactured.The photoelectric conversion system and the signal acquisition software and hardware have been designed.The optical and coupling metal module different from the optical fiber coupler from the view of the application status of the plastic optical fiber have been designed and adopted.In order to get a better signal output,a shielding module to reduce electromagnetic interference have been designed and manufactured.In order to real-time data acquisition,storage and communication with the computer functions,data acquisition hardware circuit and software programming have been designed,this article has prepared the one-chip computer software programming and the upper computer programming based on Labview.(4)The use of 1mm diameter plastic optical fiber has produced a reflective vibration sensor,this article has investigated through experiments the applicability of the intensity modulation type reflective fiber optic sensor to measure the vibration characteristic parameters,an experimental platform to simulate the vibration of the tail shaft of helicopter has been designed and built.The simulation of the tail axis vibration experiment has been carried out by using aluminum foil as the eccentric reflection edge of the disc.The plane mirror as the reflection surface,the displacement in the 0～1100μm measurement range,the sensitivity is 1.3mV/μm,aluminum foil as the reflective surface,the displacement in the 0-1500μm measurement range,the sensitivity is 1.31mV/μm,in the simulated vibration experiment,the relative standard deviation of the amplitude at the eccentricity of 0.5mm is 0.047226,the relative standard deviation of the frequency at the voltage of 8 V is 0.01194,the relative error of the amplitude is 2.8901%.The amplitude and frequency measurement of the simulated tail axis vibration experiment are realized.