Research On Fiber Tip-timing Sensor

Aircraft engine plays a very important role in aeronautical industry,while the engine blade is the most prone to malfunction when it is running.The engine blade is easy to vibrate under the action of various complicated exciting forces.The real-time and on-line vibration detection of the engine blade is an important guarantee to ensure the safe operation of the engine blade.At present,the most widely used and the most popular vibration measurement technology is the tip-timing method,which monitors the blade vibration by accurately extracting the time when the blade reaches the sensor.In this method,only a small number of tip timing sensors are installed on the casing to realize the non-contact measurement of the vibration of the whole blade.At present,the measurement accuracy of this method is mainly affected by the precision of the time of arrival of the extracted blade.The traditional method of extracting time is mainly to set the trigger threshold to extract the time of arrival of the leaf.However,the time signal of the tip of the blade is affected by many factors.For example,the change of tip clearance,the influence of tip surface roughness,circuit noise and optical path noise which can make the extraction of blade arrival time inaccurate.In this paper,a new method of blade arrival time is presented,which is based on the microstructure of tip surface.By machining the tip surface of the blade,the one-dimensional micro-surface with characteristic structure is formed.The scattered light signal of the microstructure surface is collected and compared with the pre-calibrated signal.Then the algorithm calculates the time of arrival of the blade.Instead of relying on a single or several trigger signal,the method extracts time by processing the whole characteristic scattered light signal,which can effectively reduce the error caused by the random signal jitter that originating from the gap change,tip erosion,and rough blade tip surface,greatly improves the precision of tip timing and the stability of the system.This paper focuses on the accuracy of blade tip timing.Firstly,the main structure of the tip timing system is introduced.The tip fixed timing probe,photoelectric conversion circuit and tip-timing algorithm are described respectively.Then,the characteristics of the tip timing signal,the main factors affecting the tip timing signal are analyzed and the current mainstream timing methods and their errors are analyzed.After that,a new timing method based on the micro-structure of the tip surface is proposed,and a series of studies on the feasibility and superiority of the new method are carried out.Secondly,the surface scattering characteristics of the characteristic microstructures are studied by simulation,and it is proved that the scattering light carries the characteristic micro-structure topography information.The scattering characteristics of different machining methods and different roughness surfaces are tested through experiments,so that the most suitable processing methods and geometric characteristics of machining are found out.The precision of extracting the time of arrival of the blade by using the tip microstructure is tested by using the set up tip timing system.It is proved that the tip timing method based on the microstructure of the tip surface has obvious accuracy advantage in resisting the change of the gap and the circuit noise compared with the method of the threshold trigger.Finally,the tip-timing signal with characteristics of the rotating blade was texted by using the rotating test system.When the blade has no vibration at low speed,the timing time of the thick blade is measured and the error of the rotating system is calibrated.The vibration of the thin blade was measured by using the timing method based on the microstructure of the tip surface.The experimental results were compared with the results of the finite element simulation and the true vibration frequency of the blade was analyzed and calculated.