Method For Coaxiality Measurement Of Low-pressure Turbine Shaft Of Aeroengine Based On Multi-bias Error Separation

As "the most dazzling pearl in the crown of industry",aeroengine is one of the key research fields of “Made in China 2025”.The low-pressure trubine shaft is a key component that throughout the entire aeroengine multi-stage rotor system and ensure coaxiality,which has the characteristics of a large length-to-diameter ratio and is a typical elongated step shaft.Due to its special structure,mult-bais errors of the measurement system such as eccentricity,tilt,probe offset,etc.are introduced and transmitted,coupled with each other and amplified,seriously reducing the coaxiality measurement accuracy,causing severe vibration of the aviation engine,shortening failure time and life.Therefore,it is urgent to study the measurement method for coaxiality of aeroengine low-pressure trubine shaft to improve the measurement accuracy.Aiming at the problem that system errors affect the measurement accuracy of low-pressure turbine shafts,this paper proposes a coaxiality measurement method based on multi-bias error separation.This method obtains "pure" surface data by establishing the cylinder profile measurement and error separation model.On this basis,non-equispaced morphological filter and intelligent evaluation algorithm are proposed to realize the accurate measurement of coaxiality of low-pressure turbine shaft.The main research contents include:Firstly,aiming at the principle defects of the traditional measurement model,the measurement model of cylinder profile with multi-bias error is established.Based on the structural characteristics and measurement technology of low-pressure turbine shaft,the multi-error sources of coaxiality measurement are identified and the influence mechanism is analyzed,and a seven-bias error measurement model is established.Based on the traditional model,the influence law of the bias errors on the cylinder profile measurement and the influence law of the combined effect of bias errors,profile radius and sampling height on the cylinder profile measurement are analyzed.Simulation results show that the model is more effective for measurement with larger bias errors,larger sampling height,and smaller profile radius.Secondly,aiming at the principle defects of the linear estimation method,a multi-bias error separation method based on parameter estimation is proposed.This method is based on the coupling relationship between the errors,and uses the feature recognition method and the downhill simplex(N-M)algorithm to achieve the order estimation and separation of the verification parameters,cross-sectional parameters and spatial parameters.The simulation results show that when the eccentricity error is 30 ?m and the workpiece height is 900 mm,the estimation accuracy of the eccentricity error is improved by 0.71 ?m,the measurement accuracy of the error is improved by 57.88%.Thirdly,in order to realize the effective processing of the low-pressure turbine shaft surface data,a non-equispaced morphological filter and coaxiality assessment algorithm are proposed.Aiming at the problem of non-uniform distribution of actual sampling angles,combining morphology and envelope extraction(alpha shape)theory,non-equispaced three-dimensional morphological filter method is proposed.Compared with equispaced filter,the coaxiality measurement accuracy is improved by 2.34 ?m.Based on the principle of genetic algorithm and support vector regression algorithm,two coaxiality intelligent evaluation methods are proposed.Compared with the least square method,the coaxiality measurement accuracy is improved by 0.48 ?m and 0.41 ?m,respectively.Finally,based on the super-large coaxiality standard equipment,experimental verification of the coaxiality measurement of aeroengine low-pressure turbine shaft was carried out.The experimental results show that,compared with the traditional measurement method,the measurement method in this paper can obtain more accurate coaxiality.The measurement accuracy of the coaxiality standard with a length of 1000 mm is increased by 28.14%,and the measurement accuracy of the coaxiality with a length of 1500 mm is improved by 27.41%,verifying the effectiveness of the coaxiality measurement method of the low-pressure turbine shaft based on multi-bias error separation for improving the accuracy of the coaxiality measurement.Finally,taking the coaxiality standard with a length of 1500 mm as an example to evaluate the uncertainty,the measurement result is(12.79 ± 0.45)?m.