| Blades are key components of aeroengine,and its geometry,position and attitude have a great influence on the aerodynamic performance of aeroengine.Blades have characteristics of complex profile,thin shape,serious twist and wide curvature change,which cause many difficulties to measurement.So the measurement and evaluation of blades have important significance and theoretical value.The existing technologies are generally applicable to blades with geometric model and design parameters and defective in measurement accuracy and quality characterization,which can not meet the needs of precision engineering.However,in scientific research and industrial practice,the measurement and evaluation of blades without nominal information has always been a significant demand.In this dissertation,the key technologies of high-precision measurement and three-dimensional quality evaluation for blades without geometric nominal information are researched around the measurement accuracy,model reconstruction algorithm,quality characterization method,error evaluation theory and so on,and the technical problems are solved.There are two research objectives in this study.The first objective is solving the problem of form-free acquisition of geometric information for blades,that is,automatically accomplishing high-precision and efficient acquisition of profile data without theoretical model data and attitude fine-tuning of the blade.The second objective is solving the problem of form-free evaluation of geometric information,that is,automatically accomplishing parameter calculation and profile quality evaluation of blades based on self-construction of blade theoretical model and research of error evaluation algorithm.The research contents of this dissertation further deepen the theory of blade measurement,which are of great value to improve the accuracy,flexibility and intelligence of blade measurement.The research contents of this dissertation are as follows:(1)Research on measurement system for aeroengine blades based on form-free thought.The overall technical scheme of form-free measurement system for aeroengine blades is designed,and the mechanical basic machine and motion control system of are designed and analyzed.A form-free high-precision probe system based on “Synchronization of Planning and Measurement” and a novel blade fixture based on adjustable dovetail groove structure are developed.The overall structure and workflow of form-free measurement software for blades are analyzed,and the form-free measurement software of Pblade 1.0 is developed.The results show that the form-free measurement system for blades is developed based on the technologies of precision shafting,roller guide,high-precision grating and loop-locked digital motion control.The comprehensive accuracy reaches 10 μm level,which can meet the technical requirements of form-free measurement of blades.(2)A form-free high-precision method for blade measurement based on “Synchronization of Planning and Measurement” is studied.The principle of form-free measurement based on “Synchronization of Planning and Measurement” is analyzed,the accuracy model of the method is derived,the error control principle of the method is expounded,and the key technologies of “Synchronization of Planning and Measurement” are researched in detail,including model analysis of coordinate system,measurement and transformation of coordinates,establishment method of workpiece coordinate system based on least squares principle,dynamic path planning method based on piecewise normal linkage,etc.The results show that the measurement for blade profile is executed automatically based on “Synchronization of Planning and Measurement” without theoretical model data,and the comprehensive measurement error is no more than 10 μm,which can meet the measuring requirements of aeroturbine blades with first precision grade.(3)A reconstruction method of blade theoretical model based on feature recognition and parametric modeling is proposed.The spectrum of blade parameters is summarized and condensed,and the self-construction principle of blade theoretical model based on parametric modeling is expounded.The parametric model of twodimensional blade profile is derived based on mathematical analysis and feature modeling technology,the parametric modeling program of two-dimensional blade profile is developed with VC++ 6.0 software.A parametric modeling method of threedimensional blade surface based on feature recognition is proposed.The change rules of blade profile parameters along the direction of blade height are extracted based on the least squares fitting algorithm of quartic polynomial,and the parametric models of each profile are solved discretely,then the three-dimensional theoretical model of blade surface is constructed.The results show that the self-construction method of the blade theoretical model proposed in this paper is effective.The blade modeling is automatically executed by inputting blade parameters,which lays the foundation for the form-free evaluation of the blade.(4)The characterization and evaluation technology for 3D quality of blade is analyzed,and the principle and method of 3D quality evaluation of blade based on form-free are proposed.The accuracy index system for 3D quality characterization of blade is summarized and condensed,and the blade is synthetically characterized and evaluated in three-dimensional space with two-dimensional profile parameters,spatial torsion parameters and surface profile parameters.A fast extraction method of blade profile parameters based on coordinate transformation is proposed,the extraction algorithm of blade profile parameters in parametric coordinate system is derived,the coordinate transformation model and the solution method of chord angle and origin of parametric coordinate system are analyzed,and the measurement software of blade profile parameters is designed.Thus,the fast and accurate extraction of twodimensional blade profile parameters is achieved.The form-free measurement and evaluation methods of parameters,such as profile camber angle,2D blade profile,blade twist and 3D blade surface profile are studied,and the technical problems of characterization and evaluation for three-dimensional quality of blades are solved.(5)Experimental study and analysis.The accuracy of the measurement technology and evaluation method is verified by the experimental study of form-free measurement method for blades based on “Synchronization of Planning and Measurement” and the three-dimensional quality characterization and evaluation method of blade. |
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