Research On In-situ Measurement Method And Experimental Study For Free-form Surface Of Blade

Blades are the key parts in many power equipment such as aero-engine,steam turbine and marine propeller whose manufacture quality has the decisive effect on the whole machine working performance.After mechanical process there is finishing machining by grinding and polishing.The current finishing process is separated from the measurement,which can hardly realize the high efficiency and high quality finishing machining.Aiming at this problem,the free-form surface measurement,and the in-situ measurement system are being studied combined with blade grinding and polishing machine to improve the efficiency and precision of blade finishing process,which has an important application value.The non-contact in-situ measurement system is developed based on the built machine and existent measurement technology.The system brings the blade surface measurement into the machining process,and can collect the blade surface data without changing the clamping position,which can reduce the positioning error.Three surface data acquisition methods are proposed: dense points,feature points and polar coordinates rotary to adapt to the requirements of different processing stages.The measurement control software is developed and the program interface is designed to realize the automatic measurement of blade free-form surface.The point by point measurement of blade surface involves the problem of measuring points planning.The distribution of measuring points has an important influence on the measurement speed,matching and accuracy.Two measuring points adaptive planning algorithm based on entire surface are studied,centroid method and rectangle subdivide method.Centroid method uses the centroid balance principle,assimilates the curvature index of each point to the mass,determines the measuring points position by iteration.The rectangle subdivide method replaces curved surface with plane according to a setting threshold.Improve the algorithm to make them applicable to free-form curved surface.Make the simulation analysis of measuring points planning on blade surface,to lay the foundation for the feature points method which focus on accuracy and efficiency.The error factors of in-situ measurement system is analyzed,and the result shows the machine motion error,surface color,PLS nonlinear error and tilt angle error have the obvious effects.Topological relationship of moving parts is studied,and develop the machine motion model.Establish the tilt angle error model based on Lambert rule which describes the spatial distribution of scattered light.The error compensation strategy is proposed based on the two error models above.The measured object is the outer and inner arc of aero-engine blade surface.Obtain the point cloud data with high precision scanner,based on which make the measuring points adaptive planning.Design four groups of comparative experiments,in each group,guarantee the same number of points,using feature points method and equal length step method to measure the blade surface.Reverse the measured data to curved surface,and compare it with the point cloud model to compare the accuracy of different measurement methods.The experimental results show that: the built in-situ measurement system has enough accuracy to meet the acquisition of blade surface measurement.The comparative experimental results show that: when measuring method are the same,the more the number of measured points,the higher the precision of the reverse surface;and when points number are the same,the reverse surface measured by feature points method has higher precision,which prove the superiority of feature points method based on points adaptive planning.