Study On Profile Evaluation Of Free-form Surface Of Propeller Blade

With the world's countries to further accelerate the pace of Marine development,China is attaching more and more importance to the development of ship and Marine structure manufacture.As a typical free-form surface part,the machining quality of propeller blades directly affects the working performance of ships and offshore structures.Existing methods are difficult to evaluate the profile error of propeller blade free-form surface with high efficiency and accuracy.In response to this question,the paper focuses on the digital evaluation method for the profile error of propeller blade free-form surfaces with high efficiency and high accuracy.The main research contents are as follows:(1)Research on Data Processing for Measuring Discrete Point Cloud.Firstly,the laser probe of the CMM is used to obtain the discrete point cloud data on the surface of the propeller blade.Secondly,the mixed simplification algorithm is used to process the measured surface discrete point cloud data,and then the holes in the processed discrete point cloud data are completed.Next,the completed data is smoothed by filtering.Finally,the least square method is used to pretreat the reduced discrete point cloud data set.(2)Research on the error evaluation model of AVG(Adapted Virtual Gauge).Using the theory of small displacement rotation to describe the motion state of measuring point set data under AVG boundary.Combining with NURBS method to create AVG boundary,then,the matrix rank is used to determine the motion termination condition of the AVG boundary.Finally,the contact point as the termination condition is taken into the segmentation approximation method to obtain the minimum distance between the contact point and the measured surface.So as to realize that the error of profile of free surface of propeller blade is evaluated by using AVG.(3)Analyze the uncertainty of measurement evaluation.Analyse the factors of uncertainty in measurement and evaluation.Then,according to the self-adaptive virtual gauge profile error evaluation model and uncertainty propagation law of free surface of propeller blade,a method for estimating the uncertainty of propeller blade free-form surface profile error to satisfy the minimum region condition is obtained.(4)Experimental verification.The feasibility and effectiveness of the contour error evaluation method and the uncertainty estimation method proposed in this paper are verified by the measurement experiment of the actual propeller blade parts.Finally,it is shown that the proposed method is feasible and effective by the experimental results.