Study On Measuring Method Of Surface And Measuring Simulation

According to the mathematics model,the surface can be classified to conventional surface or free surface.According to the features of measured surface,the surface can also be classified to surface known CAD model or surface unknown CAD model.The measurement of surface is the base of precision verifying or reverse CAD model.The application of Three-Coordinate Measuring Machine(CMM) is very broad,because of its high measure precision,clear measuring objective,flexible measuring method,it can meet the measure requirement of many parameters like shape error,location error etc.With these advantages,it is widely used to measure the surface.Focusing on increasing the measuring accuracy and efficiency in surface measurement,we have studied on the foundation of workpiece coordinate,measuring path programming,measuring points distributing,probe radius compensation,measuring error assessing,auto-measuring etc.In this thesis,the principle in surface measuring path programming was analyzed at first,then we proposed eight measuring path planning strategies,summarized the methods of probe error compensation,advantage,disadvantage and applicable area,given the method of measuring error assessment.We also studied the influence factors of surface measuring accuracy:(1)on aspect of machine equipment,the factors that caused machine equipment error were analyzed,including geometry error,probe error,software error,transmogrification error,dynamic error;(2)on aspect of measuring method,the factors that caused measuring method error were analyzed,including the foundation of workpiece coordinate,measuring path programming,probe radius compensation,gauger's diathesis,and a method to minish the measuring method error was presented.The measured surface known CAD model and unknown CAD model were studied separately.For the surface known CAD model,we proposed least squares method depending on coarse benchmark founded by three-plan method on the base of measuring experiment, which improved the uniform precision between the workpiece and CAD model.Then curvature difference method and line angle method were presented in order to achieve auto- -distributing measuring points with inputting the amount of points.The measuring error after path programming and probe radius compensation along planar vector and three-dimensional vector were compared by measuring experiment of lamina.We developed simulation routine of surface known CAD model,which included transforming the initial coordinate by least squares method,auto-distributing measuring points,verifying the measuring path,setting safety points,making DMIS file,reading the output file of CMM,assessing measuring error.The measuring of surface unknown CAD model was studied.First,we proposed circle tangent method to forecast the coordinate value and vector,thus,we achieved the auto-following measuring of points on the base of the implement of circle extension method and polynomial method.Then,we proposed secondary measuring method that measuring surface point-by-point after scanning measuring which improved the measuring precision. Last,simulation routine of surface unknown CAD model was presented,the content included forecasting the coordinate value and vector of following point,calculating the vector of scanned data,making DMIS file.The study of this thesis was based on measuring experiment of lamina , path programming routine and simulation routine were validated by measuring experiment.