Research About Surface Reconstruction Based On CMM Measuring Technology

In the field of modern manufacturing and design,the role of reverse engineering becomes more and more obvious.Reverse engineering has already been a research focus in study of advanced manufacturing.Based on converse thinking, reverse engineering is a process of establishing and resolving of mathematical model.Therefore,the development of reverse engineering is complicated system engineering.Reverse engineering,which refers to many subjects,is comprehensive application of a series of mathematical methods.In this paper,development status,application field and relative technology of reverse engineering is studied,mainly focusing on measuring equipment CMM,probe,path planning,data pre-processing,curve reconstruction and surface reconstruction.Data measuring is obtained by CMM,in which probe is a key part.Thus,a new probe is designed and groups of test are carried out.Results demonstrate that the new probe can realize higher accuracy.On the probe contacting work-piece,the force makes spring take place deformation. So it can avoid damaging probe and work-piece.When measuring angle is small, error aroused by radius can be neglected,because the radius is small.In this situation,efficiency of processing data later is enhanced.Meanwhile,control system is analyzed.Secondly,path planning of CMM is also studied.It is a ideal situation that CAD model is represented with lest points.In application, it is unlikely realized to slightly complex work-piece.However,on the premise of meeting the demanding of accuracy,the model of measuring points with probability knowledge is put forward in this paper.Path planning makes the points distributed adaptively on work-piece.So this mathematical model can shorten measuring time,enhancing measuring efficiency.On the principal of path planning,the path planning of CMM is carried out and flow diagram is given out.Then data processing is studied to make the points including less error. When using CMM,the position of work-piece is changed,because of measuring range of CMM and obtaining partial character of work-piece.The technology of data merging is needed and sample which illustrates the procedures of data merging is given out.Additionally,abnormal points of "cloud points" are analyzed,considering the measuring points with abnormal points.And the method of processing abnormal points is programmed with Matlab.And then,curve reconstruction and surface reconstruction is disused in this paper. Bezier Curve is defined solely by control polygon.The shape of Bezier curve inclines to the shape of control polygon and changing the vertex of control polygon can change the shape of Bezier curve.But approximation level is poor and local modification of Bezier curve can not be achieved.B-spline Curve is much nearer and smoother than Bezier curve.The order of B-spline curve is given out according to the need of design.Except that,the outstanding advantage of B-spline Curve is its local modification.Because B-spline Curve is comprised partially,the vertex of control polygon can make the B-spline curve change flexibly and obviously.Changing the position of one vertex of control polygon induces variation of shape of next to curve;additional curves can not be influenced.This advantage makes B-spline Curve widely used in design of free curve.At last,the method of surface reconstruction is researched. B-spline Surface is two-dimensional extension of B-spline Curve. B-spline Surface is comprised of B-spline curve.When generating B-spline Surface,a group of B-spline Curve is got only by changing one parameter,another group B-spline curve is got seemingly.Similarly with B-splineCurve,B-splineSurface does not pass by the vertex of control grid. In this paper,the evaluation index of surface reconstruction is put forward. In experiment,σof plane equals to 4.1μm,σof cylinder equals to 2.9μm.