Study On Measurement Planning Of The Plane Mold Free Curved Surface

With the continuous development of manufacturing, reverse engineering has beenincreasingly applied to many fields, and collecting the measurement points of surface is animportant step of reverse engineering and surface measurement. Therefore, the study ofsurface measurement for engineering practice has an important role in guiding. Currentmethods used to collect the data of the surface parts of the surface are divided into twocategories: contact and non-contact. As a contact measurement instrument, CMM has thecharacteristics of high intelligence and high reliability, and it is able to measure the physicalefficiently and accurately, so it is widely used. In this paper, in order to improve themeasurement efficiency of CMM, the methods of surface measurement and surfacereconstruction are studied.In this paper, the composition and operation of the CMM process has been described indetail, compared to the commonly used method of probe radius compensation, the bestmethod of probe radius compensation-a total of four-ball method is proposed. It is proposedWhen the surface is measured, the automatic compensation function of CMM should beclosed, firstly the coordinates of the global probe need to be measured,and then a total offour-ball method of compensation should be used, and finally the actual coordinates of thevalue of the measured surface is calculated. The principles of measurement path planning areproposed and avoidance points are set legitimately.For the known free-form surface, according to the three-dimensional model of the centerof a figure of a homogeneous object, an adaptive digital algorithm is raised, this algorithm canconverge to a random grid of rectangular mesh topology, by implementing thealgorithm,measurement points can be adaptive distributed. On the basis,the curvature measure is deeply studied, by the comparison of three different models, can we find that thebest description of the degree of curvature of a point on the free surface is mean curvaturemodel, and combined with the example to verify the feasibility of the modal of known surfacedigitizing.The measurement planning methods of free-form surface are proposed, the number anddistribution of free-form surface measurement points are determined legitimately, a method ofcollecting twice is proposed. The first collecting is extracting the physical boundary line andfeature line to construct the initial surface. The second collecting that is based on the initialsurface，at this time the initial surface transformed into a known surface, we can use themethod of known surface algorithm of adaptive digital to make the measuring pointsdistributed adaptively. We do simulation experiments by aircraft composite mold to verify themeasurement point distribution reasonable.After introducting the NURBS surface fitting method of regular points and scatteredpoints,put the result of the second collecting and the model of initial surface in the CMMtogether, and then measure the surface.After obtaining the data points, making NURBSsurface fitting to verify the feasibility of the above measurement plan. Through the above plan,we can use as few measurement points to reflect the shape of the characteristics of the surface.