Research On Bidirectional Profile Construction Of Globoidal Indexing Cam Based On NURBS

With the development of all kinds of mechanical equipment in the modern machinery industry,the requirements for the performance of globoidal cam mechanism,such as speed,accuracy,are constantly improving.For high speed and heavy load,globoidal indexing cam has the following advantages: high precision,superior dynamic performance,good stability and so on.With the development of practical industrial application,there are higher requirements for Globoidal Indexing Cam in curve design,profile construction,efficient modeling development and manufacturing.This paper focuses on the optimization of the order and control points of NURBS curve,the comprehensive performance evaluation of characteristic value of NURBS curve,the design of bi-directional curve cluster and its surface of globoidal cam profile,the construction of adaptive distance between curves,the optimization of control points,the evaluation of the comprehensive performance of characteristic value of NURBS curve,the design of bi-directional curve cluster and its surface of globoidal cam profile Based on the secondary development of VS and NX,the parametric modeling of globoidal cam mechanism and multi axis NC machining of globoidal cam are studied to improve the performance of globoidal indexing cam.Firstly,starting from the construction of the most basic cam curve,combined with the existing 33 curves,the advantages and disadvantages of the modified sine curve,modified trapezoid curve and polynomial curve in the simple harmonic trapezoid combination curve are compared and analyzed,the curve characteristic value diagram is drawn and the applicable working conditions are summarized.In order to further improve the motion performance of cam curve,based on the theory of non-uniform rational B-spline,the NURBS curve suitable for cam mechanism is constructed and its expression is obtained.By using its local adjustability,the corresponding value of node vector is obtained by equidistant node method,the boundary constraint is set,and the motion control points are solved by motion control equation.Secondly,comparing and analyzing the maximum characteristic values of several cam curves,it is found that the speed of one curve is smaller than that of another curve,the acceleration is larger,and the jump may be smaller or larger,so it is impossible to judge which cam curve is better.There is an urgent need for a single comprehensive performance evaluation method to evaluate the excellent cam curve.Therefore,a comprehensive performance evaluation method is proposed to evaluate the single comprehensive performance of the five maximum characteristic values of the cam curve.The judgment matrix is established based on fuzzy mathematics,and the analytic hierarchy process is proposed to determine the weight of the maximum characteristic value of cam curve.After the eigenvectors and eigenvalues are calculated and the consistency is checked,the comprehensive performance index can be obtained.This method solves the problem that the comprehensive performance of cam curve can not be evaluated in the past.The 3 ～ 13 degree standard double dwell NURBS cam curve is optimized,and the comprehensive performance evaluation method is proposed to determine the NURBS cam curve with the best degree of performance.Under the condition of determining the optimal order of NURBS cam curve,the standard double dwell NURBS cam curve with 6～ 16 control points is optimized by repeated iteration of a group of control points.A comprehensive performance evaluation method is proposed to determine the NURBS cam curve with the optimal control points.The result is compared with the modified sine cam curve,and the 7-degree NURBS optimization II cam curve with good performance is obtained.Thirdly,the accuracy of one direction surface can only be controlled by one-way curve clustering,but the accuracy of the other direction surface can not be guaranteed.There is an urgent need for a way to construct bi-directional curve cluster to improve the accuracy of the contour surface.This paper proposes to construct the contour surface through bi-directional curve cluster,because it can control the accuracy of two direction surface generation,so the generation accuracy of the contour surface is higher.After importing the expression,the expression controls the curve related data,and then uses the "regular curve" command to generate the U and V bi-directional curve clusters on the profile.The u-direction curve is the track of a conjugate point between the roller and the cam,and the v-direction curve is formed by the contact conjugate curve between the roller and the cam at a certain time.The distance between curves is fixed,there are too few curves with large curvature,the accuracy of generating contour surface is low,and too many curves with small curvature result in too much calculation.There is an urgent need for a method to determine the distance between curves according to the curvature of the curve.Based on chord height method,the span of V(U)curve cluster is adaptively determined by curvature of U(V)curve,which improves the efficiency of constructing curve cluster and reduces the amount of calculation.The three-dimensional model of globoidal cam can be constructed by combining the generated ridge and cam base.This paper makes a comparative analysis of different configuration modes,and makes a modal analysis of the existing globoidal cam model.Fourthly,aiming at the problems of complex modeling,difficult surface contour construction and low modeling efficiency of globoidal cam,combined with the characteristics of NX,the globoidal indexing cam software is built independently based on VC + +environment.The software is developed by vs and NX,uses block style editor to build user interface,and uses the concept of group to design different modules,which simplifies the interface and reduces the difficulty of development.After the interface is built in NX,the userdefined encapsulation function is used to realize the interface selection and enumeration function and simplify the code writing.After setting the parameters,the three-dimensional model of the globoidal cam mechanism can be generated quickly and efficiently,which shortens the development cycle of the globoidal cam mechanism,and greatly reduces the repetitive labor and improves the efficiency.Fifthly,the profile surface of Globoidal Cam is more complex than other parts,which also increases the difficulty of processing.The non equivalent free-form surface method is used to process globoidal cam.Based on the NX built-in processing module,the machining of Globoidal Cam is simulated,the clamping of fixture,machine tool and parts is simulated,and the corresponding pre-processing and post-processing are done.The variable axis profile milling in NX-Cam module is used to process the profile surface.The axis direction of the variable axis profile milling tool can be changed during the machining process,which can adapt to the complex surface machining of globoidal cam.The machining path is generated based on the method of circle cutter and ball cutter driving surface machining,and then Heidenhain’s post processor is built to generate programming code,The free-form surface method is of great significance in the actual process of globoidal cam machining.