Research On Modification Optimization Of Double Meshing Tooth Needle Cam Indexing Mechanism

Double-meshing needle-tooth cam indexing mechanism is a new indexing mechanism,in which cam and inner cycloid are the core components to ensure the rotation accuracy and load-bearing capacity of the mechanism.In order to compensate for various errors in the manufacturing and assembly process of the mechanism and meet the lubrication conditions of the mechanism to improve the transmission quality,cam and inner cycloid must be modified.Firstly,the transmission principle of double meshing needle-tooth cam indexing mechanism and the transmission ratio of the mechanism are introduced.This paper expounds the forming principle of cam and inner cycloid gear profile,and deduces the parametric equation of cam and inner cycloid gear profile curve of this mechanism based on coordinate transformation method.Secondly,the method of combined cam modification is put forward for the first time in this paper.Referring to the common methods of equidistant modification and displacement modification of cycloidal gear,the calculation equation of cam backlash and initial clearance under this method is deduced.An optimum modification method based on contact stress of cam-pin-tooth meshing is proposed.A finite element model is established for the meshing of cam and pin teeth before and after modification,and the contact stress nephogram is calculated.The contact stress of each tooth surface of the modified cam is similar to that of the standard cam.The contact stress distribution of each tooth surface is more uniform,which verifies the effectiveness of the cam profile modification method based on bearing capacity to improve the stress state of the cam tooth profile.Thirdly,aiming at the transmission characteristic that the engagement between cycloid gear and pin teeth is external engagement,based on the common methods of equidistant modification and displacement modification,the curve equation of combined modification tooth profile which is applicable to the internal engagement transmission of cycloid gear and pin teeth of this mechanism is deduced.Equations for calculating the cyclic errors and initial clearances of the inner cycloid under equidistant and displacement modifications are presented.A combined modification method based on meshing contact stress optimization of inner cycloid gear and pin teeth is proposed.The optimal modification quantity is found through optimization.The finite element model of inner cycloid gear-pin teeth transmission before and after modification is established,and the contact stress nephogram is obtained by calculation and analysis.Based on the contact stress optimization,the maximum contact stress of each tooth surface of the internal cycloid gear is smaller or close to the maximum contact stress of each tooth surface of the standard internal cycloid gear,which proves the correctness of the modification method.Finally,the torsional stiffness of the modified cam,the inner cycloid wheel and the standard theoretical cam and the inner cycloid wheel are analyzed.The validity of the method based on load optimization is verified.The virtual prototype of the mechanism before and after carrying capacity optimization and combined modification is established and analyzed by regression simulation.The simulation results of the virtual prototype show that the load optimization modification method is effective to reduce the backlash of the indexing mechanism of the double meshing pin-tooth cam,and verify the feasibility of the load optimization modification method.