| Closely combined with the actual requirements of automatic machinery for the innovation on high-speed indexing mechanism,the configuration synthesis method of a novel coaxial indexing cam mechanism which can realize high-speed indexing motion is researched.Then,the kinematics,statics,dynamics analysis and experimental research of a parallelogram cam-linkage indexing mechanism are investigated systematically in the thesis.The main contents are as follows:Configuration synthesis: Based on the analysis of the structure and working principle of a coaxial eccentric indexing cam mechanism,the topology characteristics and design requirements of input and output coaxial compact layout and higher pair are summarized,and the mathematical modeling method of adjacency matrix,automatic isomorphism discrimination and number synthesis of kinematic chains with higher pairs are studied by breaking through the existing adjacency matrix theory of planar kinematic chain.The atlas of kinematic chain with higher pairs are established based on the kinematic chains containing only lower pairs with different number of components.On this basis,the corresponding relationship between the higher pair and the number of links with multiple pairs,and the coaxial layout of input/output and the number of components in the loops.The configuration synthesis method of the novel coaxial indexing cam mechanism is proposed by setting the frame,input/output components and the specific forms of the kinematic pairs reasonably.Finally,the feasible mechanism configuration schemes are obtained by taking the planar 6-bar kinematic chain as an example.The configuration synthesis method of the new mechanism provides a new idea for the configuration innovation of the coaxial indexing cam mechanism and the configuration synthesis of the mechanism with higher pairs.Geometric and kinematic characteristics analysis: The equations of the cam profile and radius of curvature are derived by taking a parallelogram cam-linkage indexing mechanism as the object.The effects of the dimension parameters and initial configuration of the parallelogram linkages and motion law on the geometric characteristics of cam profile are analyzed.On this basis,the region of the minimum radius of curvature during deceleration period is analyzed to establish the approximate analytical solution,and the range of the linkage length ratio to avoid the undercut of cam profile is analyzed.According to the characteristics that the mechanism realizes indexing motion through the change of parallelogram’ configuration,the pressure angle and meshing angles of the mechanism in transmission process are defined,and the intrinsic relation among meshing angles,motion law and parallelogram dimensional parameters is established.Finally,the influence of design parameters such as linkage length ratio and initial angle on the pressure angle and meshing angles are analyzed,which lays the foundation for the dimensional synthesis of the mechanism.Dimensional synthesis: Based on the systematic analysis of the types and quantities of overconstraints in the mechanism,the compatibility equations of distortion are investigated.The dynamic static analysis model is established,and the variation of the forces of kinematic pairs versus the linkage length ratio in indexing period are analyzed.Based on analyzing the possible singular configurations,the evaluation indexes of motion and force transmission in active period are constructed according to the distance between the instantaneous and singular configuration of the parallelogram,and the influence of the linkage length ratio on the transmission performance is analyzed.The constraint conditions of avoiding cam profile undercut and maximum pressure angle are established,and the variation of motion/force transmission efficiency and the contact force coefficient versus linkage length ratio are investigated.Then,the general dimensional synthesis method of the mechanism is established,which provides an important technical support for parameter design of the new mechanism.Dynamic analysis: The translation-torsion elastodynamic model of the mechanism considering the contact stiffness between conjugate cams and rollers is established by Lagrange method.In the modeling process,according to the characteristics that the parallelogram’ configuration affects the output of the mechanism,a virtual equivalent component is established at the hinge points between the parallelogram and input/output links,and its overall inertia and stiffness parameters are calculated,and the relative elastic displacements between the parallelogram and input/output components are analyzed.The variation of the natural frequencies and mode shapes of the mechanism in indexing period and the influence of dimensional,stiffness,and inertial parameters on the first-four order natural frequencies are analyzed.On this basis,the nonlinear torsion elastodynamic model of the mechanism considering time-varying clearances and damping is established,and the residual vibration response spectrums of mechanism with different motion laws are analyzed.Finally,the dynamic simulation model is established by using ADAMS to verify the validity of the analytical model.The dynamic research provides a theoretical support for the dynamic characteristic analysis and real mechanical structure design of the new mechanism.Dynamics experimental research: According to the results of dimensional synthesis,the experimental prototype is developed,and the dynamic characteristic testing system is built.The natural frequencies of the experimental prototype at different positions in one indexing period are measured,and the angular acceleration response of the load plate is tested.The natural frequencies of the mechanism measured by the experiment are basically consistent with the simulation results of the theoretical model,which verifies the validity of the dynamic model. |
