| With the development of science and technology and the improvement of productivity,the traditional manufacturing industry is transforming to the intelligent manufacturing,and various types of complex and advanced mechanical systems are increasingly used in industrial production.Industrial robots and precision CNC machine tools focusing on aerospace,automobile,manufacturing,military industry and other industries have been greatly developed.Strength inspection,structural optimization,reliability analysis and stability analysis are essential in the design,manufacture and application of various high-end machines.Dynamic analysis,the basis for these analyses and calculations,can provide key dynamic characteristic parameters that help engineers better control the operating state of mechanical systems.However,most mechanical systems are not constant and their dynamic characteristics often vary with the changes of the key system parameters.Therefore,it is of great significance for the design,manufacture and application of high-end mechanical equipment to explore and study the dynamic modeling methods and analysis technologies which are more applicable for mechanical systems with variable dynamic characteristics.Under the above-mentioned industry development background and engineering requirements,this dissertation studies the frequency response function(FRF)modeling method for mechanical systems with variable dynamic characteristics and proposes the generalized receptance coupling substructure analysis(GRCSA).Based on the GRCSA,the applications of this method in various mechanical systems with variable dynamic characteristics are studied.The FRF prediction model of a new 5-DOF hybrid robot is established,and the influence of spatial attitude on the frequency response characteristics of the system is analyzed.The accurate modeling method for drilling and milling cutters is studied,and the equivalent ring method is proposed.Finally,based on the GRCSA and the accurate modeling method of drilling and milling cutters,the FRF prediction model for the tool tip of the hybrid robot machining system is established,and the stability of hybrid robot milling carbon fiber reinforced plastic is studied.The main contents of this research are li sted as follows:The modeling method for FRF of mechanical systems with variable dynamic characteristics was studied.The generalized receptance coupling substructure analysis was proposed by comprehensively considering the variability of interfaces,spatial attitude relations and substructures in the mechanical systems with variable dynamic characteristics.By modeling and calculating the substructures,interfaces and spatial attitude relations in the system,and coupling each substructure in the frequency domain,the analytic function model of the system frequency response characteristics with respect to the system variables can finally be obtained.Based on the derivation process and results of the GRCSA,the mechanical systems with variable dynamic characteristics are classified into three basic categories:variable interface systems,variable spatial attitude systems,and variable substructure systems.In order to fully illustrate the application of GRCSA in the dynamic analysis of mechanical systems with variable dynamic characteristics,typical cases of three basic categories in engineering practice were selected for study:a bolt-fastening system(variable interface system),a 3R robot(variable spatial attitude system),and a machining system(variable substructure system).The modeling processes of three mechanical systems with variable dynamic characteristics were elaborated,and the FRF prediction model of each system was derived in detail.The calculation methods for FRF matrices of various substructures and the calibration methods for interface parameters were given.The influence of system variables on natural frequency was analyzed.The frequency response characteristics of a 2UPU/SP+RR hybrid robot were studied.Based on the kinematic analysis of the hybrid robot,the spatial attitude relations between components during the motion were obtained.The flexibility of the substructures and joints(driven and non-driven directions)was taken into account,and the FRF prediction model of the hybrid robot was established based on the GRCSA.Based on the established prediction model,the FRFs of the hybrid robot end in different spatial attitudes were predicted.The influence laws ofjoint variables on the frequency response characteristics of the hybrid robot were studied in a large range of spatial attitudes.In order to solve the problem of difficulty in dynamic modeling of the fluted part of drilling and milling cutters,a new equivalent diameter calculation method,the equivalent ring method,was proposed.The main idea of this method is to divide the circumcircle of the cross-section of the fluted part into a series of rings,and the ratio of intersection of the ring and th e crosssection is used as the weight of the moment of inertia of the ring,and the weight is defined as the ring coefficient.The products of the moment of inertia of rings and the corresponding ring coefficients are summed to obtain the moment of inertia of the cross-section,and then the equivalent diameter of the cross-section can be calculated.The method takes into account the complex shape of the cross-section of the fluted part and the average mechanical properties of the change in the cross-sectional phase caused by the helix angle,and the calculation process is simple.Based on the equivalent ring method,four common drilling and milling cutters were studied,and the validity of the equivalent ring method was verified by experiments and simulations.Combining the FRF prediction model of the hybrid robot and the accurate modeling method of drilling and milling cutters,the FRF prediction model for the tool tip of the hybrid robot machining system was established based on the GRCSA,and the FRFs of the tool tip in different spatial attitudes were predicted.A cutting force model for milling carbon fiber reinforced plastic was established,and a decay function was introduced into the edge force terms to make the prediction of the milling force more accurate near the cutter tooth cutting in and cutting out.A 2-DOF dynamic system for milling carbon fiber reinforced plastic was established,and the calculation formula for stability limit was derived based on the zero-order approximation.The milling stability of the hybrid robot in different spatial attitudes was analyzed,and the validity of the prediction results of milling stability was verified by a series of milling experiments. |
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