| Hybrid machines had the respective advantages of series and parallel machines,and could also solve the limitations caused by simple series and parallel machines.Therefore,it was an important direction for future research and development of machine tools.In this paper,the 3UPS+1RPU parallel mechanism was used as the main body of the hybrid machine tool,and then the mechanism was connected in the slide rail of y-axis,so as to build a new type hybrid machine tool of five-degree-of-freedom.Firstly,the characteristics of each type of branch and the branch composition were studied,and a new type of 3UPS+1RPU parallel mechanism was constructed by comparing the types of branch composition.The helix theory was used to analyze the property of freedom of the mechanism.Then the modified G-K formula was used to solve the number of degrees of freedom.On this basis,a reasonable active input pair was selected.Finally,a type of five-degree-of-freedom hybrid machine tool was constructed with a 3UPS+1RPU parallel mechanism as the main body of the hybrid machine tool.Secondly,the rotational transformation matrix expression was used to express the relationship between the coordinate systems of each member of the parallel mechanism,so that the inverse solution of the position was obtained.Then using the influence coefficient method to solve the expression of the velocity and acceleration of the center point of the moving platform.And using the limit search method and the simulation method based on MATLAB/SimMechanics to solve the reachable working space of the mechanism respectively.Finally,Jacobi algebraic method was used to study the singularity.Then,the dynamic performance of the 3UPS+1RPU parallel mechanism was analyzed by using the principle of virtual work principle.The ADAMS software was used to simulate the kinematics performance of the mechanism,and it was found that the mechanism had good kinematics performance.Finally,the dynamics simulation of this mechanism was studied.The curve of each parameter of the drive motor over time was obtained,which provided atheoretical reference for selecting the motor for practical application.Again,the stiffness of the hybrid machine was studied.The finite element model of the machine was builded.The deformation cloud and stiffness values of the hybrid machine tool in five different poses are obtained by simulation.Through the analysis of the simulation results,the law of the variation of the stiffness of the hybrid machine with posture was obtained,and the weakness of the stiffness of the hybrid machine was found out.This was of great significance for improving the machining accuracy of the machine tool.Finally,the modal analysis was performed by ANSYS software.We obtained the low-order natural frequency and mode shape of the hybrid machine tool in different poses,and found the location where the machine tool was susceptible to resonance.Through the harmonic response analysis,the vibration displacement characteristics of the moving platform of the machine tool could be obtained,and the sensitive frequency range that the machine tool should avoid was found out.Then the Transient kinetics was performed to obtain the deformation of the hybrid machine tool under different position and posture under the impact load.Finally,it was concluded that the dynamic characteristics of the hybrid machine under the extreme posture were the worst.Therefore,the machine should avoid reaching the limit position during the processing of the parts,so that the machine tool could maintain better dynamic characteristics. |
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