| Compared with the traditional six degrees of freedom(DOFs)parallel mechanism,the lower-mobility parallel mechanism has many advantages,such as compact structure,easy design and manufacture,high precision,high stiffness and easy control.Nowadays,it has become an important part in the research of parallel mechanisms.Because of their great potential and prospects for industrial applications,the three DOFs parallel mechanisms with two rotations and one translation have been attracted increasing attention in both academia and industry.In this paper,the three DOFs 2-PUR-RPU parallel mechanism with two rotations and one translation is proposed as the research object,and the corresponding kinematics analysis,dynamic modelling and dynamic performance index analysis are carried out respectively.The main research contents are divided as follows:Firstly,the three-dimensional model of 2-PUR-RPU parallel mechanism is developed,and the corresponding coordinate system are established in detail.Based on the screw theory,the mobility of the 2-PUR-RPU parallel mechanism in the initial and general configurations is analyzed,and the results show that the 2-PUR-RPU parallel mechanism has three DOFs:two rotations and one translation.The inverse kinematics of the 2-PUR-RPU parallel mechanism is carried out by using closed-loop vector method.Then on the basic of the position analysis,the mapping relationship between the generalized velocity and acceleration of the parallel mechanism and the moving platform is established by using the expression of the matrix form.Using the Newton-Euler method,the dynamic model of the 2-PUR-RPU parallel mechanism is developed.And on this basis,the deformation compatibility equations of the links are added to obtain the modified dynamic modelling equations.The dynamic model of the 2-PUR-RPU parallel mechanism is established and simulated by using the simulation software ADAMS,and the results are basically consistent with the numerical simulation results obtained from MATLAB,which further verifies the correctness of the dynamic modelling.Taken the dynamic manipulability ellipsoid as the dynamic performance index,the dynamic performance of the 2-PUR-RPU parallel mechanism is analyzed,and the dynamic manipulability ellipsoid distribution under different link parameters is also discussed.Taken the dynamic manipulability ellipsoid coefficient as an index,the dynamic performance is explained.The research work in this paper lays an important theoretical foundation for the design of dynamic control system and multi-objective dynamic optimization of 2-PUR-RPU parallel mechanism in the future. |
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