| Equipment in aerospace,vehicles and ships,sustain lots of multi-dimensional vibrations and impacts,which affect their performance and life severely.The traditional theory and method about multi-dimensional vibration isolation can’t meet the requirement of practical engineering well.Parallel mechanism is a kind of multi-degrees-of-freedom system with multiply inputs and outputs,which has many advantages such as simple construction,high stiffness,easiness of manufacture and strong bearing.Relevant researches show that by installing the spring-damper systems on the actives joints,the mechanism becomes a vibration isolation system and it can achieve multi-dimensional vibration isolation.Supported by the National Natural Science Foundation of China-Hybrid energy flow method for broadband acoustic vibration prediction of high iron and other large structures(51675306),Active control study on multi-dimensional vibration of precision equipment based on flexible metamorphic mechanism(51275275),and National Key Research and Development Program of China-Research and development of noise and welding fume protection technology equipment for large machine and workshop(2016YFC0801704),Research and development of protective equipment and technology for dust and vibration in intensive polishing workshop(2016YFC0801702),this paper focuses on the multi-dimensional vibration,constructs a multi-dimensional vibration isolator based on a parallel mechanism,and tries to make the scientific performance index and achieve the parameters optimum design of the multi-dimensional vibration isolator.Firstly,based on the most common mode of multi-dimensional vibration in practical engineering and the research made by our group before,a kind of 3-PRC parallel mechanism is selected as the main structure of the multi-dimensional vibration isolator.For eliminating some defects,revised design is carried,and the 3-PRC mechanism is upgraded into a novel 3-PRRP(4R)mechanism.The motion output analysis shows that the 3-PRRP(4R)mechanism satisfies the requirement of multi-dimensional vibration isolator for motion output.Secondly,the kinematics model of the 3-PRRP(4R)mechanism is built,and the theory model is verified by simulation results.The workspace,singularity and dexterity of the mechanism is analyzed,considering the requirement of multi-dimensional vibration isolator for the shape of workspace and kinematical performance of the mechanism,the superior spherical workspace is put forward,and the effects of size parameters of mechanism on the volume of workspace,superior workspace and superior spherical workspace of the mechanism are analyzed in detail.Thirdly,the multi-dimensional vibration isolator based on the 3-PRRP(4R)parallel mechanism is built,the static model are derived,and the theory model is verified by simulation results.To describe the stiffness characteristics in an approachable and intuitive way,the equivalent stiffness is put forward.The free vibration differential equation of the system is derived,and the theory model is verified by simulation results.The effect of the mass of upper platform on the accuracy of theory model is analyzed.The response characteristic and the working frequency range of the isolator is obtained through frequency response simulation.The effects of parameters on the natural frequencies and modal shape of the isolator are analyzed,and the equilibrium position regulating apparatus is designed.Finally,by way of genetic algorithm,the parameters optimum design of the isolator based on the special natural frequencies is achieved,and considering the general working conditions,the parameters optimum design of the isolator based on the volume of superior spherical workspace and the maximal natural frequency is achieved.The optimal device has better kinematic performance,greater working frequency range,and significant vibration isolation performance.The device is made out according to the optimal sizes.In the study of multi-dimensional vibration isolator based on the parallel mechanism of this paper,the superior spherical workspace combining the requirement of isolator for the shape of workspace and kinematical performance of the mechanism,is scientific and reasonable,the equivalent stiffness is approachable and intuitive,and the parameters optimum design is connected with practical engineering tightly.This paper provides guidance for the design and evaluation,promotion and application of multi-dimensional vibration isolator based on the parallel mechanism. |
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