Research On Synthesis Method And Application Of 5-Dof Weaklycoupled Compliant Parallel Mechanism

Compliant mechanism has many potential merits,such as zero backlashes,no need for lubrication and reduced wear etc,which have been widely concerned by many scholars.And,they have a good application prospect in biological engineering,precision manufacturing and aerospace fields.As a kind of compliant mechanism,series-parallel hybrid compliant mechanism has the property of weakly coupled,which reduces the coupling error and easy to control.However,the traditional series-parallel hybrid compliant mechanism requires an additional intermediate platform,which not only increases the weight of the mechanism,but also reduces the carrying capacity of the mechanism.Therefore,a class of weaklycoupled compliant parallel mechanisms(CPMs)without intermediate platform is proposed in this paper.The synthesis method of weakly-coupled CPM with has larger carrying capacity is obtained.By using this synthesis method,five degree of freedom(5-DOF)weakly-coupled CPMs are carried out.Facing the background of aerospace application,new4-PPPU(P denotes the prismatic hinge,U denotes the universal hinge)weakly-coupled CPM is selected as secondary mirror adjustment mechanism.The kinetostatics model and dynamics model of the new 4-PPPU weakly-coupled compliant secondary mirror adjusting mechanism are established.The parametric optimization design of the mechanism is carried out.Thus,relevant theoretical and experimental research work is carried out on the application of new 4-PPPU weakly-coupled compliant secondary mirror adjusting mechanism.The main research contents of the thesis are as follows:(1)Research on synthesis method of weakly-coupled CPM.Based on the screw theory,a synthesis idea of connecting sub-modules by sharing flexible hinges is proposed.In order to improve the carrying capacity of the mechanism,the redundant actuation compliant parallel mechanism with larger carrying capacity is selected as sub-modules.Based on the freedom and constraint space topology method,the synthesis method of the CPM with redundant actuation is proposed.Based on modular method,the synthesis method of weakly-coupled CPM is obtained.Then,two judgment conditions of shared flexible hinge and weakly-coupled are proposed,and the synthesis process is formulated,which provide a theoretical basis for weakly-coupled synthesis.(2)Synthesis of the CPM with redundant actuation.Based on the synthesis method of CPM with redundant actuation,the CPMs with two rotational and one translational(2R1T)motion are synthesized and the CPMs with two translational(2T)motion are synthesized.According to the judgment condition,motion modules of flexible branched chain and motion modules compliant mechanism are proposed.The CPMs with 2R1 T motion and 2T motion are proposed by choosing the flexible hinges to achieve the mapping of motion modules to physical modules.The degrees of freedom and the property of the motion of the new mechanisms are verified.(3)Synthesis of 5-DOF weakly-coupled CPM.Based on the new synthesis method of weakly-coupled CPM,three translational and two rotational(2R3T)motion weakly-coupled CPMs.According to the new synthesis method,the 2R1 T motion and 2T motion CPMs with redundant actuation are selected as the sub-modules.According to the judgment conditions of sharing flexible hinge and weakly-coupled,the combined mechanisms and the weaklycoupled CPMs are obtained in sequence.Thus,the new configurations of the fully symmetric and the bisymmetric weakly-coupled CPMs are obtained.Lots of new configurations are provided for secondary mirror adjusting mechanism.(4)Research on the structural design and mechanical analysis of new 4-PPPU weaklycoupled compliant secondary mirror adjusting mechanism.The fully symmetric 4-PPPU weakly-coupled CPM is selected as the new configuration of secondary mirror adjustment mechanism.Its structure is designed.Based on the structure matrix method,geometric principle and motion superposition principle,a new kinetostatic modelling method for weakly-coupled compliant parallel mechanism is proposed.The kinetostatic model of new4-PPPU weakly-coupled compliant secondary mirror adjusting mechanism is established.Based on Lagrange method and pseudo-rigid body method,the kinetic energy and potential energy of the mechanism are analyzed.Then,the dynamics model of the mechanism is established.The finite element software is used to verify the correctness and rationality of the kinetostatic model and the dynamics model.(5)Research on the optimization and experiment of new 4-PPPU weakly-coupled compliant secondary mirror adjusting mechanism.According to the kinetostatics model of new 4-PPPU weakly-coupled compliant secondary mirror adjusting mechanism,the global off-axis stiffness ratio index and equivalent input stiffness index are proposed.The global off-axis stiffness ratio index can represent the precision of the mechanism,and the equivalent input stiffness index can represent the travel of the mechanism.The global offaxis stiffness ratio and equivalent input stiffness are taken as optimization objectives,and stress and inherent frequency are taken as constraint conditions.The multi-objective optimization model of the mechanism is established and the structure of the mechanism is optimized.A physical prototype of new 4-PPPU weakly-coupled compliant secondary mirror adjusting mechanism is manufactured and the experiment test platform are built.The performances of the static stiffness,stroke,accuracy and modal are studied by experimental.In this paper,new 5-DOF weakly-coupled compliant parallel mechanisms are obtained.The structure of new weakly-coupled compliant secondary mirror adjusting mechanism is designed.The kinetostatics model and dynamics model of the mechanism are established.The parametric optimization design of the mechanism is carried out.Facing the application,relevant theoretical and experimental research works of new weakly-coupled compliant secondary mirror adjusting mechanism are carried out.The results will further enrichs the theory of mechanism and provides theoretical,technical support and experience accumulation for the development of secondary mirror adjustment mechanism of space telescope.Additional,it will help break the existing bottleneck and change the situation that key technologies are disciplined by others.It is great significant for the improvement of our country’s aerospace level.