| With the increase in demand for precision machining represented by aviation blades,the performance requirements for positioning devices are also getting higher and higher.The traditional precision positioning platform can only achieve micron-level positioning accuracy due to its structural characteristics and drive performance.With the application of smart material drives in recent years,the development of flexible mechanism technology and machine learning algorithms,a technical approach has been provided to solve the problems of ultra-precision,large stroke and high rigidity of ultra-precision worktables.Aiming at the need for ultra-precision positioning platform during the machining of aviation blades,this thesis proposes a spatial six-degree-of-freedom flexible parallel mechanism workbench based on PZT and flexible amplification mechanisms,and carry out systematic research on its performance and its motion control methods.Aiming at the problem of insufficient positioning accuracy of the existing precision positioning platform,this thesis proposes a design scheme of a spatial six-degree-offreedom flexible parallel motion platform based on the 6-PSS parallel mechanism.The use of two-axis straight round flexible hinges overcomes the lack of precision caused by the movement gap,friction and wear in the traditional rigid hinges,and the micro-nano drive capability of PZT lays the technical foundation for the movement platform to obtain micronano precision.Firstly,carry out the design of the six-degree-of-freedom flexible parallel actuator of the positioning table.The main structural dimensions of the actuator are analyzed and designed based on the requirements of the working space and bearing capacity of the positioning platform.The static structure of the positioning platform actuator is established based on the Workbench finite element simulation platform.The mechanics simulation model is used to analyze the kinematics of the mechanism,obtain the kinematic Jacobi matrix of the mechanism,and verify the accuracy of the Jacobi matrix.In order to increase the working space of the motion platform,design a two-stage cascaded flexible lever displacement drive magnification mechanism,and the finite element model is used to analyze the magnification of the displacement magnification mechanism,which can effectively magnify the stroke of the driver.Complete the overall structure design of the sports platform.Based on the finite element model,study the performance of the spatial six-degree-offreedom flexible parallel mechanism.The finite element stiffness analysis of the mechanism is carried out to study the stiffness of the moving platform under different load conditions.The elastic deformation of the mechanism is calculated by adding loads in the respective directions of the positioning table;the driving force is calculated and analyzed by providing a basis for the selection of the driver.Analyze the reachable working space of the platform,perform the inverse kinematics solution of the mechanism through the Jacobi matrix obtained by the finite element model of the mechanism,considering the limit of the stroke range of the piezoelectric ceramic drive system,the limit boundary search method is used to calculate the reachable working space of the positioning platform.The influence of the structure size of the positioning table actuator on the working space,bearing stiffness and driving force is calculated and analyzed.In order to realize the motion control of the spatial six-degree-of-freedom flexible parallel mechanism,carry out the motion modeling of the mechanism.Based on the pseudo-rigid body method,carry out the kinematics analysis of the mechanism,and the mathematical model of the mechanism is obtained.The result is compared with the finite element model of the mechanism,and find that its accuracy is low and cannot be used for the motion control of the mechanism.In order to obtain an accurate motion analysis model of the mechanism,use the Karnofsky's second theorem to derive the calculation formula of the flexibility matrix of the flexible branch chain;the finite element analysis is used to verify the accuracy of the flexibility matrix results.The motion balance equation and static balance equation of the spatial six-degree-of-freedom flexible parallel mechanism are solved in parallel,and obtain the Jacobi matrix of the kinematics analysis model of the mechanism.Compare with the Jacobi matrix of the finite element model to verify the accuracy of the analytical model.Taking into account the positioning error caused by the bearing deformation of the positioning table,based on the kinematics analysis model of the mechanism,the machine learning algorithm of polynomial regression is used to realize the compensation of the motion error caused by the stiffness,and further improve the positioning accuracy of the motion platform.The research in this paper provides a theoretical and technical basis for the development of ultra-precision positioning tables such as aviation blades. |
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