| This thesis addresses the major strategic requirements for the development of high-end intelligent equipment in the aerospace field.Aiming at the problems of the complex surface of aerospace large workpiece,configuration design and performance research of serial-parallel processing equipment based on large workspace are developed.According to the requirements of functional degrees of freedom for machining complex surfaces,three types of 1T2 R,2T2R and 3T2 R parallel manipulators with two rotational degrees of freedom are adopted as the main actuators,focusing on the configuration synthesis of three types of parallel manipulators including 1T2 R,2T2R and 3T2 R,and a typical 1T2 R over-constrained parallel manipulator that can be connected in series to linear guides,ring guides,or industrial robots is proposed.Taking the 2RPU-2SPR over-constrained parallel manipulator applied to complex surface machining as the research object,the kinematics and dynamics modeling,performance evaluation and multi-objective optimization are conducted in detail.Based on the optimal structural parameters,the trajectory tracking controllers are researched,the digital simulation analysis of the virtual prototype are completed,and the experimental performance tests are performed based on the test prototype to verify the trajectory tracking performance of the controllers to provide theoretical guidance for the parallel manipulator in the processing of complex surfaces.The main research contents are as follows:(1)Research on the configuration design of hybrid mechanisms based on the requirements of complex surface machining tasks.According to the task requirements of complex surface processing of the heat-insulation layer of aerospace large workpiece,the types and number of functional degrees of freedom of the parallel manipulators applying in the processing equipment of the hybrid machine tool are determined.The constrained synthesis method based on the screw theory is utilized to systematically study the configuration design of the lower mobility parallel manipulators.Using the dual relationships between twist and wrench screw,motion and constraint to determine the type and configuration of the kinematic joints and the constraint geometric relationship of the joints axis in the branch chain,and configure the typical kinematic branch chains including constrained force and constrained couple.Based on the properities of Grassmann line geometric to judge the correlation of constraint force/couple,and then three types of parallel manipulators with lower mobility,namely,1T2 R,2T2R and 3T2 R with two rotational degrees of freedom,are constructed to meet the requirements of functional degrees of freedom and kinematic characteristics.(2)According to the principles of structural similarity and function correlation analog design selection,a novel redundantly actuated 2RPU-2SPR over-constrained parallel manipulator for complex surface machining is proposed,and its kinematics and dynamics mathematical modeling are performed.Firstly,based on the screw theory,the mobility characteristics and kinematics were analyzed,and the degree of freedom calculation was performed by using the modified Grübler Kutzbach formula.The mechanism was determined to be a 1T2 R three-degree of freedom redundantly actuated over-constrained parallel manipulator.Secondly,the kinematics equations of the parallel manipulator are established based on the closed vector method,the velocity and acceleration are analyzed,and the Jacobian and Hessian matrices representing the mapping relationship of the velocity and acceleration between the actuated joints and operation joints are deduced in detail.Finally,the dynamic formulation of the parallel manipulator are established on the basis of the principle of virtual work,and collaborative simulation of force and position actuation are performed via Recur Dyn and Simulink to verify the correctness of the kinematics and dynamics derivation.(3)Research on multi-objective collaborative optimization design method based on integrated performance evaluation system.According to the requirements of the processing characteristics of complex surface,the 2RPU-2SPR over-constrained parallel manipulator is integrated with performance evaluation indices such as workspace,motion/force transmission characheristics,stiffness,kinematics/dynamics dexterity,energy transmission efficiency and inertia coupling characheristics.An improved multi-objective particle swam optimization algorithm based on the orthogonal experimental design is proposed to carry out multi-objective optimization design with consideration of workspace,kinematic and dynamic characterisitics,as well stiffness characteristics for 2RPU-2SPR over-constrained parallel manipulator.The main effect diagram,negative effect diagram,interation effect diagram and correlation table reveal the intrinsic relationship between the design variables and objective function.The Pareto front of the performance evaluation indices indicates that the objective functions in the multi-objective optimization have non-linear distribution,and the indices are often conflicting or even contradictory.(4)Research on control strategy methods aiming at improving trajectory tracking accuracy.In order to avoid calculation problems from joint space to operation workspace,a simple,efficient and fast method for calculating and obtaining the position and orientation parameters of the moving platform in the workspace is proposed.And on this basis two intelligent control algorithms based on workspace are proposed to improve the trajectory tracking accuracy of the 2RPU-2SPR over-constrained parallel manipulator.Considering that there are some uncertain factors such as uncertain parameters,unmodeled errors,sudden loads and external disturbances in practical application,while sliding mode control can effectively resist external disturbances and parameter perturbations.An adaptive fuzzy sliding mode control algorithm is proposed for this problem.In order to further improve the trajectory tracking accuracy of the moving platform and the synchronous coupling error is introduced,an adaptive high-frequency synchronous robust control algorithm is proposed.Through the online real-time adjustment of the adaptive law,the online parameters identifications of the unknown parameters of the parallel manipulator(including the mass and inertia moment)are realized.(5)The experiment is a good method to verify the correctness of the novel configuration,novel method and novel technology.Taking the 2RPU-2SPR over-constrained parallel manipulator test prototype as the experimental objective,the proposed novel parallel manipulator is subjected to force/position hybrid control for experimental research.Based on binocular vision sensing technology,the current positions and orientations of the 2RPU-2SPR over-constrained parallel manipulator can be calculated online in real time and compared with the expected trajectory to form a tracking error.By adjusting the adaptive control parameters,the parallel manipulator can be guaranteed to move smoothly and has better tracking accuracy.The test results can provide some theoretical guidance and technical support for the complex surface processing of aerospace large workpiece heat insulation layer. |
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