| Aiming at the automatic perfusion of large-scale spherical crown honeycomb structure of the spacecraft,this paper carries out the configuration design and performance research of a series-parallel hybrid perfusion manipulator based on large workspace,high stiffness and high dexterity.Based on the analysis of the dimension parameters of spherical crown and functional requirements of perfusion robot,three configuration schemes of the perfusion manipulator are proposed.According to different configuration schemes,four perfusion manipulators are designed,which include the spherical parallel perfusion manipulator,type I and type II 1T2 R parallel perfusion manipulator and 5-DOF reconfigurable hybrid perfusion manipulator.Through the analysis and comparison of the kinematics,workspace,singularity and dexterity of the four perfusion manipulators proposed above,the 5-DOF reconfigurable hybrid perfusion manipulator is finally selected as the main research object in the following chapters.To obtain the optimal structural parameters of the hybrid mechanism with good kinematics performance in the task perfusion workspace,the kinematics optimization design is investigated.According to the optimized mechanism parameters,the analysis of dynamic,stiffness,error,trajectory planning and control simulation research for the hybrid manipulator are developed.The above research provides a theoretical basis for the manufacture of the real prototype of the hybrid manipulator and its application in the actual perfusion situation.The specific research contents are as follows:(1)According to the perfusion requirements of the honeycombs structure thermal protection layer of the large-scale spherical crown,degrees of freedom(DOFs)for the hybrid perfusion manipulator are analyzed.Three configuration schemes of the perfusion manipulator are then designed based on the determined DOFs.According to different configuration schemes,four perfusion manipulators are proposed,which are the spherical parallel perfusion manipulator based on multi-robot schemes,the type I and type II 3-DOF 3PSS-PU parallel perfusion manipulators based on gantry arc-shaped guide scheme and the 5-DOF reconfigurable 5PRR+5PUS-PRPU hybrid perfusion manipulator based on the gantry linear guide scheme.The analysis and comparisons of the kinematics,workspace,singularity,dexterity and perfusion efficiency are carried out for the above four perfusion manipulators.The 5-DOF reconfigurable 5PRR+5PUSPRPU hybrid perfusion manipulator with large workspace,high dexterity and high perfusion efficiency is finally selected as the main object in the following study.(2)Taking the 5-DOF reconfigurable hybrid perfusion manipulator as the research object,the kinematics optimization design and dynamic analysis are carried out.First,by comparing the reachable workspace and the task workspace for the separate5PUS-PRPU parallel mechanism and the 5PRR+5PUS-PRPU hybrid mechanism,the advantages of the reconfigurable 5PRR parallel base are proved.Different positions of the reconfigurable base when perfusing honeycombs at the top and boundary positions are introduced.Second,optimization variables and constraint conditions of the hybrid mechanism are designed,and a global comprehensive objective function is then proposed based on the mean and standard deviation of the unified dimension Jacobian matrix condition number.To obtain the optimal structural parameters of the hybrid mechanism with good kinematics performance in the task perfusion workspace,the kinematic optimization design of the hybrid manipulator with different positions of the reconfigurable base is developed,respectively.Then,the dynamic model of the hybrid manipulator is established based on the principle of virtual work,and the velocity and acceleration matrixes mapping the relationship between the mechanism components and the moving platform is obtained.Finally,numerical simulations are carried out for the displacement,velocity,acceleration and driving force of the driving joints under two motion trajectories of the moving platform.Through the comparisons of the obtained theoretical and simulation curves of the related motion parameters of the driving sliders,the correctness of the dynamic model has verified.(3)Based on the screw theory,a semi-analytical stiffness model of the 5-DOF reconfigurable hybrid perfusion manipulator is established.First,the method of establishing the semi-analytical stiffness model for a general parallel mechanism is introduced.According to the dual characteristics of the moving platform screw and twist,end link screw and branch twist,the stiffness models mapping between the moving platform and each branch chain as well as each branch chain and the elastic elements among branches are established.Overall stiffness model of the parallel mechanism is then obtained.Second,based on the theory of the semi-analytical stiffness model introduced above,the stiffness modeling of the 5PRR parallel mechanism and the5PUS-PRPU parallel mechanism are carried out,and then the overall stiffness model of the hybrid perfusion manipulator is obtained.Finally,the linear stiffness and angular stiffness based on the stiffness matrix are proposed to evaluate the stiffness of the hybrid manipulator.Through the comparisons of the theoretical and finite element analysis values of the linear stiffness and angular stiffness,the correctness of the semi-analytical stiffness modeling is verified.Moreover,the distributions of linear stiffness and angular stiffness of the hybrid manipulator when the moving platform is at different heights in the task orientation workspace are studied,respectively.(4)Based on the local product of exponential(POE)formula,the research of the error modeling and error simulation for the 5-DOF hybrid perfusion manipulator are studied.First,by decomposing the inverse kinematics of the branch chains into several Paden Kahan sub-problems with known solutions,the motions of the joints in each branch of the hybrid manipulator are obtained.Second,the error models of the 5PRR and 5PUS-PRPU parallel mechanisms are established by using local POE method.Through eliminating the error of unmeasurable joints in the branch based on the screw theory,the complete and continuous error model of the hybrid manipulator is obtained.Then,the redundant kinematic parameters are eliminated by constructing the orthonormal basis of the zero space and row space of the identification matrix,and the error model with independent kinematic parameters is obtained.Finally,according to the established error model of the hybrid manipulator and the numerical algorithm of the forward and inverse solutions based on the identification of the kinematic parameters,the error simulation of the hybrid manipulator is investigated without or with random disturbance.The correctness of the error model and the effectiveness of the error analysis for improving the precision of the hybrid manipulator have been verified.(5)According to the perfusion characteristics of the hybrid manipulator,three perfusion trajectories of circular,square and reciprocal rectilinear for the moving platform are designed.Trajectory planning for different perfusion trajectories is carried out,and different trajectory equations described in the fixed coordinate system are obtained.Based on the traditional PID control algorithm and the position/force hybrid control strategy,the control simulation system of the 5-DOF hybrid perfusion manipulator is designed.Also,the control simulation research of the proposed three task perfusion trajectories is developed.The error curves of different perfusion trajectories in the simulation results show that the control simulation system can track the trajectory of the moving platform of the hybrid perfusion manipulator,which verifies the reliability of the control simulation system.The above research provides theoretical guidance for the application of hybrid perfusion manipulator in actual perfusion situations. |
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