| With the rapid development of space science and technology,there is an increasing demand for heavy launch vehicles.The box body of heavy launch vehicles has the characteristics of large size,complex structure and easy deformation.The surface of the rocket tank needs to be sprayed with a layer of insulation material and processed by equal thickness.However,the processing method of the traditional processing equipment can’t meet the processing demand of the thermal insulation layer of heavy rocket tank in processing space,precision and efficiency.Therefore,it is necessary to redesign the machining equipment for the thermal insulation layer of the end face of the large tank of heavy launch vehicles,and research on the trajectory planning and control method for the machining equipment,so as to ensure the design parameters of the thermal insulation layer of the end face of the large tank.The thermal insulation layer of the end face of the large tank belongs to the workpiece with large size and complex structure,and it is not in line with the development trend to design the special machine tool with 1:1 ratio.In order to solve the processing problem of the thermal insulation layer of the end face of the large tank,the thermal insulation layer can be divided into several sub-regions,and then the sub-regions can be processed by machining equipment.Therefore,this paper adopts machining equipment consisting of XYZ axis long guides and 3T2R redundantly actuated parallel mechanism with large output rotational angles to process the thermal insulation layer of the end face of the large tank.The XYZ axis length guides can meet the processing space requirements of the thermal insulation layer of the end face of the large tank,and the 3T2R redundantly actuated parallel mechanism with large output rotational angles can meet the processing requirements of the complex surface of the thermal insulation layer of the end face of the large tank.Therefore,the research on configuration design,trajectory planning and control method of 3T2R redundantly actuated parallel mechanism with large output rotational angles is of great significance to the equal thickness processing of the thermal insulation layer of the end face of the large tank.In this paper,the configuration design of 3T2R redundantly actuated parallel mechanism with large output rotational angles is studied.A 2((2SPU)R)-(2UPR)R redundantly actuated parallel mechanism is selected to analyze its performance,and its trajectory planning and control method are studied based on the processing trajectory of the thermal insulation layer of the end face of the large tank.Specific research contents are as follows:(1)The equal thickness processing scheme design for the thermal insulation layer of the end face of the large tank.In order to meet the processing requirements of the thermal insulation layer of the end face of the large tank,based on the processing requirements of the thermal insulation layer of the end face of the large tank and the requirements of processing equipment,the processing method of fan-shaped surface and convex structure of the thermal insulation layer of the end face of the large tank is analyzed.A splicing scheme of the thermal insulation layer of the end face of the large tank is proposed.In the processing scheme,three different machining units of the machining equipment is put forward,and the advantages and disadvantages of the three machining units are analyzed,so the parallel robot machining unit is determined.In addition,based on the parallel mechanism processing unit processing the thermal insulation layer of convex structure of the end face of the large tank,the degrees of freedom of the parallel mechanism processing unit are analyzed,and the degrees of freedom of redundant actuated parallel mechanism is determined.(2)Configuration design and selection of 3T2R redundantly actuated parallel mechanism.Based on the degree of freedom requirements of redundant actuated parallel mechanism,a type synthesis method of 3T2R redundant actuated parallel mechanism with large output rotational angles is proposed.In order to solve the output rotational angles of redundantly actuated parallel mechanisms,two kinds of moving platforms with two degrees of freedom are proposed.Based on lie group theory and configuration evolution method,four types of limbs of 3T2R redundantly actuated parallel mechanisms were proposed.By further evolution of four types of 3T2R limbs without changing the degree of freedom of limbs,11 types of first-order limbs are obtained.Based on the structural characteristics of two kinds of moving platforms and 11 kinds of first-order evolution limbs,11 kinds of 3T2R redundantly actuated parallel mechanisms with large output rotational angles are configured.Based on the selective principle of parallel mechanism processing unit,a 3T2R redundantly actuated parallel mechanisms with large output rotational angles is selected for specific task functional requirements.(3)Kinematics and dynamics of the 2((2SPU)R)-(2UPR)R mechanism.Based on the closed vector method,the kinematic mathematical model of 2((2SPU)R)-(2UPR)R mechanism is derived,and Jacobi matrixes between the center point of articulated platform and the telescopic rod,oscillating rod and actuated joint are obtained,respectively.Based on the principle of virtual work,the dynamics mathematical model of the 2((2SPU)R)-(2UPR)R mechanism is derived,and dynamics models between center point of articulated platform and the telescopic rod,oscillating rod and actuated joint are obtained,respectively.In the dynamical mathematical model of the 2((2SPU)R)-(2UPR)R mechanism,dynamic inertia matrix,velocity matrix and gravity matrix are separated.Based on the inverse dynamic solution,the correctness of dynamics model of the 2((2SPU)R)-(2UPR)R mechanism is verified by Matlab and Adams.Based on kinematics and dynamics models of the 2((2SPU)R)-(2UPR)R mechanism,kinematics and dynamics performances of the mechanism are analyzed.The results show that the 2((2SPU)R)-(2UPR)R mechanism has not only larger output rotation angle and better dexterity,but also better acceleration performance and higher energy transfer efficiency.The effectiveness of the type synthesis method of redundantly actuated parallel mechanisms with large output rotational angles is proved.(4)Path planning and trajectory planning of the 2((2SPU)R)-(2UPR)R mechanism.Based on structure characteristics of the thermal insulation layer of the end face of the large tank,the segmentation method of the thermal insulation layer of the end face of the large tank is studied,the processing area and processing path of the thermal insulation layer of the end face of the large tank are analyzed,and the movement path and processing path of the 2((2SPU)R)-(2UPR)R mechanism are planned.Based on processing requirements of the 2((2SPU)R)-(2UPR)R mechanism for the thermal insulation layer of the end face of the large tank,a new trajectory planning method of combined acceleration mode is designed to solve the problem of large inertia force,impact on the large tank and internal impact of the 2((2SPU)R)-(2UPR)R mechanism in the moving path and processing path,and a mathematical model of the new trajectory planning method is deduced.Based on the new trajectory planning method of combined acceleration mode,the trajectory,velocity,acceleration and jerk of the 2((2SPU)R)-(2UPR)R mechanism in L-shaped motion path and circular path are planned,and a path calculation example is given to verify the new trajectory planning method.The results show that the 2((2SPU)R)-(2UPR)R mechanism along the L-shaped path and arc path can ensure stability and non-impact of the mechanism under the new combined acceleration mode trajectory planning method,and the effectiveness of the new trajectory planning method in linear path,arc path and two-point path is proved.The vibration impact and large inertia force of the mechanism are avoided,and the reliability and movement accuracy of 2((2SPU)R)-(2UPR)R mechanism in the process of movement processing are improved.(5)Research on control method of the 2((2SPU)R)-(2UPR)R mechanism.Based on structural characteristics of the 2((2SPU)R)-(2UPR)R mechanism and movement accuracy requirements of the 2((2SPU)R)-(2UPR)R mechanism,a force-position control strategy of the 2((2SPU)R)-(2UPR)R mechanism is proposed,that is,non-redundant limb adopts position control mode,and redundant limb adopts force control mode.In order to avoid external interference of the 2((2SPU)R)-(2UPR)R mechanism,A new discrete reaching law control method is designed.An adaptive fuzzy sliding mode control method based on super-twisting algorithm is proposed to solve the chattering phenomenon in control the 2((2SPU)R)-(2UPR)R mechanism,and enhance the stability of movement accuracy of the mechanism.The PID control method,a new discrete reaching law control method and an adaptive fuzzy sliding mode control based on super-twisting algorithm method are simulated and verified based on the new combined acceleration mode trajectory planning method and the planned circular arc calculation example in Chapter 5.The results show that the stability of the 2((2SPU)R)-(2UPR)R mechanism moving along the arc path is better than PID control method under a new discrete reaching law control method,and the 2((2SPU)R)-(2UPR)R mechanism has higher movement accuracy and better stability under an adaptive fuzzy sliding mode control based on super-twisting algorithm.At the same time,the correctness of the new combined acceleration trajectory planning method in Chapter 5 is verified.This paper provides theoretical guidance and technical support for the processing of the thermal insulation layer of the end face of the large tank. |
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