Modeling And Planning Of Trajectory And Anti Swing For Multi-robot Cooperative Towing Systems

Multi-robot cooperative towing system is widely used in military and civil fields due to the advantages of simple structure,reconfigurable,easy to disassemble,high degree of modularization,large working space and high cost performance.It can be used on land,water and air for lifting operation.This kind of system can be regarded as an important branch of parallel robot because of its characteristics of parallel rope robot and multi robot system.It is a new type of multi robot system,which is obviously different from the traditional single rigid support parallel robot and single body parallel cable robot due to its flexibility and unidirectional constraint characteristics of flexible cables,weak stiffness,instability and under constraint in most cases.It is of great theoretical significance and practical value to carry out the scientific research on the modeling,trajectory planning and anti swing planning of the multi-robot cooperative towing system.The main contents of the dissertation are as follows.(1)Models of kinematics and dynamics for the multi-robot cooperative towing system are established.The classification and characteristics of the system are discussed from three aspects,i.e.crane base,system constraints and the driving of the lifted object.The generalized kinematics and dynamics models of the fixed base multi-robot cooperative towing system are established according to the screw theory and Newton-Euler method.The existence of forward and inverse kinematics solutions is analyzed,and the corresponding solutions are obtained.The kinematics and dynamics models of free radical base and floating base of the multi-robot cooperative towing system are established.The kinematics and dynamics models of the multi-robot cooperative towing system with different bases are established combining the kinematics and dynamics models of the base with the ones of the multi-robot cooperative towing system on fixed base.(2)The motion realization of the multi-robot cooperative towing system is discussed when the helicopter is taken as an example in order to make the complex multi-robot cooperative towing system practical.The space problem is reduced to a plane problem by limiting the motion of the helicopter on the basis of keeping the basic structural parameters of the system.The translational and rotational motion equations of the system are obtained by using the balance equation and vector closure theory.The motion realization process of the numerical calculation system verifies the correctness of the kinematic model.(3)The constraint factors of working space of the multi-robot cooperative towing system are analyzed.The Monte-Carlo algorithm is improved and the partition and block workspace solution method is proposed combined with the finite element method due to the boundary of the workspace is not clear when the Monte-Carlo algorithm is used to solve the position and attitude space of the system.The working space of the system is extended effectively and the pose workspace with clearer boundary can be obtained by improved Monte-Carlo method.(4)The trajectory planning of the multi-robot cooperative towing system is studied.The overall scheme of system planning is given based on the analysis of constraint characteristics of motion planning of the multi-robot cooperative towing system.a hierarchical trajectory search strategy and a step-by-step trajectory optimization method are proposed based on the trajectory planning of the lifted object.The optimal trajectory of the robot end is obtained when the change rate of cable tension and the stability of force posture are taken as the optimization evaluation indexes in order to ensure that the lifted object can move quickly and smoothly from the starting point to the target point in the system workspace.The correctness and effectiveness of the proposed planning method is verified by simulation with a specific configuration multi-robot cooperative towing system as an example.(5)The swing problem of the lifted object in multi-robot cooperative towing system is studied.A flexible cable constrained expected control method is proposed to solve the problem of fast positioning of the lifted objects.Acceleration planning strategy is adopted to prevent the swing of the lifted object during transportation.The anti swing principle and anti swing strategy are determined in order to solve the swing when the lifted object reaches the target point or prevents collision with obstacles in the multi-robot cooperative towing system.(6)The virtual simulation and experiment platform of multi-robot cooperative towing system is built and the correctness of the system trajectory planning and anti swing planning method is verified.A virtual simulation and physical experiment platform for the multi-robot cooperative towing system is built,which verifies the correctness of the motion trajectory planning and swing planning methods.The virtual simulation experiment platform of the multi-robot cooperative towing system is established by using the joint simulation technology of UG,ADAMS and Matlab.The kinematics,dynamics model and trajectory planning method of the system are verified by simulation when the mobile multi-robot cooperative towing system is taken as an example.The entity experimental platform of the fixed base multi-robot cooperative towing system is established,and the design scheme of mechanical body,electrical hardware system,upper computer interface and control application program of the experimental platform is analyzed.The experimental results show that the tracking ability,trajectory planning and anti swing method of the system are correct and feasible under the condition of given expected translational motion and attitude trajectory of the lifted object.