Research Of Trajectory Tracking Control And Anti-swing For Under-constrained Multi-robot Parallel Towing System

With the increasing degree of social mechanization and the large-scale and complex engineering tasks,the single hoisting robot can no longer meet the task under many special conditions.At the same time,blindly increasing the carrying capacity of the lifting robot will not only make its volume too large and structure too complex,but also cost a lot for its development and maintenance.The multi-robot parallel lifting system composed of several conventional lifting robots in parallel with flexible cables can greatly enhance the carrying capacity and easily change the position and posture of the robot,thus simplifying the lifting task.The under-constrained flexible multi-robot parallel coordinated lifting system combines the characteristics of multi-robot system and flexible parallel robot system.It has many advantages such as versatility,flexibility,reconfigurability,large workspace,strong adaptability and fast response speed.Under-constrained multi-robot parallel hoisting system has strong kinematics and dynamics coupling relationship,and the flexibility and unidirectional force of flexible cables,which makes the system become a research hotspot in the field of control and robotics.The in-depth study of the system has great theoretical research value and engineering practice value.Firstly,the configuration of the under-constrained multi-machine parallel lifting system is analyzed.On this basis,the closed vector method,D-H coordinate transformation method are used to establish the kinematics model of the system,Lagrange equation dynamics model and matrix total differential method are used to establish the motion error model,and the comprehensive error source of the system is obtained.Through the establishment and analysis of the kinematics model and dynamic model of the system,the theoretical foundation is laid for the study of the trajectory tracking control and anti-swing control of the system.Through the analysis of the error source of the under-constrained multi-robot parallel lifting system,the error of the space position of the lifted object in the process of lifting can be reduced fundamentally,and it is crucial to improve the accuracy of the space position of the lifted object.Secondly,a semi-closed-loop trajectory tracking control strategy is adopted for the trajectory tracking control of under-constrained multi-machine parallel crane system,which makes the actual trajectory of the lifted object tend to the desired trajectory.Based on the kinematics and dynamics model of the system,the trajectory of the end of the space three-joint robot is obtained by inverse kinematics model,so that the position of each joint of the robot can be controlled to meet the desired position of the end trajectory of the robot.An adaptive PID control method based on neural network is proposed and verified by simulation.The results show that the proposed trajectory tracking control method can track the desiredtrajectory of the robot well.Meanwhile,the actual trajectory of the lifted object quickly approaches the desired trajectory,and the trajectory tracking error remains in a minimum range.The trajectory tracking control effect is good.Thirdly,a fully closed-loop trajectory tracking control strategy for under-constrained multi-machine parallel crane system is proposed.On this strategy,a control method based on dynamic feed-forward compensation and PD feedback is designed.Considering the inaccuracy and unknown disturbance of the established dynamic model,a predictive feedforward control method is applied to compensate for this shortcoming.At the same time,feedback control is necessary for the trajectory tracking of the lifted object to achieve good results.Therefore,a feedback control method based on dynamic feedforward compensation is proposed.In order to improve the control performance of the controller,the proportional P and differential D coefficients of the PD control are optimized by genetic algorithm.Finally,the numerical simulation analysis shows that the control effect is good,the trajectory tracking error is minimal,and the control method is feasible.Then,the anti-swing control problem of under-constrained multi-robot parallel hoisting system is studied.The anti-swing control strategy of the system in the vertical lifting stage and the start-stop direction-changing stage is analyzed.The trajectory planning method based on high-order quintic polynomial interpolation is adopted to make the acceleration of the lifted object change continuously during the whole lifting process without sudden change of acceleration.The numerical simulation results show that the lifted object can maintain the continuous and smooth transition of acceleration,the cable tension changes reasonably,the cable length changes continuously,and the anti-swing control effect is obvious under the condition that the lifted object meets the desired trajectory after the high-order quintic polynomial interpolation programming.Finally,the experimental platform of the under-constrained multi-machine parallel crane system is designed and built,and the relevant performance of the motion test is carried out to verify the correctness of the mathematical model and the effectiveness of the anti-swing control strategy.