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

With the improvement of the social mechanization,higher and higher requirements which are reflected in the diversification of towing applications,Complication of towing environment,diversification of the objects,are put forward to towing technology and system.In order to reduce the complexity of the design and manufacture for the towing system,a number of robots are used in parallel to form the parallel cable-driven towing system,which is multi-robot coordinative towing system.The system,combined with the characteristics of multi-robot system and flexible cable parallel robot,not only has the advantages of reconfiguration,versatility,well flexibility,modularization,large working space,fast response and good environmental adaptability but also can solve the problems of low load capacity and unable to adjust the attitude of the object for a single robot.The internal dynamic characteristics of the under-constrained parallel cable-driven towing system are complex,and the Flexible cable with flexible and one-way constraints.Therefore,it is of great engineering practice and theoretical research value to study under-constrained multi-robot coordinative towing system.First,the configuration analysis of under-constrained multi-robot coordinative towing system is carried out,which mainly studies the kinematics,Dynamics model and error analysis of the multi-robot coordinative towing system for 3R3 T,and establishes the system model with error source problems surrounding this issue.On the basis of the kinematic analysis,the Newton Euler equation,which is the dynamic model of the system,is obtained according to the spatial geometry and d'Alembert's principle.Considering the error of mechanism and the flexible error of flexible cable,in addition,adding the Disturbance of external uncertainty,the system model with error source is obtained.Aiming at the shortcomings of a large number and complex for errors in the system,the error index,which can accurately and objectively reflect the whole error level of the object,is proposed and named Error entropy.Through the numerical simulation,the correctness of the kinematic and dynamic models,the error-source model of multi-robot coordinative towing system,and the proposed error-entropy index are verified.Secondly,analyzing the movement of under-constrained multi-robot coordinative towing system,the trajectory tracking control needs to be completed during the movement so that the actual moving trajectory tends to the ideal trajectory.Based on the error model of unconstrained multi-machine coordinated lifting system,it also has high frequency low amplitude vibration and system modeling errors.Combined with error factors which are analyzed and in line with the force-position hybrid control strategy,the system trajectory tracking control is achieved,using the methods which are based on BP neural Intelligent PID control network and fuzzy self-tuning immune PID control.The simulation results show that when the control parameters are reasonable,two kinds of control strategy can realize the system trajectory tracking.And the immune PID controller based on fuzzy self-tuning,which has better control effect on the system trajectory tracking control,is superior to the intelligent PID control based on BP neural network.Then,the swing analysis of the under-constrained multi-robot coordinative towing system is carried out.The swing conditions in the process of acceleration mutation are proposed,which is added to the planning control,to realize the anti-swing control of the system.Analyzing the process of the system swing,the system swing conditions are obtained.In view of the characteristics of the system,its starting and braking are divided into three situations.The acceleration and speed planning methods in different situations are proposed respectively.The flow chart of system's motion planning control is received by planning the motion process for the system from starting to stopping.In order to obtain the programming equation,complete acceleration and velocity planning are proposed for the linear motion and the curve motion respectively.The dynamic simulation of the anti-swing system control for the system is carried out,and the tension of the ropes under the linear motion and the curvilinear motion is obtained respectively.It can be verified that the acceleration planning control can quickly achieve the anti-swing control of the system.It is of great significance for improving the comprehensive performance of the under-constrained multi-robot coordinative towing system.Then,analyzing the positioning of under-constrained multi-robot coordinative towing system,model and control strategy of the swing for positioning are put forward.The swing of rapid positioning process of under-constrained multi-robot coordinative towing system is studied,and the swing caused by the rapid positioning is alternated by the double line pendulum and the single pendulum until the energy is exhausted.Then,according to the characteristics of the system,the flexible cable constraint predictive control is proposed.The controller based on the energy method is designed to achieve the fast positioning of the towing.And the simulation results show that it can realize the positioning control of the towing system quickly.Finally,the experimental prototype of under-constrained multi-robot coordinative towing system is designed and constructed,and the motion test is carried out.The correctness of the proposed model and the feasibility of method for planning anti-swing are verified by experiments.