Joint Space Motion Planning And Fuzzy Weighted Hybrid Force/Position Control For Redundant Robot Manipulators

On the premise of completing the terminal task,redundant robot manipulators can achieve additional functions,such as obstacle avoidance,avoiding exceeding joint limits,avoiding singularity,etc.Therefore,redundant robot manipulators can flexibly complete a variety of fine and complex operations.They are widely used in manufacturing,service,military and medical.However,compared with non-redundant robot manipulators,the model of redundant robot manipulators is more complex,and the inverse kinematics has infinite solutions.For contact tasks,such as assembly,grinding,polishing and engraving,not only the position accuracy of the redundant robot manipulator should be ensured in the presence of obstacles,but also there are strict requirements for its terminal contact force.Therefore,the motion planning and control of redundant robot manipulators are more challenging than those of non-redundant robot manipulators.To improve the planning efficiency of redundant robot manipulators,bidirectional planning algorithms are generally adopted.However,due to the uncertainty of inverse kinematics solution of redundant robot manipulators,in the case that the bidirectional planning algorithms are adopted to plan the path in the task space,the planned path in the joint space cannot be guaranteed to be continuous,which leads to the infeasibility of actual motion.In addition,traditional hybrid force/position control can avoid the dependence of impedance control on precise impedance models,but it also has the problem of dividing and switching the force and position spaces.Moreover,in the case that there is movement in the force direction of the robot manipulator,it is difficult to ensure the accuracy of position control and force control simultaneously for the traditional hybrid force/position control method.For many tasks,it is necessary for dual redundant robot manipulators to tightly coordinate.In this case,the dual redundant robot manipulators and the workpiece would form a closed chain structure.Then the terminal position,speed,and contact force of the two redundant robot manipulators will be restricted and constrained by each other.It is necessary to ensure that the closed chain kinematic constraints,the dynamic constraints,and the friction cone constraints can be met during the planning and control.Therefore,it would increase the difficulty of planning and control for tight coordination of dual redundant robot manipulators.To solve the above problems,the motion planning and hybrid force/position control of redundant robot manipulators are systematically studied in the thesis.The main research contents are described as follows:(1)To solve the problem that the planned path of bidirectional rapidly-exploring random tree(RRT)and its derived algorithms in the task space cannot ensure that the corresponding path in the joint space is continuous,a novel potential guided bidirectional RRT* algorithm in the joint space is proposed.This algorithm combines goal-biased RRT,bidirectional RRT,RRT* and artificial potential field method.To solve the problem that artificial potential field methods cannot be applied directly in the joint space,the artificial potential field method is improved by the way that joint angles colliding with obstacles are adopted to describe obstacles.It can ensure that the path of the redundant robot manipulator is continuous in both the task space and joint space.Besides,a direct connection strategy is designed to further accelerate the convergence speed.(2)To solve the problem that the traditional hybrid force/control method cannot ensure the accuracy of position control and force control simultaneously in the case that there is movement in the force direction,a fuzzy weighted hybrid force/position control method is proposed.The dynamics model of redundant robot manipulators in the joint space is transformed into the one in the task space by the minimum norm solution of inverse kinematics.Then,a weighted hybrid force/position controller is designed accordingly.It can eliminate the selection matrix of the traditional hybrid force/control by directly summing the force and position control laws through a weighted way.To increase the adaptability of this method to different working conditions and improve its control accuracy,a fuzzy self-tuning strategy is designed to adaptively adjust the weighted control coefficient.(3)To solve the problem that there are closed chain kinematic constraints for tight coordination of dual redundant robot manipulators,a novel potential guided bidirectional RRT* algorithm with closed chain constraints is proposed.The novel potential guided bidirectional RRT*algorithm of the single redundant robot manipulator is adopted to plan the path of one redundant robot manipulator,and then the corresponding path of the other redundant robot manipulator can be obtained by the speed constraints of the closed chain kinematics that replace the position constraints.To improve the efficiency of motion planning,the connectivity judgment method of the two trees is improved,and a local path replanning strategy is proposed according to the joint self-motion characteristics of redundant robot manipulators.(4)To solve the problem that there are dynamic constraints for tight coordination of dual redundant robot manipulators,a force-closure-based fuzzy weighted hybrid force/position coordination control method is proposed.The dynamic constraints are combined with the friction cone constraints.Then,the minimum energy consumption principle is adopted to optimize the distribution of the terminal contact force of dual redundant robot manipulators accordingly.To improve the coordination ability of dual redundant robot manipulators,the synchronization error is added to the weighted hybrid force/position control method.To enhance the operation ability of tight coordination of dual redundant robot manipulators,a fuzzy self-tuning strategy is designed to adaptively adjust the coordination control coefficient.(5)The experimental platforms of dual redundant robot manipulators are built.The experiments of joint space motion planning and fuzzy weighted hybrid force/position control are carried out.Results show the effectiveness and superiority of the proposed methods.