Research On Obstacle Avoidance Algorithm Of Seven-Axis Redundant Manipulator Based On Null Space Self-Motion

In the background of industry 4.0 and made in China 2025,the competition of robot industry has become a key force in intelligent manufacturing industry,which also promotes the vigorous development of robot technology.With the continuous participation of the manipulator in the process of industrial production,its working space and tasks are more and more complex,and the demand of personalized customization production is becoming more and more diversified.The traditional six axis manipulator has the disadvantage of poor flexibility,which makes it not able to meet the needs of flexible production line.The seven axis redundant manipulator is more flexible than the traditional six axis manipulator.Its self motion characteristics can make the manipulator realize the tasks of avoiding obstacles,avoiding strange position and joint torque optimization,which is more in line with the needs of enterprises in industrial production.Therefore,the kinematics and obstacle avoidance planning of the redundant manipulator with the configuration of SRS(Sphere-Roll-Sphere)are studied.The main work of this thesis is as follows:Firstly,the kinematics of the redundant seven axis manipulator is analyzed.Based on DH(Denavit-Hartenberg)modeling method,the kinematics model of redundant seven axis manipulator is established and forward kinematics is derived.In addition,based on the self motion characteristics of redundant manipulator,the arm angle is defined as redundancy parameter outside the target pose matrix of the manipulator.An analytic solution algorithm for inverse kinematics of the seven axis redundant manipulator is derived by using the target pose matrix and the arm angle constraints.Secondly,the collision detection between the redundant seven axis manipulator and its working environment is analyzed.In order to reduce the complicated calculation in the process of collision detection,the model of redundant manipulator and obstacle model in environment is simplified by OBB(Oriented Bounding Box)direction bounding box modeling method.The collision detection problem between the seven axis redundant manipulator and the obstacles in the working environment is simplified into the geometric problem of the relationship between the space center line and the line,the line and the plane.According to the above geometric problems,three common collision detection methods,which are based on cylinder envelope collision detection algorithm,box envelope collision detection algorithm and sphere envelope collision detection algorithm,are introduced,and the detailed analysis and comparison are made.Then,the problem of obstacle avoidance planning for redundant manipulator with obstacles in its workspace is studied.An improved RRT~*(Rapidly-exploring Random Tree Star)null space obstacle avoidance algorithm is proposed.In view of the obstacle avoidance problem in some specific tasks of given robot arm end trajectory,based on the redundancy characteristics of the seven axis redundant manipulator,this thesis introduces a new obstacle avoidance algorithm based on null space self motion.In addition,some existing obstacle avoidance planning algorithms based on fast random search tree are introduced,and their advantages and disadvantages are analyzed in detail.In view of the shortcomings of RRT~*,combined with null space self motion and heuristic bias sampling strategy,the RRT~* algorithm is improved.An improved RRT~*null space obstacle avoidance algorithm is proposed,which improves the planning speed of the algorithm.Finally,the kinematics of the redundant seven axis manipulator and the simulation experiment of obstacle avoidance motion planning are carried out.This thesis introduces in detail how to transform the model files recognized in MATLAB from Solidworks model of seven axis redundant manipulator,and establish the three-dimensional simulation model of the manipulator;carry out the kinematics simulation experiment of the seven axis redundant manipulator,and verify its kinematics algorithm;simulate and verify the obstacle avoidance motion planning of the seven axis redundant manipulator arm,and the simulation content includes null space obstacle avoidance algorithm and null space obstacle avoidance algorithm The simulation results of the improved RRT~* obstacle avoidance algorithm show the effectiveness of the algorithm.