Motion Planning Of A Six-degree-of-freedom Manipulator

The service robot has become a hotspot in the field of robotics due to its huge commercial application and theoretical research value.Mechanical arm can simulate human upper limb operation,which is an advanced subject in the research of service robot.In order to enable the manipulator to complete the operation autonomously in a complex environment,the robot arms need to have the ability of obstacle avoidance.After more than half a century of research about motion planning of robotic arm,many achievements are obtained and robotic arms are used in industrial production widely.But the mechanical arm motion planning in the family environment is still far from mature.Based on the self-developed service robot,Sun @ Home,some main problems about the motion planning of six degrees of freedom mechanical arms are studied,which include the mechanical arm modeling and kinematics analysis and trajectory planning,collision detection and obstacle avoidance motion planning are studied respectively.The main contents of the paper are shown as follows:Firstly,a mathematical model of the mechanical arm is established by using the standard DH(Denavit-Hartenberg)method for the first three joints of the 6DOF series manipulator,and the inverse kinematics is quickly solved.Through monte carlo method,the working space of the manipulator is simulated,which lays the foundation for the follow-up motion planning.Secondly,according to the characteristics of the task,the trajectory planning of the manipulator in free space is divided into two categories,namely,trajectory planning under joint space and trajectory planning under cartesian space.During the point-to-point movement of mechanical arms,USES high order polynomial in joint space trajectory of robot arm interpolation should meet the boundary conditions of the starting point and target.While,the configuration of starting point and the target can be obtained based on the inverse kinematics equation.During the path tracking of mechanical arms,a straight line or arc interpolation is used for the mechanical arm movement path interpolation in cartesian space.Finally,the path point sequence is obtained by interpolation inverse kinematics solution.Thirdly,the obstacle models in the workspace are simplified.And then the conditions of collisions are analyzed.Finally,the efficiency of collision detection is improved based on the method of hierarchical bounding box.Finally,according to the features of mechanical arm obstacle avoidance movement,the motion trajectory of the manipulator arm in the joint space is described in two sections.Based on the method of multiple objective weighting,a fitness evaluation function can be obtained,which is about joint Angle trajectory length increment and mechanical arm,joint maximum acceleration,movement time and collision.The related parameters of control points in the two paths are optimized by using the genetic algorithm.And finally,a path which makes the mechanical arm avoid complex obstacles is obtained.