Research On Motion Planning And Trajectory Tracking Control Of Six-DOF Serial Robots

In 1954, the first electronic programmable robot was born in the U.S. Since then, robot is no long a science fiction of Czech novelist, but the life-long goal struggled by many scientists and engineers. After 50 years of development, foreign technology and application of robots gradually matured, and a number of well-known companies such as Yaskawa, Panasonic, KUKA, ABB and iRobot were brought up. Today, robot has become an essential unit of automatic production lines and flexible manufacturing systems. At the end of 2004, totoal number of the world's industrial robots was more than one million, and the annual growth rate in 2005 was 30 percent, which created a new record, and the growth rate in Asia was up to 43%. In 2007, the world's newly installed industrial robots were more than one million sets. Research and application of robot is far from stopped, but developing day by day with the trend of intelligent, modular and systematic. Its applications are expanding from traditional field of manufacturing to new fileds of architecture, agriculture, disaster prevention, medical care, the universe, the ocean, and even the fields closely related to human activities such as entertainment, home service.However, robotics is a high-tech technology which integrating the electronics technology, computer technology, sensor technology, control theory, artificial intelligence and bionics, etc. For the reasons of basic manufacturing technology, multi-disciplinary integration, promotion of industrialization and many other factors, although the research and development of robot began in 1972 in our country, but so far there is no successful domestic branch of robot, so the robots demanded still rely on imports. Therefore, whether for tracking the international advanced theory and technology, or for suppling services of robot application for domestic manufacturing, further research of key and common theories and technologies in robotics, and discovery of problems and solutions of domestic robot industrialization, are of great importance.In this paper, an arc welding robot named Qianjiang I is designed, theoretical research and experimental verification are carried out systematicly and deeply on serial robot, especially serial robot with six degrees of freedom. The research focuses on real-time inverse kinematics, trajectory planning, trajectory optimizing, dynamics coupling characteristics and high-precision tracking control, and aims to finding the constraints on domestic robot industrialization, as well as obtaining an effective solution of theory and technology for the development and application of serial robots.The thesis is divided into seven chapters, each chapter is summarized as follows: In the first chapter, development and application of serial robots at home and abroad are investigated and analyesed. Key theoretical and technical problems existing in serial robots, especially industrial robots, are pointed out. Then the significances, difficulties and contents are presented according to status quo of research and application of industrial robots.In chapterâ…¡, coordinate systems of links are set up, and D-H parameters are obtained. Then equations of kinematics and inverse kinematics are derived. Because the one-to-many relationship of variable in task space and joint space, stability and real-time performance of inverse kinematics are focused on. The geometry of serial robots with six degree of freedom is extended from the style which satisfies Pieper's rules to general structure, and a real-time inverse kinematics algorithm based on matrix decompostion is proposed for general 6R robots, which have six rotate joints and general geometry. By combining with the closure method, Newton - Raphson iterative algorithm, a set of algorithm is obtained, and the inverse kinematics problem of serial robots with six rotate joints and various geometries can be solved efficiently. At last, C++ programming language is adopted to realize the set of algortithms, so it can be used for real-time control systems of 6R robots.In chapterâ…¢, the construction of trajectories in task space and joint space are established. Equations that describe line, arc and spline curve in three-dimensional space are derivated, which are the basic elements of any complex trajectory. In order to achieve flexibility of motion, cubic spline is adopted to contruct smooth trajectory of posiotn in task space, and spherical quaternion interpolation method is exploited to generate smooth trajectory of orientation in task space. Because the output torque of driving and transmitting components of every joint is limited and smooth movement is required, a smooth trajectory planning method that considers kinematic constraints is proposed. B-spline is utilized to generate joint trajectory, so joint velocity, acceleration and jerk are continuous, and, the velocity, acceleration and jerk at the starting and stopping points can be configured. In order to enhance the working efficiency of robot, time optimal trajectory planning method is researched. By setting the total executing time of trajectory as goal of optimization, and transforming the kinematic constraints to constraints on control points of B-spline, the optimal time nodes are seeked with sequential quadratic programming algorithm, then time-optimal and jerk-continous trajectory is generated. Similar procedures are used to generate smoothness-optimal trajectory by setting the cumulative jerk as the goal of optimization. The trajectory planning and optimization algorithm construct the foundation for robots to execute tasks efficiently and smoothly.In chapterâ…£, the arc welding robot named "Qianjiang I" and its key technologies are introduced, including system architecture, mechanical structrue, hardware and software of embedded teaching box, main controller and main software, motion controller and motion control software, digital transfer module of manual arc welding machine. Lagrange method is exploited to obtain the dynamic equations of serial robot with six degrees of freedom. Then structural parameters of "Qianjiang I" are substituted into the equations, and its characteristics of inertia, Coriolis force and centrifugal force, and gravitational moment are analyzed. The results provide a theoretical basis for optimal design of mechanical structure and reasonable selection of drivers and actuators, and also provide dynamic model for research and design of joint controller and trajectory tracking controller.In chapterâ…¤, firstly, the control model of single joint driven by motor is analyzed. PID controller for AC servo motor is created in Matlab, by setting the transient characteristics and steady-state properties of step response as the optimizing target, optimal parameters of PI controller in velocity loop and PID controller in postion loop are seeked using the sequential quadratic programming method. And optimal parameters according to the largest inertial and the smallest inertial are obtained separately. Then, taking into account the dynamic, coupling and nonlinear characteristics when joints are runing simultaneously, fuzzy adaptive PID controller and PID controller with compensation of gravitational moment are designed. The performance of fuzzy adaptive PID controller in improving trajectory tracking accuracy is analyzed. The feasibility and effectiveness of PID controller with complete compensation of gravitational moment is discussed.In chapterâ…¥, iterative learning techniques are researched. Because tasks that industrial robots execute are often repeated, so, dynamic characteristics can be learned and adapted while the robot executes a certain task repeatedly, the dynamic characteristics include coupling inertia, coupling torque, friction and noise, etc. An adaptive iterative learning controller for trajectory tracking is proposed, which learns from trajectory tracking error and error derivative, and generates an incremental value that appends to the output of PD controller, so the trajectory tracking accuracy is improved. Then, an input-type iterative learning strategy is discussed, which does not change the model and parameters of controller, but modifies the input reference trajectory to achieve improved tracking accuracy of desired trajectory. At last, experiments are carried out on "Qianjiang I", and results verify the effectiveness of input-type iterative learning strategy.In chapterâ…¦, the main work, results and innovations of the thesis are summarized. Further research and domestic industrialization of serial robot are prospected, which provides a reference for the following research and design.