Trajectory Planning And Research On Friction Compensation Of Six-axis Palletizing Robot

With the modernization of China's manufacturing industry,industrial robots are using more and more widely in production,instead of human labor to complete the stacking,spraying,welding and other types of work.However,industrial robot are limited by their low efficiency and low precision in movement.Non-optimal of the trajectory planning is one of the main reasons for the inefficiency of these robots.Moreover,friction widely exists in robotic systems,which is one of the main reasons for the low precision of these robots.In order to solve the above problems,this paper studies the kinematics,trajectory planning,dynamics and joint friction compensation of six-axis robots.This research is based on the six axis joint type robot.The kinematic model of the robot is established by the standard D-H parameter method and the forward kinematic equation is deduced to get the positive solution.The inverse solution is obtained by algebraic method.Then,Robotics Toolbox for MATLAB is used to verify the forward and inverse algorithm.The workspace is solved by the method of “limit fixed interval angle”.On the basis of kinematic analysis,the implementation of the planned palletizing trajectory is carried out.For the trajectory in the joint space,the smooth function is cubic spline function.Genetic algorithm is used to solve the problem of time optimal trajectory considering the constraints on angular velocity,angular acceleration and jerk.For the trajectory in the Cartesian space,trapezoidal acceleration and deceleration control algorithm is used with cubic spline curve to complete the straight line and circular interpolation.In MATLAB simulation environment,the robot runs the palletizing trajectory,stable,vibration-free and time optimal.The motion control strategy using joint friction compensation is an effective method to improve the running precision.Based on the Lagrangian method,the dynamic model of the six-axis robot is established and the relevant parameters of the dynamic equation are determined.Then,the dynamic simulation analysis and modal analysis are carried out in ADAMS and ANSYS.Based on the study of the dynamics,a series of friction models are introduced from the physical characteristics of the friction.The Stribeck model is adopted as the compensation model of the robot joint friction,which lays the foundation for the subsequent friction compensation experiments.The Stribeck curve is obtained by the constant velocity tracking experiment in MATLAB.The friction parameter identification is completed by genetic algorithm and the accuracy of the friction model is verified.The simulation results of friction compensation of the end joint in the Simulink module of MATLAB are compared using the methods of PD control and feed-forward PD control based on the Stribeck friction compensation.It is shown that the latter control method can eliminate the "flat-top" and "low-speed crawling" phenomenons,the tracking error is smaller and the operation is more accurate.The software design of the control system is presented in this paper.Based on the analysis of teaching data of Keba and Yasuoki robotic company,this paper summarizes the process of "Teaching and Playback",and uses QT to develop a simple and easy teaching box control interface.Then,based on the API function of Googol motion controller,the trajectory planning of linear and circular arcs is successfully carried out on the six-axis robot platform.