Smooth Motion Trajectory Planning And Control Method Research For Robot

Nowadays,robots are being widely used in welding manufacture and are significantly needed in most welding manufacture cases to track the weld seam for welding operations.Has the motion trajectory of the robot is not smooth,not only will it cause welding defects and affect the welding quality,but also decrease trajectory tracking accuracy,and even result in shock and vibration of the joints which will affect the equipment’s service life.Robot trajectory planning and control is a complex process which goes orderly through three processes,namely,the Cartesian space motion trajectory planning,joint space motion trajectory planning and joint control.Any inappropriate design of the three above-mentioned processes will affect the robot’s actual trajectory smoothness.This thesis aims to solve this problem and to realize the smooth motion trajectory planning of Cartesian space and joint space,and accurate joint motion control by researching on the robot’s smooth trajectory planning and control method and designing the robot trajectory planning and motion control system,so that the robot’s actual trajectory smoothness can be guaranteed.The author focuses on the problem that the trajectory of the Cartesian space for the 6-DOF industrial robot is constrained by the shape of the weld,being not able to be freely planned,which leads to the study of a two-degree-of-freedom positioner being used to extend the freedom of the robot and of the synchronous trajectory planning of the robot.The coordinate system of the robot and the positioner is established and the calibrated.In this thesis,the coordinate system of the robot and the positioner is established and calibrated,then weld key point coordinates are obtained and used to fit the welding line parameter equation.According to welding line parameter equation fitting by weld key point coordinates,motion trajectory of the positioner is planned and interpolated while the robot follows.This thesis establishes an experimental platform which consists of a robot and a positioned,and carries out the experiment that the synchronous motion planning and the interpolation method are programmed into a motion control system.Its result shows that the smooth trajectory of the Cartesian space can be realized.Since the smooth motion trajectory of Cartesian space cannot guarantee the smooth trajectory of the joint space,the author intends to further research on the method of smooth trajectory planning of the joint space.Four key points,obtaining from the Cartesian space interpolation points by means of the arithmetic of inverse kinematics in turn,are adopted to construct the quadratic polynomial curve.Then,by respectively obtaining the first and second derivatives of the curve,the angular velocity and angular acceleration of the interpolation point,which are used as the boundary condition to fit the fifth-order spline curve as smooth trajectory of joint space,will be estimated.This thesis will program this method into the motion control system to conduct the experiment.The experimental result shows that this method can effectively reduce the abrupt change of acceleration and can realize a smooth motion trajectory.The realization of smooth joint space motion trajectory planning requires precise joint control.The model-based joint control can improve the joint control precision.Dynamic parameters identification is the foundation of the model-based control method,whose identification precision directly affects the control performance.Based on the dynamic model established by recursive Newton-Euler equation,by means of decoupling and simplification,the basic dynamics parameters are obtained.The optimized finite Fourier series will be used as the excitation trajectory for excitation.Then the author will collect the data and calculate the basic dynamic parameters by applying the physical feasibility identification algorithm based on semi-definite programming.With the identification parameters,this thesis studies respectively on the model-based feed forward control and the torque constraint control,and conducts the experiments.The results show that the control method can effectively improve the trajectory tracking precision and realize the smooth motion.