Grinding Trajectory Planning And Motion Control Of Industrial Robot Based On Force Sensing Servo

When the industrial robot performs a task,the motion trajectory of the robot is often limited by some additional constraints.For example,when grinding the surfaces such as plane,cylinder,cone,sphere,and other irregular surfaces,we have to control the robot's end effector to chase the pre-planned track on the surface accurately,so as to ensure the quality of surface grinding process.However,before grinding,the workpiece often has dimensional error,which requires the robot to adjust the motion trajectory in accordance with the grinding surface in real time,so that the force between the robot end tool and the workpiece could always maintain within a certain range,and ensure that the robot grinding process is not stuck and grinding quality is guaranteed.In this paper,the UR5 industrial robot is used to study the trajectory planning,the grinding and polishing motion control based on the force sensing servo.The robot can adjust the trajectory in real time according to the force of the end tool while moving in accordance with the pre-planned trajectory.This paper firstly analyzed the characteristics of the robot grinding operation,designed the overall scheme of robot control system,and set up the robot grinding experiment platform.Kinematics analysis was carried out on the UR5 industrial robots,by applying the method of D-H.Robot kinematics model was established and the kinematic forward and inverse solution was deduced.Through the analysis of the robot's singularity,it was improved for the design of the experimental platform.Aiming at meeting the constant pressure control requirement during the process of grinding and polishing,the force acquisition and signal processing equipment were designed.In order to obtain the reliable estimate of the contact force,it is necessary to compensate for the loss caused by tool's gravity,zero-drift of the sensor,force deviation after installation and force of friction generated in grinding and polishing process.Secondly,this paper designed the grinding trajectory for free-form surface.Using STL three-dimensional model and Bezier triangular surface fitting method to proceed the three-dimensional reconstruction and match towards the free-form surface of the workpiece.In the Cartesian space,isoparametric method was employed to build up the track of robot's grinding and polishing which provide track reference to the usage of robot end effector's constant pressure control.Then,motion control was implemented for industrial robot during grinding and polishing operation.The robot force/position hybrid control algorithm with the PID algorithm was combined to adjust the final position of the robot in motion.Eventually the constant pressure control of the robot end tool was achieved.The robot's control system architecture and motion controller was designed,using the robot end speed control to achieve force/position hybrid controller design.Finally,the trajectory planning and motion control method based on force sensing servo were verified on the UR5 grinding and polishing platform.Based on the scanning trajectory and helical parameters,the ATI six-dimensional force sensor was used to monitor the force information of the robot end-effector and feedback to the host computer,and then the constant pressure control reciprocal parameter trajectory was used to make precise adjustment.The experimental results show that the force sensing servo method can effectively solve the machining problems caused by the inaccuracy of the model,and provides a feasible solution for the robot grinding and polishing control.