Research On Robot Grinding And Polishing Method Based On Passive Compliance Control

In recent years,along with the rapid development of robot technology as well as the transformation and upgrading of manufacturing industry,more and more robots have been applied in industrial fields.As robots have greater stiffness and low positioning accuracy,when contact operation such as grinding and polishing is in progress,operation requirements cannot be met through conventional position control.It is necessary to add compliance control to the grinding and polishing robot which requires to test and control grinding and polishing contact force.Currently,there are two major ways to realize the control of contact force,namely active force control and passive force control.The active control method requires the robot controller to realize the control of both force and position;due to the existence of force/position coupling,the implementation is relatively complex.Comparatively,the passive force control has introduced the compliance device that is independent of the robot and is capable of separating the force control function from the robot controller.Being simpler and more feasible than active force control,it is realized through the compliance device,and thus has wider application prospects in industrial application occasions.Based on the structure of passive compliance device,the paper analyzed its main actuators,established the theoretical model of input control quantity and output force through servo valve flow equation,cylinder mass flow continuity equation and force equilibrium equation of the system,and identified device model parameters by applying the experimental determination method,which had laid the foundation for successive research on force control algorithm.According to the control principles of compliance device,servo valve control quantity,feedback quantity and the relationship among upper chamber pressure of the cylinder,contact force and feedback force were calibrated through experiments,thus achieve the control of the cylinder pressure and the device output force.In order to realize flexible grinding and polishing on curved surface parts,by integrating with the structure and model of compliance device,joint kinematics model of the grinding and polishing robot was established.Then,joint inverse kinematics was applied for finding solutions to the model.The paper also established a model with curved surfaces,and proposed the optimal grinding and polishing pose planning method on the basis of error threshold path point planning method and normal contacts of grinding and polishing tools and workpieces along the direction of principal curvature.The motion trajectory planning of robot in the obtained grinding and polishing point pose is carried out,and a continuous variable angular acceleration motion mode is obtained,which makes robot running more stable with the machining trajectory.The paper carried out studies on constant force control method of the compliance device and force position control strategies of the robot grinding and polishing system.By focusing on the shortcomings of the conventional PID control method that has been widely applied in industrial fields,the paper researched multiple improved PID control methods.It compared various control methods,and analyzed influences of various control parameters on the control performance through simulation.On the basis of above,a position compensation control strategy based on compliant device is proposed for the robot polishing system,and the strategy is proved to be feasible through system simulation.The paper conducted experiments to verify the above control algorithm and simulation results by establishing robot flexible grinding and polishing platform.By integrating with the path planning techniques,running program of the robot was generated through offline programming to perform experimental verification and comparative analysis on various force control methods.According to the experiments,the control method that combines fuzzy control and PID control has not only integrated merits of fuzzy control and PID control,so that the system can have relatively good dynamic performance and static characteristics at the same time,but also achieved the simpler and more feasible control.The paper has carried out supplementation studies on the optimization of grinding and polishing techniques.The ultimate blade grinding and polishing experiment has verified that the force control algorithm of the compliant device studied in this paper can realize the constant force control in the process of grinding and polishing;the path point position and pose planning algorithm make the blade surface polished more evenly;combined with the grinding and polishing process and the force/position control strategy of robot grinding and polishing based on the compliant device can realize the polishing process of the blade robot and obtain a better polishing surface roughness,which proves that the method of the robot polishing based on passive compliant control is feasible.