Hybrid Force/Stress Control Method for Robotic Polishing System Based on Hertzian Contact Theory

At present, high-speed railways have high design speeds and require high surface machining quality. Traditionally, automatic polishing systems are performed using a constant-force adaptive flange, In the face of complex surfaces, especially at the corners, unevenly and excessively polishing occurs. After subsequent spray treatment, problems such as surface ripples and streaks will appear that seriously affect product quality. This paper studies a robotic system that is suitable for polishing complex surface putty layers and develops a force controller to deal with abrupt changes in curvature at the corner of the surface. In order to realize even polishing, a hybrid control strategy based on Hertzian contact theory is proposed. By installing an active compliant device on the robot end-effector, the force control and position control of the tool are decoupled. While the robot controller is used to control the position and orientation of the tool mounted on the robot end-effector, the compliant device controller is used to control the contact force between the tool and the workpiece directly. The simulation results show that the method can track and compensate the target trajectory and realize rapid adjustment of the desired force. The experiment results show that the proposed control method can obtain good surface quality for polishing the vehicle putty layer.