Development of a Hybrid Motion/Force Control Strategy for Ball End Abrasive Tools and Its Application to Polishing Robots for PET Bottle Molds

In this paper, a polishing robot with a hybrid motion/force controller is proposed for polishing of PET bottle molds. A ball end abrasive tool is attached to the tip of the robot arm via a force sensor. The polishing robot has two main features. One is that the surface of the mold is polished by the polishing force acting between the mold and the abrasive tool. The polishing force is assumed to be considered as a composite force of the contact and kinetic friction forces, in which the friction consists of Coulomb and viscous frictions. The polishing force is controlled by a feedback loop action. When a PET bottle mold with curved surface is polished by the proposed robot, not only the orientation of the abrasive tool is fixed but also its revolution is locked. The other is that no complicated teaching task is needed. The motion of the abrasive tool is feedforwardly controlled based on a prepared initial trajectory, i.e., cutter location data. The velocities of the tool in normal and tangential directions are delicately regulated so that the polishing force can track a desired value. The effectiveness of the proposed system is proved by experiments using two industrial robots with an open architectural controller.