Development of Pneumatic Force-Controlled Actuator for Automatic Robot Polishing Complex Curved Plexiglass Parts

Due to the temperature-sensitive characteristic of plexiglass materials, it is necessary to maintain a constant small contact force to avoid surface burn damage when polishing complex curved plexiglass parts. To handle the issue, in this paper a pneumatic force-controlled actuator was developed to keep the normal contact force between the polishing tool and the workpiece constant during the robotic polishing process. The force-controlled actuator is configured with a double-acting cylinder as the driving element, and two electrical proportional valves are used to control the output force by adjusting the pressure difference between the two air chambers of the cylinder. In this case, a small contact force can be exactly achieved, and the cylinder can always work within the optimal pressure range. In order to judge the stability of the system and reduce the commissioning time of the force-controlled actuator, a mathematical model of the force-controlled actuator is established. Meanwhile, for eliminating the influence of the gravity of the polishing tool on the contact force control, a gravity compensation algorithm is also given according to the roll-pitch-yaw (RPY) angle calculation method. Since there are some nonlinear factors in the operation of the force-controlled actuator, a fuzzy proportion-integral-derivative (PID) control strategy is adopted without steady-state errors. Finally, the polishing experiment of a complex curved plexiglass part was carried out by using the robot automatic polishing system. The experimental results show that the contact force control effect of the force-controlled actuator meets the processing requirements, and the curved plexiglass part has good surface quality and optical performance after polishing.