Accuracy improvement of robotic machining based on robot’s structural properties

Industrial robots are increasingly used as alternatives for specialized machine tools; however, the correct choice of a robot for a specific task or even programing the robot may present a problem if the robot’s structural properties and its accuracy throughout the workspace are unknown. In the article, an approach to improve the robot’s accuracy based on its structural properties is described. Manipulability, structural stiffness, structural inertia, damping ratios, and natural frequencies are chosen as the considered kinematic, static, and dynamic properties. Surrogate models to associate each property with the robot’s posture are established, and the relevant robot postures to machine a set of representative parts are derived. Analysis of the machined parts shows that machining accuracy depends on all considered property measures. By adjusting the robot’s posture, the machining accuracy for milling a hole was improved in diameter from 1.86 to 0.23 mm and in cylindricity from 0.87 to 0.16 mm. To evaluate robotic accuracy, a unique quality criterion is introduced and a predictive robotic machining accuracy model is established.