Off-line path correction of robotic face milling using static tool force and robot stiffness

In this paper the developed method for off-line compensation of tool deflections when milling aluminum with an industrial robot is presented. The efficiency of this approach is verified with high precision measurements of deflections using a laser tracker. The compensation method includes both the static milling process model which can predict the mean value components of the tool forces and a new combined local/global approach for estimating the combined stiffnesses of joints. With a process model such as the one presented in this paper and estimates of the robot's joint stiffness values, the tool path can be adjusted to counteract deflections of the tool during milling operations. The model was estimated from a large set of machining experiments and is valid for a given tool and material. The stiffness of each joint is a combination of several effects: (i) stiffness of the links, (ii) stiffness of joint bearings and gears and (iii) stiffness of the position control loops given by the individual axis controller gains in the controller software. The method presented in this paper increases accuracy when using an industrial robot for milling in relatively hard materials.