Deformation Error Prediction and Compensation for Robot Multi-axis Milling

Robot milling is an alternative to the expensive multi-axis NC for the large components, such as large scale marine propeller, with the advantage of less expensive and more flexible. However, the machining error mainly caused by poor stiffness of the joint is a critical obstacle for robot milling application. Especially for the robot multi-axis milling, the machining error is more difficult to predict and compensate due to the complicated coordinate transformation between the deformation of tool point and the cutting force feedback. The static stiffness model of robot milling system is established based on the joint stiffness matrix and Jacobian matrix. Using the static stiffness model and the cutting force model, an equilibrium equation with the variable of tool point deformation is established based on the constructed coordinate transformation for the theoretical cutting position and the actual cutting position in different coordinate systems. The analyzed results indicate that the milling error is mainly influenced by the translation of tool point. The proposed error prediction and compensation method is validated by the cutting experiments.