Continuously Variable Posture Selection in Robotic Milling for Increased Chatter Stability

Official URL: https://risc01.sabanciuniv.edu/record=b2486439_(Table of contents)

The demand for the usage of industrial robots for milling applications has surged owing to their superiority in terms of the large working envelope, reconfigurability, and low capital investment. Albeit such advantages, utilization of industrial robots for milling applications is yet to be a wonderland, where there are major challenges such as low tool path contouring accuracy, less static and dynamic rigidity. The former may be bearable for milling operations requiring less accuracy, such as roughing cycles. However, lowered dynamic rigidity causes decreased chatter stability, which is a roadblock towards effective robotic milling applications as a result of high vibration marks, bad surface quality, tool breakage and damage to the entire system. The position and orientation of the robots have a significant impact on milling stability. Therefore, identification of improved stable conditions is important to achieve increased productivity and process quality. In this thesis, dynamic modeling of the robots is studied to predict the variation in the robot dynamics with robot posture. Simulation results are compared to experimental modal analysis results and possible error sources are discussed. Milling dynamics and stability analysis are further extended to propose an alternative approach to increase chatter stability limits by benefiting the redundant axis of the 6-axis industrial robot. Different configurations of the robot based on the utilization of the redundant axis result in different stability limits by maintaining the same position of the tool. Preferable configuration sequences are generated for the improved cutting conditions through stability simulations based on measured frequency response functions of the tooltip. A proper robot programming scheme is also proposed in order to enable industrial application of the proposed methodology. Furthermore, the advantages of the proposed approach are discussed in accordance with the simulation results