Rapid prediction of posture-dependent FRF of the tool tip in robotic milling

• Published in: Robotics and computer-integrated manufacturing 2020-08, Vol.64, p.101906, Article 101906
• Main Authors: Chen, Chen, Peng, Fangyu, Yan, Rong, Tang, Xiaowei, Li, Yuting, Fan, Zheng
• Format: Article
• Language: English
• Subjects: Chatter; Coupling; Degrees of freedom; Frequency response functions; FRF; Impact tests; Industrial robot; Industrial robots; Mathematical analysis; Milling; Milling (machining); Posture; Posture-dependent; RCSA; Robotics; Robots; Stability; Standardization; Stiffness; Substructures; Surface properties
• ISSN: 0736-5845; 1879-2537
• DOI: 10.1016/j.rcim.2019.101906

•The model to predict the FRF at the holder tip is extended to a six DOF robot, since the structures of the six DOF robot and one DOF robot are similar.•Based on the FRF acquisition tests at the arranged postures and a standardization process, the holder FRF of the six DOF robot at any posture is calculated.•Considering the coupling effects between the holder and the tool, the tool tip FRF at any posture of the milling robot is calculated using the RCSA method.•Both the low-frequency modes at around 10 to 20 Hz and high-frequency modes at around 800 to 1000Hz are simulated and compared with the experimental results, which validate that the tool tip FRFs can be calculated using the proposed method.•The dynamic stiffness, which significantly affects the machining stability, is validated to be varied with different postures. During the robotic milling process, vibration is one of the main factors that affect the machining accuracy and surface quality due to the low stiffness of the robot structure. The robotic milling stability is a function of the frequency response function (FRF) at the tool tip, which is posture-dependent within the workspace. This paper introduces an approach for rapidly predicting the tool tip FRF for industrial robotic milling at any posture. In this method, the models of the one degree-of-freedom (DOF) robot and two DOF robot are extended to a six DOF industrial robot to calculate the FRF at the holder tip based on the FRF acquisition tests at the arranged postures and a standardization process. Considering the coupling effects between the holder and the tool, the tool tip FRF at any posture of the milling robot is calculated using the receptance coupling substructure analysis (RCSA) method. Accordingly, the proposed method is applied to an industrial robot, and the feasibility of this method for predicting the posture-dependent FRF at high frequency in the workspace is validated though the impact tests. Moreover, the stability lobe diagram is calculated and the chatter tests are performed to validate its accuracy. At last, the robot structural modes are observed at the low-frequency dominant modes, whose frequencies are around 10 to 20 Hz.