Output-only complete mode shape identification of milling robot body structures using a limited number of current sensors

Milling robots have the advantage of large workspace and high flexibility compared to machine tools, and are more suitable for machining large and complex surfaces. However, the stiffness of robots is significantly lower than that of machine tools, and they are more prone to chattering. Compared to machine tools, robots mainly occur mode coupling chatter. Analyzing chatter in robots is a great challenge due to the highly flexible and pose-dependent position of the robotic arm. Mode coupling chatter is caused by the most flexible and dominant structural modes of the robot milling system. Available methods are unable to identify the structural modal parameters of a milling robot at all poses in the actual working state. This paper proposes a modal analysis method for robots, which can realize the automatic traversal of the pose of the milling robot and the automatic identification of modal parameters. This paper analyzes the robot multi-joint flexibility characteristics, spatial structure characteristics, and machining vibration characteristics, correlates the joint motor control system and current power characteristics, finds the correlation between the current information and the vibration information, and identifies the modal frequency through the current signals, and realizes the modal frequency identification in the entire workspace. This method is capable of output-only complete mode shape identification, can quickly analyze the main vibration modes, and is of great significance for the study of robot milling chattering.