Research on the directionality of end dynamic compliance dominated by milling robot body structure and milling vibration suppression

The end dynamic characteristics dominated by the milling robot's body structure play a crucial role in vibration control and chatter avoidance in robotic milling. As the excitation source, the milling force may exist in any direction under different process parameters. Consequently, investigating the directional distribution of the end dynamic characteristics becomes essential for studying the direction-dependent dynamic response of a milling robot. In this paper, firstly, the directionality of the end modal vibration is proved based on the body structure mode shape of the milling robot. Subsequently, combined with the multi-body dynamics model of milling robots, the distribution of the end dynamic compliance with the excitation direction in the robot mode is modeled and found to be double-sphere, which is verified experimentally. A convenient method for acquiring the double-sphere dynamic compliance (DSDC) is given and its portability is shown. Then, two application cases of the DSDC in milling vibration suppression are given. In Case 1, based on the DSDC, the milling vibration amplitude is found to be distributed as an eccentric ellipse with a non-orthogonal basis with the feed angle in a robot mode, wherein a feed direction selection method for reducing milling vibration without traversal calculation is given with experimental validation. Case 2 shows that according to the guidance of the DSDC, the tuned mass damper can significantly suppress the milling vibration. It is worth noting that the directionality of the end modal vibration and DSDC constitute fundamental dynamic properties of milling robots, which may provide a new theoretical basis for the research related to the robotic end dynamic characteristics (such as frequency response function identification, mode coupling chatter mechanism and its suppression, etc.), which are well worth exploring.