Model-Based Stability Prediction of a Machining Robot

Machining with anthropomorphic robotic manipulators is used to increase the flexibility and reduce the costs of production. The productivity in robotic machining process is limited by low rigidity of robot structure and vibration instability in machining (chatter). Chatter analysis in robotic machining process is a challenging issue due to the variability of the dynamic behavior of the serial robot in its workspace. Hence, a dynamic model which correctly takes into account these variations is important to define adequate cutting parameters and adequate robot configurations to be adapted along the machining path. In this paper, a multi-body dynamic model of a machining robot is elaborated using beam elements which can be easily simulated for machining trajectory planning. The beam elements geometry, elasticity and damping parameters are adjusted by experimental identifications. A stability diagram based on regenerative chatter in milling operations is established. Due to variations in the robot’s dynamic behavior along a machining trajectory each posture of the robot has its own stable cutting conditions. Therefore, this paper proposes a three-dimensional representation of a stability lobes diagram for the prediction of chatter vibrations in robotic machining. Stability prediction established through the proposed numeric model is validated by experimental machining tests with the ABB IRB 6660 industrial robot.