Low-frequency chatter suppression in robotic milling using Magnetorheological Joint Damper (MRJD)

Low-frequency structural vibrations caused by poor rigidity are one of the main obstacles limiting the machining efficiency of robotic milling. Existing vibration suppression strategies primarily focus on passive vibration absorption at the robotic end and feedback control at the joint motor. Although these strategies have a certain vibration suppression effect, the limitations of robotic flexibility and the extremely limited applicable speed range remain to be overcome. In this study, a Magnetorheological Joint Damper (MRJD) is developed. The joint-mounted feature ensures machining flexibility of the robot, and the millisecond response time of the Magnetorheological Fluid (MRF) ensures a large effective spindle speed range. More importantly, the evolution law of the damping performance of MRJD was revealed based on a low-frequency chatter mechanism, which guarantees the application of MRJD in robotic milling machining. To analyze the influence of the robotic joint angle on the suppression effect of the MRJD, the joint braking coefficient and end braking coefficient were proposed. Parallel coordinate plots were used to visualize the joint range with the optimal vibration suppression effect. Finally, a combination of different postures and cutting parameters was used to verify the vibration suppression effect and feasibility of the joint angle optimization. The experimental results show that the MRJD, which directly improves the joint vibration resistance, can effectively suppress the low-frequency vibration of robotic milling under a variety of cutting conditions.