Robotically Assisted Active Vibration Control in Milling

The role of robots has been increasing in machining applications, with new concepts such as robotic-assisted machining where a robot supports the workpiece while it is machined by a machine tool. This method improves chatter stability to a certain extent. However, forced vibrations or unstable vibrations such as chatter can still be a limiting factor for the productivity and quality of the machining process. In this thesis, the robotic-assisted milling approach is extended to consider an actively controlled robot arm, to suppress the chatter vibrations for milling operation. To assess the feasibility of the method, a proof-mass actuator is assembled on a beam structure that is representative of the robot system. The beam structure is designed to exhibit two degrees of freedom in its structural dynamics, thereby emulating the robots' dynamic response. Many standard active control methods are evaluated, namely direct velocity feedback (DVF), virtual passive absorber (VPA), proportional integrated derivative (PID), linear quadratic regulator (LQR), H infinity (H∞) and μ synthesis control. To optimise the controller parameters, a self adaptive differential (SADE) algorithm is used. To validate the simulated frequency response function (FRF) results, several experimental tests are carried out for each control method. It is shown that the critical limiting depth of cut can be significantly increased, compared to the scenario where the robot has no active control applied. Then, the concept was examined under the real milling conditions. The experimental results showed that the chatter stability and the critical limiting depth of cut (b_min) were considerably improved. An actuator saturation model is proposed and the predicted results are considerably matched with the experimental results.