Robotically assisted active vibration control in milling: A feasibility study

Abstract

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 paper, the robotically 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. The effect of active control is evaluated. Frequency domain results show that the actively controlled robot arm increases the chatter stability and critical limiting depth of cut. A range of 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 validate the simulated frequency response function (FRF) results, several experimental tests are carried out for each control method. Furthermore, a time domain model is used to validate the stability lobe diagrams by detecting the chatter boundaries with/without actuator force saturation. It is shown that the critical limiting depth of cut can be increased by a factor of 2.6, compared to the scenario where the robot has no active control applied.