Active Chatter Mitigation by Optimal Control of Regenerative Machining Process Dynamics

Chatter vibrations are a type of self-exited vibrations observed in many subtractive manufacturing processes. They limit achievable material remove rate (MRR), reduce tool life, resulting in poor surface finish, and even damage the manufacturing equipment. This article proposes a novel control system design for machine tool feed drives, which modulates cutting tool motion based on the in-process vibration measurements to mitigate chatter vibrations. The proposed approach has two key contributions. First, as opposed to introducing modal damping to the structure, the proposed approach stabilizes machining process dynamics by controlling its governing delay differential equation. H∞ control framework is used to design the controller and ensures robust process stability. The controller design problem is postulated as a convex optimization problem with linear matrix inequalities, which is solved to global optimality. Second, the proposed controller is implemented as an add-on compensator that works jointly with an existing servo motion control system to realize both positioning and chatter vibration control. Experimental validations are conducted on a lathe equipped with a fast tool servo actuator. It is shown that regenerative chatter vibrations in the orthogonal turning process can be suppressed robustly and up to five times increase in MRR (productivity) can be achieved.