The feasibility of eigenstructure assignment for machining chatter control

The eigenstructure assignment algorithm is proposed for controlling machining chatter by changing the response of the machine tool structure to dynamic cutting forces through the change of its modal properties so that the interaction between the tool and workpiece can be altered. The determination of the desired modal shapes is derived from a concept similar to gain scheduling in adaptive control system theory. By using computer simulations, the desired eigenstructure of the machine tool structure for different cutting conditions is determined and used to form the scheduling table. The gain matrix is adjusted according to the scheduling table and cutting conditions. It was found from experimental results that by changing the principal direction of the machine tool structure, the machining system could be stabilized and that the use of the proper eigenstructure to suppress machine tool chatter could significantly increase the material removal rate. Simulations have shown that the responses of the controlled machining system have been altered from unstable to stable, proving the feasibility of the proposed chatter control concept.