Enhancement of dynamic quality of a machine tool using a frequency response optimisation method

Abstract

A recently developed method of structural dynamic optimisation has been applied to a complex engineering structure e.g. a high speed machining centre. The method does not require identification of mass and stiffness matrices as well as modal parameters of the considered structure, and thus avoids somewhat arbitrary curve fitting and mode truncation procedures. The method deals with raw experimental frequency response functions: by solving an optimisation problem, the physical structural changes which yield specified dynamic requirements at a minimum cost are determined. In order to get a preliminary estimate of the effectiveness of each structural change a sensitivity analysis can also be performed prior to the formulation of the optimisation problem. It is found that addition of masses to various locations on the structure does not result in substantial improvements, while a small dynamic absorber with highly damped elastic connections provides the required improvements in dynamic characteristics. Experimental tests using a prototype dynamic absorber are in good agreement with the analytical predictions, showing considerable reduction in the dynamic response of the machine tool.