Design of an optimal damper to minimize the vibration of machine tool structures subject to random excitation
The vibration of machine tools during machining adversely affects machining accuracy and tool life, and therefore must be minimized. The cutting forces for stable turning are generally known to be random, and hence excite all the resonance modes. Of all these modes, those that generate relative motions between a cutting tool and a workpiece are of concern.This paper presents a new approach for designing an optimal damper to minimize the relative vibration between the cutting tool and workpiece during stable machining. An approximate normal mode method is employed to calculate the response of a machine tool system with nonproportional damping subject to random excitation. The major advantage of this method is that it reduces the amount of computation greatly for higher-order systems when responses have to be calculated repeatedly in the process of optimization. An optimal design procedure is presented based on a representative lumped parameter model that can be constructed by using existing experimental or analytical techniques. The two-step optimization procedure based on the modified pattern search and univariate search effectively leads the numerical solution to the global minimun irrespectively of initial values even under the existence of many local minima.
An Investigation on Optimal Designing of Dynamic Vibration Absorbers Using Genetic Algorithm
Abstract. In this study reducing of the unwanted phenomenon in machine tools, Vibration, has been investigated. The machine tools has been simulated as a five-degree-of-freedom discrete system consisting of cutting tool, work piece, body, head and cantilever of the machine. In order to reduce the undesired vibrations, a dynamic vibration absorber (DVA) with three unknown parameters (mass absorber, damping coefficient , stiffness absorber has been added to the system in different positions. Utilizing Newton’s second law, the governing equations have been obtained and solved. A genetic algorithm is proposed to efficiently achieve the optimum value for each 3-fold parameters in each positions of the system. The effectiveness of the proposed algorithm and the designed DVA is evaluated through comparing the vibration amplitude of the machine tool in the presence and absence of the DVA, and the paper concludes the best place to situate the vibration absorber and its specifications.
Identification of the Modal Properties of an Elastic Structure From Measured Transfer Function Data
A technique for identifying the modal properties of an elastic structure in a testing laboratory is presented. The technique is based upon the use of digital processing and the fast Fourier transform (FFT) to obtain transfer function data, and then the use of a least squared error estimator t o identify modal properties from the transfer function data. Both analytical and experimental results are presented.