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Published Articles

The Volume 14, No 1, March 2009

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Tool Wear Monitoring in Turning Processes Using Vibratory Analysis

Wafaa Rmili, Abdeljalil Ouahabi, Roger Serra, Mecheri Kious


The main objective of this paper is to develop a signal processing strategy using vibratory signals in order to provide an efficient tool wear monitoring system able to increase machining performance. The method is based on the changes in the vibration signatures acquired during the turning operation over the tool life. Several signal processing techniques based on time and frequency domain analysis are proposed in order to extract a large number of indicators of the cutting tool state as variance, kurtosis, skewness, and coherence function. In this work, one of the innovative results is the tracking of tool wear by variance and coherence estimation. All of these indicators are correlated and validated by using white light interferometry measurements. This paper focuses on the technologies used in monitoring conventional cutting operations and presents important findings related to this field.

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Electromechanical Dynamics For Microplate

Lizhong Xu and ZhentongWu


In this paper, an electromechanical coupled dynamic model of the microplate subjected to electrostatic force is presented. The dynamic equations and the static equations of the electromechanical coupled microplate are obtained. For three different boundary conditions, the dynamic equations and the static equations are resolved, and the natural frequencies and the vibrating modes of the microplate subjected to electrostatic force are investigated. Influences of the boundary conditions on the natural frequencies and the vibrating modes are analyzed. Influences of the main electromechanical parameters on the natural frequencies are investigated as well. The natural frequencies of the microplate subjected to electrostatic force are affected by mechanical and electric parameters such as microplate size, voltage, clearance, etc.

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Cluster Control of Distributed-Parameter Structures

Nobuo Tanaka


When suppressing the vibration of a distributed parameter structure, control designers face the problem of its infinite number of vibration modes. It is, however, possible to group all the structural modes into a finite number of clusters, wherein all the structural modes belonging to a particular cluster have the same common attributes. If the structural modes within a given cluster are orthogonal to those in other clusters, the clusters may be controlled independently, thereby enabling cluster control with a simple control strategy without causing spillover problems. Grouping all the structural modes into a finite number of clusters is called cluster filtering, while independent control of each cluster is termed cluster actuation. Utilizing both cluster filtering and cluster actuation, cluster control may be performed. Cluster control offers the benefits of stability and control law simplicity analogous to low authority control (LAC), while providing the high control performance and some flexibility of control gain assignment of high authority control (HAC) ? hence middle authority control (MAC). Some examples are demonstrated for the purpose of clarifying cluster control. By expanding on the concept of cluster control, this paper further presents a control strategy that enables the creation of a stable, vibration-free state in the designated region of a targeted structure. To this end, a cluster vector that serves as the common link between cluster filtering and cluster actuation is introduced. It is shown that the suppression of a performance index, expressed in terms of the cluster vector, leads to the generation of a vibration-free state, whereas the suppression of conventional orthogonal contributors, such as radiation modes (sometimes termed power modes), does not.

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Wave Equations and Solutions of In Vacuo and Fluid-Filled Elliptical Cylindrical Shells

Abhijit Sarkar and Venkata R. Sonti


A perturbation-based approach is used to formulate the governing equations for wave propagation at high frequencies in infinite in vacuo and fluid-filled elliptical cylindrical shells. The in vacuo equations thus formulated have the form of a perturbation over the corresponding equations for the circular cylindrical shell. Here, eccentricity of the cross-section is assumed to be small and used as the perturbation parameter. Next, the coupled equations for the fluid-filled elliptical shell are obtained as a perturbation over the in vacuo shell equations (by using a single fluid-loading parameter). Asymptotic arguments are used to neglect various terms in the derivation, and a compact form of the non-dimensional governing equations is found. Presenting the governing equations in this form is the main contribution of this work. Due to the eccentricity, all spatial quantities need to be represented in terms of a harmonic series instead of a single harmonic term. Using symmetry and asymptotic arguments, the nature of the harmonic series is obtained. Using the harmonic series expansion, the dispersion relation is formulated for both the in vacuo and the fluid-filled cases. The in vacuo dispersion equation is solved using the regular perturbation method, while the transcendental coupled dispersion equation is solved numerically.

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