Vibrations are the root cause of many mechanical and civil structure failures. Dynamic characteristics of a structure must be extracted to better understand structural vibrational problems. Modal analysis is used to determine the dynamic characteristics of a system like natural frequencies, damping ratios and mode shapes. Some of the applications of modal analysis include damage detection, design of a structure/machine for dynamic loading conditions and structural health monitoring. The techniques used for modal analysis are experimental modal analysis (EMA), operational modal analysis (OMA) and a less known technique called impact synchronous modal analysis (ISMA), which is a new development. EMA is performed in simulated controlled environment, while OMA and ISMA are performed when the system is in operation. Although EMA is the oldest modal analysis technique, there is an increasing interest in operational modal analysis techniques in recent years. In this paper, operational modal analysis techniques OMA and ISMA are reviewed with their development over the years and their pros and cons discussed.

A review of operational modal analysis techniques for in-service modal identification

A review on the advanced design techniques and methods of vibrating screen for coal preparation

Effects of intense pulsed light on Cronobacter sakazakii inoculated in non-fat dry milk

The minerals processing enterprises are widely using vibrating machines to separate different fractions of materials. Sieving efficiency is greatly dependent on particle trajectories, or orbit, of periodical motion over the sieving decks. A screening process is very dependable on design parameters such as the vibrator power, synchronisation of their drives, and oscillation frequency as well as the stiffness of supporting springs. Deterioration of supporting springs (stiffness reduction and cracks) due to cyclic loading and fatigue is difficult to determine by the visual inspection, static loading tests, or nondestructive testing techniques. Vibration monitoring systems of different vendors are analysed where vibration sensors usually installed on the bearings of vibrators are as well used for supporting springs diagnostics. However, strong cyclic components from the unbalanced exciters and stochastic disturbances from the input stream and vibrating pieces of the material make analysis a not trivial task. The considered vibrating screen is investigated on the 6-DOF (degree-of-freedom) dynamical model to reflect all linear and rotational components of spatial motion. Besides the main periodic motion, the model accounts for stochastic alpha-stable distributed impacts from the material. Instead, the Gaussian normal distribution is considered for the position of equivalent force application point. Supporting springs are represented by the bilinear stiffness characteristics. Specific features of vibration signals (angle of orbit inclination, natural frequency change, harmonics of natural frequency, and phase space plots) are analysed to recognise the weak nonlinear features of a system under conditions of small stiffness changes in springs. The extensive measurements are conducted on the industrial vibrating screen, and the dynamic model is verified by the measurement data. Recommendations are given on failure diagnostics of springs in the industrial vibrating screens.

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Development and Verification of the Diagnostic Model of the Sieving Screen

Motion analysis of a linear vibratory feeder: Dynamic modeling and experimental verification

Dynamic analysis of vibratory feeder and their effect on feed particle speed on conveying surface

Helical springs are mostly subjected to compression and expansion in their life cycles under working conditions in vibratory feeder. The continuous reversal stress leads to permanent deformations in pitch of coils of the helical springs due to creep phenomenon in which reversal stresses under various ambient conditions act as catalyst. The reduced pitch in coils of helical springs over period of time change the dynamic behavior of the vibratory feeder unit. The reduction in pitch in springs also leads to performance loss of the vibratory feeder. Therefore, it is essential to understand the dynamic characteristics of the feeder unit in order avoid catastrophic failures and performance losses. The objective of this research is to study the variations in dynamic behavior of vibratory feeder with old (reduced pitch) springs through modal analyses using FEM and EMA methods. The modal analysis using FEM technique is conducted in ANSYS workbench 14 using a three-dimensional model, which was developed in SolidWorks software. A working model of vibratory feeder was fabricated similar to the FE model for the experimental modal analysis (EMA). The instruments used in the EMA method are: one 4-channel FFT analyzer, one dynamic shaker, three accelerometers and a force transducer.

Analysis of variations in vibration behavior of vibratory feeder due to change in stiffness of helical springs using FEM and EMA methods

Modal analysis is a powerful tool to identify the dynamic characteristics of structures. Every structure vibrates with high amplitude of vibration at its resonant frequency. It is imperative to know the modal parameters — resonant frequency, mode shape and damping characteristics of the structure at its varying operating conditions for improving its strength and reliability at the design stage. The paper elucidates the behavior of a two storey metallic structure modeled to understand its dynamic characteristics of structure with the help of vibration dynamic signal analyzer, accelerometer, impact hammer and post-data analysis software. Single reference testing method has been used for the experimental analysis. Frequency response functions (FRFs) have been analysed with the help of modal analysis software. The theoretical modal analysis technique has also been investigated using finite element method (FEM). The results obtained from the theoretical and experimental analysis have been compared to draw the conclusion.Copyright © 2013 by ASME

Modal Analysis of Structural Vibration

The demand of ultra-precision micro-machine tools is growing day by day due to exigent requirements of miniaturized components. High accuracy, good dimensional precision and smooth surface finish are the major characteristics of these ultra-precision machine tools. High-speed machining has been adopted to increase the productivity using high-speed spindles. However, machine tool vibration is a major issue in high-speed machining. Vibration significantly deteriorates the quality of micro-machining in terms of dimensional precision and surface finish. This article describes a design methodology of a closed type machine structure for vibration minimization of a high-speed micro-milling center. The rigid machine structure has provided high stiffness and the damping capability to the machine tool without utilizing vibration absorbers. The models of the machine structures have been generated and assembled in AutoCAD 3D. The performance of the integrated micro-milling machine tools was determined by finite element analysis. The best model has been selected and proposed for manufacturing. Additionally, simulation results were validated by comparing with experimental results. Eventually, after manufacturing and assembly, experiments have been performed and it was observed that the amplitude of vibration was approaching towards nanometer level throughout the working range of the high-speed spindle. The machine tool was capable to fabricate miniaturized components with smooth surface finish.

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Development of a vibration free machine structure for high-speed micro-milling center

In vibratory feeder, material feeding occurs due to the vibration of a trough mounted on helical springs. High vibration amplitude of trough causes the springs to jump and usually results in higher...

M. L. Chandravanshi

Papers

Dynamic analysis of vibratory feeder and their effect on feed particle speed on conveying surface

Analysis of variations in vibration behavior of vibratory feeder due to change in stiffness of helical springs using FEM and EMA methods

Modal Analysis of Structural Vibration

Development of a vibration free machine structure for high-speed micro-milling center

Performance and noise analysis of vibratory feeder using dynamic rubber spring model