A high efficient frequency analysis method for closed flexible mechanism systems

This article presents the results of numerical and experimental modal analyses of a planar four-bar (4R) mechanism having three dimensional geometry due to the offsets between its links. An experimental mechanism is built and modern modal testing techniques are used. A five-node isoparametric finite element is developed and used to model the mass and flexibility of the links and joints, link offsets, and drive and load shafts. The results obtained from the finite element solution matched closely the experimental results, a testimony to the accuracy of the proposed element. The results indicated that link offsets have considerable influence on the dynamic characteristics of a mechanism system and should be considered in dynamic modeling of planar mechanisms.

Experimental and Finite Element Modal Analyses of Planar Mechanisms With Three-Dimensional Geometries

Natural frequencies and modes of Nipper Mechanism on Comber in motion are studied in this paper with emphasis on
the effects of gyroscopic effects. They are assumed to be different from those calculated based on assumptions of
instantaneous structure, neglecting the coupling of rigid body motion and elastic deformation, and so on, which is not
examined. In this study, finite element method is applied to simulate flexible links with those assumptions dropped and
gyroscopic effects is thus included due to the consideration of the coupling of rigid body motion and elastic deformation.
State space approach is applied to translate the second order differential equations into the first order with double degrees
of freedom. Because of the positive definition of global mass and stiffness matrix, Cholesky can be used to obtain the
standard gyroscopic eigenvalue equations which can be solved easily. Comparisons show that natural frequencies
affected by gyroscopic effects are growing quickly with the speed increasing, especially for the third natural frequency
which is much higher than that of simplified model. Therefore, much care needs to be taken when calculating
frequencies of mechanisms with high speeds and light weight.

Effects of gyroscopic effects on natural frequencies and modes of Nipper Mechanism on a Comber

Worse than common vibration, resonance is a form of severe vibration. It is very important and useful to know what factors and conditions can result in resonance of flexible manipulators, when both link flexibility and joint flexibility are taken into account. In this paper, resonance analysis of the flexible manipulator with both link flexibility and joint flexibility is studied. Based on the flexible dynamic equations, main factors resulting in resonance of the flexible manipulator are analyzed. Furthermore, several conditions exciting resonance are derived and verified with numerical simulations. These conclusions are helpful to predict resonance and useful to the structure design and motion planning for a flexible manipulator to evade resonance

Resonance Analysis of Manipulators with Flexible Link and Flexible Joint

The paper highlights the importance of optimal design model in the design evaluation of complex sealing mechanism. Sealing mechanism of the high-speed assembly machine is taken as the research object and construct rigid-flexible coupling dynamic equation. Dynamic characteristics of the sealing mechanism are analyzed by MATLAB. The maximum dynamic stress and reducing the acceleration of the end F are regarded as the optimization object. Cam profile curve parameter and the link cross section parameter are designed as the variables to construct the optimization design model of the whole sealing mechanism, and nonlinear constraint problem is transformed into a linear constraint problem. Based on the MATLAB genetic algorithm toolbox, the optimal design model of the sealing mechanism is solved, and the optimal result is obtained.

S. Nagarajan

Papers

Experimental Verification of Critical Speed Ranges for Elastic Closed Loop Linkage Systems

Dynamic Stability Considerations in Elastic Closed Loop Linkage Systems