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Kinematically singular pre-stressed mechanisms as new semi-active variable stiffness springs for vibration isolation Open Access


Other title
Stiffness control
Antagonistic Variable stiffness Spring
Variable stiffness engine mount
Cable driven parallel manipulator
Antagonistic stiffness
Compliance control
Prestressable mechanism
Vibration isolation
Semi active stiffness
Variable stiffness
Variable stiffness isolator
Variable stiffness spring
Vibration isolator
Prestress stiffness
Cable driven Mechanism
Antagonistic Variable Stiffness Mount
Singular Mechanism
Piezo-electric actuator
Type of item
Degree grantor
University of Alberta
Author or creator
Azadi Sohi, Mojtaba
Supervisor and department
Faulkner, Gary (Department of Mechanical Engineering)
Behzadipour, Saeed (Department of Mechanical Engineering)
Examining committee member and department
Grondin, Gilbert (Department of Civil and Environmental Engineering)
Gosselin, Clément (Department of Mechanical Engineering, Laval University)
Raboud, Donal (Department of Mechanical Engineering)
Department of Mechanical Engineering

Date accepted
Graduation date
Doctor of Philosophy
Degree level
Researchers have offered a variety of solutions for overcoming the old and challenging problem of undesired vibrations. The optimum vibration-control solution that can be a passive, semi-active or active solution, is chosen based on the desired level of vibration-control, the budget and the nature of the vibration source. Mechanical vibration-control systems, which work based on variable stiffness control, are categorized as semi-active solutions. They are advantageous for applications with multiple excitation frequencies, such as seismic applications. The available mechanical variable stiffness systems that are used for vibration-control, however, are slow and usually big, and their slowness and size have limited their application. A new semi-active variable stiffness solution is introduced and developed in this thesis to address these challenges by providing a faster vibration-control system with a feasible size. The new solution proposed in this thesis is a semi-active variable stiffness mount/isolator called the antagonistic Variable Stiffness Mount (VSM), which uses a variable stiffness spring called the Antagonistic Variable stiffness Spring (AVS). The AVS is a kinematically singular prestressable mechanism. Its stiffness can be changed by controlling the prestress of the mechanism’s links. The AVS provides additional stiffness for a VSM when such stiffness is needed and remains inactive when it is not needed. The damping of the VSM is constant and an additional constant stiffness in the VSM supports the deadweight. Two cable-mechanisms - kinematically singular cable-driven mechanisms and Prism Tensegrities - are developed as AVSs in this thesis. Their optimal configurations are identified and a general formulation for their prestress stiffness is provided by using the notion of infinitesimal mechanism. The feasibility and practicality of the AVS and VSM are demonstrated through a case study of a typical engine mount by simulation of the mathematical models and by extensive experimental analysis. A VSM with an adjustable design, a piezo-actuation mechanism and a simple on-off controller is fabricated and tested for performance evaluation. The performance is measured based on four criteria: (1) how much the VSM controls the displacement near the resonance, (2) how well the VSM isolates the vibration at high frequencies, (3) how well the VSM controls the motion caused by shock, and (4) how fast the VSM reacts to control the vibration. For this evaluation, first the stiffness of the VSM was characterized through static and dynamic tests. Then performance of the VSM was evaluated and compared with an equivalent passive mount in two main areas of transmissibility and shock absorption. The response time of the VSM is also measured in a realistic scenario.
License granted by Mojtaba Azadi Sohi ( on 2010-09-28T20:20:42Z (GMT): Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of the above terms. The author reserves all other publication and other rights in association with the copyright in the thesis, and except as herein provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
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