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 mechanisms 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.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:AEU.10048/1490 |
| Date | 11 1900 |
| Creators | Azadi Sohi, Mojtaba |
| Contributors | Behzadipour, Saeed (Department of Mechanical Engineering), Faulkner, Gary (Department of Mechanical Engineering), Raboud, Donal (Department of Mechanical Engineering), Grondin, Gilbert (Department of Civil and Environmental Engineering), Gosselin, Clment (Department of Mechanical Engineering, Laval University) |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Detected Language | English |
| Type | Thesis |
| Format | 10127698 bytes, application/pdf |
| Relation | Azadi, M., Behzadipour, S., Faulkner, G., Antagonistic Variable Stiffness Elements, Mechanism and Machine Theory, Vol. 44, No.9, 2009, 1746-1758., Azadi, M., Behzadipour, S., Faulkner, G., A Variable Spring Using a Tensegrity Prism, Accepted for publication at ASME Journal of Mechanisms and Robotics, April 2010., Azadi, M., Behzadipour, S., Guest, S. D., A New Variable Stiffness Spring Using A Prestressed mechanism, Proceeding of 2010 ASME International Design Engineering Technical Conferences, August 2010, DETC2010-28496., Azadi, M., Behzadipour, S., Faulkner, G., Variable Stiffness Tensegrity Prism Spring, Proceeding of 2009 ASME International Design Engineering Technical Conferences, August 2009, DETC2009-87407., Azadi, M., Behzadipour, S., An application of parallel singularity in variable stiffness elements, Proceeding of 2008 ASME International Design Engineering Technical Conferences, August 2008 , DETC2008-49414., Azadi, M., Behzadipour, S., Variable antagonistic stiffness element using tensegrity structure, Proceeding of ASME International Mechanical Engineering Congress, IMECE2007-42475, Nov 2007., Behzadipour, S., Azadi, M., Antagonistic Stiffness in Cable-driven Mechanisms, Proceedings of IFToMM World Congress, June 2007., Azadi, M., Behzadipour, S., A Planar Cable-driven Mechanism as a New Variable Stiffness Element , SAE 2007 Noise and Vibration Conference, SAE Paper No., 2007-01-2421. |
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