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Research Papers

Variable Stiffness Spring Using Tensegrity Prisms

[+] Author and Article Information
Mojtaba Azadi

Department of Mechanical Engineering, Room 4-9, Mechanical Engineering Building, University of Alberta, Edmonton, AB, T6G2G8, Canadamojtaba.azadi@ualberta.ca

Saeed Behzadipour

Department of Mechanical Engineering, Room 4-9, Mechanical Engineering Building, University of Alberta, Edmonton, AB, T6G2G8, Canadasaeed.behzadipour@ualberta.ca

Gary Faulkner

Department of Mechanical Engineering, Room 4-9, Mechanical Engineering Building, University of Alberta, Edmonton, AB, T6G2G8, Canadagary.faulkner@ualberta.ca

As an estimate, the stiffness of one commercial rubber mount designed with tight tolerances on dynamic stiffness for accurate vibration calculation was measured to be 0.7% in its working range. The stiffness of regular engine mounts is expected to be even more nonlinear.

J. Mechanisms Robotics 2(4), 041001 (Aug 30, 2010) (13 pages) doi:10.1115/1.4001776 History: Received August 06, 2009; Revised March 25, 2010; Published August 30, 2010; Online August 30, 2010

A novel variable stiffness mechanism (i.e., variable spring) based on the concept of tensegrity structures is presented. Variable springs have extensive applications in noise and vibration control. The proposed method builds upon the prestress stiffness in tensegrities, which occurs along infinitesimal mechanisms and is fully controllable through force control in the members. A criterion is given to select a suitable tensegrity structure and an infinitesimal mechanism to develop a variable spring. Also, a mathematical model is developed for the stiffness components in an n-gon tensegrity prism. The variable components of the stiffness are then utilized to create a translational or rotational variable spring. In order to elaborate on the feasibility of the concept, a case study is presented on the engine mount of a vehicle. Parameters of a possible design of a variable stiffness mount are given, and the characteristics are compared with those of a conventional passive mount. This is followed by a detailed discussion on the properties of such a variable spring and the effects of various parameters.

Copyright © 2010 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Two examples of tensegrity structures (20)

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Figure 2

A regular truncated icosahedral tensegrity (courtesy of Dr. Murakami and Dr. Nishimura)

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Figure 3

Two TPs: (a) triangular TP and (b) square TP

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Figure 4

How an n-gon tensegrity prism (n-gon TP) is built: (a) n-gon truncated pyramid. (b) Right hand TP (studied in this paper). (c) Left hand TP.

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Figure 5

Top and side views of the second FOIM of a square TP

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Figure 6

Translational TPS

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Figure 8

(a) Variable stiffness engine mount made with a soft rubber mount and a square TP. (b) Regular PM.

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Figure 9

(a) A one DOF engine vibration model with VSM. (b) A one DOF engine vibration model with PM.

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Figure 10

Displacement transmissibility

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Figure 11

Force transmissibility

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Figure 12

Force-displacement relation of the square TP spring (prestress, 2200 N)

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Figure 13

Stiffness change with displacement of the square TP spring (prestress, 2200 N)

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Figure 14

Effects of prestress on translational TPS

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Figure 15

Effect of height ratio on translational TPS

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Figure 16

Effects of platform ratio on translational TPS

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Figure 17

Effects of overall size on a translational TPS

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Figure 18

Effects of the number of bars on translational TPS

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