Research Papers

Equilibrium Conditions of a Polygonal Object When Grasped by Soft-Rolling Contacts

[+] Author and Article Information
John Fasoulas

Department of Electrical and Computer Engineering, Aristotle University of Thessaloniki, Thessaloniki 54124, Greecejfasoula@egnatia.ee.auth.gr

Zoe Doulgeri

Department of Electrical and Computer Engineering, Aristotle University of Thessaloniki, Thessaloniki 54124, Greecedoulgeri@vergina.eng.auth.gr

J. Dyn. Sys., Meas., Control 130(2), 021011 (Feb 29, 2008) (8 pages) doi:10.1115/1.2837449 History: Received October 10, 2005; Revised September 04, 2007; Published February 29, 2008

In this paper, we study two soft spherical fingertips grasping a rigid polygonal object as a kinematically constrained system. We assume that the contact locations of the soft fingertips are not fixed on the object but are able to move due to rolling constraints. A contact motion model is proposed for soft-rolling fingertips based on previously reported experimental findings on the rolling distance for a variety of soft materials. The equilibrium conditions are derived from the system dynamics and depend on the deformation and on the kind of soft material with regard to the fingertip’s rolling distance characteristics. Also, a discussion on contact forces and a grasp analysis at object’s equilibrium is made. It is shown that using the model of point contact with friction in soft-rolling contacts is not adequate for describing the real system with fingertips of low or medium stiffness characteristics. In general, the equilibrium conditions of the three contacted bodies (soft fingertips object) show that no-collinear interaction forces act on the object’s surface and they correspond to the equilibrium of an “internal object” held by two point contacts with friction.

Copyright © 2008 by American Society of Mechanical Engineers
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Figure 1

Normal force fn, tangential force ft, shear strength fs, and friction cone

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Figure 2

Rolling distance versus finger deformation

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Figure 3

Soft fingertips in contact with a rigid object

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Figure 4

Contact forces and torques in soft-rolling contacts

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Figure 5

Equilibrium with a “symmetric” grasp (Yc1=Yc2)

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Figure 6

Equilibrium with a nonsymmetric grasp (Yc1≠Yc2)

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Figure 7

General interaction line with parallel contact sides



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