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Technical Briefs

Geometry and Kinematic Analysis of a Redundantly Actuated Parallel Mechanism That Eliminates Singularities and Improves Dexterity

[+] Author and Article Information
Jody A. Saglia

Department of Mechanical Engineering, King’s College London, University of London, WC2R 2LS, England, UK; Italian Institute of Technology, Via Morego 30, Genova 16163, Italyjody.saglia@kcl.ac.uk

Jian S. Dai

Department of Mechanical Engineering, King’s College London, University of London, WC2R 2LS, England, UK; Italian Institute of Technology, Via Morego 30, Genova 16163, Italyjian.dai@kcl.ac.uk

Darwin G. Caldwell

 Italian Institute of Technology, Via Morego 30, Genova 16163, Italydrawin.caldwell@iit.it

J. Mech. Des 130(12), 124501 (Oct 08, 2008) (5 pages) doi:10.1115/1.2988472 History: Received June 12, 2007; Revised August 22, 2008; Published October 08, 2008

This paper investigates the behavior of a type of parallel mechanisms with a central strut. The mechanism is of lower mobility, redundantly actuated, and used for sprained ankle rehabilitation. Singularity and dexterity are investigated for this type of parallel mechanisms based on the Jacobian matrix in terms of rank deficiency and condition number, throughout the workspace. The nonredundant cases with three and two limbs are compared with the redundantly actuated case with three limbs. The analysis demonstrates the advantage of introducing the actuation redundancy to eliminate singularities and to improve dexterity and justifies the choice of the presented mechanism for ankle rehabilitation.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

3SPS/U parallel mechanism

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Figure 2

Geometry of the parallel mechanism

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Figure 3

Determinant of the Jacobian matrix Jω for different combinations of orientation angles α and β

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Figure 4

Lateral view of Fig. 3

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Figure 5

Contours of the surface of the determinant of the Jacobian matrix Jω on the α-β plane

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Figure 6

Dexterity analysis of parallel mechanisms with three limbs: (a) local dexterity of a nonredundant parallel mechanism and (b) local dexterity of a redundant parallel mechanism

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Figure 7

Local dexterity of a redundant parallel mechanism with rb=1/2ra

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Figure 8

Dexterity of the parallel mechanisms with two limbs and a central strut: (a) local dexterity of the 2DOF mechanism with Limbs 1 and 2 arranged at 120 deg, (b) local dexterity of the 2 DOF mechanism with Limbs 2 and 3 arranged at 120 deg, and (c) local dexterity of the 2DOF parallel mechanism with two limbs arranged at 90 deg

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