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Research Papers

Design and Analysis of 3R2T and 3R3T Parallel Mechanisms With High Rotational Capability

[+] Author and Article Information
Congzhe Wang, Sheng Guo

School of Mechanical, Electronic,
and Control Engineering,
Beijing Jiaotong University,
Beijing 100044, China

Yuefa Fang

School of Mechanical, Electronic,
and Control Engineering,
Beijing Jiaotong University,
Beijing 100044, China
e-mail: yffang@bjtu.edu.cn

1Corresponding author.

Manuscript received August 14, 2014; final manuscript received February 3, 2015; published online August 18, 2015. Assoc. Editor: Leila Notash.

J. Mechanisms Robotics 8(1), 011004 (Aug 18, 2015) (11 pages) Paper No: JMR-14-1213; doi: 10.1115/1.4029834 History: Received August 14, 2014

This paper describes the design, kinematics, and workspace analysis of 3R2T and 3R3T parallel mechanisms (PMs) with large rotational angles about three axes. Since the design of PMs with high rotational capability is still a challenge, we propose the use of a new nonrigid (or articulated) moving platform with passive joints in order to reduce the interference between limbs and the moving platform. According to the proposed nonrigid platform and Lie subgroup of displacement theory, several 3R2T and 3R3T PMs are presented. Subsequently, the inverse kinematics and velocity analysis of one of the proposed mechanisms are detailed. Based on the derived inverse kinematic model, the constant-orientation workspace is computed numerically. Then, the analysis of rotational capability about the three axes is performed. The result shows that even if interference and singularity are taken into account, the proposed mechanisms still reveal the high continuously rotational capability about the three axes, by means of actuation redundancy.

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Figures

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Fig. 1

Kinematic diagram (a) and CAD model (b) of the new nonrigid platform

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Fig. 2

The constructed 3R2T PMs

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Fig. 3

Joint-and-loop graph of the 3R2T PMs

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Fig. 4

The constructed 3R3T PMs

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Fig. 5

Joint-and-loop graph of the 3R3T PMs

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Fig. 6

The 3R3T PM with the redesigned nonrigid platform

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Fig. 7

Geometrical model of the 3R3T_R PM

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Fig. 8

The infinitesimal screws and wrenches of the RRPaR chain

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Fig. 9

The constant-orientation workspace

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Fig. 10

The contour curves of the constant-orientation workspace of different points on the YbZb-plane

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Fig. 11

Platform configurations when β or γ takes different values: (a) β=45 deg, (b) β=90 deg, (c) γ=25 deg, and (d) γ=45 deg

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Fig. 12

Platform configurations when α takes different values: (a) α=60 deg and (b) α=120 deg

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Fig. 13

The configuration of limb 1 and limb 2

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Fig. 14

The relationships between 1/κx and α (a), between 1/κx and β (b), and between 1/κx and γ (c)

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Fig. 15

The relationship between κx and α for the redundant 3R3T_R PM

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Fig. 16

The distributions of 1/κx for the nonredundant ((a), (c), and (e)) and redundant 3R3T_R PMs ((b), (d), and (f))

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