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Research Papers

Design and Kinematical Performance Analysis of a 3-RUS/RRR Redundantly Actuated Parallel Mechanism for Ankle Rehabilitation

[+] Author and Article Information
Congzhe Wang

e-mail: 09116321@bjtu.edu.cn

Yuefa Fang

e-mail: yffang@bjtu.edu.cn

Yaqiong Chen

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

1Corresponding author.

Contributed by the Mechanisms and Robotics Committee of ASME for publication in the JOURNAL OF MECHANISMS AND ROBOTICS. Manuscript received July 27, 2012; final manuscript received April 20, 2013; published online July 16, 2013. Assoc. Editor: J. M. Selig.

J. Mechanisms Robotics 5(4), 041003 (Jul 16, 2013) (11 pages) Paper No: JMR-12-1107; doi: 10.1115/1.4024736 History: Received July 27, 2012; Revised April 20, 2013

In this paper, we present the design of a novel 3-RUS/RRR redundantly actuated parallel mechanism for ankle rehabilitation based on the principle from the conceptual design. The proposed mechanism can actualize the rotational movements of the ankle in three directions while at the same time the mechanism center of rotations can match the ankle axes of rotations compared with other multi-degree-of-freedom devices, owing to the structural characteristics of the special constraint limb and platform. A new actuator redundancy scheme is used, which not only still maintains all inherent advantages from actuator redundancy but also possesses the kinematic partially decouple feature that improves the flexibility of the robotic system. Kinematic performances, such as dexterity, singularity and stiffness, are analyzed based on the computed Jacobian. Then simulation is performed. All the results show that the redundant robot has no singularity, better dexterity and stiffness within the prescribed workspace in comparison with the corresponding 3-RUS/RRR nonredundant robot, and is suitable for rehabilitation exercise.

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References

Figures

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Fig. 1

Ankle joint complex [13]

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Fig. 2

JCS for the ankle complex [17]

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Fig. 3

Design process of the new mechanism: a single spherical joint (a); a serial spherical mechanism with arbitrary axes (b), orthogonal axes (c), orthogonal axes with symmetrical structure (d)

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Fig. 4

3D model of the redundant rehabilitation robot: (a) 3D view and (b) front view

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Fig. 5

Geometrical model of the mechanism

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Fig. 6

The available workspace of the redundant manipulator

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Fig. 7

The distribution of dexterity for the nonredundant (a) and redundant (b) in the plane of γ = 0 deg; the nonredundant (c) and redundant (d) within the whole prescribed workspace

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Fig. 8

Regions close to singularity with condition number >1000 for the nonredundant manipulator

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Fig. 9

The distribution of the maximum eigenvalues for the nonredundant (a) and redundant (b) in the plane of γ = 0 deg; the distribution of the minimum eigenvalues for the nonredundant (c) and redundant (d) in the plane of γ = 0 deg

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Fig. 10

Platform orientation (a) and torque (b) curves; one actuator torque for the redundant manipulator (c) and the nonredundant manipulator (d)

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