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Research Papers

Design and Validation of a Compatible 3-Degrees of Freedom Shoulder Exoskeleton With an Adaptive Center of Rotation

[+] Author and Article Information
Hua Yan

State Key Laboratory of Fluid Power
Transmission and Control,
Zhejiang University,
Hangzhou 310027, China
e-mail: wereyh@zju.edu.cn

Canjun Yang

State Key Laboratory of Fluid Power
Transmission and Control,
Zhejiang University,
Hangzhou 310027, China
e-mail: ycj@zju.edu.cn

Yansong Zhang

State Key Laboratory of Fluid Power
Transmission and Control,
Zhejiang University,
Hangzhou 310027, China
e-mail: zyansld@163.com

Yiqi Wang

State Key Laboratory of Fluid Power
Transmission and Control,
Zhejiang University,
Hangzhou 310027, China
e-mail: jialeng@zju.edu.cn

1Corresponding author.

Contributed by the Mechanisms and Robotics Committee of ASME for publication in the JOURNAL OF MECHANICAL DESIGN. Manuscript received February 4, 2013; final manuscript received March 19, 2014; published online April 28, 2014. Assoc. Editor: Matthew B. Parkinson.

J. Mech. Des 136(7), 071006 (Apr 28, 2014) (9 pages) Paper No: MD-13-1064; doi: 10.1115/1.4027284 History: Received February 04, 2013; Revised March 19, 2014

This paper outlines an experimentally based design method for a compatible 3-DOF shoulder exoskeleton with an adaptive center of rotation (CoR) by matching the mechanical CoR with the anatomical CoR to reduce human–machine interaction forces and improve comfort during dynamic humeral motion. The spatial–temporal description for anatomical CoR motion is obtained via a specific experimental task conducted on six healthy subjects. The task is comprised of a static section and a dynamic section, both of which are recorded with an infrared motion capture system using body-attached markers. To reduce the influence of human soft tissues, a custom-made four-marker group block was placed on the upper arm instead of using discrete markers. In the static section, the position of anatomical CoR is kept stationary and calculated using a well-known functional method. Based on the static results, the dynamic section determines the statistical relationship between the dynamic CoR position and the humeral orientation using an optimization method when subjects move their upper arm freely in the sagittal and coronal planes. Based on the resolved anatomical CoR motion, a new mechanical CoR model derived from a traditional ball-and-socket joint is applied to match the experimental results as closely as possible. In this mechanical model, the CoR motion in three-dimensional space is adjusted by translating two of the three intersecting joint axes, including the shoulder abduction/adduction and flexion/extension. A set of optimal translation parameters is obtained through proper matching criterion for the two CoRs. Based on the translation parameters, a compatible shoulder exoskeleton was manufactured and compared with a traditional shoulder exoskeleton with a fixed CoR. An experimental test was conducted to validate the CoR motion adaptation ability by measuring the human–machine interaction force during passive shoulder joint motion. The results provide a promising direction for future anthropomorphic shoulder exoskeleton design.

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Figures

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Fig. 1

Bones and joints of the shoulder complex

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Fig. 2

Marker location on the human body

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Fig. 3

Coordinate systems and vectors of one marker on an arm

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Fig. 4

Diagrams of the CoR position during humerus lifting movements in the sagittal plane (a) and coronal plane (b)

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Fig. 5

(a) Translation of the axes for abduction/adduction (X) and flexion/extension (Z), (b) flexion around a new axis (Z′), (c) abduction around a new axis (X′), and (d) new CoR position C

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Fig. 6

Three-dimensional description of the mechanical CoR (point C) motion under different translation parameters. (a) α0 = 270 deg, ρ0 = 1 cm and α1 = 90 deg, ρ1 = 1 cm and (b) α0 = 180 deg, ρ0 = 1 cm and α1 = 135 deg, ρ1 = 2 cm.

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Fig. 7

Matching between the mechanical CoR motion (grid) calculated using the optimal translation parameters and the anatomical CoR motion (red and blue lines) obtained in the experimental task

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Fig. 8

Shoulder exoskeleton and subject in experimental test

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Fig. 9

Exploded view of the semi-circular guide rail

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Fig. 10

Interaction force comparison between the new and traditional exoskeleton robots

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