Research Papers

Kinematic Analysis and Design of a Novel Shoulder Exoskeleton Using a Double Parallelogram Linkage

[+] Author and Article Information
Simon Christensen

Department of Material and Production,
Aalborg University,
Aalborg 9220, Denmark
e-mail: sic@mp.aau.dk

Shaoping Bai

Department of Material and Production,
Aalborg University,
Aalborg 9220, Denmark
e-mail: shb@mp.aau.dk

Contributed by the Mechanisms and Robotics Committee of ASME for publication in the JOURNAL OF MECHANISMS AND ROBOTICS. Manuscript received July 3, 2017; final manuscript received April 20, 2018; published online May 31, 2018. Assoc. Editor: Robert J. Wood.

J. Mechanisms Robotics 10(4), 041008 (May 31, 2018) (10 pages) Paper No: JMR-17-1199; doi: 10.1115/1.4040132 History: Received July 03, 2017; Revised April 20, 2018

The design of an innovative spherical mechanism with three degrees-of-freedom (DOFs) for a shoulder joint exoskeleton is presented in this paper. The spherical mechanism is designed with a double parallelogram linkage (DPL), which connects two revolute joints to implement the motion as a spherical joint, while maintaining the remote center (RC) of rotation. The design has several new features compared to the current state-of-the-art: (1) a relative large range of motion (RoM) free of singularity, (2) high overall stiffness, (3) lightweight, and (4) compact, which make it suitable for assistive exoskeletons. In this paper, the kinematics and singularities are analyzed for the spherical mechanism and DPL. Dimensional analysis is carried out to find the design with maximum RoM. The new shoulder joint is finally designed, constructed, and integrated in a four degree-of-freedom wearable upper-body exoskeleton. A finite element analysis (FEA) study is used to assess the structural stiffness of the proposed design in comparison to the conventional 3R mechanism.

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Fig. 5

Working principle of DPL in the shoulder mechanism

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Fig. 3

RoM of the shoulder complex

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Fig. 2

The shoulder complex: (a) segments and joints and (b) scapulohumeral rhythm

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Fig. 1

Illustration of shoulder joint mechanisms using (a) three-revolute joints, (b) two-revolute joints and a circular guide, (c) three-revolute joints with one placed at the elbow, and (d) a redundant joint

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Fig. 4

Kinematic model of the shoulder mechanism

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Fig. 7

The DPL with ϕ1=30deg and ϕ2=10deg in a kinematic configuration with (a) ψ=50deg, (b) ψ=−ϕ1, (c) ψ=180deg−ϕ1, (d) ψ=−ϕ2, and (e) ψ=180deg−ϕ2

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Fig. 6

The manipulability index of the DPM

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Fig. 8

Maximum and minimum internal/external rotation of the shoulder mechanism for (a) baseline design, (b) variation of lengths of L1 and L4, (c) variation of lengths of L2 and L3, (d) variation of length relation between L2 and L3, and (e) variation of offset angles ϕ1 and ϕ2

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Fig. 12

The shoulder joint mechanism in the AAU exoskeleton in (a) 0 deg shoulder extension, (b) 170 deg shoulder flexion, (c) 0 deg shoulder adduction, (d) 120 deg shoulder abduction, (e) 90 deg shoulder internal rotation, and (f) 20 deg shoulder external rotation

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Fig. 9

Workspace analysis of the DPM (cyan) within the human arm workspace (magenta): (a) coordinate setup, (b) isotropic view, (c) front plane view human workspace, (d) front plane view of DPM workspace, (e) sagittal plane view of human workspace, and (f) sagittal plane view of DPM workspace

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Fig. 10

Spherical shoulder joint built with parallelogram mechanism

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Fig. 11

The shoulder joint mechanism in the 4DOF AAU exoskeleton, with joints 1, 3, and 4 active and joint 2 passive

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Fig. 14

Displacement of the RC of rotation (RC-displacement) of the DPM and 3R spherical mechanisms, under a force of 10 N along the x-, y-, and z-axis of the end effector frame

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Fig. 13

Structural stiffness analysis of DPM and 3R spherical mechanisms



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