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Research Papers

A Compact 3 Degree of Freedom Spherical Joint

[+] Author and Article Information
Mark L. Guckert

Michael D. Naish1

Department of Mechanical and Materials Engineering,  The University of Western Ontario, London, ON, N6A 5B9, Canada;mnaish@uwo.caCanadian Surgical Technologies and Advanced Robotics (CSTAR),  Lawson Health Research Institute, London, ON, N6A 5A5, Canadamnaish@uwo.ca

1

1 Corresponding author.

J. Mechanisms Robotics 3(3), 031005 (Jul 27, 2011) (9 pages) doi:10.1115/1.4004028 History: Received June 05, 2010; Revised February 04, 2011; Published July 27, 2011; Online July 27, 2011

Spherical joints have evolved into a critical component of many robotic systems, often used to provide dexterity at the wrist of a manipulator. In this work, a novel 3 degree of freedom spherical joint is proposed, actuated by tendons that run along the surface of the sphere. The joint is mechanically simple and avoids mechanical singularities. The kinematics and mechanics of the joint are modeled and used to develop both open- and closed-loop control systems. Simulated and experimental assessment of the joint performance demonstrates that it can be successfully controlled in 3 degrees of freedom. It is expected that the joint will be a useful option in the development of emerging robotic applications, particularly those requiring miniaturization.

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Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Joint ball, socket, and assembly with tendons. Note that only two of four origin–insertion pairs are labeled. Tendons are shown as dashed lines in the left figure.

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Figure 2

Kinematic diagram of the idealized joint, with curved prismatic joints illustrating tendon paths

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Figure 3

Experimental joint apparatus with optical tracking system

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Figure 4

Tendon configurations from initial guess (a) and optimization (b). The inner circle represents the origins and the outer the insertions. The origin and insertion points are separated by (a) 1.66 mm and (b) 1.5 mm in the x-direction, respectively.

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Figure 5

Reachable workspace from (a) initial and (b) optimized tendon layouts. The circle represents the target workspace and markers •,∘ and + represent θ3 = 0 deg, 20 deg and -20 deg, respectively.

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Figure 6

Tracking of a θ1 reference under different control strategies

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Figure 7

Tracking of a θ1 reference under different control strategies, with a load of 0.3 N·mm applied to θ1

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Figure 8

Tracking of a θ1 reference under closed-loop control, with a load of 0.3 N mm applied to θ1, for both nylon and Dyneema tendons

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Figure 9

The angle between the reaction force of the ball on the socket and the center of the socket, for (a) θ3=0deg and (b) θ3=20deg rotation

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Figure 10

Driving θ1 through a sine wave using open-loop control

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Figure 11

Driving θ3 through a sine wave using open-loop control

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Figure 12

Joint angles as recorded by optical tracking while driving angles (a) θ1 and (b) θ3 through a sine wave using visual servoing

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