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Research Papers

A Bio-Inspired Condylar Hinge for Robotic Limbs

[+] Author and Article Information
Appolinaire C. Etoundi

Queen's Building - University Walk,
Clifton BS8 1TR,
Bristol, UK
e-mail: A.C.Etoundi@bristol.ac.uk

Stuart C. Burgess

Queen's Building - University Walk,
Clifton BS8 1TR,
Bristol, UK
e-mail: S.C.Burgess@bristol.ac.uk

Ravi Vaidyanathan

South Kensington Campus,
Exhibition Road SW7 2AZ,
London, UK
e-mail: R.Vaidyanathan@imperial.ac.uk

Contributed by the Mechanisms and Robotics Committee of ASME for publication in the JOURNAL OF MECHANISMS AND ROBOTICS. The Manuscript was submitted on 22nd November 2011; final manuscript received May 3, 2013; published online June 27, 2013. Assoc. Editor: Qiaode Jeffrey Ge.

J. Mechanisms Robotics 5(3), 031011 (Jun 27, 2013) (8 pages) Paper No: JMR-11-1134; doi: 10.1115/1.4024471 History: Received November 22, 2011; Revised May 03, 2013

This paper presents a novel condylar hinge for robotic limbs which was inspired by the human knee joint. The ligaments in the human knee joint can be modeled as an inverted parallelogram four-bar mechanism. The knee joint also has a condylar cam mechanism between the femur and tibia bones. The bio-inspired joint mimics the four-bar mechanism and the cam mechanism of the human knee joint. The bio-inspired design has the same desirable features of a human knee joint including compactness, high mechanical advantage, high strength, high stiffness and locking in the upright position. These characteristics are important for robotic limbs where there are often tight space and mass limitations. A prototype hinge joint similar in size to the human knee joint has been designed and tested. Experimental tests have shown that the new condylar hinge joint has superior performance to a pin-jointed hinge in terms of mechanical advantage and stiffness. The prototype hinge has a mechanical advantage that is greater than a pin-jointed hinge by up to 35% which leads to a corresponding reduction in the peak force of the actuator of up to 35% for a squatting movement. The paper also presents a five-step design procedure to produce a combined inverted parallelogram mechanism with a cam mechanism.

Copyright © 2013 by ASME
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References

Figures

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Fig. 1

Typical robotic limb with pin hinge joints adapted from Ref. [6]

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Fig. 2

Front view of the human knee: (a) adult specimen and (b) schematic

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Fig. 3

The four-bar mechanism of the human knee joint (θ = knee angle)

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Fig. 4

Movement of the initial contact point C1

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Fig. 5

Animation of the femur motion to derive the tibia profile

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Fig. 6

Slide ratio versus knee angle for the prototype

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Fig. 7

Prototype condylar joint

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Fig. 8

Prototype condylar joint at different angles of rotation (θ = 45, 95, 110 deg)

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Fig. 9

Transition from tension to compression in a ligament (T = tension, C = compression)

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Fig. 10

Forces acting at the cam interface

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Fig. 11

Critical coefficient of friction versus knee angle

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Fig. 12

Moment arm, r(θ) versus hinge angle and moment arm of an equivalent pin joint

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Fig. 13

Actuator force required for a squatting motion for a four-bar hinge and a pin joint

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Fig. 14

Measured lateral bending stiffness of the condylar joint and human knee joint [38]

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Fig. 15

Condylar hinge joint friction versus knee angle

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Fig. 16

The endurance test rig

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