Research Papers

Design and Manufacturing of Embedded Air-Muscles for a Magnetic Resonance Imaging Compatible Prostate Cancer Binary Manipulator

[+] Author and Article Information
Geneviève Miron

e-mail: genevieve.miron@usherbrooke.ca

Alexandre Girard

e-mail: alexandre.girard2@usherbrooke.ca

Jean-Sébastien Plante

e-mail: jean-sebastien.plante@usherbrooke.caDepartment of Mechanical Engineering, Université de Sherbrooke, Sherbrooke, QC, J1K 2R1, Canada

Martin Lepage

Department of Nuclear Medicine and Radiobiology, Université de Sherbrooke, Sherbrooke, QC, J1H 5N4, Canada e-mail: martin.lepage@usherbrooke.ca

Contributed by the Mechanisms and Robotics Committee of ASME for publication in the Journal of Mechanical Design. Manuscript received May 30, 2012; final manuscript received September 28, 2012; published online November 19, 2012. Assoc. Editor: Oscar Altuzarra.

J. Mech. Des 135(1), 011003 (Nov 19, 2012) (10 pages) Paper No: MD-12-1289; doi: 10.1115/1.4007932 History: Received May 30, 2012; Revised September 28, 2012

Magnetic resonance imaging (MRI) compatible robots can assist physicians with the insertion of biopsy needles and needle-like therapeutic instruments directly into millimeter-size tumors, using MR images as feedback. However, MRI systems present a challenging environment with high magnetic fields and limited space, making the development of MRI-compatible robots complex. This paper presents an MRI-compatible pneumatic actuation technology consisting of molded polymer structures with embedded air-muscles operated in a binary fashion. Along with its good positioning accuracy, the technology presents advantages of compactness, perfect MRI-compatibility, simplicity and low cost. Here, we specifically report the design and validation of a transperineal prostate cancer manipulator prototype that has 20 embedded air-muscles distributed in four star-like polymer structures. These compliant structures are made of silicone elastomer, using lost-core injection molding. Low motion hysteresis and good precision are achieved by designing molded joints that eliminate sliding surfaces. An effective design method for such embedded polymer air-muscles is proposed, using a manipulator model and four air-muscle design models: geometrical, finite elements, uniaxial analytic, and experimental. Binary control of each air-muscle ensures stability and accuracy with minimized costs and complexity. The prototype is found MRI-compatible with no observable effects on the signal-to-noise ratio and, with appropriate image feedback, is found to reach targets with precision and accuracy under 0.5 mm. The embedded approach reveals to be a key feature since it reduces hysteresis errors by a factor of ≈7 compared to a previous nonembedded version of the manipulator. The successful validation of this binary manipulator opens the door to a new design paradigm for low cost and highly capable pneumatic robots.

Copyright © 2013 by ASME
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Fig. 1

Prototype using 12 nonembedded air-muscles (left) and muscle details (right) [22]

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Fig. 2

Left: MRI control room. Right: Manipulator and patient on MRI table.

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Fig. 3

Left: Manipulator and star-like structure. Right: Inside geometry of an air-muscle with three molded ribs.

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Fig. 4

Air-muscles cross-section

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Fig. 5

Half-mold with wax inserts

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Fig. 6

Proposed design process

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Fig. 7

Simplified manipulator representations for geometrical design

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Fig. 8

FEA comparative study of ribs influence on membrane stress, air-muscle lengthening and radius increase under 220 kPa

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Fig. 9

2D axisymmetrical FEA model of the air-muscle in the undeformed and deformed states

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Fig. 10

Spring representation of air-muscle for 1D analytical model and principal directions

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Fig. 11

Air-muscle 1D model (Yeoh), FEA, and experimental curves. Note the almost constant offset FP and the almost linear behavior denoted by k.

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Fig. 12

Experimental double-laser set-up

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Fig. 13

Left: Predicted workspace (needle tip positions) of the manipulator using 12 nonembedded air-muscles. Right: Predicted workspace of the manipulator using 20 embedded air-muscles. Dotted line: Required workspace. Full line: Healthy prostate

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Fig. 14

Validation of the manipulator model (20 random targets)

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Fig. 15

Elastically averaged effect (gray arrow) of the actuation of one air-muscle (black) on end-effector

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Fig. 16

Manipulator during MRI gel insertions

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Fig. 17

Insertion tests in ballistic gel




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