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Research Papers

Millimeter-Scale Robotic Mechanisms Using Carbon Nanotube Composite Structures

[+] Author and Article Information
Jordan D. Tanner, Clayton Grames, Brian D. Jensen, Spencer P. Magleby

Department of Mechanical Engineering,
Brigham Young University,
Provo, UT 84602

Larry L. Howell

Department of Mechanical Engineering,
Brigham Young University,
Provo, UT 84602
e-mail: lhowell@byu.edu

1Corresponding author.

Manuscript received August 21, 2014; final manuscript received December 15, 2014; published online February 27, 2015. Assoc. Editor: Aaron M. Dollar.

J. Mechanisms Robotics 7(2), 021001 (May 01, 2015) (7 pages) Paper No: JMR-14-1228; doi: 10.1115/1.4029436 History: Received August 21, 2014; Revised December 15, 2014; Online February 27, 2015

This paper presents a method for fabricating millimeter-scale robotic components for minimally invasive surgery. Photolithographic patterning is used to create a framework of carbon nanotubes (CNTs) that can be infiltrated with a variety of materials, depending on the desired material properties. For the examples shown in this paper, amorphous carbon is used as the infiltration material. The planar frameworks are then stacked to create the 3D device. The detail and precision are affected by large changes in cross section in the direction of stacking. Methods for improving the definition of the 3D object due to changing cross section are discussed. The process is demonstrated in a two-degree-of-freedom (2DOF) wrist mechanism and a 2DOF surgical gripping mechanism, which have the potential of decreasing the size of future minimally invasive surgical instruments.

Copyright © 2015 by ASME
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Figures

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Fig. 1

A CNT composite structure patterned using photolithography. The layer thickness shown here is approximately 100 μm.

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Fig. 2

A SEM micrograph of a carbon-infiltrated CNT forest that has been broken open to observe the inner structure. Because the CNTs are coated in carbon, they are more visible at this scale.

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Fig. 3

The process used to assemble the CNT composite layers after the growth and infiltration processes. (a) Step 1: lithographically pattern and infiltrate CNT composite layers. (b) Step 2: separate layers from silicon substrate. (c) Step 3: stack layers using alignment pins. (d) Step 4: bond layers together and remove alignment pins.

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Fig. 4

Schematic showing the end effector (split CORE grips shown here) attached to the end of the instrument shaft. Cables are set up in a pull–pull configuration and are robotically actuated at the base of the instrument.

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Fig. 5

An illustration showing the similarities and distinctions between the traditional CORE joint (left) and the split CORE joint used in the gripping mechanism design (right)

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Fig. 6

A rendering of the base component and the upper grip components of the split CORE grips

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Fig. 7

The upper cylinder is able to roll along the axial direction of the lower cylinder. It can also roll about the axis of the lower cylinder, as shown by the arrows.

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Fig. 8

A rendering of a completed component for the crossed cylinder wrist showing the two different gear profiles and the staggered tooth configurations to prevent torsion and shear

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Fig. 9

Rendering of the split CORE grips divided into the three unique layers and the square holes used for alignment. The smooth circular section is repeated on either side of the geared portion.

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Fig. 10

Photograph of the assembled geared portion of the split CORE grips (left) and a view of all the assembled elements (base piece and two grips) of the mechanism (right)

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Fig. 11

Split CORE grips assembled onto a surgical instrument shaft. Cables are used to actuate the grips to a desired angle. Each grip is controlled by two cables in a pull–pull configuration. (a) Grips in partially open position and (b) grips in closed position.

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Fig. 12

Optical micrograph of one portion of the crossed cylinder wrist comprised of 19 layers that are 110 μm in thickness

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Fig. 13

Micrograph of the assembled crossed cylinder wrist with a more coarse stacking assembly (110 μm layer thickness). The upper piece is rotated slightly about the axis of the lower and rolled slightly forward to demonstrate both directions of motion.

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Fig. 14

One portion of the crossed cylinder wrist layers stacked on the alignment pin prior to the final alignment process and bonding. The full assembly is comprised of 50 layers that are 40 μm in thickness.

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Fig. 15

A comparison of the two crossed cylinder wrist versions—110 μm (a) and 40 μm (b) layer thickness. The illustrations in the top left corner show cross sections of a tooth for the respective layer thicknesses where the solid lines depict the CNT layers and the dotted lines depict the ideal profile.

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