Design Innovation Paper

An Experimental Investigation of Digging Via Localized Fluidization, Tested With RoboClam: A Robot Inspired by Atlantic Razor Clams

[+] Author and Article Information
Monica Isava

Global Engineering and Research Laboratory,
Department of Mechanical Engineering,
Massachusetts Institute of Technology,
Cambridge, MA 02139
e-mail: misava@mit.edu

Amos G. Winter V

Assistant Professor
Global Engineering and Research Laboratory,
Department of Mechanical Engineering,
Massachusetts Institute of Technology,
Cambridge, MA 02139
e-mail: awinter@mit.edu

1Corresponding author.

Contributed by the Mechanisms and Robotics Committee of ASME for publication in the JOURNAL OF MECHANICAL DESIGN. Manuscript received October 2, 2015; final manuscript received July 8, 2016; published online September 14, 2016. Assoc. Editor: David Myszka.

J. Mech. Des 138(12), 125001 (Sep 14, 2016) (6 pages) Paper No: MD-15-1684; doi: 10.1115/1.4034218 History: Received October 02, 2015; Revised July 08, 2016

The Atlantic razor clam, Ensis directus, burrows underwater by expanding and contracting its valves to fluidize the surrounding soil. Its digging method uses an order of magnitude less energy than would be needed to push the clam directly into soil, which could be useful in applications such as anchoring and sensor placement. This paper presents the theoretical basis for the timescales necessary to achieve such efficient digging and gives design parameters for a device to move at these timescales. It then uses RoboClam, a robot designed to imitate the razor clam's movements, to test the design rules. It was found that the minimum contraction time is the most critical timescale for efficient digging and that efficient expansion times vary more widely. The results of this paper can be used as design rules for other robot architectures for efficient digging, optimized for the size scale and soil type of the application.

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Grahic Jump Location
Fig. 1

E. directus digging pattern. Dashed horizontal line denotes a reference depth, white arrows denote clam motions, blue shaded area represents fluidized soil around the animal. (a) Reference position before beginning the digging cycle. (b) E. directus extends its foot down prior to moving its valves. (c)E. directus moves its valves slightly up before contraction. (d) E. directus contracts its valves, which fluidizes the soil around it and pushes blood into its foot. (e) E. directus's foot pulls its valves down through the fluidized soil. (f) E. directus reopens its valves to begin another digging cycle, now at a lower depth than in part a.

Grahic Jump Location
Fig. 2

RoboClam architecture and digging motions. (a) RoboClam architecture. The upper piston moves the end effector in and out; the lower piston moves it up and down. (b) Inset of the end effector. The wedge mechanism connected to the upper piston translates vertical (piston) motion to horizontal (in/out) motion. (c–g) RoboClam movements, which map to the E. directus motions shown in parts b–f of Fig. 1. Dotted line represents a reference depth; gray areas indicate anticipated fluidized areas.

Grahic Jump Location
Fig. 3

RoboClam end effector design. (a) Exploded view of end effector, with exact constraints of shells labeled. (b) Free body diagram of a shell and the wedge.

Grahic Jump Location
Fig. 4

Initial results from 847 digging tests on RoboClam. (a) Efficiency results of all 847 tests. (b) Subset of (A), showing greater detail on the Measured Inward Time axis. For each test, the end effector contracted and expanded at desired timescales, and the robot dug under its own weight. Tests were analyzed for the power law exponent, α, with an exponent of 1.0 corresponding to fluidized digging and 2.0 corresponding to static soil digging.

Grahic Jump Location
Fig. 5

Normalized results from 847 digging tests on RoboClam. (a) Results of all 847 tests, with a box around the zoomed in area. (b) Zoomed in version of (A), showing more detail on the Measured Inward Time axis. Tests were analyzed for the power law exponent, α, as in Fig. 4, but results were normalized such that an exponent of 1.0 corresponded to fluidized digging and 1.62 corresponded to blunt body digging.



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