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Research Papers

An Underactuated, Magnetic-Foot Robot for Steel Bridge Inspection

[+] Author and Article Information
Anirban Mazumdar1

Department of Mechanical Engineering, D’Arbeloff Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139amazumda@mit.edu

H. Harry Asada

Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139asada@mit.edu

1

Corresponding author.

J. Mechanisms Robotics 2(3), 031007 (Jul 21, 2010) (9 pages) doi:10.1115/1.4001778 History: Received August 27, 2009; Revised January 21, 2010; Published July 21, 2010; Online July 21, 2010

A legged robot that moves across a steel structure is developed for steel bridge inspection. Powerful permanent magnets imbedded in each foot allow the robot to hang from a steel ceiling powerlessly. Although the magnets are passive, the attractive force is modulated by tilting the foot against the steel surface. This allows the robot to slide its feet along the surface using “moonwalk” and “shuffle” gait patterns. The robot can also detach its feet and “swing” them over small obstacles. These diverse walking patterns are created with a single servoed joint and two sets of simple locking mechanisms. Kinematic and static conditions are obtained for the underactuated legged robot to perform each gait pattern safely and stably. A dynamic model is built for swinging a leg, and a desirable swing trajectory that keeps the foot reaction force lower than its limit is obtained. A proof-of-concept prototype robot is designed, built, and tested. Experiments demonstrate the feasibility of the design concept and verify the analytical results.

Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

The test course for the Mag-Foot prototype. The robot is designed to walk on the underside of steel bridge structures.

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Figure 2

A schematic illustration of the foot dimensions and the tilting foot concept

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Figure 3

The basic mechanism design

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Figure 4

Idealized time sequences for the moonwalk (a), the shuffle (b), and swinging (c)

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Figure 5

Equivalent kinematic diagrams for (a) tilting, (b) sliding, and (c) swinging

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Figure 6

The free body diagrams for (a) tilting and (b) detachment

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Figure 7

The normalized torque required to tilt the foot

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Figure 8

The normalized torque required to detach the foot

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Figure 9

An illustration of the reaction force for two different incline angles

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Figure 10

The model used for the swinging mode dynamics

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Figure 11

The pseudo-optimal trajectories

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Figure 12

The double sigmoid parameterization

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Figure 13

The parametric trajectories

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Figure 14

The full set of parametric results

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Figure 15

A photograph of the Mag-Foot prototype

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Figure 16

Video frames from a swinging motion

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Figure 17

Closed loop control over moonwalk

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Figure 18

Closed loop control over shuffle on an inclined surface

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Figure 19

A comparison of the actuated trajectory θ(t) with the parametric trajectory

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Figure 20

A comparison of the measured reaction force FxA with the simulated result

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Figure 21

A comparison of the measured reaction force FxA with the experimental results from an arbitrary trajectory

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