Hull, deck plate, and tank inspection for corrosion, deformation, and fractures is a necessary part of ship maintenance to ensure functional integrity and proper operation of the ship. These inspections are labor intensive, expensive, and often dangerous. A multi-segmented magnetic wheeled robot can assist the surveyors in these tasks.

Figure 1. MSMR system overview

The Multi-Segmented Magnetic Robot (MSMR) is designed to provide acoustically quiet climbing and turning ability over a typical ferrous hull that often includes discontinuities in the form of protrusions and indentations, especially where hull-plating sections meet. The key to its effective climbing lies in the design of its wheels and the multi-segmented approach. The wheels are designed to provide maximum magnetic adhesion while the multi-segmented body provides surface adaptability.

The MSMR is composed of the robot modules, linkages, and magnetic wheels (Figure1) that provide attraction and traction with the ferrous surface being climbed. The robot modules contain the system electronics, motors, and batteries. The exterior of the robot module protects its contents from water, dust, dirt, and impacts with obstacles. The flexible linkages allow relative motion between robot modules, so the system can turn, negotiate obstacles, and traverse around corners.

Each robot module contains control electronics, drive modules, and a battery (Figure 2). A plastic prototyping machine was used to fabricate the robot module chassis with a polycarbonate ABS blend to achieve a rapid turnaround time.

The magnetic wheel provides the attractive force between the MSMR and the surface it is climbing, allowing the robot to traverse vertical and even inverted surfaces. Two magnetic wheel designs were prototyped and tested. The conformal wheel consists of a high-flex elastomer wheel, radial magnet array, magnet locator, rigid hub, and elastomeric tread. The highly flexible structure of this wheel will allow the wheel to deform so that it flattens somewhat where the wheel contacts the ferrous surface. This flattened portion of the wheel creates a larger surface area of contact, increasing both adhesion force and traction.

The flux-plate wheel consists of an elastomer wheel, two flux-plates, fluxplate locators, rigid hub, and an array of magnets oriented parallel to the central axis of the wheel. The flux-plates direct the magnetic flux of the magnet array through the surface climbed, providing adhesion.

Figure 2. Exploded view of the robot module

The drive module provides the torque to rotate the wheels and move the robot. The main components are the motor, gearbox, output shaft, housing, motor-shaft shock isolator, and bearings.

The drive module was designed to mitigate the effects of large shock loads when the robot falls and lands on the wheels. If the wheel experiences an impact force, the radial loads are distributed through the output shaft to the drive module housing and back to the robot chassis instead of to the gearbox output shaft.

The linkage, which makes the mechanical connection between the robot modules, must be flexible to allow the robot to turn and maintain wheel contact with the ferrous surface being climbed. It must also be able to transfer push (compressive) and pull (tension) forces between the robot modules so they can work in concert to overcome obstacles greater than the capability of any one robot module.

The electronics are grouped into four major categories: power, processing, sensing, and output. The power group consists of the battery and circuitry to manage and distribute power throughout the system. The processing group consists of the processor, radio, and circuitry to distribute communications. The sensing group includes the wheel encoders, linkage encoders, camera, and future payloads that may be added to gather information. The output group consists of the motors and motor drivers.

This work was done by Aaron Burmeister, Narek Pezeshkian, Kurt Talke, Saam Ostovari, H.R. Everett, Abraham Hart, Gary Gilbreath, and Hoa G. Nguyen of the Space and Naval Warfare Systems Center Pacific. SPAWAR-0005

This Brief includes a Technical Support Package (TSP).
Design of a Multi-Segmented Magnetic Robot for Hull Inspection

(reference SPAWAR-0005) is currently available for download from the TSP library.

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