Machine Design

Giving underwater robots a firm grip

Massachusetts Institute of Technology

If an underwater robot has a task to perform, such as opening a stuck valve or repairing a leaking pipe, it must anchor itself so it can apply force without the reaction pushing it away. A team of engineers at the Massachusetts Institute of Technology have devised a solution: Give the robot a way to “grab hold” of ferrous surfaces.

The MIT gripper, or controllable adhesion system, uses controllable electromagnets, magnets that can be turned on and off using little energy. Their original gripper module contained two parallel-bar magnets. One is neodymium-iron-boron and is relatively strong. The other, weaker one is wire wrapped and made of aluminum-nickel-cobalt (AlNiCo).

At first, the magnets are mirror images of each other, with their north-south orientations reversed and their magnetic fields canceling each other out. But if a current pulse is sent through the weaker magnet’s coil, its north and south poles switch, making the overall module a strong electromagnet, capable of anchoring a robot to a pipe or ship’s hull. A second pulse sent through the coil switches polarity back, and the module is no longer magnetic. One major advantage of this setup is the module stays in either state with no energy applied.

Researchers changed the layout of the magnets so that a cylindrical AlNiCo magnet is surrounded by a hollow toroid NIB magnet. The coil wraps around both magnets, but the NIB magnet is too strong to be affected by the current pulse. A steel cup confines and focuses the magnetic field when the module gets clamped onto a surface, This arrangement creates a stronger magnet than the parallel bar configuration.

Connecting up to three modules using a flexible silicon rubber sheet lets the gripper modules conform to curved surfaces. For example, the three modules can surround a pipe, And the three magnets do not interfere with each other.

The team will check to see if protective plastic coatings or biological organisms on surfaces will interfere with the grippers.

© 2012 Penton Media, Inc.

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