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Scientist poses new approaches to contactless magnetic gear configuration

18 February 2016

Magnetic couplings are certainly not new, but this scientist wants to take the method further, exploring applications from paddle boats to nano-sized mechanisms.

Johannes Schönke's theoretical paddle boat example of a triangular magnetic coupling geometry

Johannes Schönke, a postdoctoral scholar at the Okinawa Institute of Science and Technology (OIST), hopes to extend the possibilities and applications for smooth magnetic couplings, which can produce an even motion without any counterforce. His research has several potential applications in nanotechnology, microfluidics and robotics.

Magnetic gears have several advantages over mechanical gears. The main one is the absence of direct contact between the parts. While mechanical gears, such as the meshing gears inside a watch, transmit the motion through the contact between moving teeth, magnetic gears are contactless.

Magnetic gears require less maintenance, no lubrication, they have also better reliability, and efficiency, and they produce lower vibration and noise. Magnetic gears are often based on an alloy of iron, boron and neodymium, which creates the strongest permanent magnets known to date.

“I wanted to explore the possibility of positioning the input and output axes at any desired inclination angle,” explains Dr Schönke.  “Furthermore, there are certain configurations of the two magnets that allow the addition of a third magnet at a specific position and still maintain a smooth coupling”.

As an illustrative example, Dr Schönke modelled a paddle boat where two magnets are connected to the paddles and one to the driving system. If the magnet of the driving system is rotated, the paddles move in a synchronised way to push the boat forward. Because of the contactless nature of the magnetic coupling, the paddle axle is fixed outside of the boat, and it does not need to penetrate the hull.

However, the specific triangle geometry between the positions of the three magnets is crucial, to make the coupling work smoothly. In the future, this type of technology might be particularly useful in micro- and nanosystems. As for the paddles of the boat model, the motion of mini pumps and valves placed inside micro-channels can be controlled from outside in a contactless way.

The same analogy between mechanical and magnetic gears can be further explored by considering the interaction between a quadrupole and a magnet, each rotating around a specific axis. One way to construct a quadrupole is to place four magnets like a cross, positioned in a way that two north poles and two south poles alternatively face the centre.

The quadrupole can be thought of as a gear with twice as many teeth as the single magnet. So that when the magnet is rotated by a full cycle, the quadrupole rotates only half a cycle. By rotating the magnet, the quadrupole rotates correspondingly, as it would happen with a mechanical gear wheel mechanism.

“The next step is to build a 3D printed toy-size car based on the design principle of the paddle boat using three strong, inch-sized spherical magnets," says Dr Schönke. "The new Objet Connex 500 3D printer which just arrived at OIST will be perfect for this proof of concept project.” 

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