Surface Based Wireless Power Transmission and Bidirectional Communication for Autonomous Robot Swarms
October 6, 2008 by Travis Deyle
This paper from ICRA 2008 details the construction of a 60cm x 60 cm surface that provides wireless (battery-free) power and bidirectional communication to an initial swarm consisting of five line-following robots, each consuming 200 mW. Power transmission in the system was achieved through magnetic flux coupling between a high Q L-C resonator placed beneath the operating surface and a non-resonant pickup coil on each robot. The average power density demonstrated was 4.1mW/cm2 for a static load, and the paper demonstrates much greater peak power for dynamic loads via capacitor storage and power conditioning circuitry.
See the paper (and related blog post) by Travis Deyle (myself) for additional details. The slides from the ICRA 2008 presentation are also available here. Finally, a video of the swarm operating battery-free on the surface is shown below. Also shown in the video is an LED being powered by the surface.
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Comments
1:06 am
This is the coolest thing I have seen in a long time. I am going to build my own gang of robots. I am taking a class on UHF RFID systems and I think I can use this idea for my class project.
Q1: How do you calculate the interrogation zones and the distortion distance between tags/robots?
Q2: Is the charging sequential (as in the Alien antenna and reader device)?
Before I ask more details, I am going to read the paper.
Any suggestions?
-CT
1:43 pm
Hey CT,
Thanks for the interest. I should probably note that while the communication and power harvesting concepts are similar to UHF RFID, the actual operating regime (magnetic coupling) is much more like HF and LF RFID. A UHF RFID apparatus would need to be operating in a completely different regime (electromagnetic coupling between the transmit antenna and robot receive antennas -- where the antennas are generally dipoles or patches).
Because this is magnetic coupling, the "interrogation zone" falls off precipitously with distance from the secondary (resonant) transmit coil. For the system we built, it is likely to be useful only up to ~10 cm (see paper), though this is largely a function of your robots' power consumption and the Q of the transmit coil.
As for charging, the robots are all powered in parallel by the changing magnetic flux through each robot's coil. To prevent interference between robots (and thus allow simultaneous power transfer), the receive coils were intentionally made non-resonant. Again, details are in the paper.
6:55 am
Most interesting project! If it were possible to add localization and orientation as well You'd have created _the_ ultimate robotics tool :)
Even if one used the power surface just as an uncomplicated way to reload a robot's battery it would already be helpful. In this case it wouldn't even be necessary to encircle the whole floor with the coil. Instead one could introduce "feeding areas" for reloading (and debriefing) robots.
Very inspiring :)
Christoph
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