Self-Feeding Robots: Robots that Plug Themselves Into Wall Outlets

Intel Research Labs Robot Marvin Plugging Itself into Powered Wall Outlets

Autonomously seeking out power for battery recharging is a pretty crucial capability for advanced mobile robots.  While Roomba-like docking stations are a quick fix, "plugging in" to existing infrastructures is preferable.  Not long ago, the robotics world was abuzz with the Willow Garage Milestone 2, where (among other things) a PR-2 robot plugged itself into 9 different wall outlets.  My curiosity on this subject was further piqued when I saw Intel's Marvin robot use electric fields emanating from an outlet's internal wiring to finely localize an outlet/plug and adeptly plug itself in, all sans camera.  I'd like to share some photos and videos of recent efforts (by both the Willow and Intel folks), as well as examine the history of robots plugging themselves into wall outlets.

Going in reverse chronological order, lets take a look at the latest Intel Research Lab efforts first.  

Intel's mobile manipulating robot, named Marvin, appears to be a Segway RMP 100 with Barrett WAM Arm and runs the Willow Garage ROS NavStack.  The thing that makes this work really cool is the power plug, which is specially 3D-printed for the robot's end-effector and contains integrated electric field (E-Field) sensing electronics.  The plug has antennas (electrodes) that sense the 60Hz electric fields emanating from a powered outlet in order to facilitate highly-accurate plug-outlet localization and subsequent plugging-in.  Take a look at the photos and videos to get a better idea of what I mean.

Intel Marvin Robot Plugging Itself into a Wall Outlet  Intel Marvin Robot Specialized Power Plug

One of the reasons this is so clever is that the plug-outlet localization utilizes a signal that is explicitly created by the target, much in the spirit of Shwetak Patel's "infrastructure mediated sensing."  This is in contrast to the visual methods employed by most other researchers.  Plus, the circuitry is rather straight forward (see below left) and produces amazingly accurate localization (see below right).  Thankfully, the originator of this work (Brian Mayton) has shared an ICRA 2010 pre-print that details the solution.

Electric Field Sensing Circuit  Electric Field Sensing Accuracy


An alternative approach, championed by Willow Garage and their PR-2 robots back in June 2009, is to employ visual techniques to facilitate plug-outlet localization.  Plugging in was part of their wildly successful Milestone 2, where the PR-2 autonomously plugged itself into 9 different office outlets.  While early versions relied on a visual fiducials on the plug (checkboard pattern) and worked only on orange outlets (though quickly extended to many others), I'm sure subsequent efforts are making inroads into more robust / generalized behaviors.  Personally, I'm looking forward to the detailed systems papers to be presented at ICRA 2010, as promised by Gary Bradski.  Anyway, Willow has videos of Milestone 2 and an explanation of how it was accomplished -- photos and videos embedded below.  

Willow Garage PR-2 Plugging Itself In

Willow Garage PR-2 Plugging Itself In


Now for some historical context... Amazingly enough, the first robots capable of plugging themselves into wall outlets were developed in 1960 -- the Johns Hopkins "Beast" Robot:

Hopkins Beast Robot Plugging itself into wall outlets  Hopkins Beast Robot Plugging itself into wall outlets 

Controlled by dozens of transistors, the Johns Hopkins University Applied Physics Lab's "Beast" wandered white hallways, centering by sonar, until its batteries ran low. Then it would seek black wall outlets with special photocell optics, and plug itself in by feel with its special recharging arm. After feeding, it would resume patrolling. Much more complex than Elsie, the Beast's deliberate coordinated actions can be compared to the bacteria hunting behaviors of large nucleated cells like paramecia or amoebae.


A quality treatise on the subject of robots plugging themselves in to wall outlets is Eduardo Torres-Jara's 2002 MIT Masters thesis, entitled "A Self-Feeding Robot." Curiously, his robot bears a striking resemblance to the Beast robots of old, except that his used a two DoF linear actuator "arm" to plug itself in and located / localized outlets using boosted visual classifiers.

Eduardo Torres-Jara's Self-Feeding Robot


While Roomba-like docking stations are an option for low-cost commercial robots, I believe that autonomously plugging into unmodified power outlets for recharging is a baseline capability for advanced home/office robots.   Non-roboticists certainly marginalize the difficulty of this fundamental capability; however, having hand coded a number of robot behaviors myself, I can certainly appreciate the capabilities recently demonstrated by researchers -- kudos guys!



I had mentioned that the electric field sensing method was elegant and straight forward.  True to form, such advances rarely occur in isolation.  For example, an undergraduate senior design project (composed of Ani Bagepalli, Moses Zamora, and David Sanchez) at the University of Texas-Pan American (UTPA) demonstrated a robot plugging itself into powered wall outlets using electric field sensing back in 2005.

UTPA Electric Field Sensing Robot Plugs Itself In  UTPA Electric Field Sensing Robot Plugs Itself In  UTPA Electric Field Sensing Robot Plugs Itself In

To quote from their project:

The robot we have proposed building will automatically guide itself around a room and through the use of an electromagnetic sensor move towards a potential wall socket. when it reaches the socket, it will use an onboard camera and image processing board to see whether the source is a socket or not. if it is, it will proceed to plug itself in to recharge.

Their final Powerpoint report can be found here, and a video of their robot operating is embedded below.

I knew about this work when I penned the original post.  However, the UTPA Electrical Engineering website was undergoing a major overhaul and the files were temporarily unavailable -- but alas, now they are here for posterity.

While the senior design project is interesting, the documentation, testing, and experimentation performed by the Intel folks is vastly superior (and worth reading).

—Travis Deyle

I see that Willow Garage has updated their PR2 robot's self-plugging capabilities.  Check out the new video.


—Travis Deyle

Back in the early 70's my father used to read an italian electronics magazine (CQ Elettronica) and I used to give it a peek. A guy had designed a self roving sort of robot (it would ramble around with no mean, just a motor and a free wheel). Processors had yet to come to the consumer but the guy designed it in such a way that the rover would find and follow a stripe of white scotch tape on the floor to reach a DC connector and recharge its own batteries.  I have to say that at that time it seemed very futuristic.