RFID-Based Robots Come to the Rescue

Passive RFID Mapping Experiments
The first experiment, utilizing Tagsys' Ario passive 13.56 MHz RFID tags and Medio S002 interrogators, was carried out by a six-person team in Freiburg in April 2007. Each individual was equipped with an electronic compass, an electronic pedometer and a glove, developed by TZI Bremen, with a built-in wireless RFID interrogator.

The devices were all connected to a small, notebook-style PDA carried by each team member. During this experiment, the humans explored 9 kilometers (5.6 miles) of an urban area consisting mainly of residential buildings with up to six floors. They used the basic navigational technique of dead reckoning—estimating current position based on a previously determined fix, then estimating subsequent positions base on speed, elapsed time and course traveled—to calculate their positions with an error of about 70 meters (230 feet). By reading the 20 RFID tags embedded in self-adhesive labels they had placed on buildings at intersections, then combining this information with that collected via dead reckoning, the team was able to calculate their positions with an error of 10 meters (33 feet). However, Kleiner says, it was difficult to produce a high-quality map because of the large error in the estimates, since people climbed stairs, walked up slopes and ran.

In one experiment, participants wore a glove with a built-in RFID interrogator.

"If you use passive RFID, you can only collect information by getting very close to the tag," Kleiner notes. "Hence, passive tags only help rescue workers know if they have already been to a certain place. Dead reckoning gives an initial guess of the track. However, its error continuously grows the longer you travel. By using RFID to recognize when a pedestrian has walked a 'loop,' the system can map a whole track. Mathematically speaking, second readings of RFID tags are 'hard constraints.' The algorithm rearranges the track so that all re-visited places fit." The procedure, he says, is known as Simultaneous Location and Mapping (SLAM), and consists of combining associated RFID data with location estimates.

In addition, participants also carried GPS devices, with location data collected via GPS used to verify the maps.

In a separate experiment, conducted in August 2007, a human and a robot jointly created a map by employing RFID to improve dead-reckoning estimates. The robot was equipped with a compass, a wheel-based odometer and an RFID reader with its antenna mounted parallel to the ground so it could read tags placed in the ground as it rode over them. Both the robot and the human explored an area approximately 900 square meters (2,953 square feet), reading 10 passive RFID tags previously embedded in the ground. They were able to improve their dead-reckoning estimates from an error of 150 meters (492 feet) for the human and 50 meters (164 feet) for the robot, down to 5 meters (16 feet) for both. Separately, the researchers also tested a device in a basement for automatically distributing RFID tags.