Last week, SCDigest published an article on a new drone system developed by researchers at MIT that claims some breakthroughs in RFID reading technology for capturing inventory levels inside a distribution center.
That story is repeated below, but after the article was published SCDigest conducted a brief email Q&A with the head of the project, MIT's Fadel Adib, on some specifics relative to the RFID reading technology which add a lot to the understanding on how this system works.
That Q&A is as follows:
SCDigest: If the RFID reader It is not on the drone, then where is it?
Adib: The reader is on the ground or on a shelf, depending on the experiment. As long as it is ~50m away from the (circuit on the) drone, the drone can pick up its signal.
SCDigest: Can you just briefly explain how that works? How does the drone pick up a tag signal to send to the reader without a reader?
Adib: At a high level, the drone acts as an "intelligent repeater,", similar to WiFi/cellular repeaters that are used to increase coverage area. The key difference, however, is that RFIDs are battery-free, so the repeater not only needs to repeat the signal, but also power them up and communicate the protocol to them.
So, when the repeater-on-drone gets the signal from the reader, it boosts its power using the drone's built-in battery and forwards it to the RFIDs in its vicinity. When the RFIDs respond, the repeater-on-drone also captures their IDs and forwards this information to the reader.
To get the RFID’s location, we leverage the fact that as the drone moves it traces a virtual antenna array in space, which can be used to find the angle from which each RFID response comes from.
SCDigest: Why does this approach increase read range so much?
Adib: Because the drone has an intelligent repeater which can boost the signal power from the reader. Because the repeater is powered by the drone's battery (consumes <3% of its battery), the distance from the drone to the reader can be 10x larger (in every direction) than the distance from a typical RFID reader to an RFID tag.
Original Story
SCDigest recently reported on a new ground-based robotic system from Surgere and Fetch Robotics that uses RFID to do continuous cycle counting in a distribution center. (See New System Uses Robots and RFID Readers to Perform Continuous Cycle Counting.)
That article referenced the strong at least initial interest by many companies in drone-based systems that fly the aisles of distribution centers, taking inventory by using imaging systems to capture pallet and location bar codes.
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In fact, Walmart invited members of the press in to one of its DCs near it Bentonville, Arkansas headquarters in mid-2016 to see the tests it was doing with this type of inventory drone system.
But drone systems based on imaging have two potential weaknesses: (1) they require clear "line of site" to the bar codes in order to capture them; and (2) relatedly, such systems are really only usable for full pallets of inventory, not reading cases on a pallet because the bar codes are likely not exposed.
With that backdrop, some researchers from MIT last week announced a new drone-based inventory system that they claim achieves some breakthroughs in RFID reading technology to deliver highly accurate inventory accuracy.
MIT says the system uses "small, safe, aerial drones to read RFID tags from tens of meters away while identifying the tags' locations with an average error of about 19 centimeters," one that is capable of identifying cases on shelves as well as full pallets.
The central challenge in designing the system, MIT says, was that with the current state of autonomous navigation, the only drones safe enough to fly within close range of humans are small, lightweight drones with plastic rotors, so they wouldn't cause injuries in the event of a collision. But those drones are too small to carry RFID readers with a range of more than a few centimeters.
The MIT researchers met this challenge by using the drones to relay signals emitted by a standard RFID reader. This not only solves the safety problem but also means that drones could be deployed in conjunction with existing RFID inventory systems, without the need for new tags, readers, or reader software.
The MIT researchers call the system RFly, and presented the idea in a paper at the recent annual conference of the Association for Computing Machinery's Special Interest Group on Data Communications.
Fadel Adib, an associate professor at MIT, is the senior author of the paper, aided by Yunfei Ma, a postdoc in the MIT Media Lab, and Nicholas Selby, an MIT graduate student in mechanical engineering.
Relaying RFID signals and using them to determine THE locations of tags poses some thorny signal-processing problems. One is that, because the RFID tag is powered wirelessly by the reader, the reader and the tag transmit simultaneously at the same frequency. A relay system adds another pair of simultaneous transmissions: two between the relay and the tag and two between the relay and the reader. That's four simultaneous transmissions at the same frequency, all interfering with each other.
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 This problem is compounded by the requirement that the system determine the location of the RFID tag. The location-detection - or "localization" - system uses a variation on a device called an antenna array. If several antennas are clustered together, a signal broadcast toward them at an angle will reach each antenna at a slightly different time. That means that the signals detected by the antennas will be slightly out of phase: The troughs and crests of their electromagnetic waves won't coincide perfectly. From those phase differences, software can deduce the angle of transmission and thus the location of the transmitter.
The drone is too small to carry an array of antennas, but it is continuously moving, so readings it takes at different times are also taken at different locations, simulating the multiple antenna elements of an array, MIT says.
There are other complex technical details of the system, but you get the idea. The net result is that the RFID read range has been increased some 10-fold in all directions, and can locate that inventory within about 19 centimeters. Not stated by MIT, but the assumption is the X-Y-Z location for a given RFID tag is then mapped to actual inventory locations in the DC.
Is this just a theory? The researchers say after initial successful testing in its labs, it is now doing further testing with a major retailers somewhere in Massachusetts.
A major question of course is whether companies will want to bear the cost of putting RFID tags on every case of inventory. Doing so at a pallet level would seem to offer a clear payback.
A brief video of the system can be found here: MIT's RFly Inventory System
What do you think of this MIT RFID drone system? Why can't we better accuracy with bar code scanning? Let us know your thoughts at the Feedback section below or the link above to send an email.
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