Early this year, SCDigest reported on a potentially breakthrough development by a trio of MIT engineers in terms of maintaining DC or store inventory accuracy using a combination of drones and RFID (see MIT Released New Drone and RFID System for Distribution Center Inventories.)
We now looked more closely at the system based on an MIT paper written by Yunfei Ma, Nicholas Selby, and Fadel Adib that describes the invention in great technical detail, though we will try to keep it high level here. The trio say the breakthrough will enable much improved read rates for passive (battery-less) RFID tags in a distribution center or retail store environment.
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| 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. |
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A number of vendors and shippers have been looking at using drones with RFID readers to take inventories of tagged products (pallets, cartons or individual items) to keep a near constant pulse of inventory quantities and locations.
But there are some issues. First, the read range currently for a passive tag is in practice just a few meters. That means a drone with an RFID reader would have to fly very close to inventory to power the tags and get reads.
Second, the read rates are significantly impacted by line-of-sight issues. That means the tags on cartons on a pallet, or a the tag on a sweater beneath a pile of sweaters may not achieve high read rates, making the value of the system degraded or even dubious.
Third, the readers needed to achieve even the few meter read range level are today heavy enough that a drone that could carry it is unsafe and cannot be flown around humans.
Fourth, exact positioning of inventory has been tough to achieve.
Because of these challenges, vendors and shippers - including Walmart - have been experimenting with use of imaging technology rather than RFID
The MIT researchers say they have addressed all these issues, in large measure by putting a relay or signal repeater on to the drone, which picks up signals from the tags and sends them to stationary readers for full identification (see graphic below), in a system they call RFly.
Technically why this is better involves areas such as bidirectional, full-duplex data communications and the phase and timing of the data packets that we will leave to the engineers to sort through.
MIT's RFly Design Uses a Relay on Drone from Tags to Reader
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But the researchers say the proven result are read ranges of 50 meters or more – a 10-fold improvement on current technologies that means a drone does not have to get so close to the inventory/tags, reducing the time it takes to survey a given area.
What's more, through a sophisticated algorithm based on signals from both the inventory and the drone, the system can locate a given item to within 19 centimeters of its location.
The system also has far fewer issues with line-of-sight constraints, the trio says. While achieving read rates of near 100% for line-of-site scenarios, the read rate drops only 75% at an impressive 50 meters away.
The relay approach is also lightweight, allowing drones that are safe to be used indoors and around people (workers, customers) to be deployed.
Unable to find a reader that met their needs fully, the MIT team built their own device. The system also uses technology from OptiTrack, which is an optical tracking system, as a “ground truth” for location measurements. The system consists of an array of infrared cameras mounted on a ceiling, and can achieve sub-centimeter localization accuracy in tracking objects tagged with infrared-reflective markers in its line-of-sight.
The current system has some limitations, notably that for now only one drone can be used at a time in an area. However, the researchers say future research is likely to eliminate that constraint.
As we reported in our September article, the MIT researchers say after initial successful testing in its labs, it is now doing further testing with a major retailer 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.
If you want to wade through it, the full technical paper is here: Drone Relays for Battery-Free Networks
Could this RFly system be a real breakhrough? Let us know your thoughts at the Feedback section below.
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