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Taking Stock: Drones help Inventory Management and More

Posted on September 18th, 2017 by in New Materials & Applications


Source: SupplyChain 247, Walmart Testing Warehouse Drones to Catalog and Manage Inventory,, June 3, 2016

By now most have heard about companies like Amazon and Walmart planning to deliver packages using drones.  Just imagine hundreds of bird-like machines buzzing while carrying packages to you and to your neighbors. Similar to a scene from movies such as Star Wars – chaotic enough to give everyone at the US Federal Aviation Administration a headache.  Another application of drones being pursued currently is in managing warehouses inventories.  Flying a few of these vehicles inside a warehouse seems far less dramatic than a sky full of humming machines.

Any company selling parts and materials must keep track of the inventories of goods and materials it keeps in its warehouses and stores.  That requires the company to take periodic stock of its warehouses.  This practice yields physical inventory data that can be analyzed and reviewed.  Taking physical inventory involves measuring the goods and materials that actually exist on the shelves in the warehouse (and stores) at the time of the audit.  It sounds simple, yet it is anything but.  As the number of items a company carries increases the chances grow for significant variances between the records and the actual physical inventory.

Professor Adlib from Massachusetts Institute of Technology (MIT) Media Lab says the United States Army lost $5.8 billion of supplies in its warehouses during the 2003 to 2011 period.  “In 2016, the U.S. National Retail Federation reported that shrinkage — loss of items in retail stores — averaged around $45.2 billion annually. By enabling drones to find and localize items and equipment, this research will provide a fundamental technological advancement for solving these problems.”  Shrinkage is defined as the loss of inventory attributed to factors such as employee theft, shoplifting, administrative error, vendor fraud, damage in transit or in store, and cashier errors that benefit the customer. (Source: MIT News,, August 25, 2017).

Commercial incentives for the development of more accurate methods are immense.  Just in 2013 Walmart lost $3 billion in revenue because of mismatches between its inventory records and its stock.  The retail giant is at the forefront of developing drone aided inventory management.  Interest in this technology is quite strong among retail corporations, which sell or handle physical objects.  The sizable magnitude of the shrinkage of tens of billions of dollars, across the commercial and government sectors, has resulted in a great deal of investigations at the industrial and academic institutions.

The enabling device for taking inventory by means of drones is RFID (Radio Frequency Identification Device) that was developed decades ago.  It allows the use of radio waves to read and capture information stored on a tag attached to an object.  A RFID system is made up of two parts: a tag or label and a reader.  RFID tags or labels are embedded with a transmitter and a receiver.  The RFID components on the tags have two parts: a microchip that stores and processes information, and an antenna to receive and transmit a signal.  The tag contains the specific serial number for one specific object.  To read the information encoded on a tag, a two-way radio transmitter-receiver called an interrogator or reader emits a signal to the tag using an antenna. The tag responds with the information written in its memory bank.  The interrogator will then transmit the read results to an RFID computer program.  RFID tags are inexpensive and do not require batteries.

Currently, to take inventory, someone has to aim a reader at each RFID tag to read and record the stored information.  Hand-held readers and WIFI data transmission have simplified the task of reading RFIDs.  Taking inventory is still manual requiring humans to walk the long isles of massive warehouses and stores.  Cost of labor, time to take inventory, errors, and the cost and difficulty of correcting those errors are among the shortcomings of taking inventory by humans.  Even with RFID technology, it can take a single large retail store three months to perform a complete inventory review.  And yet mismatches often go undiscovered until exposed by a customer request.  The overall size of the task of taking inventory in all warehouses and stores in the world is simply gigantic.

Drone use promises to overcome the impediments of the manual system, if successful technology is developed. MIT researchers have designed a system that enables small, safe, aerial drones to read RFID tags from tens of meters away (see the video below).  The tags’ locations are identified with an average positional error of 19 centimeters (about 1.5 feet). The researchers envision that the system could be used in large warehouses for both continuous monitoring, to prevent inventory mismatches, and location of individual items, so that employees can rapidly and reliably retrieve requested items (Source: Y. Ma, N. Selby, and F. Adib, Drone Relays for Battery-Free Networks, Association for Computing Machinery, SIGCOMM, August 21-25, 2017,

The central challenge in designing the system 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, which would not 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 (Source: MIT News,, August 25, 2017).

A remaining problem is due to the drone movement; the phase shift of the signals that reach the reader result from not only the drone’s position relative to the RFID tag but also its position relative to the reader. On the basis of the received signal alone, the reader has no way to tell how much each of those two factors contributed to the total phase shift.  So the MIT researchers also equipped each drone with its own RFID tag. A drone alternates between relaying the reader’s signal to a tagged item and simply letting its own tag reflect the signal back, so that the reader can estimate the drone’s contribution to the total phase shift and remove it.

In experiments in the Media Lab that involved tagged objects, many of which were intentionally hidden to approximate the condition of merchandise heaped in piles on warehouse shelves, the system, dubbed RFly, was able to localize RFID tags with 19-centimeter accuracy while extending the range of the reader tenfold in all directions, or one hundred fold cumulatively.  In spite of its limitations the RFly System is an important step toward enabling long-range communication and localization in battery-free networks.  The MIT researchers are currently conducting a second set of experiments in the warehouse of a major Massachusetts retailer.

A number of other drone applications are being considered.  According to a March 17, 2017, article in Fortune Magazine (Source: Walmart was granted a patent in March 2017 for a system in which drones would shuttle products between different departments in its stores.  The idea is to free customers from having to walk across its super-sized emporiums to find goods and waiting while employees retrieve customer-requested items from far-away storerooms.

The day a person can send a personal drone to pick up a carton of milk, fetched by another drone in a super market, can’t be too far away!


All opinions shared in this post are the author’s own.

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