Overview
Several supply chains are moving
to the use of RFID (radio
frequency identification) in
logistics applications. RFID has
many desirable capabilities but
based on extensive testing and
dealing with the laws of
physics, there are real and
practical limitations. In order
to help those implementing RFID-based
logistics systems, this white
paper will identify some of
limitations and propose ways to
deal with them.
In
October of 2004 at the Truth In
Technology Forum sponsored by
the AIDC 100 (www.aidc100.org),
representatives from Energizer
(a supplier to Wal-mart, a
major proponent of RFID) and the
other representatives of the
Department of Defense
(conducting large scale tests)
as well as others, indicated
that there are some significant
limitations to the use of RFID
in logistics applications. As of
May of 2005, further testing
continues to point to practical
limitations to many of the
anticipated RFID operation
benefits.
RFID was selected over barcode
as the technology to encode the
Electronic Product Code (EPC), a
product identification method
providing a serial number for
every product produced. The EPC
is being advanced through GS-1
(formerly the Uniform Code
Council (UCC)) because RFID is
believed to offer superior
reading performance
characteristics. Among the
important characteristics cited
are the following:
-
Unlike barcode, RFID does
not require Line-of-Sight
between the reader and the
tag.
-
Tags can be read at greater
distances.
-
Groups of tags can be read
all at once.
These properties permit a high
level of automation in capturing
data as goods flow between
trading partners in many supply
chains. The ideally accepted
form of this automation employs
RFID instrumented portals at
shipping and receiving
facilities. Such portals have
been designed to capture all the
data from palletized loads as
they are being transported on
forklifts in and out of each
facility.
The efficiency of this type of
operation is derived from the
fact that it is not necessary to
manually scan each and every
case in order to receive it.
Furthermore, as pallets and
cases are dispersed throughout a
given facility, strategically
located readers will
automatically capture the data
needed to track pallets and
cases.
Active RFID may possess
properties that will permit the
capture of all EPCs from a
pallet of cases traveling
through instrumented portals.
The passive RFID tags that have
been specified for use in
several supply chains have been
shown to have a number of
limitations that reduce the read
rate for pallet loads from 100%
to a range between 50% and 80%,
depending on the size and
content of the cases involved.
Limitations
The limitations of passive RFID
arise from the need of these
tags to absorb enough power from
the reader to transmit the
stored tag data. In order to
accomplish this, the tags must
utilize directional antennas
large enough to intercept the
needed power from the reader.
The view that RFID does not need
a “Line-of-Sight” between the
tag and the reader has to be
modified as follows:
The need for the tag to be
powered by the reader’s RF
radiation pattern further limits
the distance between tag and
reader. The amount of reader
radiation is also limited by the
need to avoid interference from
adjacent reader installations as
well as restrictions placed by
the FCC, and the BRH.
Many people believe that future
developments will overcome most
of these limitations; however,
field testing indicates that the
read rate for pallet loads will
always be less than what is
acceptable for Shipping and
Receiving applications, and
other methods must be found to
retrieve the lost data.
System Design
The limitations of RFID need to
be considered when designing
data collection systems for use
by trading partners in the
supply chain. Currently, orders
have to be received by scanning
barcodes on each case manually.
The promise of RFID is that
orders can be received
automatically by reading all the
tags for each case on a pallet
load.
Given the less than perfect
readability of tags because of
everyday obstructions and
interference from the physical
properties of the products
carrying the RFID tags, a higher
level of data synchronization
will be required in order to
derive the missing tag
readings. This can come about
by requiring shippers to provide
the additional data needed for
synchronization in advance of
the physical arrival of a given
order. In addition to the
currently supplied data for
receiving an order, the receiver
will need access to data that
permits the reconstruction of
all RFID case data associated
with a tagged pallet. In this
type of environment, the reading
of as little as a single RFID
tag, since it contains a unique
serial number, can be used to
derive all of the following
data:
-
Location based on the
physical location of the
reader reading the tag.
-
Time and date based on a
“time stamp” by the reader
or the computer receiving
the read.
-
Inbound or outbound status
derived from lookup of the
tag number or the associated
pallet number in the
synchronization database.
-
The pallet number and all
case tags initially assigned
to the pallet derived from
lookup in the
synchronization database.
With this additional capability,
these low level systems will
provide higher-level
applications with the perfect
transaction data needed for
smooth operation.
Shipping Point Requirements
In
order to comply with this extra
need for data synchronization,
hardware and software will need
to be acquired and installed
that can accomplish at least the
following.
-
Prepare an RFID tag for
application to each case and
pallet scheduled for
shipment to a trading
partner.
-
At the point of tag
application to a case, read
the case tag and transmit
the data to a system that
can add all the needed
fields to describe the
contents of the case.
-
At the point where pallets
are being loaded with cases,
RFID readers are required to
read tagged pallets and each
case as it is being loaded
onto the pallet. The
readers transmit the data to
a system that can add the
pallet tag reading to a
pre-existing record of the
case tag.
-
A computer system that can
receive data from the RFID
readers, and build the
database of case records and
associated pallet tag
numbers.
-
The capability to integrate
the case/pallet data with
other systems needed for
Shipping/Receiving,
Inventory, WMS, ERP, etc.
-
The capability to share the
data with various trading
partners for data
synchronization.
Receiving Point Requirements
In
order to automatically receive
orders of palletized goods, a
system will be required that has
access to synchronized data from
each trading partner. This
system will require at least the
following:
-
Strategically installed RFID
scanners to read at least
one RFID tag from each
pallet.
-
Each RFID reading will be
transmitted to a system that
can derive the data needed
for receiving all the cases
on the pallet.
-
The resultant data will be
configured into the
necessary transactions for
receiving by higher-level
applications.
Conclusion
RFID and EPC have always been
envisioned as requiring
middleware to support data
capture and derive transactions
for higher-level applications.
By requiring the linkage of a
pallet EPC to case EPCs loaded
on the pallet, RFID reader
requirements can be simplified
as follows:
-
Case tags are read one at a
time, as they are loaded
onto pallets.
-
Readers at receiving portals
need only read any of the
RFID tags on a pallet loaded
with cases. The direction
(inbound/outbound), and
unread tag numbers can be
derived from the
synchronization database.
The need to develop RFID pallet
readers that can read the pallet
tag and 100% of the case tags on
the pallet is not possible due
to the limitations of RFID by
the laws of physics (because of
the material characteristics of
the products and the
interference or obstruction they
produce. By linking pallet tags
with associated case tags, and
synchronizing the data between
trading partners, the
requirement for 100% readability
of pallet loads is eliminated.
