History of AGVS
1953 First AGV
Automatic Guided Vehicles have played a role in moving material and product for more
than 40 years. The first AGV system was built and introduced in 1953. It was a
modified towing tractor that was used to pull a trailer and follow an overhead wire in a
grocery warehouse. By the late 50’s and early 60’s towing AGVs were in operation in
many types of factories and warehouses.
History of AGVS
1973 Volvo Assembly Plant
In 1973, Volvo in Kalmar, Sweden set out to develop non-synchronous assembly
equipment as an alternative to the conventional conveyor assembly line. The result was
280 computer-controlled assembly AGVs.
History of AGVS
1970s First Unit Load
The first big development for the AGV industry was the introduction of a unit load
vehicle in the mid 1970s. These unit load AGVs gained widespread acceptance in the
material handling marketplace because of their ability to serve several functions; a work
platform, a transportation device and a link in the control and information system for
the factory. Today there are several hundred systems using unit load vehicles in
operation which were produced by a number of manufacturers. These systems
transport material in warehouses, factories, mills, hospitals, and other industrial and
commercial settings
History of AGVS
Smart Floors and Dumb Vehicles
In the 1970’s the principal guidance technology was to induce an electronic frequency through a
wire that was buried in the floor. A device called a ‘floor controller’ turned the frequency on
the wires on and off and directed the AGV through its intended route. The AGV was considered
‘dumb’ since the vehicle was just following signals in the floor. The intelligence for the routing of
the vehicles was in the floor controllers. So, the systems of this day were considered “smart
floors” and “dumb vehicles”.
An antenna on the AGV would seek out the frequency and guide the vehicle based on the
strength of the signal. This technology required embedding multiple wires in the floor in order
to handle intersections or other decision points. The system would energize the wire that would
correspond to the intended direction of travel. For example, at an intersection three separate
wires might be required.
These first generation navigation schemes were expensive to install. All floor cuts needed
to follow the exact path of the AGV. The cut for a turn had to follow the radius curve
that the vehicle would make when turning. Many systems had to embed four wires three for guidance and one for communications. Often, rebar or electronic signals
would interfere with the guidance signals imposed on the wires.
History of AGVS
Dead Reckoning Capability
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As electronics and microprocessors advanced, so did AGV applications. As the vehicles
became more intelligent, the path became less sophisticated. One of the first major
breakthroughs was the development of dead reckoning capabilities. Dead reckoning is a
term that describes the ability of a vehicle to traverse steel expansion joints on the
factory floor or to cross a steel grate. The biggest advantage was that dead reckoning
eliminated the need to make the cut radius turns at intersections. The vehicles could
leave the wire, turn at a programmed radius, and then pick-up the wire to continue its
course of travel. The path still required multiple wires in the floor, but the installation
was greatly simplified.
History of AGVS
1980s Non-Wire Guidance
During the late 1980s, non-wire guidance for AGV systems was introduced. Laser and
inertia guidance are two examples of non-wire guidance which allow for increased
system flexibility and accuracy. When changes to the original guidepath are needed,
there is no need for floor alterations or production interruption. These and other
methods of navigation are explained more fully in the section on navigation.
History of AGVS
Computer Functions
As with all high-technology products based on electronic and computer software,
without a doubt, AGVs have been greatly influenced and have benefited from the
advances and reductions in cost of microcomputers and microelectronics. The
computers used in AGV systems can store instructions, make decisions and execute
procedures. In practice, AGVs are capable of performing almost all of the decisions and
control functions currently controlled by humans in managing the material handling
process. They can schedule factory time, maintain inventories, manage system details
and control many types of mechanical systems in the overall operation.
History of AGVS
Applications and Controls
The use of AGVs has evolved drastically from traditional distribution-oriented
applications at one end of the spectrum to complex computer-controlled automobile
assembly systems with robotic interfaces at the other end. They can be stand-alone
systems, an integral part of another system, or aid in pulling together islands of
automation. Originally designed for horizontal transportation of palletized material, the
design and application of vehicles and controls are now as varied as those of industrial
robots.
History of AGVS
AGV Manufacturers
The market demand for AGVs can be measured by the increased number of AGV
manufacturers. During the late 1970s there were fewer than 6 AGV vendors in the
United States and only 3 different types of vehicles. By 1990 there were more than 40
worldwide vendors and more than 15 vehicle types, with an increasing emphasis on
standard design. The future will be marked by still more change which will be driven
partly by even more technological advances. But it will also be driven by increases in
the use of AGVS, which in turn will foster more investment in research and
development
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Vehicle Navigation
The principles which make it possible for an AGV to navigate its way between any two
locations are really quite simple. All navigation methods use a path. The vehicle is
instructed to FOLLOW a Fixed Path or TAKE an Open Path.
Fixed Path Navigation
Following a Path
Vehicles that FOLLOW a path use the earliest methods of AGVS navigation. The
general features of these methods are:



The paths are well marked on the floor
The paths are continuous
The paths are fixed, but can be changed
Fixed Path Navigation:
Creating a Path
The principle techniques for creating paths are to:
1.
2.
3.
4.
Apply a narrow magnetic tape on the surface of the floor
Apply a narrow photo sensitive chemical strip on the surface of the floor
Apply a narrow photo reflective tape on the surface of the floor
Bury a wire just below the surface of the floor
The first three methods require a sensor on the underside of the vehicle which can detect the
presence of the surface mounted path. The sensor’s mission is to keep the vehicle directly over
the guide path. If the path makes a turn the sensor detects the turn, provides feedback to the
onboard vehicle controller, which in turn causes the vehicle to steer in the direction of the path.
The sensor’s role in connection with the onboard controller and steering mechanism is to cause
the vehicle to FOLLOW the path.
Buried Wire Path
1.
2.
3.
4.
Apply a narrow magnetic tape on the surface of the floor
Apply a narrow photo sensitive chemical strip on the surface of the floor
Apply a narrow photo reflective tape on the surface of the floor
Bury a wire just below the surface of the floor
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When the fourth method of “path following” is employed using a current-carrying buried wire,
the under vehicle sensor takes the form of a small antennae consisting of magnetic coils. With
current flowing, a magnetic field surrounds the buried wire. The closer the buried wire is to the
AGV antennae, the stronger the field.
The magnetic field is completely symmetrical around the conductor or the buried wire. At a
given distance from the wire the field has the same strength on either side of the cable. The field
strength is detected by the antennae’s magnetic coil and induces voltage in the coil.
Fixed Path Navigation:
Steering Correction Coils
Like the three other path following methods, the vehicle steers itself to FOLLOW the
magnetic field surrounding the buried wire. To get a steering correction signal the
vehicle’s sensing antennae consists of two coils. When the vehicle is centered directly
above the buried wires equal voltages are induced in the two coils. If the vehicle moves a
bit to one side of the wires, the induced voltages would be of different strength. The
difference in signal strength in the coils is proportional to side displacement of the coil.
This difference is amplified and fed back to control an onboard servo motor, which
turns the guide wheel or wheels until both coils receive equal signals, and the course is
corrected.
Fixed Path Navigation:
Path Selection
In this illustration, a vehicle at “A” has two choices on how to get to “B”. A computer
either on board the vehicle or at some central location selects a path based on
established criteria. That criteria may be the shortest distance or the path with the least
traffic at the present time. Once selected the vehicle is dispatched and navigation begins.
All of the “PATH FOLLOWING” navigation methods permit routing options that
include guide path switching and merging.
Open Path Navigation:
Taking a Path
Navigation methods that direct a vehicle to “TAKE A PATH” employ developments that
came into their own in the early to mid 90’s. They utilize a different set of technologies.
Unlike “path following navigation,” where the guide paths are fixed, and more or less
permanent, vehicles operating in the “Take a Path” category are actually offered more
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variation if not an infinite number of ways to navigate the open space between two
points.
Open Path Navigation:
Navigation Requirements
From a practical point of view, the choices are limited by known permanent or
temporary obstructions and the path selection criteria, such as take the shortest path.
To navigate in an open, unrestricted space without the benefit of a fixed path, a vehicle
must have a way of knowing where it is and be capable of taking a heading to where it
wants to go. All open space navigation methods require:

A map of the area in which the vehicle can operate that is contained in the
vehicle’s computer memory.
 Multiple, fixed reference points located within the operating area that can be
detected or “seen” by the vehicle.
Open Path Navigation:
Navigation Methods
The three most common open space navigation methods are Laser Guidance, Inertial
Guidance, and Cartesian Guidance. The choice of navigation method for a particular
application is often a simple matter of preference. Each method offers different benefits
and costs associated with system set up and operation which is application dependent.
Unless there is a definite preference, users should work closely with suppliers to evaluate
the options in relation to the intended application. Each method is backed by a rich
history of its successful use in practice.



Laser Guidance
Inertial Guidance
Cartesian Guidance
AGVS Dispatching
AGVS dispatching is essential to every AGVS, whether simple or complex. Dispatching
AGVS is much the same as dispatching taxi cabs. The dispatch function makes sure that
all customers get timely services from the vehicle best able to service a request. Without
a dispatching function, nothing would move. With inefficient dispatching, a system will
not obtain maximum benefits.
The dispatch function maximizes the benefits of any AGVS and ensures that all
customers get serviced in a timely manner. Remote and local dispatch are most
commonly described as offboard and onboard dispatchers respectively.
Remote Dispatching
Methods of Communication
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Remote dispatch occurs when the AGVs receive dispatching information from a central
controller. This type of dispatch requires methods of communications to send the command
from the Dispatcher to the AGVs. These methods of communications include:
 An RF Network (Broadband or Spread Spectrum) including a base station and antennas
transmitting a signal throughout the airwaves with a receiver mounted aboard each
vehicle.
 Inductive RF through a wire in the floor with antennas mounted aboard each vehicle. In
many cases, the guidance wire will be used as the RF communication antenna and in other
cases, the inductive signal is communicated through a separate buried wire.
 Infrared communications with multiple IR transmitters mounted throughout a facility
with an IR receiver mounted aboard the AGVS.
Remote Dispatching
The Dispatcher
The remote dispatch function generally resides in a computer (PC), Programmable
Controller (PLC), or other microprocessor, known as the Dispatcher. The Dispatcher
accepts input from the various system components (generally transport requests) and
directs the AGVS to fulfill the command in the most efficient manner. This function
directly compares to the taxi Dispatcher back at the terminal, receiving calls from many
customers and then dispatching each driver via radio to the pickup station. Remote
dispatch can occur with vehicles at single or various dispatch points.
Remote Dispatching
Single Point Dispatch
A single dispatch point requires the AGVs to return to the same location every time to
receive commands and transport requests. Single point dispatch generally has
predetermined shortest path routings and works on strict FIFO requests. As vehicles
are available and reach the dispatch point, they are given a transport command.
Remote Dispatching
Vehicle Manager
Using various dispatch locations, vehicles are given transport commands as soon as they
complete their previous transport. The Dispatcher attempts to choose the closest
available vehicle to fulfill the command. Should a vehicle be given a command and a
closer vehicle becomes available, the more complex Dispatchers will be able to reassign
the transport request to the closer vehicle. The Dispatcher, also known as the Vehicle
Manager, generally includes an algorithm for priorities governing system movement.
Remote Dispatching
Dispatcher Commands
The Dispatcher commands can also take multiple forms where an AGV can be sent a
full command, a half command, or a point-to-point command.
For example:
Full command (pick up at “A” and deliver to “B”)
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Half command (pick up at “A”)
Point-to-point (move from point 1 to 2, from point 2 to 3, etc.)
With full and half commands, the AGV has a system map resident in its onboard vehicle
controller. With point-to-point routing, the system map is resident with the Dispatcher.
Local Dispatching
Signals and Occurances
Local dispatch occurs when an AGV is dispatched by means of a signal or occurrence
originating at the location of the AGV. Local dispatch is generally associated with
simpler AGV systems and where repetitive tasks are predominant.
The signals and occurrences include:

Photo-electric or data couplers where simple commands are given at the
point of dispatch.

Automatic Identification with barcode, RF tag, magnetic stripe, etc.

Onboard sensors for load presence, pushbutton, keypad, etc.
Local Dispatching
Taxi Cab Analogy
Local dispatch is simpler by design and nearly always requires the system map to be
resident in the onboard vehicle controller. Reverting back to the taxi cab analogy, local
dispatch is comparable to a taxi driving the streets, picking up fares as they yell for a
cab. No central Dispatchers are needed and the vehicle reacts to simple, generally single
source inputs from sensors, keypads and devices.
Local Dispatching
Common Input Sources
The following are more common input sources for local dispatch:

When a Pushbutton is depressed, the AGV controller is programmed to go
forward to stop points and await release. The release signal is an onboard
pushbutton input, causing the AGV to dispatch itself to the next stop point.

Additionally, systems may include multiple destinations requiring a series
of pushbuttons (one for each), or a keypad which accommodates a larger
selection of origins and destinations.
Local Dispatching
Signal Detection
Data Couplers or Photoelectrics external to the vehicle can also be used to send a signal
to the AGV vehicle controller indicating an origin and/or a destination. These devices
can be in a singular location or at multiple points along the pathway.
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A load aboard signal from a photoelectric source or proximity switch can be used to
detect the presence of a load conveyed or placed on the AGV. This signal may be
enough in a simple system with a singular destination for each origin to cause the AGV
onboard vehicle controller to dispatch itself.
Local Dispatching
Load Identification
Automatic Identification systems can be placed on board the AGV to sense the type of
product received on the vehicle. If each load type has a particular destination, as
determined by height, weight, size, barcode ID, RF ID tag, or magnetic stripe ID, then
the AGV onboard vehicle controller will dispatch the AGV per the particular load
characteristics or identities.
Traffic Control
Crucial to all AGV systems is the automatic stopping, starting and routing of vehicles.
To ensure against one vehicle entering an already occupied zone or intersection of a
guidepath and to provide for orderly and efficient routing in general, the location of
each vehicle is monitored and decisions are made based on this knowledge. In the
context of traffic control, all forms of automatic stopping and starting are known as
blocking.
Two types of blocking in general use are Zone Blocking and Accumulative Blocking.
AGVS Communications
Communications include message commands such as where to go, when to start, when
to slow down and when to stop. It may also include fault condition reporting.
Computer-controlled systems overseeing remote objects need a means of
communicating commands, and in many cases confirming replies, between a supervisory
computer and the objects being controlled. Depending on the application, there are four
types of basic communication media being used within AGV Systems.
Radio Communication
Radio provides maximum flexibility in system control. Vehicles can be programmed
“on the fly”, new routings or maps can be downloaded quickly, and system speed of
response to changing load movement demands is improved. It provides almost constant
communication between the vehicles and the system and makes the AGVS system a very
responsive tool that can react to the changing dynamics of the work environment.
Radio Communication
RF Radio Waves
Radio waves can be used to communicate information and data, from a fixed base
station to the modems on each vehicle. Radio waves simply perform the function of
delivering energy to the remote receiver. The actual information is superimposed on the
radio wave so that it can be accurately extracted from the wave at the receiving end.
This provides a continuous two-way data link with the vehicles. There are two basic
systems in use today, narrow-band and spread spectrum. A plant survey is generally
done to determine what other frequencies are operating in the environment, if there are
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any dead zones in the system that would inhibit radio transmission and to determine the
number, type and location of antennas.
Radio Communication
Narrow-band Radio System
A narrow-band radio system transmits and receives user information on a specific radio
frequency. Narrow-band radio keeps the radio signal frequency as narrow as possible
to pass data. AGVS systems generally operate in the 450-MHz band on 25-Khz
channels. Undesirable crosstalk between communications channels is avoided by
carefully coordinating different users on different channel frequencies. The radio
receiver filters out all radio signals except the ones on its designated channel frequency.
Radio Communication
Spread Spectrum Channels
There are Federal Communications Commission (FCC) assigned frequency channels
assigned to qualified users who request them. This is done by licensing that business to
transmit on a given frequency in a given area. Licensing has been very effective in
providing secure communications, but has placed an ever-increasing burden on the FCC
to coordinate and assign radio channels. Spread spectrum was established by the FCC
to ease the burden by allowing unlicensed radio usage.
Infrared Communication
Optical infrared communication is highly reliable but has the disadvantage of not being
continuous; it is point to point. Vehicles may be stopped during this data exchange which
usually occurs at load stations where the fixed and mobile units are aligned and in close
proximity. Or, the vehicle communicates at fixed points along its guide path as the vehicle
travels through a given zone.
The picture shows optical sensors at a conveyor pick-up/deposit stand. One sensor is
for transmitting and the other for receiving.
Vehicles are usually not dispatched from a communication point unless the path to the
next destination is free of traffic. In large systems this could present a problem in meeting
throughput. Alarm conditions also cannot be reported as they occur. As a result, infrared
communication is best suited for small systems with few vehicles and load stations.
Guide Wire Data Communication
Data transmitted on the guide wire by the guide line driver provides almost the same
flexibility as radio, with the exception of vehicle movement off the wire. Since the
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distance between the guide wire and the on board responders is constant, there are no
transmission dead spots, as there may be with radio. The techniques to accomplish this
type of data link are not widespread.
Inductive Loops Communication
Inductive loops are another means of point-to-point communication. In-floor wire loops
are located adjacent to the guide wire and connected to the central controller for data
transmission. They are usually 3 to 10 feet long and must be located at every point
where communication with vehicles is desired. Electronic messages or simple
commands in the form of prescribed frequencies are sent out via the wire loops.
Antennas on the under side of the vehicles sense the frequencies which are then decoded
and acted on by the vehicle. A vehicle can likewise send messages back to a central
controller. This is an inexpensive but limited method of data transfer. Most systems
using this method do not require vehicles to stop while receiving data from inductive
loops.
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