2. 1. Introduction to Automated Guided
Vehicles
An Automated Guided Vehicle System (AGVS) is a
material handling system that uses independently
operated, self-propelled vehicles guided along
defined pathways in the facility floor
• Transport material from loading to unloading
stations
• Highly flexible, intelligent and versatile material
handling systems.
• AGVS is a Computer-Controlled, Non-manned,
Electric Powered Vehicle Capable of Handling
Material
3. • A very flexible solution for the problem of
integrating a new automated transportation line
into an existing transportation environment by
using automatic guided vehicle.
• What is AGV? Driverless Vehicle, Electric
motors, battery powered, System Discipline,
Programming capabilities:
- Destination
- Path selection
- Positioning
- Collision avoidance
• Types of AGV:
– Driverless trains
– Pallet trucks
– Unit load AGVs
4. Driverless Automated Guided Train
• First type of AGVS to
be introduced around
1954
• Common application is
moving heavy
payloads over long
distances in
warehouses and
factories without
intermediate stops
along the route
5. AGV Pallet Truck
• Used to move
palletized loads
along predetermined
routes
• Vehicle is backed
into loaded pallet by
worker; pallet is
then elevated from
floor
• Worker drives pallet
truck to AGV guide
path and programs
destination
6. Unit Load Carrier
• Used to move unit loads from station to station
• Often equipped for automatic loading/unloading of
pallets and tote pans using roller conveyors, moving
belts, or mechanized lift platforms
7. 2. History of AGVS
• The first AGV system was built and introduced in
1953( A modified towing tractor that was used to
pull a trailer and follow an overhead wire in a
grocery warehouse)
• AGV developed in 1954 by A.M.Barrett,Jr. Using
a overhead wire to guide a modified towing truck
pulling a trailer in a grocery warehouse.
Subsequently, commercial AGV were introduced
by Barrett.
• 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
8. • Volvo developed automated
guided vehicles to serve assembly
platforms for moving car bodies
through its final assembly plants.
• Later, Volvo marketed their unit
load AGVs to other car
companies.
• In the 1970’s the principal
guidance technology was to
induce an electronic frequency
through a wire that was buried in
the floor. ‘floor controller’
• These first generation navigation
schemes were expensive to
install.
• All floor cuts needed to follow
the exact path of the AGV.
9. • Introduction of a unit load vehicle
- They have the ability to serve several
functions;
- a work platform,
- a transportation device, and
- a link in the control and information system
• They transport material in warehouses, factories,
mills, hospitals, and other industrial and
commercial settings
10.
11.
12. 3. Vehicle functions
• Man / vehicle functions
- Inputs made via operator panel with its keyboard and display
- Destination input to the vehicle
- Plug-in manual control and diagnosis module
• Route (destination) finding
- High vehicle intelligence
- Travel route topology stored in the vehicle
- Destination code processing
- Load-sensing and empty location recognition
• Guide track following
Guided movements using:
- optical track
- inductive track
- "free-flight" (partly guide-trackless)
- "free-navigation" (guide-trackless
13. • Data exchange
- Infrared
- Radio
• Special functions
- Battery reserve monitoring
- Control of battery charging
- Obstacle recognition
• Load handling
- Load acceptance
- Load depositing
- Load monitoring
- Load transfer synchronization
• Travel control
- Speed
- Safety gap maintenance
- Collision protection
14. Modern AGVS
• Modern AGVs are computer
controlled vehicles with
onboard microprocessors.
• Position feedback system to
correct path
• Communication between
vehicles via system controller
– RF communication
– Electric signals
• System management
computers
• Optimizing the AGV
utilization
• Tracking the material in
transfer and directing the
AGV traffic.
15. 4. Components of AGVS
• The Vehicle – No operator
• The guide path – The path for the AGV
• The control Unit – Monitors and Directs
system operations including feedback on
moves, inventory, and vehicle status.
• The computer interface – Interfaces with other
mainframe host computer, the automated
storage and retrieval system (AS/RS), and the
flexible manufacturing system.
18. 5. Types of AGVSs
AGVS Towing Vehicles
• First type of AGV
introduced.
• Towing vehicle is called an
automated guided tractor
• Flatbed trailers, pallet
trucks, custom trailers can
be used.
• Generally, used for large
volumes (>1000 lb) and
long moving distances
(>1000 feet).
20. AGVS Forklift Trucks
• Ability to pickup and drop
palletized load both at floor
level and on stands.
• Pickup and drop off heights
can be different
• Vehicle can position its
fork according to load
stands with different heights
• Very expensive
• Selected where complete
automation is
necessary/required.
25. 6. AGVS Guidance system
• The goal of an AGVS guidance system keep the AGV
on track/predefined path
• One of the major advantage of AGV is ease in
modification given by the guidance system for
changing the guide path at low cost compared to
conveyors, chains, etc.
• Another benefit is: guide path is flexible which means
intersection of path is possible.
• Generally, guide path does not obstruct another
systems.
• The guidance systems can be selected based on the
type of AGV selected, its application, requirement and
environmental limitation
26. Vehicle Guidance Technology
• Method by which AGVS pathways are defined, and vehicles
are controlled to follow the pathways
• Three main technologies:
– Imbedded guide wires - guide wires in the floor emit
electromagnetic signal that the vehicles follow
– Paint strips - optical sensors on-board vehicles track the
white paint strips
– Self-guided vehicles - vehicles use a combination of
• Dead reckoning - vehicle counts wheel turns in given
direction to move without guidance
• Beacons located throughout facility - vehicle uses
triangulation to compute locations
28. AGV Navigation
• The introduction of laser and inertia guidance.
– Allow for increased system flexibility and
accuracy
– No need for floor alterations or production
interruption
• 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
29. • Fixed Path Navigation Following a Path
• The paths are well marked on the floor
• The paths are continuous
• The paths are fixed, but can be changed
30. Creating a Path:
The principal techniques for
creating paths are to:
• 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
• Bury a current-carrying wire just
below the surface of the floor
32. 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.
• Criteria:
– The shortest distance
– The path with the least traffic
at the present time
• All of the “PATH
FOLLOWING” methods permit
routing options that include guide
path switching and merging.
33. Open Path Navigation: Taking a Path
• 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
variation if not an infinite
number of ways to
navigate the open space
between two points.
34. Typical navigation systems for AGVs
• Laser triangulation
• Inertial
• Magnetic tape
• Magnetic grid
• Natural feature
• Wire
• Optical
On certain applications more than one form of
navigation may be used by a vehicle
35. How do the vehicles know where they are going?
Laser triangulation navigation
systems
• Most popular method of AGV
navigation
• Reflective targets are mounted
throughout the facility at known
positions
• A laser scanner is mounted on top
of the vehicle
• The laser scanner strobes for
reflective targets
• The vehicle control algorithms
calculate the exact vehicle position
via triangulation
36. • Reference points are
strategically located
targets
• A beacon on top of the
vehicle emits a rotating
laser beam which is
reflected back to the
vehicle when it strikes
(sees) a target.
37. Inertial navigation systems
• Reference points (often
magnets) are embedded in the
floor at certain x,y coordinates in
a map of the system
• Reference points are detected
by a sensor on the vehicle as it
passes over the reference point
• A gyroscope on the vehicle
measures/maintains vehicle’s
heading
• A wheel encoder on the vehicle
calculates the distance traveled
• Vehicle uses feedback from all
three devices to determine
location
38. • An on-board gyroscope
establishes and
maintains a vehicle’s
heading.
• Distance traveled is
calculated by an on
board encoder which
counts wheel rotations
39. Magnetic tape
navigation systems
• Magnetic tape is
adhered on the surface of
the floor
• A sensor on underside
of vehicle detects the
magnetic tape
• Can operate off tape
path via dead reckoning
• Similar to wire
guidance (described on
future slide)
40. Grid Navigation Systems
• Reference points (often
magnets) are embedded in the
floor in a grid pattern in the
operating area
• Reference points are given x,y
coordinates which are stored in
the vehicle’s memory
• The reference points are
detected by an on-board
sensing device
• A gyroscope on the vehicle
measures/maintains heading
• A wheel encoder on the
vehicle calculates the distance
traveled
• Vehicle uses all three devices
to determine location
41. Natural feature navigation
systems
• Reference images of the
operating area are recorded and
stored in the vehicle’s memory
• Uniquely identifiable, naturally
occurring features are identified in
the operating area
• Vehicle’s actual position is
calculated based on its relative
position compared to those natural
features
• A camera or laser can be used to
record features during setup and
sense features during navigation
42. Wire navigation systems
• Navigates using a
continuous wire embedded
in the floor
• Antennas located on the
vehicle detect signal from
the wire
• Uses encoders on wheels
to calculate distance
• Typically used in
retrofits, system
replacements and
expansions
43. Optical navigation systems
• Chemical or tape strip is
fixed or painted to the floor
• Vehicle has an onboard
sensor which allows it to
detect the path
• Some systems use an
ultraviolet (UV) light source
under vehicle to illuminate
the strip which may not be
visible with non-UV lighting
• Not typically used in plants
or warehouses because floor
line needs to be cleaned or
reapplied
44. Will vehicles be able to move the loads?
Master vehicles
• The most flexible vehicle type
• Able to interface with the floor
and block stacking, racking,
stands and conveyors
• Resemble typical manual lift
truck models (counterbalanced,
reach, outrigger)
• Can be fitted with typical
manual lift truck load handling
attachments (forked, clamp,
single/double)
45. Unit load vehicles
• Very compact design with
vehicle typically directly
under the load
• Able to interface with
stands, and conveyors
• Load handling typically via
conveyor or lift on the top of
the vehicle
• May have no load handling
ability if loaded/unloaded by
external means (crane, etc)
46. Tow vehicles
• Sometimes called
tugger vehicle
• Tows several (typically
up to 3) wheeled carts
• Loads must be placed
on and off carts manually
or via some other
automated machinery
• Provides most
economical solution
(fewer vehicles) than
solutions where only one
load is carried per trip
47. 7. What about Safety?
• Most industrial-use AGVs travel at a speed between 100 and
300 feet per minute
50. 8. AGVS Control Systems
Computer controlled system
• The path controller controls the guide path of
GVS. Sends information to AGVS process
controller.
• Process controller directs movement of vehicles
• Interchanges information with the host computer
• Most Expensive and complex type of control.
51. Remote dispatch control system
• Instructions are issued to vehicle from a remote control station via a
human operator.
• Control system sends instruction directly to vehicle.
• The human operator does have the direct control over the vehicles.
• This type of system generally have automatic loading and
unloading
• capability.
Manual control system
• The destination is fed on the onboard control on the vehicle via a
human operator after loading.
• The vehicles moves through the guide path for the destination by
itself.
• Reaching destination, it stops for the human operator to direct
unloading.
• Least expensive control system.
• Efficiency depends on operators performance and varies.
52. AGVS Communications
• Communications include message commands such
as:
– where to go,
– when to start,
– when to slow down,
– when to stop.
• Four types of basic communication media:
– Radio Communication
– Infrared Communication
– Guide Wire Data Communication
– Inductive Loops Communication
53. Radio Communication
• Maximum flexibility in
system control
• Vehicles can be
programmed “on the fly”
• system speed of
response to changing
load movement demands
is improved
54. 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.
Infrared communication is best
suited for small systems with few
vehicles and load stations
55. 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.
* Remote dispatch can occur with vehicles at single
or various dispatch points.
56. AGVS Monitoring
• Types of monitoring :
–System monitoring
–Vehicle monitoring
• The functions and
reporting capabilities
of each are important
to the safe operation of
the AGVs.
57. 9. AGVs design features
Stopping Accuracy:
• Automatic load transfer- High accuracy
• Manual load transfer- Low accuracy
• Unit load transporters are used for systems requiring high accuracy.
• Feedback system can be used to provide stopping accuracy
• Depends on the requirement/application.
Facility: Environmental compatibility, elevator, sensors, etc facilities
must be considered while designing AGVS.
Safety features: Emergency buttons, object detection for collision
avoidance, warning signals, must be built into the system.
Maintenance:
• Preventive maintenance intervals should be specified.
• Routine and repair maintenance including lubrication, checking
systems electrical/electronic parts .
• Service manual.
• Maintenance facilities: Vehicle jack stands, Low-level power
indicators.
58. 10. AGVS System Design
Many issues must be considered before designing
system for an AGVS:
• Selection of guidepath and vehicle
• Guidepath layout / Flow path design
• Number of vehicles
There are several other issues regarding timing of
AGVs, dispatching rules, routes, etc. Also, there
must be interaction between design and operational
issues for system design.
59. Attributes for selection of guidance & AGVS
Vehicle Related attributes:
• Cost of the vehicle system
• Cost of guidance system
• Vehicle dimensions
• Load capacity
- Maximum weight
- Maximum Volume (depending on AGV inner dimensions)
• Maximum speed at loaded/unloaded condition
• Maintenance facilities: Modular components for maintenance, self
• diagnosis, etc.
• Charging related attributes such as charging time, on-line charging.
• Turning Radius
• Position sensors
• Loading system i.e. unit load, pallet, or other attachments required.
60. Flow path design
• Type of flowpath within the layout i.e. unidirectional,
bidirectional or combination
• Type of guidepath layout
• Position of load transfer or loading /unloading stations
• Number of stoppage stations
• Storage space of the stations.
For developing a flow path design simulation software
can be used. These software takes into consideration the
layout, locations of P/D stations, timings of AGV,
material flow intensities between stations, etc.
61. Number of vehicles
General notations:
• Dd = total average loaded travel distance
• De = total average empty travel distance
• Ndr = Number of deliveries required per hour
• Nd = Number of deliveries per vehicle per hour
• Th = loading and unloading time
• Tdv = total time per delivery per vehicle
• Tf = traffic factor that accounts for blocking and waiting of vehicles
and at intersections.
if only 1 vehicle than Tf =1
if Number of vehicles > 1 than Tf <1
• v = vehicle speed
Tdv = (Dd / v) + Th + (De / v)
= loaded travel time + loading/unloading time + empty travel time
Nd = ( 60*Tf ) / Tdv
Number of automated guided vehicles = Ndr / Nd
62. Advantages of AGV’s
• Unobstructed movement
• Flexibility
- Locations, path, P/D points can be reprogrammed
- Easy to change guide path system
- Number of vehicles can be altered depending on requirement
• Greater reliability
- Less environmental problems
- AGV can be replaced by another, in case of failure.
• Lower investment
• Higher operating savings on long run
- Minimal labor cost
- Easy maintenance
• Easy to interface with other systems
- Best choice for AS/RS, FMS
63. AGVs Applications
1. Driverless train operations - movement of large
quantities of material over long distances
2. Storage and distribution - movement of pallet loads
between shipping/receiving docks and storage racks
3. Assembly line operations - movement of car bodies
and major subassemblies (motors) through the
assembly stations
4. Flexible manufacturing systems - movement of work-
parts between machine tools
5. Miscellaneous - mail delivery and hospital supplies
64. 11. Analysis of Vehicle-Based
Systems
• Equipment used in vehicle-based material
transport systems includes industrial trucks (both
hand trucks and powered trucks), automated
guided vehicles, rail-guided vehicles, and certain
types of conveyor systems.
• These systems are commonly used to deliver
individual loads between origination and
destination points.
• Two graphical tools that are useful for displaying
and analyzing data in these deliveries are the
from-to chart and the network diagram.
65. • The from-to chart is a table that can be used to indicate
material flow data and/or distances between multiple locations.
• A network diagram consists of nodes and arrows, and the
arrows indicate relationships among the nodes.
66. Mathematical equations
• It is assumed that the vehicle moves at a constant
velocity throughout its operation and that effects of
acceleration, deceleration' and other speed differences
are ignored.
• The time for a typical delivery cycle in the operation
of a vehicle-based transport system consists of (1)
loading at the pickup station, (2) travel time to the
drop-off station, (3) unloading at tire drop-off station,
and (4) empty travel time of the vehicle between
deliveries. The total cycle time per delivery per
vehicle is given by
67. where Tc : delivery cycle time, min/del;
TL : time to-load at load station, min;
Ld : distance the vehicle travels between load and
unload station, m (ft)
vc : carrier velocity, m/min (ft/min)
Tu : time to unload at unload station, min;
Le : distance the vehicle travels empty until the start
of the next delivery cycle, m (ft).
The Tc must be considered an ideal value, because it
ignores any time losses due to reliability problems,
traffic congestion, and other factors that may slow
down a delivery. In addition, not all delivery cycles
are the same
68. • Originations and destinations may be different from one
delivery to the next, which affect the Ld and Le terms
in the equation.
• Accordingly, these terms are considered to be average
value for the loaded and empty distances traveled by
the vehicle during a shift or other period of analysis.
• The delivery cycle time Tc can be used to determine
two values of interest in a vehicle-based transport
system: (1) rate of deliveries per vehicle and (2)
number of vehicles required to satisfy a specified total
delivery requirement.
• The possible time losses include (1) availability, (2)
traffic congestion, and (3) efficiency of manual drivers
in the case of manually operated trucks.
69. • The traffic factor Ft is defined as a parameter for
estimating the effect of these losses on system
performance.
• Sources of inefficiency accounted for by the traffic
factor include waiting at intersections, blocking of
vehicles (as in an AGVS); and waiting in a queue at
load/unload stations.
• If these situations do not occur, then Ft = 1.0. As
blocking increases, the value of Ft decreases. Ft is
affected by the number of vehicles in the system
relative to the size of the layout.
• If there is only one vehicle in the system, no blocking
should occur, and the traffic factor will be 1.0. For
systems with many vehicles, there will be more
instances of blocking and congestion, and the traffic
factor will take a lower value. Typical values of traffic
factor for an AGVS range between 0.85 and 1.0.
70. • For systems based on industrial trucks,
including both hand trucks and powered trucks
that are operated by human workers, traffic
congestion is probably not the main cause of
low operating performance.
• Instead, performance depends primarily on the
work efficiency of the operators who drive the
trucks. Worker efficiency is defined as the
actual work rate of the human operator relative
to the work rate expected under standard or
normal performance.
• Let Ew symbolize worker efficiency
71. • With these factors defined, the available time per hour
per vehicle can now be expressed as 60 min adjusted by
A, Ft, and Ew. That is,
AT = 60 A Ft Ew
where AT : available time, min/hr per vehicle;
A : availability; Ft: traffic factor, and
Ew : worker efficiency. The parameters A, Ft, and Ew do
not take into account poor vehicle routing, poor guide-
path layout, or poor management of the vehicles in the
system.
• These factors should be minimized, but if present they
are accounted for in the values of Ld, Le, Tl, and Tu.
• Equations for the two performance parameters of
interest can now be written. The rate of deliveries per
vehicle is given by
72. where Rdv : hourly delivery rate per vehicle,
deliveries/hr per vehicle;
• Tc: delivery cycle time computed by previous
Equation, min/del;
• and AT : the available time in t hour, adjusted for
time losses, min/hr.
• The total number of vehicles (trucks, AGVs,
trolleys, carts, etc.) needed to satisfy a specified
total delivery schedule Rf in the system can be
estimated by first calculating the total workload
required and then dividing by the available time
per vehicle. Workload is defined as the total
amount of work, expressed in terms of time, that
must be accomplished by the material transport
system in t hr. This can be expressed as
WL = Rf . Tc
73. where WL : workload, min/hr;
• Rf : specified flow rate of total deliveries per hour
for the system, deliveries/hr;
• and Tc: delivery cycle time, min/del.
• Now the number of vehicles required to
accomplish this workload can be written as
• where nc : number of carriers (vehicles) required,
• WL : workload, min/hr; and
• AT : available time per vehicle, min/hr per
vehicle.
74. where nc : number of carriers required,
• Rf : total delivery requirements in the system,
deliveries/hr;
• and Rdv : delivery rate per vehicle, deliveries/hr
per vehicle. Although the traffic factor accounts
for delays experienced by the vehicles, it does not
include delays encountered by a load/unload
station that must wait for the arrival of a vehicle.
• The preceding equations do not consider this idle
time or its impact on operating cost.
• Mathematical models based on queuing theory are
appropriate to analyze this more complex
stochastic situation
75. Example 1
• Consider the AGVS layout in Figure . Vehicles travel
counterclockwise around the loop to deliver loads from the
load station to the unload station. Loading time at the load
station : 0.75 min, and unloading time at the unload station :
0.50 min. The following performance parameters are given:
• vehicle speed : 50 m/min, availability : 0.95, and traffic
factor : 0.90.
• Operator efficiency does not apply, so Ew : 1.0. Determine
• (a) travel distances loaded and empty,
• (b) ideal delivery cycle time, and
• (c) number of vehicles required to satisfy the delivery
demand if a total of 40 deliveries per hour must be
completed by the AGVS
76. • (a) Ignoring effects of slightly shorter distances around
the curves at corners of the loop, the values of Ld and
Le are readily determined from the layout to be 110 m
and 80 m, respectively.
77.
78. • Determining the average travel distances, Ld
and Le, requires the particular analysis of
AGVS layout and how the vehicles are
managed. For a simple loop layout such
Figure, determining these values
straightforward. For a complex AGVS layout,
the problem is more difficult. The following
example illustrates the issue.
79. Example 2
The layout for this example is shown in Figure, and the
from-to chart is presented in table. The AGVS includes
load station 1 where raw parts enter the system for
delivery to any of three production stations 2, 3, and 4.
unload station 5 receives finished parts from the
production stations. Load and unload times at stations 1
and 5 are each 0.5 min. Production rates for each
workstation are indicated by the delivery requirements in
Table. A complicating factor is that some parts must be
transshipped between stations 3 and 4. Vehicles move in
the direction indicated by the arrows in the figure.
Determine the average delivery distance, Ld
80. • Proc: processing operation, Aut: automated; Man: manual operation
• Dimensions in meter (m)
81. • To determine the value of Ld, a weighted average must be
calculated based on the number of trips and corresponding
distances shown in the from-to chart for the Problem:
82. • Determining Le the average distance a vehicle
travels empty during a delivery cycle, is more
complicated. It depends on the dispatching and
scheduling methods used to decide how a vehicle
should proceed from its last drop-off to its next
pickup.
• In Figure, if each vehicle must travel back to
station 1 after each drop-off at stations 2, 3, and 4,
then the empty distance between pick-ups would
be very long indeed. Le would be greater than Ld.
• On the other hand, if a vehicle could exchange a
raw work part for a finished part while stopped at
a given workstation, then empty travel time for
the vehicle would be minimized.
83. • However, this would require a two-position
platform at each station to enable the exchange.
So this issue must be considered in the initial
design of the AGVS.
• Ideally, Le should be reduced to zero. It is highly
desirable to minimize the average distance a
vehicle travels empty through good design of the
AGVS and good scheduling of the vehicles.
• The mathematical model of vehicle-based
systems indicates that the delivery cycle time will
be reduced if Le is minimized, and this will have
a beneficial effect on the vehicle delivery rate and
the number of vehicles required to operate the
system.
