Seminar on AGV

Emergency stop

Status indicator

Obstacle sensor

Protective bar

Flasher

Protective bar

Photobarrier

Audible signal

Side protectionrails

Department of Mechanical Engineering RCPIT, Shirpur (2010-11)

CHAPTER 1

INTRODUCTION

An automated guided vehicle system is a material handling system that

uses independently operated , self propelled vehicle that are guided along defined

pathways on the floor. The vehicles are powered by means of on board batteries

that allow operation for several hours (8-16 hrs.) between recharging. Guidance is

achieved by using sensors on the vehicles that follow the guide wires. The vehicle

is controlled by an off board controller or a microprocessor. This controller

sends commands to the vehicle such as identification of load, its destination and

other special instructions. An AGV system provides a material handling system

i.e. both flexible and readily adaptable to either production or production changes.

Figure 1.1

Basic Diagram of Automated Guided Vehicle

Page 1 of 20AUTOMATED GUIDED VEHICLE


AGV systems are originally developed for the distribution of material in

warehouse environments although this is an imp. use, two major growth areas

have been evolved the movement of material to and from production areas in

manufacturing facilities, reflecting manufacturing work lifts and use of carriers of

work in progress in assembly plants, replacing serial type asynchronous or fixed

index assembly conveyor system and small packages, in hospitals to deliver

meals, and for material handling. (Miller, 1987).

AGV system were first introduced in 1950 in USA and later in Europe in

early 1960, the technology caught on much faster in Europe.



CHAPTER 2

TYPES OF VEHICLES

2.1 Towing Vehicles:

These vehicles consist of an AGV with no load carrying facility but

with a hitch or tow bar that can pull trailers, carts pallets jacks and wheeled racks.

They are used where large volume of product to be moved or in retro fit

applications where product in historically been moved by trailers. These vehicles

can move loads up to 50,000 pounds.

Figure 2.1

Towing type Automated Guided Vehicle



2.2 Unit load Transporters:

These vehicles are designed to carry individual loads. Unit load

transporter can have an extremely versatile deck design, which permits them to be

equipped with rollers, belt conveyors, power lifts, special fixtures, or on board

robot arm, These AGV can be either bi-directional or unidirectional and are used

in house as well as on factory flowers. Unit load transporter scan lift loads

ranging between 12,000 to 60,000 pounds.

Figure 2.2

Unit Load Transporter Type Automated Guided Vehicle

2.3 Standard Automatic Guided pallet Trucks:

These vehicles are designed to service palletized loads to and from

floor level positions. The shadow fork region has limited fork travel and is

designed to move pallets to and from floor positions exclusively. The fork truck

version has travel up to 20 feet and can move pallets both at floor level and on

stands or racks.



2.4 Assembly Line Vehicles:

These vehicles have a fixture on board that accept the frame initial

parts of the product that is to be assembled. The vehicle is routed through the

various manufacturing stations of the factory where parts and assembly are added

to the product. these AVG can provide total automatic transfer of material these

are known as material handling system on automated assembly line. They can

skip assembly section if required in particular section breaks down.

2.5 Light Load Transporters:

These vehicles are design to carry boxes, baskets, small parts, etc.

with any other unitized container. It generally has a footprint allowing its use in

tight spaces and narrow aisles. These vehicles are used for a wide range of

functions from mailrooms to clean rooms in every type of manufacturing and

office environments.



CHAPTER 3

AGV SYSTEM COMPONENTS

Although all AGV system are different, in general they consist of

following components:

3.1 Vehicles:

The component of an AGV system that is most readily identified is

vehicle itself. The vehicle consists of a frame, batteries on board charging

unit, electrical system drive unit, steering, precision stop unit, on board

controller, communication unit, safety system and work platform.

3.1.1 Frame :

The frame is usually constructed of welded steel member with

aluminum cover Plate.

3.1.2 Batteries and charging :

AGV systems are typically powered by 24 or 48v D.C. industrial

batteries. Battery charging is accomplished by one of two techniques viz.

Opportunity charging or full cycle charging.

3.1.3 Drive unit :

The main components of motor speed controller and drive

mechanism. The driver speed controller mechanism is usually a pulse width

modulated four-quadrant servo drive unit. The carrier drive commands are

generated either through the microprocessor or at the hand control unit.



3.1.4 Steering:

Vehicles are designed to maneuver in three different ways forward

only, forward and reverse, four directional. The major components of

power steering system are the steering antenna, the steering motors and

their controllers, steering linkage and steering limit switches.

3.1.5 Precision stop controller :

A precision stop controller is used to stop AGV with close location

accuracy at workstation and charge station. At some point before an up

coming precision stop location, the vehicle will receive a precision stop

command from off board controller or by code bar on board on the floor.

AS it approaches stop point the vehicle’s metal detector is activated and

AGV slows to the end of the plate.

3.1.6 On board controller :

The vehicle controller is used to monitor vehicle performance

through encoder data to determine position and velocity discrete digital

input, monitor functions as controls, activation of safety devices, battery

conditions, steering limit, break release, running light drive controller

status.

3.1.7 Communication Unit :

Instructions to the vehicle microprocessor are usually

generated by the Area controller and then relayed to the vehicle. The

communication System may be either continuous or discrete.

3.1.8 Safety :

Safety systems may be divided in to three specific categories,

vehicle to Vehicle, vehicle to object, and vehicle to people. The first

system uses photo cells mounted on AGVs leading edge and reflecting

material on trailing edge to avoid collision of vehicles. Vehicle to object



system uses bumpers , toe born limit switches, proximity sensors to

protect both vehicle and any object in AGV path generally vehicle have

warning light buzzers or toner which flashes or sounds to indicate

automatic mode.

3.2 GUIDE PATH AND GUIDENCE SYSTEM;

Generally most AGV s need guide path to follow. The guide path

techniques used are known as passive or active tracking. Passive tracking depends

upon either optical or metal detection principles where as active tracking involves

inductive principle’s.( (Taghaboni and Tanchoco, 1988; Gaskins et al., 1989))

3.2.1 Passive Tracking :

The optical method may be simply involved a light sensitive

photocell mounted on the vehicle, which follows the tape on floor. It depends

upon contrasting floor surface so that variation in reflecting light that is sensed

by photocell can be detect ed when the vehicle begins to stray from them guide

path. If guide path becomes dirty, faded, or damaged or if the ambient light

distorts the light level sensed, the vehicle may stray from guide path.

A variation of optical method is lightening patented optical system. It

is based on bonding fluorescent particles to the floor surface and stimulating

these particles with ultra violet light and causing them to omit a generated light

in the sensing head an oscillation mirror scans the guide path and reflect the

generated light in to photo reflector, which intern relays signal to

microprocessor.

The other passive tracking techniques involve vehicle with metal detecting

sensor s following a stainless steel ribbon. Tran scar patterned guidance system

consists of two sensors packs each containing five sensors and located at each

end of AGV. The three central sensors allow the vehicle to center itself on the

guide path. The two remaining sensors assist the vehicle in transverse curve.



The sensor locates the presence of guide tape and transmit this information to

the onboard microprocessor.

3.2.2 Active Tracking :

Active tracking involves use of guide wire and most commonly

used Technique in industry. A low voltage ( less than 40 v), low current (less

than 400 ma), low frequency (Ñ to 15 kHz.) and signal is conducted through a

wire buried in a slot in the floor. A small electromagnetic field is radiated

from the wire and two inductive type sensors are compared and as long as

they are equal, the vehicle is centered on the guide path if vehicle begins to

stray, signal magnitudes sensed are no longer equal and sensor difference is

used to steer the vehicle back on the guide path.

3.3 Floor and system controls:

The controller is the brain of the whole system, trying the vehicle

to the guide path and integrating the system. Not only does it control the AGV

system but it also integrates with automatic assembly facility. The AGV

system itself will usually contain three levels of controller architecture,

vehicle control system, floor control system and vehicle on board processor.

3.3.1 vehicle control system :

The top level of vehicle control system often

communicates with and under the control the facility’s host computer. Most of

the decision making takes place at this level as it oversees the system

operation. The vehicle system stores in memory exact vehicle location at all

the times and provides network access.

3.3.2 Floor control Unit :

This level is referred to as the data concentrator and acts as

traffic manager and communicating directly with the vehicles and providing

them with formatted detailed commands.



3.4 Vehicle processor :

. Generally the vehicle processor knows the vehicle location, and it

can interpret commands received from floor control unit and can monitor on

board safety devices. The two type of vehicle control processors are intelligent

type and non-intelligent type



CHAPTER 4

AGV GUIDENCE & CONTROLES

INTRIDUCTION

Some AGV system use vehicles, which have sophisticated

microprocessor on board and are known as smart or intelligent vehicles. Other

systems have minimal vehicle computing ability and use a central computer

for all process. In such systems central computer decides location, direction,

proper rout and path of the vehicle. This is accomplished by turning on and

off the path at decision points or by commanding vehicle to follow a particular

frequency. All decision is making is made by central computer in smart

vehicles. The central computer dispatches the vehicle to next location, though

it’s on board microprocessor, the vehicle it self makes decision as to which

path it takes.

(et al. (1990) and Smith et al. (1992))

Figure 4.1

Controlling Of Automated Guided VehiclePage 11 of 20

AUTOMATED GUIDED VEHICLE


4.1 method of Programming

the smallest system uses manual programming to direct the vehicle

to specific destination and to dispatch the vehicle. These system ranges from

basic toggle switches, thumbwheel switches or push button numeric pad for

programming the vehicle to go to specific station. The advantage of manual

system is that it is the least expensive and simplest system. The disadvantages

of manual system are that its efficiency depends upon operators. Finally these

types of systems controller cannot determine vehicle location while it is in

transits.( (Ozden, 1988; Bartholdi and Platzman, 1989).)

The second level of sophistication in control system is referred to as

remote dispatch. In such systems operator intersects with the local controller

who in turn transmit information such as destination , rout and automatic load/

unload commands to the vehicle this control system allows the vehicle to

circulate on guide path looking for work. this system does not allowed

tracking capabilities. The third level is more complex and expensive and is

referred to as the central computer controlled system.( (Egbelu and Tanchoco,

1984; Russell and Tanchoco, 1984))

4.2 Guide Path Techniques:

a. passive techniques:

It involves the use of chemical, paint and adhesive strips or tape

where by the AGV focuses a beam of light on the reflective tape and tracks

the path by measuring the amplitude of reflected beam. Another passive

method involves vehicles with metal detecting sensors following stainless

steel tape. Communication of commands and positional information to the

vehicle may be accomplished by placing guide path codes along the guide

path.



Active Techniques :

By for most commonly used method in industry is the wire guide path.

This method involves cutting a slot in the floor (1/8 to ¾ inch wide ) and (1/2

to 1.5 inch deep), in to which one or more wires are placed and grouted and

epoxyed. There are two different wire guide path techniques, one using either

one wire in the slot operating on one frequency or one multiple overlaid

frequencies and other using several wires in the slot each operating at a

different frequency. With multiple wire method a path is selected at decision

points according to the assigned frequency. The vehicle can be programmed

by system controller at decision points to follow the appropriate frequencies

and thus the vehicle is directed on the desired path.

4.3 Communication Technique :

Irrespective of guidance technique used it is essential for

individual vehicle to be able to communicate with the system controller. The

vehicle must be able to receive such commands as work assignments,

destinations, route frequency, speed, blocking instruction, when to start and

stop and auxiliary equipment commands used similarly vehicle must be able

to transmit it’s status to the system controller by sending such informations as

vehicle identification, location, direction of travel speed of travel & battery

status. There are two AGV systems viz. continuous & discrete. Continuous

indicates that the area controller always communicates with any vehicle where

as discrete means that area controller can only communicate with a particular

vehicle at times.

Radio frequency communication is widely used from in an

continuous communication. Each AGV is equipped with transmit / receive

antenna. Each AGV may be on a different frequency.

The optical method involves stopping the AGV at set stations

along the guide path where information is passed to the vehicle using infrared

light.



CHAPTER 5

APPLICATION OF AGVS

Introduction :

AGV is used in various growing number and a variety of

applications.

5.1 Driverless train operation :

These applications involved the movement of large quantities of

material over large distances. e.g. the moves within a large factory building or

buildings in large storage depot. For the movement of trains consisting of ¹ to

10 trailers, this become an efficient handling method.

Figure 5.1

AGV Used In Driverless Train



5.2 Storage / Distribution system :

Unit load carriers and pallet trucks are particularly used in these

applications. In these storage or distribution operation, the movement of

material is in unit load form. The application often interfaces the AGV with

some other automated handling or storage system this type of storage /

distribution can also be used in light manufacturing and Assembly operation

in which work in process is stored in a central storage area and distributed to

different work station for assembly or processing.

Figure 5.2

AGV Used in ASRS

5.3 Assembly line operation :

AGV system is being used in a growing number of assembly line

applications. In these applications rate is relatively low and there are variety

of different models made on production line.

5.4 Miscellaneous Applications :

Other applications of AGV system including non-manufacturing and

non-warehouse applications such as mail delivery in office building and

hospital material handling applications between different floors of the

hospital.



CHAPTER 6

FUTURE TRENDS

Although it is difficult to predict the future with absolute certainty, it can be

concluded from the trends that seem to indicate future status of AGV systems.

6.1 Guidance :

The research is being accomplished to expand capability and

even to eliminate the need for guidance using guide path on board controller.

On board controller is becoming more sophisticated and at same time they are

becoming smaller and less expensive the vehicle controllers are exhibiting

such features as expanding diagnostics. Although vehicle cannot repair

themselves, they can at least indicate their problems to maintenance and repair

person. Controller sophistification will also allow the vehicle to operator more

intelligently in complex handling situation and will increase the system

integrity in the event of host computer failure.

6.2 Vehicle communication:

The trend is towards continuous as opposed to discrete

communication

So that vehicle will be able to communicate and receive updated instruction

at any time.

6.3 system controller:

System will be designed to have capability to track material and

store this information. They will be able to follow and control material flow to

support just in time concepts. The system controller will also be able to be

integrated with network allowing it to communicate with any other facility

controller.



6.4 Vehicle :

Vehicle will become more standard requiring less engineering to

adapt the vehicle to a particulate task, thus lowering the coast of vehicle to a

particular task, thus lowering the coast of vehicle to a great extent this will

make them easier to justify for many users.

6.5 Improved Graphical Display :

There will be probability the increased use of color graphical

display showing entire guide path, every vehicle location, the vehicle

identification, the vehicle status and vehicle load.

6.6 Safety:

New safety sensors for proximity detection will be developed

and coupled with computing power of on board controller to produce on even

vehicle that readily negotiate pedestrian clogged aisle.

Figure 6.1

Safety Features of Automated Guided Vehicle



7. Advantages and Disadvantages

7.1 Advantages of AGV

Following are the advantages of AGV

1. Reduction in labor force.

2. Improved productivity and quality.

3. Job enrichment and worker satisfaction.

4. Reduction in space requirement

5. Reduction in product damage.

6. Improvement in house keeping.

7. Ease of removal and relocation.

8. Integration with other type of automations.

9. System adaptability and flexibility.

7.2 Disadvantages of AGV

Following are the disadvantages of AGV

1. Expensive

2. Requirement of specially designed floor space.

3. Performance is affected if guide path bed is not stable.



CONCLUSION

This paper presents a classification scheme for automated guided vehicle

systems. This scheme is developed from a system control perspective. The

paper provides a discussion of the functionalities required of a generic AGVS

controller. The classification scheme is then developed based on the impact

the AGVS design alternatives have on the control system.

The scheme is useful as a structured method for understanding the impact of

design decisions on the control system. It provides a mechanism for

organizing the academic literature on AGVS and comparing the application

domains of different techniques. It also provides helpful information to the

system designer about the impact of design decisions on the required

controller functionality and resulting complexity. The ultimate goal is to use

the classification scheme as a design aid.

The classification scheme presented in this paper provides an organization

mechanism for AGVS from a control perspective. More importantly, it

provides the foundation for the long-term development of an automated

guided vehicle system design aid.

REFRANCESPage 19 of 20

AUTOMATED GUIDED VEHICLE


1. Bakkalbasi, O. and McGinnis, L.F., 1988, “ABC’s of Preliminary In-House Planning and Analysis of AGVS Applications,” Proceedings of AGVS’88, MHI, Cincinnati, OH, September 27-28.

2. Baumgartner, E.T. and Skaar, S.B., 1994, “An Autonomous Vision-based Mobile Robot,” IEEE Transactions on Automatic Control, vol. 39, pp. 493-502.

3. Christensen, J.H., Struger, O.J., Norrie, D. and Schaeffer, C., 1994, “Material Handling Requirements in Holonic Manufacturing Systems,” Proceedings of the 1994 International Material Handling Research Colloquium, Grand Rapids, Michigan, June.

4. M. P. Groover “Automation, Production Systems and Computer integrated Manufacturing “ TATA McGraw Hills Publications,”Second Edition,1995.

5. Flexible Manufacturing Systems: Recent Developments (Manufacturing Research and Technology) by A. Raouf and M. Ben-Daya (Hardcover - 9 Feb 1995)

6. Flexible Manufacturing Systems: Design, Analysis and Simulation (Manufacturing Engineering and Materials Processing) by Joseph Talavage (Hardcover - 18 Dec 1987)

7. J.H. Fuchs “Advanced Manufacturing Methods”, Tata McGraw Hills Publications, First Edition,1992

8. Journal paper of Flexible Manufacturing System with AGV based material handling by FUHONG DAI, BASc northest university of technology of P.R. Chaina 1982.

9. Modeling, Simulation, and Control of Flexible Manufacturing Systems: A Petri Net Approach (Series in Intelligent Control and Intelligent Automation) by MengChu Zhou and Kurapati Venkatesh (Hardcover - 1 May 1999)

10. A controle classification of Automobile vehicle system by Brett A. Peters, Department of Industrial Engineering, Texas A&M University


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Seminar on AGV