Automated Guided Vehicle GENERALS

8/19/2019 Automated Guided Vehicle GENERALS

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Automated guided vehicle

Anurag Bhardwaj

1RC09ME012

Introduction

The AGV can tow objects behind them in trailers to which they can autonomously attach. The

trailers can be used to move raw materials or finished product. The AGV can also store objects

on a bed. The objects can be placed on a set of motorized rollers (conveyor) and then pushed off by reversing them. AGVs are employed in nearly every industry including pulp paper metals

newspaper and general manufacturing. Transporting materials such as food linen or medicine in

hospitals is also done.

An AGV can also be called a laser guided vehicle (!GV). "n Germany the technology is alsocalled Fahrerlose Transportsysteme (#T$) and in $weden förarlösa truckar . !ower cost versions

of AGVs are often called Automated Guided %arts (AG%s) and are usually guided by magnetic

tape. AG%s are available in a variety of models and can be used to move products on an

assembly line transport goods throughout a plant or warehouse and deliver loads.

The first AGV was brought to mar&et in the '*s by +arrett ,lectronics of -orthbroo& "llinois

and at the time it was simply a tow truc& that followed a wire in the floor instead of a rail. "n

'/ ,gemin Automation (0olland 1") started wor&ing on the development of an automaticdriverless control system for use in several industrial and commercial applications. 2ut of this

technology came a new type of AGV which follows invisible 3V mar&ers on the floor instead of

being towed by a chain. The first such system was deployed at the 4illis Tower (formerly $ears

Tower) in %hicago "llinois to deliver mail throughout its offices.

5ac&mobile with trailer AGV

2ver the years the technology has become more sophisticated and today automated vehicles are

mainly !aser navigated e.g. !GV (!aser Guided Vehicle). "n an automated process !GVs are

programmed to communicate with other robots to ensure product is moved smoothly through thewarehouse whether it is being stored for future use or sent directly to shipping areas. Today the

AGV plays an important role in the design of new factories and warehouses safely moving

goods to their rightful destination.


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Navigation

Wired

A slot is cut in to the floor and a wire is placed appro6imately ' inch below the surface. This slot

is cut along the path the AGV is to follow. This wire is used to transmit a radio signal. A sensor is

installed on the bottom of the AGV close to the ground. The sensor detects the relative positionof the radio signal being transmitted from the wire. This information is used to regulate the

steering circuit ma&ing the AGV follow the wire.

Guide tape

AGVs (some &nown as automated guided carts or AG%s) use tape for the guide path. The tapes

can be one of two styles7 magnetic or colored. The AG% is fitted with the appropriate guide

sensor to follow the path of the tape. 2ne major advantage of tape over wired guidance is that itcan be easily removed and relocated if the course needs to change. %olored tape is initially less

e6pensive but lac&s the advantage of being embedded in high traffic areas where the tape may

become damaged or dirty. A fle6ible magnetic bar can also be embedded in the floor li&e wire

but wor&s under the same provision as magnetic tape and so remains unpowered or passive.Another advantage of magnetic guide tape is the dual polarity. small pieces of magnetic tape may

be placed to change states of the AG% based on polarity and se8uence of the tags.

Laser target navigation

The navigation is done by mounting reflective tape on walls poles or fi6ed machines. The AGV

carries a laser transmitter and receiver on a rotating turret. The laser is transmitted and received

by the same sensor. The angle and (sometimes) distance to any reflectors that in line of sight andin range are automatically calculated. This information is compared to the map of the reflector

layout stored in the AGV9s memory. This allows the navigation system to triangulate the current

position of the AGV. The current position is compared to the path programmed in to the reflector layout map. The steering is adjusted accordingly to &eep the AGV on trac&. "t can then navigate

to a desired target using the constantly updating position.

• Modulated Lasers The use of modulated laser light gives greater range and accuracy

over pulsed laser systems. +y emitting a continuous fan of modulated laser light a systemcan obtain an uninterrupted reflection as soon as the scanner achieves line of sight with a

reflector. The reflection ceases at the trailing edge of the reflector which ensures an

accurate and consistent measurement from every reflector on every scan. +y using amodulated laser a system can achieve an angular resolution of : *.' mrad (*.**/;) at <

scanner revolutions per second.

• Pulsed Lasers A typical pulsed laser scanner emits pulsed laser light at a rate of

'==** 0z which gives a ma6imum possible resolution of : >. mrad (*.?;) at < scanner

revolutions per second. To achieve a wor&able navigation the readings must be

https://en.wikipedia.org/wiki/Laserhttps://en.wikipedia.org/wiki/Laser


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interpolated based on the intensity of the reflected laser light to identify the centre of the

reflector.

Inertial (Gyroscopic) navigation

Another form of an AGV guidance is inertial navigation. 4ith inertial guidance a computer control system directs and assigns tas&s to the vehicles. Transponders are embedded in the floor

of the wor& place. The AGV uses these transponders to verify that the vehicle is on course. Agyroscope is able to detect the slightest change in the direction of the vehicle and corrects it in

order to &eep the AGV on its path. The margin of error for the inertial method is @' inch.'B

"nertial can operate in nearly any environment including tight aisles or e6treme temperatures. ?B

"nertial navigation can include use of magnets embedded in the floor of the facility that the

vehicle can read and follow.>B

'B 3nitCload AGV using naturalCfeatures navigation to carry steel to 8uality assurance lab

Natural features (Natural Targeting) navigation

-avigation without retrofitting of the wor&space is called -atural #eatures or -atural Targeting

-avigation. 2ne method uses one or more rangeCfinding sensors such as a laser rangeCfinder as

well as gyroscopes or inertial measurement units with 1onteC%arloD1ar&ov localizationtechni8ues to understand where it is as it dynamically plans the shortest permitted path to its

goal. The advantage of such systems is that they are highly fle6ible for onCdemand delivery to

any location. They can handle failure without bringing down the entire manufacturing operationsince AGVs can plan paths around the failed device. They also are 8uic& to install with less

downCtime for the factory.=B

Vision guidance

VisionCGuided AGVs can be installed with no modifications to the environment or infrastructure.

They operate by using cameras to record features along the route allowing the AGV to replay the

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route by using the recorded features to navigate. VisionCGuided AGVs use ,vidence Grid

technology an application of probabilistic volumetric sensing and was invented and initially

developed by Er. 1oravec at %arnegie 1ellon 3niversity. The ,vidence Grid technology uses probabilities of occupancy for each point in space to compensate for the uncertainty in the

performance of sensors and in the environment. The primary navigation sensors are specially

designed stereo cameras. The visionCguided AGV uses >/*Cdegree images and build a >E mapwhich allows the visionCguided AGVs to follow a trained route without human assistance or the

addition of special features landmar&s or positioning systems.

Geoguidance

A geoguided AGV recognizes its environment to establish its location. 4ithout any

infrastructure the for&lift e8uipped with geoguidance technology detects and identifies columns

rac&s and walls within the warehouse. 3sing these fi6ed references it can position itself in realtime and determine its route. There are no limitations on distances to cover or number of pic&Cup

or dropCoff locations. Foutes are infinitely modifiable.

Steering control

To help an AGV navigate it can use three different steer control systems.B The differential speedcontrol is the most common. "n this method there are two independent drive wheels. ,ach drive

is driven at different speeds in order to turn or the same speed to allow the AGV to go forwards

or bac&wards. The AGV turns in a similar fashion to a tan& . This method of steering is thesimplest as it does not re8uire additional steering motors and mechanism. 1ore often than not

this is seen on an AGV that is used to transport and turn in tight spaces or when the AGV is

wor&ing near machines. This setup for the wheels is not used in towing applications because the

AGV would cause the trailer to jac&&nife when it turned.

The second type of steering used is steered wheel control AGV. This type of steering can be

similar to a cars steering. +ut this is not very manoeuvrable. "t is more common to use a threeC

wheeled vehicle similar to a conventional three wheeled for&lift. The drive wheel is the turning

wheel. "t is more precise in following the programmed path than the differential speed controlledmethod. This type of AGV has smoother turning. $teered wheel control AGV can be used in all

applications unli&e the differential controlled.'B $teered wheel control is used for towing and can

also at times have an operator control it.

The third type is a combination of differential and steered. Two independent steerDdrive motors

are placed on diagonal corners of the AGV and swivelling castors are placed on the other

corners. "t can turn li&e a car (rotating in an arc) in any direction. "t can crab in any direction andit can drive in differential mode in any direction.

Path decision

AGVs have to ma&e decisions on path selection. This is done through different methods7

fre8uency select mode (wired navigation only) and path select mode (wireless navigation only)

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or via a magnetic tape on the floor not only to guide the AGV but also to issue steering

commands and speed commands.

re!uency select "ode

#re8uency select mode bases its decision on the fre8uencies being emitted from the floor. 4henan AGV approaches a point on the wire which splits the AGV detects the two fre8uencies and

through a table stored in its memory decides on the best path. The different fre8uencies arere8uired only at the decision point for the AGV. The fre8uencies can change bac& to one set

signal after this point. This method is not easily e6pandable and re8uires e6tra cutting meaning

more money.

Path select "ode

An AGV using the path select mode chooses a path based on preprogrammed paths. "t uses the

measurements ta&en from the sensors and compares them to values given to them by

programmers. 4hen an AGV approaches a decision point it only has to decide whether to follow path ' ? > etc. This decision is rather simple since it already &nows its path from its

programming. This method can increase the cost of an AGV because it is re8uired to have a teamof programmers to program the AGV with the correct paths and change the paths when

necessary. This method is easy to change and set up.

Magnetic tape "ode

The magnetic tape is laid on the surface of the floor or buried in a '*mm channel not only does

it provide the path for the AGV to follow but also strips of the tape in different combos of

polarity se8uence and distance laid alongside the trac& tell the AGV to change lane speed up

slow down and stop.

Traffic control

#le6ible manufacturing systems containing more than one AGV may re8uire it to have traffic

control so the AGVHs will not run into one another. Traffic control can be carried out locally or by software running on a fi6ed computer elsewhere in the facility. !ocal methods include zone

control forward sensing control and combination control. ,ach method has its advantages and

disadvantages./B

#one control

Ione control is the favorite of most environments because it is simple to install and easy to

e6pand.'B Ione control uses a wireless transmitter to transmit a signal in a fi6ed area. ,ach AGVcontains a sensing device to receive this signal and transmit bac& to the transmitter. "f the area is

clear the signal is set at JclearK allowing any AGV to enter and pass through the area. 4hen an

AGV is in the area the JstopK signal is sent and all AGV attempting to enter the area stop and

wait for their turn. 2nce the AGV in the zone has moved out beyond the zone the JclearK signal

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is sent to one of the waiting AGVs. Another way to set up zone control traffic management is to

e8uip each individual robot with its own small transmitterDreceiver. The individual AGV then

sends its own Jdo not enterK message to all the AGVs getting to close to its zone in the area. A problem with this method is if one zone goes down all the AGVHs are at ris& to collide with any

other AGV. Ione control is a cost efficient way to control the AGV in an area.

#or&lift AGV with safety laser sensors. (fully automated.)

#orward sensing control uses collision avoidance sensors to avoid collisions with other AGV in

the area. These sensors include7 sonic which wor& li&e radar optical which uses an infrared

sensor and bumper physical contact sensor. 1ost AGVs are e8uipped with a bumper sensor of some sort as a fail safe. $onic sensors send a JchirpK or high fre8uency signal out and then wait

for a reply from the outline of the reply the AGV can determine if an object is ahead of it and

ta&e the necessary actions to avoid collision.B The optical uses an infrared transmitterDreceiver and sends an infrared signal which then gets reflected bac& wor&ing on a similar concept as the

sonic sensor. The problems with these are they can only protect the AGV from so many sides.

They are relatively hard to install and wor& with as well.

Vehicle types

• Towing Vehicles were the first type introduced and are still a very popular type today.

Towing vehicles can pull a multitude of trailer types and have capacities ranging from


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Tugger AGV towing multiple trailers in a warehouse environment

• AGVS Unit Loa Vehicles are e8uipped with dec&s which permit unit load transportation

and often automatic load transfer. The dec&s can either be lift and lower type powered or

nonCpowered roller chain or belt dec&s or custom dec&s with multiple compartments.

See also

• !ist of driverless trains

4i&imedia %ommons has media related to Automated guided vehicles.

$eferences

'.

JThe +asics of Automated Guided VehiclesK. AGV $ystems. $avant. 1arch ?**/ LGuidance options for AGVsL Mervis +. 4ebb %ompany ?**. L"nertial (1agnet)-avigationL ,gemin Automation "nc. ?*'=.

$pecifications for 5latforms AGV Erive and $teering 2ptions Transbotics %orp. ?** !lmi" #oberto $%&''() Traffic *anagement of Automate Guie Vehicles in Fle+ible *anufacturing Systems) Ferrara $,taly(- Uni.ersity of Ferrara)

J$onar sensor and mountingK. 3niversity of +irmingham. 1arch ?**/ LTowing AGVs L. 0iCTech Fobotic $ystemz !td. "ndia ?** L0ybrid AGVsL . ,gemin Automation "nc. ?*'=
https://en.wikipedia.org/wiki/List_of_driverless_trainshttps://commons.wikimedia.org/wiki/Category:Automated_guided_vehicleshttp://www.agvsystems.com/basics/vehicle.htmhttp://www.jervisbwebb.com/Products/guidance_options.aspx?pid=308&qs=1_6_http://www.egeminusa.com/pages/software/agvs_ensor.htmlhttp://forkliftsystems.com/wp-content/uploads/2014/01/specifications-for-platforms.pdfhttp://www.transbotics.com/agvsteeringoptions.htmhttp://eprints.unife.it/404/http://eprints.unife.it/404/http://www.cs.bham.ac.uk/resources/courses/robotics/halloffame/1999/team2/Sonar1.htmlhttp://www.hitechroboticsystemz.com/agv.htmlhttp://www.hitechroboticsystemz.com/agv.htmlhttp://www.egeminusa.com/pages/agvs/agvs_hybrid.htmlhttps://en.wikipedia.org/wiki/List_of_driverless_trainshttps://commons.wikimedia.org/wiki/Category:Automated_guided_vehicleshttp://www.agvsystems.com/basics/vehicle.htmhttp://www.jervisbwebb.com/Products/guidance_options.aspx?pid=308&qs=1_6_http://www.egeminusa.com/pages/software/agvs_ensor.htmlhttp://forkliftsystems.com/wp-content/uploads/2014/01/specifications-for-platforms.pdfhttp://www.transbotics.com/agvsteeringoptions.htmhttp://eprints.unife.it/404/http://eprints.unife.it/404/http://www.cs.bham.ac.uk/resources/courses/robotics/halloffame/1999/team2/Sonar1.htmlhttp://www.hitechroboticsystemz.com/agv.htmlhttp://www.egeminusa.com/pages/agvs/agvs_hybrid.html

Automated Guided Vehicle GENERALS

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