An automated guided vehicle

Anautomated guided vehicle (AGV) is a driverless material handlingsystem used for horizontal movement of materials. AGVs wereintroduced in 1955 (Muller, 1983). The use of AGVs has grownenormously since their introduction. The number of areas ofapplication and variation in types has increased significantly. AGVscan be used in inside and outside environments, such asmanufacturing, distribution, transshipment and (external)transportation areas. At manufacturing areas, AGVs are used totransport all types of materials related to the manufacturingprocess. According to Gotting (2000) over 20,000 AGVs were used inindustrial applications. The author states that the usage of AGVswill pay off for environments with repeating transportation patterns.Examples of these environments are distribution, transshipment andtransportation systems. Warehouses and cross docking centers areexamples of distribution areas. AGVs are used in these areas for theinternal transport of, for example, pallets between the variousdepartments, such as receiving, storage, sorting and shipment areas.At transshipment systems, such as container terminals, AGVs take careof the transport of products between the various modes of transport.Gotting (2000) presented an overview of available technology forautomation in container terminals. Furthermore, navigation andvehicle guidance systems applicable in various indoor/outdoorenvironments are described. Haefner and Bieschke (1998) stated thatAGV systems can provide benefits to both the port and its customersby executing transportation requests between vessels and inlandtransportation.

Towing

AGVStowing applications were the earliest and are still the most numerousAGV type. Towing applications can involve the bulk movement ofproduct into and out of warehouse areas or direct service to amanufacturing/assembly operation. Usually side path spurs are placedin receiving or shipping areas so that trains can be loaded orunloaded off the main line and thereby not hinder the movement ofother trains on the main path.

Chainmovement of product with AGVS trains is also popular. In this case,the AGVS trains are loaded with product destined for specificdestinations along the guide path route. The train will make severalstops in order for the product to be unloaded at the correctlocations.

Trainssystems are generally used where movement of product is over longdistances, sometimes between buildings, outdoors or in very largedistributed systems where the runs are long. Since each train canmove as much as 16 pallet loads at a given time, this becomes a veryefficient method and can usually be justified easily based on theelimination of fork trucks or manual trains and operators.

PalletTrucks

AGVSpallet trucks are used generally in distribution functions. Vehiclescan be loaded in two ways, either they are capable of automaticallyreversing into pallets on the floor or operators will manually boardthe vehicles and back them into pallets.

Forthe product delivery the vehicles normally proceed down the path tospecific destinations in storage areas, pull off onto a spur, lowertheir pallet forks to the floor and pull out from under the pallets,then automatically return empty to the loading areas. Manyapplications have been done whereby the vehicles are manually boardedin the loading areas and driven off the path to load staging areaswhere they are manually loaded. The vehicles are backed up under theloads, driven back to the path, given a destination by an operatorand automatically proceed to the drop off spurs in the warehouseareas. Automatically reversing a guided pallet truck addsconsiderable expense to the system and the necessity for accuratepositioning loads on the floor for pickup. They can only be justifiedin limited applications at this time. Manually loading the vehiclegives operators flexibility to position loads anywhere off the pathand still be able to retrieve them with the vehicles which thenautomatically proceed without operators into the warehouse droplocations

ForkTrucks

AGVSfork truck applications are relatively new. Guided fork trucks areused when the system requires automatic pickup and drop off of loadsfrom floor or stand level and where the heights of load transfer varyat stop locations. The guided fork truck has the ability toautomatically pickup a load or discharge the load without any humaninterface.

Thevehicle can position its forks to any height so that conveyors orload stands of varying height in a given system can all be serviced.

Sincethese vehicles are some of the most expensive AGVS types, they canonly be justified where total automation is required. AGVS for trucksrequire more intricate path layout and a method of accuratelypositioning loads on the floor or on stands for vehicles to service.This normally requires greater system discipline than with othersystems, but the benefits include greater flexibility in integratingother subsystems together through Assembly Line

Assemblyline AGVS applications are only now being introduced in the U.S. Thisis an adaptation of the small light load AGVS for an assembly lineprocess. Here the guided vehicles carry major subassemblies such asmotors or transmissions to which parts are added in a serial assemblyprocess. Prior to each assembly area is a parts staging area wheresmall parts are placed in a tray onboard the vehicle beneath themajor subassembly. The vehicle the proceeds into an assembly areawhere it stops at assembly work station. The assembler takes theparts from the tray onboard the vehicle and then assembles them ontothe major subassembly. When that process is completed, he thenreleases the vehicle, which proceeds to the next parts assembly areathe process repeats several more times. When the assembly process iscomplete, the finished assembly such as an engine block or chassis isunloaded from the vehicle, which is then sent to the start area forthe assembly process. There it is again loaded with a rawsubassembly.

AGVSassembly systems give good flexibility to a manufacturing process byallowing parallel operations. They also allow for individual trackingof items and measured work rates. Normally these systems areintegrated into an overall production system, which requires computercontrol and extensive planning.

Acommon misconception is that guided vehicles can be made to doanything and with so many new vendors on the market it is verydifficult to differentiate what is practical from what is not. It isvery useful to have a basic understanding of guided vehicle controlsin order to appreciate what you can and cannot do with them.

AssemblyLine

Assemblyline AGVS applications are only now being introduced in the U.S. Thisis an adaptation of the small light load AGVS for an assembly lineprocess. Here the guided vehicles carry major subassemblies such asmotors or transmissions to which parts are added in a serial assemblyprocess. Prior to each assembly area is a parts staging area wheresmall parts are placed in a tray onboard the vehicle beneath themajor subassembly. The vehicle the proceeds into an assembly areawhere it stops at assembly work station. The assembler takes theparts from the tray onboard the vehicle and then assembles them ontothe major subassembly. When that process is completed, he thenreleases the vehicle, which proceeds to the next parts assembly areathe process repeats several more times. When the assembly process iscomplete, the finished assembly such as an engine block or chassis isunloaded from the vehicle, which is then sent to the start area forthe assembly process. There it is again loaded with a rawsubassembly.

AGVSassembly systems give good flexibility to a manufacturing process byallowing parallel operations. They also allow for individual trackingof items and measured work rates. Normally these systems areintegrated into an overall production system, which requires computercontrol and extensive planning.

Acommon misconception is that guided vehicles can be made to doanything and with so many new vendors on the market it is verydifficult to differentiate what is practical from what is not. It isvery useful to have a basic understanding of guided vehicle controlsin order to appreciate what you can and cannot do with them.

AGVSload transfer can be accomplished in many different ways:

ManualLoad TransferManualmethods of load transfer include manually coupling and uncouplingtowed trailers, loading and unloading by fork lift and manuallyloading and unloading AGVS vehicles.

Manualmethods can include uncoupling trailers and moving the trailer offthe AGVS system to given work stations or it can involve simpleroller bed transfer from the AGVS to fixed roller stations bymanually pushing the load off the vehicles. The most popularconventional AGVS approach uses fork trucks to manually load andunload the trailers towed by an AGVS vehicle. Fork trucks are alsoused to directly load and unload AGVS unit load carriers.

AutomaticCouple and UncoupleAutomaticuncouple load transfer methods are relatively easy to implement. Thevehicle usually stops on a side spur and automatically uncouplestrailers, which it is pulling. The AGV then pulls forward and waitsor proceeds to another location to receive a new string of trailersto tow. Typically, an operator will manually couple the new trailersto the AGV hugger.

Automaticcouple capability is a more challenging capability than automaticuncouple. First, the carts/trailers to which the AGV is coupling mustbe in a precise position so that the AGV hitch and the trailer hitchengage properly. Second, controls must be provided to insure trailersleft on the path are identified so that other AGVs do not collidewith them. Third, sophisticated AGV management software and controlsneed to be provided to support an automatic coupling operation. Forexample, an operator must ‘call’ from a terminal when they havesome carts ready for an AGV to pick up. This requires a softwaremanagement program to decide where the closest AGV is that is 1) notcurrently towing carts and 2) is available for a new task. Ifoperators move the waiting carts or override the automaticdispatching of AGVs to pick up carts, then the system will notfunction well. So, increased operator and supervisory disciplineneeds to be provided.

PowerRoller, Belt, Chain.Poweredroller belt or chain transfer for guided vehicles has been a standardtechnique for many years. Unit load carriers can be equipped withthese power decks so that they may automatically transfer loads toand from fixed stations. In certain cases, under light loadconditions, parasitic drives can be used which allow the AGV unitload carrier vehicle to interface with a non-powered roller stand.Most applications involve the AGV vehicle dropping off to a poweredor gravity type conveyor. A roller deck transfer method can be usedon AGVS towing systems where the towed trailers are equipped withpowered transfer deck mechanisms. In all cases, the vehicles mustprecisely align with the given transfer station before the loadtransfer can be achieved. Normal stopping tolerances are + or -1/2″which is well within the tolerances required at conveyor transferstations.

Whenevera vehicle is automatically transferring a load, a method or“handshake” logic must be employed. Handshake logic is the methodby which the vehicle checks to make sure a load stand is empty beforeit automatically transfers a load onto the stand. Or when a vehiclecomes to pickup a load it must make sure that there is a load on thestand for pick up before the load transfer occurs. The handshakesignals between the vehicle and the load stand allow transfer drivesto be activated simultaneously to achieve the load transfer. Thesignals also turn off the drives when the transfer is complete. Thehandshake method usually involve sensors onboard the vehicle whichinterface with sensors on the stand that exchange signals when a loadtransfer is about to occur. If the proper signals are not exchanged,then the vehicle will not attempt the transfer. It can blow its hornor abort the mission and proceed to another destination.

PowerLift/LowerThere arethree general power lift/lower methods of load transfer:

  • Pallet fork lift/lower

  • Unit load lift/lower

  • Fork truck lift/lower

Inthe pallet truck lift/lower method the AGVS pallet truck can pick uploads or drop them off directly to the floor. The vehicle must pullstraight ahead after depositing a load on the floor so that thepallet forks clear the load before it reenters the main guide path.

Thelift/lower unit load carrier can interface with special ‘horseshoe’conveyor load stands or with fixed load pickup deposit stations. Thevehicle approaches a load transfer area and makes a right angle turninto a horseshoe shaped load station. It decelerates and pulls intothe load station where it accurately stops and lowers or lifts itsload deck. The load is then transferred to/from the load stand andthe vehicle reverses its direction, and proceeds to its nextassignment.

Thelift/lower fork truck is a concept that allows the guided vehicle topick loads up off the floor and deposit them on the load stands or inracks. This gives the AGVS system more versatility in larger systemswhere not all of the conveyors or load stands are at the same height.The vehicle can service an infinite number of different heightswithin a given lifting range.

PowerPush/PullA lessfrequently used method of automatic load transfer is the push or pulltype. Here a vehicle with a non- powered deck or trailers positionsitself in front of of fixed stations which is equipped with anautomatic push or pull mechanism. This mechanism will reach out tothe load and push or pull it off the vehicle or trailers. Thispermits the vehicles to be extremely simple. This method is quiteuseful if the automatic load transfer is centralized because the costof multiple load transfer points can be prohibitive. A good exampleof this approach would be a central storage area supportingmanufacturing. Parts baskets can be loaded onto an AGVS train by apowered shuttle automatically. The train proceeds into themanufacturing area. The parts baskets are unloaded manually or byfork truck and are moved to machining centers. Parts baskets arereturned to the central storage area on the AGVS train and unloadedautomatically by the powered shuttle. Another possible permutationwould be to have a powered device load or unload the AGV at certainlocations and employ a manual approach to transferring loads at otherlocations in the system.

SystemManagement: System Monitoring

AGVSsystem monitoring is an important consideration in many systems.Simple systems do not require extensive monitoring or control.Sophisticated systems benefit greatly from monitoring. When asophisticated system is installed, usually there is a high degree ofautomation and throughput required. A breakdown or slowdown in thesystem could cause serious problems if not detected immediately.There are three approaches to monitoring:

  • Locator Panel

  • CRT Color Graphics Display

  • Central Logging and Report

Asimple monitoring system for AGVS systems can be a locator panelwhich merely indicates if a vehicle is in a given area of the guidepath. It does not identify the vehicle specifically or its condition.A light next to the area a vehicle occupies illuminates to indicatethat there is a vehicle in that location. Sometimes a timer is usedfor each zone to indicate if that zone has been occupied for too longwhich might indicate that a vehicle problem exists in that location.A CRT color graphics display specifically shows where each vehicle isincluding its status.

CRTcolor graphics is usually a real time monitoring type, which caninstantly detect a problem, identify specific vehicles, and show thelocation of the failure on the graphics display.&nbsp Other usefulinformation includes whether the vehicle is moving or is blocked bythe other traffic, whether the vehicle is loaded or empty, if thebattery is O.K. and where the vehicle is going. Operators can spotblockages and slowdowns quickly and take corrective action asrequired. The CRT color monitor can show system condition either ingraphic form or in a table form.

Thetable form lists each vehicle ID, its location, destination, andcondition, mode of control, load status, and alarm condition in acolumn format listing which is continually updated.&nbsp A centrallogging and report capability for monitoring an AGVS system ishelpful when attempting to develop historical data on the systemsperformance. Periodically, performance reports can be printed outindicating such things as how long the vehicles were moving, how manyloads a given vehicle transported to a given stop station, and wherewere they taken or even when did a vehicle have a low battery or whendid a specific load get picked up and where did it TypicalApplicationsWarehouseAutomation

AGVscan be used to in a warehouse environment to automated specific taskor as part of a completely automated system. Some example warehouseoperations to which AGVs are well suited include:

  • Finished Product Handling: Transporting finished goods from manufacturing plants into storage and then from storage to shipping is the final and most delicate stage before delivery. This handling operation is the most delicate in the process as finished products can be subjected to damage from rough handling. Because NDC Automated Guided Vehicles operate with precision navigation and control systems they represent the absolute minimum in risk to the finished products. Accurate computer control over position, speed and acceleration means every loading and unloading operation is precise, safe and repeatable.&nbsp

  • Empty Pallet Handling: Any operation that uses pallets to store and transport goods must also deal with empty pallets. Moving stacks of empty pallets around a warehouse or production facility is a necessary but repetitive task. An AGV system can easily automate this simple task and ensure that every transport is controlled and predictable.

  • Truck/Container Loading: AGVs are capable of delivering goods from your warehouse directly into the final transport that will carry them to your customers. Automatic loading of Roll-On-Roll-Offs can be done quickly and space permitting the AGVs can also drive directly into shipping containers or truck bodies.

ProductionAutomation

Productionenvironments have a different set of challenges to warehousingfacilities, but many are well suited to automation, a few examplesinclude:

  • Raw Materials Handling: Timely and reliable delivery of raw materials is a necessity for any manufacturing operation. Whether you are working with steel, plastic, rubber or any other material an NDC Automated Guided Vehicle system can provide a constant just-in-time flow of raw materials to keep your production machines operating at maximum capacity. Requests for delivery of raw materials can be automatically scheduled via an interface with your production control software, or manually by production machine operators.&nbsp

  • Hazardous Materials Handling: Some material handling is better left to an automated system. In some cases the material or product to be moved may be dangerous, or it could be that the environment in which the machine must run would be harmful to an operator.

ProductTransport

Ifyour production and warehousing is done on the same site it is likelythat finished or partially finished products need to be moved largedistances between facilities. NDC has a range of Automated GuidedVehicles designed for mass transport of goods through outdoorenvironments.

SpecializedApplications

TheSpecialized Applications detailed below are more than just theautomation of existing tasks, they can alter the way you do business.NDC Specialized Application AGVs are based on our newest and mostinnovative technology and offer new opportunities to your business.

Hospital

HospitalAGV Applications are different to most other AGV applications as itrequires transports in narrow corridors and between different levelsthrough elevators.

NDCssolution with Range Navigation is especially developed for thetypical narrow corridors in a hospital facilities and our stainlesssteel hospital AGVs are designed to run in clean room gradeenvironments.

NarrowAisle

Theheart of NDCs Narrow Aisle Solution is our Side-Loading AGV. Unliketradition forklifts that must turn and drive on a straight line intoa load or unload point our Side-Loading AGV uses a turreted-mastarrangement that allows it to pickup and drop off at 90 degrees fromthe way it is facing.

Theadvantages to this can be enormous. Since no turning is requireddrive lanes in your warehouse need only be large enough to allow thepassage of the vehicle in a straight line. NDC has developed avehicle that can operate in a very narrow 1.8m wide lane. Add to thisthe ability to reach up to 10.5m height and consider how much extraspace you can make.

Pick-n-Go

Pick-n-Gois a new control system for AGVs that gives a large advantages tooperations where order picking is a primary activity. In a typicalmanual order picking system an operator will drive a forklift throughthe warehouse occasionally stepping off to pick items from theshelves and load them onto the vehicles then drive to another sectionetc..

Anautomated Pick-n-Go system replaces the forklift with an AGV whichwill follow the operator to each location as they pick the items inthe order. Once the vehicle is full it will return to dispatching anda new AGV will already be waiting at the next pickup point.

APick-n-Go system means less time wasted hopping on and off offorklifts, less damage to items caused by forklift handling and lessrisk of injury to your staff. All these benefits result in increasesin the productivity of your staff and less mistakes as well as costsavings from reduced damage to the warehouse and products fromforklift accidents.

Finally,the curvature estimation based adaptive weight fitting method isproposed for the parameters regression of the three models. Therefined parameters are used to compensate system errors, whichimproves the accuracy of vision measurement. Guide-path forvision-guided AGV can be divided into bidirectional path and crosspath. A new hierarchical recognition method based on the real-timeability of knowledge acquisition and the similarity of classes ispresented to robustly recognize the cross path models forbidirectional vision-guided AGV in real time by the combination ofthe rough set theory and the multi-class support vector machine Theknowledge granularities conception and the hierarchical reductionrules of roughest theory are both used to obtain the minimum decisionrule, which effectively reduce the complexity of the classification.To improve the robustness of recognition, the learning method of safearea for classification is presented, which makes the linearinseparable uncertain problem become linear separable conditionally.Finally, the tests and experiments at various environments verify thevalidity and reliability of the method. A prototype of bidirectionalvision-based AGV, NHV-II, is implemented based on the study of thetheory. TMS320DM642DSP is used as the vision system processor ofNHV-II. The multitask algorithms related to video capturing videoprocessing, and communications, etc are performed on the real-timeembedded system DSP/BIOS. The RFID reader, the industrial wirelesslocal area network communication and the center control workstationare integrated to implement map building, station identification,path planning, scheduling and state monitoring of the AGV system.Finally, the methods and technologies presented in this paper aretested by using NHV-II on different environment conditions.Experimental results show that the problems of real time ability,robustness and accuracy of the vision-guided technology are improvedsignificantly, which lay fundaments for the promotion ofvision-guided AGV. Finally, the main research results of the thesisare summarized. The difficult problems and valuable directions forfurther researching on vision-based AGV are pointed out, which areexpected to be solved and improved gradually in future studies.

Refference.

Aized,T.: Modelling and performance maximization of an integratedautomated guided vehicle system using coloured Petri net and responsesurface methods. Computers &amp Industrial Engineering&nbsp57,822–831

Ashayeri,J., Gelders, L.F.: Interactive GPSS-PC Program Generator forAutomated Material Handling Systems. International Journal ofAdvanced Manufacturing Technology&nbsp

Fazlollahtabar,H., Es’haghzadeh, A., Hajmohammadi, H., Taheri-Ahangar, A.: A MonteCarlo simulation to estimate TAGV production time in a stochasticflexible automated manufacturing system: a case study. InternationalJournal of Industrial and Systems Engineering&nbsp12(3), 243–258(2012)

Guan,X., Dai, X.: Deadlock-free multi-attribute dispatching method for AGVsystems. International Journal of Advanced ManufacturingTechnology&nbsp45, 603–615 (2009)

Kim,B., Shin, J., Chae, J.: Simple blocking prevention for bay typepath-based automated material handling systems. International Journalof Advanced Manufacturing Technology&nbsp44, 809–816 (2009)

An automated guided vehicle

Anautomated guided vehicle (AGV) is a driverless material handlingsystem used for horizontal movement of materials. AGVs wereintroduced in 1955 (Muller, 1983). The use of AGVs has grownenormously since their introduction. The number of areas ofapplication and variation in types has increased significantly. AGVscan be used in inside and outside environments, such asmanufacturing, distribution, transshipment and (external)transportation areas. At manufacturing areas, AGVs are used totransport all types of materials related to the manufacturingprocess. According to Gotting (2000) over 20,000 AGVs were used inindustrial applications. The author states that the usage of AGVswill pay off for environments with repeating transportation patterns.Examples of these environments are distribution, transshipment andtransportation systems. Warehouses and cross docking centers areexamples of distribution areas. AGVs are used in these areas for theinternal transport of, for example, pallets between the variousdepartments, such as receiving, storage, sorting and shipment areas.At transshipment systems, such as container terminals, AGVs take careof the transport of products between the various modes of transport.Gotting (2000) presented an overview of available technology forautomation in container terminals. Furthermore, navigation andvehicle guidance systems applicable in various indoor/outdoorenvironments are described. Haefner and Bieschke (1998) stated thatAGV systems can provide benefits to both the port and its customersby executing transportation requests between vessels and inlandtransportation.

Towing

AGVStowing applications were the earliest and are still the most numerousAGV type. Towing applications can involve the bulk movement ofproduct into and out of warehouse areas or direct service to amanufacturing/assembly operation. Usually side path spurs are placedin receiving or shipping areas so that trains can be loaded orunloaded off the main line and thereby not hinder the movement ofother trains on the main path.

Chainmovement of product with AGVS trains is also popular. In this case,the AGVS trains are loaded with product destined for specificdestinations along the guide path route. The train will make severalstops in order for the product to be unloaded at the correctlocations.

Trainssystems are generally used where movement of product is over longdistances, sometimes between buildings, outdoors or in very largedistributed systems where the runs are long. Since each train canmove as much as 16 pallet loads at a given time, this becomes a veryefficient method and can usually be justified easily based on theelimination of fork trucks or manual trains and operators.

PalletTrucks

AGVSpallet trucks are used generally in distribution functions. Vehiclescan be loaded in two ways, either they are capable of automaticallyreversing into pallets on the floor or operators will manually boardthe vehicles and back them into pallets.

Forthe product delivery the vehicles normally proceed down the path tospecific destinations in storage areas, pull off onto a spur, lowertheir pallet forks to the floor and pull out from under the pallets,then automatically return empty to the loading areas. Manyapplications have been done whereby the vehicles are manually boardedin the loading areas and driven off the path to load staging areaswhere they are manually loaded. The vehicles are backed up under theloads, driven back to the path, given a destination by an operatorand automatically proceed to the drop off spurs in the warehouseareas. Automatically reversing a guided pallet truck addsconsiderable expense to the system and the necessity for accuratepositioning loads on the floor for pickup. They can only be justifiedin limited applications at this time. Manually loading the vehiclegives operators flexibility to position loads anywhere off the pathand still be able to retrieve them with the vehicles which thenautomatically proceed without operators into the warehouse droplocations

ForkTrucks

AGVSfork truck applications are relatively new. Guided fork trucks areused when the system requires automatic pickup and drop off of loadsfrom floor or stand level and where the heights of load transfer varyat stop locations. The guided fork truck has the ability toautomatically pickup a load or discharge the load without any humaninterface.

Thevehicle can position its forks to any height so that conveyors orload stands of varying height in a given system can all be serviced.

Sincethese vehicles are some of the most expensive AGVS types, they canonly be justified where total automation is required. AGVS for trucksrequire more intricate path layout and a method of accuratelypositioning loads on the floor or on stands for vehicles to service.This normally requires greater system discipline than with othersystems, but the benefits include greater flexibility in integratingother subsystems together through Assembly Line

Assemblyline AGVS applications are only now being introduced in the U.S. Thisis an adaptation of the small light load AGVS for an assembly lineprocess. Here the guided vehicles carry major subassemblies such asmotors or transmissions to which parts are added in a serial assemblyprocess. Prior to each assembly area is a parts staging area wheresmall parts are placed in a tray onboard the vehicle beneath themajor subassembly. The vehicle the proceeds into an assembly areawhere it stops at assembly work station. The assembler takes theparts from the tray onboard the vehicle and then assembles them ontothe major subassembly. When that process is completed, he thenreleases the vehicle, which proceeds to the next parts assembly areathe process repeats several more times. When the assembly process iscomplete, the finished assembly such as an engine block or chassis isunloaded from the vehicle, which is then sent to the start area forthe assembly process. There it is again loaded with a rawsubassembly.

AGVSassembly systems give good flexibility to a manufacturing process byallowing parallel operations. They also allow for individual trackingof items and measured work rates. Normally these systems areintegrated into an overall production system, which requires computercontrol and extensive planning.

Acommon misconception is that guided vehicles can be made to doanything and with so many new vendors on the market it is verydifficult to differentiate what is practical from what is not. It isvery useful to have a basic understanding of guided vehicle controlsin order to appreciate what you can and cannot do with them.

AssemblyLine

Assemblyline AGVS applications are only now being introduced in the U.S. Thisis an adaptation of the small light load AGVS for an assembly lineprocess. Here the guided vehicles carry major subassemblies such asmotors or transmissions to which parts are added in a serial assemblyprocess. Prior to each assembly area is a parts staging area wheresmall parts are placed in a tray onboard the vehicle beneath themajor subassembly. The vehicle the proceeds into an assembly areawhere it stops at assembly work station. The assembler takes theparts from the tray onboard the vehicle and then assembles them ontothe major subassembly. When that process is completed, he thenreleases the vehicle, which proceeds to the next parts assembly areathe process repeats several more times. When the assembly process iscomplete, the finished assembly such as an engine block or chassis isunloaded from the vehicle, which is then sent to the start area forthe assembly process. There it is again loaded with a rawsubassembly.

AGVSassembly systems give good flexibility to a manufacturing process byallowing parallel operations. They also allow for individual trackingof items and measured work rates. Normally these systems areintegrated into an overall production system, which requires computercontrol and extensive planning.

Acommon misconception is that guided vehicles can be made to doanything and with so many new vendors on the market it is verydifficult to differentiate what is practical from what is not. It isvery useful to have a basic understanding of guided vehicle controlsin order to appreciate what you can and cannot do with them.

AGVSload transfer can be accomplished in many different ways:

ManualLoad TransferManualmethods of load transfer include manually coupling and uncouplingtowed trailers, loading and unloading by fork lift and manuallyloading and unloading AGVS vehicles.

Manualmethods can include uncoupling trailers and moving the trailer offthe AGVS system to given work stations or it can involve simpleroller bed transfer from the AGVS to fixed roller stations bymanually pushing the load off the vehicles. The most popularconventional AGVS approach uses fork trucks to manually load andunload the trailers towed by an AGVS vehicle. Fork trucks are alsoused to directly load and unload AGVS unit load carriers.

AutomaticCouple and UncoupleAutomaticuncouple load transfer methods are relatively easy to implement. Thevehicle usually stops on a side spur and automatically uncouplestrailers, which it is pulling. The AGV then pulls forward and waitsor proceeds to another location to receive a new string of trailersto tow. Typically, an operator will manually couple the new trailersto the AGV hugger.

Automaticcouple capability is a more challenging capability than automaticuncouple. First, the carts/trailers to which the AGV is coupling mustbe in a precise position so that the AGV hitch and the trailer hitchengage properly. Second, controls must be provided to insure trailersleft on the path are identified so that other AGVs do not collidewith them. Third, sophisticated AGV management software and controlsneed to be provided to support an automatic coupling operation. Forexample, an operator must ‘call’ from a terminal when they havesome carts ready for an AGV to pick up. This requires a softwaremanagement program to decide where the closest AGV is that is 1) notcurrently towing carts and 2) is available for a new task. Ifoperators move the waiting carts or override the automaticdispatching of AGVs to pick up carts, then the system will notfunction well. So, increased operator and supervisory disciplineneeds to be provided.

PowerRoller, Belt, Chain.Poweredroller belt or chain transfer for guided vehicles has been a standardtechnique for many years. Unit load carriers can be equipped withthese power decks so that they may automatically transfer loads toand from fixed stations. In certain cases, under light loadconditions, parasitic drives can be used which allow the AGV unitload carrier vehicle to interface with a non-powered roller stand.Most applications involve the AGV vehicle dropping off to a poweredor gravity type conveyor. A roller deck transfer method can be usedon AGVS towing systems where the towed trailers are equipped withpowered transfer deck mechanisms. In all cases, the vehicles mustprecisely align with the given transfer station before the loadtransfer can be achieved. Normal stopping tolerances are + or -1/2″which is well within the tolerances required at conveyor transferstations.

Whenevera vehicle is automatically transferring a load, a method or“handshake” logic must be employed. Handshake logic is the methodby which the vehicle checks to make sure a load stand is empty beforeit automatically transfers a load onto the stand. Or when a vehiclecomes to pickup a load it must make sure that there is a load on thestand for pick up before the load transfer occurs. The handshakesignals between the vehicle and the load stand allow transfer drivesto be activated simultaneously to achieve the load transfer. Thesignals also turn off the drives when the transfer is complete. Thehandshake method usually involve sensors onboard the vehicle whichinterface with sensors on the stand that exchange signals when a loadtransfer is about to occur. If the proper signals are not exchanged,then the vehicle will not attempt the transfer. It can blow its hornor abort the mission and proceed to another destination.

PowerLift/LowerThere arethree general power lift/lower methods of load transfer:

  • Pallet fork lift/lower

  • Unit load lift/lower

  • Fork truck lift/lower

Inthe pallet truck lift/lower method the AGVS pallet truck can pick uploads or drop them off directly to the floor. The vehicle must pullstraight ahead after depositing a load on the floor so that thepallet forks clear the load before it reenters the main guide path.

Thelift/lower unit load carrier can interface with special ‘horseshoe’conveyor load stands or with fixed load pickup deposit stations. Thevehicle approaches a load transfer area and makes a right angle turninto a horseshoe shaped load station. It decelerates and pulls intothe load station where it accurately stops and lowers or lifts itsload deck. The load is then transferred to/from the load stand andthe vehicle reverses its direction, and proceeds to its nextassignment.

Thelift/lower fork truck is a concept that allows the guided vehicle topick loads up off the floor and deposit them on the load stands or inracks. This gives the AGVS system more versatility in larger systemswhere not all of the conveyors or load stands are at the same height.The vehicle can service an infinite number of different heightswithin a given lifting range.

PowerPush/PullA lessfrequently used method of automatic load transfer is the push or pulltype. Here a vehicle with a non- powered deck or trailers positionsitself in front of of fixed stations which is equipped with anautomatic push or pull mechanism. This mechanism will reach out tothe load and push or pull it off the vehicle or trailers. Thispermits the vehicles to be extremely simple. This method is quiteuseful if the automatic load transfer is centralized because the costof multiple load transfer points can be prohibitive. A good exampleof this approach would be a central storage area supportingmanufacturing. Parts baskets can be loaded onto an AGVS train by apowered shuttle automatically. The train proceeds into themanufacturing area. The parts baskets are unloaded manually or byfork truck and are moved to machining centers. Parts baskets arereturned to the central storage area on the AGVS train and unloadedautomatically by the powered shuttle. Another possible permutationwould be to have a powered device load or unload the AGV at certainlocations and employ a manual approach to transferring loads at otherlocations in the system.

SystemManagement: System Monitoring

AGVSsystem monitoring is an important consideration in many systems.Simple systems do not require extensive monitoring or control.Sophisticated systems benefit greatly from monitoring. When asophisticated system is installed, usually there is a high degree ofautomation and throughput required. A breakdown or slowdown in thesystem could cause serious problems if not detected immediately.There are three approaches to monitoring:

  • Locator Panel

  • CRT Color Graphics Display

  • Central Logging and Report

Asimple monitoring system for AGVS systems can be a locator panelwhich merely indicates if a vehicle is in a given area of the guidepath. It does not identify the vehicle specifically or its condition.A light next to the area a vehicle occupies illuminates to indicatethat there is a vehicle in that location. Sometimes a timer is usedfor each zone to indicate if that zone has been occupied for too longwhich might indicate that a vehicle problem exists in that location.A CRT color graphics display specifically shows where each vehicle isincluding its status.

CRTcolor graphics is usually a real time monitoring type, which caninstantly detect a problem, identify specific vehicles, and show thelocation of the failure on the graphics display.&nbsp Other usefulinformation includes whether the vehicle is moving or is blocked bythe other traffic, whether the vehicle is loaded or empty, if thebattery is O.K. and where the vehicle is going. Operators can spotblockages and slowdowns quickly and take corrective action asrequired. The CRT color monitor can show system condition either ingraphic form or in a table form.

Thetable form lists each vehicle ID, its location, destination, andcondition, mode of control, load status, and alarm condition in acolumn format listing which is continually updated.&nbsp A centrallogging and report capability for monitoring an AGVS system ishelpful when attempting to develop historical data on the systemsperformance. Periodically, performance reports can be printed outindicating such things as how long the vehicles were moving, how manyloads a given vehicle transported to a given stop station, and wherewere they taken or even when did a vehicle have a low battery or whendid a specific load get picked up and where did it TypicalApplicationsWarehouseAutomation

AGVscan be used to in a warehouse environment to automated specific taskor as part of a completely automated system. Some example warehouseoperations to which AGVs are well suited include:

  • Finished Product Handling: Transporting finished goods from manufacturing plants into storage and then from storage to shipping is the final and most delicate stage before delivery. This handling operation is the most delicate in the process as finished products can be subjected to damage from rough handling. Because NDC Automated Guided Vehicles operate with precision navigation and control systems they represent the absolute minimum in risk to the finished products. Accurate computer control over position, speed and acceleration means every loading and unloading operation is precise, safe and repeatable.&nbsp

  • Empty Pallet Handling: Any operation that uses pallets to store and transport goods must also deal with empty pallets. Moving stacks of empty pallets around a warehouse or production facility is a necessary but repetitive task. An AGV system can easily automate this simple task and ensure that every transport is controlled and predictable.

  • Truck/Container Loading: AGVs are capable of delivering goods from your warehouse directly into the final transport that will carry them to your customers. Automatic loading of Roll-On-Roll-Offs can be done quickly and space permitting the AGVs can also drive directly into shipping containers or truck bodies.

ProductionAutomation

Productionenvironments have a different set of challenges to warehousingfacilities, but many are well suited to automation, a few examplesinclude:

  • Raw Materials Handling: Timely and reliable delivery of raw materials is a necessity for any manufacturing operation. Whether you are working with steel, plastic, rubber or any other material an NDC Automated Guided Vehicle system can provide a constant just-in-time flow of raw materials to keep your production machines operating at maximum capacity. Requests for delivery of raw materials can be automatically scheduled via an interface with your production control software, or manually by production machine operators.&nbsp

  • Hazardous Materials Handling: Some material handling is better left to an automated system. In some cases the material or product to be moved may be dangerous, or it could be that the environment in which the machine must run would be harmful to an operator.

ProductTransport

Ifyour production and warehousing is done on the same site it is likelythat finished or partially finished products need to be moved largedistances between facilities. NDC has a range of Automated GuidedVehicles designed for mass transport of goods through outdoorenvironments.

SpecializedApplications

TheSpecialized Applications detailed below are more than just theautomation of existing tasks, they can alter the way you do business.NDC Specialized Application AGVs are based on our newest and mostinnovative technology and offer new opportunities to your business.

Hospital

HospitalAGV Applications are different to most other AGV applications as itrequires transports in narrow corridors and between different levelsthrough elevators.

NDCssolution with Range Navigation is especially developed for thetypical narrow corridors in a hospital facilities and our stainlesssteel hospital AGVs are designed to run in clean room gradeenvironments.

NarrowAisle

Theheart of NDCs Narrow Aisle Solution is our Side-Loading AGV. Unliketradition forklifts that must turn and drive on a straight line intoa load or unload point our Side-Loading AGV uses a turreted-mastarrangement that allows it to pickup and drop off at 90 degrees fromthe way it is facing.

Theadvantages to this can be enormous. Since no turning is requireddrive lanes in your warehouse need only be large enough to allow thepassage of the vehicle in a straight line. NDC has developed avehicle that can operate in a very narrow 1.8m wide lane. Add to thisthe ability to reach up to 10.5m height and consider how much extraspace you can make.

Pick-n-Go

Pick-n-Gois a new control system for AGVs that gives a large advantages tooperations where order picking is a primary activity. In a typicalmanual order picking system an operator will drive a forklift throughthe warehouse occasionally stepping off to pick items from theshelves and load them onto the vehicles then drive to another sectionetc..

Anautomated Pick-n-Go system replaces the forklift with an AGV whichwill follow the operator to each location as they pick the items inthe order. Once the vehicle is full it will return to dispatching anda new AGV will already be waiting at the next pickup point.

APick-n-Go system means less time wasted hopping on and off offorklifts, less damage to items caused by forklift handling and lessrisk of injury to your staff. All these benefits result in increasesin the productivity of your staff and less mistakes as well as costsavings from reduced damage to the warehouse and products fromforklift accidents.

Finally,the curvature estimation based adaptive weight fitting method isproposed for the parameters regression of the three models. Therefined parameters are used to compensate system errors, whichimproves the accuracy of vision measurement. Guide-path forvision-guided AGV can be divided into bidirectional path and crosspath. A new hierarchical recognition method based on the real-timeability of knowledge acquisition and the similarity of classes ispresented to robustly recognize the cross path models forbidirectional vision-guided AGV in real time by the combination ofthe rough set theory and the multi-class support vector machine Theknowledge granularities conception and the hierarchical reductionrules of roughest theory are both used to obtain the minimum decisionrule, which effectively reduce the complexity of the classification.To improve the robustness of recognition, the learning method of safearea for classification is presented, which makes the linearinseparable uncertain problem become linear separable conditionally.Finally, the tests and experiments at various environments verify thevalidity and reliability of the method. A prototype of bidirectionalvision-based AGV, NHV-II, is implemented based on the study of thetheory. TMS320DM642DSP is used as the vision system processor ofNHV-II. The multitask algorithms related to video capturing videoprocessing, and communications, etc are performed on the real-timeembedded system DSP/BIOS. The RFID reader, the industrial wirelesslocal area network communication and the center control workstationare integrated to implement map building, station identification,path planning, scheduling and state monitoring of the AGV system.Finally, the methods and technologies presented in this paper aretested by using NHV-II on different environment conditions.Experimental results show that the problems of real time ability,robustness and accuracy of the vision-guided technology are improvedsignificantly, which lay fundaments for the promotion ofvision-guided AGV. Finally, the main research results of the thesisare summarized. The difficult problems and valuable directions forfurther researching on vision-based AGV are pointed out, which areexpected to be solved and improved gradually in future studies.

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