Building a Warehouse Control System using RIDE

Building a Warehouse Control System using RIDE Joaquín López1, Diego Pérez2, Iago Vaamonde2, Enrique Paz1, Alba Vaamonde1 and Jorge Cabaleiro1. 1. Systems Engineering and Automation Department. University of Vigo. 2. Robotics and Control Unit. AIMEN Technology Centre.

Abstract There is a growing interest in the use of Autonomous Guided Vehicles (AGVs) in the Warehouse Control Systems (WCS) in order to avoid installing fixed structures that complicate and reduce the flexibility to future changes. In this paper a highly flexible and hybrid operated WCS, developed using the Robotics Integrated Development Environment (RIDE), is presented. The prototype is a forklift with cognitive capabilities that can be operated manually or autonomously and it is now being tested in a warehouse located in the Parque Tecnológico Logístico (PTL) of Vigo. The main advantages and drawbacks on this kind of implementation are also discussed in the paper. Keywords: Warehouse control system, Autonomous Guided Vehicle, robot control architecture, navigation.

1

Introduction

It is well documented that warehouse automation can increase throughput speed, accuracy, safety, and traceability [1]. The major activity in a warehouse is material handling, which is focused on the input and output of stored goods usually packed in pallets. The service that this kind of warehouses provides to its clients requires guaranteeing some time restrictions in delivering the products. The functions of the kind of warehouse we are dealing with can be divided into storage and repackaging of products. Different factors are forcing changes in the logistics market, most notably the ecommerce and the manufacturing of custom-made products. Customers look for personalized products and mass customization is pushing the industry to reduce time to market and enhance production flexibility, where the batch size tends to one. This fact is highly linked with warehouses management, where the exploitation costs increase with the value-added tasks, where Third Party Logistics Providers (TPLs) have to raise the service quality while maintaining the operation costs. Automated warehouses are evolving into more intelligent storage systems without need of installing fixed structures that complicate and reduce the scalability and flexibility to future changes. The current trend is to make them as flexible as possible. For that purpose, the Automatic Guided Vehicles (AGVs) are the ideal automation technology [2].

adfa, p. 1, 2011. © Springer-Verlag Berlin Heidelberg 2011

The advantages of using AGVs continue to increase as new applications are researched and explored:  Flexibility. One of the main advantages comes from the flexibility of the technology because it does not require conventional material-handling infrastructures.  Dynamic Design solution. Vehicles can be quickly reprogrammed to change their tasks or the path of operation, eliminating the need for expensive physical equipment installation. New paths, nodes, tasks, and work cells can be created almost instantaneously without the need for expensive retrofitting.  Efficiency. Using this technology we can optimize the transport work flows distributed dynamically between different AGVs. Also, with this solution we have the possibility of 24/7 operation without human intervention.  Modular systems. AGVs can be added as required by the growth of the operation as demand increases, allowing for a gradual implementation depending on the workload. Besides, these systems can be easily integrated with robot/palletization robotic cells and other storage machinery.  Precision. As technology improves a more precise space localization is available obtaining a good stock management precision. Time precision can also be obtained thanks to the optimization systems, allowing for a just-in-time delivery.  Economic. An excellent price/quality ratio can be obtained decreasing the running and maintenance costs.  Safety. AGVs offer a safe and predictable method of pallet management, while avoiding interference with human and building factors. There are already many companies that provide different solutions depending on the kind of products to be handled, from small items such as the KIVA solution [3] to full pallets such as the AGVs provided by JBT Corporation, Savant Automation Inc, American in Motion, etc. The AGVs can be seen as autonomous mobile robots able to perform some transport operations and in this paper we present a hybrid approach that allows using the forklift in its original manual operation mode or in the new implemented autonomous operation mode, showing the advantages and drawbacks of using a commercial forklift adapted (in particular RIDE) to develop a warehouse control system based on AGVs. Furthermore, the proposed solution includes a vision system installed onboard the AGV to detect the pallets in the working environment. This approach reduces the number of sensors installed in the warehouse facilities, increases the flexibility and reduces both the installation costs and the deployment time. The rest of this paper is organized as follows. Next section introduces the global description of the system. The control architecture is presented in section III. After describing the AGV control architecture in section IV, the task programming details are shown in section V. Finally, section VII presents the results and concludes the paper.

2

Glob G bal deescrripttion n of o th he sysstem m

Th he flow f w off thee paalletts in n th his syst s tem m is rep preseenteed in Fig. F 1. Cusstom merss leave theeir palle p ets in i thhe rece r eptioon area a a andd piick them t m up u inn thee Sh hippping g areea. AG A GVs shoould d be in chaarge of moving g thhe palle p ets betw b ween thhe reecepptio on area, a , thee peerm maneent stor s age areea, the t tem t mporral stora s age areea, th he wor w rking arrea and a d thee shiippiing areaa.

Fig. F 1. 1 Im magee off the sys tem from m th he usser poin p nt off view w.

Wee caarrieed oout a deetailled anaalysiis of th he fllow of palllets in the log gistics w wareho ouse of KA ALE EIDO OS SCM M. In n Fig. 2 th he flow f w off paallets beetweeen thee fiv ve zone z es th that deffine thee op peraation n off thee wareh w hou use are a reppreseenteed. The T en flow fl w nuumb bers reppreseent thee 12 difffereent task ks thhat can n bee com mm mandded to the GVs.. We W will w see s lateer thhat onee of the t AG advvan ntagees of o ussing g RIIDE E is the t taskk deefinitionn flexibbilitty.

Fig g. 2.. Geeneraal floow oof th he ittemss in tthe ware w ehouuse.

g too thee RIDE R E arrchitectturee [4]], AGV A Vs aare con c neccted to a ceentrral cont Accordding c trol serrverr viaa Wi-F W Fi (F Fig. 3). Th he man m nageemeent systtem m reqquirres robo r ot serv s vicess ussingg ann intterfaace deffined ass a set of messsagges. Fo or neew taskk reequeests,, thee ceentrral sserv ver will w l decidee whhich h roobott to send. Emp E ployyeess and main m ntenaance sttaff can n mo onittor tthe systtem m froom any c nneccted to the loccal netw k orr Inttern net usin u ng a GU UI. Sin nce this t a y terrminnal con n work

useer GUI G I is prog p gram mm med in Java J a, it cann bee ex xecu uted fro om a coomp puterr, Smarrtph honee orr anyy po ortaable devvicee.

F Fig.. 3. Gen G nerall sch hemee off the warreho ouse autoomaationn sysstem m.

unniing GU UIs and d the Build B ding g Autom A mattion n Sy ystem m (BA ( AS) are alsso conAlll thee ru nected d to thee centraal seerveer. Som S me of o thhe elem mentts coontrrolleed by b th he BAS B S thhat need n d to intteract with w h thee WCS sysstem m aree:  Occup panccy ddetectorrs. Som S me sens s sorss are seettleed tto dete d ct the t presencce oof man m nuall a peo oplee in som me areas iin orde o coontrool the t trafffic andd avvoid d deeadforkliffts and o er to ple,, som me sen nsorrs arre lo ocatted to ddeteect the t presen nce of o ootheer foorkloccks. Forr exxamp n narrrow w co orrid dorss. lifts in  Au utom maticc dooorss. The T patth of o somee AGV c incclude soomee do oorss. T GVs A Vs can The AG quesst th he oopen ning g off an n au utom matic door to cenntrall seerveer. This T s serverr in nteraacts req he BAS B S to opeen thhe door d r. witth th S me sensors aree loccateed to o deetecct th he occu o upan ncy of ssom me spes  Chargiing sennsorrs. Som potss suuch as the t chaargiing stattion ns. This T s is necesssaryy to o bee abble tto inclu cial sp i ude nd aauto omattic vehi v iclees. maanuaal an GVs can n bee co onneecteed and a discconnneccted at anyy tim me. A cent c tral serrver com mpuuterr AG keeps all thee relevaant info i rmaation n abboutt the gllobaal sttate of the t systtem m. All A thhe com c mponennts or mod m dulees need n d to req quest annd ssend d daata th hrouugh h thee ceentraal serveer. F For exaamplee, AGV n d to: A Vs need  Sen nd info i ormaation ab bouut th heir staate ((possitio on in n thhe map m p, taask bein ng exec e cuteed, ongs, etc.). boaard sensor reading  Req queest othe o er elem e mentts (m mod dulees) to exec omm mand ds such s h a s “o openn a e cutee soomee co or”. doo

 Recceiv ve in nforrmaation n abboutt eveentss suuch as a “doo or oppen ned”” or “areea occu o upieed”. ve taask exeecuttion req quessts.  Recceiv

3

Syystem m co ontroll arrch hitectu ure

Thee co onneectionss bettween diff d ferennt elem mentts in n thee au utom mation syst s tem aree shownn in n Figg. 4. Alll th he build ding g deevicees in n thhe B BAS S aree co onneected to o Modb bus inte i erfacces. Thhese intterfaacess aree coonneecteed too th he LAN N usiing Ethhern net. A prog p gram m in n thee cenntraal co ompputer (cen ntraal seerveer) man m nagees alll th he Mod M dbuss co omm muniicattions. The T AG GVs aree alsso conc nected d to thee cenntraal seerveer viia Wi-F W Fi, eeven n thooug gh ottherr waays of com c mmuunic atio on suuch h as GP PRS or 3G 3 cou uld also a o be useed. Em mplo oyeees aand maainteenan nce staaff can n moni m itor thee sy ystem usin u ng two t o diifferrentt graaphic user u intterfaacess (G GUIss). Rob R bots thaat arre not n ddoinng a tassk shou s uld be con nneccted d to thee chargiing station n. A typ picaal taask mig ght start w whenn th he ware w ehou use maanag gem mentt Syystem m reequestss thee Wareh W hou use Con C ntroll Sy ystem m to om movee a pall p et. Thee modu m ules on thee conntro ol arrchitectturee conntaiinedd in RID DE can n be divvide d in nto two t disstincct parts p s. Thhe first f t corrresspon nds to tthe set of mod m dulees th hat run r on the t hosst co ompputer thaat is on boaard thee moobille platfform m, while w e th he seecond is thhe man m nageemeent systtem m and ceentrralizzed con ntroll thaat ru uns on a seerveer.

Fiig. 4. 4 Gllobaal co ontrool arrchittectu ure.

o nizaational struuctu ure faciilitaates the scaalabbilityy off thee sy ystem, bothh in n terrms Thiis orga of con ntro ol modu m ules, su uch as the t depployyment of o more m e au uton nom mouss veehiclles, to havve a cenntraalizeed man m nageemen nt systeem mul m lti-rrobo ot annd mult m ti-user.

This modular architecture has the same layers and shares most of the modules with other mobile robot applications developed with RIDE such as WatchBot [5] or GuideBot [6]. The global architecture shown in Fig. 4 is a modular centralized framework where modules are independent processes, most of them running in different CPUs. These modules exchange information using a message publish/subscribe mechanism named JIPC. JIPC provides a central communication process named JCentral (Fig. 4) and an interface (Java class) to be used by the different modules that want to communicate through JCentral. The navigation control architecture in each robot, that is going to be explained in detail in the next section, includes a module to connect to the central unit using a wireless connection available in the building. So far we have been using a couple of alternatives: Wi-Fi because it is present in most modern buildings and a 3G modem for the rest of the cases. The robotics development environment (RIDE [4]) includes a tool named RoboGraph [7] that implements the executive layer (Fig. 4). Besides RoboGraph and the robots, the main modules connected via JIPC are:  Task manager. This module can start new tasks as a result of an event such as a request of an user. Also assigns tasks to robots and manages the queues of waiting tasks. An important issue in AGV systems is deciding what task should be assigned to a particular AGV [8][9].  Traffic manager. This module does the path planning and manages the access of restricted areas where only a robot can be at the same time such as narrow corridors and elevators. The path obtained by this module is a sequence of topological nodes that can include doors. When a robot is following one of these paths, it should make a request to the traffic manager before entering a restricted area.  Building interface. The communications with all the building devices including elevators are managed by this module.  ERP interface. The Enterprise Resource Planning Software (ERP) handles end-toend operational planning and is responsible with the Warehouse Management Systems (WMS) to send those tasks to the Warehouse Control System. This module is the interface between the Management and the control units of the warehouse.

4

AGV control architecture.

The scheme of the on board control architecture is shown in 5. Each module running on-board the robot is a Linux process that exchanges information with other modules using IPC [10]. The framework implemented here uses IPC in centralized mode. IPC has been developed at Carnegie Mellon’s Robotics Institute, and provides, among others, a publication–subscription model. An IPC based system consists of an application independent central server and a number of application-specific processes. Each process connects with the central server and specifies what types of messages it publishes and what types it listens for. Any message that is passed to the central server is immediately copied to all other processes subscribed.

Fig. 5. 5 Roobott con ntro ol arcchiteectu ure.

d ded d intto foour leveels soft s twarre: Thee arrchittectture is divi  Ha ardw warre d drivers layyer. Th his laye l er in nclu udess a sseries of o prog p gram ms aime a ed at a conwaree deevicces. Thee main modules in n thhis layeer arre: trolllingg haardw he mov m emeentss off thee baase (wh ( heelss, foork,, etcc) are a cont c trollled by the ─ BA B SE.. Alll th PLC marrtCo ontrrolleer XL X type t e R3360. Thhis mod m dulee co onneectss to the PL P C Sm LC usin u ng a USB CAN N in nterffacee to com mm mandd th he base andd fo ork movem men nts and a inteegraates U B-C the orm matio on from f m the diifferrentt enccod ders.. t info R 1 and LAS L SER R 3 are thee drriverrs for f tthe seccuritty laserrs locaated in the ─ LA L SER fronnt an nd rrearr of the AG GV. R 2 is th he driv d ver for f the t NA NAV 350 on laaserr. ─ LA L SER 3 locaalizzatio ERA A mo odu ule hand h dless thee tw d in thee AG GV to ddeteect and a d ─ CAME wo cam c meraas innstallled man ulatee th he palleets. The T e firrst ccamera is a RG GB cam meraa in nstallled undder the lom nipu caliizatiion laseer and a the t secondd caamerra iss a NIR N R installled bettweeen the t ffork ks. The T RG c era is used u d to dettect thee pallletss in thee near envi e iron nmen nt whil w le th he NIR NR R B came is used u d to perrform m prec p isio on posit p tion ning g in the loaad and a unload d acttionns. The T infrarred cam c meraa is also a o used to t reead thee palllet labeels to t ensu e ure the t trac t ceabbility y.  Co ontrrol laye l er. Thiis laayerr inccluddes thee alggoriithm ms resp r onssiblee fo or diiffeerentt fuuncns such s h ass detterm miniing thee positioon of r ot (L Loccalizzatiion)) maaneeuveers colc tion o thhe robo g an nd ddeliv veriing pallletss maanaager thaat make m e usse of o thhe info i ormatioon com g lecting c ming t cam c meraas (M Man neu uverrs man m nageer) and a thee alggoriithm m th hat is i reespoonsible forr from the wing g thee plaanneed path p h (Path h folllow wer)). folllow

 Execu utivee laayerr. It is resp r ponssiblee foor th he exec e cutioon of o th he sequ s uencce of o acctions that t t aree part of o a task. It I cooord dinaates thee acctionns of o aall thhe othe o er modu m uless too carrry outt eacch taask.. Thhe mod m dules in n thiis laayerr are paart of o R Rob boGrraphh [7 7] an nd the t task ks will w l be describ bed lateer.  Intterfface layyer. Th heree arre tw wo kinnd of o modu m uless in n thiis laayerr. First F t, thhe grap g phic inteerfaaces (G GUI Ro obott an nd GUI G I N Navigatiion)) ussed prim marrily forr deebugggin ng and a d mo onitoorin ng thhe syst s tem. Seecon nd, theere is i a mo oduule (Rob ( botW Web b in nterrfacee) used u d to con nnecct with w thee cen ntraal sy ystem m.

5

Task k prog gra amm min ng

Wee use Robo R oGraaph [7]] to defi fine,, exeecute, mon m nitor an nd trracee thee ex xecuutionn off evveryy tassk assiggned d to thee WCS.. Ro oboG Grap aph uusess PN Ns for f T Taskk Mode M elin ng. Even E n thhoug gh PNs P proovid de no n mea m ans for moodellling g thhe cconn nection bettween an algo a orith hm andd itss ennvi(SIIPN ronnmeent, wee usse an a exten e nsio on of o the t Sig gnal Intterpreteed Petr P ri Nets N Ns) [11] [ ] to strress thee facct thhat the t influ i uen nce of o thhe eenviiron nment oon thhe syste s em is base b ed oon mess m sages sen nt beetweeen thee difffereent mod m dulees oof th he arrchiitectturee [4]].

F 6. Robo Fig. R oGraaph GU UI in edittor mod m de.

Thee coontrrol aarch hiteccturre (F Fig.. 4 and a d Fig g. 5) in ncluudes sev veraal in ndep penddennt modu m ules thaat im mpllemeent prim mitiive actionss annd rrepo ort even e nts abo out thei t ir sttate. Thhesee modu m ules aree co onneecteed w with h tw wo inteer-prroceess com mm municatiion meechaanism ms. We W uuse hierrarchicall intterpreteed bina b ary Petr P ri neets to t ccoorrdin nate thee acttivitty of o th hesee mooduules. Taasks aree deescrribed d using g an n innterp pretted Petr P ri net n edit e or aand sav ved in a XML X L fiile. A disd pattcheer looadss these filees annd exec e cutees thhe diffe d eren nt Peetri netss unnderr useer requuestss. As sho own n in Fig g. 4, RoboG Grap ph incluudes tw wo mod m dules:  Ro oboG Gra aph GU UI is thhe prrogrram mminng IDE I E forr deefiniing andd deebug gginng aapplicattionn task ks (Pet ( tri nnets)). Taasks arre deefinned as Petr P ri Nets and d sto oredd in an XM ML ffile.. Figg. 6 sho ows this G GUI in edito e or mod m de with w thee Sh hER RPA pro ojecct thhat inclu udes 122 diifferrentt task ks repr r reseented d in n Fiig. 2 an nd othe o er basicc tasks succh as a “Cha “ argee” that t sen nds the rob bot to t th he ccharrging g sttatio on and a plug p gs itt in..  Ro obog grap ph disp patcch load ds from f m ann xm ml file andd exxecu utess tasks deffineed as a Petri netts. Whe W en executin ng a tassk th his mod m dulee schhed duless the diifferrentt acttionns off thee fuunction nal (baasic acttion ns), exeecuttive (ottherr Peetri netss) and a inteerfaace layers (usser and a d web b in nterfacees) and d recceiv ves infoorm matio on abou a ut thhe even e nts pro oducced.. Thhe in nterraction n with w othher mod m dulees in n th he arrchiitecturee is donne by b publ p lish hing andd suubsccribbing g meessagges..

6

Resu R ultss an nd con ncllusiion ns.

ype oof th his Waareh housse Cont C trol Sysstem m is beiing testted in th he stor s ragee facciliA prot p toty tiees th hat the t logi l isticcs co omppany y KAL K LEID M man m nagees in n Vaalad darees –V Viggo (S Spaain). DO SCM Thhe fo orkllift auto a omaation n (F Fig. 7) that t t incclud des the t addditio on of o a set of sens s sorss and acctuatoors conn t PLC P C, has h been b n caarrieed out o by b tthe com c mpanny GAL G LMA AN A. c nected to the N S.A

F A omatted forkl f lift used u d in the t proj p ject. Thee NA AV3350 is lo ocateed on o to op off thee forrk annd Fig. 7. Auto thhe contr c rol box b that t inclludees a com mputter iss loccated d onn thee roo of.

Thee fo orkss havve four f rth deg d reess off freeedo om (up-dow wn,, lefft-rigght,, forrwaard-bbackwaard, tiltt) an nd the t BA ASE E driiverr caan comm c mannd the t PLC Cw with h veelociity com mmaandss fo or eachh onne of o thhem m. A At th he sam s me tiime, diifferrentt sennsorrs ggivee the feeedb back k abbouut th he fork f k poositio on, read dingg th he seensoor data d on inpuut/o outp put mod m dulees co onnecteed to o thhe C CAN N buus. Thee AGV A Vs arre conn c nectted via Wii-Fi to the cen ntraal coontrrol syst s em thaat is in chaarge of com mm mand dingg new task t ks an nd cont c trollling g the trraffiic. The T refoore, thee AG GV Vs depennds onn thee Wi-Fi W i to receeivee neew orde o ers but b the inteegriity iis sttill guar g rantteed d wiithouut the WiW Fi sig gnal. Th he w way y thee trraffiic iss coontrrolleed iss th hat tto each e h roobott a safe s e noon-cconfflictt poortio on of th he rooutee is prov p videed at a anny ttimee. When W n thhe roobot is app proaachiing the endd off thaat po ortion of o thhe rout r te annoth her safe s e poortio on of o ro oute is prov p videed. The T erefoore,, if ther t re is anyy prrobllem m witth th he wire w esless sign s nal thhe robo r ots will w l sto op at a saafe posi p itionns w waitting forr thee sig gnall to com me back b k aggain n. Forr thee po ositiioniing systtem m wee usse a com mmeerciial N NAV V35 50 from f m SIICK K wiith a sett off TA AGss maade using refl r ectiive tape t e. At A thhe startiing stepp, thhe lase l r2 driv d ver read r ds th he map m of tags from a H HTM ML file f and d seend it too thee NAV N V3500. Once O e thee sy ystem m iss ruunning, the lasser2 2 driiverr is rreceeivin ng peri p odiccallly thhe posit p tion n froom the t NA NAV350.

Fig g. 8. Usser innterfacee maain w wind dow

g. 8 sho ows thee Usser wind w dow w with tthe noddes thatt co onstiitutee the po ossiible patths and a d Fig thee ro obott po ositioons. Fo or thhe first f t tessts we aree usiing onlly one o phy ysiccal AGV A V and a the othher onee is sim s mulatted. c clussion n, we haave thee foollow g addvan ntagges on using RID DE to iimplem mentt As a conc wing thee waarehhousse cconttrol systtem m:

 Hardware abstraction. Hardware server modules provide a hardware abstraction layer. Therefore, when a device is changed, the only part of the system that has to be updated is the driver if we keep the same interface (messages)  Enhanced scalability. The framework is modular, flexible and easily extended.  Maintainability. Modular systems are usually easy to maintain, update and scale. Tracing and debugging problems are easier when the system state can be seen by looking at the evolution of a Petri net rather than monitoring a set of variables.  Module reusability. A key requirement to promote software reuse is to loosen the coupling between software modules. Each module in Fig. 3 is an independent Linux process. Basic modules, and even some tasks, will remain unchanged from application to application.  Reduce development time. In similar applications, the modules remain without changes and only the edition of the Petri nets and configuration files will be necessary for a new application.  Training. Almost everybody that has worked or learned to use IEC 61131-3 compliant programming environments (Siemens S7 Graph, Graphcet, etc.) will be able to program new tasks using RoboGraph. A drawback when using the application every day is the lack of graphical tools for regular users to carry out simple operations. Since RIDE is oriented to developers, a few Graphical Interfaces should be programmed to deal with file configurations and regular operations for people that are not familiar with the implementation of the system. Our future work is oriented in two ways:  Finding low-cost and reliable solutions to solve some problems such as localization that right now are solved with expensive and environment invasive solutions.  Building a set of GUIs to help final user to execute regular operations without having to learn anything about the implementation of the system.

Acknowledgement This work has been partially supported by the FEDER-CONECTAPEME II Program under the Project “Sistema autónomo robotizado de transporte de pales (ShERPA)” IN852A 2014/36.

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