ACTA U N IVERSITATIS LO D ZIEN SIS FOLIA OECONOM ICA 157, 2002
Gianni Gadda Donato Sergiano I N N O V A T I V E P R O C E S S M O D E L F O R P L C - B A S E D S O F T W A R E M O D U L E S I N T E R C H A N G E T H R O U G H T H E I N T E R N E T The p a p e r p r o p o s e s a n e w w a y o f w o rkin g , s u p p o r te d b y p r o p e r s o ftw a re tools, w ith in th e in d u s tria l a u to m a tio n secto r, w ith p a r tic u la r re fe re n c e to P L C -b a s e d so ftw a re d e v e lo p e rs. The n e w p r o c e s s m o d e l re lie s on the In te rn e t re p r e se n tin g a v ir tu a l p la c e w h e re th e a b o v e m e n tio n e d u se rs ca n r e c ip ro c a lly p r o p o s e th e ir so lu tio n s a n d se a r c h f o r other. T h is v ir tu a l p la c e s h o u ld a ls o e n h a n c e s o ftw a re c o -d e s ig n a n d c o -d e v e lo p m e n t a m o n g d iffe r e n t P L C s o ftw a r e d e v e lo p e r s th ro u g h the a d o p tio n o f s ta n d a r d m e th o d o lo g ie s, la n g u a g e s a n d tools, b a s e d on th e IE C ň 1 131-3 sta n d a rd , th a t h a v e b e e n tu n e d w ith in the E u ro p e a n P r o je c t E P O M A T I S T - 19 9 9 -2 0 2 7 8 (E v a lu a tin g th e P e r fo r m a n c e o f an O b je c t o r ie n te d M o d e llin g b A s e d on interneT ).
Introduction
PLCs (Program m able Logic C ontrollers) and other control system s are used in a num ber of industrial and non-industrial applications, ranging from m aterial handling to autom ated warehousing, from transportation to energy production and m anagem ent, environm ental m onitoring, traffic control, and so on. T heir diffusion is increasing for the good ratio betw een system effectiveness and sim plicity o f the autom ation approach.
N evertheless, users operating in such sector are strongly specialised on som e specific typologies of PLCs and related proprietary languages so that PLC softw are deeply depends on hardware choices constraining users to develop
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sim ilar applications from scratch ju st because conceived for different PLC brands.
M oreover, the quality o f the produced softw are is often low, since m odularity and standardisation concepts do not succeed in affirm ing. Besides, industrial autom ation sector finds it difficult to exploit the results o f diffusion and affirm ation of the modern Internet-based technologies, that are determ ining a radical revolution in other sectors o f the IT.
This paper proposes a new way o f working, according to a well tested methodology and supported by proper software tools, addressed to PLC software developers but able to involve also other typologies o f industrial autom ation users and service providers, such as: PLC (and control system s, in general) hardw are suppliers, PLC system s integrators, Internet and A pplication Service Providers.
The new process model relies on the Internet, representing a virtual place where offers and dem ands can meet and the above m entioned users can reciprocally com m unicate their own experiences and their own offers. This virtual place should particularly enhance softw are co-design and co developm ent am ong different PLC software suppliers and end users through the adoption o f standard m ethodologies, languages and tools, based on the IEC 61 131-3 standard, that have been tuned within the European Project EPO M A T 1ST-1999-20278 (Evaluating the Perform ance o f an Object oriented M odelling bA sed on interneT), supported by the European C om m ission through the Inform ation Society Technologies Program m e.
The new proposed model is based on a prototype o f Internet portal, for users operating in the PLCs sector, allow ing them to m anage the results of PLC program m ing as actual digital objects to be interchanged through the Internet.
Hence, the main objectives o f the proposed process model are two: one, to im prove the actual way o f PLC program m ing at a stand-alone level, providing PLC softw are developers with new tools able to im prove the actual degree o f PLC softw are developm ent applying to this sector concepts adopted since many years ago in the PC com m on program m ing; the other, to extend the above potentialities at a global level, through a proper use of the Internet, stim ulating PLC users co-operation.
Therefore, the Internet portal should m ainly represent the virtual place w here PLC software developers, can find and dow nload PLC program s coded for many different applications and properly m anaged as actual digital objects: in such a way, new PLC users should be stim ulated to reuse and integrate PLC softw are codes, also developed by others, instead of developing new applications from scratch. M oreover, PLC suppliers should be stim ulated to
prom ote through the Internet portal new solutions, both hardw are and softw are, to be adopted and integrated within PLC users applications.
Obviously, to allow the PLC program s sharing, softw are m ust satisfy at least m odularity and standardisation requirem ents. Thus, PLC users operating through the Internet portal should develop PLC program s according to com m on rules supported by proper tools.
For these reasons, the system that has been tuned within the EPO M A T project is made of two com ponents, respectively related to the two above m entioned objects: a PLC softw are developm ent environm ent for stand-alone use; an Internet-based application allow ing PLC softw are code interchange. Digital objects, that are interchanged through the Internet, are represented in our case by PLC softw are m odules representing on their turn the basic bricks used to assem ble PLC com plete programs: these m odules, in order to be shared by many users through the Internet, require to be developed according to specific standards guaranteed by the adoption o f a com m on program m ing language, nam ely the High-Level design Language (HLL), supported by the above m entioned PLC softw are developm ent environm ent to be used as stand-alone application.
A rchitecture overview and related w orking way
In the figure below, the two main com ponents o f the proposed system are pointed out: the set of tools to be used as a stand-alone application, identified for the sake o f sim plicity as HLL Editor; the Internet portal and related tools for PLC m odules interchange, identified as EPO M A T Network.
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The HLL Editor allows PLC users to design, develop and m anage PLC softw are m odules according to object-oriented and fam ily-based concepts. Main functions offered by the HLL Editor are:
> C ollecting and verifying the requirem ents specifications provided by the custom er concerning the industrial plant/m achinery to be controlled.
> D esigning and coding the softw are functionality that m anage the industrial plant/m achinery adopting the HLL representation, that is independent of any PLC brand and therefore suitable for co-operation am ong PLC softw are developers usually adopting different PLC devices supporting their own proprietary languages. The HLL representation allow s users to easily describe both the static characteristics and the dynam ic behaviour of PLC software m odules by m eans o f finite state autom ata and integrating the Structured Text language and the Function Blocks hierarchy suggested by the IEC 61131-3 standard.
> Translating the HLL m odules (i.e. the PLC softw are m odules m odelled through the HLL representation) into specific PLC target languages, through the respective PLC drivers. C urrently, the EPO M A T system is focused on the translation into the Instruction List-based code supported by the O M R O N - SysW in32 and C X -Program m er PLC developm ent environm ents, since O M RO N ELECTR O N IC S SRL is partner o f the
EPO M A T consortium . N evertheless, the proposed architecture has been obviously conceived in order to add new PLC drivers; for instance, other two PLC drivers, respectively for SIEM EN S - S7 and SC H N EID ER ELEC TR IC - PL7, are being integrated in the H LL Editor.
> D ebugging and testing the HLL m odules, after they have been translated into specific PLC target languages also sim ulating the related autom ata; this functionality is offered for both single m odules (so that their autonom ous behaviour can be tested) and their assem bly into more com plex applications. > C reating softw are m odules library (represented by U ser DB in the above
figure) aim ed at both im proving the softw are reuse by deriving new m odules from existing ones and stim ulating PLC softw are co-design and co developm ent am ong users.
> G enerating autom atically the docum entation according to proper form ats suitable for skilled personnel but also to be published through the Internet.
Once the PLC softw are m odules (nam ely, the HLL m odules) have been developed by m eans of the HLL Editor it is necessary to transform them into actual digital objects in order to be interchanged through the Internet. T his phase is aim ed at a tw ofold purpose: on one hand, HLL m odules have to be properly catalogued so as to be searched by other users through the Internet portal; on the other hand, HLL m odules interchange through the Internet is ruled by eC om m erce procedures making the EPO M A T Netw ork a virtual m arket place for PLC users.
For these reasons HLL m odules are properly encrypted before being uploaded to the Internet portal so as to protect m odules authors from hackers attacks. On the other hand, to allow m odules search it is necessary that their main properties (but not their HLL representation, that in our case is the actual core o f knowledge and business) are visible; therefore, during their encryption they are provided with a public docum entation. Encryption and public docum entation are perform ed by means of the tools respectively identified as C rypto and Summ ary Translators in the above figure.
Finally, the Internet portal is provided with a Search Engine, specifically conceived for HLL modules, allow ing users to find out the m ost suitable HLL module.
This can be perform ed according to general requirem ents, such as specific keyw ords or industrial sectors, or very technical ones. Am ong these, user can search for m odules characterised by certain HLL prim itives or on the basis o f their potential reuse in other contexts. As to this last aspect, tw o powerful concepts have been adopted to catalogue the m odules: com patibility and
com parability. T he former, given the characteristics o f a certain m odule, allows to search for the m odules that could be interfaced with it to build more com plex m odules. The latter, once indicated a certain m odule, allow s to search for m odules sim ilar to it: i.e. providing the sam e functions but w orking in a different way.
HLL representation advantages
The m odules representation supported by the High-Level design Language constrains users to split PLC softw are controls into many basic com ponents, namely functional units, characterised by independent and autonom ous behaviour. These units can be further assem bled, through their proper interfaces, to build more com plex com ponents: from the HLL point o f view, basic and com plex com ponents represent the PLC software m odules interchanged through the EPO M A T Network.
M oreover, according to the fam ily-based approach, the H LL representation stim ulates users to generalise PLC software controls with com m on characteristics, in order to group the corresponding m odules into fam ilies from which variants related to different specific applications can be further derived. T his particularly enhance softw are reuse not only allow ing m odules integration within new applications but also (and m ostly) developing new m odules (variants) sim ply adding new functions to existing ones rather than starting from scratch.
M odules param etrisation, i.e. grouping different variants o f m odules into fam ilies, not only refers to the functional characteristics o f the m odules but also to hardw are aspects. This means that softw are m odules could require to be properly configured according to the PLC equipm ent that will be adopted: hence, in order to keep PLC softw are as independent as possible from PLC devices (so as to enhance software reuse), user is allow ed to derive from the sam e softw are m odule many variants, with the sam e behaviour, suitable for different PLC devices.
HLL representation im proves softw are reuse not only through the m anagem ent of families o f m odules and their com position hierarchy, represented by the whole structure o f the PLC softw are control, but it also assists users to define the internal structure of the individual m odules. In fact, each m odule is characterised by:
> A static section listing the signals related to sensors and actuators and com m unication with operators.
> An interface section aimed at connecting the m odule with other ones in more com plex applications.
> A dynam ic section, represented by a finite state autom aton and m odelled by means o f states, events, state transitions and actions.
T arget and further results
Possible targets of the E PO M A T system can be catalogued into two main categories depending on its use: direct users, directly taking advantage o f the functions offered by the tools and specifically conceived for the PLC softw are developm ent; indirect users, indirectly taking advantage o f the EPO M A T m ethodology.
O bviously, the sam e user could belong to the form er or latter category according to circum stances:
> PLC users. These are the users actually adopting the E PO M A T tools to develop PLC software. These can be further distinguished according to their way o f w orking, w hether they separately develop softw are or instead they collaborate with other users:
- Stand-alone users. These can be indifferently developers within a certain com pany or freelances.
- Users co-operating within a com pany. Many developers w orking for the sam e com pany co-operate to develop the same PLC program : each user develops som e different m odules locally (i.e. w orking with his own Local Library) that are afterw ards stored in the Intranet-based Library so as to be properly structured to build the whole PLC program (as to this last aspect it is worth considering that the ЕРО М А Г architecture has not been only conceived for Internet-based purposes but also to be used as an Intranet-based application within single com panies or groups o f them ).
- C lusters of com panies and/or users.
r SW integrators. These are typically com panies ordering the developm ent of m odules o r program s to other com panies or freelances and then integrate them to build the definitive control software. M ore in general, a SW integrator custom ises/integrates m odules developed by other users searching for them through the Internet portal.
> PLC technology providers. This category can be considered both direct and indirect user. It m eans that in addition to technical advices related to the direct developm ent of control softw are m odules they can offer other services
to actual users of EPOM AT, indirectly related to the use o f the EPO M A T tools. In particular, these providers could he:
- Standards com petencies providers. Since the HLL Editor is also based on the I EC 61131-3 standard, com petencies related, for instance, to the possibility to reuse PLC program s coded according to this standard (or others) within the EPO M A T local tools. This m ainly refer to the reengineering of existing program s based on S I language and lunction- blocks use into program s coded through the H LL representation.
- Languages drivers providers. These could develop new drivers to be added to the ones currently supported by the HLL Editor. It is worth considering that the architecture chosen for the EPO M A T local tools allow to manage new drivers of languages without the necessity to directly interact with the EPO M A T local tools source code.
> C ustom ers. Unlike actual PLC users, these do not develop any PLC control softw are but simply order the m anufacturing ol an industrial plant/m achinery. Hence, they simply take advantage of the EPO M A I methodology as to the possibility to search for the required com petencies through the Internet portal.
> Hardw are suppliers. Sim ilarly to custom ers, also these indirectly use the EPO M A T solution. They are involved for all the hardw are aspects related to the industrial plant/m achinery to be m anufactured and therefore can be further catalogued as:
- Device suppliers. These provide hardw are devices to be integrated in the industrial plants/m achinery (such as sensors, actuators) and are usually independent of choices related to softw are aspects. In this case, the EPO M A T system is m ainly used as a virtual showcase.
- PLCs suppliers. These provide the PLC equipm ent to actually run the control software for the exam ined industrial plant/m achinery. They can take advantage o f EPO M A T solution at both global and local level: in the form er case they can present new PLCs or functionality through the Internet portal; in the latter case, they can be interested in offering inform ation (e.g. to drivers providers) to develop new drivers for the languages supported by their PLCs.
> Internet/Application Services Providers. ISPs/A SPs can offer services related to the industrial autom ation sector, and therefore directly derived from the use o f EPO M A T solution, or extend the EPO M A T m ethodology to other contexts:
- A utom ation services providers. These represent additional nodes o f the EPO M A T Network widening in such a way the diffusion o f the EPO M A T solution.
- Intelnet/lntranet-based Libraries creation/custom isation. This service is a proper custom isation of the above one, conceived for com panies usually operating together that need to co-develop control softw are for huge projects.
General services providers. This refers to the possibility to extend the EPO M A T methodology applied at global level (i.e. through the Internet) to other contexts different from the industrial autom ation one. In fact, the architecture o f the Internet portal has been conceived to be tuned also for other cases; am ong these the follow ing ones are currently tested:
- Fluid-pow er system s sim ulation. Sim ulation o f whole fluid-pow er system s or simply som e com ponents is now adays required by many com panies that prefer to test, through num erical sim ulation, these com ponents before m anufacturing them. U nfortunately, softw are packages available on the market are very expensive and m ostly difficult to be used by personnel working outside academ ic institutions. N evertheless, m ost of these software packages are now also available as running versions able to sim ulate m odels created by m eans o f the com plete versions. Hence, in such a case, instead o f HLL m odules developers, there would be sim ulation m odels providers collecting, through the Internet, requirem ents from com pany using only m odels and uploading them, again through the Internet. Unlike the actual use o f the EPO M A T m ethodology, in this case (and also in the other one cited below ) the digital object that is exchanged (i.e. the sim ulation model instead of the HLL m odule) is always created and sold by a certain category o f network users (i.e. the providers of the m odels) and then purchased and used by another category (i.e. the users of the m odels). It m eans that these two categories of users are not interchangeable; each of them alw ays plays the same role: provider or (aut) user. Instead, as to the EPO M A T system, the same developer o f HLL m odules can behave as both provider and user according to the circum stances: once he can develop HLL m odules and provide them to other users through the Internet; another time he can pay and dow nload m odules created by other developers.
- Rapid prototyping models. Nowadays many com panies operating in som e sectors related to the m echanical engineering, such as the autom otive one, are interested in sim ulating the static/dynam ic
behaviour o f com ponents or even m anufacture small prototypes bei ore starting actual and more exhaustive tests with their final versions. This requires that the original C AD file describing the exam ined com ponent has to be converted and properly arranged into other specific form ats suitable for sim ulation packages or prototypes m anufacturing. In this case the digital objects interchanged between the users and the providers are CAD files and then results o f sim ulation or other files form atted, e.g., for rapid prototyping machinery.
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