Translation of Extended Petri Net Model into Ladder Diagram and Simulation with PLC

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1 rojniški vesnik - Journal of Mechanical Engineering 55(009)0, Paper receive: UDC 68.5 Paper accepe: Translaion of Exene Peri Ne Moel ino Laer Diagram an imulaion wih PLC Tomaž Perme DP Perme Tomaž, s. p., lovenia Universiy of Primorska, Faculy of Managemen Koper, lovenia Moelling an simulaion can significanly help wih he eaching an learning of PLC programming, raining of he operaors an mainaining personal, eveloping auomae sysems an iagnosis of he sysems operaion. The basic iea of he presene research an evelopmen was o use PLC programming ool for moelling a iscree mecharonic sysem an simulae is operaion on inusrial PLC or on emulaion of PLC on he PC compuer. For he realizaion of he iea he exensions of he basic Peri ne heory (EPN) an irec ranslaion of he EPN moel ino he laer iagram were elaborae, which enable he use of he EPN moel for simulaion on PLC. Furhermore, he builing blocks of EPN moel were evelope wihin he programme for iscree simulaion, which enable builing an verificaion of an EPN moel of he observe sysem wihin he programme for iscree simulaion before is implemenaion. The primary es of he meho an he usabiliy verificaion of he basic iea show ha he meho is applicable for eaching an learning of PLC programming an can also be use for an avance eveloping an esing of PLC programmes. 009 Journal of Mechanical Engineering. All righs reserve. Keywors: exene Peri ne, laer iagram, PLC, moelling, simulaion, elecro-eumaic sysems, iscree mecharonic sysems 0 INTODUCTION The elecro-eumaic sysems form a grea porion of auomaion in bulk proucion an inernal logisics. They are usually compose of mechanical consrucion, eumaic or elecrical rives, elecrical sensors an programmable logical conrollers (PLC). o he knowlege abou he operaion an programming of PLCs became essenial for mechanical, elecrical or mecharonic engineers ha evelop, esign, conrol, mainain, moernize or only operae auomae proucion sysems. Tha is why moern curriculum on auomaion an mecharonics has o inclue pracical courses of PLC programming, where suens have o aquire as much pracical experience as possible. The bes experience can be obaine wih hans-on real inusrial equipmen. Bu experience from pracical courses shows ha he equipmen in laboraories an classrooms is always in some way a boleneck. Therefore, new moern echniques like simulaion have o be implemene an use complemenary o an in cooperaion wih he real inusrial equipmen. Tha was he firs issue in he realisaion of he iea abou using inusrial PLC an PC emulaion of inusrial PLC for simulaion. The secon reason for using real moel base simulaion on PLC conrollers is ha he evelope PLC programmes are in mos pracical cases ese an verifie no sooner han he new or re-esigne auomae sysem is insalle an moernize respecively. Many ifferen mehos are use o moel an analyse he conrol sequence [] o [3] before implemenaion. There are some inusrial cases of using avance simulaion ools wih embee PLC programming opion, bu hey are reserve mosly for large companies an large projecs [4] an [5]. However, ever more ofen he evelopers es PLC programmes on a real or virual PLC wih he aim o verify he funcionaliy of humanmachine inerface an o check, if he PLC programme runs properly. This so calle simulaion is performe by manually seing an re-seing he variables in he PLC programme ha represens saes of he real sysem o be conrolle. More pracical an efficien is o use auomae changing of he saes of he inpu variables in he PLC programme accoring o he relevan moel of he conrolle sysem. This can also be use for verifying he funcionaliy of he * Corr. Auhor's Aress: DP, Perme Tomaž, s. p., Zgornje Gorje, 447 Zgornje Gorje, lovenia, omaz.perme@rp.si 609

2 rojniški vesnik - Journal of Mechanical Engineering 55(009)0, conrol programme regaring he requiremens of he sysem s operaion. The variables can be change by a simulaion par of he PLC programme ha represens he ynamic moel of he conrolle sysem. This was he backgroun for eveloping he concep of simulaion of elecro-eumaic sysems wih he inusrial PLC conroller. New o he concep is he iea of successive execuion of he conrol an simulaion par of he PLC programme on a real or virual PLC conroller. uens an engineers can wrie he conrol programme for he PLC conroller wih an inusrial PLC programming ool an verify is correcness an funcionaliy in a compleely inusrial environmen. Alhough he iea of using a par of he PLC programme for a simulaion moel is very simple, he realisaion encounere a significan challenge. The usefulness of he iea compleely epens on accuracy of he simulaion moel, i.e. simulaion par of PLC programme. Firs aemps o ranslae a formal moel of ouble-acing eumaic cyliner conrolle by a 4/-way valve ino a laer iagram poine ou he ifficuly of accurae moelling as well as he verificaion an valiaion of he simulaion moel wihin he ool for PLC programming. PLC programme is primarily inene o conrol he sysem in he space of esire saes accoring o he specifie algorihm. On he conrary, he simulaion moel has o inclue all possible or reachable saes of he sysem. In an avance simulaion moel also unexpece saes of he sysem like failures have o be consiere as a par of he possible sae space of he sysem. The paper presens he realisaion of he iea ha is he resul of he auhor s research an evelopmen on virual environmen [6] an remoe laboraory [7] for eucaion an raining [8] as well as he implemenaion of Peri ne for moelling an simulaion as suppor for planning of proucion sysems [9] o []. For he realizaion of he iea he basic heory of Peri ne was exene in a way ha he operaion an conrol of elecro-eumaic sysems can be moelle. The EPN moel is hen ranslae accoring o he elaborae rules ino he laer iagram. The ranslaion enables using he EPN moel of he sysem wih he conrol algorihm for simulaion on PLC or emulaion of PLC. IMULATION UING POGAMMABLE LOGICAL CONTOLLE A moel of he sysem can be use for several purposes. The moel is mos of all neee in he esign sage of a new sysem or for a reesign of an exisen sysem [9] or a sysem componen [] for obaining is srucure an ynamic behaviour. The moel is also use for planning [3] or conrol an iagnosic purposes [3]. The moel can also be use as a plaform for eucaion an raining [6]. In all hese cases he moel has o be a reliable an consisen represenaion of he real sysem. The ransformaion of he elemens of he observe sysem an he relaions beween hem ino he aa space has o be comprehensible o he engineer as well as o he machine. The engineer nees o efine heir requiremens an requess in a form of insrucions, on he basis of which he machine can operae an fulfil he require funcionaliy.. The Concep of imulaion wih he PLC Programme imulaion is a meho an a ool for obaining he srucure an ynamic behaviour of he observe sysem, which canno be obaine wih oher mehos an ools in an economical way or in accepable ime frame. Usually he evelopmen of PLC programmes oes no inclue simulaion, so he PLC programme is ese only afer he sysem is insalle. Alreay a he esign sage of he sysem mos aa for he moelling an simulaion are available incluing a require operaion of he sysem an he funcionaliy of he conrol programme, Bu he simulaion is sill no use o help o evelop error-free PLC programme. Because he users o no expec he simulaion suppor from he programming ools, mos PLC proviers have no inclue simulaion in heir programming ools, a leas no irecly. Bu wih he PLC conroller he simulaion can be performe in he same way as wih he PC compuer. For he es of he PLC programme on he PLC he response of he conrolle sysem on he conrol signals from he PLC is neee. The response is he sae of he real sysem in paricular ime or ime frame capure by he sensors an pu ino he PLC as inpus (Fig. ). 60 Perme, T.

3 rojniški vesnik - Journal of Mechanical Engineering 55(009)0, PLC reas he sae of he inpus cyclically, so he response from he real sysem has o be permanen. This can be achieve wih he wo pars of he PLC programme ha is running on he real PLC or in he emulaion of PLC on a PC. Firs par is he conrol programme ha conrols he machine or sysem. The secon par of he PLC programme reas he inpus, simulaes he behaviour of conrolle machine or sysem an wries he oupus. This means ha he simulaion par of he programme changes he sae of he inpus o he conrol programme on he basis of he se oupus: This is one in he same way an he real sysem oes ha by means of he sensors an acuaors (Fig. ). avanage is ha he conrol par of he PLC programme is he same as he PLC programme ha will conrol he real sysem. The limiaions are mosly relae o he characerisics of PLC conrollers like limie inernal memory an so he size of he simulaion moel, spee of he processor an so he ime for execuion of he simulaion, an specificiy of he PLC programming languages. The firs wo limiaions can be solve wih a more powerful PLC, programmable auomaion conrollers (PAC) or wih he emulaion of PLC on PCs. Emulaion refers o he abiliy of a compuer program or elecronic evice o imiae anoher program or evice. An emulaor uplicaes he funcions of one sysem using a ifferen sysem, so ha he secon sysem behaves like he firs sysem. This means ha he PLC programme evelope for a paricular ype or a paricular PLC conroller can also run on he PC. If he PLC programme also inclues he simulaion par, he conrol par of he PLC programme can be ese an so errors can be ienifie an remove.. PLC Programming Languages Fig.. Common conrol scheme of a sysem conrolle wih PLC Fig.. Conrol scheme of a simulaion wih PLC imulaion wih he PLC has some avanages, bu also some limiaions. The main The PLC programming languages are also he encounere moelling limiaion. There are five programming languages for PLCs efine in he IEC 63 sanar. The insrucion lis (IL) is he firs exual an laer iagram (LD), he firs graphical PLC programming language. LD is sill mos frequenly use in all kins of PLC evices. Boh languages are base on he logic of relay conrol, which is sill he basic logic of PLC evices. The nex graphical programming language are funcion block iagram (FBD) an sequenial funcion char (FC), which are use for higher level programming. Avance exual PLC programming language is srucure ex (T), which is very similar o he programming language Pascal. The avanage of graphical languages in comparison o exual is mosly he graphical inerface ha allows a visualisaion of PLC programme execuion an is more user frienly for programming [] an [3]. Ou of all sanarise PLC programming languages he laer iagram was chosen for he realisaion of he iea of simulaion wih a PLC programme, because he LD: Translaion of Exene Peri Ne Moel ino Laer Diagram an imulaion wih PLC 6

4 rojniški vesnik - Journal of Mechanical Engineering 55(009)0, is he mos frequenly use PLC programming language an is available in pracically all PLCs, - offers a comprehensible an unersanable escripion of operaion ha is base on relay logic an bool algebra, - is very convenien for sequenial algorihms on low operaion level, - comprehens graphical way of programming an - enables a visualisaion of programme execuion. More complicae han jus selecing an appropriae programming language was solving he specificiy an aequacy of he PLC programming language incluing he laer iagram for builing he simulaion moel. The fac is ha he programming languages are aime for he builing of he conrol programmes an no for he moelling of he processes an sysems uner conrol. The escribe moelling problem can be solve wih an appropriae moelling ool ha also enables he ranslaion of he moel ino he PLC programme. Many PN-base mehos an ools have alreay prove he PN capabiliy an compeence for he moelling an conrol esign of iscree-even sysems as well as a ranslaion of PN-base conrol sequence ino laer iagram or sequenial funcion char (IEC 63-3) [4] o [7]. The PN also has goo mahemaical backgroun [8] an [9] an an inherie graphic presenaion ha feaures grea moelling, analysing an simulaion capabiliies [0]. PETI NET AND LADDE DIAGAM The elecro-eumaic componens for auomae assembly an hanling evices are ypical sysems where properies are change in iscree poins in ime. uch sysems are escribe as iscree-even sysems an can be moelle wih Peri nes. Bu for ifferen applicaions here are also ifferen moelling requiremens.. equiremens on Peri Ne Exensions For he conrol of a iscree sysem we have o know he sae of he sysem an he way how o move he sysem in cerain ime ino nex require sae. For example, he eumaic -axes hanling evice has four en posiions ha form he sae space of he sysem. The movemen of he eumaic cyliners changes hese saes accoring o he conrol sequence wrien in he conrol programme ha makes he conroller sen signals o he solenoi valve of he eumaic cyliner. In normal operaion coniions an wih an error free conrol programme he saes of he valves ha irecly conrol he movemen of he eumaic cyliners is no imporan o know. Bu for he simulaion, he consisen moel of he valve-cyliner sysem is funamenal. There are also several inernal saes in he valve-cyliner sysem an he uraion of he aciviies ha have o be pu ino a moel, an ha wih he basic heory of Peri ne canno be accuraely moelle. Anoher reason for PN exensions is he aequae ranslaion of PN moel o he PLC programme wrien in he laer iagram. The laer iagram consiss of elemens an relaions beween hem. The basic elemens are inpu, oupu an inernal variables, imers an couners. The main relaions beween hese elemens are AND, O an NOT operan of Boolean algebra. The combinaion of elemens an relaions forms he saemens ha have no always an aequae represenaion wihin he basic heory of Peri ne. Besies he negaion here is also a lack of proper inerpreaion of inpu variables of LD in he PN moel. In he laer iagram he inpu variable oes no change he sae when he programme is execue. In PN moel, however, he execuion of enable ransiion akes a corresponing number of okens from inpu places an so i changes he sae of he inpu places. These requiremens efine he exensions of Peri ne, which are negaion of coniion, signal connecion an ime ransiion.. Theoreical Backgroun of Peri Nes Exensions The formal efiniion of a Peri ne [8] an [9] wih he finie capaciy (place/ransiion ne) [0] exene wih negaion, signal connecion an ime is given by as an 6-uple C = (P, T, F, W, M, Z) where: P = { p, p,...p m } is a finie se of places, T = {,,... n } is a finie se of ransiions, P T = 0 in P T 0 F s (P T) (T P) is a se of normal arcs, F i (P T) (T P) is a se of signal arcs, 6 Perme, T.

5 rojniški vesnik - Journal of Mechanical Engineering 55(009)0, F = F s F i in F s F i = 0 W: F {-, } is a weigh funcion, M 0 : P {0, } is he iniial marking, Z: T {0,,,3,..} efines he ime for each ransiion. The rule for ransiion enabling an firing is an execuion rule, which can be escribe for an EPN in he: s := {p (p,) F s } is a se of inpu places wih normal connecions o he ransiion, s := {p (,p) F s } is a se of oupu places wih normal connecions o he ransiion, i : = {p (p,) F i } is a se of inpu places wih signal connecions o he ransiion, i : = {p (,p) F i } is a se of oupu places wih signal connecions o he ransiion, = s i is a se of inpu places of ransiion an := s i is a se of oupu places of ransiion. A ransiion is enable uner marking M, if: M( p) = W( p, ) = p : M( p) = 0 W( p, ) =, () M( p) = 0 W(, p) = p : M( p) = W(, p) =. () Eq. () means ha each inpu place o he ransiion shoul be marke or no marke, if w(p, ) is an 0 respecively. Eq. () means ha he oupu places of he ransiion shoul no be marke, if w(p, ) is, or shoul be marke, if w(p, ) is -. Negaive weigh acually means negaion. EPN oes no solve nor envisage conflic siuaions an muual exclusions which remain he subjec of moelling. ubse of ransiions T T is enable uner marking M, if T is enable uner he marking M. If a ransiion is enable an is ime is null, i can fire. An enable ransiion can fire epening on he uraion of he ransiion in wo ways. Zero-ime ransiions (z() = 0) fire compleely a once an change he sae accoring o M( p) W( p, ) p s \ s, M( p) + W(, p) p s \ s, M'( p) =. M( p) W( p, ) + W(, p) p s s, M( p) else. (3) A firing of an enable ransiion removes one oken from each inpu place p of ransiion, an as one oken o each oupu place p of ransiion. This is rue for each place p ha is connece o he ransiion wih he normal connecion. For places p connece o he ransiion wih signal connecion, nohing is change uring he firing of ransiion. Nonzero-ime ransiions (z() > 0) fire in wo seps. In he firs sep enable ransiion is ae o he T -, where T - is a se of enable nonzero-ime ransiions {(, ) (, )...( n, n )} wih elemens ( k, k ), k T in k {,,3...}, where k are enable bu no je fire nonzero-ime ransiions an k heir remaining imes o firing. In he secon sep he nonzero-ime ransiion fires o he en. Firing o he en of nonzero-ime ransiion k happens when he remaining ime k = 0 an he coniions () an () are fulfille (ransiion is sill enable). Pracically fires of he ransiion wih he smalles remaining ime k : (,) T - k : k. (4) Firing o he en of enable () () nonzero-ime ransiion from T - uner M is execue in he same way as firing of he normal ransiions (3), where: = k ( k, k ) T -. (5) T - = T - \{( k, k )} (6) (,) = (, - k ) for (,) T -. (7) Firing o he en of nonzero-ime ransiion means removing okens from inpu places an aing okens o he oupu places of ransiion (3), removing elemens ( k, k ) from T - (6) an subracing k from of all elemens in T - (7). emoving he elemen ( k, k ) from T - (6) is execue also for he ransiion (5) when hey are no enable any more. Nonzero-ime ransiion can be in he same momen only in one elemen ( k, k )..3 Gaphical epresenaion an Explanaions of PN Exensions The Peri ne is a irece, weighe, biparie graph consising of wo ypes of noes, calle places an ransiions. In a graphical represenaion places are represene by circles an ransiions by bars or recangle. Places are connece wih ransiions an ransiions wih places by arcs. The irecion of an arc is graphically represene by an arrow a he en of he arc. The irecion of an arc eermines if he Translaion of Exene Peri Ne Moel ino Laer Diagram an imulaion wih PLC 63

6 rojniški vesnik - Journal of Mechanical Engineering 55(009)0, place is he inpu or oupu place of a ransiion. If he arc beween a place an a ransiion is biirece, he place is inpu an also oupu o ha ransiion. An arc irece from a place o a ransiion pracically means a coniion ha has o be fulfille for he ransiion o fire. The fulfille coniion is represene by a oken in he place ha represens he coniion. In a graphical represenaion he okens are represene by os. An arc irece from a ransiion o a place means he consequence of he ransiion execuion. When a ransiion fires, one oken is remove from each inpu place an one oken is pu o each oupu place. All noes are usually name, so he graph as well as he moel is more comprehensible. The negaion of he coniion efine by negaive weighe funcion is graphically represene by an arc irece from a place o a ransiion an wih a circle insea of an arrow a is en. The negaion means ha he ransiion is enable if he coniion is no fulfille an he inpu place has no okens. This correspons o he negaion in he laer iagram. The informaional arc is graphically represene by a ashe line. The only ifference beween an informaional an normal arc is ha he informaional arc leaves okens in he connece inpu places when he corresponing ransiion fires. o he okens remain in he places an he coniion is sill fulfille. This is he case of he inpu signals on he PLC. The informaional arc irece from a ransiion o a place has no pracical meaning. In real sysems aciviies an processes nee some ime for execuion an canno be properly moelle by a ransiion ha fires insananeously. I is for his reason ha ime ransiion which oes no fire insananeously is inrouce. Time ransiion acually fires in wo seps. In he firs sep, only he coniion fulfilmen is verifie. If he ransiion is sill enable afer he elapse ime, i fires o he en like an orinary ransiion. o he EPN moel comprises of orinary an ime ransiions. Time ransiion is usually represene by a larger recangle, bu in he coninuaion he orinary an ime ransiions will have he same represenaion. We will isinguish beween hem only when we ranslae he EPN moel o he laer iagram..4 Translaion ules of Exene Peri Ne Moel ino he Laer Diagram EPN moel is ranslae ino he laer iagram accoring o he evelope rules. These rules efine he inerpreaion of EPN efiniion in LD synax: - Each place in he EPN moel has an inernal or exernal one-bi (Boolean) variable in he LD. An EPN place ha represens a conrol signal for he acuaor or he signal from he sensor is ranslae ino an exernal one-bi variable. Exernal variables on real PLC are mappe o he physical oupu or inpu. Oher EPN places are represene in LD by inernal variables. - Each EPN ransiion enoes one or wo saemens i.e. rungs in he laer iagram. Nonzero-ime ransiion (ime is greaer han zero) has wo rungs in LD. The firs rung conains a ranslaion of enabling coniions an a imer wih he swiching ime. The secon rung comprises he oupu variable from he imer an ranslaion of firing i.e execuion of he ransiion. Translaion of a ransiion wih insan firing is a special case of he ranslaion of nonzero-ime ransiion where he imer is eliminae an boh rungs are merge in one rung. - Each inpu or oupu place of a ransiion in EPN is ranslae ino inpu an a negaion of an inpu in he firs rung of LD respecively. Each inpu place of a ransiion, connece o he ransiion wih negae connecion, is ranslae ino negae inpu in he firs rung of LD. - Firing of a ransiion in EPN (3), i.e. aing an removing of okens o an from places, is ranslae ino seing or reseing of one-bi variable (se on or 0 respecively) in he secon rung. - A sequence of rungs in LD efines he prioriy of firing of EPN ransiions. ung wih ranslaion of firing of he ransiion wih higher prioriy has o be wrien in LD before rungs for oher concurren ransiions. ungs of ranslae nonzero-ime ransiion have o be wrien ogeher in a se orer. - An inpu place connece wih an informaional connecion o he ransiion appears jus as inpu coniion in LD. 64 Perme, T.

7 rojniški vesnik - Journal of Mechanical Engineering 55(009)0, Iniial marking M of EPN moel is ranslae ino one rung of LD, which is execue jus once in he firs cycle of he PLC programme an before oher saemens..5 Explanaion of Translaion ules A ransiion in he EPN moel efines he connecions beween inpu an oupu variables in he laer iagram accoring o he enabling coniions (), () an firing execuion (3). Each inpu place of a ransiion in EPN is an enabling coniion of ha ransiion (), herefore inpu place p of he ransiion (Fig. 3) is ranslae ino inpu in he rung of LD. Each oupu place of a ransiion in EPN moel is also a coniion (), herefore, oupu place p of he ransiion is ranslae ino a negaion of an inpu in rung. This is shown wih negae inpu in rung on Fig. 3. ung conains also a imer ha represens a elay of he ransiion. (> 0) Fig. 3. Translaion of nonzero-ime ransiion from EPN ino LD Firing of a ransiion in EPN means removing one oken from each inpu place an aing one oken o each oupu place which are connece o he ransiion wih sanar connecion (3). Token aing an removing is ranslae in LD as seing of one-bi variable on or 0 respecively. This is presene wih a saemen in rung in Fig. 3. The variable of imer ( is se o afer he elay an remains as long as imer is enable) is a coniion in he rung ha ses s variable on an on 0. In his way each nonzero-ime ransiion in EPN has wo rungs in LD, he firs one for verifying he enabling coniions an he secon one for firing execuion. Boh saemens (rungs) coul be wrien in one rung wih he imer in he cenre, bu no all PLC conrollers suppor his kin of programming. Cerainly we o his wih one rung in he case of zero-ime ransiion which fires insananeously an oes no nee a imer. Wihou a imer boh saemens are wrien in one rung as i is shown in Fig. 4. The same applies o a ranslaion of a ransiion wih n inpu places an m oupu places ino LD (Figs. 5 an 6). (=0) Fig. 4. Translaion of zero-ime ransiion from EPN ino LD (> 0) p' Fig. 5. Translaion of nonzero-ime ransiion wih n inpu places an m oupu places from EPN ino LD (=0) p' p' p' Fig. 6. Translaion of zero-ime ransiion wih n inpu places an m oupu places from EPN ino LD A sequence of saemens is also imporan because i efines he prioriy of ransiions ha compee beween hemselves. The righ sequence is significan in case of ransiions wih a leas one common inpu (Fig. 7) or oupu place (Fig. 8) since i hols ha he saemen wrien in LD before oher saemens is also execue before ohers. Therefore, he problem of muual exclusion sill remains on he moelling sage. A negaion of he connecion of an inpu or oupu place in he EPN moel is ranslae ino a negaion of inpu variable for inpu place an a negaion of he negaion of variable for oupu place respecively. The negaion also changes he firing rule because for he place connece wih he negae connecion, he sae afer firing is no change (Fig. 9). p' p' Translaion of Exene Peri Ne Moel ino Laer Diagram an imulaion wih PLC 65

8 rojniški vesnik - Journal of Mechanical Engineering 55(009)0, (... 0) n= n p' p' p' he ranslaion of informaional connecions hol he same enabling coniions () an (). The only ifference is ha he sae of he places connece o he ransiion wih informaional connecion says unchange afer firing of ransiion (Fig. 0). n- p' n (> 0) n n Fig. 7. Translaion of n non-zero ime ransiions wih same oupu place p' Fig. 0. Translaion of nonzero-ime ransiion wih informaional connecion of inpu place 3 TET CAE p (... 0) m> m p' n- p p p' p p' m The moelling wih PN exensions, ranslaion of EPN moel ino LD programme an simulaion wih PLC were iniially ese on a conrol example of a elecroeumaic sysem compose of a ouble acing eumaic cyliner A wih wo en-swiches (a 0 in a ), 4/-way valve KA an programmable logical conroller wih sar an sop buons (Fig. ). n m p Fig. 8. Translaion of n non-zero ime ransiions wih same inpu place The above rules are rue for he sanar connecions beween places an ransiions. For he ranslaion of informaional connecions have he same enabling coniions () an (). The only ifference is ha he sae of he places connece o he ransiion wih an informaional connecion says unchange afer he firing of ransiion (Fig. 0). (> 0) Fig. 9. Translaion of nonzero-ime ransiion wih negae inpu place The above escribe rules for he sanar connecions beween places an ransiions. For Fig.. Elecro-eumaic sysem an sae iagram for exen an rerac sroke 3. Formal Descripion of Operaion The iagram in Fig. escribes he forwar an backwar movemens of he cyliner A an he saes of he en swiches. When swich a 0 or a is on, he cyliner (acually a pison-ro of he cyliner) is in rerace (home posiion) an exene posiion (ou posiion) respecively. If boh swiches are off, he cyliner is in movemen. eracing an exension srokes are conrolle by signals an ha swich he valve KA. From he valve posiion i epens which chamber (air pipe) of he cyliner is uner 66 Perme, T.

9 rojniški vesnik - Journal of Mechanical Engineering 55(009)0, pressure or exhause. For he exension sroke (for movemen) he air pipe P nees o be uner pressure an P exhause, an in he oher way for he reracion sroke (back movemen). The ime scale of a soke shows ha he sroke has wo pars: he swiching par an he sroke iself. The swiching par sars when he signal for a sroke is given, an las o he momen when he pison sars moving. The sroke iself sars a he beginning of he moion of he pison an lass unil he pison sops in new posiion. In Fig. he ime for swiching par is enoe wih v an v, an he uraion of he sroke wih h an h for for an back movemen respecively. During he swiching ime v an v en swiches are urne on (signals a 0 an a are ). moel swiching par of forwar an backwar movemen, an forwar an backwar srokes. The ransiions an moel a change of a sroke irecion uring he pison movemen. aes of he places P an P are change jus by ransiions an, so he connecions from P an P o ransiions v, v, are are informaional. 3. EPN Moel of Double Acing Pneumaic Cyliner On he basis of he formal escripion of operaion of ouble acing eumaic cyliner an 4/-way valve an EPN moel was buil (Fig. ). The places in he graph represen saes of he cyliner (a 0, a, for, back), he valve (P an P ) an of he inpu signals ( in ). Transiions (,, v, h, v, h, in ) represen acions or evens ha change he sae of he sysem. egaring he conrol signals an, he 4/-way valve is in one of wo saes enoe by P or P. aes P an P inicae which oupu por of he valve is uner pressure or exhause (por or 4). A regular operaion of ouble acing eumaic valve consisenly appoins ha jus one of he air pors shoul be uner pressure an he oher one has o be exhause. Operaion of he valve is moelle by ransiions an, which accoring o he sae of he signals an remove an a a oken from an o he place P or P. If he signal is on boh solenois, he valve oes no change he sae an so he negaions of he signals in are ae o he ransiions an. The signals an o no change he sae when he valve is swiching, so he connecions from places an o he ransiions an are informaional an represene in he graph by a ashe line (Fig. ). The saes of he cyliner are moelle by he places a 0, forwar, a an backwar. The ransiions beween places v, h, v an h Fig.. EPN graph of a moel of a ouble acing eumaic cyliner conrolle by 4/-way valve 3.3 Tes of he EPN Moel Wih analyical mehos using marix equaions or wih he reachabiliy ree he EPN moel can be analyze agains bouneness, reachabiliy an liveness. The uraion of nonzero-ime ransiions has no influence on hese characerisic. However, ue o muual exclusion an concurrency, he elays of nonzero-ime ransiions have a significan influence on a firing sequence of hese ransiions an, herefore, also on reaching he require sae. Thus, he verificaion of he moel ha will prove if he moel correspons o he operaion of real sysem is neee. This can be accomplishe by execuing (playing) he graph i.e. firing he enable ransiions an changing he marking of he places (moving okens beween places). The graph can be playe manually (ha is also for he simples moel very ime consuming) or by compuer simulaion. Many compuer simulaion programmes are base on he heory of Peri ne [] an [0] Translaion of Exene Peri Ne Moel ino Laer Diagram an imulaion wih PLC 67

10 rojniški vesnik - Journal of Mechanical Engineering 55(009)0, or jus suppor moelling an playing he PN graph. Bu he elaborae exensions of a basic heory of Peri ne are isincive an require eicae moelling an simulaion programme. The alernaives were o buil a new simulaion programme for elaborae EPN or o buil EPN builing blocks wih embee firing logic wihin an exising simulaion programme. The secon alernaive was more pracical an so he iscree simulaion programme Tecnomaix Plan imulaion has been chosen for he evelopmen plaform. On he basis of sanar builing blocks of Tecnomaix Plan imulaion an he abiliy of programming heir behaviour, new cusomize builing blocks for places, ransiions an connecions were evelope. There is one ype of builing blocks for places, one ype for ransiions an hree ypes for connecions: sanar connecion (black line), informaional connecion (green line) an negae connecion (re line). Wih hese builing blocks an accurae an consisen EPN moel can be buil an he execuion of he graph accoring o he enabling an firing rules of elaborae EPN can be performe. A simulaion of he EPN moel wihin a programme for iscree simulaion enables he elays of ransiions o be arbirarily alere uring he simulaion. This is especially imporan for he verificaion of he moel in he case of swiching he irecion uring he sroke. The calculaion of he ime of ransiion h an h ha epens on he isance of he pison from he en posiion an is velociy can be easily ae o he behaviour of he builing block of hese wo ransiions. For he analysis of he EPN moel of he ouble acing eumaic cyliner an he 4/-way valve wo aiional ransiions fw an bw were place ino he moel (Fig. 3). The ransiions fw an bw acually ranomly an auomaically change he saes of he signals an, an so enable a coninual execuion of he moel for he analysis. During he es he moel was never blocke an he require sae was always reache. The resul of his analysis proves ha he EPN moel is an accurae moel of he operaion of he observe sysem. Fig. 3. Analysis of he EPN moel wihin he programme for iscree simulaion 3.4 Translaion of EPN Moel ino Laer Diagram The EPN moel of ouble acing eumaic cyliner wih he 4/-way valve (Fig.. ) was ranslae ino laer iagram (Fig. 4) accoring o he elaborae ranslaion rules. Each ransiion wih insananeous firing (,, an ) is ranslae in he laer iagram ino one rung (rungs, 3, an 3 on Fig. 4) an nonzero-ime ransiions ( v, h, v in h ) ino wo rungs (rungs form 4 o on Fig. 4). To he ransiions an he funcion ha calculaes he elay (uraion) of he ransiions h, an h (las line in rungs an 3 on Fig.4) was ae. The funcion calculaes he uraion by subracing he remaining ime of he previous sroke from he whole sroke in a new irecion an muliply ha by he raio beween he uraion of he previous sroke an he uraion of he soke in new irecion. The saemen in he firs rung of laer iagram ses he iniial sae of he moel accoring o he iniial marking of he places M 0 an is execue in he firs cycle afer he PLC programme is sare. 3.5 Tesing Example imulaion wih he PLC emulaion was ese wih he PLC programme ha consiss of a 68 Perme, T.

11 rojniški vesnik - Journal of Mechanical Engineering 55(009)0, ranslae laer iagram of he EPN moel of he cyliner-valve sysem (Fig. 4) an he conrol par wih he es sequence (Fig. 5). The conrol par of he PLC programme was also moelle wih he EPN an ranslae ino LD. The EPN moel of he conrol algorihm for he es sequence was ae o he EPN moel of he ese sysem an verifie wihin he programme for iscree simulaion (Fig. 6). connecions from an o he conrol ransiions excep from he places a 0 an a (sensors) are sanar connecions. Connecions from he places a 0 an a are informaional connecions. Place sar represens sae of he sar buon an is se or rese manually. In real PLC his correspons o he inpu variable of he sar buon. M0 a0 ( M0) P 8 ( v) a P v v v a M0 9 ( v) nzj_bw ( ) P P P P 0 ( h) nzj_ bw h h 3 ( ) P P P P h n zj_ b w ( h) a0 4 ( v) a0 v P v v 5 ( v) npr_fw 6 ( h) npr_fw h 7 ( h) a0 h h npr_fw a npr_fw P n pr_fw ( ) nz j_bw = h nzj_bw n zj_ b w P 3 ( ) n pr_ fw Fig. 4. imulaion par of PLC programme = h Fig. 6. Tesing he simulaion an conrol par of he PLC programme wihin a programme for iscree simulaion Afer he valiaion of he conrol par of he PLC programme wih EPN moel in he programme for iscree simulaion (Fig. 6), also he EPN moel of he conrol par of he PLC programme was ranslae ino he laer iagram (Fig. 7). Fig. 5. Tes sequence of srokes The algorihm for he conrol sequence uses he sep funcion mehoology. Each sep in he sequence has a corresponing ransiion an place in he EPN moel. If he coniions (marking of he places) for he nex sep are fulfille han he corresponing ransiion fires an marks he nex sep place. Inpu places o hese ransiions (from sep_ o sep_7 in he EPN moel in Fig. 6) are places ha represen sep succession of conrol algorihm (se o sep7) an he places ha efine he sae of he cyliner-valve sysem (a 0 an a ). Oupu places of hese ransiions are places for he succession of conrol algorihm an places ha represen conrol signals o he valve ( an ). All 3 M0 sep7 se sar a a0 sep7 sep7 se se se se T se T3 a0 a0 T s se sep3 T3 3 s sep6 sep7 Fig. 7. Laer iagram of he conrol par of he PLC programme The firs rung ses he iniial sae an is execue only in he firs cycle. The rungs 4, 5, 0 an are ranslaions of wo nonzero-ime ransiions ha are neee o conrol he sep wih a elay of he conrol sequence. Oher six rungs Translaion of Exene Peri Ne Moel ino Laer Diagram an imulaion wih PLC 69

12 rojniški vesnik - Journal of Mechanical Engineering 55(009)0, represen insananeous ransiions ha swich he nex sep in he conrol sequence. 3.6 Tes of he imulaion Wih he PLC Emulaion The simulaion wih PLC emulaion was ese on wo PLC programming plaforms (CX- Programmer wih CX-imulaor from Omron an TEP 7 wih 7 PLCIM from iemens) ha comprehen also simulaion i.e. emulaion of PLC on a PC compuer. The conrol (Fig. 7) an simulaion par (Fig. 4) of he PLC programme were pu ino he PLC programme in he usual way of PLC programming. The PLC programme can be wrien for virual or real PLC. In boh cases he inpu an oupu variables have he same forma. Afer he PLC programme ha been ransferre o he emulae PLC (in he same way he PLC programme is ransferre o he real PLC), he PLC programme ran an simulae he operaion of he conrolle sysem. The simulaion of he sysem operaion was observe using a graphical presenaion of PLC programme execuion which programmers usually use in heir everyay work. A racking funcion (CX- imulaor) ha capures an presens he saes of he variables in ime char (Fig. 8) was also very useful. This is very convenien for eecing an eliminaing he errors in he PLC programme. Fig. 8. Time char of he saes of he en swiches a 0 an a racke uring he simulaion wih PLC emulaion (CX-imulaor) Fig. 9. Time char of he saes of he en swiches a 0 an a racke uring he simulaion of he EPN moel in Tecnomaix Plan imulaion Visual comparison of graphical presenaion of PLC execuion showe ha he conrol an simulaion par of he PLC programme as well as he concep of simulaion wih real or emulae PLC fulfille he expecaions. A confirmaion for ha is also he comparison of he ime chars of saes a 0 an a obaine by he simulaion of EPN moel in Tecnomaix Plan imulaion (Fig. 9) an by he PLC emulaion wih CX-imulaor (Fig. 8). 4 APPLICATION CAE AND THE PEPECTIVE The elaborae meho was use for moelling of an auomae assembly saion which was use in pracical lecures for learning abou he operaion an conrol of auomae componens, an programming of PLCs. The assembly saion consiss of elecro-mechanic iviing able, -axes eumaic manipulaor wih a gripper, wo screw rivers an conrol evice [7]. All axes an rives of all he componens in he assembly saion can be regare as iscree, san-alone an wo-posiion (iniial an en posiion) sysems, so heir operaion can be moelle in he same way as he operaion of he cyliner-valve sysem on Fig.. Each of he axes an rives is also auonomous, so he EPN moel of he assembly saion consiss of 8 sub-moels ( for -axes manipulaor, one for gripper, for each screw rive an one for iviing able). Experiences wih simulaion base on emulae PLC in a pracical course have shown ha his is a very useful learning ool for he curriculum in he fiel of assembly an hanling auomaion. There are wo paricularly imporan benefis o menion: - The operaion an programming of he PLC can be escribe an explaine wihou using a real sysem. This can be one in a lecure room or in a compuer room where each suen can programme an es he PLC programme on he PC compuer. - uens can use he PLC programming ool wih PLC emulaion on PC compuers a home an can in his way o more exercises an complee he assigne pracical work. In aiion, hey can es he alreay verifie PLC programme on real PLC in laboraory or even wih remoe access from home in a so calle remoe laboraory [7]. A combinaion of simulaion wih emulae PLC an remoe laboraory using 60 Perme, T.

13 rojniški vesnik - Journal of Mechanical Engineering 55(009)0, inusrial PLC programming ools, CADA base graphical user inerface an LabVIEW remoe panel for remoe laboraory is he irecion of moern ools for learning an raining of auomaion an mecharonics. 5 CONCLUION A conrol of moern auomae machines an evices in process an bulk proucion inusry is nowaays generally accomplishe by programmable logical conrollers (PLC). Knowlege abou PLC programming is he basis for pracical work of mechanical, elecrical an mecharonic engineers along he enire lifecycle of machines or plans from engineering o operaion, mainenance an moernizaion. The moelling an simulaion can significanly help he eaching an learning of PLC programming, raining of he operaors an mainaining personal, eveloping auomae sysems an iagnosis of he sysems operaion. The challenge for he presene work was o evelop a way of builing a moel an running a simulaion by he ools commonly use in he inusrial environmen. The basic iea was o use he PLC programming ool for moelling a iscree mecharonic sysem an simulae is operaion on inusrial PLC or on emulaion of PLC on he PC compuer. The main issue was o buil an accurae an vali simulaion moel wih a ool esigne for wriing he conrol programmes. For he realizaion of he iea he exensions of he basic Peri ne heory (EPN) were elaborae, which enable a builing of an accurae moel of a iscree sysem incluing a relae conrol programme. Unifie, irec ranslaion of he EPN moel ino he laer iagram was evelope, which enable he use of he EPN moel for simulaion on PLC or emulaion of PLC. Furhermore, he builing blocks of he EPN moel were evelope wihin he programme for iscree simulaion, which enable he builing an verificaion of an EPN moel wihin he programme for iscree simulaion. The elaborae exensions an evelope ools were primarily ese on a case of operaion of ouble acing eumaic cyliner wih a 4/- way valve. The resuls of he verificaion of he EPN moel wih iscree simulaion an he simulaion of he cyliner-valve sysem on he emulae PLC show ha he elaborae exensions of Peri ne an he evelope ranslaion of EPN moel ino he laer iagram compleely fulfil he sele requiremens an can be use in pracice. The usabiliy of he basic iea was verifie uring he pracical course on assembly auomaion. The simulaion on emulae PLC was use for explaining he basics of PLC programming an for eveloping he conrol programme for a real auomae assembly saion. The resuls show ha he meho is applicable for eaching an learning of PLC programming as well as for avance eveloping an esing of PLC programmes. The fuure of he meho in inusry is in he fiel of raining an inroucing of operaors an mainainers before sysem insallaion, an for moel base iagnosic of auomae sysem. 6 EFEENCE [] Frey, G., Lohar, L. Formal mehos in PLC programming, Proceeings of he IEEE Conference on ysems Man an Cyberneics MC 000, Nashville, Oc. 8 -, 000. [] Bogan,., molić-očak, N., Kovačić, Z. A esbe for analysis of PLC-conrolle manufacuring sysems. Proceeings of he 0h Meierranean Conference on Conrol an Auomaion - MED00, Lisbon, Porugal, July, 9 -, 00. [3] Polič, A., Jezernik, K. Close-loop marix base moel of iscree even sysems for machine logic conrol esign. IEEE ransacions on inusrial informaics, February 005, vol., no., p [4] Iversen, W. Digial manufacuring: Chasing he vision, AuomaionWorl, April 008. [5] Waurzyniak, P. (007) Ener he virual worl: A new generaion of igial manufacuring sofware ools offer manufacurers a beer virual facory, Manufacuring Engineering, vol. 39, no. 4. [6] Perme, T., Noe, D. A "Low-cos" soluion of virual manufacuring sysems. Preprins of he 3 h worl congress Inernaional Feeraion of Auomaic Conrol, an Francisco, UA, June, 30 - July, vol. E, [an Francisco]: IFAC, 996, p Translaion of Exene Peri Ne Moel ino Laer Diagram an imulaion wih PLC 6

14 rojniški vesnik - Journal of Mechanical Engineering 55(009)0, [7] Perme, T., Drev, V., Noe, D. emoe assembly sysem for eucaion. Inernaional ymposium on emoe Engineering an Virual Insrumenaion 006, June, 9-30, 006, Maribor. [8] Perme, T., Noe, D. E-raining remoe assembly sysems. IFAC Mulirack Conference on Avance Conrol raegies for ocial an Economic ysems, Vienna, epember, - 4, 004. [9] Kopacek, P., Kronreif, G., Perme, T. imulaion wihin CAD-environmen. In: Branimare, P. (eior), Villa, A. (eior). Moeling manufacuring sysems: from aggregae planning o real-ime conrol. Berlin [ec.]: pringer, 999, p [0] Perme, T., Noe, D. Erweiere Perineze zur inelligenen Planung von Proukionssysemen. In. j. auom. Ausria, 00, vol. 0, no., p. -4. [] Perme, T., Noe, D. imulaion mi Erweieren Peri-Nezen zur Planung von Monagesysemen. In. j. auom. Ausria, 004, vol., no., p. -6. [] Kunc, M. A., Kunc, V., Diaci, J., Karba,. (008), Moelling an analysis of a combine elecronic an micro-mechanical sysem, rojniški vesnik - Journal of Mechanical Engineering, vol. 54, no. 7-8, p [3] Maa, A., emeraro, Q., (eiors) Design of Avance manufacuring ysems: Moels for Cpaciy Planing in Avance Manufacuring ysems, pringer 005. [4] Mušič, G, Graišar, D. Mako, D. IEC 63-3 Complian Conrol Coe Generaion from Discree Even Moels, Proceeings of he 3 h Meierranean Conference on Conrol an Auomaion, Limassol, June, 7-9, 005, p [5] Peng,.,., Zhou, M., C. Laer Diagram an Peri-Ne base Discree-Even Conrol Design Mehos, IEEE Transacions on ysem, Man, an Cyberneics, vol. 34, no. 4, November 004. [6] Peng,., Zhou, M.C. ensor-base Peri ne moeling for PLC sage programming of iscree-even conrol esign, Proceeings of he 00 IEEE Inernaional Conference on oboics an Auomaion, Washingon DC, May 00. [7] Laha, K., Umamaheswari, B. upervisory conrol of an auomae sysem wih lae logic programming an analysis using Peri nes. In: Proceeings of he secon IEEE Inernaional Conference on ysems, Man an Cyberneics (MC'0), Ocober, 6-9, 00, Hammame, vol. 3, IEEE Compuer ociey Press, Ocober 00. [8] Peerson L.J. 98, Peri ne heory an moeling of sysems. Prenice-Hall Inernaional. [9] eisig, W. Perineze; Eine Einführung, pringer-verlag, 99. [0] Muraa, T. (989), Peri nes: properies, analysis an applicaions, Proceeings of he IEEE, vol. 77, no. 4, p [] Arsovski,., Arsovski, Z., Mirovic, Z. (009) The inegraing role of simulaion in moern manufacuring planning an scheuling. ojniški vesnik - Journal of Mechanical Engineering, vol. 55, no., p Perme, T.