USING SIMULATION TOOLS IN THE DEVELOPMENT OF A NETWORKED CONTROL SYSTEMS RESEARCH PLATFORM

Transcription

1 ABCM Syposiu Seies in Mechatonics - Vol. 4 - pp Copyight Poceedings of COBEM by ABCM 9 Copyight 9 by ABCM th Intenational Congess of Mechanical Engineeing Novebe 5-, 9, RS, Bazil USING SIMULAION OOLS IN HE DEVELOPMEN OF A NEWORKED CONROL SYSEMS RESEARCH PLAFORM Eduado Paciência Godoy, epgodoy@yahoo.co.b Athu José Vieia Poto, ajvpoto@sc.usp.b Depatent of Mechanical Engineeing, EESC - Engineeing School of São Calos, USP Univesity of São Paulo Avenida abalhado São calense, 4 CEP , São Calos, São Paulo, Bazil Ricado Yassushi Inaasu, icado@cnpdia.ebapa.b EMBRAPA - Bazilian Agicultual Instuentation Reseach Copoation Rua XV de Novebo, 45 CEP , São Calos, São Paulo, Bazil Abstact. he intoduction of fieldbus achitectues in industial systes can ipove the efficiency and the eliability of the contol syste educing tie and costs of installation and aintenance. A cuent tendency in the eseach of fieldbus based contol systes such as CAN (Contolle Netwok Aea) is the use of netwoked contol systes (NCS). his new appoach diffes to the taditional fieldbus systes since the contolle and the plant ae physically sepaated and connected though an industial netwok. he ain challenges elated to the developent of NCS ae the effects caused by the inclusion of the counication netwok in the closed loop contol syste. he pesence of netwok delays between the sensos, actuatos and contolles of the contol syste can degade the pefoance and destabilize the syste. o iniize these effects, siulation tools fo NCS have been developed to assist the designe in the study of the netwok influence in the pefoance of the contol syste. hese tools also allow the developent and application of contol ethodologies to handle the netwok delay effect in these systes ipoving thei pefoances and stability. his pape pesents the application of these siulation tools in the developent of a NCS eseach platfo coposed by seveal contol systes connected though a CAN-based netwok. he tools ae used to analyze the netwok delays effects, to obtain pefoance paaetes and to design contol ethodologies fo all contol systes of the NCS platfo. he esults of the siulations allow the definition of design paaetes such as sapling ties and contolle gains, and the veification of how sensitive the contol loops ae unde vaious tiing conditions including sapling ties and netwok delays. heefoe, the utilization of siulations tools can ease the developent of NCS and helps the designe to evaluate the contol syste pio to its ipleentation. Keywods: netwoked contol syste, tiing uieents, netwok delays, pefoance paaetes. INRODUCION Recent applications of distibuted fieldbus based contol systes deonstate a new appoach fo the use of industial netwoks. In this type of application, called of Netwoked Contol Systes (NCS), the contolle, the senso and the plant ae physically sepaated and connected though a counication netwok (Yang, 6) as shown in Fig.. he contol signal is sent to the contolle by a essage tansitted ove the netwok while the senso saples the plant output and etuns the infoation to the contolle also tansitting a essage ove the netwok. Netwoked contol systes have eplaced the taditional centalized contol systes in anufactuing systes because of seveal benefits such as educed cost and aount of wiing, inceased eliability and inteopeability, ipoved capacity fo syste econfiguation and ease of aintenance (Moyne and ilbuy, 7). Physical Physical u y u y Plant Plant n Actuatos Sensos Actuatos n Sensos n sg sg sg sg delay Contolle Netwok delay netwokinduced delay delay Contolle n Figue. Stuctue of a NCS Although the NCS offes seveal advantages ove taditional centalized contol systes, the existence of counication netwoks ake the analysis and design of a NCS coplex. Netwoked contol systes ipose additional pobles inheent in contol applications that ae usually difficult to eet due to the vaiations and uncetainties intoduced by the counication netwok: delays, jitte, bandwih liitations and packet losses

2 ABCM Syposiu Seies in Mechatonics - Vol. 4 - pp Copyight by ABCM (Baillieul and Antsaklis, 7). he netwok-induced delays and data packet dopouts occu when sensos, actuatos, and contolles exchange data acoss the netwok. he chaacteistics of netwok-induced delays ae ainly deteined by the potocol used in the NCS (Lian, Moyne and ilbuy, ). Godoy, Poto and Inaasu (8) descibe the coponents of the netwok-induced delays in NCS and pesent the possible effects of the counication netwok in the pefoance and stability of NCS. Because of the netwok delays vaiability, the NCS can pesent chaacteistics of tie vaiant systes doing the analysis and design of these systes even oe coplicated. Othe pobles elated to the NCS ae the coect choice of the netwok configuation paaetes such as the netwok bandwih, essages data length and essages sapling tie. hese paaetes also influence the netwok pefoance (Lian, Moyne and ilbuy, ). he NCS ust saple and tansit data at a sapling tie appopiate to achieve uied pefoance etics. Howeve, if this sapling tie is highe than the netwok bandwih available, the netwok becoes oveloaded, oiginating additional netwok delays and jitte, and causing packet losses and eos tansissions (Al- Haoui, Banicky and Libeatoe, 8). heefoe, NCS geneally ust eet two ain citeia: bounded netwok delay and guaanteed tansission; that is, a essage should be tansitted successfully within a bounded netwok delay. Unsuccessfully tansitted o lage netwok delay in essages fo a senso to an actuato ay deteioate syste pefoance o ake systes unstable (Godoy, Poto and Inaasu, 8). Cuently two ain eseach diections can be distinguished in the NCS aea. One focused in the developent and use of specific tools to siulate the opeation and to ease the analysis of the netwok influence in the pefoance and stability of the NCS (Cevin et al, 3, ongen et al, 6; Al-Haoui, Banicky and Libeatoe, 8). And othe in the developent of contol and design ethodologies to handle the netwok effects ipoving the pefoance and guaanteeing the stability of the NCS (Zhang, Banicky and Phillips, ; ipsuwan and Chow, 3; Hespanha, Naghshtabizi and Xu, 7). Designing a NCS is essentially a ultidisciplinay poble. Definitions ade in the counication netwok design will affect the contol design and vice vesa. he use of these specific tools can allow veification and evaluation of how NCS pobles affect the opeation of the syste and siulation of the tiing behavio of the NCS pio to its ipleentation saving tie and educing design costs. Following this guideline, this pape pesents the application of two siulation tools in the developent of a NCS eseach platfo coposed by seveal contol systes connected though a CAN-based netwok. he ueie and Jittebug tools (Cevin et al., 3) wee used to analyze the netwok delays effects, to obtain pefoance paaetes and to design contol ethodologies fo all NCS of the platfo. he esults of the siulations allow the definition of design paaetes such as essage sapling ties and contolle gains and the veification of how sensitive the contol loops ae unde vaious tiing conditions including sapling ties, netwok delays and jitte pobles. 3. SIMULAION OOLS FOR NCS 3. Backgound and Coon Pefoance Metics Many woks in ecent yeas has been developing specific tools to help the analysis and design of NCS that ege knowledge of thee topics: contol systes, counication netwoks and eal-tie systes (ongen et al, 6; Al- Haoui, Banicky and Libeatoe, 8). he ajoity of these tools have been developed in the Matlab/Siulink envionent, stiulated by its lage acceptance and disseination in the acadeic and industial aeas. Each of these tools was developed in the acadeic aea and is dedicated to one o a few tasks usually focused in one of these topics. he ueie and Jittebug tools (Cevin et al, 3) ae specifically developed fo contol design tasks. In ueie the designe can odel the entie NCS using a Siulink block libay. his libay allows the definition of paaetes fo the netwok potocol, the developent of the contol technique used and the selection of the plant odel. he Jittebug tool has a high level of abstaction in the definition of netwok delays and jitte but allow the calculation of a pefoance index elated to the NCS quality of contol. he AIDA (Redell, El-Khouy and ongen, 4) and ORSCHE (Sucha et al, 6) ae tools fo design and analysis of eal-tie chaacteistics of NCS. he AIDA is used fo tiing analysis and the application of scheduling schees fo optiization of tie esponse is the ajo pupose of the ORSCHE tool. he PiccSIM (Nethi et al, 7) tools povide the functionality of use in the Intenet. he designe can upload his contol algoith, define soe paaetes and use a few plant odels fo the siulation of the NCS. Despite of these Matlab based tools, is not difficult to find tools fo NCS developed in othe platfos such as Labview (Pinnoti J e Bandão, 5) and Modelica (Liu and Fey, 8). hese specific tools povide facilities to analyze the behavio and opeation of the NCS by eans of siulation. he siulation eases the evaluation of esults, because lets the eplication of the expeient fo the sae odel of the NCS. Vaying only desied paaetes in these eplications, oe specific infoation about the NCS can be achieved (Cevin et al, 3). With this functionality, the designe can bette evaluate the changes done o the defined paaetes in the NCS design accoding to coon pefoance etics used in these systes (Acton et al, 6). hus the evaluation of NCS has been usually focused in the following tasks: o analyze which factos (netwok delays, counication netwok paaetes, signal sapling ties) can affect the pefoance o stability of NCS; o analyze how facto is the ost significant o that oe influence in the design of NCS;

3 ABCM Syposiu Seies in Mechatonics - Vol. 4 - pp Copyight Poceedings of COBEM by ABCM 9 Copyight 9 by ABCM th Intenational Congess of Mechanical Engineeing Novebe 5-, 9, RS, Bazil 3.. ueie ool o analyze pefoance etics elated to contol and stability of the NCS such as settling tie, ise tie, oveshoot, steady state eo, stability agin and phase agin; o analyze pefoance etics elated to the counication netwok such as netwok utilization, netwok delays, netwok bandwih and essages sapling ties); o analyze pefoance etics elated to eal-tie systes such as jitte, pocesso utilization, esponse tie, deadlines, latency, scheduling and pioitization. he ueie tool ( is a MALAB/Siulink toolbox used to ease the siulation of opeation and tiing behavio of NCS, ebedded systes o distibuted systes with ultiple contolles opeating in eal-tie. he tool consists of a Siulink block libay, basically with a copute kenel block and wied and wieless netwok blocks, as shown in Fig., and a collection of Matlab MEX files. he entie NCS can be defined in the tool using the available blocks since the plant odel, the contolle algoith until the counication netwok used (Cevin et al., 3). he blocks ae vaiable-step, discete, MALAB S-functions witten in C++. D/A A/D Snd Inteupts Schedule Monitos Rcv P ueie Kenel Rcv Snd Schedule ueie Netwok cv data ttgetmsg data snd ttsendmsg Snd Rcv P E x Schedule ueie Battey y P ueie Wieless Netwok Figue. ueie Block Libay he kenel block siulates a eal-tie kenel executing use-defined tasks and inteupt handles epesenting I/O tasks, A/D and D/A convetes, contol algoiths and netwok intefaces. he scheduling policy of the kenel block is abitay and decided by the use. he netwok blocks distibute essages between copute nodes accoding to a chosen netwok odel. he blocks ae connected with odinay continuous-tie Siulink blocks to fo a eal-tie distibuted counication syste. All outputs ae discete-tie signals (Ohlin, Heniksson and Cevin, 7). he vaious netwok blocks allow nodes (kenel blocks) to counicate ove siulated wied o wieless netwoks. he ueie netwok blocks siulate the physical laye and the ediu-access laye of vaious local-aea netwoks. he blocks only siulate the ediu access (the scheduling), possible collisions o intefeence, and the point-to-point and boadcast tansissions. Fo wied netwoks, six odels ae suppoted: Ethenet switched Ethenet, CAN, token-ing, FDMA, and DMA. he wieless netwok block suppots siulation of the IEEE 8. WLAN and IEEE ZigBee standads. ueie uses have been developing high laye potocols using the netwok blocks fo NCS siulations such as CP based on the CSMA/CD and FlexRay based on the DMA. In the netwoks odels ipleented in ueie, only the inteactions between nodes elevant fo the tiing behavio of the tansissions ae odeled. hat includes pe and post pocessing delays, collision detection and collision avoidance echaniss, and pobabilities of lost packets. A essage contains infoation about the sending and the eceiving copute node, abitay use data (typically easueent signals o contol signals), the length of the essage, and optional eal-tie attibutes such as a pioity (Ohlin, Heniksson and Cevin, 7). ueie siulation is pogaed in the sae way as a eal NCS syste. he application is witten in Matlab code o in C++. he execution of tasks and inteupts ae defined by code functions. Each task is defined by a set of attibutes (pioity, deadline, peiod, etc.) he ain diffeence fo eal pogaing is that the execution/tansission ties ust be specified by the develope. his appoach gives high flexibility to the ueie siulation tool. 3.. Jittebug ool he Jittebug tool ( is a MALAB toolbox that allows the application of the Linea Quadatic Gaussian optial contol theoy (LQG) fo NCS. he tool is coposed by a set of Matlab functions that ake inteface to the Contol Systes toolbox. hese functions execute the tool initialization, configuation of NCS paaetes and the calculation of a pefoance index o a cost function elated to the contol of the NCS. he cost function can easily be evaluated fo a lage set of design paaetes and can be used as a basis fo the contol and eal-tie design. Highe values of the cost function usually indicates oe oscillatoy o less stable closed loops of the NCS. Infinite cost eans that the contol loop is unstable. Jittebug can be used to deive tiing uieents fo contol pefoance specifications. he deived uieents ae expessed in tes of the sapling ties, latency, jitte, and netwok delays (Cevin and Lincoln, 6). An ipotant aspect in this tool is the possibility

4 ABCM Syposiu Seies in Mechatonics - Vol. 4 - pp Copyight by ABCM the copute a gaphic of the spectal density of the tiing conditions in the NCS elated to the quality of contol. Fo exaple, a cuve elating the quality of contol of a plant in closed loop to the sapling tie and jitte of the NCS. In the Jittebug tool, the NCS is descibed by two odels showed in Fig.3: the signal odel and the tiing odel (Cevin and Lincoln, 6). he signal odel coesponds to the connection diaga of the continuous tie and discete tie linea systes that copose the NCS (plant, contolle, senso and actuato). he tiing odel is quite siplistic and descibes the execution suence of the NCS discete systes duing a contol peiod. he netwok delays in a contol peiod ae assued to be independent fo peiod to peiod. In the siplest case, a peiodic tiing odel with ando delays is used to descibe the execution of the discete-tie systes, fo exaple the contol task. Figue 3 pesents an exaple of the two odels uied fo the use of the Jittebug tool in a NCS. Fo NCS, the contol syste is descibed by fou subsystes. he signal odel showed in Fig 3(a) define the plant o pocess as a continuous tie syste (G), and the senso (H), the actuato (H3) and the contolle (H) as discete tie systes. Iplicit in each discete-tie block is a saple at the input and a zeo-ode-hold cicuit at the output. he tiing odel showed in Fig. 3(b) define the execution of a contol peiod of the NCS. he subsyste H o the senso is executed fist with a ando netwok delay (τ). Afte, the contolle (H) is executed with a defined netwok delay (τ). Finally occu the execution of the subsyste H3 epesenting the actuato. he netwok delays in the tiing odel can be used to odel delays induced by any kind of task in the NCS such as codification and pocessing ties, scheduling ties, and essage tansission ties in a counication netwok. his option povides a high flexibility of use fo the tool because it can be applied to siulate any kind of netwok potocol fo NCS. Howeve, the netwok influence will be odeled in a siplistic way and the designe of the NCS o the tool use will have to know the bette value distibution to odel the netwok delays. (a) (b) Figue 3. Jittebug Model of a NCS: (a) Signal Model (b) iing Model 4. DEVELOPMEN OF HE NCS PLAFORM 4.. Poposed NCS Platfo Accoding to Pinotti J and Bandão (5), the inceasing use of distibuted contol systes with coon bus achitectues in industial contol has deanded the inclusion of fieldbus systes in acadeic teaching and educational laboatoies. Many woks have been developing this platfos fo fieldbus eseach and teaching (Matín and adeo, 6; Kolla, 7). But fo NCS, that epesents a diffeent application of fieldbus technologies, these platfos ae not so fuent. he platfo poposed in this pape is being developed fo NCS study and would epesent a sall-scale anufactuing syste coposed by seveal closed loop contol systes. he counication netwok used fo the contol systes integation and infoation exchange is the CAN potocol. he achitectue of the poposed NCS platfo is shown in Fig. 4. Coon contol systes used in the industial aea such as DC oto velocity and position contol, tepeatue contol, tank level contol and belt conveyo contol ae selected fo the platfo. Each of the defined systes has an electonic contol unit () esponsible fo the data acquisition, actuation in the plant and counication with the CAN-based netwok. wo desktops with LabVIEW and PCI-CAN intefaces (NI, 8) fo National Instuents ae used fo the developent of the contol ethodologies of the NCS. he achitectue poposed has high flexibility fo the eseach and teaching of NCS. In addition to the aied tasks fo NCS such as analysis, odeling, siulation and contol, the platfo povides capabilities to study and applies advanced techniques fo NCS developent. Aong these techniques ae the eal-tie evaluation, hadwae-in-the-loop siulation and apid contol pototyping. Fo each of the NCS that coposes the platfo, the tie-diven senso node saples the plant o pocess peiodically and sends the saples to the contolle node ove the CAN netwok. Upon eceiving a saple, the contolle coputes a contol signal which is sent to the actuato node, whee it is subsuently actuated. he theads executing in the contolle and actuato nodes ae both event-diven. All the closed loop contol systes in the platfo ae shaing both liited CAN-based netwok bandwih and contolle CPU. he copetition fo these constained esouces will cetainly incease the netwok-induced delays of the contol loops can degading the oveall pefoance of NCS in the platfo.

5 ABCM Syposiu Seies in Mechatonics - Vol. 4 - pp Copyight Poceedings of COBEM by ABCM 9 Copyight 9 by ABCM th Intenational Congess of Mechanical Engineeing Novebe 5-, 9, RS, Bazil DESKOP CONROLLERS CLOSED LOOP - LEVEL Senso ON/OFF CONROL -BEL CONVEYOR SUPERVISORY AND DAA LOGGING NI PCI-CAN Actuato NI USB-CAN CAN Netwok Senso Actuato Senso Actuato CLOSED LOOP - VELOCIY Senso CLOSED LOOP 3 - EMPERAURE MICRO- CONROLLERS Actuato CLOSED LOOP 4 - POSIION Figue 4. Achitectue of the NCS Platfo he chosen of the CAN potocol (Bosch, 6) fo the counication netwok due to its low cost of developent and lage acceptance in the industial and acadeic aeas. he CAN was oiginally developed to inteconnect electonic contol units () in autootive aea, but ecently has also been applied in any othe netwoked contol applications. Cuently, CAN-based netwoks ae applied as a solution fo distibuted contol systes in seveal aeas, such as obotic, autoated anufactuing and pocess contol envionents, and used in popietay achitectues such as Device Net and CAN Open (CIA, 6). As descibed in Johansson, ongen and Nielsen (5), in CAN-based netwoks data ae tansitted and eceived using essage faes that cay data fo a tansitting node to one o oe eceiving nodes. An identifie, unique thoughout the netwok, labels each essage of the node and its value defines the pioity of the essage to access the netwok. he CAN potocol is optiized fo shot essages and uses a CSMA/CD with NDBA (Caie Sense Multiple Access / Collision Detection with Non-Destuctive Bitwise Abitation) abitation access ethod. he bit stea of a tansission is synchonized on the stat bit, and the abitation is pefoed on the following essage identifie, in which a logic zeo is doinant ove a logic one. 4.. Siulation and Analysis he use of siulation tools is necessay fo the developent of the NCS platfo because they help the designe to evaluate the contol syste pio to its ipleentation saving tie and educing design costs. Selecting a tool fo NCS design depends on the syste specifications and the uied esults. In consuence, the ueie and Jittebug tools wee selected to be used in the NCS platfo developent. Fo the platfo poposed, the ueie tool ae used to analyze the CAN netwok delays effects, to obtain pefoance paaetes and to design contol ethodologies fo all contol systes. he Jittebug tool is used to evaluate how sensitive one contol loop of the platfo is unde vaious tiing conditions iposed by the dynaics of the whole NCS platfo opeation. Fistly the entie odel of the NCS platfo was developed in the ueie tool. he atheatical odel of each contol syste was obtained by available uations and expeiental pocedues. In a known ethod, a step esponse gaph of the open loop plants was used too fo the paaetes estiation of the plants tansfe functions. he belt conveyo syste was not included in the platfo odel because it uses an on/off contolle. Its influence in the platfo opeation was included by a node that only sends and eceive essages in the CAN netwok. he DC oto used fo velocity contol was a Moton M-9 (4V). he Eq. () to (4) ae the basic elations fo atheatical odeling of DC otos. With the paaetes: R oto esistance (Ω); V voltage applied to the oto (V); I cuent applied to the oto (A); L oto inductance (H); V ef back ef voltage (V); Ke oto ef constant (V.s/ad); w angula velocity of the oto shaft (ad/s); θ angula otation of the oto shaft (ad); K oto toque constant (N./A); toque applied to the oto shaft (N.); η oto efficiency (%); J inetia of the oto shaft (Kg. ); B uivalent viscous fiction (N..s/ad). di V R. I + L. + V ef () V K. w, with w ef e dθ () η. K I (3). dw w (4) J. + B.

6 ABCM Syposiu Seies in Mechatonics - Vol. 4 - pp Copyight by ABCM Applying the Laplace tansfo and eaanging the uations, the tansfe function fo the DC oto velocity contol can be done by the Eq. (5). he final tansfe function was obtained with the eplaceent of the paaetes fo datasheets and expeiental pocedues and disegading the effects of the lowe values of the oto inductance. w V () s η J. L. s + ( B. K. L + J. R). s + K. K + B e.886. R,798. s +,844 (5) Fo the position contol, a DC oto Maxon REax (4V) with planetay geabox was selected to be used. he atheatical odeling fo this case needs additional elations. Fo this pupose, the Eq. (6) to (9) was used with the basic elations descibed ealie in Eq. () to (4). With the paaetes: k geabox eduction (9:); θ angula otation of the geabox shaft (ad); toque in the geabox output (N.); η geabox efficiency (%); J inetia of the geabox (Kg. ); J uivalent inetia of the syste (Kg. ). θ k. θ (6) J d θ. + (7) η. k d θ dθ J. B. (8) J J +η. k. J (9) Using the uations and applying the Laplace tansfo, the tansfe function fo position contol of a DC oto with geabox is showed in the Eq. (). he tansfe function was obtained with the eplaceent of the paaetes fo datasheets and expeiental pocedues and disegading the effects of the lowe values of the oto inductance. θ η. k. η. K 38 () s () 3 V J. Ls. + ( B. L+ J. R). s + ( η. k. η. K. K + B. R). s,476. s + 3,59. s e he atheatical odeling fo the one esevoi level contol uses the elations given by the ass balance and tubulent flow in systes. hus, the Eq. () and () wee used fo the odeling. he lineaization of the nonlinea Eq. () can be done in a selected opeation point ( ( h, q), in Eq. (3), consideing that eos in the odel fo low vaiations aound this point ae insignificant, esulting in the final Eq. (4). With the paaetes: q i input flow of pup in esevoi [c 3 /s]; q o output flow of esevoi [c 3 /s]; h level in esevoi [c]; k valve chaacteistics consideing tubulent flow (obtained expeientally k 8); A coss section of the esevoi (79.5 c ). dh A. q i q o () q o k. h () dh. h. h R (3) dq q k dh A. qi. h (4) R Applying the Laplace tansfo and eaanging the uations, the tansfe function fo the esevoi level contol can be done by the Eq. (5). he final tansfe function was obtained with the eplaceent of the paaetes fo expeiental pocedues and using the selecting point h 9 c. h( s) q ( s) i A. s + R R 375 A. R. s + 67,3. s + (5) he atheatical odeling fo the tepeatue contol uses the elations given by the enegy consevation and convection heat tansfe in theal systes. hus, the Eq. (6) to (8) wee used fo the odeling. With the paaetes: q o output heat flow [W]; q i input heat flow (using a W and 3,9Ω esisto)[w] ; s tepeatue easued by the senso [ C]; d( s a ) qi qo C. (6)

7 ABCM Syposiu Seies in Mechatonics - Vol. 4 - pp Copyight Poceedings of COBEM by ABCM 9 Copyight 9 by ABCM th Intenational Congess of Mechanical Engineeing Novebe 5-, 9, RS, Bazil a abient tepeatue [ C]; tepeatue change [ C]; R theal esistance [ C/W]; θ dead tie elated to the step esponse of the syste [s]; C theal capacitance (J/ C]. q o.( s a ) (7) R s (8) a Using the uations descibed plus the coon dead tie inheent to theal systes and applying the Laplace tansfo, the tansfe function fo tepeatue contol can be done by the Eq. (9). he final tansfe function was obtained with expeiental pocedues based on the step esponse gaph. ( s) R θ. S 7,9 S (9) e e q s. ( ) R. C. s s +. i With the plant odels fo the NCS of the platfo, the contolles could be designed fo each syste. hese contolles have to conside all issues pesented in the NCS of the platfo such as actuatos satuation and sapling ties copatible to the hadwae s used. Accoding to Pohjola (6), contolles fo NCS cannot be designed with classical contol theoy of continuous tie systes because the esulting pefoance is unsatisfactoy. he contolles fo NCS have to handle the netwok delay effects in the systes. Based on the flexibility and lage application, a PID contolle was defined to be designed fo the systes in the NCS platfo. he contolle is a discete-tie PID contolle deived with the backwad deivative appoxiation and with setpoint weighting, efeence off and filteing on deivative pat. his contolle has been applied fo NCS with good esults (Pohjola, 6). In this wok, an antiwindup of the integal action was added to this contolle to wok with satuation of the actuatos. hus, the esulting discete-tie contolle with constant sapling tie (h) and constant filteing of the deivative pat (N) is showed in the Fig. (5): e( ( y( u ( K. e( p K. h K. h ui ( ui ( k ) + e( + es ( k ) t u d ( u( u p d d Kd N u d ( k ) + + Nh + Nh ( + u ( + u i i d ( d [ y( y( k ) ] (a) (b) Figue 5. Discete-ie PID Contolle fo NCS: (a) Scheatic (b) Paaetes Ipleentation With all systes (contolles, actuatos and sensos) of the platfo defined and ipleented in the ueie tool, seveal siulations of the NCS platfo opeation wee done. A netwok tansission speed of 5Kbit/s and essages data length of two bytes fo all the s wee defined fo the CAN netwok. Dealing to the hadwae used in the s (PIC icocontolles), a sapling tie of s (.s) was deteined fo the NCS of the platfo. A value of N was used in the constant filteing of the contolles. he objective of the siulations wee to design and tuning the contol ethodologies based on PID contolles and to obtain pefoance paaetes such as oveshot and settling tie that achieves the uieents defined fo all contol systes of the NCS platfo. Fo exaple, the ain uieent fo the NCS of DC oto position contol is do not pesent oveshoot. Afte soe siulations and analysis, the pefoance achieved fo the NCS of the platfo ae showed in Fig. 6 and 7. he ab. pesents a synthesis of the infoation obtained afte the siulations of the NCS platfo. he best pefoance etics achieved fo all of the NCS ae showed. he PID contolle gains could have been defined in ageeent to othe necessay design paaetes such as sapling tie. hei values ae also showed in the ab. able. Infoation about PID Contolles and Pefoance fo the NCS of the Platfo NCS of the Platfo Contolle Paaetes NCS Pefoance Measues K i d Oveshoot (%) Peak tie (s) Rise ie (s) Settling ie (s) DC Moto Velocity Contol,36,65 6,5,9.,5 DC Moto Position Contol 3,,84,9 epeatue Contol 7.,, 5 8, Level Contol,9 5,39 49,88 4,3 65,

8 ABCM Syposiu Seies in Mechatonics - Vol. 4 - pp Copyight by ABCM DC Moto Velocity - w (ad/s) Step Response - Velocity Contol ie (s) DC Moto Position - theta (ad) Step Response - Position Contol ie (s) Contol Signal - u (V) ie (s) Contol Signal - u (V) ie (s) (a) (b) Figue 6. Pefoance of the DC Motos NCS: (a) Response and Contol Signal fo Velocity Contol (b) Response and Contol Signal fo Position Contol epeatue Change - ( C) 5 5 Step Response - epeatue Contol ie (s) Resevoi Level - h (c) 9 5 Step Response - Level Contol ie (s) Contol Signal - u (W) ie (s) Contol Signal - u (c 3 /s) ie (s) (a) (b) Figue 7. Pefoance of the othe NCS: (a) Response and Contol Signal fo epeatue Contol (b) Response and Contol Signal fo Level Contol he siulations allow veify that seveal paaetes can influence the pefoance of a NCS. Aong these paaetes ae the netwok speed and load, essage pioitization, netwok delays and sapling tie. But the ost ipotant paaete that affected the NCS of the platfo was the sapling tie. o evaluate the contol sensitivity of the NCS unde diffeent sapling ties the Jittebug was used. his tool calculates a pefoance index elated to the contol of the NCS. Highe values of the cost function usually indicates oe oscillatoy o less stable closed loops of the NCS o even oe its instability. he netwok delays in the NCS of the platfo wee odeled by the two ando vaiables τ and τ. he total delay fo sapling to actuation is given by τ total τ + τ. As a cost function, the su of the squaed pocess input and the squaed pocess output was chosen deteining the uation (X). J li [ y ( t) u ( t)] + (X) he Fig. 8 and 9 shows the esults fo two (the DC oto position contol and the level contol) of the NCS of the platfo. he gaph in these figues pesents the values of the cost function o the quality of contol of the NCS elated to diffeent tiing conditions of sapling ties and netwok delays. he analysis of these gaphs allows veify that despite the sapling tie is the ost significant facto in the design of NCS, its influence was elated to the kind of syste. In Fig. (8) the NCS fo DC oto position contol epesents a NCS fast dynaics. In this type of syste, the influence of the sapling tie is big. Looking in the gaph, sall vaiations in the sapling tie can hadly affect the pefoance of the syste. he NCS was siulated fo sapling tie fo to.5s. his conclusion could be veified too in siulations fo the DC oto velocity contol, which epesents a syste with fast dynaics too.

9 ABCM Syposiu Seies in Mechatonics - Vol. 4 - pp Copyight Poceedings of COBEM by ABCM 9 Copyight 9 by ABCM th Intenational Congess of Mechanical Engineeing Novebe 5-, 9, RS, Bazil Quality of Contol - Cost Function - J Sapling ie - h [s] Netwok Delay (in % of h) Figue 8. Sensitivity of the NCS Position Contol unde Diffeent iing Conditions On the othe hand, the influence of the sapling tie in NCS with lowe dynaics is salle. In the gaph of the Fig. (9) that epesents the esults of the NCS fo level contol, this fact can be veified. he effect in the pefoance of this type of NCS is salle fo bigge vaiations in the sapling tie. Look that te NCS was siulated fo sapling tie fo to s. Quality of Contol - Cost Function - J Sapling ie - h [s] Netwok Delay (in % of h) Figue 9. Sensitivity of the NCS Level Contol unde Diffeent iing Conditions Futue wok will be done to finish the constuction and integation of all NCS of the platfo. With the platfo woking in laboatoy, the designed contolles will be ipleented in each NCS and seveal expeients could have been ade to veify the contolle design and evaluate the use of siulation tools fo NCS. 5. CONCLUSIONS Designing a NCS is essentially a ultidisciplinay poble. Definitions ade in the counication netwok design will affect the contol design and vice vesa. Because of this, the use of siulation tools is necessay fo the developent of the NCS platfo. In this pape was pesented the application of two siulation tools fo the developent of a NCS eseach platfo. A bief evision about specific tools developed to help the design of NCS and coon pefoance etics used to evaluate its pefoance wee also pesented. he ueie tool was used to analyze the netwok delays effects and to evaluate the influence of design paaetes such as sapling ties in the pefoance of the NCS. he application of this tool also allows the design of contol ethodologies fo all NCS platfo. he poposed PID contolles wee designed and the contolle gains ae deteined in ageeent to necessay design uieents such as sapling tie, oveshoot and settling tie. he esults of the siulations in Jittebug allow to evidence that the sapling tie is one of the ajo paaetes that affect NCS pefoance and to veify of the sensitivity of the NCS ae unde vaious tiing conditions including diffeent sapling ties and netwok delays. An ipotant conclusion is that the influence of the sapling tie is bigge in NCS with fast dynaics (fo exaple DC oto contol) than in NCS with low dynaics (fo exaple level contol). As a esult, the utilization of the siulations tools facilitated the developent of NCS platfo and helped the designe in the evaluation of the NCS pio to its ipleentation saving tie and educing design costs.

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