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Experience from Various Technological Concepts Applied in Virtual Control Laboratory
3rd IFAC Workshop on Internet Based Control Education November 4-6, Brescia, Italy November 4-6, 2015. 2015.on Brescia, Italy 3rd IFAC Workshop Internet Based Control Education 3rd IFAC Workshop on Internet BasedAvailable Control Education online at www.sciencedirect.com November 4-6, 2015. Brescia, Italy November 4-6, 2015. Brescia, Italy
ScienceDirect IFAC-PapersOnLine 48-29 (2015) 277–282 Experience from from Various Various Technological Concepts Applied in in Virtual Virtual Control Control Experience Technological Concepts Applied Experience from Various Technological Concepts Applied in Virtual Laboratory Laboratory Experience from Various Technological Concepts Applied in Virtual Control Control Laboratory Laboratory
Stanislav Vrána*. Vrána*. Bohumil Bohumil Šulc** Šulc** Stanislav Pavel Trnka***. Trnka***. Matěj Kuře٭ Kuře٭ Pavel Matěj Stanislav Vrána*. Bohumil Šulc** Stanislav Vrána*. Bohumil Šulc** Pavel Trnka***. Matěj Kuře٭ Pavel Trnka***. Matěj Kuře٭ Czech Faculty Czech Technical Technical University University in in Prague, Prague, Faculty of of Mechanical Mechanical Engineering Engineering Department of Instrumentation & Control Engineering, Prague, Republic Department of Instrumentation Control Faculty Engineering, Prague, Czech Czech Republic Czech Technical University in&Prague, of Mechanical Engineering Czech(Tel: Technical University in Prague, Faculty of Mechanical Engineering +420 2 2435 2769*; e-mail: [email protected]*, (Tel:of+420 2 2435 2769*; e-mail:Engineering, [email protected]*, Department Instrumentation & Control Prague, Czech Republic Department of Instrumentation & Control Engineering,[email protected]})٭ Prague, Czech Republic [email protected]**, [email protected]**, [email protected]***, [email protected]})٭ (Tel: +420 2 2435 [email protected]***, 2769*; e-mail: [email protected]*, (Tel: +420 2 2435 2769*; e-mail: [email protected]*, [email protected]**, [email protected]***, [email protected]})٭ [email protected]**, [email protected]***, [email protected]})٭ Abstract: Nowadays, Abstract: Nowadays, tuition tuition of of Control Control Engineering Engineering in in the the courses, courses, which which are are usually usually obligatory obligatory for for all all students attending technical universities, is unimaginable without passing a practical part in laboratories. students technical is unimaginable without passing practical part in laboratories. Abstract:attending Nowadays, tuitionuniversities, of Control Engineering in the courses, whicha are usually obligatory for all Abstract: Nowadays, tuition have of Control Engineering in the courses, which are of usually obligatorycontrol for all Set-ups in in such laboratories laboratories undergone its evolution. evolution. Instead of demos realpart industrial Set-ups such have undergone its Instead of demos of real industrial control students attending technical universities, is unimaginable without passing a practical in laboratories. students attending technical universities, is unimaginable withoutispassing a practical part in laboratories. solutions on small-scale laboratory models, increasing interest paid to the tasks presenting control solutions small-scale laboratory models, increasing interest is paid to the of tasks Set-ups inonsuch laboratories have undergone its evolution. Instead of demos realpresenting industrial control Set-ups inon such laboratories have undergone its interest evolution. of mastering demos of them. real industrial control problems attractive models invoking natural forInstead heuristic These specially specially problems attractive models invoking natural interestinterest for heuristic them. These solutions on small-scale laboratory models, increasing is paidmastering to the tasks presenting control solutions model on small-scale laboratory models, increasing interest realistic is paid to theand, tasksthen, presenting control designed devices are linked with PCs in order to provide HMI of course, with designed devices models are linked with PCs in order to provide realisticmastering HMI and,them. then,These of course, with problems model on attractive invoking natural interest for heuristic specially problems on attractive models invoking natural interest for heuristic mastering them.characterizing These specially Internet. The aim of the paper is a short presentation of these set-ups by their names the Internet. The aimdevices of the are paper is a with shortPCs presentation of provide these set-ups byHMI their and, names characterizing the designed model linked in order to realistic then, of course, with designed model devicesInareaddition linked with PCs to in order to our provide realisticfrom HMIthe and,application then, of course, with demonstrated activity. we wish present experience of various demonstrated activity. addition to presentofour experience application of various Internet. The aim of theInpaper is a we shortwish presentation these set-ups byfrom theirthe names characterizing the Internet. The used aim of papervirtual is a short presentation of these set-ups their names the technologies in the creating version of present these tasks. tasks. The virtualby versions try to characterizing be true trueofcomputer computer technologies used in creating virtualweversion of these virtual versions to be demonstrated activity. In addition wish to our The experience from the try application various demonstrated activity. In addition we wish to present our experience from the application of various copies of of the the real real models. Thisvirtual makesversion possibleofaa these preliminary preparation of the the students students for the given given task copies This makes possible preliminary preparation of the task technologies usedmodels. in creating tasks. The virtual versions try to for be true computer technologies used in creating virtual of version of these tasks. The virtualinversions try to be out truesimilar computer and after that a certain confrontation the results with those obtained reality carrying out and after that a certain confrontation of the results with those obtained in reality carrying out similar out copies of the real models. This makes possible a preliminary preparation of the students for the given task copies of the real models. This makes possible a preliminary preparation ofvia theInternet. students for the given task similar experiment on the place in the laboratory or through remote access similar experiment on the place in the laboratory or through remote access via Internet. and after that a certain confrontation of the results with those obtained in reality carrying out similar out and after that a certain confrontation of the results with those obtained in reality carrying out similar out similar on the place in theaids, laboratory or through access via Internet. © 2015,experiment IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. Allmodels, rights reserved. Keywords: education, educational automatic control,remote interactive, laboratory, computer similar experiment on the place in theaids, laboratory or through remote access via Internet. Keywords: education, educational automatic control, interactive, laboratory, models, computer programs programs Keywords: education, educational aids, automatic control, interactive, laboratory, models, computer Keywords: education, educational aids, automatic control, interactive, laboratory, models, computer programs programs 1. 2. 1. INTRODUCTION INTRODUCTION 2. DEVELOPMENT DEVELOPMENT TOWARDS TOWARDS VIRTUAL VIRTUAL LABS LABS
1. INTRODUCTION 2. DEVELOPMENT TOWARDS VIRTUAL LABS In aa permanently of education, the 1. INTRODUCTION DEVELOPMENT TOWARDS VIRTUAL LABS In university university education, education, permanently growing growing trend trend can can be be In In the the2. field field of automatic automatic control control education, the development development observed changing students’ wish to replace an obligatory towards virtual labs has had in the Czech Republic specific observed changing students’ wish to replace obligatory virtual labs has had in the Czech Republic specific In university education, a permanently growingantrend can be towards In the field of automatic control education, the development In universityineducation, a permanently growing trend certain can be character In the fielddetectable of automatic controlineducation, the development attendance lectures or seminars by doing probably all other former socialist attendance in lectures or wish seminars by doing certain character detectable probably otherRepublic former socialist observed changing students’ to replace an obligatory towards virtual labs has had inintheallCzech specific observed changing students’ wish Usually, to replace anremote obligatory towards virtual labs has had in thelast Czech Republic specific assignments remotely via form Up of century, demand for assignments remotely via Internet. Internet. Usually, this remotecertain form countries. countries. Up to to nineties nineties of the the last other century, demand for attendance in lectures or seminars bythis doing character detectable probably in all former socialist attendance in lectures or seminars by doing certain character detectable probably in all other former socialist is offered as an computer access to some text study materials. control engineers was very intensive, because each larger is offered as an computer access to some text study materials. control engineers was very intensive, because each larger assignments remotely via Internet. Usually, this remote form countries. Up to nineties of the last century, demand for assignments remotely via Internet. Usually, this remote form countries. Up tothese nineties of the inlast century, demand for Sometimes Internet provided illustrative factory to capable to Sometimes via Internet are are provided illustrative supporting factory needed needed these specialists in order order to be be each capable to is offered asvia an computer access to some text studysupporting materials. control engineers wasspecialists very intensive, because larger is offered as an computer access to etc. someIntext study materials. control engineers wassystem. very intensive, because each larger tools such as figures, links, videos principle, the issue develop own control It was the time of do-it-self, tools such asvia figures, links, etc. illustrative In principle,supporting the issue develop own control It was the time do-it-self, Sometimes Internet are videos provided factory needed these system. specialists in order to beof capable to Sometimes viastudy Internet aretoprovided illustrative supporting factory needed these specialists in order tocomplexes be capablewas to is to place web pages in form of import of is to such place study texts texts web etc. pages in the the the formissue of because because import of ready-made ready-made production complexes was tools as figures, links, to videos In principle, develop own control system. It production was the time of do-it-self, tools such as figures, links, videos etc. In principle, theCzech issue very develop own Practically, control system. Itwere was no the delivers time of capable do-it-self, downloadable PDF files or the wiki texts (e.g. in the limited. there to downloadable PDF files wiki pages texts (e.g. in the Czech limited. Practically, there were no delivers capablewas to is to place study textsortotheweb in the form of very because import of ready-made production complexes is to place studyfaculties texts to Czech web pages in the form of satisfy becauseactual import of and ready-made production complexes was Republic, medical and Republic, medical at and Slovak Slovak universities actual needs needs and requirements requirements on instrumentation and downloadable PDFfaculties files or at theCzech wiki texts (e.g. inuniversities the Czech satisfy very limited. Practically, there were on no instrumentation delivers capableand to downloadable PDF files or the wikisotexts (e.g. in the Czech very limited. Practically, enterprises there were no delivers capable to offer on address wikiskripta.eu called WikiSkripta). In Some producing necessary offer on the the addressfaculties wikiskripta.eu so and called WikiSkripta). In services. services. Some state enterprises on producing necessary Republic, medical at Czech Slovak universities satisfy actual needsstate and requirements instrumentation and Republic, medical faculties at Czech and Slovak universities satisfy actual needs and requirements on instrumentation and the of an to texts had keep quotes, which the universities of technology, technology, an access access to study study texts is is not not equipment had strictly strictly toenterprises keep 5-year-plan 5-year-plan quotes, which offeruniversities on the address wikiskripta.eu so called WikiSkripta). In equipment services. Some state to producing necessary offer on the address wikiskripta.eu so called WikiSkripta). In services. Some Only state own enterprises producing necessary sufficient solution. Many subjects taught at technically were insufficient. development of control systems aathesufficient solution. Many subjects taught at technically were insufficient. Only own development of control systems universities of technology, an access to study texts is not equipment had strictly to keep 5-year-plan quotes, which the universities of technology, an access to study texts is not equipment had strictlytheto way keephow 5-year-plan quotes, which oriented require aa strong each factory progress in oriented universities require strong experimental in each factory was was how to to ensure ensure progress in a sufficientuniversities solution. Many subjects taught atexperimental technically in were insufficient. Onlythe ownway development of control systems abackground sufficient provided solution. Many subjects taught at technically were insufficient. Onlyrequirements own development of control systems traditionally in laboratories. Falling production. Evidently, on good knowledge and background provided traditionally laboratories. Falling production. Evidently, requirements knowledge oriented universities require a in strong experimental in each factory was the way howontogood ensure progressand in oriented universities require a strong experimental understanding in each factory was the problems way how to ensure progress of in down interest to technological and the quite high. down interestprovided to study studytraditionally technological areas and increasing increasing the control control problems were were quiteknowledge high. Most Mostand of background in areas laboratories. Falling understanding production. Evidently, requirements on good background provided sophisticated traditionally inlaboratories laboratories.with Falling production. Evidently, requirements on obligatory good knowledge and costs for building the the technological universities included courses on costs for building sophisticated with the the technological included obligatory courses down interest to study technologicallaboratories areas and increasing understanding the universities control problems were quite high. Most on of down interest to study technological areas and increasing understanding the control problems were quite high.involving Most of equipment contemporary level industry Control in study equipment corresponding contemporary level of of with industry Automatic Control in their their included study programmes programmes involving costs for corresponding building sophisticated laboratories the Automatic the technological universities obligatory courses on costs for building sophisticatedsearch laboratories with the the technological universities included obligatory courses on make academic staff of tuition in the Mostly, the of make academic staff intensively intensively search for for new ways of experimental experimental tuition in the labs. Mostly, the concept concept of the the equipment corresponding contemporary levelnew of ways industry Automatic Control theirlabs. study programmes involving equipment corresponding contemporary level of industry Automatic Control in their study programmes involving replacement noneconomic laboratories by at was to demonstrate industrial control based replacement noneconomic laboratories by software software solutions. labs at that that time time was in to the demonstrate industrial control of based make academic staff intensively search for new solutions. ways of labs experimental tuition labs. Mostly, the concept the make academic staffare intensively search for either new ways of experimental tuition in the labs. Mostly, the The concept of the Even if real devices replaced by models as their on real industrial (available) instrumentation. controlled Even if real devices are replaced by models either as their on real industrial (available) instrumentation. The controlled replacement noneconomic laboratories by software solutions. labs at that time was to demonstrate industrial control based replacement noneconomic laboratories by software solutions. labs at that time was small to demonstrate industrial control based small physical more as usually physical the small scale physicalaremodels, models, or, more frequently, frequently, as objects objects were usually small scale scale physical models models ofcontrolled the most most Even ifscale real devices replaced or, by models either as their on real were industrial (available) instrumentation. Theof Even if realmodels, devicesthearenecessary replaced costs by models either as their on real industrial (available) instrumentation. The controlled simulation are still too high for common control problems such as level, pressure and simulation the necessary are still too high for control such as level, pressure and small scalemodels, physical models, costs or, more frequently, as common objects were usuallyproblems small scale physical models of the most small scale physicalTherefore, models, the or, more frequently, as objects werecontrol usually(Piteľ, small scale physical models of the were most many universities. solution via virtual temperature 2008). Such demonstrations many universities. Therefore, via high virtual controlproblems (Piteľ, 2008). demonstrations simulation models, the necessary the costssolution are still too for temperature common control suchSuch as level, pressure were and simulation models, the necessary costs are still too high for common control problems such aswould level,notpressure and laboratories has very even for students who laboratories has become become very popular, popular, recently. useful even control for the the(Piteľ, students who would not be be control control many universities. Therefore, the recently. solution via virtual useful temperature 2008). Such demonstrations were many universities. Therefore, the solution via virtual temperature control (Piteľ, 2008). Such demonstrations were laboratories has become very popular, recently. useful even for the students who would not be control laboratories has become very popular, recently. Copyright © 2015 IFAC 277 useful even for the students who would not be control Copyright © 2015, 2015 IFAC 277Hosting by Elsevier Ltd. All rights reserved. 2405-8963 © IFAC (International Federation of Automatic Control) Peer review©under of International Federation of Automatic Copyright 2015 responsibility IFAC 277Control. Copyright © 2015 IFAC 277 10.1016/j.ifacol.2015.11.248
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engineers, but they could meet with such equipment in their jobs. To make them acquainted with control instrumentation was not so difficult task, because at that time, offer of the automatic control means was restricted to products of one or two producers.
Control Engineering Laboratory existing in reality. The setups in this real laboratory can be approached physically in the laboratory room or remotely, via Internet. Therefore we call the problems to be solved as tasks. There are four groups of tasks we can choose for the access to the set-ups:
Consequence of the political change 1989 reflected undoubtedly in changes concerning the way of teaching control engineering. First of all, open market brought competition, huge offer of products including not only control instrumentation area. Necessity to make own, domestic development went down enormously. Number of students interested to study control engineering has started to sink.
pure virtual tasks in Java, tasks, where real set-ups are operated via Java, tasks, where real set-ups or simulations are operated via Matlab pure HTML/JavaScript on-line control of the real set-ups Originally, the demand of the virtual laboratory came from the need to present the laboratory set-ups to students before they really could see them during the basic course of subject Automatic Control. As a result, the static webpages describing all laboratory models appeared first. However, the static pages could not give to students the experience with using the set-up.
Another very important new phenomenon has started massively at that time: use of personal computers. It was unthinkable not to react to this new situation in the concept of control engineering laboratory. Instead of a classical demonstration of real industrial control applied on simple processes together with its instrumentation, various set-up models attracting student’s attention than demonstrating industrial solution. The issue was that the students could use a PC connected with a simple device performing a mechanical movement (usually unstable, or difficult controllable - inverted pendulum may be a typical example) in order to manipulation with it. After an unsuccessful manual control they could convince that after switching in the automatic mode the given control task can be achieved. Various control algorithms and their parameter setting was possible to test. In this way it was possible to increase difficulty of solved tasks gradually and to adapt them to the level of the course.
To bring to students the possibility of experiencing control the set-up, the mathematical models of the set-ups were created and made available in the form of virtual set-up. This gave to students the possibility practicing solving the problems in advance before they met the real set-up. Moreover, the virtual set-up has an advantage in higher safety and security during interaction of student with the virtual setup at both sides; the student cannot damage the set-up and the set-up cannot harm the student. Also, it does not need a supervising person who would supervise inexperienced students, ensure the correct starting and stopping of set-up, etc. Those virtual set-ups were created on the base of Java Technology, which made the virtual set-ups accessible in a form of Java applets. No other software needed to be downloaded and installed. All virtual set-ups were created as full software copies of everything that can be observed on the real set-ups existing physically in the laboratory room. The virtual set-ups are of two types, supporting both assignment from the area of logic control (Entrance Gate, Rotary Table with the Conveyor Belt, Water Level Control, Railway Model, Pneumatic Cylinder and Sucking Disk, and Parcel Lifting Platform – the names are self-explanatory enough to imagine what problems need to be solved) and from the area of continuous control (Bathyscaphe – controlling the submerge depth, Ball and Elliptic Rail – controlling the position of a ball on the elliptic rail, Ball and Beam – controlling the position of a ball on the rotating beam, Water Reservoir – controlling of a water level, Water Levitation, , Air Levitation – controlling of height of a ball on a water, resp. air stream, and Vehicle Position Control).
The described approach has become a basis for the virtual laboratory referred further on. Advantages of the virtual concept can be summarized as follows: the laboratory is universally exploitable in the courses of various level work in the laboratory recalls computer games, therefore is attractive for students and may influence those standing before decision which specialisation to study most of the models have been designed and produced by the Department and purchase of expensive factory products could be avoided it is possible to create new purely virtual clones of existing set-ups by internet connectivity the laboratory can be used in various regimes of operation providing direct, remote, or simulated access. The virtual laboratory can be also useful as a training tool how to deal in certain cases and for learning, how the controlled plant may react (Sánchez et al., 2002).
Both types of the virtual set-up need different approach. The virtual set-ups supporting the logic control assignments consist of three parts: library of function blocks, working area, and set-up visualisation, including elements for manual input. The virtual set-up operates in two regimes. The logical functions are created in the editing mode, when the function blocks are dragged from the library into the working area and mutually connected. Switching into the simulation regime allows verify the created function using the manual control
3. TASKS IN THE VIRTUAL LABORATORY At present, under the name Virtual Control Laboratory are meant pages accessible through the address vlab.fs.cvut.cz. as a part of web presentation of the Instrumentation and Control Engineering Department at the Mechanical Engineering Faculty of the Czech Technical University in Prague. The Virtual Control Laboratory is certain internet image of the 278
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point, control error, controlled variable, manipulated variable, disturbance), and the area where the process is visualised, i.e. where the control circuit variables get the (virtual) physical representation. Examples of the screen used in the user communication are shown in Fig. 1 and Fig. 2. One remark: the whole group of the virtual tasks contains models fully created in Java and the only support from HTML represents initial values of some parameters, e.g. limits, defaults etc. These virtual set-ups offer the standard types of controllers and also the manual control. They allow performing the task of tuning the controller, finding the critical state, try out the response based controller tuning methods, and other task based on time domain course evaluation. 3.1 Real set-ups controlled via Java The virtual set-ups, even graphically corresponding to the real set-ups, do not represent the real set-ups fully, as they are based on a mathematical model. The mathematical model is simplified, so it does not reflect some phenomena, i.e. presence of noise, certain types of non-linearities, limitations, and saturations that occur in the real set-ups.
Fig. 1. An example of logic control virtual set-up HMI elements; the visualisation reacts on the student actions. The idea is that the created and verified logical circuit will be transferred from this virtual set-up to the real set-up; however the transfer needs a conversion from the function block diagram into a programming language of PLC controlling the real set-up.
To push students to a deeper understanding real-world control problems (e.g. in the model occurring non-linearities), the set of virtual set-ups has been extended with a set-up that provides the same HMI but instead of using a mathematical model, the real set-up is used. And the camera showing the current state of the set-up is used instead of a software visualisation, see Fig. 3.
The virtual set-ups supporting the continuous control assignments were designed to provide common HMI in a form typically available in control software packages, however in a simplified form and unified for all virtual setups focused on continuous control. The HMI consists of area where the operating conditions (set point, disturbances) are set, the area of choosing controller type and its parameters, the area showing the courses of control circuit variables (set
However, the connection to a real device brings problems that do not appear in a fully virtual set-ups use – no more than one student can access this remotely controlled real setup. To ensure that more than one student can access the setup simultaneously, four identical set-ups are present in the laboratory physically and the student is directed to that one which is currently free. If there are no free set-ups available, the student has to wait till any other student finishes his experiment. One session duration is limited to five minutes.
Fig. 2. An example of continuous control virtual set-up HMI
Fig. 3. An example of continuous control real set-up HMI 279
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3.2 Remotely accessed Matlab simulations
to access the set-up control algorithm directly including the possibility of replacing it by another control algorithm.
The Java technology has become problematic recently. The problems started with the conflict between Sun and Microsoft resulting in not including Java package into MS Windows installations. This meant that the majority of those who wanted to access the virtual set-ups needed to install the Java package himself. Moreover, incompatibilities between newer and older versions of Java became significant and running the Java applets has brought the need of the setting several exceptions in the web browser. Those were the motivations to try incorporating other technologies into the Virtual Control Laboratory.
To fulfil those demands we created new generation of remotely accessed set-ups based on the mini-computer Raspberry Pi with operating system Raspbian. That allowed using any software tool executable under the operating system Linux to control the tasks. Therefore, we focused to the control system REX. It has been chosen from two reasons: firstly, we had obtained a previous experience with this system in experiments with the boiler Verner A25 (Šulc et al., 2009) and the boiler Fiedler (Vrána et al., 2014) and also with its usage in the laboratory model Cascade of Three Tanks (Vrána, 2008), and secondly, the latest versions of the REX control system allows to create the visualisation based only on HTML technologies, so no other computer with the OPC server is required (Ožana, 2015).
Our choice was simulation package Matlab allowing remote access via Matweb. It proved well in simulations, however the approach required setting of the simulation parameters and they cannot be changed during the simulation run. Further disadvantage is that we cannot see the simulation progress, because the results are available in a form of numbers or graphs until the simulation finishes. Our attempts to remove these disadvantages were unsuccessful.
The main supporting software tools are the programs RexDraw and RexView. These two programs allow remote access to real devices, so they can be used for remote access to the laboratory set-ups directly. There is also supporting tool for creating web interfaces to the tasks in a form of plugin into a graphic editor Inkscape (Rex Controls, 2014b). The set-ups can be accessed also directly from Matlab. Those three ways of the remote access make the use of set-ups very universal.
In spite of these disadvantages we created three simple online accessed simulation models; however, as the Matweb technology is no longer supported, the tasks are not assigned any more. It is possible to replace Matlab for example by C++ (Costa et al., 2010) and Scilab (Magyar and Zakova, 2012),
4.1 Description of the Laboratory Set-ups with Extended Use
4. THE SET-UPS WITH EXTENDED USE
The first two set-ups created in the new generation concept based on REX running on Raspberry Pi are Rover on a Sloped Plane (Fig. 4) and Cascade of Two Interconnected Tanks (Fig. 5).
The virtual set-ups based on Java are single purposed set-ups that can be used to demonstrate solving elementary problems. Thus, they are suitable for the basic course in Automatic Control, however they are not suitable for the advanced courses of automatic control. For this purpose, the models should make possible to solve more demanding tasks, like identification of the device dynamics, creating the mathematical model of set-up behaviour, and demonstration of advanced control strategies such as the MIMO control and the state control. From this demand, it follows that the internet accessed set-up should be accessed not only via predefined web based interface, but also it should be possible
The arrangement of the set-up Rover on a Sloped Plane is depicted in Fig. 4. The rover position (controlled variable y) is measured with an optical sensor. The rover wheel revolutions are manipulated by setting of the PWM duty cycle changing the delivered power from the motor M (manipulated variable u). The rover can move only forward, its reverse movement is possible only by drifting of the rover e
Controller
u
u
M
y
e
h1 h2
SM
w
Controller
Fig. 4. A functional scheme of the laboratory set-up Rover on a Sloped Plane
Fig. 5. A functional scheme of the laboratory set-up Cascade of Two Interconnected Tanks 280
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by the moving belt simulating a roadway. The sloped plane is represented by a pair of parallel moving belts simulating the roadway, the rover is moving on them. The belts are actuated with a pair of the stepper motors SM, the speed of the belts represents the disturbance d. The rover position should be kept either manually or automatically with a chosen type of the controller.
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If the web user interface is accessed from a mobile device, the two column layout is turned into single column layout with the online video and the graph placed below the controller setting options. There was a discussion if it is more suitable to equip the web user interface with an online video or with an animation. The Rover on a Sloped plane has no hidden manipulated elements, the online video was preferred. On the other hand, to use the online video does not show the activity of water pump in Cascade of Two Interconnected Tanks, so the animation has been chosen to visualise this set-up.
The set-up Cascade of Two Interconnected Tanks consists of two mutually interconnected water tanks, a pump, and a water reservoir, see Fig. 5. The pump is reversible; it can feed water not only from the reservoir to the tank, but also from the tank back to the reservoir. It is possible to measure water level in both tanks. The outlet flowrate can be set only manually with the valve. This set-up is principally a simple physical model, whose mathematical description can be derived using the first principle. However, its real behaviour is quite different from those obtained by the theoretical way. There are phenomena that are not typically respected in modelling, e.g. friction in the pump, non-linear dependence of flow-rate on the power supply, etc. – all these are the reasons why to use such a “trivial” set-up to demonstrate some problems of real application of control algorithms to students.
Except the browser Internet Explorer, all current mayor browsers allow showing video in the format MJPEG. Internet Explorer does not support standard MJPEG, the object ActiveX is necessary to use. Typically, this object is provided with web cameras. However, the web user interface needs to conduct a test, which browser is used to view the web user interface. Typical test rely on the presence of the string MSIE in the user-agent field, but this test fails when it is conducted on Internet Explorer 10 in the standard mode, because it provides the string MSIE only in quirk mode. The presence of string trident needs to be tested to ensure correct choice between showing as MJPEG or via the ActiveX object.
4.2 Possibilities of Web Interface in pure HTML/JavaScript
The possibilities of RexHMI can be extended with of JavaScript libraries REX.UI and REX.UI.CHARTS that allow to include in the web user interface the items such as display, slider, bar graph, and running graph of variable courses (Skyba, 2013). In the case of Rover on a Sloped Plane only the running graph is used in the web user interface, the other interface elements are the elements provided by HTML5.
Except already mentioned possibilities, the REX allows creating user interface in the form of a web page based on technologies from HTML5 family (RexControls, 2014a). The RexHMI provides a complete JavaScript library WebBuDi for the complete design of user interface from predefined graphical and textual control elements. However, it is also possible to use the RexHMI only in order to read and set values of variables and to create an own user interface directly in the HTML. It is possible to place the functions for reading and setting into the respective tags as the values of parameters ONCLICK, ONCHANGE, etc., eventually to execute those functions periodically via the JavaScript function setInterval or setTimeout. It is more comfortable to use the jQuery that allows placing all those functions into one place of HTML page code.
What also had to be solved was the access from more devices simultaneously. One option was simply to restrict the number
The web user interface was created directly in the HTML with the use of RexHMI functions for reading and setting the variables in the control algorithm. With the increase of mobile device use to browse the internet; the mobile devices have different requirements to page layouts, the adaptive layout has been chosen. When accessed from a computer, the web page is divided into two columns. The left column contains the control panel of the set-up; the right column contains an online video that is used to see the current state of the task and the graph of control algorithm variable courses, see Fig. 6. The common variables for all control modes, i.e. the rover position (controlled variable y), setpoint (w), and manipulated variable (the PWM duty cycle in %), are placed at the top of the left column, while the parameters of chosen controller are placed to the bottom of the left column and only the parameters required by selected controller are shown.
Fig. 6. The web user interface of the set-up Rover on a Sloped Plane 281
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of simultaneous accesses to one, as in case of real set-up controlled via Java described above. The other option is to allow to access the set-up from more than one device simultaneously, that means to ensure the changes done in one instance of web user interface are automatically displayed in the other instances. The second option has been chosen, because it allows to use the set-up for a kind of a game when one student can manipulate the disturbance while the other student can manipulate the manipulated variable manually to reach the set-point. Also, permission of more simultaneous accesses provides possibility to the teacher to supervise the student activity remotely. Even implementing this second option still left opened the possibility to limit the number to simultaneously accesses to one if necessary.
REFERENCES Costa, R., Valles, M., Jimenez, L., Diaz-Guerra, L., Valera, A., and Puerto, R. (2010). Integración de dispositivos físicos en un laboratorio remoto de control mediante diferentes plataformas: Labview, Matlab y C/C++. Revista Iberoamericana de Automática e Informática Industrial RIAI, 7(1), 23-34. Magyar, Z. and Zakova, K. (2012). Scilab based remote control of experiments. Advances in Control Education, 9(1), 206-211. Ožana, Š. (2015) Possibilities in control and visualisation of educational physical models controlled with REX control system. Automa, 2015(1), 12-13. (in Czech, Možnosti řízení a vizualizace výukových fyzikálních modelů pomocí řídicího systému REX) Piteľ, J. (2008) Modelling and Simulation of Electromechanical Systems for Heating. Control. In: Modelovanie, simulácia a verifikácia vybraných mechatronických systémov, 113-134. Tribun EU, Brno. RexControls (2014a). HMI for pool automation with Raspberry Pi [online]. Published 2014-07-02, updated 2014-12-15. Retrieved from https://www.rexcontrols.com/articles/hmi-for-poolautomation-with-raspberry-pi RexControls (2014b). Finishing the HMI for the pool automation project. [online], Published 2014-08-13, updated 2014-12-12, Retrieved from https://www.rexcontrols.com/articles/finishing-the-hmifor-the-pool-automation-project Sánchez, J., Morilla, F., Dormido, S., Aranda, J., and Ruipérez, P. (2002). Virtual and remote control labs using Java: a qualitative approach. IEEE Control Systems Magazine, 22(2), 8-20. Skyba, J. (2013). Development of remote and virtual laboratory experiments based on HTML 5. University of West Bohemia, Pilsen (in Czech, Vývoj úloh vzdálené a virtuální laboratoře založených na technologii HTML 5) Šulc, B., Hrdlička, J., Lepold, M., and Vrána, S. (2009) Control for Ecological Improvement of Small Biomass Boilers. In: Majanne, Y. (ed), Proceedings of IFAC Symposium on Power Plant and Power Systems, 120-125 IFAC, Tampere Vrána, S. (2008) Three Tanks Cascade Control with the Use of Rex Control System. In: Nové metody a postupy v oblasti přístrojové techniky, automatického řízení a informatiky. 128-133. Czech Technical University in Prague Vrána, S., Oswald, C., Plaček, V., Šulc, B., and Neuman, P. (2014) Neural Network Evaluation of Combustion Process for Continuous Control of Small Scale Biomass Fired Boilers. In: Boje, E. and Xia, X. (eds), Proceedings of the 19th World Congress of the International Federation of Automatic Control, 1440-1445. IFAC: Cape Town
5. CONCLUSIONS The presented concept based on the existence of the set-ups in two versions, the fully virtual and the real, has proved to be useful mainly in the basic courses in Automatic Control. The students accepted with great interest the possibility to communicate via computers and the alternative of home preparation. As the latest development shows, the trend towards preference of pure virtual task grows up not only from the practical reasons (less demands to instrumentation, access to the laboratory, time schedule, etc.). Also the software offer, especially using the Linux operating system, and the financial availability of necessary instrumentation have very positive effects in inspiration of gifted students to engage in creation new versions of the tasks according to their own design, or to find new solutions of the given control tasks. It allows to demonstrate any control algorithm and also to apply identification procedures, and moreover, it allows the verification of controller tuning methods arising in the framework of doctoral study. The development of the set-ups, both virtual set-ups and remotely accessed real set-ups was influenced by the reaction of students, which led to focus on other technologies than Java in newly developed remotely accessed set-ups. Another important factor is translation of the user interface into the foreign languages (Control Virtual Laboratory exists in Czech, English, German, and French) makes the usage of virtual set-ups and remote accessed real set-ups easier for increasing number of foreign students, e.g. within the framework of program Erasmus. The virtual presentations performed regularly on Open Door Days play also an important role in motivating the students to choose Control Engineering as a field of their study. The experience with the user interfaces in pure HTML/JavaScript proved that it can fully replace the previously used Java technology and overcome the problems caused by this programming tool. ACKNOWLEDGEMENTS This work was supported by the Grant Agency of the Czech Technical University in Prague, grant No. SGS13/179/OHK2/3T/12. 282
ScienceDirect IFAC-PapersOnLine 48-29 (2015) 277–282 Experience from from Various Various Technological Concepts Applied in in Virtual Virtual Control Control Experience Technological Concepts Applied Experience from Various Technological Concepts Applied in Virtual Laboratory Laboratory Experience from Various Technological Concepts Applied in Virtual Control Control Laboratory Laboratory
Stanislav Vrána*. Vrána*. Bohumil Bohumil Šulc** Šulc** Stanislav Pavel Trnka***. Trnka***. Matěj Kuře٭ Kuře٭ Pavel Matěj Stanislav Vrána*. Bohumil Šulc** Stanislav Vrána*. Bohumil Šulc** Pavel Trnka***. Matěj Kuře٭ Pavel Trnka***. Matěj Kuře٭ Czech Faculty Czech Technical Technical University University in in Prague, Prague, Faculty of of Mechanical Mechanical Engineering Engineering Department of Instrumentation & Control Engineering, Prague, Republic Department of Instrumentation Control Faculty Engineering, Prague, Czech Czech Republic Czech Technical University in&Prague, of Mechanical Engineering Czech(Tel: Technical University in Prague, Faculty of Mechanical Engineering +420 2 2435 2769*; e-mail: [email protected]*, (Tel:of+420 2 2435 2769*; e-mail:Engineering, [email protected]*, Department Instrumentation & Control Prague, Czech Republic Department of Instrumentation & Control Engineering,[email protected]})٭ Prague, Czech Republic [email protected]**, [email protected]**, [email protected]***, [email protected]})٭ (Tel: +420 2 2435 [email protected]***, 2769*; e-mail: [email protected]*, (Tel: +420 2 2435 2769*; e-mail: [email protected]*, [email protected]**, [email protected]***, [email protected]})٭ [email protected]**, [email protected]***, [email protected]})٭ Abstract: Nowadays, Abstract: Nowadays, tuition tuition of of Control Control Engineering Engineering in in the the courses, courses, which which are are usually usually obligatory obligatory for for all all students attending technical universities, is unimaginable without passing a practical part in laboratories. students technical is unimaginable without passing practical part in laboratories. Abstract:attending Nowadays, tuitionuniversities, of Control Engineering in the courses, whicha are usually obligatory for all Abstract: Nowadays, tuition have of Control Engineering in the courses, which are of usually obligatorycontrol for all Set-ups in in such laboratories laboratories undergone its evolution. evolution. Instead of demos realpart industrial Set-ups such have undergone its Instead of demos of real industrial control students attending technical universities, is unimaginable without passing a practical in laboratories. students attending technical universities, is unimaginable withoutispassing a practical part in laboratories. solutions on small-scale laboratory models, increasing interest paid to the tasks presenting control solutions small-scale laboratory models, increasing interest is paid to the of tasks Set-ups inonsuch laboratories have undergone its evolution. Instead of demos realpresenting industrial control Set-ups inon such laboratories have undergone its interest evolution. of mastering demos of them. real industrial control problems attractive models invoking natural forInstead heuristic These specially specially problems attractive models invoking natural interestinterest for heuristic them. These solutions on small-scale laboratory models, increasing is paidmastering to the tasks presenting control solutions model on small-scale laboratory models, increasing interest realistic is paid to theand, tasksthen, presenting control designed devices are linked with PCs in order to provide HMI of course, with designed devices models are linked with PCs in order to provide realisticmastering HMI and,them. then,These of course, with problems model on attractive invoking natural interest for heuristic specially problems on attractive models invoking natural interest for heuristic mastering them.characterizing These specially Internet. The aim of the paper is a short presentation of these set-ups by their names the Internet. The aimdevices of the are paper is a with shortPCs presentation of provide these set-ups byHMI their and, names characterizing the designed model linked in order to realistic then, of course, with designed model devicesInareaddition linked with PCs to in order to our provide realisticfrom HMIthe and,application then, of course, with demonstrated activity. we wish present experience of various demonstrated activity. addition to presentofour experience application of various Internet. The aim of theInpaper is a we shortwish presentation these set-ups byfrom theirthe names characterizing the Internet. The used aim of papervirtual is a short presentation of these set-ups their names the technologies in the creating version of present these tasks. tasks. The virtualby versions try to characterizing be true trueofcomputer computer technologies used in creating virtualweversion of these virtual versions to be demonstrated activity. In addition wish to our The experience from the try application various demonstrated activity. In addition we wish to present our experience from the application of various copies of of the the real real models. Thisvirtual makesversion possibleofaa these preliminary preparation of the the students students for the given given task copies This makes possible preliminary preparation of the task technologies usedmodels. in creating tasks. The virtual versions try to for be true computer technologies used in creating virtual of version of these tasks. The virtualinversions try to be out truesimilar computer and after that a certain confrontation the results with those obtained reality carrying out and after that a certain confrontation of the results with those obtained in reality carrying out similar out copies of the real models. This makes possible a preliminary preparation of the students for the given task copies of the real models. This makes possible a preliminary preparation ofvia theInternet. students for the given task similar experiment on the place in the laboratory or through remote access similar experiment on the place in the laboratory or through remote access via Internet. and after that a certain confrontation of the results with those obtained in reality carrying out similar out and after that a certain confrontation of the results with those obtained in reality carrying out similar out similar on the place in theaids, laboratory or through access via Internet. © 2015,experiment IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. Allmodels, rights reserved. Keywords: education, educational automatic control,remote interactive, laboratory, computer similar experiment on the place in theaids, laboratory or through remote access via Internet. Keywords: education, educational automatic control, interactive, laboratory, models, computer programs programs Keywords: education, educational aids, automatic control, interactive, laboratory, models, computer Keywords: education, educational aids, automatic control, interactive, laboratory, models, computer programs programs 1. 2. 1. INTRODUCTION INTRODUCTION 2. DEVELOPMENT DEVELOPMENT TOWARDS TOWARDS VIRTUAL VIRTUAL LABS LABS
1. INTRODUCTION 2. DEVELOPMENT TOWARDS VIRTUAL LABS In aa permanently of education, the 1. INTRODUCTION DEVELOPMENT TOWARDS VIRTUAL LABS In university university education, education, permanently growing growing trend trend can can be be In In the the2. field field of automatic automatic control control education, the development development observed changing students’ wish to replace an obligatory towards virtual labs has had in the Czech Republic specific observed changing students’ wish to replace obligatory virtual labs has had in the Czech Republic specific In university education, a permanently growingantrend can be towards In the field of automatic control education, the development In universityineducation, a permanently growing trend certain can be character In the fielddetectable of automatic controlineducation, the development attendance lectures or seminars by doing probably all other former socialist attendance in lectures or wish seminars by doing certain character detectable probably otherRepublic former socialist observed changing students’ to replace an obligatory towards virtual labs has had inintheallCzech specific observed changing students’ wish Usually, to replace anremote obligatory towards virtual labs has had in thelast Czech Republic specific assignments remotely via form Up of century, demand for assignments remotely via Internet. Internet. Usually, this remotecertain form countries. countries. Up to to nineties nineties of the the last other century, demand for attendance in lectures or seminars bythis doing character detectable probably in all former socialist attendance in lectures or seminars by doing certain character detectable probably in all other former socialist is offered as an computer access to some text study materials. control engineers was very intensive, because each larger is offered as an computer access to some text study materials. control engineers was very intensive, because each larger assignments remotely via Internet. Usually, this remote form countries. Up to nineties of the last century, demand for assignments remotely via Internet. Usually, this remote form countries. Up tothese nineties of the inlast century, demand for Sometimes Internet provided illustrative factory to capable to Sometimes via Internet are are provided illustrative supporting factory needed needed these specialists in order order to be be each capable to is offered asvia an computer access to some text studysupporting materials. control engineers wasspecialists very intensive, because larger is offered as an computer access to etc. someIntext study materials. control engineers wassystem. very intensive, because each larger tools such as figures, links, videos principle, the issue develop own control It was the time of do-it-self, tools such asvia figures, links, etc. illustrative In principle,supporting the issue develop own control It was the time do-it-self, Sometimes Internet are videos provided factory needed these system. specialists in order to beof capable to Sometimes viastudy Internet aretoprovided illustrative supporting factory needed these specialists in order tocomplexes be capablewas to is to place web pages in form of import of is to such place study texts texts web etc. pages in the the the formissue of because because import of ready-made ready-made production complexes was tools as figures, links, to videos In principle, develop own control system. It production was the time of do-it-self, tools such as figures, links, videos etc. In principle, theCzech issue very develop own Practically, control system. Itwere was no the delivers time of capable do-it-self, downloadable PDF files or the wiki texts (e.g. in the limited. there to downloadable PDF files wiki pages texts (e.g. in the Czech limited. Practically, there were no delivers capablewas to is to place study textsortotheweb in the form of very because import of ready-made production complexes is to place studyfaculties texts to Czech web pages in the form of satisfy becauseactual import of and ready-made production complexes was Republic, medical and Republic, medical at and Slovak Slovak universities actual needs needs and requirements requirements on instrumentation and downloadable PDFfaculties files or at theCzech wiki texts (e.g. inuniversities the Czech satisfy very limited. Practically, there were on no instrumentation delivers capableand to downloadable PDF files or the wikisotexts (e.g. in the Czech very limited. Practically, enterprises there were no delivers capable to offer on address wikiskripta.eu called WikiSkripta). In Some producing necessary offer on the the addressfaculties wikiskripta.eu so and called WikiSkripta). In services. services. Some state enterprises on producing necessary Republic, medical at Czech Slovak universities satisfy actual needsstate and requirements instrumentation and Republic, medical faculties at Czech and Slovak universities satisfy actual needs and requirements on instrumentation and the of an to texts had keep quotes, which the universities of technology, technology, an access access to study study texts is is not not equipment had strictly strictly toenterprises keep 5-year-plan 5-year-plan quotes, which offeruniversities on the address wikiskripta.eu so called WikiSkripta). In equipment services. Some state to producing necessary offer on the address wikiskripta.eu so called WikiSkripta). In services. Some Only state own enterprises producing necessary sufficient solution. Many subjects taught at technically were insufficient. development of control systems aathesufficient solution. Many subjects taught at technically were insufficient. Only own development of control systems universities of technology, an access to study texts is not equipment had strictly to keep 5-year-plan quotes, which the universities of technology, an access to study texts is not equipment had strictlytheto way keephow 5-year-plan quotes, which oriented require aa strong each factory progress in oriented universities require strong experimental in each factory was was how to to ensure ensure progress in a sufficientuniversities solution. Many subjects taught atexperimental technically in were insufficient. Onlythe ownway development of control systems abackground sufficient provided solution. Many subjects taught at technically were insufficient. Onlyrequirements own development of control systems traditionally in laboratories. Falling production. Evidently, on good knowledge and background provided traditionally laboratories. Falling production. Evidently, requirements knowledge oriented universities require a in strong experimental in each factory was the way howontogood ensure progressand in oriented universities require a strong experimental understanding in each factory was the problems way how to ensure progress of in down interest to technological and the quite high. down interestprovided to study studytraditionally technological areas and increasing increasing the control control problems were were quiteknowledge high. Most Mostand of background in areas laboratories. Falling understanding production. Evidently, requirements on good background provided sophisticated traditionally inlaboratories laboratories.with Falling production. Evidently, requirements on obligatory good knowledge and costs for building the the technological universities included courses on costs for building sophisticated with the the technological included obligatory courses down interest to study technologicallaboratories areas and increasing understanding the universities control problems were quite high. Most on of down interest to study technological areas and increasing understanding the control problems were quite high.involving Most of equipment contemporary level industry Control in study equipment corresponding contemporary level of of with industry Automatic Control in their their included study programmes programmes involving costs for corresponding building sophisticated laboratories the Automatic the technological universities obligatory courses on costs for building sophisticatedsearch laboratories with the the technological universities included obligatory courses on make academic staff of tuition in the Mostly, the of make academic staff intensively intensively search for for new ways of experimental experimental tuition in the labs. Mostly, the concept concept of the the equipment corresponding contemporary levelnew of ways industry Automatic Control theirlabs. study programmes involving equipment corresponding contemporary level of industry Automatic Control in their study programmes involving replacement noneconomic laboratories by at was to demonstrate industrial control based replacement noneconomic laboratories by software software solutions. labs at that that time time was in to the demonstrate industrial control of based make academic staff intensively search for new solutions. ways of labs experimental tuition labs. Mostly, the concept the make academic staffare intensively search for either new ways of experimental tuition in the labs. Mostly, the The concept of the Even if real devices replaced by models as their on real industrial (available) instrumentation. controlled Even if real devices are replaced by models either as their on real industrial (available) instrumentation. The controlled replacement noneconomic laboratories by software solutions. labs at that time was to demonstrate industrial control based replacement noneconomic laboratories by software solutions. labs at that time was small to demonstrate industrial control based small physical more as usually physical the small scale physicalaremodels, models, or, more frequently, frequently, as objects objects were usually small scale scale physical models models ofcontrolled the most most Even ifscale real devices replaced or, by models either as their on real were industrial (available) instrumentation. Theof Even if realmodels, devicesthearenecessary replaced costs by models either as their on real industrial (available) instrumentation. The controlled simulation are still too high for common control problems such as level, pressure and simulation the necessary are still too high for control such as level, pressure and small scalemodels, physical models, costs or, more frequently, as common objects were usuallyproblems small scale physical models of the most small scale physicalTherefore, models, the or, more frequently, as objects werecontrol usually(Piteľ, small scale physical models of the were most many universities. solution via virtual temperature 2008). Such demonstrations many universities. Therefore, via high virtual controlproblems (Piteľ, 2008). demonstrations simulation models, the necessary the costssolution are still too for temperature common control suchSuch as level, pressure were and simulation models, the necessary costs are still too high for common control problems such aswould level,notpressure and laboratories has very even for students who laboratories has become become very popular, popular, recently. useful even control for the the(Piteľ, students who would not be be control control many universities. Therefore, the recently. solution via virtual useful temperature 2008). Such demonstrations were many universities. Therefore, the solution via virtual temperature control (Piteľ, 2008). Such demonstrations were laboratories has become very popular, recently. useful even for the students who would not be control laboratories has become very popular, recently. Copyright © 2015 IFAC 277 useful even for the students who would not be control Copyright © 2015, 2015 IFAC 277Hosting by Elsevier Ltd. All rights reserved. 2405-8963 © IFAC (International Federation of Automatic Control) Peer review©under of International Federation of Automatic Copyright 2015 responsibility IFAC 277Control. Copyright © 2015 IFAC 277 10.1016/j.ifacol.2015.11.248
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engineers, but they could meet with such equipment in their jobs. To make them acquainted with control instrumentation was not so difficult task, because at that time, offer of the automatic control means was restricted to products of one or two producers.
Control Engineering Laboratory existing in reality. The setups in this real laboratory can be approached physically in the laboratory room or remotely, via Internet. Therefore we call the problems to be solved as tasks. There are four groups of tasks we can choose for the access to the set-ups:
Consequence of the political change 1989 reflected undoubtedly in changes concerning the way of teaching control engineering. First of all, open market brought competition, huge offer of products including not only control instrumentation area. Necessity to make own, domestic development went down enormously. Number of students interested to study control engineering has started to sink.
pure virtual tasks in Java, tasks, where real set-ups are operated via Java, tasks, where real set-ups or simulations are operated via Matlab pure HTML/JavaScript on-line control of the real set-ups Originally, the demand of the virtual laboratory came from the need to present the laboratory set-ups to students before they really could see them during the basic course of subject Automatic Control. As a result, the static webpages describing all laboratory models appeared first. However, the static pages could not give to students the experience with using the set-up.
Another very important new phenomenon has started massively at that time: use of personal computers. It was unthinkable not to react to this new situation in the concept of control engineering laboratory. Instead of a classical demonstration of real industrial control applied on simple processes together with its instrumentation, various set-up models attracting student’s attention than demonstrating industrial solution. The issue was that the students could use a PC connected with a simple device performing a mechanical movement (usually unstable, or difficult controllable - inverted pendulum may be a typical example) in order to manipulation with it. After an unsuccessful manual control they could convince that after switching in the automatic mode the given control task can be achieved. Various control algorithms and their parameter setting was possible to test. In this way it was possible to increase difficulty of solved tasks gradually and to adapt them to the level of the course.
To bring to students the possibility of experiencing control the set-up, the mathematical models of the set-ups were created and made available in the form of virtual set-up. This gave to students the possibility practicing solving the problems in advance before they met the real set-up. Moreover, the virtual set-up has an advantage in higher safety and security during interaction of student with the virtual setup at both sides; the student cannot damage the set-up and the set-up cannot harm the student. Also, it does not need a supervising person who would supervise inexperienced students, ensure the correct starting and stopping of set-up, etc. Those virtual set-ups were created on the base of Java Technology, which made the virtual set-ups accessible in a form of Java applets. No other software needed to be downloaded and installed. All virtual set-ups were created as full software copies of everything that can be observed on the real set-ups existing physically in the laboratory room. The virtual set-ups are of two types, supporting both assignment from the area of logic control (Entrance Gate, Rotary Table with the Conveyor Belt, Water Level Control, Railway Model, Pneumatic Cylinder and Sucking Disk, and Parcel Lifting Platform – the names are self-explanatory enough to imagine what problems need to be solved) and from the area of continuous control (Bathyscaphe – controlling the submerge depth, Ball and Elliptic Rail – controlling the position of a ball on the elliptic rail, Ball and Beam – controlling the position of a ball on the rotating beam, Water Reservoir – controlling of a water level, Water Levitation, , Air Levitation – controlling of height of a ball on a water, resp. air stream, and Vehicle Position Control).
The described approach has become a basis for the virtual laboratory referred further on. Advantages of the virtual concept can be summarized as follows: the laboratory is universally exploitable in the courses of various level work in the laboratory recalls computer games, therefore is attractive for students and may influence those standing before decision which specialisation to study most of the models have been designed and produced by the Department and purchase of expensive factory products could be avoided it is possible to create new purely virtual clones of existing set-ups by internet connectivity the laboratory can be used in various regimes of operation providing direct, remote, or simulated access. The virtual laboratory can be also useful as a training tool how to deal in certain cases and for learning, how the controlled plant may react (Sánchez et al., 2002).
Both types of the virtual set-up need different approach. The virtual set-ups supporting the logic control assignments consist of three parts: library of function blocks, working area, and set-up visualisation, including elements for manual input. The virtual set-up operates in two regimes. The logical functions are created in the editing mode, when the function blocks are dragged from the library into the working area and mutually connected. Switching into the simulation regime allows verify the created function using the manual control
3. TASKS IN THE VIRTUAL LABORATORY At present, under the name Virtual Control Laboratory are meant pages accessible through the address vlab.fs.cvut.cz. as a part of web presentation of the Instrumentation and Control Engineering Department at the Mechanical Engineering Faculty of the Czech Technical University in Prague. The Virtual Control Laboratory is certain internet image of the 278
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point, control error, controlled variable, manipulated variable, disturbance), and the area where the process is visualised, i.e. where the control circuit variables get the (virtual) physical representation. Examples of the screen used in the user communication are shown in Fig. 1 and Fig. 2. One remark: the whole group of the virtual tasks contains models fully created in Java and the only support from HTML represents initial values of some parameters, e.g. limits, defaults etc. These virtual set-ups offer the standard types of controllers and also the manual control. They allow performing the task of tuning the controller, finding the critical state, try out the response based controller tuning methods, and other task based on time domain course evaluation. 3.1 Real set-ups controlled via Java The virtual set-ups, even graphically corresponding to the real set-ups, do not represent the real set-ups fully, as they are based on a mathematical model. The mathematical model is simplified, so it does not reflect some phenomena, i.e. presence of noise, certain types of non-linearities, limitations, and saturations that occur in the real set-ups.
Fig. 1. An example of logic control virtual set-up HMI elements; the visualisation reacts on the student actions. The idea is that the created and verified logical circuit will be transferred from this virtual set-up to the real set-up; however the transfer needs a conversion from the function block diagram into a programming language of PLC controlling the real set-up.
To push students to a deeper understanding real-world control problems (e.g. in the model occurring non-linearities), the set of virtual set-ups has been extended with a set-up that provides the same HMI but instead of using a mathematical model, the real set-up is used. And the camera showing the current state of the set-up is used instead of a software visualisation, see Fig. 3.
The virtual set-ups supporting the continuous control assignments were designed to provide common HMI in a form typically available in control software packages, however in a simplified form and unified for all virtual setups focused on continuous control. The HMI consists of area where the operating conditions (set point, disturbances) are set, the area of choosing controller type and its parameters, the area showing the courses of control circuit variables (set
However, the connection to a real device brings problems that do not appear in a fully virtual set-ups use – no more than one student can access this remotely controlled real setup. To ensure that more than one student can access the setup simultaneously, four identical set-ups are present in the laboratory physically and the student is directed to that one which is currently free. If there are no free set-ups available, the student has to wait till any other student finishes his experiment. One session duration is limited to five minutes.
Fig. 2. An example of continuous control virtual set-up HMI
Fig. 3. An example of continuous control real set-up HMI 279
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3.2 Remotely accessed Matlab simulations
to access the set-up control algorithm directly including the possibility of replacing it by another control algorithm.
The Java technology has become problematic recently. The problems started with the conflict between Sun and Microsoft resulting in not including Java package into MS Windows installations. This meant that the majority of those who wanted to access the virtual set-ups needed to install the Java package himself. Moreover, incompatibilities between newer and older versions of Java became significant and running the Java applets has brought the need of the setting several exceptions in the web browser. Those were the motivations to try incorporating other technologies into the Virtual Control Laboratory.
To fulfil those demands we created new generation of remotely accessed set-ups based on the mini-computer Raspberry Pi with operating system Raspbian. That allowed using any software tool executable under the operating system Linux to control the tasks. Therefore, we focused to the control system REX. It has been chosen from two reasons: firstly, we had obtained a previous experience with this system in experiments with the boiler Verner A25 (Šulc et al., 2009) and the boiler Fiedler (Vrána et al., 2014) and also with its usage in the laboratory model Cascade of Three Tanks (Vrána, 2008), and secondly, the latest versions of the REX control system allows to create the visualisation based only on HTML technologies, so no other computer with the OPC server is required (Ožana, 2015).
Our choice was simulation package Matlab allowing remote access via Matweb. It proved well in simulations, however the approach required setting of the simulation parameters and they cannot be changed during the simulation run. Further disadvantage is that we cannot see the simulation progress, because the results are available in a form of numbers or graphs until the simulation finishes. Our attempts to remove these disadvantages were unsuccessful.
The main supporting software tools are the programs RexDraw and RexView. These two programs allow remote access to real devices, so they can be used for remote access to the laboratory set-ups directly. There is also supporting tool for creating web interfaces to the tasks in a form of plugin into a graphic editor Inkscape (Rex Controls, 2014b). The set-ups can be accessed also directly from Matlab. Those three ways of the remote access make the use of set-ups very universal.
In spite of these disadvantages we created three simple online accessed simulation models; however, as the Matweb technology is no longer supported, the tasks are not assigned any more. It is possible to replace Matlab for example by C++ (Costa et al., 2010) and Scilab (Magyar and Zakova, 2012),
4.1 Description of the Laboratory Set-ups with Extended Use
4. THE SET-UPS WITH EXTENDED USE
The first two set-ups created in the new generation concept based on REX running on Raspberry Pi are Rover on a Sloped Plane (Fig. 4) and Cascade of Two Interconnected Tanks (Fig. 5).
The virtual set-ups based on Java are single purposed set-ups that can be used to demonstrate solving elementary problems. Thus, they are suitable for the basic course in Automatic Control, however they are not suitable for the advanced courses of automatic control. For this purpose, the models should make possible to solve more demanding tasks, like identification of the device dynamics, creating the mathematical model of set-up behaviour, and demonstration of advanced control strategies such as the MIMO control and the state control. From this demand, it follows that the internet accessed set-up should be accessed not only via predefined web based interface, but also it should be possible
The arrangement of the set-up Rover on a Sloped Plane is depicted in Fig. 4. The rover position (controlled variable y) is measured with an optical sensor. The rover wheel revolutions are manipulated by setting of the PWM duty cycle changing the delivered power from the motor M (manipulated variable u). The rover can move only forward, its reverse movement is possible only by drifting of the rover e
Controller
u
u
M
y
e
h1 h2
SM
w
Controller
Fig. 4. A functional scheme of the laboratory set-up Rover on a Sloped Plane
Fig. 5. A functional scheme of the laboratory set-up Cascade of Two Interconnected Tanks 280
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by the moving belt simulating a roadway. The sloped plane is represented by a pair of parallel moving belts simulating the roadway, the rover is moving on them. The belts are actuated with a pair of the stepper motors SM, the speed of the belts represents the disturbance d. The rover position should be kept either manually or automatically with a chosen type of the controller.
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If the web user interface is accessed from a mobile device, the two column layout is turned into single column layout with the online video and the graph placed below the controller setting options. There was a discussion if it is more suitable to equip the web user interface with an online video or with an animation. The Rover on a Sloped plane has no hidden manipulated elements, the online video was preferred. On the other hand, to use the online video does not show the activity of water pump in Cascade of Two Interconnected Tanks, so the animation has been chosen to visualise this set-up.
The set-up Cascade of Two Interconnected Tanks consists of two mutually interconnected water tanks, a pump, and a water reservoir, see Fig. 5. The pump is reversible; it can feed water not only from the reservoir to the tank, but also from the tank back to the reservoir. It is possible to measure water level in both tanks. The outlet flowrate can be set only manually with the valve. This set-up is principally a simple physical model, whose mathematical description can be derived using the first principle. However, its real behaviour is quite different from those obtained by the theoretical way. There are phenomena that are not typically respected in modelling, e.g. friction in the pump, non-linear dependence of flow-rate on the power supply, etc. – all these are the reasons why to use such a “trivial” set-up to demonstrate some problems of real application of control algorithms to students.
Except the browser Internet Explorer, all current mayor browsers allow showing video in the format MJPEG. Internet Explorer does not support standard MJPEG, the object ActiveX is necessary to use. Typically, this object is provided with web cameras. However, the web user interface needs to conduct a test, which browser is used to view the web user interface. Typical test rely on the presence of the string MSIE in the user-agent field, but this test fails when it is conducted on Internet Explorer 10 in the standard mode, because it provides the string MSIE only in quirk mode. The presence of string trident needs to be tested to ensure correct choice between showing as MJPEG or via the ActiveX object.
4.2 Possibilities of Web Interface in pure HTML/JavaScript
The possibilities of RexHMI can be extended with of JavaScript libraries REX.UI and REX.UI.CHARTS that allow to include in the web user interface the items such as display, slider, bar graph, and running graph of variable courses (Skyba, 2013). In the case of Rover on a Sloped Plane only the running graph is used in the web user interface, the other interface elements are the elements provided by HTML5.
Except already mentioned possibilities, the REX allows creating user interface in the form of a web page based on technologies from HTML5 family (RexControls, 2014a). The RexHMI provides a complete JavaScript library WebBuDi for the complete design of user interface from predefined graphical and textual control elements. However, it is also possible to use the RexHMI only in order to read and set values of variables and to create an own user interface directly in the HTML. It is possible to place the functions for reading and setting into the respective tags as the values of parameters ONCLICK, ONCHANGE, etc., eventually to execute those functions periodically via the JavaScript function setInterval or setTimeout. It is more comfortable to use the jQuery that allows placing all those functions into one place of HTML page code.
What also had to be solved was the access from more devices simultaneously. One option was simply to restrict the number
The web user interface was created directly in the HTML with the use of RexHMI functions for reading and setting the variables in the control algorithm. With the increase of mobile device use to browse the internet; the mobile devices have different requirements to page layouts, the adaptive layout has been chosen. When accessed from a computer, the web page is divided into two columns. The left column contains the control panel of the set-up; the right column contains an online video that is used to see the current state of the task and the graph of control algorithm variable courses, see Fig. 6. The common variables for all control modes, i.e. the rover position (controlled variable y), setpoint (w), and manipulated variable (the PWM duty cycle in %), are placed at the top of the left column, while the parameters of chosen controller are placed to the bottom of the left column and only the parameters required by selected controller are shown.
Fig. 6. The web user interface of the set-up Rover on a Sloped Plane 281
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of simultaneous accesses to one, as in case of real set-up controlled via Java described above. The other option is to allow to access the set-up from more than one device simultaneously, that means to ensure the changes done in one instance of web user interface are automatically displayed in the other instances. The second option has been chosen, because it allows to use the set-up for a kind of a game when one student can manipulate the disturbance while the other student can manipulate the manipulated variable manually to reach the set-point. Also, permission of more simultaneous accesses provides possibility to the teacher to supervise the student activity remotely. Even implementing this second option still left opened the possibility to limit the number to simultaneously accesses to one if necessary.
REFERENCES Costa, R., Valles, M., Jimenez, L., Diaz-Guerra, L., Valera, A., and Puerto, R. (2010). Integración de dispositivos físicos en un laboratorio remoto de control mediante diferentes plataformas: Labview, Matlab y C/C++. Revista Iberoamericana de Automática e Informática Industrial RIAI, 7(1), 23-34. Magyar, Z. and Zakova, K. (2012). Scilab based remote control of experiments. Advances in Control Education, 9(1), 206-211. Ožana, Š. (2015) Possibilities in control and visualisation of educational physical models controlled with REX control system. Automa, 2015(1), 12-13. (in Czech, Možnosti řízení a vizualizace výukových fyzikálních modelů pomocí řídicího systému REX) Piteľ, J. (2008) Modelling and Simulation of Electromechanical Systems for Heating. Control. In: Modelovanie, simulácia a verifikácia vybraných mechatronických systémov, 113-134. Tribun EU, Brno. RexControls (2014a). HMI for pool automation with Raspberry Pi [online]. Published 2014-07-02, updated 2014-12-15. Retrieved from https://www.rexcontrols.com/articles/hmi-for-poolautomation-with-raspberry-pi RexControls (2014b). Finishing the HMI for the pool automation project. [online], Published 2014-08-13, updated 2014-12-12, Retrieved from https://www.rexcontrols.com/articles/finishing-the-hmifor-the-pool-automation-project Sánchez, J., Morilla, F., Dormido, S., Aranda, J., and Ruipérez, P. (2002). Virtual and remote control labs using Java: a qualitative approach. IEEE Control Systems Magazine, 22(2), 8-20. Skyba, J. (2013). Development of remote and virtual laboratory experiments based on HTML 5. University of West Bohemia, Pilsen (in Czech, Vývoj úloh vzdálené a virtuální laboratoře založených na technologii HTML 5) Šulc, B., Hrdlička, J., Lepold, M., and Vrána, S. (2009) Control for Ecological Improvement of Small Biomass Boilers. In: Majanne, Y. (ed), Proceedings of IFAC Symposium on Power Plant and Power Systems, 120-125 IFAC, Tampere Vrána, S. (2008) Three Tanks Cascade Control with the Use of Rex Control System. In: Nové metody a postupy v oblasti přístrojové techniky, automatického řízení a informatiky. 128-133. Czech Technical University in Prague Vrána, S., Oswald, C., Plaček, V., Šulc, B., and Neuman, P. (2014) Neural Network Evaluation of Combustion Process for Continuous Control of Small Scale Biomass Fired Boilers. In: Boje, E. and Xia, X. (eds), Proceedings of the 19th World Congress of the International Federation of Automatic Control, 1440-1445. IFAC: Cape Town
5. CONCLUSIONS The presented concept based on the existence of the set-ups in two versions, the fully virtual and the real, has proved to be useful mainly in the basic courses in Automatic Control. The students accepted with great interest the possibility to communicate via computers and the alternative of home preparation. As the latest development shows, the trend towards preference of pure virtual task grows up not only from the practical reasons (less demands to instrumentation, access to the laboratory, time schedule, etc.). Also the software offer, especially using the Linux operating system, and the financial availability of necessary instrumentation have very positive effects in inspiration of gifted students to engage in creation new versions of the tasks according to their own design, or to find new solutions of the given control tasks. It allows to demonstrate any control algorithm and also to apply identification procedures, and moreover, it allows the verification of controller tuning methods arising in the framework of doctoral study. The development of the set-ups, both virtual set-ups and remotely accessed real set-ups was influenced by the reaction of students, which led to focus on other technologies than Java in newly developed remotely accessed set-ups. Another important factor is translation of the user interface into the foreign languages (Control Virtual Laboratory exists in Czech, English, German, and French) makes the usage of virtual set-ups and remote accessed real set-ups easier for increasing number of foreign students, e.g. within the framework of program Erasmus. The virtual presentations performed regularly on Open Door Days play also an important role in motivating the students to choose Control Engineering as a field of their study. The experience with the user interfaces in pure HTML/JavaScript proved that it can fully replace the previously used Java technology and overcome the problems caused by this programming tool. ACKNOWLEDGEMENTS This work was supported by the Grant Agency of the Czech Technical University in Prague, grant No. SGS13/179/OHK2/3T/12. 282