Virtual 3D Controllable Machine Models for ...

Session T2C

Virtual 3D Controllable Machine Models for implementation of Automations Laboratories Erick A. Salazar, Manuel E. Macías Electrical and Computing Engineering, ITESM Campus Monterrey Av. Garza Sada 2501, 64849 Monterrey, N.L. México [email protected], [email protected] Abstract - Nowadays engineer students, typically of automation, need to prove their PLC logic programs against diverse automatic systems, this gives the student a competitive approach to the working world. For a student to prove their knowledge, a fully equipped laboratory oriented for this course is needed. For the purpose of automation only, it is required at least a PLC for control, a PC for communication and of course that something to control. Evidently not all the universities can afford this fully equipped laboratory. For this problematic situation we propose an innovative solution: Virtual Machine Models, which substitute completely the entire components of the previously mentioned laboratory, for one or many virtual not expensive cells or stations. These Virtual Models behave identically to a real mechanical model, but with several advantages. These machines are in 3D, so the user can explore them entirely, they are inexpensive, easy to reproduce, unbreakable, light weighted and can run in any computer. They also are adaptable to be used not only in automation but in other engineering areas. Index Terms - Automation, Laboratory Education, Virtual Machines, Virtual Models. INTRODUCTION Nowadays companies are demanding even more competitive engineers not only with solid knowledge but with plenty of experience, well prepared, able to achieve successfully the emerging day by day problems [3]. Knowing this, universities cannot continue teaching its students the way they have been doing it for years, the teaching methods have to evolve as the requirements in the real world are evolving. Universities around the world are aware of this tendency therefore they have started to implement new ways for preparing their students, developing studying and investigation centers, company alliances and of course fully equipped laboratories. The purpose of this paper is to better describe an economic solution to fully equip any engineering laboratory, such as an automation laboratory, microcontrollers laboratory and tele-engineer laboratory, jus to mention a few. It is not as easy as it sounds for universities, to evolve their method of teaching only by developing new laboratories for

their distinct subjects, because they imply facilities and the acquisition of expensive equipment. For these, there have been ways to reduce these costs without sacrificing the functionality or efficiency of the laboratory. A very outstanding solution is what the authors call as controlled virtual machines, which are fully explained in this paper. The solution we present has multiple applications and variations; it can be applied to different engineering laboratories which give it advantage against similar solutions. CONTROLLABLE VIRTUAL MACHINES AS A SOLUTION Taking automation classes for example, the students have to learn how to program in LAD, STL, SFC or similar PLC’s languages; a class could be made in which theory for the student will be taught, but the best way for the student to learn is by experience. In this particular case, the better way to learn how to program PLC’s is of course by programming PLC’s. But for any university to provide this benefit to their students, having a facility specially designed for these purposes, in this case a laboratory is important [4]. But a laboratory is expensive because it needs real industrial equipment, most of the times too expensive for a college to pay. A common automation station will need the following equipment: • • • •

A PC utilized for programming and communicating with the PLC. A PLC used for controlling the plant and communicating with distinct human interfaces. A Panel Operator or Touch Panel utilized by the student to order directly any action to the PLC. Finally, any controllable process or machine.

It has to be taken into account that it is not functional to have only one station, due to the number of students in a classroom. If it is of desire to have multi stations it will raise the price enormously, making it almost impossible to finally have one station per student.

/978-1-4244-4714-5/09/$25.00 ©2009 IEEE October 18 - 21, 2009, San Antonio, TX 39th ASEE/IEEE Frontiers in Education Conference T2C-1

Session T2C Operator Panel

Because of this reason, it is a very expensive solution to develop enough stations to fit a classroom.

Programmable Controller PROFIBUS

II. How about exchanging the mechanical model instead of a virtual model?

I/O Transport & Sorting Line

MPI

High End PC

FIGURE 1 STATION COMPONENTS CONECTION SCHEMATIC

FIGURE 2 REAL MECHANICAL MODEL MACHINE UTILIZED AS CONTROLLED PLANT AT ITESM LABORATORIES

The solutions we present have different variations, these solution enables the user to posses multi-stations without spending large amounts of money, these solutions are detailed below: I. To equip laboratories with real mechanical models is not an affordable option The image above shows a station completely equipped with industrial components. The computer where the student or engineer programs the control, linked via Ethernet or a fieldbus with the PLC, which controls the plant; also the PLC is connected with an HMI via Ethernet in which the user can control the process. Finally, PLC sends digital signals to the real model process. Figure 1 explains the previous with a schematic. The only difference between this station and industry is the process to control. Evidently it is almost impossible to have a real distribution line process within the facility of the university, because of this reason a real model of this distribution line, which behaves mechanically and controllably exactly as the real one is needed. This means having a mechanical model of the distribution line with the same number of actuators and the same numbers of sensors as the real, all of them sending their signal to the PLC. A mechanical model like this can be as expensive as a midsized car and are produced by companies like Dessault Systems or FESTO. It is important to understand that having one mechanical model means to have only one station. A station that can be used by 2 or 3 students simultaneously, but no more.

Imagine not to spend big amounts of money in these expensive mechanical models each time you need to equip a station, instead of this option spend only a moderate amount and get a virtual model who behaves exactly as the mechanical one, but with the advantage that this virtual model can be reproduced several times (as many as needed) to equip several stations, because its virtual! These virtual models are 3D, with high definition and high level of detail. They have all the same actuators and sensors a mechanical model has, and all of them are connected as one via Profibus or any Industrial Network to the PLC. The virtual model is not software, is an application (like an *.exe file), this means that once you own it you don’t need to install anything to use it. But these virtual models are programmed in LABVIEW, and the application extension file is *.vi; for this reason, your computer needs to recognize this extension, and for that it needs to download the LABVIEW Run-Time Engine from the National Instrument webpage [2]. Once the extension is recognized any computer can run the virtual model. It is important to emphasize that with this solution the station will be equipped with: • A PC in which the student programs the PLC, downloads or uploads the PLC information, and runs the Virtual Model. • A real PLC that communicates with the HMI and the Virtual Model. • Finally an HMI in which the student controls the PLC in real time. If 5 stations are desired it will be needed 5 PLC’s, 5 PC’s, 5 HMI’s but only one purchase of a Virtual Model, which can be easily reproduced “n” number of times, enough to fulfill this 5 stations. Operator Panel

Programmable Controller PROFIBUS

Virtual I/O Transport & Sorting Line

MPI

High End PC

FIGURE 3 STATION COMPONENTS CONECTION SCHEMATIC


Session T2C • Industrial processes are too complex to be controlled just by one PLC, although the PLC can be expanded to control “n” I/O signals, this is not recommendable, extra PLC’s for controlling are needed because of this.

FIGURE 4 VIRTUAL MODEL MACHINE

Currently there is software like the DELMIA V5 Automation Platform from Dessault Systems [6] or SIMIT from Siemens, which presents a similar concept as the solution we present here. These software provide tools that can be taken from the library, for example previously defined virtual smart devices and assemble them into a virtual automation system along with control logic and a complete set of I/O. This means the user can buy this software with several licenses and will be able to make its own simulation of a mechanical plant, and this simulation could be controllable as well [6]. Other options are the COSIMIR virtuelle Lernumgebungen (Virtual Learning Environments) from FESTO or the Automation Studio, which are predefined buyable simulations. The disadvantages about these kinds of solutions are the following: • They can be more expensive than the actual mechanical model. • The user must have plenty experience using DELMIA or SIMIT, just to get started running the simulation. • The simulation is connected to a virtual PLC, which is implanted in to the software itself; although this embedded PLC has the same applications as a normal PLC it lacks of one particular application mode. This will be explained below. DISTRIBUTED CONTROL, POSIBLE AS PART OF THE SOLUTION

As the reader may know, in many industries there are big processing plants that are not controlled by just one PLC. When a Process is large enough to be controlled by 2 or more PLC’s and each controls a different section of the plant, it is called Distributed Control. Distributed Control arises due to two primary reasons: • Having plenty PLC’s controlling a process means back up. Having just one PLC brings the problem that if it fails then the process must stop. With Distributed Control the process won’t stop unless every PLC controlling that section malfunctions.

Having a Distributed Control implies multiple topics to be revised, such as industrial networks, control logics, and concepts related with device communication. Also teaching these subjects in an automation class will complement perfectly the course, forming a better preparation for future engineers. The Virtual Machine solution we propose here has embedded in its programming a very complete protocol which allows a complete communication with any Siemens PLC of the Simatic family, also enabling fully modus application. This way, the user can build multi stations with different sections of a process, with a virtual machine each station and an independent Siemens PLC’s controlling each section. Of course, every PLC has to be interconnected via any industrial network, obtaining as a result a complex controlled plant constituted by separated modules of virtual machines and independent PLC’s, running at last as one completely integrated process line. A process that finally will embed all the necessary subjects an automation engineer needs to know, and now can be experimented while being a student thanks to this solution. ADAPTING A SIMULATED PLC TO CONTROL THE VIRTUAL MACHINE

One of the most challenging implications of this solution is the communication of the simulation with the Siemens Simatic PLC. A development that resulted in a library of functions that interprets the signals generated inside LABVIEW to the Simatic PLC. Nowadays, if any new simulation is generated, first it is programmed within LABVIEW environment, and when finished, it is simply linked with the library protocols to the Simatic PLC, enabling communication [1]. The reason why our virtual models are compatible only with the Siemens Simatic PLC family is because those are the controllers the ITESM owns and are at our disposal to study. Fortunately Siemens is the World Leader controller seller. At the moment, when you buy a Siemens PLC you acquire the Simatic Software, for example STEP 7. In which the user can program its logic, and download the information to the PLC. This software also includes a simulation of the PLC in which you can download your logic programming and see what happens. Our Virtual Machines also communicate with this simulated PLC as well as they do with the real PLC. This gets you the advantage of having no real PLC at all, and to have the complete controllable station within one computer. Allowing the student to program his logic in STEP 7, he can be able to download his program to the simulated PLC, and see how this program interacts with the virtual machine, all this in his own computer, which means he can be anywhere and not necessarily placed in the laboratory [3].


Session T2C Although having complete communication with the Siemens Simatic family is a good advantage (The Controller Seller World Leader), it could be seen as a disadvantage not to be compatible with any other PLC in the market. Because of this we are working in a next generation of virtual machines compatible with the OPC protocol, which is independent of the PLC itself. THE VIRTUAL MACHINE DEVELOPMENT

LABVIEW is a graphic programming software, which has revolutionized the development of measurements, control, and applications. The authors have plenty experience utilizing this software, and several projects involving it have been developed. In this particular case, this “Virtual Machine” project emerged due to the necessity to develop and equip laboratories for educational purposes here at ITESM. At first, the laboratories were equipped with real mechanical models like the one showed in figure 2, but we got to the problem that students damaged the machines in their intention to learn. Due to this, the next step was to develop 2D simulations of the same model machines present in the laboratory, in which the students could continue learning to program but without risking the expensive mechanical models [1]. This step was a challenge, because we met with the problem of how to interact the simulation with a real PLC. At overcoming this challenge, the base of every next simulation arose. Is the protocol of communication that enables recognition, by the real PLC, of every signal processed inside any VI (Virtual Interface). Due to this protocol we were able to program some basic solids with LABVIEW tools to be controlled by the PLC, giving the result of the first 2D virtual machines. Which were immediately given to the students to prove their progressing in automation, avoiding with this way any malfunctions to the expensive real machine models. They were a success. These 2D models behave exactly the same way as the real mechanical machine, but they look so much different from the real machine, which makes them sometimes difficult to understand.

Regarding this, it was decided to develop these same models but now looking exactly like the real mechanical machines. This was the next step, which was also a challenge. The reason why we decided to use SOLIDWORKS to draw each part of the mechanical model machine was because is the only CAD software that can save files in VRML97 extension, extension which LABVIEW requires for reading the file. Once the solid part was finished and saved as an VRML97 file, it was exported to LABVIEW in which every part is read, opened and displayed in a scene window [5]. The assembly of the solid parts is made within LABVIEW, as also the programming logic for movement of each solid part, contemplating each to communicate independently to each I/O within the PLC through the protocol developed before. Resulting in the 3D virtual model machine, which looks exactly the same as the real mechanical model and of course behaves exactly the same as the real one too. Because of the basis of construction of each model, the result is simply an executable file, which due to the nature of LABVIEW it is extended as *.vi, extension which can run in any PC for free and without having the LABVIEW software installed, but just by downloading a Run Time application from the NI webpage to make the *.vi file recognizable for your computer [2]. REQUIREMENTS Each virtual model machine is an application developed within the tools LABVIEW provides. When the programming of the simulation is completed it is needed to convert the program into an executable file. LABVIEW itself names this executable files as *.VI, which can be read by any computer as soon as them recognize the extension file. The previous is important just to the developer of the virtual machine, below is what is important to the user. For the purpose of recognizing the extension file is not necessary to posses the software itself. Just by downloading the LABVIEW Run-Time Engine from the National Instrument webpage (www.ni.com/labview) any computer will be able to successfully run the simulation and any other LABVIEW application [2]. If the PLC is well connected to the PC then the simulation can easily be controlled. EDUCATIONAL APPLICATION When students are coursing academic subjects the best way to learn is by practicing, if the subject is in engineering, the best way to practice is within the laboratories carefully designed by universities or teachers to fulfill the areas the subject requires. Laboratories bring plenty advantages to the teaching methods:

Enhance Concepts: Having a laboratory enables the student to continue its learning beyond the classroom. Provides an extra knowledge besides just the theoretical, introducing the student engineer to the practical knowledge [1]. /978-1-4244-4714-5/09/$25.00 ©2009 IEEE October 18 - 21, 2009, San Antonio, TX 39th ASEE/IEEE Frontiers in Education Conference T2C-4 FIGURE 5 2D ELEVATOR MODEL

Session T2C Trial: A laboratory well designed usually introduces a problem to the students for them to solve (sometimes a referenced industrial problem). They are drop into action and in time limit they will manage the way they think better to solve successfully the problem. This not only develops the learning method but also the teamwork and under pressure work in the student. Motivation: A well-equipped laboratory with instruments or machines with presence in industry is an extra motivation for the student to learn. This because this way the student feels that his efforts are aimed to something useful, something that can be implemented as soon as they graduate [2]. Instead, laboratories equipped with virtual components bring a lot of other advantages:

Cost: The most noticeable benefit. Industrial equipment is very expensive, and many Universities cannot afford this. A solution for these Universities to develop their own laboratory is with no doubt the virtual option we present [5], [1]. Debugging: When the student is learning the way to program in i.e. Ladder Logic (LLD) he will commit errors. If the equipment he is using is a real one these mistakes can develop into some malfunction in the machines, which can be unfixable or expensive. Using virtual machines, this mistake will traduce into just restarting the simulation again. In both ways the student will learn to not commit this kind of mistakes and eventually will be specialized in programming PLC’s. Availability: Laboratories are workstations, and usually are under the supervision of a student or teacher in charge. For the disposal of several groups of the same subject the laboratory effective time is divided in sessions of 2, 3 or 4 continuous hours respectively. These restricted sessions are the only moment when the student can practice his knowledge of that respective subject. But instead imagine if the student has his own virtual machine in his computer and his own PLC simulation in his computer too, then he can take his own virtual station to his home to work if he desires. The limitation of time is not longer a problem. This extra time results in extra experience for the student at the end of the day [3]. Diversity: Using these virtual machines, a laboratory could easily posses an assortment of similar machines or processes, which will add diversity to each laboratory session, and which will put the student to program diverse processes. Overall understanding: With a 3D virtual machine the student can explore entirely the machine from any angle, giving him the fully understanding of how the machine works, and the function of each sensor or actuator. This characteristic is important because finally the student will have to program the PLC to control the actuators due to the sensor signals, and previously

knowing the position and how they move will ease the programming work [4]. CONCLUSIONS Having laboratories as a complement of scholar subjects motivates the students to learn more and strengthens the theory they already know. But to have a well-equipped laboratory that covers every student is a very expensive solution. Not to mention that a laboratory has time and recourses limitations. The authors present a proved solution that equipping a laboratory with virtual machines removes the time and resources limitations, and also adds new technology and safeness to the laboratory. Not to mention that its less expensive. REFERENCES [1] Macías M., Guridi E. and Ortiz A., “Extending the Laboratory Concept with Computer Emulations in Automation”, 37th ASEE/IEEE Frontiers in Education Conference, 2007 [2] Debevec, K., Shih, Kashyap, V., “Learning Strategies and Performance in a Technology Integrated Classroom”, Journal of Research on Technology in Education, Vol.38, No. 3, 2006. [3] Gomis, Montesinos, Galceran, Bergas and Sudriá, “A Chemical Process Automation Virtual Laboratory to Teach PLC Programming”, Int. J. Engng Ed., Vol. 23, No. 2, 2007 [4] Kezunovic, M., Abur, A., Huang, G., Bose A. and Tomsovic, K., “The Role of Digital Modeling and Simulation in Power Engineering Education”, IEEE transactions on power systems, Vol. 19, No. 1, 2004. [5] Stoeppler, G., Menzel, T., Douglas, S., “Simulation of machine tools and manufacturing systems”, IEE Computing & Control Engineering, February/March 2005. [6] Caie, J., “Discrete Manufacturers Driving Results with DELMIA V5 Automation Platform”, ARC white paper, January 2008 [7] Macías, M., Guridi, E., “Computer Emulations to Support Training in Automation”, IFAC Conference on Cost Effective Automation IFAC-CEA 2007. [8] Liu, J., and Landers, R., “Modular Control Laboratory System with Integrated Simulation, Animation, Emulation and Experimental Components”, Int. J. Engng Ed., Vol. 21, No. 6, 2005.
