7th IFAC Symposium on Advances in Control Education 21/06/2006 MadridIn this paper we present a java based simulator for control education in basiccourses.  The  application  has  been  developed  using  the  well  known  tool  Easy  JavaSimulation.The  objective  of  the  application  is  to  help  the  student  to  learn  the  design  of  classiccontrollers such as P,PI, PID, etc testing the tuning procedures to control the position ofan antenna controlled by a DC motor. Thus the application allows the student to choosethe parameters of the antenna and the DC motor, to choose the controller to be used andits parameters and finally to simulate the closed loop system observing the evolution ofthe signals as well as a 3-D view. Furthermore, in order to show the real behavior of thesystem, dead zone, saturation, disturbances and non-linearities can be added to the model.This application has been used by the authors to teach a basic control course at EscuelaSuperior de Ingenieros (University of Seville) as virtual laboratory.Moreover, since the application is java based, this can be used by the students from theauthors’ web pages and this can also be installed in the student’s laptop (whichever theplatform is) by downloading it from the authors web page (Limon and Salas, 2003Ministerio de Ciencia y Tecnología  DPI2004-07444Ministerio de Ciencia y Tecnología DPI2003-0042

Alamo, Teodoro

Camacho, Eduardo F.

Limón Marruedo, Daniel

Rodríguez Ramírez, Daniel

Salas Gómez, Francisco

English

idUS. Depósito de Investigación Universidad de Sevilla

A JAVA BASED SIMULATOR FOR BASIC CONTROLEDUCATIOND. Limon 1 F. Salas 1 D.R. Ramı´rez 1 T. Alamo 1E.F. Camacho 1Abstract: In this paper we present a java based simulator for control education in basiccourses. The application has been developed using the well known tool Easy JavaSimulation.The objective of the application is to help the student to learn the design of classiccontrollers such as P,PI, PID, etc testing the tuning procedures to control the position ofan antenna controlled by a DC motor. Thus the application allows the student to choosethe parameters of the antenna and the DC motor, to choose the controller to be used andits parameters and finally to simulate the closed loop system observing the evolution ofthe signals as well as a 3-D view. Furthermore, in order to show the real behavior of thesystem, dead zone, saturation, disturbances and non-linearities can be added to the model.This application has been used by the authors to teach a basic control course at EscuelaSuperior de Ingenieros (University of Seville) as virtual laboratory.Moreover, since the application is java based, this can be used by the students from theauthors’ web pages and this can also be installed in the student’s laptop (whichever theplatform is) by downloading it from the authors web page (Limon and Salas, 2003).1. INTRODUCTIONComputer-Enhanced Learning (CEL) techniques areof great interest in teaching control or more generallyengineering topics to under-graduated or graduatedstudents (Heck, 1999; Dormido, 2004). In recent yearsthe engineering programs at most universities in devel-oped countries have change to include CEL techniquesas a basic tool in the typical engineering courseware.Interactive simulators allow the students to learn thecontrol systems design methodology interactively byselecting the most adequate control strategy or evendeveloping their own control algorithms. The resultsof their choices are quickly displayed on the computerscreen so they can asses their level of assimilationof control design methods and explore the effect ofchanging from a given controller to a different one.Moreover, it allows the teacher to concentrate in theconceptual aspects of the design methods preventing1 Dpto de Ingenierı´a de Sistemas y Automa´tica, University ofSeville, Seville 41092 , Spain, {limon, salas, danirr,alamo, eduardo}@cartuja.us.es2 The authors gracefully acknowledges funding by DPI2004-07444and DPI2003-00429 of M.Y.C.T.the unwilled effect of making control design appearas a mathematical problem without connection to theengineering practice (Dormido et al., 2004).The increased computational power also allows theuse of more realistic models removing the need of ex-cessive simplifications of real systems dynamics. CELtechniques can also be used to establish virtual controllaboratories with two main advantages: the student canpractice control methods wherever he is with just acomputer and also institutions that cannot afford largelaboratories can introduce practice to lower grade sub-jects that are usually crowded with many students.This paper presents a CEL program designed to helpthe students to train in the classic design of controllersapplied to a motivating example: the control of anantenna controlled by a DC motor. Some of the pa-rameters describing the dynamics of the motor and theantenna can be set so that the system to be controlledis effectively different for each student. This proved tobe essential to get a clear view of its understanding ofthe subject since makes the student to be involved inthe solution of his/her own problem.The implemented controllers are the classic P, PI orPID types as well as lead and/or lag networks. Alltheir parameters can be set to test the closed loop sys-tem. The graphical interface of the program quicklydisplays the results of the simulation as well as a 3-D view of the antenna in motion. Furthermore, certainnonlinearities such as saturation and dead-zones canbe added to the system in order to raise the difficulty offinding the correct parameters of the controller. Also,the student can get a more realistic experience of PIDcontroller design.The program presented here is written using the EasyJava Simulations (EJS) package. This tool provides avery convenient way to develop CEL simulation pro-grams for many scientific disciplines. The program-ming is not as difficult as using a bare programminglanguage. One of the greatest benefits of using thistool is that being it based in java it produces programsthat can be run in different hardware platforms, andalso they can be used in any computer with an in-ternet browser capable of running java applications.An additional benefit is that the code is royalty-free,thus institutions with tight budgets can save in buyinglarge quantities of licenses of well known mathemati-cal packages.The paper is organized as follows: first a brief de-scription of the Easy Java Simulations is presented insection 2. In section 3 the problem to be solved bythe students is formulated. In the following section theapplication is described and the paper draws to a closewith some conclusions.2. EASY JAVA SIMULATIONSEasy Java Simulations is a software tool designedfor the creation of computer simulations (Esquembre,2004). Easy Java Simulations was developed in thecontext of the Open Source Physics Project at the Uni-versity of Murcia, Spain (Esquembre, 2002). The soft-ware platform, and the simulations created with it, canbe used as independent programs under different op-erating systems, or be distributed via the internet andrun within html pages by most popular web browsers.Easy Java Simulations is designed for people whoare more interested in the content of the simulation,the simulated phenomenon itself, and much less inthe technical aspects needed to build the simulationprogram. Hence, it provides a conceptual structure andsimplified tools that allow designers to concentratemost of their time on the description of the model ofthe phenomenon they want to be simulated. The typ-ical audience includes science students, teachers andresearchers who have a basic knowledge of program-ming, but who cannot afford the big investment of timeneeded to create a complete graphical simulation.Most computer simulations of scientific phenomenacan be described in terms of the model-control-viewparadigm. This paradigm states that a simulation iscomposed of the model, which describes the phe-nomenon under study, the control, which defines theactions to be performed on the simulation and theview, which shows a graphical representation of thedifferent states of the phenomenon through the simu-lation. To simplify the construction of a simulation,Easy Java Simulations suppresses the control part,merging it half into the view, half into the model.Creating a simulation using this tool consists in defin-ing its model and its view (i.e., the GUI or graphicaluser interface) and establishing the mutual connec-tions needed for the correct visualization of the state ofthe phenomenon being simulated and the appropriateinteraction of the user with the view (either to modifythis state or to perform the actions defined on themodel).This explicit separation in parts reinforces conceptu-ally the central role of the model of a simulation. It isthe model that defines what the program simulates andhow. There may be different views for a given model.Teachers can create the same simulation with differentGUIs for different tasks or different students.In addition to the Model and View, Easy Java Simu-lations has one more component from which a sim-ulation is built the Introduction. For pedagogical orscientific purposes, it is always helpful to include adescription of what a simulation does, including theinstructions on how to operate it and other pertinentinformation. This information appears in the Introduc-tion, which is used to generate the content of the htmlweb page. Therefore, there are three major parts to theinterface: Introduction, Model and View.3. PROBLEM FORMULATIONThe objective of this application is to teach engineer-ing students the design of classic controllers in basiccontrol courses. The student receives the theoreticalfoundation in the lectures and some numerical prob-lems are solved during the classes. In order to makethe student solves a realistic control problem, a pro-totype problem is proposed: the control of the posi-tion of a servomechanism. A different set of physicalparameters of the servomechanism is chosen for eachstudent and they must design and test the explainedcontrollers according to some given specifications.Currently, one of the actual problems in control educa-tion is the shortage of money and space to create andmaintain laboratories. Due to this, many developmentsin virtual and remote labs through the Internet havereceived great attention in the last few years. Makinguse of computer simulations in an educational contextmeans using the computer to build theoretical modelsor to model real-world phenomena in order to helpstudents gain insight into the behavior of complex sys-tems. Interacting with an instructional simulation canhelp students to gain a better understanding of a realsystem, process, or phenomenon through exploring,Fig. 1. Main Window: System model paneltesting hypotheses, and discovering explanations forthe mechanisms and processes.Therefore, to test the solution of the proposed ser-vomechanism and experiment the real engineeringproblem they are dealing with, an interactive simulatorhas been designed. The different parts of this applica-tion will be shown later on. In what follows, a briefdescription of the problem to solve is given.The tool tries to show (with a very simple and wellknown system) the effects of the different parts ofthe controllers introduced in the theoretical lecturesand motivate the students to analyze the effects of un-desired perturbations and nonlinearities in the globalbehavior of a system modeled and controlled by linear(classical) methods.3.1 System modelThis example has a electrical part that models a ”per-manent magnet DC motor” (PMDC) with a stator ofpermanent magnets with speed controlled by armaturevoltage and a mechanical part modeled by a load withfriction and inertia (Ong, 1998).The system model is:V −Vce = Ri+L didt (1)where V is the armature voltage; R and L are themotor’s resistance and inductance. Vce is the back(counter)-e.m.f. of the motor i.e. the voltage generatedacross the motor’s terminals as the windings movethrough the motor’s magnetic field. The back-e.m.f.actually opposes the drive voltage and is proportionalto the motor’s velocity :Vce = Kcemdθdt(2)The motor converts the electrical armature current intoa mechanical torque applied to the shaft trough thetorque constant Cp.T =Cpi (3)The applied torque produces an angular velocity ω =dθ/dt according to the inertia J and coulomb frictionB of the motor and antenna.T = Jd2θdt2+Bdθdt(4)so that the system can be modeled by the transferfunctionθ(s)V (s)= G(s) =Cps(LJs2+(RJ+LB)s+CpKcem)(5)or the normalized parameter description:G(s) =Ks(s2+2δωns+ω2n) (6)with K the static gain; δ the damping factor and ωnthe natural frequency.Additionally to this linear model the student can intro-duce nonlinear parts to the model such as dead-zoneFig. 2. Main Window: Control paneland/or saturation in the actuator, output disturbanceand dynamical nonlinearities by means of parametricuncertainties.4. PROGRAM DESCRIPTIONThe java based application simulates the open loopand the closed loop behavior of a servomechanism.This program has been developed using the EasyJava Simulation which allows one to add interactionwith the user during the simulation (Limon and Salas,2003).The program has been designed in two windows:Main Window : it is the Graphical User Interfaceof the simulator and allows the user to configurethe system to be tested. This is divided in threepanels: one to describe the system to be controlled(System panel), one where the controller is selectedand tuned (Control panel) and the last one where thesimulation is carried out in an interactive fashion(Simulation panel).3-D view Window where the physical system, an an-tenna, is shown in motion in a realistic way.In what follows, the panels of the main window aredescribed.4.1 System model panelIn this panel the user describe the system to be con-trolled by means of the defining parameters of themodel (see figure 1). These parameters can be intro-duced in the two aforementioned forms: real and nor-malized parameters. The transfer function is displayedaccording to the chosen way of parameter introduc-tion. An additional help has been added to the windowabout the transfer function of the system and theirparameters.Moreover, in this panel the student can also add thenonlinearities by marking the corresponding check-box (ON/OFF) and configuring them by introducingtheir defining parameters: the value of dead-zone, thesaturating value and the percentage of variation for thedamping factor.It is worth remarking that the different forms of the pa-rameters are appropriate to introduce models obtainedby identification of a real servomechanism.4.2 Control panelThis panel is shown in figure 2 and shows the differentcontrollers that the student can use to control thedescribed system (PID classic controllers and lead, lagand lead-lag phase network (Ogata, 2002)).The defining parameters of the controllers and net-works (Ogata, 2002) can be introduced. One of theseFig. 3. Main Window: Simulation panelcontrollers can be selected by marking in the checkingbox close to the controller. The selected controller isimplemented in the closed-loop system and the usercan modify the controller parameters or change ofcontroller while the simulation is running.Moreover some help has been added showing in thebottom of the panel the transfer functions correspond-ing to the selected controller.4.3 Simulation panelIn this panel the simulation is configured and con-trolled in an interactive way and the evolution of thesignals of the system are depicted. Hence this is thepanel where the program user can see the results of hisor her control design and the effect of the nonlineari-ties introduced in the system model panel (see figure3).Given that the simulator has been designed for educa-tional purposes, it is very important not only show-ing the graphics commonly used in control such astrajectories, but also a realistic representation of theevolution of the controlled system. This is achieved inthe 3-D view window, linked to the simulation panel,which will be described later on.A second requirement in the design of this panel wasto provide a set of interactive elements that could bemanipulated by the students to make changes in adynamic way during an experiment.The panel is therefore structured in three differentparts. The main part is located in the right-hand sideof the panel. In this part the time response is shown.There are four sliding controls to set the limits of thedisplay and a sliding bar showing the time variation.In this part it is possible to fix or change the stop timefor the experiment.In the upper-left part of the panel user can checkdifferent choices of the simulation. These are:• Closed-loop or open-loop simulation• If the reference is constant (by default) or a rampsignal (of unitary slope)• If a constant disturbance is added to the output ofthe signal and the amplitude of this signal.In this part the user can also select the variables todisplay in the main part by selecting the appropriatecheckbox (re f : Reference for the angular position ofthe antenna (rd); y: Main output, angular position ofthe antenna; v: Antenna velocity; u: Control signal;and e: position error).The bottom-left part of the simulation panel is filledwith three buttons that allow the user to manage theprogram. With these elements the user can select toRun, Stop or Reset the experiment.Once the simulation results are satisfactory all thevariables displayed can be saved (in plain text formatready to be read by Matlab) to be analyzed and dis-played with other programs.4.4 3-D View windowThis is shown in figure 4. As it has been stated be-fore, one requirement of the simulator is to providea visualization that displays the physical system asrealistically as possible. So that, in this window ananimation of the antenna is given.The set point can be changed interactively by draggingthe sliding control left or right or with the referencevalue in the simulation panel. The desired position ofthe antenna is depicted by a red bar in the 3-D viewand thus, the objective of the control is to reach thisposition with a suitable evolution.This window helps the student to understand the sys-tem behavior and the effect of the different controllersand nonlinearities present in the system.User can change the point of view by dragging theantenna with the mouse pointer.Fig. 4. 3-D View window5. CONCLUSIONSIn this paper it has been shown an application to beused for education in control of lower courses. Thisapplication has been designed by means of Easy JavaSimulation. The objective of this simulator is to helpthe student to understand and get matured the controlproblem and the usage and design of classic con-trollers. The main properties of the developed applica-tion that can be highlighted are its interactive nature,the multi-platform application, the availability of theapplication by www or downloading and installing(Limon and Salas, 2003).The simulator allows the user to configure the system,the desired controller and simulate the closed loopevolution of the system showing a 3-D view of theantenna. Moreover usual real nonlinearities and dis-turbances can also be added.This application has been successfully used in basiccontrol courses by the authors at the University ofSeville for the last three years.REFERENCESDormido, S. (2004). Control learning: Present andfuture. IFAC Annual Control Reviews 28, 115–136.Dormido, S., C. Matrin, R. Pastor, J. Sanchez andF. Esquembre (2004). Magnetic levitation sys-tem: A virtual lab in ”Easy Java Simulations”. In:American Control Conference.Esquembre, F. (2002). Easy Java Simulations 3.1.http://fem.um.es/Ejs.Esquembre, F. (2004). Easy Java Simulations: A soft-ware tool to create scientific simulations in Java.Comp. Pys. Comm. 156, 199–204.Heck, B.S. (1999). Special report: Future directions incontrol education. IEEE Control System Maga-zine 19, No 5, 35–58.Limon, D. and F. Salas (2003). Virtual lab of ser-vomechanism. In:http://www.esi2.us.es/˜fsalas/en/LabVirServo.html.Ogata, K. (2002). Modern Control Engenieering.Prentice Hall. Fourth Edition.Ong, Chee-Mun (1998). Dynamic Simulation of Elec-tric Machinery using Matlab/Simulink. PrenticeHall Ptr.

A Java based simulation for basic control

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A Java based simulation for basic control

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