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Teaching Analog and Digital Control Theory in One Course Session 3663 Teaching Analog And Digital Control Theory In One Course Hakan B. Gurocak Manufacturing Engineering Washington State University 14204 NE Salmon Creek Ave. Vancouver, WA 98686 Abstract: Today's trend is towards a high level of manufacturing automation and design of smart products. All of these products or their manufacturing processes contain control systems. As indicated in a recent survey, both analog and digital control modes are used by the industry to implement controllers. In a typical undergraduate engineering curriculum a control systems course introducing the fundamental notions of analog control theory is offered. To learn digital control theory, students would have to take an extra course on digital control systems, usually at the graduate level. This paper explains the development of a hybrid classical/digital control systems course*. Also, laboratory experiments designed to support the new format are presented. Introduction Manufacturing engineering is a very broad discipline. Consequently, manufacturing engineers typically engage in a diverse range of activities such as plant engineering, manufacturing processes, machine design, and product design. In just about any of these roles a manufacturing engineer is challenged by a control system since today's trend is towards a high level of manufacturing automation and design of smart products. For example, such products include active suspensions in cars that can adjust to the road conditions or video cameras that can stabilize images that would otherwise be fuzzy due to the shaking of the hand holding the camera. As the industry continues to introduce more sophisticated control applications in its products and manufacturing processes, the engineers who design, develop and build these products and systems will face a challenging, dramatic change in their role. Therefore, they need to better understand and be able to apply control systems theory. Page 4.478.1 Page * Partial support for this work was provided by the National Science Foundation's Division of Undergraduate Education through grant DUE # 9796330. One difficulty in teaching control systems is to provide a balance between theory and practice1. A control systems laboratory that provides the connection between the abstract control theory and the real world applications is an invaluable tool for this purpose. However, given today's trend, this is not the only dilemma the control engineering educator is facing. Because of the ability of a digital computer to process immense quantities of information and base control strategies on that information, more and more control system designs involve a digital controller as part of the control strategy2. A typical introductory control systems course found in the undergraduate curriculum of many universities introduces the theory of analog controllers. These are controllers that are implemented by analog signal processing circuitry. Usually these introductory courses are followed by other control systems courses such as digital control systems where the theory of the digital controllers is introduced. These controllers are implemented by using a computer as opposed to analog signal processing circuitry. Because industrial applications involve both digital and analog control modes, a good control systems education should contain the relevant theory of both fields. However, in many cases due to the limitations on the maximum credit requirements it is not possible to offer a digital control systems course at the undergraduate level. As a result the students either have to take such a course at the graduate level or, as is usually the case, they graduate without the digital control systems knowledge. The Manufacturing Engineering degree program at Washington State University in Vancouver requires 128 credits for graduation. When the curriculum was designed a single control systems course was planned. There is no graduate program at the Vancouver campus and also there is no digital control elective in the curriculum. This paper presents a hybrid analog/digital undergraduate control systems course with laboratory experiments. The course enables the students to learn the most fundamental theory of both analog and digital control systems, as well as their actual physical implementation in a single course. Consequently, the total credit requirement for the degree is not increased yet the students graduate with a working knowledge of both analog and digital control systems. Course Content ME 375 Manufacturing Control Systems course is a three semester-credit course with two hours of lectures and three hours of laboratory per week. The course was offered for the first time in Spring 1998 in the Manufacturing Engineering program at Washington State University in Vancouver. The course content (Table 1) has been carefully organized to reflect the basic concepts, namely, dynamic system specifications, stability, concept of feedback and dynamic compensation, that a control engineer must understand. A recent survey1 indicates that classical control techniques, as opposed to state space techniques, still dominate the industry. Therefore, the course content places more emphasis on classical control theory than the state space approach. Since the theory of digital control systems very much parallels that of analog control systems, many of the concepts are covered in parallel for both digital and analog control systems. The integrated, parallel approach taken in the course highlights the differences and 4.478.2 Page similarities in both control modes as new theory is introduced throughout the semester. Table 1. Course content of ME 375. 1) DYNAMIC RESPONSE 4) ROOT-LOCUS DESIGN METHOD 1.1 Continuous-time systems (analog) For both continuous and discrete-time systems 1.1.a Transfer functions, block diagrams 4.1 Root-locus properties 1.1.b Poles and zeros 4.2 Rules for sketching the root locus 1.1.c First order response 1.1.d Second order response 1.1.e Transient response requirements 1.2 Discrete-time systems (digital) 1.2.a Difference equations and z-transform 1.2.b Pulse trans. func. and sampling theorem 1.2.c Solution techniques for difference eq. 2) FREQUENCY RESPONSE 5) COMPENSATOR DESIGN VIA 2.1 Bode plots for continuous systems. ROOT LOCUS METHOD For both continuous and discrete-time systems 5.1 PI, PD and PID design 5.2 Ziegler-Nichols PID tuning technique 3) PRINCIPLES OF FEEDBACK 6) STATE SPACE DESIGN For both continuous and discrete-time systems For continuous-time systems 3.1 Open, closed loop systems 6.1 Brief discussion of state space representation 3.2 Types of feedback (P, PI, PD, PID) 3.3 Steady state accuracy and system type 3.4 Stability 3.5 Actuators, feedback devices, PLCs. Laboratory The controller designs discussed in the lectures are based on MATLAB/SIMULINK simulations. This is certainly useful, but it cannot replace real equipment1,3-8. It is important that the students learn about the real world issues such as measurement noise, friction and actuator saturation that are hard to incorporate into a simulation. In addition, they need to get familiar with some of the technology such as tachometers, encoders, etc., used in the implementation of control systems. The laboratory sessions are designed to fill these gaps. At the beginning of each session a lecture related to the experiments is given. This lecture complements the formal lectures of the course and in many ways gives a chance to relate the theory discussed in the formal lectures to the practical issues and implementations. Equipment The equipment needed to develop the new laboratory includes servo fundamentals training units by Feedback Inc., function generators, oscilloscopes and software for simulation and design. Table 2 gives a list of the hardware and software that are used in the laboratory. Figure 1 shows the servo fundamentals unit by Feedback Inc. It consists of three parts: (1) mechanical unit, (2) analog unit, and (3) digital unit and its software. The mechanical unit has a DC motor, gear reduction, tachometer, encoders and potentiometer position sensors. The analog unit has analog electronics (with Op Amps) to drive the mechanical unit. The digital unit has interface 4.478.3 Page electronics for interfacing a computer to the mechanical unit. It also comes with a tutorial style software. Using these units students can quickly construct control circuits by plugging wires into the units. Parts of the units such as the error channel on the analog unit can also be used for experimentation. Table 2. Hardware/software used in the laboratory. Feedback 33 Series Analog and Data Acquisition Cards (DAQ) Digital Servo Fundamentals Trainers ComputerBoards, Inc. Product 33-001 CIO-DAS1600/16 DAQ card (Includes: Mechanical, analog (Includes driver software) and digital unit as well as a driver software) Function Generators (Hewlett-Packard 33120A) MATLAB functional unit (MATLAB) Oscilloscopes (Control systems toolbox ) (Tektronix TDS 220) (SIMULINK) Triple Output Power Supplies (Hewlett-Packard E3631A) QuickBASIC compiler Figure 1. Analog unit (with wires), mechanical unit and the digital unit of the servo fundamentals trainer by Feedback, Inc. Laboratory Sessions ME 375 contains thirteen weekly laboratory sessions. The objectives are to (1) provide a better understanding of the concepts of abstract control systems theory, (2) highlight the differences and similarities between the digital and analog control modes, and (3) teach the hardware/software implementation of the mathematical controller designs
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