FCS Chapter 1 PDF

Chapter 1 Introduction A control system consists of subsystems and processes (or plants) assembled for the purpose of obtaining a desired output with desired performance, given a specified input. Figure 1.1 shows a control system in its simplest form,...

Chapter 1 Introduction A control system consists of subsystems and processes (or plants) assembled for the purpose of obtaining a desired output with desired performance, given a specified input. Figure 1.1 shows a control system in its simplest form, where the input represents a desired output. EXAMPLES OF CS: Radar system We build control systems for four primary reasons: Satellite system 1. Power amplification – or power gain Rover ( moon explorations) Elevators 2. Remote control – or dangerous locations Mobile robots ( mobot ) last sem project 3. Convenience of input form - provide desired output Regulated power supply 4. Compensation for disturbances - ability to compensate (control dvd players/cd players/ vhs/ legendary betamax ( wala pa kayo noon, pero meron na ako) Smartphones ( not so smart ) And many others Two major measures of performance are apparent: (1) the transient response (2) the steady-state error 1.2 A History of Control Systems mechanism closes with the ascending flyballs and opens with the descending flyballs, thus regulating the speed. Liquid-Level Control Stability, Stabilization, and Steering The Greeks began engineering feedback systems around 300 B.C. A water clock invented by Ktesibios. Latter half of the nineteenth century, The idea of liquid-level control was applied to an oil lamp by Philon of In 1868, James Clerk Maxwell published the stability criterion for a third- Byzantium. order system based on the coefficients of the differential equation. Steam Pressure and Temperature Controls In 1874, Edward John Routh, using a suggestion from William Kingdon Clifford that was ignored earlier by Maxwell, was able to extend the stability Regulation of steam pressure began around 1681 with Denis Papin’s criterion to fifth-order systems. invention of the safety valve. In 1877, the topic for the Adams Prize was “The Criterion of Dynamical In the seventeenth century, Cornelis Drebbel in Holland invented a purely Stability.” mechanical temperature control system for hatching eggs. (floater) Routh submitted a paper entitled A Treatise on the Stability of a Given State Speed Control of Motion and won the prize. This paper contains what is now known as the In 1745, speed control was applied to a windmill by Edmund Lee. Routh-Hurwitz criterion for stability. William Cubitt improved on the idea in 1809 by dividing the windmill sail into Alexandr Michailovich Lyapunov also contributed to the development and movable louvers. formulation of today’s theories and practice of control system stability. In the eighteenth century, James Watt invented the flyball speed governor to A student of P. L. Chebyshev at the University of St. Petersburg in Russia, control the speed of steam engines. A steam valve connected to the flyball Lyapunov extended the work of Routh to nonlinear systems in his 1892 doctoral thesis, entitled The General Problem of Stability of Motion. During the second half of the 1800s, the development of control systems focused In the late 1920s and early 1930s, H. W. Bode and H. Nyquist at Bell on the steering and stabilizing of ships. Telephone Laboratories developed the analysis of feedback amplifiers. These contributions evolved into sinusoidal frequency analysis and design In 1874, Henry Bessemer, using a gyro to sense a ship’s motion and applying techniques currently used for feedback control system. power generated by the ship’s hydraulic system, moved the ship’s saloon to In 1948, Walter R. Evans, working in the aircraft industry, developed a keep it stable (whether this made a difference to the patrons is doubtful). graphical technique to plot the roots of a characteristic equation of a Other efforts were made to stabilize platforms for guns as well as to stabilize feedback system whose parameters changed over a particular range of entire ships, using pendulums to sense the motion. values. This technique, now known as the root locus, takes its place with the work of Bode and Nyquist in forming the foundation of linear control systems Twentieth-Century Developments analysis and design theory. It was not until the early 1900s that automatic steering of ships was achieved. 1.3 System Configurations In 1922, the Sperry Gyroscope Company installed an automatic steering (2) Two major configurations of control systems: system that used the elements of compensation and adaptive control to improve performance. However, much of the general theory used today to 1. open loop improve the performance of automatic control systems is attributed to 2. closed loop Nicholas Minorsky, a Russian born in 1885. It was his theoretical development applied to the automatic steering of ships that led to what we call today proportional-plus-integral-plus-derivative (PID), or three-mode, controllers. 1. Open loop - the input transducer converts the form of the input to the form used by the - it cannot compensate for any disturbances that add to the controller’s driving controller. An output transducer, or sensor, measures the output response signal and converts it into the form used by the controller. Computer-Controlled - do not correct for disturbances and are simply commanded by the input. Systems - open-loop systems are mechanical systems consisting of a mass, spring, - In many modern systems, the controller (or compensator) is a digital and damper with a constant force positioning the mass. The greater the force, computer. The advantage of using a computer is that many loops can be the greater the displacement. Again, the system position will change with a controlled or compensated by the same computer through time sharing. disturbance, such as an additional force, and the system will not detect or - Advantages of Closed-loop system correct for the disturbance. Greater accuracy - Advantage of open-loop system Less sensitive to noise, disturbances, and changes in the environment Cheap Transient response and steady-state error can be controlled more Easier to implement conveniently and with greater flexibility often by simple adjustment of Easier to maintain gain in the loop and sometimes by redesigning the controller. Good for applications that require set parameters DISADVANTAGES More complex 2. Closed-Loop More expensive - namely sensitivity to disturbances and inability to correct for these disturbances, may be overcome in closed-loop systems. 1.4 Analysis and Design Objectives Analysis is the process by which a system’s performance is determined. - We are concerned about the accuracy of the steady-state response - Example: - elevator must be level enough to with the floor for the For example: evaluate transient response and steady-state error to determine if they passengers to exit. meet the desired specs. - -- an antenna tracking a satellite must keep the satellite within its Design is the process by which a system’s performance is created or changed beamwidth in order not to lose track. Transient Response - -- disk drive finally stopped at the right track Example: If transient response and steady-state error are analyzed & found not to (3.) Stability meet the specifications, then we change parameters or add additional components - Control sytems must be designed to be stable That is, their natural to meet the specifications. response must decay to zero as time approaches infinity, or oscillate. -- instability could lead to self destruction of the physical device if limit stops (3) Three main primary objectives of control system analysis and design are not part of the design. 1. Transient Response 2. Steady-State Response 1.5 The Design Process 3. Stability Step 1 Transform Requirements Into a Physical System (1.) Transient response is important. In a computer, transient response Step 2 Draw a functional block diagram contributes to the time required to read or write to the computer’s disk Step 3 Create a Schematic storage. (2.) Steady-State Response Step 4 Develop a Mathematical Model (Block Diagram) - This response resembles the input and is usually what remains after the the Step 5 Reduce the block diagram transient have decayed to zero. Step 6 Analyze and design 1.6 Computer-Aided Design 2. Name three reasons for using feedback control systems and at least one reason for not using them. Included are - Yes – power gain, remote control (1) Simulink, which uses a graphical user interface (GUI); - No - expensive (2) the LTI Viewer, which permits measurements to be made directly 3. Give three examples of open-loop systems. from time and frequency response curves; - Low pass Filter (3) the SISO Design Tool, a convenient and intuitive analysis and design - Motor - Inertia Supported between two bearings tool; and 4. Functionally, how do closed-loop systems differ from open-loop systems? (4) the Symbolic Math Toolbox, which saves labor when making - Closed-loop systems compensate for disturbances by measuring the response, symbolic calculations required in control system analysis and design. comparing it to the input response (the desired output), and then correcting the output response. 5. State one condition under which the error signal of a feedback control system would not be the difference between the input and the output. - Under the condition that the feedback element is other than unity 6. If the error signal is not the difference between input and output, by what general name can we describe the error signal? - Actuating signal 7. Name two advantages of having a computer in the loop. Review Questions - Multiple subsystems can time share the controller 1. Name three applications for feedback control systems. - Any adjustments to the controller can be implemented with simply software - Samples given in ppt cs1-intro changes 8. Name the three major design criteria for control systems. - Transfer Function - Stability - State-Space - Transient Response - Differential Equation - Steady-State Error 16. Briefly describe each of your answers to Question 15. 9. Name the two parts of a system’s response. Transfer function - the Laplace transform of the differential equation - Steady-State State-space - representation of an nth order differential equation as n simultaneous - Transient first-order differential equations 10. Physically, what happens to a system that is unstable? Differential equation - Modeling a system with its differential equation. - It follows a growing transient response until the steady-state response is no 1. The flyball governor is generally agreed to be the first automatic feedback controller longer visible. The system will either destroy itself, reach an equilibrium state used in an industrial process. True or False 2. A closed-loop control system uses a measurement of the output and feedback of the because of saturation in driving amplifiers, or hit limit stops. signal to compare it with the desired input. True or False 3. Engineering synthesis and engineering analysis are the same. True or False 11. Instability is attributable to what part of the total response? 4. The block diagram in Figure 1.31 is an example of a closed-loop feedback system. True or False - Natural Response 5. A multivariable system is a system with more than one input and/or more than one output. True or False 12. Describe a typical control system analysis task. 6. Early applications of feedback control include which of the following? a. Water clock of Ktesibios - Determine the transient response performance of the system b. Watt’s flyball governor c. Drebbel’s temperature regulator 13. Describe a typical control system design task. d. All of the above 7. Important modern applications of control systems include which of the following? - Determine system parameters to meet the transient response specifications for a. Safe automobiles b. Autonomous robots the system. c. Automated manufacturing d. All of the above 14. Adjustments of the forward path gain can cause changes in the transient response. 8. Complete the following sentence: Control of an industrial process by automatic rather than manual means is often called.____________. True or false? a. negative feedback b. automation - True c. a design gap d. a specification 15. Name three approaches to the mathematical modeling of control systems. 9. Complete the following sentence: ________ are intrinsic in the progression from an The output signal is fed back so that it subtracts from the input signal. NEGATIVE initial concept to the final product. FEEDBACK a. Closed-loop feedback systems A system that uses a measurement of the output and compares it with the desired b. Flyball governors output. CLOSED-LOOP FEEDBACK CONTROL SYSTEM c. Design gaps A set of prescribed performance criteria. SPECIFICATIONS d. Open-loop control systems A measure of the output of the system used for feedback to control the system. 10. Complete the following sentence: Control engineers are concerned with FEEDBACK SIGNAL understanding and controlling segments of their environments, often called ___. A system with more than one input variable or more than one output variable. a. systems MULTIVARIABLE CONTROL SYSTEM b. design synthesis The result of making a judgment about how much compromise must be made c. trade-offs between conflicting criteria. TRADE-OFF d. risk An interconnection of elements and devices for a desired purpose. SYSTEM 11. Early pioneers in the development of systems and control theory include: A reprogrammable, multifunctional manipulator used for a variety of tasks. ROBOT a. H. Nyquist A gap between the complex physical system and the design model intrinsic to the b. H. W. Bode c. H. S. Black progression from the initial concept to the final product. DESIGN GAP d. All of the above The intricate pattern of interwoven parts and knowledge required. COMPLEXITY OF 12. Complete the following sentence: An open-loop control system utilizes an actuating DESIGN device to control a process. The ratio of physical output to physical input of an industrial process. PRODUCTIVIY a. without using feedback The process of designing a technical system. ENGINEERING DESIGN b. using feedback c. in engineering design A system that utilizes a device to control the process without using feedback. OPEN- d. in engineering synthesis LOOP CONTROL SYSTEM 13. A system with more than one input variable or more than one output variable is known Uncertainties embodied in the unintended consequences of a design. RISK by what name? The process of conceiving or inventing the forms, parts, and details of a system to a. Closed-loop feedback system achieve a specified purpose. DESIGN b. Open-loop feedback system c. Multivariable control system The device, plant, or system under control. CONTROLLED SYSTEM d. Robust control system The output signal is fed back so that it adds to the input signal. POSITIVE FEEDBACK 14. Control engineering is applicable to which fields of engineering? An interconnection of components forming a system configuration that will provide a a. Mechanical and aerospace desired response. CONTROL SYSTEM b. Electrical and biomedical The control of a process by automatic means. AUTOMATION c. Chemical and environmental d. All of the above The adjustment of the parameters to achieve the most favorable or advantageous 15. Closed-loop control systems should have which of the following properties: design. OPTIMIZATION a. Good regulation against disturbances The process by which new physical configurations are created. SYNTHESIS b. Desirable responses to commands A mechanical device for controlling the speed of a steam engine. FLYBALL c. Low sensitivity to changes in the plant parameters GOVERNOR d. All of the above