Introduction to Control Systems: Regulation and Control System

Introduction to Control Systems:

Regulation and Control System

Basic Concepts Control System Examples Control System Design

January 11, 2005

3

Tornado Boeing 777

• Highly nonlinear, complicated dynamics!• Both are capable of transporting goods and people over long distances

BUT

• One is controlled, and the other is not.• Control is “the hidden technology that you meet every day”• It heavily relies on the notion of “feedback”

Control systems are an integral component of any industrial society and are necessary to provide useful economic products for society. Control engineering is based on the foundation of feedback theory and linear system analysis, and integrates the concepts of network theory and communication theory. Therefore, control engineering is not limited to any engineering discipline but is equally applicable for aeronautical, chemical, mechanical, environmental, civil, and electrical engineering. For example, quite often a control system includes electrical, mechanical, and chemical components.

System A collection of components which are coordinated

together to perform a function. Dynamic System

A system with a memory. For example, the input value at time t will influence

the output at future instant. A system interact with their environment through a

controlled boundary.

The interaction is defined in terms of variables.i. System inputii. System outputiii. Environmental disturbances

The system’s boundary depends upon the defined objective function of the system.

The system’s function is expressed in terms of measured output variables.

The system’s operation is manipulated through control input variables.

The system’s operation is also affected in an uncontrolled manner through disturbance input variables.

Control is the process of causing a system variable to conform to some desired value.

Manual control Automatic control (involving machines only).

A control system is an interconnection of components forming a system configuration that will provide a desired system response.

Control System

Output

Signal

Input Signa

l

Energy

Source

Control is a process of causing a system variable such as temperature or position to conform to some desired value or trajectory, called reference value or trajectory.

For example, driving a car implies controlling the vehicle to follow the desired path to arrive safely at a planned destination.i. If you are driving the car yourself, you are performing manual

control of the car.

ii. If you use design a machine, or use a computer to do it, then you have built an automatic control system.

Transient response: Gradual change of output from initial to the desired

condition Steady-state response:

Approximation to the desired response For example, consider an elevator rising from

ground to the 4th floor.

Component or process to be controlled can be represented by a block diagram.

The input-output relationship represents the cause and effect of the process.

Control systems can be classified into two categories:i. Open-loop control systemii. Closed-loop feedback control system

Process Output

Input

An open-loop control system utilizes an actuating device to control the process directly without using feedback.

A closed-loop feedback control system uses a measurement of the output and feedback of the output signal to compare it with the desired output or reference.

Actuating Device Process Output

Desired Output

Response

Desired Output

Response

Measurement

Output

Controller

ProcessComparison

Single Input Single Output (SISO) System

Open-Loop Control System

Missile Launcher System

Closed-Loop Feedback Control System

Missile Launcher System

Desired Output

Response

Measurement

Output Variabl

es

Controller

Process

Multi Input Multi Output (MIMO) System

Static or Dynamic Systems: Static systems are composed of simple linear gains or nonlinear devices and described by algebraic equations, and dynamic systems are described by differential or difference equations.

Continuous-time or Discrete-time Systems: Continuous-time dynamic systems are described by differential equations and discrete-time dynamic systems by difference equations.

i. Power Amplification (Gain) Positioning of a large radar antenna by low-power

rotation of a knob

ii. Remote Control Robotic arm used to pick up radioactive materials

iii. Convenience of Input Form Changing room temperature by thermostat position

iv. Compensation for Disturbances Controlling antenna position in the presence of large

wind disturbance torque

i. Ancient Greece (1 to 300 BC) Water float regulation, water clock, automatic oil lamp

ii. Cornellis Drebbel (17th century) Temperature control

iii. James Watt (18th century) Flyball governor

iv. Late 19th to mid 20th century Modern control theory

i. Pancreas Regulates blood glucose level

ii. Adrenaline Automatically generated to increase the heart rate and

oxygen in times of flightiii. Eye

Follow moving objectiv. Hand

Pick up an object and place it at a predetermined location

v. Temperature Regulated temperature of 36°C to 37°C

Figure shows a schematic diagram of temperature control of an electric furnace. The temperature in the electric furnace is measured by a thermometer, which is analog device. The analog temperature is converted to a digital temperature by an A/D converter. The digital temperature is fed to a controller through an interface. This digital temperature is compared with the programmed input temperature, and if there is any error , the controller sends out a signal to the heater, through an interface, amplifier and relay to bring the furnace temperature to a desired value.

Car and Driver

Objective: To control direction and speed of car Outputs: Actual direction and speed of car Control inputs: Road markings and speed signs Disturbances: Road surface and grade, wind, obstacles Possible subsystems: The car alone, power steering

system, breaking system

Functional block diagram:

Time response:

Measurement, visual and tactile

Measurement, visual and tactile

Steering Mechanism

Steering Mechanism Automobil

eAutomobil

eDriverDriver

Desired

course of

travel

Actual course

of travel

Error+

-

Consider using a radar to measure distance and velocity to autonomously maintain distance between vehicles.

Automotive: Engine regulation, active suspension, anti-lock breaking system (ABS)

Steering of missiles, planes, aircraft and ships at sear.

Control used to regulate level, pressure and pressure of refinery vessel.

For steel rolling mills, the position of rolls is controlled by the thickness of the steel coming off the finishing line.

Coordinated control system for a boiler-generator.

Consider a three-axis control system for inspecting individual semiconducting wafers with a highly sensitive camera

i. CD Players The position of the laser spot in relation to the

microscopic pits in a CD is controlled.

ii. Air-Conditioning System Uses thermostat and controls room temperature.

i. System, plant or process To be controlled

ii. Actuators Converts the control signal to a power signal

iii. Sensors Provides measurement of the system output

iv. Reference input Represents the desired output

SensorSensor

Actuator

Actuator

ProcessProcessController

Controller

++

Set-point or

Reference input

Actual Outpu

t

ErrorControll

ed Signal

Disturbance

Manipulated

Variable

Feedback Signal

+

-

++

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Flight Control Systems Modern commercial and

military aircraft are “fly by wire”

Autoland systems, unmanned aerial vehicles (UAVs) are already in place

Robotics High accuracy positioning

for flexible manufacturing Remote environments:

space, sea, non-invasive surgery, etc.

Chemical Process Control Regulation of flow rates,

temperature, concentrations, etc.

Long time scales, but only crude models of process

Communications and Networks Amplifiers and repeaters Congestion control of the

Internet Power management for

wireless communications Automotive

Engine control, transmission control, cruise control, climate control, etc

Luxury sedans: 12 control devices in 1976, 42 in 1988, 67 in 1991

AND MANY MORE...

“The right half of the brain controls the left half of the body. This means that only left handed people are in their right mind…”