C.01 Basic Concepts and Terminology

8/12/2019 C.01 Basic Concepts and Terminology

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HCM City Univ. of Technology, Faculty of Mechanical Engineering Nguyen Tan Tien

1. BASIC CONCEPTS AND

TERMINOLOGY

Control System Technology 1.01 Basic Concepts and Terminology




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1. Introduction

- A control system is a group of components that maintains a desired result by

manipulating the value of another variable in the system

- Example: I. Polzunovswater level float regulator - 1765



1. Introduction- Example: Wallsfly-ball governor - 1769



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2. Block Diagrams and Transfer Functions

- The block diagram (skhi) is a method of representing a control system thatretains only this important feature of each component

- Signal lines (ng tn hiu) indicate the input and output signals of thecomponent

- The energy source is not shown on block diagrams. However, many componentsdo have an external energy source that makes amplification of the input signal

possible



2. Block Diagrams and Transfer Functions2.1 Block diagrams

- A block diagram consists a block representing each component in a control

system connected by lines that represent the signal paths

- Example: An simple block diagram of a person driving an automobile



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2.1 Block diagrams

- Example: Block representations of various components

Thermocouple temperature sensor: a thermocouple is a junction between twodifferent metals that produces a voltagerelated to a temperaturedifference




Amplifier: an amplifier or simply amp, is a device for increasing thepowerof asignal



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2.1 Block diagrams

DC Motor




Valve: valve is used to control flow rate by opening/closing the gate positionresponse to signals received from controllers



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2.1 Block diagrams

Liquid flow transmitter: a device used to measure the flow of liquids in

pipelines and convert the results intoproportional electric signals




Driver of automobile



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2.1 Block diagrams

Automobile power steering unit: steering is the term applied to the collection of

linkages which will allow a vehicle to follow the desired course




Automobile



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2.2 Transfer functions

- The most important characteristic of a component is the relationship between

the input signal and the output signal. This relationship is expressed by thetransfer function of the component

- A transfer function () is defined as the output divided by the input

=

=

()

()

- Steady state values for the , which is sometimes called simply the gain

= =



2. Block Diagrams and Transfer Functions2.2 Transfer functions

- Example: A potentiometer is used as a position sensor. The pot is configured in

such a way that 0of rotation yields 0and 300yields 10. Find the transfer

function of the pot

Solution

The transfer function is output divided by input. In this

case, the input to the pot is position in degreesandoutput is volts

=

=

10

30 = 0.0333 /

The transfer function of a component is an extremely

useful number. It allows you to calculate the output of

a component if you know the input



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2.2 Transfer functions

- Example: For a temperature-measuring sensor, the input is temperature, and the

output is voltage. The sensor transfer function is given as 0.01/deg. Find thesensor output voltage if the temperature is 600

Solution

The sensor output voltage if the temperature is 600

= = 600 0.01

= 6

- can be a series of connection

= =



2. Block Diagrams and Transfer Functions2.2 Transfer functions

- can be a parallel of connection

= = +

- can be a feedback connection

= =

1 +



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3. Open-Loop Control

- An open-loop control system utilizes an actuating device to control the process

directly without using feedback

- An open loop control system does not compare the actual result with the desired

result to determine the control action

- An calibrated setting, previously determined by some sort of calibration procedure

or calculation, is need to obtain the desired result



3. Open-Loop Control- Example: A simple robot arm open-loop position system



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3. Open-Loop Control

- Example: The system consists of an electric motor driving a gear train, which is

driving a winch. The motor turns at 100 for each volt () supplied. The

output shaft of the gear train rotates at 1/2of the motor speed. The winch (with a

3 shaft circumference) converts the rotary motion () to linear speed.



3. Open-Loop ControlSolution

The transfer function of the whole system

or

We have shown that the transfer function of the complete system

= =100

1

0,5

1

3/

1= 150

/

Knowing this value, we can calculate the system output for any system input. For

example, if the input to the this system is 12(to the motor), the output speed of

the winch is calculated as follows

= = 12 150/

= 1800/



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4. Closed-Loop Control

- A closed-loop control system uses a measurement of the output and feedback of

this signal to compare it with the desired output (reference or command)

Open-loop control

Closed-loop control

- In a closed-loop control system, the output of the process (controlled variable) is

constantly monitored by a sensor



4. Closed-Loop Control- Example: A simple robot arm closed-loop position system

Open-loop control

Closed-loop control



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4. Closed-Loop Control- Example: position control of machine tool table

Machine tool table moves from left to right with = 400and = 640. The

sampling time of the system is = 0.1



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4. Closed-Loop Control- Compare between open-loop control and close-loop control


Open-loop Control Close-loop Control

- shows a open-loop action: simple,

low cost

- can only counteract against

disturbances, for which it has been

designed; other disturbances cannot

be removed

- cannot become unstable - as long as

the controlled object is stable

- need to calibrate the system regularly

- shows a open-loop action: complex,

high cost

- can counteract against disturbances

- can become unstable

- no need to calibrate the system


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5. Linear vs Nonlinear

- Linear Element

Sinusoidal input waveform Linear Element Output waveform ?

Use the input/output graph to determine the value of the output for each value ofthe input:

at time , input value yields output value

Notice the sinusoidal shape of the output waveform: A linear element alwayspreserves the shape of the input waveform



5. Linear vs Nonlinear- Nonlinear Element

Sinusoidal input waveform Nonlinear Element Output waveform ?

Notice how the nonlinear element distorts the shape of the input waveform,resulting in a non-sinusoidal output waveform



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- Linear Element with Dead Band Nonlinearity

Dead band is range of values through which an input can be changed without

producing an observable change in the output The dead band effect occurs whenever the input change direction, example:

backlash in mechanical gear trains

Sinusoidal input waveform Dead Band NonlinearityOutput waveform ?

Notice the distortion in the output waveform caused by the dead band. Once thedead band is crossed, it has no further effect until the input changes direction

again



5. Linear vs Nonlinear- Nonlinear Element with Hysteresis

Hysteresis occurs when the I/O graph follows different curved paths when theinput increase and decrease

The result in I/O graph that forms a loop, and the value of the output for anygiven input depends on the history of the previous inputs

Notice the distortion in the output waveform caused by the hysteresis



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- Linear Element with a Saturation Nonlinearity

Saturation refers to the limitations on the range of values for the output of a

component All real components reach a saturation limit when the input is increased or

decreased beyond its limit values



6. Damping and Stability- The gain of the controller determines a very important characteristic of a control

systems response: the type of damping or stability that the system displays inresponse to a disturbance



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7. Objectives of a Control System

- Control Objectives: after a load or set-point change, the control system should

Minimize the maximum value of the error: min ( )

Minimize the setting time: min ()

Minimize the residual error (steady-state): min ( 1)



8. Control Performance Criteria- To evaluate a control system effectively, two decisions must be made

the test must be specified

the criteria of good control must be selected

- A step change in set-point or load is the most common test

- The three most common criteria of good control

Quarter amplitude decay (suy gimmtphntbin )

Minimum integral of absolute error (tch phn sai lchtithiu)

Critical damping (gimchntihn)



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8. Control Performance Criteria

1. Quarter amplitude decay

+ This criterion specifies a damped oscillation in which each successive positive

peak value is of the preceding positive peak value

+ Quarter amplitude decay is a popular criterion because it easy to apply andprovides a nearly optimum compromise of 3 control objectives

+ A variation of this criterion is peak percentage overshoot = 100



8. Control Performance Criteria2. Minimum integral of absolute error

+ This criterion specifies that the total area under the error curve should be

minimum

+ The error is the distance between and the controlled variable curve

+ This criterion is easy to used when a mathematical model is used to evaluate

a control system



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8. Control Performance Criteria

3. Critical damping

+ This criterion is used when overshoot above the set-point is undesirable

+ Critical damping is the least amount of damping that will produce a response

with no overshoot an no oscillation



9. Block Diagram Simplification- Block reduction can be used to simplify more elaborate block diagrams containing

multiple closed loop. The method involves the reduction of portions of the block

diagram until the desired simplification is obtained

- Block diagrams reduction procedure

Example: Reduce the block diagram shown in the figure into a single block

1. Assign variable names to all signal lines in the original diagram

Assign the variable names as shown in the figure

2. Select the blocks to reduce to a single block

Select the summing junction, block and block for reduction



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9. Block Diagram Simplification

3. Use the block transfer functions to obtain the input/output equation for each

block selected in step 2

+ The output of a block =the input to the block the block transfer function

+ The output of the summing junction= the algebraic sum of its inputs

Write the I/O equations for each block

= (1)

= (2)

= (3)

4. Use algebraic substitution to combine the equations into a single equation with

only two signals

Combine the three equations into a single equation in and

+ Substitute Eq.(1) in to Eq.(2) = ( ) (4)

+ Substitute Eq.(3) in to Eq.(4) = ( ) (5)



9. Block Diagram Simplification5. Solve the equation from step 4 for the ratio of the output signal over the input

signal. The right hand side of the resulting equation is the single block that

replaces the blocks selected in step 2

Solve Eq.(5) for / = )

+ =

(1 + ) =

=

1 +

Finally,

=

=

1 +



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10. Classification of Control Systems

1. Classification of control systems

- Control systems are classified in a number of different ways

- Classification of control systemsa. Feedback

with feedback: close-loop control

without feedback: open-loop control

b. Types of signal

continuous: analog control

discrete: digital control

c. Set-point

seldom changed: regulator systems

frequently changed: follow-up systems

d. Location of the controller

central control room: centralized control

near sensors and actuators: distributed control



10. Classification of Control Systemse. Industry

processing: process control

+ continuous systems

+ batch systems

discrete-part manufacturing: machine control

+ numerical control systems

+ robotic control systems

f. Other categories

servo-mechanisms

sequential control

+ event-sequenced control

+ time-sequenced control

programmable controllers



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2. Analog and Digital Control

A digital controlled system An analog controlled system



10. Classification of Control Systems2. Analog and Digital Control

- Analog controlled system

consists of traditional analog devices and circuits, that is, linear amplifiers

the feedback signal is updated continuously

- Digital controlled system

the controller uses a digital circuit. In most cases, this circuit is actually acomputer, usually microprocessor/microcontroller-based

the feedback signal is updated after every sampling time



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3. Process Control

- Process control system maintains a variable in a process at its set-point

- Example: A closed-loop oven-heating system



10. Classification of Control Systems3. Process Control

- Example: Process control in mixing paint

Automatic flow control

Manual control

Automatic color control



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3. Process Control

- Example: Multi-process control

Individual local controllers

Direct computer control system

Distributed control system



10. Classification of Control Systems4. Sequential Control

- A sequential control system performs a set

of operations in a prescribed manner

- Example: washing machine



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5. Servomechanism

- Servomechanisms are feedback control systems in which the controlled variable

is physical position or motion- Example: the positioning system for a radar antenna



10. Classification of Control Systems6. Numerical Control

- A numerical control (NC)

system uses a program to

control a sequence of

manufacturing operations

- Example: Basics of a numerical

control milling machine



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7. Robotics

- A robot is a programmable manipulator that moves various objects through a

sequence of motion to accomplish a specified task- Example: Pick-and-Place Robots



10. Classification of Control Systems7. Robotics

- Example: Industrial Robots in car assembly lines



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8. Work-Cell

- A work-cell is an arrangement of

resources in a manufacturingenvironment to improve the quality,

speed and cost of the process.

Work-cells are designed to improve

these by improving process flow

and eliminating waste



10. Classification of Control Systems9. Control System Examples

- Mechanical Speed

Control System



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9. Control System Examples

- DC Motor Speed Control System



10. Classification of Control Systems9. Control System Examples

- Water Level Control System



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9. Control System Examples

- Temperature Control System


C.01 Basic Concepts and Terminology

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