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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
HCM City Univ. of Technology, Faculty of Mechanical Engineering Nguyen Tan Tien
Control System Technology 1.02 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
Control System Technology 1.03 Basic Concepts and Terminology
HCM City Univ. of Technology, Faculty of Mechanical Engineering Nguyen Tan Tien
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
Control System Technology 1.05 Basic Concepts and Terminology
HCM City Univ. of Technology, Faculty of Mechanical Engineering Nguyen Tan Tien
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. Block Diagrams and Transfer Functions
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
Control System Technology 1.07 Basic Concepts and Terminology
HCM City Univ. of Technology, Faculty of Mechanical Engineering Nguyen Tan Tien
2. Block Diagrams and Transfer Functions2.1 Block diagrams
Amplifier: an amplifier or simply amp, is a device for increasing thepowerof asignal
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2. Block Diagrams and Transfer Functions
2.1 Block diagrams
DC Motor
Control System Technology 1.09 Basic Concepts and Terminology
HCM City Univ. of Technology, Faculty of Mechanical Engineering Nguyen Tan Tien
2. Block Diagrams and Transfer Functions2.1 Block diagrams
Valve: valve is used to control flow rate by opening/closing the gate positionresponse to signals received from controllers
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2. Block Diagrams and Transfer Functions
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
Control System Technology 1.11 Basic Concepts and Terminology
HCM City Univ. of Technology, Faculty of Mechanical Engineering Nguyen Tan Tien
2. Block Diagrams and Transfer Functions2.1 Block diagrams
Driver of automobile
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2. Block Diagrams and Transfer Functions
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
Control System Technology 1.13 Basic Concepts and Terminology
HCM City Univ. of Technology, Faculty of Mechanical Engineering Nguyen Tan Tien
2. Block Diagrams and Transfer Functions2.1 Block diagrams
Automobile
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2. Block Diagrams and Transfer Functions
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
= =
Control System Technology 1.15 Basic Concepts and Terminology
HCM City Univ. of Technology, Faculty of Mechanical Engineering Nguyen Tan Tien
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. Block Diagrams and Transfer Functions
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
= =
Control System Technology 1.17 Basic Concepts and Terminology
HCM City Univ. of Technology, Faculty of Mechanical Engineering Nguyen Tan Tien
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
Control System Technology 1.19 Basic Concepts and Terminology
HCM City Univ. of Technology, Faculty of Mechanical Engineering Nguyen Tan Tien
3. Open-Loop Control- Example: A simple robot arm open-loop position system
Control System Technology 1.20 Basic Concepts and Terminology
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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.
Control System Technology 1.21 Basic Concepts and Terminology
HCM City Univ. of Technology, Faculty of Mechanical Engineering Nguyen Tan Tien
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
Control System Technology 1.23 Basic Concepts and Terminology
HCM City Univ. of Technology, Faculty of Mechanical Engineering Nguyen Tan Tien
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
Control System Technology 1.25 Basic Concepts and Terminology
HCM City Univ. of Technology, Faculty of Mechanical Engineering Nguyen Tan Tien
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
Control System Technology 1.27 Basic Concepts and Terminology
HCM City Univ. of Technology, Faculty of Mechanical Engineering Nguyen Tan Tien
4. Closed-Loop Control- Compare between open-loop control and close-loop control
Control System Technology 1.28 Basic Concepts and Terminology
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
Control System Technology 1.29 Basic Concepts and Terminology
HCM City Univ. of Technology, Faculty of Mechanical Engineering Nguyen Tan Tien
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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5. Linear vs Nonlinear
- 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
Control System Technology 1.31 Basic Concepts and Terminology
HCM City Univ. of Technology, Faculty of Mechanical Engineering Nguyen Tan Tien
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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5. Linear vs Nonlinear
- 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
Control System Technology 1.33 Basic Concepts and Terminology
HCM City Univ. of Technology, Faculty of Mechanical Engineering Nguyen Tan Tien
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)
Control System Technology 1.35 Basic Concepts and Terminology
HCM City Univ. of Technology, Faculty of Mechanical Engineering Nguyen Tan Tien
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
Control System Technology 1.37 Basic Concepts and Terminology
HCM City Univ. of Technology, Faculty of Mechanical Engineering Nguyen Tan Tien
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
Control System Technology 1.39 Basic Concepts and Terminology
HCM City Univ. of Technology, Faculty of Mechanical Engineering Nguyen Tan Tien
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)
Control System Technology 1.41 Basic Concepts and Terminology
HCM City Univ. of Technology, Faculty of Mechanical Engineering Nguyen Tan Tien
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
Control System Technology 1.43 Basic Concepts and Terminology
HCM City Univ. of Technology, Faculty of Mechanical Engineering Nguyen Tan Tien
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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10. Classification of Control Systems
2. Analog and Digital Control
A digital controlled system An analog controlled system
Control System Technology 1.45 Basic Concepts and Terminology
HCM City Univ. of Technology, Faculty of Mechanical Engineering Nguyen Tan Tien
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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10. Classification of Control Systems
3. Process Control
- Process control system maintains a variable in a process at its set-point
- Example: A closed-loop oven-heating system
Control System Technology 1.47 Basic Concepts and Terminology
HCM City Univ. of Technology, Faculty of Mechanical Engineering Nguyen Tan Tien
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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10. Classification of Control Systems
3. Process Control
- Example: Multi-process control
Individual local controllers
Direct computer control system
Distributed control system
Control System Technology 1.49 Basic Concepts and Terminology
HCM City Univ. of Technology, Faculty of Mechanical Engineering Nguyen Tan Tien
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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10. Classification of Control Systems
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
Control System Technology 1.51 Basic Concepts and Terminology
HCM City Univ. of Technology, Faculty of Mechanical Engineering Nguyen Tan Tien
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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10. Classification of Control Systems
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
Control System Technology 1.53 Basic Concepts and Terminology
HCM City Univ. of Technology, Faculty of Mechanical Engineering Nguyen Tan Tien
10. Classification of Control Systems7. Robotics
- Example: Industrial Robots in car assembly lines
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10. Classification of Control Systems
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
Control System Technology 1.55 Basic Concepts and Terminology
HCM City Univ. of Technology, Faculty of Mechanical Engineering Nguyen Tan Tien
10. Classification of Control Systems9. Control System Examples
- Mechanical Speed
Control System
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10. Classification of Control Systems
9. Control System Examples
- DC Motor Speed Control System
Control System Technology 1.57 Basic Concepts and Terminology
HCM City Univ. of Technology, Faculty of Mechanical Engineering Nguyen Tan Tien
10. Classification of Control Systems9. Control System Examples
- Water Level Control System
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10. Classification of Control Systems
9. Control System Examples
- Temperature Control System
Control System Technology 1.59 Basic Concepts and Terminology
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