Automatic Control
Engineering
BY CHOOPONG CHUAYPEN
MECHANICAL DEPT., ENGINEERING FACULTY, NARESURN UNIVERSITY
Lecture 1:
Introduction
Aims and Objectives
Control
System modelling
Transfer functions
System performance
System frequency response
System identification
Controller design
Sensors and Actuators
Today’s Lecture
Introduction to Control
Examples
Control Basics
Open- and Closed-loop control
Control System Design Steps
Example Models
Introduction to Control
What is a control system?
Common example in the human body: temperature control
,
Body
/
Action
Introduction to Control
Application in:
Physiology
Economics เศรษฐศาสต)
Many fields of engineering:
• Hydraulics
• Electronics
• Mechanics
• etc.
Simple Examples
Car speed
Desired speed
Actual speed
Throttle
Engine
Vehicle
Controller
System or Plant
Room fan
Desired cooling
Switch
Electrical
power
Actual cooling
Wall fan
Example
Control systems are required in complex machines,
devices
Aircraft control systems
Anti-lock braking systems
Manufacturing process
Examples
Inverted Pendulum
https://www.youtube.com/watch?v=855O9x0Pgf0
Videos
https://www.youtube.com/watch?v=cyN-CRNrb3E
https://www.youtube.com/watch?v=bI06lujiD7E
https://www.youtube.com/watch?v=cNZPRsrwumQ&feature=yout
u.be&t=22s
https://www.youtube.com/watch?v=_03F49thJ6s
Control Basics
What is common for all these systems?
A physical quantity has to be maintained at a fixed value
(or series of values).
What information is necessary?
What the system needs to do
How well is the system is doing
What control action keeps maintains the action
Open and Closed Loop Control
Open Loop
Turntable example
Desire Speed
Control Device
Actuator
Process
(Voltage)
Amplifier
DC Motor
Turntable
Actual Speed
Open and Closed Loop Control
Closed Loop
Turntable example
Desire Speed
(Voltage)
+
Error
-
Control Device
Actuator
Process
Amplifier
DC Motor
Turntable
Measured Speed
Sensor
(Voltage)
Tachometer
Actual Speed
Open and Closed Loop Control
Cruise control example
Closed loop
Desired +
speed
Error
-
Throttle
Feedback
Engine
Speed Sensor
Output compared to the input
Error is used to drive the system
Vehicle
Actual
speed
Open and Closed Loop Control
Oven example
Closed loop
Desired
Temperature
+
Error
-
Switch
Feedback
Electrical
power
Heating element
Temperature
Sensor
Output compared to the input
Error is used to drive the system
Actual
Temperature
Open and Closed Loop Control
Components in a Closed Loop System
Demand
+
Error
-
Controller
Feedback
Plant
Sensor
Output
Open and Closed Loop Control
Normally depicted in a block diagram
Plant provides the system output
Controller takes the control input and provides a control
output
Sensor takes the output and feeds it to the subtractor (or
comparator) that compares the demand (the setpoint
value) with the output of the sensor to produce an error
All connected by arrows, which represent signals
Control System Design
Understand the general schemes that can be used to
control a system.
Understand the system you’re trying to control. You need
to predict how a system behaves – mathematical techniques
that involve differential equation solution.
Control System Design Steps
1. System analysis – establish requirements (talk to users)
2. Formal specification of require system performance
3. System modelling – system must be accurately modelled
before controller design can commence. Usually a
differential equation (some quantity that changes w.r.t.
time)
4. Control algorithm development – the controller is
developed using the model and standard control theory
to meet the specifications.
System Modelling
Dynamic behavior of the system
Linear or non-linear fashion
System dynamics – how its output changes in response to
a particular input
Example
Furnace
The temperature of the furnace does not change
instantaneously for changes in fuel rate
Differential equation describes the influence of time on
the input response
Differential equations are derived from first principles
Example
Liquid level tank
RC circuit
Car suspension
Example 1: Liquid Level
Flow in – Flow out = rate of accumulation of liquid in the
tank
𝑑ℎ
𝑄𝑖𝑛 − 𝑄𝑜𝑢𝑡 = 𝐴
𝑑𝑡
𝑑ℎ
𝑄𝑖𝑛 − 𝑘ℎ = 𝐴
𝑑𝑡
𝑑ℎ
𝑄𝑖𝑛 = 𝐴
+ 𝑘ℎ
𝑑𝑡
Example 2: RC Circuit
Differential equation that related Vout to Vin
𝑑𝑣
Capacitor current: 𝑖 = 𝐶
𝑑𝑡
𝑑𝑉𝑜𝑢𝑡
𝑉𝑖𝑛 − 𝑉𝑜𝑢𝑡 = 𝑖𝑅 = 𝐶
𝑅
𝑑𝑡
𝑑𝑉𝑜𝑢𝑡
𝑉𝑖𝑛 = 𝑉𝑜𝑢𝑡 + 𝐶𝑅
𝑑𝑡
Example 3: Car Suspension
Mass/spring/damper system
Inertia:
𝐹 = 𝑚𝑎
Damping: 𝐹 = 𝐷𝑣
Spring: 𝐹 = 𝑘𝑥
𝑑2 𝑥
=𝑀 2
𝑑𝑡
𝑑𝑥
=𝐷
𝑑𝑡
Apply Newton’s second law:
𝑑2 𝑥𝑜𝑢𝑡
𝑑𝑥
𝑀
= −𝑘𝑥 − 𝐷
+ 𝐹𝑖𝑛
2
𝑑𝑡
𝑑𝑡
𝑑2 𝑥𝑜𝑢𝑡
𝑑𝑥
𝑀
+ 𝑘𝑥 + 𝐷
= 𝐹𝑖𝑛
2
𝑑𝑡
𝑑𝑡
Conclusion
Control is an intrinsic part of humans and a vital part of
many engineering systems
In order to control a system, we need to know the
system/plant itself and control methods
Description of a system to be controlled – system model is
a starting point of the control system design