1. Kyoung-Chul Koh(kckoh@sunmoon.ac.kr)
DIGITAL CONTROL
목 차
1. Introduction to Digital Control System
Kyoung-Chul
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2. 강의진도
[1주] 1장 서론
참고문헌
[1] 고경철, 이호길저, C언어로 구현하는 디지털제어 이론 및 실습, HS미디어, 2010
[2] Ogata, Discrete-Time Control System,
[3] Dorf, Modern Control Systems, Wesley, 1998
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3. Fig.1.1 Intelligent service robot
1-1. Digital systems
Recently,
- rapidly increasing use of digital controller in control system
- digital controller
> productivity
> profit
> low manufacturing cost
> low energy consumption
Environment
system
s/w
electric
mechanical
chemical
biological
social
Fig.1.1 Intelligent service robot
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4. Fig.1.2 Industrial robots controlled by digital controllers
Computerized control
> intelligence to industrial robots
> optimal fuel injection control of automobiles
> precise control of consumer electronics facilities
Merits of digital control systems
> decision capability
> flexibility
Dynamic systems
> analogue control -> digital control
> continuous signal -> digital signal
Fig.1.2 Industrial robots controlled
by digital controllers
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5. Fig.1.3 classification of control signals
1-3. Digital Signal
classification of signals,
- continuous-time analogue signal
> defined in continuous time domain
> magnitude
>> continuous domain
- continuous-time quantized signal
>> finite number domain : quantization
>>> finite word length: 32bit, 64bit
- sampled analogue signal
> discrete time domain
> continuous value domain
- digital signal
> quantized value domain
X(t)
X(t) t t
(a) continuous signal
(b) sampled signal
X(t)
X(t) t t
(c) quantised signal
(d) digital signal
Fig.1.3 classification of control signals
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6. Fig.1.4 Open loop control system
1-4. Terminologies
linear system
time variant vs. time invariant sytems
discrete time control system vs, continuous time control system
interpolation
differential equation vs. linear difference equation
sampling process
- Radar tracking system : scanning by beam
- Plant process control: very slow response
- sampling vs. discretization
Digital control system +
Feedforward
controller +
Plant
Fig.1.4 Open loop control system
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7. Feedback control system
1-4. Terminologies
Feedback control system
Feedback
Loop
Controller + + +
Plant -
Fig.1.5 Closed loop control system
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8. 1-4. Terminologies Sampling - Discretization > opp. data hold
A/D conversion
- encoding
- quantization
- sample and hold -> AD conversion
Sample and hold
D/A conversion
- decoder
Plant
- approximate mode
- linearization
- ex: furnace, chemical process, servo mechanism, aircraft, mechanical devices
Process
- chemical, economical, biological processes
s/w
electric
mechanical
chemical
biological
social
Environment
system
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9. 1-5. Quantization Fig.1.6 Quantisation process Quantization
- nearest approximation
where FSR is full-scale range
Quantizer
- MSB vs. LSB
Fig.1.6 Quantisation process
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10. 1-5. Quantization Fig.1.7 Quntisation error Quantization error
- finite resolution
- round-off error
Fig.1.7 Quntisation error
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11. 1-6. Digital Control System
Feedforward
controller
S.H
and
A/D
Feedback
D/A
Hold
Plant
Clock
Digital
Filter
Digital controller
Noise
Transducer
or sensor
Disturbances + _
Output
input
Fig.1.8 Block diagram of digital control system
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12. 1-6. Digital Control System
Signal processing
- multiplexing and demultiplexing
- sample and hold
- AD conversion (Quantization)
- DA conversion (Decoding)
- filtering
S.H
and
A/D
converter
Digital
computer
D/A
Hold
circuit
Actuator
Plant or
process
Clock
Filter + _
001
010
100
011
Fig.1.9 Signal processing of digital control systems
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13. 1-6. Digital Control System
Physical
variable
Transducer
Amplifier
Low pass
Filter
Analog
multiplexer
Sample &
Hold
A/D
converter
To digital
controller
(a) A/D conversion process
From digital
controller
Register
Demultiplexer
D/A
converter
Hold
To actuator
(b) D/A conversion process
Fig.10. Digital signal processors
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14. 1-6. Digital Control System
Analogue multiplexer
- electrical swithes
Demultiplexer
sample &
Hold
Input channels
Select control
Fig.1.11 Multiplexer
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15. 1-6. Digital Control System
Sample and hold circuit
- hold capacitor
- buffer with high input impedance
- tracking mode and hole mode
Analog
output
Analog
input
Amp.1
Amp.2
Sampler
Sample and hold
command
Fig.1.12 Sample and hold circuit
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16. 1-6. Digital Control System
Sample and holer
- tracking mode and hold mode
- aperture time
Hold mode
droop
x(t)
Sample to hold offset
Input
signal
output
signal
Aperture
time t
Tracking
Mode
Hold
Mode
Hold command
Is given here
Fig.1.13 Operation mode of sample and hold circuit
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17. 1-6. Digital Control System
AD conversion
- quantization
- types
> successive approximation
- MSB -> LSM
- conversion time = 2usec for 12bit conversion
> integrating type
> counter type
> parallel type
D/A
converter
Digital output
….. …
Successive
Approximation
register
Clock
Analog input
comparator
Fig.1.14 A/D converter circuit
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18. 1-6. Digital Control System
AD conversion error
- offset
- non-linearity
- gain error
111
111
111
100
100
100
000
000
000
1/2FS FS
1/2FS FS
1/2FS FS
(c)
Gain error
(a)
Offset error
(b)
Linearity error
Fig.1.15 AD conversion error
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19. 1-6. Digital Control System
DA converter
- binary register R 2R 4R 8R Vo b0 b1 b2 b3
Vref
Fig.1.16 Binary register circuit
ref. [1] pp.32-33
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20. 1-6. Digital Control System
DA converter
- R-2R ladder circuit 3R 2R R R R 2R Vo 2R 2R 2R 2R 2R b0 b1
br-3
br-2
br-1
-Vref
Fig.1.17 R-2R ladder circuit
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21. Fig.1.18. Signal from zero order hold circuit
1-7. Hold circuits
Zero order hold
Output
Output t
Fig Signal from zero order hold circuit
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22. Fig.1.18. Signal from the first order hold circuit
1-7. Hold circuits
First order hold
- efficient for slowly varying signal
Output
Output
Fig Signal from the first order hold circuit
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23. Fig.1.20 Signal from polygon hold circuit
1-7. Hold circuits
polygonal hold
- instability problem
Output
Fig.1.20 Signal from polygon hold circuit
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24. Fig.1.21 Perspective of digital control systems
1.8 The future evolution of control systems
Control system
- flexibility
- high level of autonomy
Sensory limitation
- computer vision
- no adaptibility to environment
> need human supervision
Advanced robotics system
- task adaptibility
- artificial intelligence
- sensor integration
- off-line programming
- human-machine interface
> database management
> communications
> programming language
FactoryAutomation
Power tools
Hand tools
Robotics
NC Machines
Automated society
Improvements:
*Sensors
*Vision
*Languages
*Artificial
intelligence
Electric
machines
Automatic machine
Automatic Control
Systems
Computer Control Systems
(programmable)
Intelligent controller
*Man-machine
interface
*Supervisory
control
LOW
HIGH
Flexibility
Autonomy
Fig.1.21 Perspective of digital control systems
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25. HW#1
문제 1.1, 문제 1.3
Due: Next week this time
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