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Professor Walter W. Olson Department of Mechanical, Industrial and Manufacturing Engineering University of Toledo. Feedback. Outline of Today’s Lecture. Actuate. Sense. Review Class Policy What is Control? Feedback Open Loop Systems Closed Loop System Positive Feedback - PowerPoint PPT Presentation
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Feedback
Professor Walter W. OlsonDepartment of Mechanical, Industrial and Manufacturing Engineering
University of Toledo
Outline of Today’s Lecture
• Review• Class Policy• What is Control?
• Feedback• Open Loop Systems• Closed Loop System
• Positive Feedback• Negative Feedback• Control actions using feedback
Sense
Compute
Actuate
Class Policies
• Syllabus• Students are expected to be at class on time. • Book: Online at
• http://www.cds.caltech.edu/~murray/amwiki/index.php/Version_2.10e• You will be required to read this BEFORE coming to class.• Recitation points come from your reading!
• Homework is due on the date shown in the syllabus at the beginning of the class period• Late homework will not be accepted• Neatness Counts!• Individual work
• Academic dishonesty (cheating, plagiarizing, and related offenses,) will be harshly dealt with.
Control
• Control =• Sensing +
• {Where are you at? Is it where you want to be?}• Computation +
• {Can you find a path to where you want to go?}• Actuation
• { Make things happen to get you there!}
Why Controls?• Why Controls?
• Things move• Too many things happening• Things move too fast for the human brain to
compute and for muscles to act• Noise and disturbances• Accuracy and precision• Cost
Where Do You Find Controls?
• Everywhere!
Controls: What are differences here?
• Control = Sense + Compute + Actuate
Bench rest• TOW explained
Open Loop Control
• Usually “set point” systems• Advantages
• Simple• Sensitive to environment• Set and forget
• Disadvantages• Non correcting• Sensitive to disturbances• Insensitive to environment
• Examples• Irrigation systems• Washing machines
Sensing Compute Actuate
Closed Loop Control
• Adds a feedback loop to the control system
• For computational purposes, it is shown as
Sense
Compute
Actuate
Controller Plant
Sensor
Input Output
Disturbance
+ or -
+ or -+ or -
+ or -
Positive Feedback
Positive Feedback Clip
Controller Plant
Sensor
++
+ +
VibratingGuitar String
MagneticPickup
AmplifierSpeaker
Plucked String String Vibrations
Controller Plant
Sensor
++
+ + Sound
Guitar String w/ pickup
Amplifier Speaker
Ambient Sound
2 possible models
Background sound
Previous Vibrations
Positive Feedback
• Positive feedback is used to increase the actuation in the loop.• Advantages
• Increased results• Faster results• Finds extremes
• (maxima and minima)• Disadvantages
• Consumes energy• Subject to local extremes (introns)• May become unstable• May destroy system
• Examples:• Metal finders• Searches• Stock market programs• Genetic Algorithm
build population
createmutations
test
performancemeasure
Results
Culled fromPopulation
BestWorst
Negative Feedback
Input Controller Plant
Sensor
Output
Disturbance
+-
+ +
Error Signal
homeostasis
DesiredHeart Beat
Controller Plant
Sensor
Heart Beat
Salt
+-
+ +
Heart
Nerves
Parasympathetic/Sympathetic System
Negative Feedback
• Negative Feedback is used to reduce error• Advantages
• Controls to a set point• Robustness to disturbances (uncertainty)• Rejection of distortion
• Disadvantages• Prone to oscillation• Instability• Complexity• Coupling
• Examples• Set point control• Tracking• Chang the system dynamics
Basic Control Actions
• Bang – Bang• Most are on – off controls where either something
is turned on or turned off in response to sensor:• If the error signal is greater than e1, turn system on• If error is signal is less than e2, turn system off• e1 and e2 are usually not be the same value• The control action could be reversed
• Example: Sump pump• if water level is above 20, turn pump on• if water level is below 5, turn pump off
Basic Control Actions
• Proportional• Control action is
proportional to the error sensed• command = K * error signal• K is often called the “gain” of
the controller• Example: Volume knob on
the radio
Basic Control Actions
• Integral control• control command is based
on the size of the error and the length of time the error has existed
• Example: Ripening of fruit• when fruit ripen they release
ethylene• the ethylene increases the rate
of ripening
command edtRipening fruit
Basic Control Actions
• Derivative control• control command is based
on the magnitude and the rate of change of the error
• Rarely alone used because of instabilities created by the speed of changes
• Example: Pollution control of furnace
ecommandt
Basic Control Actions
• Combined• PID (Proportional – Integral
– Derivative)• sums all three actions
• Most used control strategy
• Example: Motor controllers
( )( ) ( )p i de tcommand K e t K e t dt Kt
Summary
• Open Loop• Closed Loop• Feedback
• Positive feedback• Negative Feedback
• Basic Control Actions• Bang-bang• Proportional• Integral• Deriviative• PID
• Next: Modeling