Principles of Feedback Control

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Principles of Feedback Control

• Mafuyu Kitahara
• English Theme8
• 2006-05-08
• Summary of Chapter 2, Carver Scheier (1998), On
  the Self-Regulation of Behavior, Cambridge Univ.
  Press.

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Feedback control

• Goal of Chapter 2
• To show abstract princples
• Examples from domains other than psychology
• Feedback process
• Control of regulation of values within a system
• Cybernetics coined by Wiener (1948)
• Background
• First computer in history ENIAC (1946)
• Information science bit, entropy, noise
• Systems without internal control e.g., clock,
  camera

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Negative feedback (1)

• Concept
• 4 elements input, reference, comparator, output

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Negative feedback (2)

• Example thermostat

Effect on evironment? Output has indirect
connection with input
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Additional issues (1)

• Sloppy vs. Tight control
• how precisely the comparator works
• Thermostat 0.01, 0.1, or 1 degree deviation?
• Lag Time
• Output function cannot work immediately
• Thermostat
• Slow heater (steam) vs. Quick heater (gas)

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Additional issues (2)

• Intermittent feedback
• Discontinuous
• Output side heater is only ON or OFF
• Input side sensor works occasionally
• Continuous
• Automatic steering system in a ship

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Further constructs (1)

• Positive feedback loops

Thermostat example set goal as more than 20C
(needs upper limit)
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Further constructs (2)

• Open loop systems
• No checking on the consequences
• e.g. Spark plugs in a car engine
• Order prespecified
• Timing depends on the speed
• Useful for high-speed control
• Precise, No lag time, No intermittency
• Not useful for psychology

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Feedforward

• Anticipatory output
• Best estimate
• First cycle
• No input is available

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Interdependency

• Interaction between feedback loops
• Not explicitly connected but disturbing each other

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Reference value and input function

• Slow adjustment of reference value
• e.g.
• Sleep hours

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Hierarchies

• Superordinate and subordinate systems
• e.g., person and thermostat