L5 - Control Theory

What is a regulatory/control system?

A system that uses closed-loop feedback (homeostasis) to maintain a desired state by continuously sensing and correcting deviations

What is closed-loop feedback control also known as in biological systems?

Homeostasis

What historical device from 1788 is an early example of a closed-loop regulatory system?

James Watt's flyball governor

Give four real-world examples of regulatory/control systems

Thermostat, cruise control, fly-by-wire aircraft, and toilet cistern refill mechanism

What is the continuous cycle described in the Actions and Consequences model?

Actions enter the World transform (fw), producing Consequences, which feed back to inform future Actions — a continuous cycle of cause and effect

In the agent-world model, what does fw represent?

The world transform — the function that converts actions into consequences

In the agent-world model, what does ga represent?

The agent transform — the function that converts intentions into actions

What is open-loop control also known as?

Feedforward control or dead reckoning

What is the key limitation of open-loop control?

It requires extensive trial-and-error to find a good ga, and is vulnerable to disturbances in fw or the output because there is no feedback

What is the open-loop configuration using an inverse model also known as?

Inverse kinematics

In open-loop control using an inverse model, what does the agent compute?

The inverse of the forward world transform (fw⁻¹) to determine the actions needed to achieve desired consequences

What is the key limitation of using an inverse model in open-loop control?

The inverse transform fw⁻¹ can be difficult to calculate, and the system is still susceptible to disturbances in fw or the output

What is closed-loop control also known as?

Feedback control or a servomechanism

What mechanism does closed-loop control use to achieve stability?

Negative feedback — the deviation between desired and actual output is used to drive corrective action

What is the British Standards Institution's definition of a closed-loop control system?

A control system possessing monitoring feedback, the deviation signal formed as a result of this feedback being used to control the action of a final control element in such a way as to tend to reduce the deviation to zero

What is the key advantage of closed-loop control over open-loop control?

The system automatically compensates for disturbances to fw and/or the output without manual recalibration

List the five steps of closed-loop feedback control

1. Set intended result. 2. Sense current situation. 3. Compare the two. 4. If different, act to bring current situation closer to intention. 5. Loop to step 2 until consequence equals intention

What are the three steps of open-loop control?

1. Issue command. 2. Action is initiated. 3. Effect may or may not be as intended, even after extensive calibration

In a negative-feedback control diagram, what is the actuating (error) signal?

The difference between the reference input (r) and the feedback signal (b), expressed as e = r − b

In a negative-feedback control diagram, what is the role of the feedforward (control) elements?

To process the error signal and produce a manipulated variable that drives the plant or process

In a negative-feedback control diagram, what is the role of the feedback elements?

To measure the controlled output and feed a signal back to be compared with the reference input

What are the three main functional components of a negative-feedback control system?

Controller (including feedforward elements), actuator (plant/process), and sensor (feedback elements)

What is the reference input also called in control theory?

The set point

What does disturbance (n) represent in a negative-feedback control diagram?

An unwanted external signal that interferes with the plant or process, causing the controlled output to deviate from the desired value

In the thermostat example, what maps to the reference input?

The desired temperature set by the user

In the thermostat example, what maps to the actuator?

The heater or cooler

In the thermostat example, what maps to the sensor in the feedback path?

The temperature sensor

In the thermostat example, what maps to the disturbance input?

Open or closed windows and doors (and ambient temperature changes)

In the thermostat example, what maps to the controlled output?

The ambient room temperature

What is a servomechanism?

Another name for a closed-loop negative-feedback control system (servomechanism)

In a servo motor, what component acts as the feedback sensor?

A potentiometer that measures the output shaft position

In a servo motor, what component acts as the actuator?

The electric motor

In a servo motor, what is the error signal used for?

It is fed into an amplifier that drives the motor to reduce the difference between the commanded and actual shaft positions

Why can most real-world control problems not be solved with a single controller?

Because complex tasks involve multiple interdependent variables that must be controlled simultaneously or hierarchically

What are the two configurations in which multiple control loops can be arranged?

In parallel (running simultaneously) or stacked in a hierarchy (hierarchical control)

What is Perceptual Control Theory (PCT)?

A theory pioneered by William T. Powers stating that behaviour is the control of perception — living systems act to keep their perceptions matching internal reference signals

Who pioneered Perceptual Control Theory and when?

William T. Powers, in his 1973 book Behaviour: The Control of Perception

What is the central claim of Perceptual Control Theory?

Behaviour is the control of perception

From what field did Perceptual Control Theory emerge, and in what decade?

Cybernetics, in the 1960s

What is Hierarchical Perceptual Control Theory (HPCT)?

An extension of PCT in which multiple closed-loop control systems are stacked in a hierarchy, with higher levels setting reference signals for lower levels

How many levels does Powers' HPCT hierarchy contain?

11 levels

List the 11 levels of the HPCT hierarchy from lowest to highest

1. Intensities, 2. Sensations, 3. Configurations, 4. Transitions, 5. Events, 6. Relationships, 7. Categories, 8. Sequences, 9. Programs, 10. Principles, 11. System concepts

What does Level 1 (Intensities) perceive in HPCT?

The intensity of sensory information

What does Level 11 (System Concepts) perceive in HPCT?

Coherent organisation of principles

Why is hierarchical control not common in engineering systems?

Due to a lack of good design principles for systems with more than two levels

What are the pros of the Subsumption architecture for layered control?

It established the principles of behaviour-based robotics

What are the cons of the Subsumption architecture?

Tasks are accomplished sequentially, it uses open-loop control, it is susceptible to disturbances, and it is hard to design beyond two levels

What are the pros of Hierarchical Feedback Control for layered control?

It aligns with behaviour-based robotics principles, tasks run in parallel, it uses closed-loop control, and it is protected from disturbances

What are the cons of Hierarchical Feedback Control?

It is hard to design beyond two levels

How does Hierarchical Feedback Control differ from Subsumption in handling multiple tasks?

Hierarchical Feedback Control runs tasks in parallel using closed loops; Subsumption runs tasks sequentially using open loops

What does the notation e = r − b represent in control theory?

The error (actuating signal) equals the reference input minus the feedback signal

What is the significance of negative feedback providing stability?

It ensures that any deviation between the desired and actual output generates a corrective signal that drives the system back towards the set point, reducing the deviation to zero

"In closed-loop control, observations of {{c1::consequences}} are fed back and subtracted from {{c2::intentions}} to produce an error signal that drives corrective action."

consequences; intentions

"Open-loop control is also known as {{c1::feedforward control}} or {{c2::dead reckoning}}."

feedforward control; dead reckoning

"In PCT, behaviour is the control of {{c1::perception}}."

perception

"A servomechanism uses {{c1::negative feedback}} to reduce the deviation between desired and actual output to {{c2::zero}}."

negative feedback; zero

What is the difference between the forward path and the feedback path in a negative-feedback control system?

The forward path carries the error signal through the controller and actuator to produce the controlled output; the feedback path carries the measured output back to the comparator

Why does negative feedback provide stability rather than positive feedback?

Negative feedback opposes deviations from the set point, reducing error; positive feedback amplifies deviations, leading to instability

What is the key practical difference between open-loop control with a basic agent transform (ga) and open-loop control using an inverse model (fw⁻¹)?

Using ga requires trial-and-error calibration; using fw⁻¹ attempts to mathematically invert the world model, but both remain vulnerable to disturbances

In the Lego robot proximity and orientation demo, what type of control architecture was used?

Two closed feedback loops running in parallel — one for proximity control and one for orientation control

What does the term "set point" refer to in control theory?

The desired reference value that the control system aims to maintain as the controlled output