Feedback Control - Microcontroller Systems - Lecture Slides, Slides of Microcontrollers

In the class of computer sciences, we have a special class for the Microcontroller Systems. The main points in these slides are:Feedback Control, Simple Abstraction, Open Loop Control System, Inaccurate Effector, Static Environment, Feed Forward Control, Errors, Wall Following Robot, Oscillation and Set Point, Sensor Noise, Control Theory

Typology: Slides

2012/2013

Uploaded on 04/24/2013

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Download Feedback Control - Microcontroller Systems - Lecture Slides and more Slides Microcontrollers in PDF only on Docsity!

Feedback Control

A Simple Abstraction

  • An open loop control system
  • Goal/desired state

Controller

The process

Under control

Desired

output

Process

Process output

input

Open Loop Control

  • May use expected disturbance
    • Static environment

Controller

The process

Under control

Desired

output

Process

output

Process

input

Disturbance

Predicted

disturbance

Examples

  • Putting book on a desk
  • Activating an event
    • Start a sensor
    • Play a sound
    • Conduct a scripted movement
  • Question: What about inserting a light bulb?

Feedback Control (Closed Loop)

  • Include all the parameters as included into the output.

Controller

The process

Under control

Desired

output

Process

output

Process

input

Disturbance

Sensors

Feedback Control

  • Another diagram

Controller

The process

Under control

Desired

output

Process

output

Process

input

Sensors

Errors

  • Direction (sign)
  • Magnitude (distance)
  • Frequent feedback is needed
    • Sensor rates can effect response
  • Control may not be immediate
    • May be a delay from when you decide to change, and when a change actually occurs!

A Wall Following Robot

  • How would you use feedback control to implement a wall-following behavior in a robot?
  • What sensors would you use?
  • Would they provide magnitude and direction of the error?
  • What will this robot's behavior look like?

Sensor Noise

  • What happens when there is sensor noise in the system?
  • Example:
    • Sensor tells the robot it is far from a wall, when it is close?
    • vice versa?
  • How might we fix these problems?

Control Theory

  • Studies the behavior of control systems
  • Major basic controllers:
    • P: proportional control
    • PD: proportional derivative control
    • PID: proportional integral derivative control

P: Proportional Control

  • Q: What happens if the gain is increased?
  • A: Loop may go unstable
  • Q: What if the gain is decreased?
  • A: It takes along time to get close enough to the setpoint.
  • Determining the gain: hard problem
    • analytically (mathematics)
    • empirically (trial and error)

Setting Gain

  • Determining the gain depends on the physics of the system:
  • Analytical approaches:
    • System should be understood well
    • System should be characterized mathematically.
  • Trial and error (ad hoc, system-specific):
    • System should be tested extensively.
    • Can be done
      • manually
      • Automatically by the system
  • Wrong gain may put the system into oscillation!

Damping

  • The process of systematically decreasing oscillation
  • Properly damped : Reduces and removes oscillation in a reasonable amount of time.

P: Proportional Control

  • Q: What happens if the system is very dynamic?
    • Example: Following another robot
  • A: P control does not work well.
    • It senses the present time.
  • Q: What happens close to the setpoint?
  • A:
    • If gain is fixed: May not work for low errors
      • Leaves some offset
    • If gain is high: Tends to overshoot