Feedback Control
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Feedback Control. Control System Terminology. Input – Excitation applied from external source Output - Response obtained from a system Feedback – System output returned to modify input Error - Difference between input and output. Example of Negative Feedback Control System. Air Temp.

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Feedback Control

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Feedback control

Feedback Control


Control system terminology

Control System Terminology

  • Input – Excitation applied from external source

  • Output - Response obtained from a system

  • Feedback – System output returned to modify input

  • Error - Difference between input and output.


Feedback control

Example of Negative Feedback Control System

Air Temp

Heater Control

Thermostat

Temp Wanted


Types of control systems

Types of Control Systems

  • Open-Loop

    • Simple system which performs function without concern for initial conditions or external inputs

    • Must be closely monitored

  • Closed-Loop (feedback)

    • Uses the output of the process to modify the process to produce the desired result

    • Continually adjusts the process


Advantages of closed loop feedback system

Advantages of Closed-Loop Feedback System

  • Increased Accuracy

    • Ability to reproduce output with varied input

  • Reduced Sensitivity to Disturbance

    • Self-correcting minimizes effects of system changes

  • Smoothing and Filtering

    • System induced noise and distortion are reduced

  • Increased Bandwidth

    • Produces satisfactory response to increased range of input changes


Major types of feedback used

Major Types of Feedback Used

  • Position Feedback

    • Used when the output is a linear distance or angular measurement.

  • Rate & Acceleration Feedback

    • Feeds back rate of motion or rate of change of motion (acceleration)

    • Motion smoothing

    • Uses a electrical/mechanical device called an accelerometer


Feedback control

Job Description:

Train the gun turret to the proper firing

position by moving a joy stick left or

right depending on the direction needed.

This must be performed as fast as possible.

Safety Consideration

:

For your protection,

you will be located inside

a windowless protective

enclosure inside the gun

turret.

Building a Gun Fire Control System


Feedback control

New

Position

Turret Position with Feedback

Old Position

Time


Feedback control

Dampening

Damping

New Position

Old Position


Automatic tracking systems related to feedback

Automatic Tracking Systems (Related to Feedback)

1. Target Tracking Parameters

2. Line-of-Sight(LOS)

3. Tracking Line


Target tracking parameters

Target Tracking Parameters

  • Azimuth

  • Elevation

  • Range

  • Relative Target Velocity

    • Target’s motion with respect to the platform’s motion


Tracking terms

Tracking Terms

Error

Line-of-Sight

Tracking Line

Tracking

Element


Angle tracking servo systems

Angle-Tracking Servo Systems

  • Five Basic Functions

    • Sense position error magnitude and direction

    • Provide position feedback

    • Provide data smoothing / stabilization

    • Provide velocity feedback

    • Provide a power-driving device


Uses of angle tracking servo systems

Uses of Angle-Tracking Servo Systems

  • Monotrack fire control radars

  • Homing missiles

  • Acoustic homing torpedoes

  • Aviation fire control tracking systems


Methods of tracking

Methods of tracking

  • Conical scan

  • Conical scan on receive only (COSRO)

  • Monopulse


Position error magnitude direction

Basic Principle: Target energy return is strongest

on the axis of the beam, diminishes further from the axis.

Methods of Tracking:

* Sequential Lobing

* Conical Scan

* COSRO

* Monopulse

axis

Position Error Magnitude & Direction


Sequential lobing

L

R

L

R

R

L

* Simplest Method

* Multiple Beams

* Compare Returns

* Relatively Slow

* Still used by some

countries

Antenna looking

left of target

Antenna Pointing

directly at target

Antenna looking

right of target

Return Signals form Two Beams

Sequential Lobing


Conical scanning

Conical Scanning

Lobe Of

Energy

Pattern of scanning

* Rotates a beam in a circle producing a cone of energy.

*Rotate the feed horn in a small circle around the axis of the fixed parabolic antenna.

Antenna


Determining tracking error using conical scan

Locus of Beam Centers

Antenna Axis

Equal Amplitude

Sensor Return Signal

Beam

Pulse

Return

Amplitude

Time

Target Position is in the Center of the Conical Scan (On Antenna Axis)

Determining Tracking Error Using Conical Scan


Determining tracking error using conical scan1

Locus of Beam Centers

Antenna Axis

Varying Amplitude

Sensor Return Signal

Beam

Pulse

Return

Amplitude

Time

Target Position Off the Center of the Antenna Axis

Determining Tracking Error Using Conical Scan


Cosro conical scan on receive only

*Transmits pulses on antenna axis

* Measures strength of return

around axis of the antenna

* Positions antenna based on return

Antenna

COSROConical Scan on Receive Only


Monopulse

Monopulse

  • Developed to overcome tracking errors involved with conical scanning and sequential lobing

  • Two or more beams transmitted simultaneously and amplitude comparison is mode between returns

    • One reflector but uses two or more feed horns

    • Each simultaneous beam can be identified by tagging it with some type of information such as slight polarization

  • Very complex and expensive!!!!


Providing a stable tracking system

Providing a Stable Tracking System

  • All tracking systems require some stabilization

  • Three classes of tracking system stabilization

    • Unstabilized - Not stabilized in any axis

    • Partially Stabilized - Stabilized on one axis

    • Fully Stabilized - Free of all rotational disturbances

  • Gyroscopes provide the stable reference


Basic gyroscopic principles

Basic Gyroscopic Principles

  • Gyro spins at a very high velocity

    • Spin axis remains aligned with terrestrial meridians

  • Inertia

    • Rigidity - gyro will remain at a fixed orientation in space if no force is applied to it

    • A gimbaled gyro makes a good reference to cancel out platform role, pitch and yaw (ship or aircraft)


Basic gyroscopic principles1

Basic Gyroscopic Principles

  • Precession

    • A gyro’s spin axis has a tendency to turn at right angles to the direction of the force applied to it

    • Torque required to move the gyro is converted into a means of controlling system gain

  • The gyro has three axes

    • spin axis

    • torque axis

    • precession axis


Gyroscopic theory

Gyroscopic Theory

Accelerometers!!!


Now put em together

Now, put ‘em together!!!!

  • Range Tracking

  • Angle Tracking

One dead duck…………………..


Questions

Questions?


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