Control System TerminologyControl 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.

Thermostat

Temp Wanted

Air Temp

Heater Control

Example of Negative Feedback Example of Negative Feedback Control SystemControl System

Types of Control SystemsTypes 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 Advantages of Closed-Loop Feedback SystemFeedback 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 UsedMajor 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

Building a Gun Fire Control System

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 insidea windowless protectiveenclosure inside the gunturret.

Time

Old Position

NewPosition

Turret Position with Feedback

DampingDampening

Old Position

New Position

Automatic Tracking Systems Automatic Tracking Systems (Related to Feedback)(Related to Feedback)

1. Target Tracking Parameters

2. Line-of-Sight(LOS)

3. Tracking Line

Target Tracking ParametersTarget Tracking Parameters

AzimuthElevationRangeRelative Target Velocity

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

Tracking TermsTracking Terms

TrackingElement

Line-of-Sight

Tracking Line

Error

Angle-Tracking Servo SystemsAngle-Tracking Servo Systems

Five Basic FunctionsSense position error magnitude and

directionProvide position feedbackProvide data smoothing / stabilizationProvide velocity feedbackProvide a power-driving device

Uses of Angle-Tracking Servo Uses of Angle-Tracking Servo SystemsSystems

Monotrack fire control radarsHoming missilesAcoustic homing torpedoesAviation fire control tracking systems

Methods of trackingMethods of tracking

Conical scanConical scan on receive only (COSRO)Monopulse

Basic Principle: Target energy return is strongest on the axis of the beam, diminishes further from the axis.

axis

Methods of Tracking: * Sequential Lobing * Conical Scan * COSRO * Monopulse

Position Error Magnitude & Position Error Magnitude & DirectionDirection

Sequential LobingSequential LobingL L LR R R

Antenna looking left of target

Antenna Pointing directly at target

Antenna looking right of target

Return Signals form Two Beams

* Simplest Method

* Multiple Beams * Compare Returns

* Relatively Slow

* Still used by some countries

Conical ScanningConical 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

Lobe Of Energy

Pattern of scanning

Determining Tracking Error Determining Tracking Error Using Conical ScanUsing Conical Scan

Locus of Beam Centers

Beam

Time

PulseReturnAmplitude

Equal AmplitudeSensor Return Signal

Antenna Axis

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

Determining Tracking Error Determining Tracking Error Using Conical ScanUsing Conical Scan

Locus of Beam Centers

Beam

Time

PulseReturnAmplitude

Varying AmplitudeSensor Return Signal

Antenna Axis

Target Position Off the Center of the Antenna Axis

COSROCOSROConical Scan on Receive OnlyConical Scan on Receive Only

* Transmits pulses on antenna axis * Measures strength of return around axis of the antenna* Positions antenna based on return

Antenna

MonopulseMonopulse 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 Providing a Stable Tracking SystemSystem

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 PrinciplesBasic 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 PrinciplesBasic 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 TheoryGyroscopic Theory

Accelerometers!!!

Now, put ‘em together!!!!Now, put ‘em together!!!!

Range Tracking Angle Tracking

One dead duck…………………..One dead duck…………………..

Questions?Questions?