Weapons ON Target

Learning Objectives

• Know the definitions of the following terms: input, output, feedback, error, open loop, and closed loop

• Comprehend the advantages of closed-loop control in a weapon system

• Comprehend the difference between the line-of-sight (LOS) and the tracking line

• Comprehend the operation of a simple automatic tracking system

Control System Terminology

• INPUT – stimulus applied from external source

• OUTPUT – response obtained from a system

• FEEDBACK – portion of output returned to modify input

• ERROR – difference between the input and output (more specifically the feedback)

Feedback Control System

CONTROLLER

FEEDBACK ELEMENT

INPUTOUTPUT

History of Feedback Control

• Water clock of the Greeks

• Industrial Revolution– Pressure Regulators– Water Regulators– Temperature Regulators

• Fantail

Example

• Thermostat (temperature control)– Input – temperature it is initially set to

– Output – heating or cooling (exhaust)

– Feedback – ambient room temperature

– Error – difference between ambient temp and input (temp it is set to)

Thermostat

Temp Wanted

Air Temp

Heater Control

Example of Feedback Control SystemExample of Feedback Control System

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

Increased Accuracy– Ability to reproduce output with varied input

Reduced Sensitivity to Disturbance– Self-correcting minimizes effects of system

changesSmoothing and Filtering

– System induced noise and distortion are reducedIncreased Bandwidth

– Produces satisfactory response to increased range of input changes

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

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

Dampening

Old Position

New Position

Questions?

Automatic Tracking Systems

Feedback Control

Part II

Learning Objectives

• Comprehend the concepts, advantages, and limitations of conical scan, conical scan on receive only (COSRO), and monopulse

• Comprehend stabilization as associated with tracking systems

• Know the difference between range tracking and angle tracking

Automatic Tracking Systems (Related to Feedback)

1. Target Tracking Parameters

2. Line-of-Sight(LOS)

3. Tracking Line

Target Tracking Parameters

· Azimuth

· Elevation

· Range

· Relative Target Velocity- Target’s motion with respect to the platform’s

motion

Tracking Terms

TrackingElement

Line-of-Sight

Tracking Line

Error

•Tracking line = antenna boresight

•Tracking line lags line-of-sight

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

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 & Direction

Azimuth lobing

A B A B A B

Returns

Uses of Angle-Tracking Servo Systems

Monotrack fire control radars Homing missiles Acoustic homing torpedoes Aviation fire control tracking systems

Methods of tracking

Conical scan Conical scan on receive only (COSRO) Monopulse

Conical Scan

Time

Pulse Return Amplitude

Conical Scan

Time

Pulse Return Amplitude

Time

Pulse Return Amplitude

COSROConical Scan on Receive Only

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

Antenna

Monopulse

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

Two or more beams transmitted simultaneously and amplitude comparison is made 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!!!!

Monopulse

=

Summing of lobe energy

Monopulse Tracking

A B

Return Strength

A B

Return Strength

A B

Return Strength

A – B Comparison

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

Now, put ‘em together!!!!

• Range Tracking

• Angle Tracking

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

Tracking Gates

Return Strength

GATE – small volume of space monitored on each scan

Questions?