Feedback Control

1. Feedback Control

2. 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.

3. Example of Negative Feedback Control System Air Temp Heater Control Thermostat Temp Wanted

4. 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

5. 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

6. 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

7. 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

8. New Position Turret Position with Feedback Old Position Time

9. Dampening Damping New Position Old Position

10. Automatic Tracking Systems (Related to Feedback) 1. Target Tracking Parameters 2. Line-of-Sight(LOS) 3. Tracking Line

11. Target Tracking Parameters • Azimuth • Elevation • Range • Relative Target Velocity • Target’s motion with respect to the platform’s motion

12. Tracking Terms Error Line-of-Sight Tracking Line Tracking Element

13. 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

14. Uses of Angle-Tracking Servo Systems • Monotrack fire control radars • Homing missiles • Acoustic homing torpedoes • Aviation fire control tracking systems

15. Methods of tracking • Conical scan • Conical scan on receive only (COSRO) • Monopulse

16. 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

17. 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

18. 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

19. 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

20. 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

21. *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

22. 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!!!!

23. 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

24. 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)

25. 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

26. Gyroscopic Theory Accelerometers!!!

27. Now, put ‘em together!!!! • Range Tracking • Angle Tracking One dead duck…………………..

28. Questions?