Presentation on theme: "Control System Terminology S Input – Excitation applied from external source S Output - Response obtained from a system S Feedback – System output returned."— Presentation transcript:
Control System Terminology S Input – Excitation applied from external source S Output - Response obtained from a system S Feedback – System output returned to modify input S Error - Difference between input and output.
Negative Feedback Control System CONTROLLER CONTROLLED DEVICE FEEDBACK ELEMENT
Thermostat Temp Wanted Air Temp Heater Control Example of Negative Feedback Control System
Types of Control Systems ø Open-Loop –Simple system which performs function without concern for initial conditions or external inputs –Must be closely monitored ø 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 ø Increased Accuracy –Ability to reproduce output with varied input ø Reduced Sensitivity to Disturbance –Self-correcting minimizes effects of system changes ø Smoothing and Filtering –System induced noise and distortion are reduced ø Increased Bandwidth –Produces satisfactory response to increased range of input changes
Major Types of Feedback Used ø Position Feedback –Used when the output is a linear distance or angular measurement. ø 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 inside a windowless protective enclosure inside the gun turret.
Time Old Position New Position Turret Position with Feedback
Damping Dampening Old Position New Position
Automatic Tracking Systems (Related to Feedback) 1. Target Tracking Parameters 2. Line-of-Sight(LOS) 3. Tracking Line
Target Tracking Parameters ø Azimuth ø Elevation ø Range ø Relative Target Velocity –Targets motion with respect to the platforms motion
Tracking Terms Tracking Element Line-of-Sight Tracking Line Error
Angle-Tracking Servo Systems ø Five Basic Functions øSense position error magnitude and direction øProvide position feedback øProvide data smoothing / stabilization øProvide velocity feedback øProvide a power-driving device
Uses of Angle-Tracking Servo Systems ø Monotrack fire control radars ø Homing missiles ø Acoustic homing torpedoes ø Aviation fire control tracking systems
Methods of tracking ø Conical scan ø Conical scan on receive only (COSRO) ø 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 & Direction
Sequential Lobing L L L R 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 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 Using Conical Scan Locus of Beam Centers Beam Time Pulse Return Amplitude Equal Amplitude Sensor Return Signal Antenna Axis Target Position is in the Center of the Conical Scan (On Antenna Axis)
Determining Tracking Error Using Conical Scan Locus of Beam Centers Beam Time Pulse Return Amplitude Varying Amplitude Sensor Return Signal Antenna Axis Target Position Off the Center of the Antenna Axis
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
Monopulse ø Developed to overcome tracking errors involved with conical scanning and sequential lobing ø 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 ø Very complex and expensive!!!!
Providing a Stable Tracking System ø All tracking systems require some stabilization ø 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 ø Gyroscopes provide the stable reference
Basic Gyroscopic Principles l Gyro spins at a very high velocity –Spin axis remains aligned with terrestrial meridians l 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 Principles l Precession –A gyros 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 l The gyro has three axes –spin axis –torque axis –precession axis
Gyroscopic Theory Accelerometers!!!
Now, put em together!!!! l Range Tracking l Angle Tracking One dead duck…………………..
Automatic Range Tracking Uses range gate method of determining range error. The range gate pulse is centered on the expected range. Actual Return Expected Return Centered on Predicted Range. Summation of actual pulse energy that falls within the boundaries of the expected pulse. (Second half energy amount is inverted so easier to compare). AB Range