Feedback Control Weapons ON Target Dynamically or actively command, direct, or regulate themselves or other systems. 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) Discuss Slide

Feedback Control System INPUT OUTPUT CONTROLLER FEEDBACK ELEMENT

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)

Example of Feedback Control System Thermostat Temp Wanted Air Temp Heater Control Air Temp Heater Control Thermostat Input = temp wanted Output=Heater on or off Feedback=Air temp Error=Difference between desired and actual air temp Compares the temp wanted to air temp. If there is a difference, turn on the heater! Once the difference equals zero, turns off the heater. Temp Wanted

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 1. Introduction: a. Most equipment have some form of a controller to make it function. b. Most have something more than just an on/off switch as a controller. c. Two major types of controllers in use: 2. Open-Loop. a. Performs its action without regard to the output or any external input. Example: The controller on a washing machine. a. It will run the washer through the cycle without regard for the cleanliness of the clothes in the machine, if there is soap in the machine, temperature of the water, how much clothes are in the machine, etc. 3. Closed-Loop (Feedback) a. Senses the output of the controller or process. b. Uses this output to change the process to meet the desired result. c. Controller can determine how accurate the output is or if it producing the desired result. d. Control action depends on the output of the system. Example: Aircraft auto Pilot set to keep plane at altitude.

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 1. Increased Accuracy a. Ability to faithfully reproduce the output. 2. Reduced Sensitivity to Disturbances a. Ability of the system to produce the same output repeatedly in spite of variations and fluctuations within the control system (worn gears, sticky components etc.) b. Changes within the system are reduced and the effects of the changes can be minimized. 3. Smoothing and filtering. Undesirable effects of noise and distortion within the system are reduced. 4. Increased Bandwidth. Can operate satisfactorily over a wide range of frequencies or variations in the input.

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 1. Discuss slide. 2. A you can see from the example of the gun turret, these types of feedback provide additional information that is used to improve the response time of the system. - The light on when the proper position was reached. But... - The additional information modifies the system response and improve the response time. 3. This additional information when add to the feedback loop is call DAMPING.

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. 1. Congratulations: You have just been promoted to Gun Fire Control System First class. You have been assigned to a choice billet as the gun fire control system for the Navy’s newest 5” gun. 2. Show slide. Cover the job description on the graphic and the safety note. Also cover that speed at which the gun turret rotates is dependent on how far the joy stick is pushed to one side or another. The further the fast the turret moves. 3. Here comes the first target. The targeting computer has “got a lock” its now up to you. Go (pick a student to say what he is going to do). Point out without feed back he will just go in circles never getting to the proper place. - Note that because the gun turret is so big it takes a little time to stop it once you zero the joy stick. 4. After they figure out they can’t do much. ask Are you an open or closed loop control system? 5. When the students ask for a feedback loop tell them to give feedback the Navy has installed a light that comes on when you are within a half of a degree of the proper position. Tell them that should be enough feed back to make it work. - As a review go over the previous graphic identifying each block of the feed back system. Run the discussion so the try to get to the proper mark but it takes time. 6. With the Feedback light as them to describe how the position of the gun would look if plotted over time

Turret Position with Feedback New Position Old Position Time

Dampening New Position Old Position Pg. 101, Fig. 3-9 Underdamped - Oscillates around the new position, overshooting. Rapid initial response, but takes a long time to settle out at the new position. Overdamped - Damping is too large, response time is sluggish, takes a long time to arrive at new position but will not overshoot. Critically damped - System responds quickly with no overshoot. Combines quick response time with stopping at new position quickly. Dashed line is a typical system design. Optimizes response time, slightly underdamped. Maximize response time with minimal overshoot and oscillation. Old Position

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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) 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 1. Introduction: Referring to the slide where the students were the controller. We solved the problem of how to get the gun to the right angle (azimuth). But in order to hit the target (especially a moving target) we have to have more information . What other problems do we have to solve other than azimuth? 2. Relative motion is hard since the target is moving and the platform (ship) is moving plus it is also rocking, rolling, pitching and yawing. 3. We must be able to solve all of these to be able to predict ahead in time the target’s and weapon’s motion to ensure the collision point between the target and a weapon is achieved. Predict the intercept point! 4. No problem, we have computers who can do this. “Garbage in, garbage out” means that to accurately solve these parameters we must have a sensor (normally radar) locked on the target and tracking the target continuously. This method is called automatic tracking.

Tracking Terms Error Line-of-Sight Tracking Line Tracking Element 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 Sense position error magnitude and direction From where the target really is in relation to where the antenna is pointing. Provide position feedback - Change in direction required to put our antenna back on target. Provide data smoothing/stabilization - Reduces the internal noise mechanical glitches of the system. Provide velocity feedback (to aid in achieving a smooth track) - Remember the damping we talked about earlier Provide a power driving device to move the antenna.

Position Error Magnitude & Direction 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

Azimuth lobing Returns A B A B A B

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 Discuss the following slides.

Conical Scan Pulse Return Amplitude Time

Conical Scan Time Pulse Return Amplitude Pulse Return Amplitude Time

Sequential Lobing R L L L R R * 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

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 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 Antenna Axis Varying Amplitude Sensor Return Signal Beam Pulse Return Amplitude Time 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 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!!!! 1. Monopulse uses the same theory that the maximum return will be on the center of the beams axis. 2. The sequential lobing used the same transmitter and sequentially stepped the beam through various angles of transmission taking time to complete the entire cycle. The monopulse simultaneously transmits two or more beams at the same time and measures the returns from all the beams. 3. Each beam is encoded so the returns can be identified as to which beam produced the return. This is normally done by slight polarization of the beam. - Remember a beam can be polarized by tilting the dipole antenna. 4. The different beams are formed from different feed horns but they all use the same radar reflector dish.

Monopulse = Summing of lobe energy

Monopulse Tracking A – B Comparison Return Strength A B

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 1. All naval weapons systems require a stabilized reference to work so all methods to stabilize the output of the tracking device. 2. Tracking systems normally fall into three methods of stabilization a. Unstabilized: - Tracking system is not stabilized in any axis. - Tracking system’s output contains rotational errors - Compensation for errors is done externally to tracking system. b. Partially Stabilized: - One axis of the tracking system is stabilized. - Can have rotational disturbances on the other axis. - The unstabilized axis is corrected external to the tracking system c. Fully Stabilized: - Entire tracking system is gimbals-mounted and is stabilized. - No further compensation is required.

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) 1. Show slide and discuss what is inertia and precession. Similar to bicycle wheel. Also can demonstrate principles using Unit’s gyroscope. 2. Gyroscopes are used to provide the stable reference plane for the tracking system and rate gyros are used to provide the means of converting mechanical movement into an electrical signal. 3. Rate gyros also are used to provide the rate feedback to help improve the damping of the system. - Remember the gun turret position could be improved if we sensed the rate of rotation and slowed the mount the closer we came to the correct position. Lead in: 1. This completes our discussion of the angle-tracking servo systems and how we detect angular position and errors. 2. To get an accurate firing solution you need not only angular tracking information and error but range tracking information and errors. 3. We can get automatic range tracking too.

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 Accelerometers!!! 1

Now, put ‘em together!!!! Range Tracking 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). A B Range

Tracking Gates Return Strength GATE – small volume of space monitored on each scan

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