PID Control

PID CONTROL

 

Apart from sluggish performance to avoid oscillations, another problem with proportional-only control is that power application is always in direct proportion to the error. In the example above we assumed that the set temperature could be maintained with 50% power. What happens if the furnace is required in a different application where a higher set temperature will require 80% power to maintain it? If the gain was finally set to a 50° PB, then 80% power will not be applied unless the furnace is 15° below setpoint, so for this other application the operators will have to remember always to set the setpoint temperature 15° higher than actually needed. This 15° figure is not completely constant either: it will depend on the surrounding ambient temperature, as well as other factors that affect heat loss from or absorption within the furnace.

To resolve these two problems, many feedback control schemes include mathematical extensions to improve performance. The most common extensions lead to proportional-integral-derivative control, or PID control (pronounced pee-eye-dee).

  DDERIVATIVE ACTION

 

The derivative part is concerned with the rate-of-change of the error with time: If the measured variable approaches the setpoint rapidly, then the actuator is backed off early to allow it to coast to the required level; conversely if the measured value begins to move rapidly away from the setpoint, extra effort is applied—in proportion to that rapidity—to try to maintain it.

Derivative action makes a control system behave much more intelligently. On control systems like the tuning of the temperature of a furnace, or perhaps the motion-control of a heavy item like a gun or camera on a moving vehicle, the derivative action of a well-tuned PID controller can allow it to reach and maintain a setpoint better than most skilled human operators could.

If derivative action is over-applied, it can lead to oscillations too. An example would be a PV that increased rapidly towards SP, then halted early and seemed to "shy away" from the setpoint before rising towards it again.

 

INTEGRAL ACTION

The integral term magnifies the effect of long-term steady-state errors, applying ever-increasing effort until they reduce to zero. In the example of the furnace above working at various temperatures, if the heat being applied does not bring the furnace up to setpoint, for whatever reason,integral action increasingly moves the proportional band relative to the setpoint until the PV error is reduced to zero and the setpoint is achieved.In the furnace example, suppose the temperature is increasing towards a set point at which, say, 50% of the available power will be required for steady-state. At low temperatures, 100% of available power is applied

When the PV is within, say 10° of the SP the heat input begins to be reduced by the proportional controller. (Note that this implies a 20° "proportional band" (PB) from full to no power input, evenly spread around the set point value). At the set point the controller will be applying 50% power as required, but stray stored heat within the heater sub-system and in the walls of the furnace will keep the measured temperature rising beyond what is required. At 10° above SP, we reach the top of the proportional band (PB) and no power is applied, but the temperature may continue to rise even further before beginning to fall back. Eventually as the PV falls back into the PB, heat is applied again, but now the heater and the furnace walls are too cool and the temperature falls too low before its fall is arrested, so that the oscillations continue.

OTHER TECHNIQUES

It is possible to filter the PV or error signal. Doing so can reduce the response of the system to undesirable frequencies, to help reduce instability or oscillations. Some feedback systems will oscillate at just one frequency. By filtering out that frequency, more "stiff" feedback can be applied, making the system more responsive without shaking itself apart.

Feedback systems can be combined. In cascade control, one control loop applies control algorithms to a measured variable against a setpoint, but then provides a varying setpoint to another control loop rather than affecting process variables directly. If a system has several different measured variables to be controlled, separate control systems will be present for each of them.

Control Engineering in many applications produces control systems that are more complex than PID control. Examples of such fields include fly-by-wire aircraft control systems, chemical plants, and oil refineries. Model predictive control systems are designed using specialized computer-aided-design software and empirical mathematical models of the system to be controlled.

Unmanned Aerial Vehicle

 UAV

An unmanned aerial vehicle (UAV), commonly known as a drone, is an aircraft without a human pilot on board. Its flight is either controlled autonomously by computers in the vehicle, or under the remote control of a navigator, or pilot (in military UAVs called a Combat System Officer on UCAVs) on the ground or in another vehicle.

There are a wide variety of drone shapes, sizes, configurations, and characteristics. Historically, UAVs were simple remotely piloted aircraft, but autonomous control is increasingly being employed.

They are predominantly deployed for military applications, but also used in a small but growing number of civil applications, such as firefighting and nonmilitary security work, such as surveillance of pipelines. UAVs are often preferred for missions that are too 'dull, dirty, or dangerous' for manned aircraft.

 

UNMANNED AIRCRAFT SYSTEM

An unmanned aircraft system (UAS) includes ground stations and other elements besides the actual aircraft, the term was first officially used by the FAA in early 2005 and subsequently adopted by DoD that same year in their Unmanned Aircraft System Road map 2005–2030. Many people have mistakenly used the term Unmanned Aerial System, or Unmanned Air Vehicle System, as these designations were in provisional use at one time or another. The inclusion of the term aircraft emphasizes that regardless of the location of the pilot and flight crew, the operations must comply with the same regulations and procedures as do those aircraft with the pilot and flightcrew on board. The official acronym 'UAS' is also used by the (ICAO) and other government aviation regulatory organizations.

The military role of unmanned aircraft systems is growing at unprecedented rates. In 2005, tactical- and theater-level unmanned aircraft alone had flown over 100,000 flight hours in support of Operation Enduring Freedom and Operation Iraqi Freedom, in which they are organized under Task Force Liberty in Afghanistan and Task Force ODIN in Iraq. Rapid advances in technology are enabling more and more capability to be placed on smaller airframes which is spurring a large increase in the number of Small Unmanned Aircraft Systems (SUAS) being deployed on the battlefield. The use of SUAS in combat is so new that no formal DoD wide reporting procedures have been established to track SUAS flight hours. As the capabilities grow for all types of UAS, nations continue to subsidize their research and development leading to further advances enabling them to perform a multitude of missions. UAS no longer only perform intelligence, surveillance, and reconnaissance missions, although this still remains their predominant type. Their roles have expanded to areas including electronic attack, strike missions, suppression and/or destruction of enemy air defense, network node or communications relay, combat search and rescue and derivations of these themes. These UAS range in cost from a few thousand dollars to tens of millions of dollars, with aircraft ranging from less than one pound to over 40,000 pounds.

When the Obama administration announced in December 2009 the deployment of 30,000 new troops in Afghanistan, there was already an increase of attacks by pilotless Predator drones against Taliban and Al Qaeda militants in Afghanistan and Pakistan,s tribal areas, of which one probably killed a key member of Al Qaeda. However, neither Osama Bin Laden nor Ayman  Alzawahiri was the likely target, according to reports. 

According to a report of the New America Foundation, armed drone strikes had dramatically increased under President Obama – even before his deployment decision. There were 43 such attacks between January and October 2009. The report draws on what it deems to be "credible" local and national media stories about the attacks. That compared with a total of 34 in all of 2008, President Bush’s last full year in office. Since 2006, drone-launched missiles allegedly had killed between 750 and 1,000 people in Pakistan, according to the report. Of these, about 20 people were said to be leaders of Al Qaeda, Taliban, and associated groups. Overall, 66% to 68% of the people killed were militants, and 31% to 33% were civilians. US officials disputed the percentage for civilians. The U.S. Air Force has recently begun referring at least to larger UAS like Predator, Reaper, and Global Hawk as Remotely Piloted Aircraft (RPA), to highlight the fact that these systems are always controlled by a human operator at some location.

To distinguish UAVs from missiles, a UAV is defined as a "powered, aerial vehicle that does not carry a human operator, uses aerodynamic forces to provide vehicle lift, can fly autonomously or be piloted remotely, can be expendable or recoverable, and can carry a lethal or nonlethal payload". 

Therefore,  cruise missiles are not considered UAVs, because, like many other guided missiles, the vehicle itself is a weapon that is not reused, even though it is also unmanned and in some cases remotely guided.

F-16 COCKPIT

Figure: 1   F-16 Cockpit

1. LANDING GEAR HANDLE
moving the gear handle up retracts the landing gear once the aircraft is airborne.

2. AOA (Angle of Attack) Indicator
The AOA indicator is an instrument that shows the angle of attack of the aircraft. In order to generate lift, the jet needs to have a positive angle of attack or fly at a positive angle into the relative wind (airflow).

3. Airspeed Indicator
The airspeed indicator shows the aircraft's airspeed in hundreds of knots. When the red needle is on the "4", you going 400 knots.

4. MDF (Multi Functional Displays)
Two displays on either side of the centre console in the cockpit that can show all radar modes including combat and navigation, as well as other vital information.

5. THREAT WARNING SYSTEM
This system detects radar contacting your aircraft and determines its type, strength and bearing.

6. HUD (heads-up-display) A glass panel in front of the cockpit that shows important navigation and weapons information. 7. ICP (Integrated Control Panel) Panel used for weapons release, landing, navigation and Communications. 8. Oil Pressure Indicator The Oil pressure indicator displays engine oil pressure, ranging from 0 to 100 psi (pounds per square inch). 9. RPM (Revolutions Per Minute) Indicator The RPM indicator displays the engine revolutions per minute. RPM is expressed as a percentage from 0% to 100% 10. Nozzle Position Indicator This instrument displays the position of the engine nozzle. The indicator will be mostly open at idle, closed at Mil power (100% thrust), and fully open at full after burner. 11. VVI (Vertical Velocity Indicator) The vertical Velocity Indicator is an instrument that shows your rate of climb or descent in feet per minute. 12. ADI (Attitude Direction Indicator) The instrument that displays the aircraft pitch and control. 13. CONTROLSTICK: The F-16C/F users "fly-by-wire" Technology on an F16 the stick does not control cables that are linked to the surface, but  inputs to a computer which in turn controls servos or hydraulics for the flaps and rudder, etc... 14. HSI (Horizontal Situation Indicator) The HSI is a round moving dial that shows the aircraft's compass heading. When the aircraft turns, the dial moves to indicate the change in aircraft heading. 15. ALTIMETER The altimeter shows the height of the aircraft above MSL(Mean Sea Level)