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Title:
AUTOMATICALLY ALLEVIATING FORCES ON A REFUELING BOOM
Document Type and Number:
WIPO Patent Application WO/2010/071643
Kind Code:
A1
Abstract:
A method and apparatus are present for managing forces on a refueling boom (500). Force information is received from a force sensor (326) associated with the refueling boom (500). Forces on the refueling boom without a number of air loads on the refueling boom are identified to form filtered force information. A force-based command is generated using the filtered force information on the refueling boom.

Inventors:
SPEER THOMAS E (US)
HATCHER JUSTIN C (US)
MUSGRAVE JEFFREY L (US)
Application Number:
US2008/087260
Publication Date:
June 24, 2010
Filing Date:
December 17, 2008
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
BOEING CO (US)
SPEER THOMAS E (US)
HATCHER JUSTIN C (US)
MUSGRAVE JEFFREY L (US)
International Classes:
B64D39/00
Foreign References:
EP1894840A12008-03-05
US20030205643A12003-11-06
US6084371A2000-07-04
US6272924B12001-08-14
FR2569652A11986-03-07
Other References:
None
Attorney, Agent or Firm:
ASSEFA, Brook et al. (PO Box 2515MC 110-sd5, Seal Beach CA, US)
Download PDF:
Claims:
CLAIMS :

What is claimed is:

1. A method for managing forces (333) on a refueling boom (316), the method comprising: receiving (800) force information (626) from a force sensor (326) associated with the refueling boom (316); identifying (802) the forces (333) on the refueling boom (316) without a number of errors of force measurement to form filtered force information (634); and generating (804) a force-based command (640) using the filtered force information (634) for the refueling boom (316) .

2. The method of claim 1 further comprising: combining (920) the force-based command (640) with an operator command (642) to form a command (646) for an actuator system (323) capable of controlling the refueling boom (316) .

3. The method of claim 2, wherein the actuator system (323) is capable of controlling a force generator system (341) .

4. The method of claim 1, wherein the number of errors of force measurement may be at least one of noise, a sensor tolerance error, and a sensor bias error.

5. The method of claim 1, wherein the identifying (802) step comprises: limiting (908) the force information (626) associated with the number of errors of force measurement to form low pass filtered force information (742); and subtracting (909) the low pass filtered force information (742) from smoothed out force information (738) to form filtered force information (634) .

6. The method of claim 5, wherein the limiting (908) step comprises: removing (904) noise from the force information (626) to form the smoothed out force information (738); limiting (906) a portion of the smoothed out force information (738) within a sensor tolerance error to form sensor tolerance limited force information (740); and limiting (908) a portion of the sensor tolerance limited force information (740) within a sensor bias error to form the low pass filtered force information (742) .

7. The method of claim 6, wherein the step of removing (904) the noise from the force information (626) to form the smoothed out force information (738) comprises: filtering (904) the force information (626) using a second order filter (710) to remove the noise from the force information (626) to form the smoothed out force information (738) .

8. The method of claim 6, wherein the step of limiting (906) the portion of the smoothed out force information (738) within the sensor tolerance error to form the sensor tolerance limited force information (740) comprises : limiting (906) the smoothed out force information (738) with a limiter (714) to limit the portion of the smoothed out force information (738) within the sensor tolerance error to form the sensor tolerance limited force information (740) .

9. The method of claim 6, wherein the step of limiting (908) the portion of the sensor tolerance limited force information (740) within the sensor bias error to form the low pass filtered force information (742) comprises: filtering (908) the sensor tolerance limited force information (740) using a low pass filter (716) to pass the portion of the sensor tolerance limited force information (740) within the sensor bias error to form the low pass filtered force information (742) .

10. The method of claim 1, wherein the generating (804) step comprises: generating (916) the force-based command (640) using the filtered force information (634) for the refueling boom (316) and a dynamic pressure (638) for an aircraft (100) on which the refueling boom (316) is located, wherein the force-based command (640) reduces the forces (333) on the refueling boom (316) .

11. The method of claim 1, wherein the force sensor (326) is located on a strain sleeve (321) on the refueling boom (316) .

12. The method of claim 1, wherein the filtered force information (634) is for the forces (333) on the refueling boom (316) during flight without contact with a receiving aircraft (303) .

13. An apparatus comprising: a control process (339) capable of receiving (800) force information (626) from a force sensor (326) associated with a refueling boom (316); identifying (802) forces (333) on the refueling boom (316) without a number of errors of force measurement to form filtered force information (634); and generating (804) a force-based command (640) using the filtered force information (634) for the refueling boom (316); and a computer (338) capable of executing the control process (339) , wherein the control process (339) is stored on the computer (338) .

14. The apparatus of claim 13 further comprising: a sensor system (306) associated with the refueling boom (316) capable of generating the force information (626) .

15. The apparatus of claim 14, wherein the sensor system (306) comprises: a force sensor (326) .

16. The apparatus of claim 15 further comprising: a strain sleeve (321), wherein the force sensor (326) is located on the strain sleeve (321) .

17. The apparatus of claim 13 further comprising: an aircraft (100); and the refueling boom (316), wherein the refueling boom (316) and the computer (338) are located in the aircraft (100) .

18. The apparatus of claim 13, further comprising: an actuator system (323) , wherein the control process (339) is further capable of combining (920) the force-based command (640) with an operator command (642) to form a command (646) for an actuator system (323) capable of controlling the refueling boom (316) .

19. The apparatus of claim 18, wherein the actuator system (323) is capable of controlling a force generator system (341) .

20. The apparatus of claim 13, wherein the number of errors of force measurement may be at least one of noise, a sensor tolerance error, and a sensor bias error.

21. The apparatus of claim 13, wherein in identifying (802) the forces (333) on the refueling boom (316) without the number of errors of force measurement to form the filtered force information (634), the control process (339) is capable of limiting (908) force information (626) associated with the number of errors of force measurement to form low pass filtered force information (742); and subtracting (909) the low pass filtered force information (742) from smoothed out force information (738) to form filtered force information (634) .

22. The apparatus of claim 21, wherein in limiting (908) force information (626) associated with the number of errors of force measurement to form the low pass filtered force information (742), the control process (339) is capable of removing (904) noise from the force information (626) to form the smoothed out force information (738); limiting (906) a portion of the smoothed out force information (738) within a sensor tolerance error to form sensor tolerance limited force information (740); and limiting (908) a portion of the sensor tolerance limited force information (740) within a sensor bias error to form the low pass filtered force information (742) .

23. The apparatus of claim 22, wherein in removing (904) the noise from the force information (626) to form the smoothed out force information (738), the control process (339) is capable of filtering (904) the force information (626) using a second order filter (710) to remove the noise from the force information (626) to form the smoothed out force information (738) .

24. The apparatus of claim 22, wherein in limiting (906) the portion of the smoothed out force information (738) within the sensor tolerance error to form the sensor tolerance limited force information (740), the control process (339) is capable of limiting (906) the smoothed out force information (738) with a limiter (714) to limit the portion of the smoothed out force information (738) within the sensor tolerance error to form the sensor tolerance limited force information (740) .

25. The apparatus of claim 22, wherein in limiting (908) the portion of the sensor tolerance limited force information (740) containing forces (333) caused by the number of errors of force measurement to form the low pass filtered force information (742), the control process (339) is capable of filtering (908) the sensor tolerance limited force information (740) using a low pass filter (716) to pass the portion of the sensor tolerance limited force information (740) within the sensor bias error to form the low pass filtered force information (742) .

Description:
AUTOMStTICALLY ALLEVIATING FORCES ON A REFUELING BOOM

BACKGROUND

The present disclosure relates generally to aircraft and, in particular, to refueling aircraft. Still more particularly, the present disclosure relates to a method, apparatus, and computer usable program code for controlling a refueling boom.

Aerial refueling may be a process of transferring fuel from one aircraft to another aircraft. The aircraft from which the fuel originates may be referred to as a tanker, while the other aircraft receiving the fuel may be referred to as a receiver. This type of process may be applied to various types of aircraft including, for example, without limitation, fixed wing aircraft and/or helicopters .

One common approach for refueling may involve a boom and receptacle system. With a boom, a fixed tube and a telescoping tube may be present on the tank aircraft. These tubes may also be referred to as a refueling boom or a telescoping refueling boom. The refueling boom may be attached to the rear of the tanker aircraft and may be a flexible refueling boom allowing movement along an x- axis and a y-axis relative to the tanker. An operator may extend and/or position the refueling boom for insertion into a receptacle on the receiving aircraft to transfer fuel to the receiving aircraft.

Further, a refueling boom operator may control the ruddevators for a refueling boom to control the pitch and yaw of the refueling boom. The flexibility of the refueling boom may add a challenge to positioning the refueling boom when a refueling boom operator manipulates a control stick to operate the refueling boom. Movement of the ruddevators may be performed in concert or together, since the refueling boom may use a pitch and yaw pivot, while the ruddevators may be in a "V" configuration.

Physical contact between a refueling boom and the receptacle of the receiving aircraft may result in increased forces between the refueling boom and the receptacle. These forces may be due to the refueling boom not being directly in line with the receptacle, the receiving aircraft moving laterally and/or vertically, and/or the control surfaces of the refueling boom not being properly trimmed. Loads generated by contact between the refueling boom and the receiver may prevent the refueling boom from moving to a commanded position. These loads may cause boom bending and instability. Further, these loads may cause breakage or disconnecting of the refueling boom. Alleviating these loads by moving the refueling boom may allow the refueling boom to move with the receiver and may allow the receiver to move more freely .

Existing solutions may use an automatic load alleviation system (ALAS) to move the refueling boom to reduce the loads. In addition to alleviating loads, the automatic load alleviation system may allow for handling sudden transitions between the refueling boom flying free and being in contact with the receiver. Current solutions may handle these transitions by using separate modes of operation for the refueling boom being in free- flight and being coupled to the receiver. These modes may be triggered manually by an operator.

These separate modes may make it possible for the automatic load alleviation system to be in the wrong mode at the wrong time. Further, manual triggering of these modes may increase the amount of time it takes to transfer fuel and may lead to inadvertent striking of the receiving aircraft in areas outside of the receptacle. The automatic load alleviation system operating in the wrong mode at the wrong time may lead to instability of the refueling boom.

In addition, current solutions do not allow for the automatic load alleviation system and the operator of the refueling boom to control the refueling boom at the same time. Thus, periods of time may occur in which the operator has no control of the refueling boom. This may pose issues in situations where the automatic load alleviation system may be operating less than reliably.

Therefore, it would be desirable to have a method, apparatus, and computer program code that may overcome one or more of the issues described above, as well as other possible issues.

SUMMARY

In one advantageous embodiment, a method is present for managing forces on a refueling boom. Force information is received from a force sensor associated with the refueling boom. Forces on the refueling boom without a number of air loads on the refueling boom are identified to form filtered force information. A force- based command is generated using the filtered force information on the refueling boom.

In another advantageous embodiment, an apparatus comprises a control process and a computer on which the control process is stored. The control process is capable of receiving force information from a force sensor associated with the refueling boom. The control process is capable of identifying force on the refueling boom without a number of errors of force measurement to form filtered force information. The control process is capable of generating a force-based command using the filtered force information on the refueling boom. The computer is capable of executing the control process.

The features, functions, and advantages can be achieved independently in various embodiments of the present disclosure or may be combined in yet other embodiments in which further details can be seen with reference to the following description and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the advantageous embodiments are set forth in the appended claims. The advantageous embodiments, however, as well as a preferred mode of use, further objectives, and advantages thereof, will best be understood by reference to the following detailed description of an advantageous embodiment of the present disclosure when read in conjunction with the accompanying drawings, wherein:

Figure 1 is a diagram of an aircraft in which an advantageous embodiment may be implemented;

Figure 2 is a diagram of a data processing system in accordance with an illustrative embodiment;

Figure 3 is a diagram of a refueling environment in accordance with an advantageous embodiment;

Figure 4 is a diagram of one implementation for a refueling environment in accordance with an advantageous embodiment;

Figure 5 is a more detailed illustration of a refueling boom in accordance with an advantageous embodiment;

Figure 6 is a control data flow diagram of a refueling boom control environment in accordance with an advantageous embodiment;

Figure 7 is a diagram of control laws for generating a command to alleviate forces on a refueling boom in accordance with an advantageous embodiment;

Figure 8 is a flowchart of a process for managing force on a refueling boom in accordance with an advantageous embodiment; and Figure 9 is a flowchart of a process for alleviating forces on a refueling boom in accordance with an advantageous embodiment.

DETAILED DESCRIPTION

Referring more particularly to the drawings, embodiments of the disclosure may be described in the context of an aircraft, such as, for example, aircraft 100 as shown in Figure 1.

With reference now to Figure 1, a diagram of an aircraft is depicted in which an advantageous embodiment may be implemented. In this example, aircraft 100 in Figure 1 may include airframe 102 with a plurality of systems 104 and interior 106. Examples of systems 104 include one or more of propulsion system 108, electrical system 110, hydraulic system 112, environmental system 114, and refueling system 116. Any number of other systems may be included. Different advantageous embodiments may be implemented within refueling system 116 in these depicted examples. Although an aerospace example is shown, different advantageous embodiments may be applied to other industries, such as the automotive industry .

Turning now to Figure 2, a diagram of a data processing system is depicted in accordance with an illustrative embodiment. Data processing system 200 is an example of the data processing system that may be located within aircraft 200. For example, data processing system 200 may be part of electrical system 110 and/or refueling system 116. Data processing system 200 may implement different processes for managing movement of a refueling boom. In this illustrative example, data processing system 200 includes communications fabric 202, which provides communications between processor unit 204, memory 206, persistent storage 208, communications unit 210, input/output (I/O) unit 212, and display 214. Processor unit 204 serves to execute instructions for software that may be loaded into memory 206. Processor unit 204 may be a set of one or more processors or may be a multi-processor core, depending on the particular implementation. Further, processor unit 204 may be implemented using one or more heterogeneous processor systems in which a main processor is present with secondary processors on a single chip. As another illustrative example, processor unit 204 may be a symmetric multi-processor system containing multiple processors of the same type.

Memory 206 and persistent storage 208 are examples of storage devices. A storage device is any piece of hardware that is capable of storing information either on a temporary basis and/or a permanent basis. Memory 206, in these examples, may be, for example, a random access memory or any other suitable volatile or non-volatile storage device.

Persistent storage 208 may take various forms depending on the particular implementation. For example, persistent storage 208 may contain one or more components or devices. For example, persistent storage 208 may be a hard drive, a flash memory, a rewritable optical disk, a rewritable magnetic tape, or some combination of the above. The media used by persistent storage 208 also may be removable. For example, a removable hard drive may be used for persistent storage 208.

Communications unit 210, in these examples, provides for communications with other data processing systems or devices. In these examples, communications unit 210 is a network interface card. Communications unit 210 may provide communications through the use of either or both physical and wireless communications links. Input/output unit 212 allows for input and output of data with other devices that may be connected to data processing system 200. For example, input/output unit 212 may provide a connection for user input through a keyboard and mouse. Further, input/output unit 212 may send output to a printer. Display 214 provides a mechanism to display information to a user.

Instructions for the operating system and applications or programs are located on persistent storage 208. These instructions may be loaded into memory 206 for execution by processor unit 204. The processes of the different embodiments may be performed by processor unit 204 using computer implemented instructions, which may be located in a memory, such as memory 206. These instructions are referred to as program code, computer usable program code, or computer readable program code that may be read and executed by a processor in processor unit 204. The program code in the different embodiments may be embodied on different physical or tangible computer readable media, such as memory 206 or persistent storage 208.

Program code 216 is located in a functional form on computer readable medium 218 that is selectively removable and may be loaded onto or transferred to data processing system 200 for execution by processor unit 204. Program code 216 and computer readable medium 218 form computer program product 220 in these examples. In one example, computer readable medium 218 may be in a tangible form such as, for example, an optical or magnetic disc that is inserted or placed into a drive or other device that is part of persistent storage 208 for transfer onto a storage device, such as a hard drive that is part of persistent storage 208. In a tangible form, computer readable medium 218 also may take the form of a persistent storage, such as a hard drive, a thumb drive, or a flash memory that is connected to data processing system 200. The tangible form of computer readable medium 218 may be computer recordable storage media 219. In some instances, computer readable medium 218 may not be removable.

Alternatively, program code 216 may be transferred to data processing system 200 from computer readable medium 218 through communications link 222 to communications unit 210 and/or through connection 224 to input/output unit 212. Communications link 222 and/or connection 224 may be physical or wireless in the illustrative examples. Computer readable medium 218 also may take the form of non-tangible media, such as communications links or wireless transmissions containing program code 216.

In some illustrative embodiments, program code 216 may be downloaded over a network to persistent storage 208 from another device or data processing system for use within data processing system 200. For instance, program code stored in a computer readable storage medium in a server data processing system may be downloaded over a network from the server to data processing system 200. The data processing system providing program code 216 may be a server computer, a client computer, or some other device capable of storing and transmitting program code 216.

The different components illustrated for data processing system 200 are not meant to provide architectural limitations to the manner in which different embodiments may be implemented. The different illustrative embodiments may be implemented in a data processing system including components in addition to, or in place of, those illustrated for data processing system 200.

Other components shown in Figure 2 can be varied from the illustrative examples shown. The different embodiments may be implemented using any hardware device or system capable of executing program code. As one example, the data processing system may include organic components integrated with inorganic components and/or may be comprised entirely of organic components excluding a human being. For example, a storage device may be comprised of an organic semiconductor.

As another example, a storage device in data processing system 200 may be any hardware apparatus that may store data. Memory 206, persistent storage 208, and computer readable medium 218 may be examples of storage devices in a tangible form.

In another example, a bus system may be used to implement communications fabric 202 and may be comprised of one or more buses, such as a system bus or an input/output bus. Of course, the bus system may be implemented using any suitable type of architecture that provides for a transfer of data between different components or devices attached to the bus system. Additionally, a communications unit may include one or more devices used to transmit and receive data, such as a modem or a network adapter. Further, a memory may be, for example, memory 206 or a cache such as found in an interface and memory controller hub that may be present in communications fabric 202.

The different advantageous embodiments recognize that forces on a refueling boom may increase due to movement of the receiving aircraft, misalignment of the refueling boom with the receptacle of the refueling boom at contact, and/or inadequate trimming of control surfaces of the refueling boom. These forces may cause a refueling boom to move to a position not desired and/or commanded by the operator of the refueling boom. The different advantageous embodiments also recognize that these forces on the refueling boom may cause boom bending and boom instability. These forces may also cause breakage and/or disconnecting of the refueling boom.

Currently available solutions of load alleviation systems for alleviating these forces may not allow an operator to have complete control of the refueling at all times. Further, currently available load alleviation systems may operate in separate manual modes that may allow for these load alleviation systems to operate in the wrong mode at the wrong time. This may be due to a failure in the system or due to human error. In addition, manual triggering of these modes may lead to inadvertent striking of the receiving aircraft by the refueling boom, which may in turn, lead to damage to the refueling boom and/or receiving aircraft.

With reference now to Figure 3, a diagram of a refueling environment is depicted in accordance with an advantageous embodiment. In this example, refueling environment 300 may be implemented for tanker aircraft 301. Tanker aircraft 301 may be one example of aircraft 100 in Figure 1. Refueling environment 300 may also include receiving aircraft 303.

Tanker aircraft 301 may include operator refueling station 302, refueling boom unit 304, refueling control system 308, and/or other suitable components. In these illustrative examples, operator refueling station 302, refueling boom unit 304, and refueling control system 308 may be part of refueling system 116 in Figure 1. The different components may be implemented using one or more data processing systems such as, for example, data processing system 200 in Figure 2.

Operator refueling station 302 may provide a location for operator 312 to control refueling boom unit 304. Operator refueling station 302 may send operator input 347 to refueling control system 308. In turn, refueling control system 308 may generate commands 314, which are sent to refueling boom unit 304 to control refueling boom 316. For example, command 315 within commands 314 may move refueling boom 316.

Refueling boom unit 304 may include refueling boom 316, sensor system 306, cable system 327, and actuator system 323. Refueling boom 316 may have fixed tube 317, telescoping tube 318, nozzle 320, strain sleeve 321, and positioning system 322. Strain sleeve 321 may be attached to nozzle 320. In this illustrative example, positioning system 322 may be a number of force generators. A number of items, as used herein, refers to one or more items. For example, a number of force generators is one or more force generators.

In this particular example, positioning system 322 may take the form of force generator system 341. In these illustrative examples, force generator system 341 may take the form of ruddevators 329. Of course, in other advantageous embodiments, force generator system 341 may take the form of other force generators such as, for example, without limitation, control surfaces, other aerodynamic force generators, and/or some other suitable force generator. Ruddevators 329 may be arranged in a "V" shape on fixed tube 317 in these examples.

Actuator system 323 may move refueling boom 316 with respect to tanker aircraft 301 in which refueling boom unit 304 is attached. In these examples, actuator system 323 may contain actuators 325. Refueling boom 316 may move to change boom angle 343 and boom length 330 under the control of actuator system 323.

Actuators 325 may control ruddevators 329 in positioning system 322 to change boom angle 343 of refueling boom 316. Further, cable system 327 may be activated to change boom angle 343 of refueling boom 316.

In these illustrative examples, boom length 330 may be the length of fixed tube 317 plus the length of telescoping tube 318, nozzle 320, and strain sleeve 321.

Telescoping tube 318 may move with respect to fixed tube 317 to provide extension 332 for telescoping tube 318 in refueling boom 316. Extension 332 for telescoping tube 318 may be controlled by actuators 325 within actuator system 323 in these illustrative examples. Extension 332 of telescoping tube 318 may change. When extension 332 changes, boom length 330 of refueling boom 316 may change. Boom length 330 may change by changing extension 332 in a manner that may reduce boom length 330 or increase boom length 330. Boom length 330 may be identified using sensor system 306.

Sensor system 306 may include, for example, without limitation, inertial measurement unit 335, position sensor 337, force sensor 326, air data system 328, and other suitable sensors. Inertial measurement unit 335 may identify accelerations and rates in three axes for refueling boom 316. Position sensor 337 may be used to identify boom angle 343. Further, position sensor 337 also may be used to identify the length of extension 332 of refueling boom 316. Position sensor 337 may be implemented using position sensors in the form of, for example, without limitation, a potentiometer or some other suitable position sensor. Position sensor 337 may be one or more positions sensors. Force sensor 326 may be used to identify forces 333 on refueling boom 316 due to contact with receiving aircraft 303. Force sensor 326 may be located on strain sleeve 321 attached to nozzle 320 of refueling boom 316. Sensor system 306 may also include air data system 328, which may be used to measure dynamic pressure 336 for tanker aircraft 301.

In these examples, refueling control system 308 may have control computer 338, which may have processes that execute on control computer 338. Control processes 339 may have control laws, which may be examples of processes that may execute on control computer 338 within refueling control system 308 to control refueling boom unit 304. Refueling control system 308 may send information back to operator refueling station 302 for display on display 340 in operator refueling station 302. Operator refueling station 302 also may include control stick 342 to generate operator commands 344, which are sent to refueling control system 308 for processing. Operator commands 344 may include a command to move refueling boom 316 to a desired position.

Refueling control system 308 may process operator commands 344 using control processes 339 to generate commands 314. Commands 314 may be a result of modifications and/or limits to operator commands 344 generated at operator refueling station 302.

Control processes 339 may include processes for controlling refueling boom unit 304 to alleviate forces 333 on refueling boom 316. These processes may include, for example, force alleviation system 345 and command summing process 346. Force alleviation system 345 may include processes such as, for example, force filtering process 349 and force-based command generating process 350. Force alleviation system 345 and command summing process 346 may be used to generate a command such as, for example, command 315, to alleviate forces 333 to reduce boom bending and prevent boom breakage and/or disconnecting. Command 315 may move refueling boom 316 to position it more directly in line with receptacle 351 of receiving aircraft 303. In these examples, receptacle 351 may be a receptacle for nozzle 320 of refueling boom 316. Receptacle 351 may receive fuel through nozzle 320.

The illustration of refueling environment 300 is not meant to imply physical or architectural limitations to the manner in which different refueling environments may be implemented. For example, other components in addition to, or in place, of the ones illustrated may be used. Also, in some advantageous embodiments, fewer components than those illustrated for refueling environment 300 may be used.

As one example, in some advantageous embodiments, operator refueling station 302 and refueling control system 308 may be integrated as a single component or system. In yet other advantageous embodiments, a number of additional refueling boom units may be deployed in addition to refueling boom unit 304.

With reference now to Figure 4, a diagram of one implementation for a refueling environment is depicted in accordance with an advantageous embodiment. In this example, refueling environment 400 is an example of one implementation for refueling environment 300 in Figure 3.

In this illustrative example, aircraft 402 is shown in an exposed view. Aircraft 402 may have fuselage 404, wing 406, wing 408, tail 410, engine 412, and engine 414. In this example, aircraft 402 may contain operator refueling station 416, auxiliary fuel tank 418, auxiliary fuel tank 420, and refueling boom 422. In the different advantageous embodiments, an operator at operator refueling station 416 may control refueling boom 422 to perform refueling operations.

Refueling control system 424 may generate appropriate commands to refueling boom 422 in response to operator commands generated by an operator at operator refueling station 416. The different operations that refueling control system 424 may command include, for example, without limitation, movement of refueling boom 422.

With reference now to Figure 5, a more detailed illustration of a refueling boom is depicted in accordance with an advantageous embodiment. In this illustrative example, a more detailed view of refueling boom 422 is illustrated.

Refueling boom 422 may include fixed tube 500, telescoping tube 502, nozzle 504, ruddevator 506, ruddevator 508, and strain sleeve 510. Telescoping tube 502 may extend or retract along the direction of arrow 514. Refueling boom 422 also may move in an azimuth direction as indicated by arrow 516. The movement of refueling boom 422 in elevation along the direction of arrow 514 and along the azimuth direction as indicated by arrow 516 may be controlled using ruddevators 506 and 508. In these examples, ruddevators 506 and 508 may be examples of ruddevators 329 for positioning system 322 in Figure 3. Ruddevators 506 and 508 may be configured in a "V" configuration in these depicted examples. Strain sleeve 510 on nozzle 504 may be an example of strain sleeve 321 and may have a sensor such as, for example, force sensor 326 in Figure 3, for measuring forces on refueling boom 422.

With reference now to Figure 6, a control data flow diagram of a refueling boom control environment is depicted in accordance with an advantageous embodiment. Refueling boom control environment 600 may include control stick 602, control computer 604, actuator system 606, and refueling boom unit 608.

In these illustrative examples, refueling boom control environment 600 may represent one example of an implementation of refueling environment 300 in Figure 3. Control stick 602 may be one example of control stick 342 in operator refueling station 302 in Figure 3. Control computer 604 may be one example of an implementation of control computer 338. Control computer 604 may be used to execute processes such as, for example, control laws 605. Control laws 605 may be examples of processes within, for example, control processes 339. Actuator system 606 may be one example of an implementation of actuator system 323. Refueling boom unit 608 may be one example of an implementation of refueling boom unit 304.

In these illustrative examples, refueling boom unit 608 may include refueling boom 610, which may have force generator system 611. Force generator system 611 may include control surfaces 612. Control surfaces 612 may take the form of ruddevators 614, which may be controlled by actuator system 606. Further, refueling boom 610 may include nozzle 613 and strain sleeve 615 located on nozzle 613.

Refueling boom unit 608 may also include sensors 616, attached to and/or mounted onto refueling boom 610. Sensors 616 may include air data system 617, position sensor 618, inertial measurement unit (IMU) 620, and force sensor 621.

Sensors 616 may send acceleration, rate, and position information to control computer 604. Specifically, in this example, position sensor 618 may send position information 622 to control computer 604, and inertial measurement unit 620 may send acceleration information 624 and angular rate information 625 to control computer 604. Position information 622 and acceleration information 624 may be sent to control computer 604 for use by processes within control computer 604.

Force sensor 621 may send force information such as, for example, force information 626, to control computer 604 for use by force filtering process 632. Force information 626 may be information about the forces on refueling boom 610. Force information 626 may include information about vertical force 628 and horizontal force 630. Vertical force 628 may be the force on refueling boom 610 within an elevation or vertical axis with respect to the plane of the aircraft. Horizontal force 630 may be the force on refueling boom 610 within an azimuth or lateral axis with respect to the plane of the aircraft .

Force information 626 may be used by force filtering process 632 to generate filtered force information 634. Force filtering process 632 may remove disturbances and/or noise from force information 626 and may smooth out force information 626 to generate filtered force information 634. Filtered force information 634 may be then sent to force-based command generating process 636. Further, air data system 617 may send dynamic pressure information in the form of dynamic pressure 638 to control computer 604 for use by force-based command generating process 636. Force-based command generating process 636 may modify filtered force information 634 using dynamic pressure 638 in order to generate force- based command 640. Force-based command 640 may be sent to command summing process 644.

In these illustrative examples, control stick 602 may be a flight control stick that may be used by a refueling operator to generate operator commands such as, for example, operator command 642. Operator command 642 may be sent to control computer 604 for use by command summing process 644. Command summing process 644 may sum operator command 642 and force-based command 640 in order to generate command 646. Command 646 may be sent to actuator system 606 to control movement of refueling boom 610 in order to reduce force information 626. In this manner, force filtering process 632, force-based command generating process 636, and command summing process 644 may be used to continuously reduce force information 626 on refueling boom 610.

The illustration of refueling boom control environment 600 in Figure 6 is not meant to imply physical and/or architectural limitations to the manner in which refueling booms may be controlled to reduce the forces on refueling booms. For example, in other advantageous embodiments, force filtering process 632 may be implemented as one process or control law in control computer 604 or as two or more processes or control laws. In some other advantageous embodiments, force filtering process 632 and force-based command generating process 636 may be implemented as one process. In still other advantageous embodiments, force-based command generating process 636 and command summing process 644 may be combined as one process.

With reference now to Figure 7, a diagram of control laws for generating a command to alleviate forces on a refueling boom is depicted in accordance with an advantageous embodiment. Control laws 700, which may be control laws 605 in Figure 6, may be implemented in a control computer such as, for example, control computer 604 in Figure 6. Control laws 700 may include force alleviation system 701 and commands summing unit 706. Force alleviation system 701 may include force filtering unit 702 and force-based command generator 704. Force filtering unit 702 may be one implementation of force filtering process 632, and force-based command generator 704 may be one implementation for force-based command generating process 636 in Figure 6. Further, commands summing unit 706 may be one implementation for command summing process 644.

Force filtering unit 702 may include multiplier 708, second order filter 710, and nonlinear filter 712. Nonlinear filter 712 may include sensor tolerance limiter 714, low pass filter 716, and subtractor 718. Force- based command generator 704 may include dynamic pressure limiter 720, square root 722, divider 724, gain 726, and force-based command limiter 728. Commands summing unit 706 may include adder 730.

In this illustrative example, force information 732 and force system enable 734 may be multiplied by multiplier 708 in force filtering unit 702 to generate enabled force information 736. Force information 732 may be force information provided by a force sensor such as, for example, force sensor 621 in Figure 6. Force information 732 may be information about one of vertical force 628 and horizontal force 630. Force system enable 734 may be a signal with a value that indicates whether the force sensor may have failed and/or whether an operator has turned force alleviation system 701 on or off. If the force sensor has failed and/or force alleviation system 701 has been turned off, force system enable 734 may take the value of "0". Otherwise, force system enable 734 may take the value of "1". In this manner, enabled force information 736 may take the value of force information 732 for use in generating a force-based command, such as, for example, force-based command 640 or may take the value of "0" to indicate that a null force-based command may be generated. Enabled force information 736 may be sent as input to second order filter 710 to generate smoothed out force information 738. Second order filter 710 may remove disturbances and/or noise from enabled force information 736 and may smooth out enabled force information 736. Thus, smoothed out force information 738 may be force information without disturbances and/or noise. Smoothed out force information 738 may be sent as input to sensor tolerance limiter 714 within nonlinear filter 712.

Sensor tolerance limiter 714 may allow for force information within the values of sensor tolerance limiter 714 to be processed. In these illustrative examples, sensor tolerance limiter 714 may allow force information for forces within the values of a force sensor tolerance error to pass. The force sensor tolerance error may be a sensor tolerance of force sensor 621. For example, force sensor 621 may have a sensor tolerance error of around plus or minus 100 pounds of force. Sensor tolerance limiter 714 may generate sensor tolerance limited force information 740 to be sent as input to low pass filter 716.

Low pass filter 716 may further filter sensor tolerance limited force information 740 by rejecting high frequency content and allowing low frequency content to pass. In these examples, low frequency content may include forces within a sensor bias error. In these examples, the sensor bias error may be low frequency forces due to air, wind, and/or some other suitable factor during free flight.

For example, force sensor 621 may measure a force of around plus or minus 40 pounds due to wind hitting nozzle 613 during free flight. This force may be a low frequency force that may be within a sensor bias error. In these illustrative examples, the sensor bias error may be a threshold value, a range of values, or some other suitable value. In this manner, low pass filter 716 may allow force information for refueling boom 610 within a sensor bias error during free flight to pass, while rejecting force information for forces that may be due to contact with the receiving aircraft.

The forces due to sensor bias error during free flight may be low frequency forces. Low pass filter 716 may generate low pass filtered force information 742, which may be then subtracted from smoothed out force information 738 at subtractor 718 to generate filtered force information 744. This implementation may allow for force information for forces due to sensor tolerance error and low frequency forces due to sensor bias error to be ignored. These constant forces and/or sensor bias errors, which may be measured during free flight, may be ignored.

Filtered force information 744 may take a null value if force information 732 may only be attributed to sensor bias error and/or air loads experienced during free flight. A null value for filtered force information 744 may lead to a null force-based command being generated. Thus, in this manner, this implementation may allow for force alleviation system 701 to be on at all times, including free flight, without the need for operator input. Force alleviation system 701 may generate a force-based command when force information 732 has a value significant enough to cause boom bending and/or instability. Filtered force information 744 may be sent as input to divider 724 of force-based command generator 704.

In this illustrative example, dynamic pressure 746 may be dynamic pressure 638 in Figure 6. Dynamic pressure 746 may be sent to dynamic pressure limiter 720 to generate limited dynamic pressure 748. Dynamic pressure limiter 720 may prevent filtered force information 744 from being divided by zero at divider 724. In this manner, dynamic pressure limiter 720 ensures that zero is not the denominator for divider 724 when dynamic pressure 746 is zero such as, for example, when an aircraft is on the ground and not moving.

Limited dynamic pressure 748 may be then sent to square root 722 to generate square root of limited dynamic pressure 750. Square root of limited dynamic pressure 750 may be used for taking into account a changing parameter affecting force information 732 where dynamic pressure 746 may be the changing parameter. In this manner, force alleviation system 701 may use adaptive control of filtered force information 744 to allow for sensitivity to flight conditions, in particular, changing dynamic pressure. Dynamic pressure 746 may depend on aircraft speed, which may change during flight.

Filtered force information 744 may be divided by square root of limited dynamic pressure 750 using divider 724 to generate dynamic pressure scheduled force information 752. Dynamic pressure scheduled force information 752 may be then multiplied by K at gain 726. In this illustrative example, K may be a gain specified to tune the sensitivity of force alleviation system 701 in order to achieve increased stability and performance in the generation of a force-based command. In other words, gain 726 may be a value selected to increase stability in force alleviation system 701 when applied to dynamic pressure scheduled force information 752. Gain 726 may be selected by obtaining a transfer function using simulation or system identification from flight test data. Gain 726 may be then set to a value most consistent with maintaining stability in force alleviation system 701. Gain 726 may generate as an output, force-based command 754, which may be a command to control refueling boom 610.

Force-based command 754 may be sent to force-based command limiter 728 to generate limited force-based command 756. Limited force-based command 756 may be then sent to adder 730 within commands summing unit 706 to be summed with operator command 758. Operator command 758 may be an operator command such as, for example, operator command 642. The summing of limited force-based command 756 and operator command 758 may allow for limited force- based command 756 to be added to operator command 758 to generate command 760 for alleviation of force information 732 to control boom bending. Force-based command limiter 728 may allow for an operator to maintain full control of refueling boom 610 at all times. The operator may override limited force-based command 756 at any time due to force-based command limiter 728.

This implementation of force alleviation system 701 may allow for an operator to alleviate the force described by force information 732 by using a control stick such as, for example, control stick 602, to generate an operator command and work with force alleviation system 701. This implementation may also allow for an operator to remain hands-off and allow force alleviation system 701 to control refueling boom 610. Further, this implementation may allow an operator to turn off force alleviation system 701 and have complete control of alleviating the force described by force information 732 using control stick 602. In this illustrative example, operator command 758 and limited force-based command 756 may not be mutually exclusive. Thus, in this manner, force alleviation system 701 may provide a way for using force information 626 on refueling boom 610 to generate a command for controlling the forces on refueling boom 610 so as to alleviate boom bending and instability. In these illustrative examples, force alleviation system 701 may be implemented for vertical force 628 and for horizontal force 630 in parallel in order to generate command 760.

With reference now to Figure 8, a flowchart of a process for managing force on a refueling boom is depicted in accordance with an advantageous embodiment. The process in Figure 8 may be implemented within a refueling boom control environment such as, for example, refueling boom control environment 600 in Figure 6.

The process may begin by receiving force information 626 from force sensor 621 associated with refueling boom 610 (operation 800) . Force information 626 may be force information about vertical force 628 and/or horizontal force 630. The process may then identify force on refueling boom 610 without a number of errors of force measurement to form filtered force information 634 (operation 802) . In these illustrative examples, operation 802 may be performed by removing noise, sensor tolerance error, and sensor bias error from force information 626. The process may then generate force- based command 640 using filtered force information 634 on refueling boom 610 (operation 804) , with the process terminating thereafter. With reference now to Figure 9, a flowchart of a process for alleviating forces on a refueling boom is depicted in accordance with an advantageous embodiment. The process in Figure 9 may be implemented within control laws such as, for example, control laws 700 in Figure 7.

The process may begin by receiving force information from a force sensor (operation 900) . This force information may be force information 732 about the force on a refueling boom. The process then may determine whether the force sensor has failed and/or the force alleviation system has been turned off (operation 902) . In these examples, this force alleviation system may be force alleviation system 701 in Figure 7. If the sensor has not failed and force alleviation system 701 is turned on, the process may remove disturbances and/or noise from the force information to generate smoothed out force information (operation 904) .

The smoothed out force information may then be limited to include only information about forces within the sensor tolerance error values in order to generate sensor tolerance limited force information (operation 906) . The process may then further limit the sensor tolerance limited force information to include only information about forces due to sensor bias error occurring during free flight in order to generate low pass filtered force information (operation 908) . Operation 908 may be executed using a low pass filter such as, for example, low pass filter 716.

The process may then subtract the low pass filtered information from the smoothed out information to generate filtered force information (operation 909) . The process may then determine whether the force may be due only to sensor tolerance error and/or sensor bias error during free flight (operation 910) . This determination may be made by using the result of operation 909. If the forces may not be due only to sensor tolerance error and/or sensor bias error, the process may generate filtered force information (operation 912) . The filtered force information may be the result of subtracting the low pass filtered information from the smoothed out information. The filtered force information may be then modified to take into account changing dynamic pressure (operation 914) . The filtered force information may be further modified to generate a force-based command (operation 916) . Operation 916 may be executed using a gain such as, for example, gain 726.

The process may then limit the force-based command to allow an operation to override the force-based command, if necessary (operation 918) . The process may combine the force-based command with an operator command to generate a command to move a refueling boom to alleviate the forces on the refueling boom as described by the force information (operation 920), with the process terminating thereafter.

With reference again to operation 910, if the forces may be due only to sensor tolerance error and/or sensor bias error, the process may generate a null force-based command (operation 922) . In this example, subtracting the low pass filtered force information from the smoothed out force information may result in a null force or zero force being used in the processes in force alleviation system 701. The process may then continue to operation 920, with the process terminating thereafter. In the same manner, with reference again to operation 902, if the sensor has failed and/or the force alleviation system has been turned off, the process may proceed to operation 922 to generate a null force-based command. The process may then continue to operation 920, with the process terminating thereafter.

The flowcharts and block diagrams in the different depicted embodiments illustrate the architecture, functionality, and operation of some possible implementations of apparatus, methods and computer program products. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of computer usable or readable program code, which comprises one or more executable instructions for implementing the specified function or functions .

In some alternative implementations, the function or functions noted in the blocks may occur out of the order noted in the figures. For example, in some cases, two blocks shown in succession may be executed substantially concurrently, depending upon the functionality involved.

The different advantageous embodiments can take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment containing both hardware and software elements. Some embodiments are implemented in software, which includes, but is not limited to forms, such as, for example, firmware, resident software, and microcode.

Furthermore, the different embodiments can take the form of a computer program product accessible from a computer usable or computer readable medium providing program code for use by or in connection with a computer or any device or system that executes instructions. For the purposes of this disclosure, a computer usable or computer readable medium can generally be any tangible apparatus that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device.

The computer usable or computer readable medium can be, for example, without limitation, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, or a propagation medium. Non- limiting examples of a computer readable medium include a semiconductor or solid state memory, magnetic tape, a removable computer diskette, a random access memory (RAM) , a read-only memory (ROM) , a rigid magnetic disk, and an optical disk. Optical disks may include compact disk - read only memory (CD-ROM) , compact disk - read/write (CD-R/W) , and DVD.

Further, a computer usable or computer readable medium may contain or store a computer readable or usable program code such that when the computer readable or usable program code is executed on a computer, the execution of this computer readable or usable program code causes the computer to transmit another computer readable or usable program code over a communications link. This communications link may use a medium that is, for example, without limitation, physical or wireless.

A data processing system suitable for storing and/or executing computer readable or computer usable program code will include one or more processors coupled directly or indirectly to memory elements through a communications fabric, such as a system bus. The memory elements may include local memory employed during actual execution of the program code, bulk storage, and cache memories which provide temporary storage of at least some computer readable or computer usable program code to reduce the number of times code may be retrieved from bulk storage during execution of the code. Input/output or I/O devices can be coupled to the system either directly or through intervening I/O controllers. These devices may include, for example, without limitation, keyboards, touch screen displays, and pointing devices. Different communications adapters may also be coupled to the system to enable the data processing system to become coupled to other data processing systems or remote printers or storage devices through intervening private or public networks. Non- limiting examples are modems and network adapters and are just a few of the currently available types of communications adapters.

The description of the different advantageous embodiments has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the embodiments in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. Further, different advantageous embodiments may provide different advantages as compared to other advantageous embodiments.

The embodiment or embodiments selected are chosen and described in order to best explain the principles of the embodiments, the practical application, and to enable others of ordinary skill in the art to understand the disclosure for various embodiments with various modifications as are suited to the particular use contemplated.