Abstract:
A system for the hookup of either a manned or unmanned vehicle with a second vehicle which may be refueling. These vehicles may be both airborne, one airborne and the other on the ground or both on the ground. A probe extending from a first vehicle which may be refueled is joined to a paradrogue or “flycatcher” at the end of a boom on a second vehicle which may be a refueling vehicle. In bringing the probe into the paradrogue an optical sensor on one of the vehicles is employed in conjunction with optical beacons on the other vehicle with the sensor measuring the relative motion between the probe and the paradrogue and generating a control signal for controlling motion of the probe relative to the paradrogue. The positioning of the probe relative to the paradrogue is accurately controlled during the fueling operation by a reeled cable mechanism utilizing a reel which is driven to wind one end of the cable there around to retain the cable in a tensioned state. The other end of the cable is attached to the refueling vehicle . . . The cable, probe and the refueling vehicle are in a triangular configuration while allowing only small interaction forces restrains relative motion between the probe and the paradrogue.

Description:
This application is based on Provisional Application No. 60/423,178 filed Nov. 1, 2002. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to the hookup between multipurpose vehicles which may be either manned or unmanned and more particularly to such a hookup which may be but not necessarily for the purpose of refueling one of said air vehicles from the other. 
   2. Description of the Related Art 
   The capability of continuous operation of autonomous air vehicles (“UAVs”) is limited by their onboard fuel capacity. The desired capability for continuous operation 24 hours a day every day of the week of such air vehicles, which are limited by their fixed onboard fuel capacity raises a need to routinely air-refuel these vehicles. This in turn gives rise to the need for integrating a high precision navigation technology with an appropriately designed aerial refueling system which is compatible with the navigation system . . . A typical airborne refueling system is described in U.S. Pat. No. 5,326,052 issued Jul. 5, 1994 to Krispin et al. Such systems often employ hose and drogue connections between the fueling aircraft and the aircraft being fueled. To connect the hose to the drogue requires a control system such as described in U.S. Pat. No. 6,266,142 issued Jul. 24, 2001 to Junkins, et al., U.S. Pat. No. 5,326,052 issued Jul. 5, 1994 to Krispin et al., and U.S. Pat. No. 5,530,650 issued Jun. 25, 1996 to Biferno, et al. 
   The joining of two vehicles together far various purposes such as the joining of a manned aircraft with an unmanned aircraft for refueling requires a precision navigation system which is integrated with the refueling system. Prior art systems have shortcomings in that they fail to provide the combination of a precision navigation system with a precision refueling system with the accuracy and reliability to be desired. These shortcomings lie particularly in the design of the probe on the aircraft being refueled and the drogue on the refueling aircraft where the coupling between these elements and the reliable and firm retention of these two units to each other is essential for proper operation. In addition, when the probe is being brought into contact with the drogue, it is important that there be good control of the movement of the probe so that it does not improperly strike against either aircraft. 
   SUMMARY OF THE INVENTION 
   The present invention employs a system for joining two vehicles together have a boom which includes a paradrogue or docking captive device on one of the vehicles and having a modified drogue or probe with beacons mounted thereon which is joined with a newly designed probe on the other vehicle, the probe having a sensor which communicates with the beacons. 
   In a preferred embodiment, an optical sensor system known as VisNav operating in conjunction with the optical beacons measures the relative motion between a refueling probe and the drogue attached to the boom on a refueling aircraft. These measurements include relative position, velocity, acceleration, attitude, etc and the measurement of the relative motion of the universal aerial refuel receptacle slipway installation (UARRS) relative to the refueling probe of the vehicle being refueled. Such a system is shown in  FIGS. 1 and 2  and is described in U.S. Pat. No. 6,266,142 issued Jul. 24, 2001 to Junkins et al., particularly in connection with  FIG. 18  of this patent. In the present invention, this prior art system is combined with a highly accurate control system for controlling the positioning of the boom (and drogue) relative to the probe and the probe&#39;s entry therein. In addition, the positioning of the probe within the drogue is accurately controlled during the refueling operation so as to restrain relative motion between the probe and drogue with small interaction forces. This operation is enhanced by the use of a reeled cable mechanism which runs between a reel on the aircraft and a compliant joint on the boom to form a triangular configuration with the boom and aircraft body. The reel mechanism is tensioned to take up any slack in the support of the boom. The compliant joint, together with the triangular arrangement formed with the cable, has small interaction forces yet restrains relative motion between the boom and the drogue during refueling operations. 
   It is therefore an object of this invention to provide an improved aircraft refueling system particularly suited for refueling unmanned airborne vehicles; 
   It is a further object of this invention to improve the control of the motion between two vehicles that are being connected to each other; 
   It is still a further object of this invention to provide improved control of the motion between the probe of a refueling airborne vehicle and an airborne vehicle being refueled; 
   Other objects of the invention will become apparent in view of the following description taken in connection with the accompanying drawings. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic drawing illustration of a prior art aerial hookup for a aircraft refueling system; 
       FIG. 2  is a front perspective view of a prior art probe and drogue aerial refueling system; 
       FIG. 3  is a schematic drawing of a first embodiment of the invention suitable for use refueling small air vehicles; 
       FIG. 4  is a side elevational view of a retractable probe utilized in the first embodiment; 
       FIG. 5  is a side elevational view of a collapsible paradrogue used in the first embodiment; 
       FIG. 6  is a side elevational view, partially in cross section of the probe tip of the first embodiment retracted before engagement with the paradrogue; 
       FIG. 7  is a side elevational view, partially in cross section of the probe tip of the first embodiment in its extended position when engaged with the drogue; 
       FIG. 8  is a side perspective view of a second embodiment of the invention; 
       FIG. 8A  is a top plan view of the second embodiment; 
       FIG. 8B  is a top perspective view of the refueling receptacle and VisNav sensor of the embodiment of  FIG. 8 . 
       FIG. 9  is a side elevational view of a third embodiment of the invention; 
       FIG. 9A  is a top plan view of the refueling aircraft of the third embodiment; 
       FIG. 9B  is a top perspective view of the refuel receptacle of the third embodiment; 
       FIG. 10  is a side elevational view of a fourth embodiment of the invention having a mechanism for deploying the boom from the refueling aircraft; 
       FIG. 11  is a side elevational view drawing of the fourth embodiment showing the boom partially deployed from the refueling aircraft; 
       FIG. 11A  is a schematic drawing illustrating the cable/reel assembly of the fourth embodiment; 
       FIG. 12  is a schematic drawing of the fourth embodiment showing the boom fully deployed from the refueling aircraft; 
       FIG. 13   a  is a side elevational view of the fourth embodiment of the invention, with the probe extended; 
       FIG. 13   b  is a side elevational view of the fourth embodiment of the invention, with the probe retracted; 
       FIG. 14  is a side elevational view showing the fourth embodiment with its refueling probe connected to the drogue of the refueling aircraft; and 
       FIG. 15  is a side elevational view of a “docking captive” system with a VisNav sensor on an aircraft and VisNav beacons mounted on a ground vehicle. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIGS. 1 and 2 , a precision navigation system of the prior art employing a Paradrogue on the end of the boom of a refueling aircraft and a probe on the aircraft being refueled are illustrated. This prior art navigation system is known as VisNav and is illustrated in  FIG. 1  and described in U.S. Pat. No. 6,266,142 issued to Junkins, et al on Jul. 24, 2001. This precision navigation system functions to determine the relative position between the probe  13  of the vehicle being refueled and the paradrogue  18  of the refueling vehicle. The VisNav optical sensor  26  is mounted on the end of the probe  13  of the vehicle being refueled. As shown in  FIG. 1 , the optical sensor has a position sensor  12  positioned in the focal plane of the photo detector of the sensor which measures the centroid location of the structured light focused on the detector by fisheye lens  15  from one of several (at least 4) beacons  14  on the paradrogue. Beacons  14  are modulated with a known waveform (e.g. a sine wave at a frequency of 40,000 cps) such that a matched filter in the VisNav sensor will reject ambient energy which is not at the frequency of the beacons. 
   A radio communications system  17  communicates with omni-directional light source  17   a  and adjusts its light output which is received by the beacons to control the beacon outputs. In this manner, the energy received from each beacon is optimized to provide a maximum signal to noise ratio for each line of sight measurement. This feature combined with the fisheye optics provided by lens  15  assures that the range between the vehicle being refueled and the refueling vehicle can vary widely while still maintaining the received optical energy focused on the position sensor  12  with an optimum signal to noise ratio. A navigation algorithm is utilized in the line of sight measurements to determine the x, y, and z linear displacements of the center of the paradrogue  18  (a target point in the micro-coupling system) relative to a coordinate system fixed in the fuel receiving vehicle. Further, output from the navigation algorithm are the roll (phi), pitch (theta), and yaw (psi) angles which give the angular displacement between the axis of the vehicle being refueled from its target position fixed in the Para drogue. 
   Referring now to  FIGS. 3–7 , the micro-probe and micro-adapter coupling of a first embodiment of the invention for use in airborne and ground vehicles are illustrated. The micro-probe  13  is shown retracted in  FIGS. 3 and 6  and in an extended position in  FIG. 7 . Paradrogue or “docking captive device”  18  into which the micro-probe  13  is installed and which connects to the fueling hose  24  is illustrated in  FIG. 5 . The position and orientation errors (x, y, z, phi, theta, and psi) and their rates are determined by the VisNav measurements detected by VisNav sensors  26  on probe  13  and the navigation algorithm. These signals are used by the control system on the vehicle being refueled to drive the position and orientation errors towards zero at a rate consistent with safe operations. When these errors are near zero, the probe  13  drives spring  28  to the extended position as shown in  FIG. 7  from it&#39;s at rest position as shown in  FIG. 6 , which in turn drives the coupling mechanism which triggers locks onto the collar  16  of the probe and initiates fuel flow. The fuel flow causes the clamp force to greatly increase to ensure a tight coupling of the probe to the fuel coupling mechanism. 
   More specifically, referring to  FIG. 5 , as the micro-probe  13  enters the adapter  30  of Paradrogue or “docking captive device”  18 , the probe tip  13   a  encounters a soft spring loaded device  31  and initiates depression of the spring. At a critical level of depression, fuel flow initiates the locking of the adapter onto the probe, to ensure tight coupling. The fuel tank of the vehicle being refueled fills and is equipped with a fuel gauge. Upon approaching completion of the fueling operation, the fuel gauge triggers telemetry to provide a signal to a receiver in the fueling vehicle that causes shut down of the fuel pump. Upon shutdown, the reduced pressure permits the clamp on adapter  30  to release and allows the probe to be withdrawn from the paradrogue with near zero force on the probe. As a consequence, the control system of the vehicle being refueled can decelerate this vehicle and rapidly withdraw the probe from the coupling mechanism and paradrogue of the refueling vehicle. During withdrawal, the VisNav system measures the relative motion so that the controller can employ the measured position relative to the paradrogue to avoid collision of the probe with the paradrogue. Paradrogue deployment before refueling and retrieval after completion of refueling follows well established patterns and can be commanded by controllers in either the refueling vehicle or the vehicle being refueled. 
   It is to be noted that a system other than VisNav could be used to measure the position of the paradrogue relative to the vehicle being refueled. Instead of centroiding optical energy from a light emitting diode, microwave energy from suitable emitters and an appropriate microwave detector system for detecting this energy can be employed. Such a microwave system can use the same basic operation system as VisNav except for the details of the energy beacons and the detector which centroids this energy. Another alternative would be to employ digital camera technology. The beacon energy can be adjusted to optimize the centroiding accuracy of each beacon image on the detector. Pattern recognition can be employed to identify the measured images. Due to limitations of frame rate, (typically less than 200 Hz), such an embodiment will not be able to make use of high frequency modulation (e.g. 40 KHz) of the beacon energy as in the embodiments previously described. 
   Referring now to  FIGS. 8 ,  8 A, and  8 B, a second embodiment of the invention is illustrated. The VisNav sensor  26  is positioned in the air vehicle being refueled  21  adjacent to the universal aerial refuel receptacle slipway installation (UARRSI),  33 , as shown in  FIG. 8 . The VisNav “SmartLites”  14  are mounted on the refueling vehicle on the underside of both horizontal tails, the underside of the fuselage and tail cone and the refueling boom  13 . In operation, the VisNav sensor  26  mounted on the vehicle being refueled  21  detects the SmartLite transmissions and a navigation solution is calculated such that the vehicle being refueled is controlled to connect with the boom  13  and receive the transfer of fuel as in the previous embodiments. However, the beacon energy can be adjusted to optimize the centroidal accuracy of each beacon image on the detector. Pattern recognition is required to identify the measured images. 
   Referring now to  FIGS. 9 ,  9 A, AND  9   b , a further embodiment of the invention is illustrated. This embodiment is similar to the embodiment of  FIG. 8  except that the SmartLite Beacons  14  are mounted on the vehicle being refueled  21  and the VisNav sensors  26  are mounted on the refueling vehicle  20  and the tip of the refueling boom. Operation is basically the same as for the previous embodiment. 
   Referring no to  FIGS. 10–14 , a further embodiment of the invention which employs a unique triangular shaped hinged boom/receptacle deployed from the refueling aircraft is illustrated. This is a unique low speed lightweight boom and Paradrogue (“docking captive device”) system capable of operating from zero air speed with hovering vehicles up to and in excess of 200 knots. The fly catcher Paradrogue  18  of this embodiment is similar to that of the previous embodiments except that it is rigid. Further, unlike conventional systems, the boom remains stationary while the aircraft on which the probe is mounted flies the probe into the boom. 
   The boom  11  is shown in its stowed position in  FIG. 10 . The inner end of the boom is connected to the body of the refueling aircraft by means of a universal coupling joint  34  and its outer end retained to the aircraft body in receptacle  35 . In  FIG. 11 , the boom is shown partially extended from receptacle  35  on cable  36  which extends from a tensioned reel  37  mounted within the receptacle as shown in  FIG. 11A . The boom is shown fully extended in  FIG. 12 . 
   The coupling joint  34  permits compliance of the cable/reel mechanism so that lateral movement caused by forces between the air vehicle boom tip and the receptacle is absorbed by the slider joint and the tensioned reel mechanism to take up slack in the cable with low force. The compliant hinge coupled with the triangular boom take up mechanism allows small interaction forces and yet restrains relative motion during refueling. 
     FIG. 14  shows the refueling aircraft  20  connected to the aircraft being refueled  21  while  FIGS. 13   a  and  13   b  show the refueling probe  13  of the vehicle to be refueled in its extended and retracted positions respectively. The receptacle  39  on the refueling aircraft  20  for receiving the probe  11  of the aircraft being refueled  21  has a compliant universal hinge with a resistive movement that is 50 percent or less of the yield movement of the boom. This compliant joint together with the triangular boom take up mechanisms allows small interaction forces and yet restrains relative motion during the fueling operation. It is to be noted that the Smartlife beacons  14  on the refueling aircraft and boom  11  enable the VisNav sensor  26  on the aircraft being refueled to solve the approach navigation problem and maintain control of rotating relative position during refueling. 
   Referring to  FIG. 11 , initial deployment of the boom  11  from the refueling aircraft is shown. The boom is held in this position by cable  36  attached thereto at one end and wound on spring actuated reel  37  mounted within receptacle  35 . The boom is formed in telescoping sections which are spring loaded towards the retracted position. When activated by the control system, the boom is extended as shown in  FIG. 12 . The boom is firmly held in this position by cable  36  so that it cannot swing back and forth. As shown in  FIG. 14 , the boom  11  of the refueling aircraft is hooked up to the probe  13  of the aircraft being refueled. While the boom is hooked to the probe, load sensors are employed which generate signals to adjust the winch controlled cable reel  37  to minimize the load on the probe. 
   The universal joint of the cable/reel mechanism  37  on the refueling aircraft permits compliance of the system so that lateral movement caused by forces between the tip of the boom of the boom of the aircraft being refueled and the receptacle is absorbed by the triangular deployment slider joint and the tensioned reel mechanism which takes up slack in the cable. This results in low forces on the components of the system. Also, the compliant hinge  39  on the receptacle of the boom has a relatively low resistive moment which coupled with the triangular configuration results in small interactive forces and yet effectively restrains relative motion during refueling. 
   The triangle boom is a unique lightweight boom and drogue system capable of operating from zero airspeed, and therefore also useful for hovering air vehicles, up to and in excess of 200 knots, making it useful for all weight and size classes of unmanned and manned air vehicles. As pointed out above, it consists of a rigid retractable boom attached to the tanker aircraft by a universal fuel coupling joint. 
   The clam mechanism Paradrogue of this embodiment is similar to that of the previous embodiment except that it is rigid and can employ winglets for aerodynamic stabilization of its motions. Unlike conventional booms, in this embodiment the boom remains stationary while the aircraft with the probe flies itself into the boom.  FIG. 10  shows the boom and Smartlife beacons mounted on the empennage of the tanker vehicle. Smartlife beacons are also mounted on the deployed boom. Together, all of these Smartlife beacons on he tanker aircraft permit the VisNav sensor to solve the approach navigation problem and maintain knowledge of rotating positions during the entire refueling operation. 
   The deployment sequence is shown in  FIGS. 11 and 12 . The initial boom deployment, shown in  FIG. 11 , is accomplished by aerodynamic loads or by using an active hydraulic actuator for very low speeds and hover. As the boom is deployed, Smartlife beacons on the shaft of the boom activate.  FIG. 12  shows the boom telescoping to its full extended configuration.  FIGS. 13   a  and  13   b  show a typical receiver air vehicle equipped with the VisNav sensor and a microprobe. The VisNav sensor mounted on the nose of the nose of the receiver air vehicle receives emissions from the Smartlife beacons on the tanker to compute the navigation solution during a refueling operation. The microprobe is shown in the retracted position in  FIG. 13   b  and the extended position in  FIG. 13   a .  FIG. 14  shows the final portion of the refueling procedure with the receiver air vehicle mated to the boom. 
   While hooked up, the boom will track receiver movement within limits using load sensors to adjust the cable (controlled by a winch in the tanker aircraft and a hydraulic actuator to minimize loads on the probe). The universal joint of the cable/reel mechanism on the tanker aircraft permits compliance so that lateral movement, caused by forces between the receiver aircraft boom tip and the receptacle, is absorbed by the triangular deployment boom slider joint and the tensioned reel mechanism, In this manner, slack is taken up in the cable with low forces. Also the receptacle has a compliant hinge  39  ( FIG. 14 ) that has a resistive moment that is 50% or less of the yield movement of the boom. This compliant joint, together with the triangular boom take up mechanism allows small interaction forces but yet restrains the relative movement during refueling operations. 
   Referring to  FIG. 15 , the device of the invention is shown as incorporated in a “docking capture” with a VisNav sensor on an aircraft and VisNav beacons on a “flycatcher” on a ground vehicle. 
   As can be seen, the airborne vehicle  52  has a VisNav sensor  46  and a docking probe  47 . Ground vehicle  50  has stand  51  mounted thereon. VisNav beacons  53  and flycatcher micro adaptive coupler  54  are mounted on top of the stand. Beacons  53  communicate with VisNav sensors  46  to enable control of the airborne vehicle  52  to bring the docking probe  47  into engagement with flycatcher micro adaptive coupling  54 , with the docking probe maintained in such engagement. 
   Thus, the device of the invention provides precise motion measurements in bringing the probe or boom of the aircraft being refueled into the drogue of the refueling aircraft and to maintain proper retention during refueling. This end result is achieved by means of beacons on one of the aircraft which are operated at a pre-selected frequency and which are activated by and operate in conjunction with a VisNav sensor.