Abstract:
A guided parafoil system for delivering lightweight payloads provides an accurate, small and low-cost delivery system for small payloads such as chemical sensor packages. The delivery system is adapted to fit along with the payload within a standardized canister. The delivery system includes a parafoil and a guidance control system that includes a global positioning system (GPS) receiver and an electronic compass to detect a deviation and bearing from a desired target. The parafoil is guided by a single motor that turns the parafoil in a horizontal direction perpendicular to the current direction of travel in response to deviations detected from a desired course. The desired course is initially linear until the system reaches a predetermined horizontal radius from the target and then the course becomes a circular path around and above the target.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to payload delivery systems, and more specifically, to a guided parafoil system delivering lightweight payloads. 
     2. Background of the Invention 
     Chemical sensors, electronic sensing devices, as well as other lightweight packages often must be delivered via airdrop to a detection zone. In many cases, such as a possible hazardous area, the only practical way to deliver the sensor package is via aerial delivery. However, unguided airdrop of packages, particularly lightweight packages, is subject to drift error that may land the payload far from the desired drop location. 
     Guidance systems have been employed in delivery systems for large payloads (often weighing over several tons), and the added cost of the guidance system as well as the added weight of the power supplies, guidance computers, and control systems is typically justified by the size and cost of the payload. The guidance and control systems of the aforementioned delivery systems are typically very heavy, using either motorized propulsion or multi-axis guidance systems to provide sophisticated targeting capability. 
     Further, existing packages for uncontrolled drops are small with respect to the above-mentioned payload delivery systems. Canisters for deployment of electronic surveillance and countermeasures are standardized and it would be advantageous to provide a payload delivery system that is small enough to be deployed along with a payload in such a canister. 
     Therefore, it is desirable to provide a payload delivery system that is small, low cost and accurate. It would further be desirable to provide a payload delivery system that may be contained along with a small payload in a standardized canister. 
     SUMMARY OF THE INVENTION 
     The above objectives of providing a low cost, accurate and small payload delivery system for lightweight payloads are provided in a method and system that use a parafoil and a guidance system including a single motor for guidance control. The guidance system activates the motor to direct the parafoil in a horizontal direction perpendicular to a current direction of travel of the parafoil. The parafoil system is guided to a predetermined radius from the target and then is further guided in a downward spiral within a cylinder above the target until the descent is complete. Any deviations outside of the circular/spiral path are corrected by the guidance system in response to a deviation between a current position of the parafoil system and the cylinder. The parafoil is guided by a motor coupled to the guidance system that tensions a set of cables connected to the left or right side of the parafoil and loosens the other set of cables. 
     The foregoing and other objectives, features, and advantages of the invention will be apparent from the following, more particular, description of the preferred embodiment of the invention, as illustrated in the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a pictorial diagram depicting a guided parafoil delivery system in accordance with an embodiment of the present invention. 
     FIG. 2 is a pictorial diagram depicting guided parafoil delivery system  10  prior to deployment as stored in an airdrop container. 
     FIGS. 3A and 3B are pictorial diagrams depicting details of the internal components of guidance system container  16  and payload container  18  of FIG.  1 . 
     FIG. 4 is an electrical block diagram depicting details of guidance control circuit  20  of FIGS. 3A and 3B. 
     FIG. 5 is a pictorial diagram depicting a trajectory of a guided parafoil delivery system in accordance with an embodiment of the present invention. 
     FIGS. 6A and 6B are pictorial diagrams depicting the guidance system and payload container portions of guided parafoil delivery systems in accordance with alternative embodiments of the invention. 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Referring now to the figures and in particular to FIG. 1, a guided parafoil delivery system  10  in accordance with an embodiment of the present invention is shown. System  10  includes a parafoil  12  for reducing a rate of descent (via air drag) of a payload container  18 . The payloads transportable by system  10  are generally on the order of one to 100 pounds, but the weight of the payload should not be construed as a limitation on the present invention, unless as applied to a claim that recites a weight limitation. The present invention is applicable to delivery of chemical sensors and other electronic devices as well as other lightweight payloads. 
     Payload container  18  is mechanically coupled to parafoil  12  via a guidance system container  16  that houses components for controlling the flight path and descent of parafoil  12 . An optional telemetry antenna  17  is shown attached to payload container  18  for exchange of information via radio frequency broadcast with a ground station or airborne transceiver. A first set of control cables  14 A is connected to a set of connection points on parafoil  12  that are disposed on a back edge of the right side of parafoil  12 . Shortening cables  14 A increases the drag of the right side of parafoil  12 , steering parafoil  12  to the right. A second set of cables  14 C is connected to a set of connection points on parafoil  12  that are disposed on a back edge of the left side of parafoil  12 . Shortening cables  14 A increases the drag of the left side of parafoil  12 , steering parafoil  12  to the left. The first and second set of cables  14 A and  14 C are generally connected to more flexible “risers” on the back edges of parafoil  12 , while the remaining cables  14 B are connected to connection points on the main body of parafoil  12 , but other implementations are possible, such as configurations where risers are not employed and cables  14 B may also be absent, providing steering by shifting the center point of guidance system container  16  and payload container  18  with respect to parafoil  12  and supporting a payload entirely via the control cables  14 A and  14 C. 
     Parafoil  12  is steered by shortening a set of control cables  14 A or  14 C and simultaneously lengthening the other set of control cables  14 C or  14 A, causing parafoil  12  to turn in the direction of increased drag on the side of parafoil  12  controlled by the shortened cable set. 
     Referring now to FIG. 2, system  10  is shown stowed in a canister  21  of the size generally available for airdrop of countermeasures electronics and sensing systems. In particular, the size of canister may be 4″×4″ by 12″ in length, which is consistent with countermeasures canisters currently employed for the delivery of chemical sensor packages. Parafoil  12 , is folded and stowed above guidance system container  16  and is attached to payload container  18 . A removable cover  25  on which optional telemetry antenna  17  is mounted, provides access to payloads within payload container  18  prior to insertion within container  21 . Two L-shaped cover plates  23 A- 23 B surround parafoil  12  and guidance system container  16 . The cover plates are ejected after deployment of system  10  from canister  21 . A sensor S 1 , depicted as a switch, but which may be implemented as a Hall effect sensor (mounted on guidance system container  16 ) and magnet (mounted on one of cover plates  23 A- 23 B) or other suitable sensing device, provides detection of ejection of cover plates  23 A- 23 B after deployment. Sensor S 1  provides a signal to the guidance system within guidance system container  16  to activate control of parafoil  12 . An additional time delay can be set to further delay the activation of guidance system components until parafoil  12  has completely deployed and is in stable descent. 
     Referring now to FIGS. 3A and 3B, internal features of the guidance system container  16  and payload container  18  are depicted. A payload  19  is placed within payload container  18  for delivery to a target zone. A battery  29  and compass  29  are also mounted within payload container  18  and electrically connected to a guidance control  20  within guidance system container  16  via cables. In addition or alternative to compass  29 , a global positioning system (GPS) antenna  27  and receiver are employed, with GPS antenna  27  shown mounted conformal to the surface of guidance system container  16 . Compass  29  is an electronic compass such as a magnetic compass that provides horizontal bearing information to guidance control  20 . A GPS receiver within guidance control  20  and coupled to GPS antenna  27  provides periodic position information to guidance control  20  in addition to compass  29 . In some embodiments, in particular for navigation systems providing data at a higher rate than standard GPS, compass  29  may be omitted, and horizontal bearing may be calculated from changes in the GPS reported position. Further, compass  29  may be an alternative device, such as an inertial navigation system, TACAN or VOR receiver, or other device that may provide bearing information to the guidance control  20 . 
     Within guidance system container  16 , a motor  22  is coupled to control cables  14 A and  14 C of parafoil  12  via a winch drum  26 . When motor  22  is rotated, one set of cables ( 14 A or  14 C) is shortened (or tensioned) and the other set is lengthened (or loosened), steering parafoil  12  in a horizontal direction perpendicular to the trajectory of parafoil  12 . Paths and apertures within the walls of guidance system container  16  provide for smooth travel of cables  14 A and  14 C from winch drum  26  to the outside of guidance system container  16 . A position sensor  23  provides an indication of a “zero position” of winch drum (e.g., where the lengths of cables  14 A and  14 C outside of guidance system housing  16  are equal), so that guidance control  20  can be properly initialized to a neutral steering condition. A shaft position sensor incorporated within motor  22  and coupled to guidance control  20  may be incorporated to control the precise length of cables  14 A and  14 C, as well as the rate of rotation of motor  22 , permitting control over the positioning profile of motor  22 . Controlling the rate and acceleration curves of motor  22  provides improved control of parafoil  12 , providing smooth operation at the endpoints of motor positioning events. 
     Referring now to FIG. 4, a schematic of a guidance control  20  and associated electronic components is depicted in accordance with an embodiment of the present invention. Battery  28  supplies power to the circuits of guidance control  20  and other components via a voltage regulator  32 , which provides the regulated voltage required by I/O devices and processors, while unregulated battery power is supplied to motor drivers  38 . A microcontroller  34  provides computation of the parafoil trajectory in conformity with information received from an electronic compass  29  and a GPS receiver  33  (via GPS antenna  27 ). GPS receiver  33  provides positional information and electronic compass  29  provides horizontal bearing information. GPS receiver  33  generally does not provide data at a sufficient rate to determine horizontal bearing, therefore electronic compass  29  (or alternatively an inertial navigation system, etc.) is needed so that proper course correction may be calculated. 
     Further, microcontroller  34  observes the rate of change of horizontal bearing from electronic compass  29  during flight to determine whether or not the system is in an undesirable flight condition. If an undesirable flight condition is detected, motor M 1  is restored to the zero position determined by sensor  23  and the system guidance algorithm restarts after flight stability is recovered. Examples of undesirable flight conditions that can be detected using the rate of horizontal bearing changes are payload oscillation, where a heavy payload swings and causes the parafoil to change direction rapidly, and spiral divergence, where the payload swings out while the parafoil turns downward, causing the lift vector of the parafoil to become substantially horizontal. Either condition disrupts the regular flight path and thus the guided operation of the system and therefore it is desirable to detect the above-mentioned and other unstable flight conditions so that remedial action can be taken and guided operation restored. 
     Switch S 1  optionally detects deployment of the parafoil via detection of parafoil cover ejection, separation of a suspended payload housing from the guidance system container or other suitable mechanism. At deployment, microcontroller (via program instructions stored in a memory  34 B and executed by a processor core  34 A) sets the motor (and winch pulley  26 ) to the zero start position via feedback from winch position sensor  23 . Microcontroller  34  then computes the deviation of the flight path from a desired path to the ground target. Initially, the flight path is substantially a straight line toward the target, with a terminal cylindrical path above the target once the system has reached a predetermined distance from the target. 
     When microcontroller  34  determines that a course correction is needed, a motor control processor  36  is instructed to turn motor  22 , in a direction corresponding to the sign of the deviation and with a torque (motor current) proportional to the magnitude of the deviation. Motor drivers  38  supply the current from battery  28  to the motor via an H-bridge switching network, and receive feedback from the shaft sensor within motor  22 . The motor current setting can be provided by pulse width control generated by motor control processor  36 , which may follow pre-programmed profiles for acceleration/deceleration. Control is proportional to the calculated deviation and adjustment of the length of cables  14 A and  14 C controlled by motor  22  can be set very precisely due to the shaft sensor feedback to motor control processor  36 . 
     Referring now to FIG. 5, a trajectory  65  of a guided parafoil delivery system in accordance with an embodiment of the present invention is depicted. Initially, the system is guided from a start point  64  (the location of the system after deployment and initial start-up delay) in a linear path toward a target  60 . With glide ratios ranging from 2:1 to 4:1, linear flights of 2 miles for a drop height of 5000 feet can be reliably achieved. Glide ratios are dependent on the parafoil design and load as well as local air conditions and wind. 
     After the system has come within a predetermined horizontal radius above the target, guidance proceeds based on a control cylinder  62  extending axially above and symmetrically disposed circumferentially around the horizontal position of the target. 
     Control cylinder  62  is disposed around an axis  61  rising vertically above target  60 . The radius of cylinder  62  is generally 100 feet, but may be any value suitable for the aerodynamics and size of a particular system. If trajectory  65  of the system exceeds the boundary of cylinder  62  a correction is applied, turning parafoil  12  inward, thus causing parafoil  12  to veer back toward the circumference of cylinder  62 . 
     When the system is within cylinder  62 , a variety of options may be chosen for guidance, including neutral or no control. Alternatively, the set of cables  14 A or  14 C on the side facing axis  61  may be pulled to an extreme position, increasing the descent of parafoil (if cylinder  62  is exceeded at any time, the control function described above will be resumed). Alternatively, if trajectory  65  of the system falls too far inside the boundary of cylinder  62  a correction  64  may be applied, turning parafoil  12  outward from axis  61 . The outward turning control causes parafoil  12  to veer back toward the circumference of cylinder  62 , maintaining a constant control function, but generally limiting the approach to target  60  to the radius of cylinder  62 . 
     Referring now to FIG. 6A, a view of internal features of guidance system container  16  and payload container  18  are depicted in accordance with an alternative embodiment of the present invention. In the alternative embodiment, guidance system container  16  is connected to payload container  18  by a set of cables  54  that extend after deployment of the system. A GPS receiver  27 A is mounted on the top surface of payload container  18  and is connected to guidance control  20  (not shown) via a cable  55 . The above-illustrated configuration provides for operation of GPS receiver  27 A without pattern distortion and blockage due to guidance system container and its internal components shadowing GPS receiver  27 A. (Cables  54  will generally be longer than depicted, providing sufficient distance between guidance system container  16  and payload container  18 ). Alternatively, GPS receiver may also be mounted with payload container  18  and coupled to guidance control  20  via a serial or other interface. Switch S 1  is mounted on guidance system container  18  for detection of separation of guidance system container  16  from payload container  18  at deployment. 
     Referring now to FIG. 6B, a view of internal features of guidance system container  16  and payload container  18  are depicted in accordance with another alternative embodiment of the present invention. In the other alternative embodiment, guidance system container  16  is connected to payload container  18  directly. A GPS receiver  27  is mounted on the top surface of guidance system container  16  and is connected to guidance control  20 . In the depicted embodiment, battery  28 , compass  29  and motor  22  are all contained within guidance system container. 
     While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.