Abstract:
The present disclosure relates to an unmanned aerial vehicle (UAV) able to harvest energy from updrafts and a method of enhancing operation of an unmanned aerial vehicle. The unmanned aerial vehicle with a gliding capability comprises a generator arranged to be driven by a rotor, and a battery, wherein the unmanned aerial vehicle can operate in an energy harvesting mode in which the motion of the unmanned aerial vehicle drives the rotor to rotate, the rotor drives the generator, and the generator charges the battery. In the energy harvesting mode regenerative braking of the generator reduces the forward speed of the unmanned aerial vehicle to generate electricity and prevent the unmanned aerial vehicle from flying above a predetermined altitude.

Description:
PRIORITY STATEMENT 
       [0001]    This application claims priority to EP Patent Application Number 12382052, filed Feb. 17, 2012, the entire disclosure of which is incorporated by reference herein. 
       BACKGROUND INFORMATION 
       [0002]    1. Field: 
         [0003]    The present disclosure relates to an unmanned aerial vehicle (UAV) able to harvest energy from updrafts and a method of operating an unmanned aerial vehicle. 
         [0004]    2. Background: 
         [0005]    Pilots of gliders are aware of the potential to increase range and/or glide time (endurance) by utilising updrafts of air caused by the heating of the Earth&#39;s surface. These naturally occurring upward flows of air, often referred to as thermals, form in columns and can be utilised to lift or reduce the fall of a glider passing therethrough. Gliders can even circle within an updraft to gain a desired altitude up to a theoretical maximum altitude. 
         [0006]    UAVs can take advantage of updrafts in the same way as gliders. However, in many countries UAVs are prohibited from flying in controlled airspace and may therefore be subject to an artificial ceiling that is lower than the true theoretical maximum altitude. As such, it is not always possible for a UAV to achieve the theoretically available height gains from updrafts. 
         [0007]    There is therefore a need to provide a UAV that can derive benefit from an updraft when prohibited from climbing above a threshold altitude. 
       SUMMARY 
       [0008]    According to a first aspect of the present disclosure, there is provided a method of enhancing operation an unmanned aerial vehicle with a gliding capability within a geographic region. The unmanned aerial vehicle comprises a generator arranged to be driven by a rotor. 
         [0009]    The method comprises the steps of: defining a maximum altitude threshold for a geographic region, above which the UAV is not permitted to be flown; identifying the location of at least one updraft within the geographical area; manoeuvring the unmanned aerial vehicle within the identified updraft; and harvesting energy from the motion of the unmanned aerial vehicle within the updraft by regenerative braking of the rotor to thereby maintain an altitude at or below the maximum altitude threshold. 
         [0010]    According to a second aspect of the present disclosure, there is provided an unmanned aerial vehicle with a gliding capability comprising a generator arranged to be driven by a rotor, and a battery. 
         [0011]    The unmanned aerial vehicle can operate in an energy harvesting mode in which the motion of the unmanned aerial vehicle drives the rotor to rotate, the rotor drives the generator, and the generator charges the battery. 
         [0012]    In the energy harvesting mode regenerative braking of the generator reduces the forward speed of the unmanned aerial vehicle to generate electricity and prevent the unmanned aerial vehicle from flying above a predetermined altitude. 
         [0013]    Optionally, the unmanned aerial vehicle is arranged to store the harvested energy in a battery. 
         [0014]    The features, functions, and advantages that have been discussed can be achieved independently in various embodiments or may be combined in yet other embodiments further details of which can be seen with reference to the following description and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    For a better understanding of the disclosure and to show how the same may be put into effect, reference is now made, by way of example only, to the accompanying drawings in which: 
           [0016]      FIG. 1  shows a representation of a gliding UAV using updrafts; 
           [0017]      FIG. 2  shows a representation of an upper altitude threshold; 
           [0018]      FIG. 3  depicts a schematic representation of a first embodiment of a system for controlling a UAV; 
           [0019]      FIG. 4  depicts a schematic representation of a second embodiment of a system for controlling a UAV; and 
           [0020]      FIG. 5  depicts a schematic representation of a UAV. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific embodiments in which the disclosure may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the disclosure, and it is to be understood that other embodiments may be utilized and that various changes may be made without departing from the spirit and scope of the present disclosure. The following detailed description is, therefore, not to be taken in a limiting sense. 
         [0022]    As can be seen in  FIG. 1 , a UAV  10  may glide in a circular path within an updraft to ascend to a highest theoretical altitude achievable within that updraft. The UAV  10  may then descend as it glides to a neighbouring updraft, in which it may commence a further circling motion to ascend again to the highest theoretical altitude available for the new updraft. 
         [0023]    When gliding in an updraft, the UAV  10  is subject to a force balance in the vertical direction. Specifically, the weight of the UAV  10  is balanced by the sum of the force applied by the updraft, with the lift provided by the forward motion of the aerodynamic surfaces  185  of the UAV  10  through air at a particular speed. 
         [0024]    Any movable aerodynamic surfaces and the speed of the UAV  10  define the controllable parameters of the force balance. For a given angle of attack, at high speeds the aerodynamic surfaces  185  of the UAV  10  will result in a greater lift force and the UAV  10  will ascend. At low speeds the aerodynamic surfaces  185  of the UAV  10  will result in a lower lift force and the UAV  10  will descend. The altitude of a UAV  10  moving within an updraft can thus be controlled by modulating its forward speed and/or the angle of attack of its aerodynamic surfaces  185 . 
         [0025]      FIG. 2  shows controlled airspace superimposed on the updrafts of  FIG. 1 . Controlled airspace is defined above a threshold altitude. UAVs are not permitted in the controlled airspace and therefore the threshold altitude defines an artificial limitation on the altitude of UAVs. 
         [0026]    In an illustrative embodiment of the disclosure, a UAV  10  is capable of gliding and harvesting energy from the forward motion of the UAV  10 . 
         [0027]    The UAV  10  is configured and arranged to automatically seek out updrafts and maintain a track (i.e. a path defined in two lateral dimensions in a horizontal plane), such as a circular track (e.g. an approximate helical path in three dimensions), within the updraft to gain height up to, but not above, a predetermined threshold altitude corresponding to the lower boundary of controlled airspace. When within the updraft, the UAV  10  prevents its altitude from increasing above the threshold altitude by harvesting energy from its forward motion using techniques described below. 
         [0028]    As shown in  FIG. 5 , the UAV  10  preferably has a rotor  190 . The rotor  190  may act as a turbine, i.e. the rotor  190  may be driven to rotate by the relative flow of air past the UAV  10 . A motor/generator  140  is coupled to the rotor  190  to be driven thereby to generate electricity. The electricity can be used to charge a battery  200 . 
         [0029]    In illustrative embodiments, the UAV  10  is arranged to control the speed at which the rotor  190  is driven to rotate by the flow of air to control the rate at which energy is harvested from the UAV&#39;s forward motion, thereby controlling the drag on the UAV  10  and hence its forward speed and lift. By this mechanism the upward motion of the UAV  10  within the updraft can be controlled such that the threshold altitude is not exceeded. 
         [0030]    In further illustrative embodiments, the UAV  10  can control the speed at which the rotor  190  rotates when flying in a looped or generally circular track (a circular or helical path in three dimensions) by controlling the UAV  10  bank angle and thereby controlling the radius of the track followed by the UAV  10  and hence its forward speed and lift. In other words, the amount of energy drawn from the forward motion of the UAV  10  can be modulated by varying the bank angle of the UAV  10  to thereby control the rate of change in altitude. 
         [0031]    It is possible for the UAV  10  to have a separate propulsion means. In that case, motor/generator  140  may be a simple generator  140 , i.e. not configured to drive the rotor  190 . However, it is preferable that the motor/generator  140  also acts as a motor arranged to drive the rotor  190  to rotate. Thus, the rotor  190  may act as a propeller, i.e. the rotor  190  and the generator/motor  140  may be both an energy harvesting means, and a propulsion means for providing thrust. In such a UAV  10 , it is therefore possible for a single motor/generator  140  to both provide thrust and to harvest energy. Preferably, the motor/generator  140  will be a brushless motor. 
         [0032]    Preferably, the UAV  10  will comprise control surfaces  185  such as flaps or slats on the wings, and elevators or rudders on the empennage. 
         [0033]    A flight management system  210  controls the UAV  10 .  FIG. 3  shows a schematic representation of the components of the flight management system  210  and how they can control the motor/generator  140  and the battery  200 . 
         [0034]    The flight management system  210  comprises: a navigation and guidance module  100 ; a speed controller  120 ; aircraft sensors  160 ; and an updraft identification module  180 . 
         [0035]    The motor/generator  140  is coupled to and arranged to drive or be driven by the rotor  190 . In a powered mode, the motor/generator  140  acts as a motor to drive the rotor  190  to rotate. In a generator mode, energy is harvested from the forward motion of the UAV  10  by the motor/generator  140  acting as a generator such that rotation of the rotor  190  drives the generator to generate electricity. 
         [0036]    In the generator mode, the motor/generator  140  provides power to the battery  200  to charge the battery  200 . In the powered mode, the motor/generator  140  receives power from the battery  200  thereby depleting the charge stored by the battery  200 . 
         [0037]    The navigation and guidance module  100  controls how the UAV  10  manoeuvres to fly the UAV  10  from one location to another. For example, the navigation and guidance module  100  may control the control surfaces  185  of the UAV  10  (for example flaps or slats). The navigation and guidance module  100  monitors the lateral location (latitude and longitude) of the UAV  10  (for example, using a GPS receiver), and monitors the altitude of the UAV  10  using the signals from the aircraft sensors  160 . The navigation and guidance module  100  can determine the current altitude threshold to prevent the UAV  10  from entering controlled airspace. The navigation and guidance module  100  may include a memory on which the altitude threshold is stored for a given location, or may communicate with an external device, such as an air traffic control station to receive transmitted data indicating the location of controlled airspace. 
         [0038]    The navigation and guidance module  100  can provide signals to the speed controller  120  to determine the speed of rotation of the rotor  190 . The signals are transmitted via a communication means, such as bus  50 . The speed controller  120  controls the speed of revolution of the motor/generator  140 . This is explained in further detail below. 
         [0039]    Furthermore, speed controller  120  can output a signal indicative of the speed of the motor/generator  140  thereby indicating how much energy is harvested by or used by the motor/generator  140 . 
         [0040]    The aircraft sensors  160  may comprise an airspeed sensor  160   a  for determining the relative speed between the UAV  10  and the body of air through which it is travelling. 
         [0041]    Aircraft sensors  160  may also include altitude sensor  160   b , which provides a signal indicative of the altitude of the UAV  10 . For example, altitude sensor  160   b  may comprise a GPS receiver, a barometric altimeter, etc. The signal is sent via the bus  50  to the navigation and guidance module  100 . 
         [0042]    Aircraft sensors  160  preferably include a pitot sensor comprising both static and dynamic pressure sensors. 
         [0043]    The aircraft sensors  160  can therefore be arranged to measure total energy, i.e. the sum of potential and kinetic energy. 
         [0044]    The updraft identification module  180  uses data from the aircraft sensors  160  to identify the location and size of updrafts. The process by which this identification is carried out is described below. The updraft identification module  180  provides a signal to the navigation and guidance module  100  via bus  50  to indicate the location and size of updrafts having sufficient upward velocity to lift the UAV  10  when gliding. 
         [0045]    The navigation and guidance module  100  can use this signal to control the UAV  10  to manoeuvre within an updraft in order to gain height and/or harvest energy. 
         [0046]      FIG. 4  shows an alternative flight management system  210 , which is the same as that of  FIG. 3 , except that the updraft identification module  180  may be replaced by or include a communication device  184 . Communication device  184  communicates with an external system, such as a ground station  182  or another UAV  10  or aircraft. Ground station  182  may comprise sensors for identifying the location and size of updrafts, and a transmitter for transmitting data indicating the location and size of updrafts to the communication device  184  of the UAV  10 . Another UAV  10  may sense an updraft when flying therethrough (as described below), and transmit the location and size of the updraft to communications device  184 . 
         [0047]    In other words, the updraft identification module  180  of  FIG. 3  and the communication device  184  of  FIG. 4  are both means for providing signals representative of the size and location of updrafts, and can be used to identify the location of one or more updrafts having upward velocity greater than a threshold value. 
         [0048]    In illustrative embodiments, the updraft identification module  180  identifies the size and location of updrafts as follows: 
         [0049]    During flight of the UAV  10 , data indicative of height and airspeed for each location is periodically captured by the aircraft sensors  160 . The data captured by the aircraft sensors  160  is used to determine the total energy (i.e. the sum of potential energy and kinetic energy) of the UAV  10 . 
         [0050]    The updraft identification module  180  can use the signal from the speed controller  120  indicating the speed of the motor/generator  140  to determine the effect of the motor/generator  140  on total energy. This effect can therefore be filtered out by the updraft identification module  180 . 
         [0051]    A queue of readings of location of the UAV  10  along with the rate of change of the measured total energy (corrected to remove the effect of the motor/generator  140 ) is stored. 
         [0052]    “Guidance and Control of an Autonomous Soaring UAV” by Michael J. Allen of NASA Drysden Flight Research Centre, February 2007 (NASA/TM-2007-214611), the full contents of which is incorporated herein by reference, discloses mathematical methods for determining the shape of updrafts/thermals from such readings. 
         [0053]    The stored readings can be processed by these known methods to determine the location of the centre of the updraft and a distance indicating the size of the region of the updraft that is sufficient to provide lift to the UAV  10 . 
         [0054]    This can be done by defining a function representing updraft velocity as a function of distance from the updraft&#39;s centre, converting this into equivalent total energy readings, and then fitting the curve to the stored data to determine the centre location of the updraft (in the horizontal plane, e.g. in terms of longitude and latitude). 
         [0055]    Using the technique described above, it is possible for the UAV  10  to take periodic measurements of total energy and determine from a sequence of those measurements the size and location of an updraft. 
         [0056]    The speed controller  120  can be used to determine the speed of the motor/generator  140  when powered by the battery  200 . When the motor/generator  140  is used as a generator to charge the battery  200 , the speed controller  120  can be used to control the amount by which the motor/generator resists the rotation of the rotor  190 . In this way the speed controller can use the generator to carry out regenerative braking of the rotor  190 . The speed controller  120  reduces the speed of rotation of the rotor  190  by drawing more power using the generator, thereby increasing the rate at which the battery  200  is charged. This increases the drag of the UAV  10 , thus slowing the UAV  10  and reducing lift. 
         [0057]    Conversely, the speed controller  120  can allow the rotor  190  to rotate faster, reducing drag and increasing lift. This results in lower power provided by the generator to the battery  200 . 
         [0058]    Preferably, the motor/generator  140  is a brushless motor. 
         [0059]    The flight management system described above can be used to control the UAV  10  to operate in a number of modes. 
         [0060]    The UAV  10  can operate in one or more powered modes. In the powered modes, the energy stored in the battery  200  can be utilised for propulsion of the UAV  10 . In the case of the UAV  10  described above, this would mean that the battery  200  can be called upon to provide power to the motor/generator  140  to drive the rotor  190  to rotate. 
         [0061]    In the powered modes, the UAV  10  is controlled by the navigation and guidance module  100  of the flight management system to glide along a track. Optionally in such a mode, the navigation and guidance module  100  can control the UAV  10  to navigate towards an updraft. For example, an updraft identified by the communications device  184  of  FIG. 4 . 
         [0062]    The UAV  10  can operate in one or more gliding modes in which it is not propelled. In the case of the UAV  10  described above, this would mean that the battery  200  does not provide power to the motor/generator  140  to drive the rotor  190  to rotate. Instead, the motor/generator  140  is driven to rotate by the rotor  190  to harvest energy as it passes through a body of air. The speed controller  120  can be used to control whether the rotor  190  rotates freely (hindered only by friction) or is restricted from rotating by the action of the motor/generator  140  as it generates electricity. The speed controller  120  can also be used to control the extent to which the speed controller  120  restricts the rotor  190  from rotating thereby controlling the rate at which the motor/generator  140  generates electricity. 
         [0063]    In the gliding modes, the navigation and guidance module  100  can actuate the control surfaces  185  of the UAV  10  to manoeuvre the UAV  10 . 
         [0064]    One of the gliding modes may be a first gliding mode in which the UAV  10  is controlled by the navigation and guidance module  100  of the flight management system to glide along a track. 
         [0065]    Optionally in such a mode, the navigation and guidance module  100  can control the UAV  10  to navigate towards an updraft identified by the communications device  184  of  FIG. 4 . 
         [0066]    In a second gliding mode the UAV  10  is instructed to keep its lateral position within the area of an updraft to take advantage of the increase in altitude achieved. This may be achieved by manoeuvring the UAV  10  in a looped track (for example, by maintaining a circular track). In this second gliding mode, the UAV  10  altitude is allowed to increase by the upward flow of air within the updraft. When the altitude reaches the threshold altitude, the navigation and guidance module  100  can instruct the speed controller  120  to reduce the rotational speed of the rotor  190  by drawing more power from the motor/generator  140 . This in turn will increase the drag of the gliding UAV, reducing its forward speed and thus lift, to thereby prevent an increase in altitude. Preferably, the amount of power drawn from the motor/generator  140  is modulated to maintain an altitude at or slightly below the maximum permitted altitude. The motor/generator  140  can therefore harvest energy from the updraft once the UAV  10  reaches the threshold altitude. 
         [0067]    It may not always be desirable to increase the altitude of the UAV  10 . In a third gliding mode, the UAV  10  is also instructed to keep its lateral position within the area of the updraft. However, the speed of rotation of the rotor  190  may be modulated to maintain a constant altitude of the UAV  10  within the updraft by controlling the drag of the gliding UAV to thereby control its forward speed and lift. The motor/generator  140  can therefore harvest energy from the updraft without the UAV  10  altitude increasing. 
         [0068]    Finally, a fourth gliding mode may optionally be provided (in addition to or instead of the second mode) in which the motor/generator  140  draws energy from the forward motion of the UAV  10  at a rate that varies in dependence upon the bank angle of the UAV  10  whilst flying in a looped track. Specifically, the bank angle can be modulated to control the radius of the loop followed by the UAV  10 . A loop with a larger bank angle will result in a loop with a smaller radius in which the forward speed of the UAV  10  is greater and thus more power is harvested by the rotor  190 . Conversely, a loop with a smaller bank angle will result in a loop with a larger radius in which the forward speed of the UAV  10  is lower and thus less power is harvested by the rotor  190 . In this fourth gliding mode, the UAV  10  altitude is allowed to increase by the upward flow of air within the updraft until the maximum permitted altitude is reached, and then the altitude of the UAV  10  is maintained by flying the UAV  10  in a looped track (preferably, a generally circular track) and modulating the bank angle of the UAV  10 . 
         [0069]    A fifth gliding mode may be provided in which the UAV  10  altitude is not allowed to increase by the upward flow of air within the updraft, but is simply maintained at a desired height by flying the UAV  10  in a looped track (preferably, a generally circular track) and modulating the bank angle of the UAV  10 . 
         [0070]    In the second to fifth gliding modes, it is possible that the updraft location may drift (perhaps because of prevailing winds). Therefore, since the UAV  10  maintains its position in the updraft, it will drift with the updraft whilst flying in the looped track. In other words, the looped track followed by the UAV  10  will move with the updraft. 
         [0071]    Preferably, in the second to fifth gliding modes, the UAV  10  will fly in an approximate circular track about the identified centre of the updraft, within the updraft at a distance of 65% the width of the updraft. 
         [0072]    Although this disclosure has been described in terms of certain preferred embodiments, other embodiments that are apparent to those of ordinary skill in the art, including embodiments that do not provide all of the features and advantages set forth herein, are also within the scope of this disclosure. Accordingly, the scope of the present disclosure is defined only by reference to the appended claims and equivalents thereof.