Abstract:
Using power line rights of way for UAV routing provides a direct, uninterrupted, aerially clear path to the vast majority of lots and buildings from nearby substations and generating stations. Segmenting or separating the UAV traffic by airframe glide ratio improves safety for people on the ground and utilization of the limited airspace. Further segmenting UAV traffic by airframe speed and size allows greater traffic throughput.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of provisional patent application Ser. No. 62/360,954 filed 2016 Jul. 11 by the present inventor. 
     
    
     BACKGROUND 
     Prior Art 
       [0002]    Electric power transmission and distribution primarily uses overhead lines. The power utility company has an easement on a right of way (ROW) around the overhead line. For high voltage transmission lines the ROW may be two hundred feet wide; whereas for a neighborhood distribution line the ROW may be thirty feet wide; and for distribution along the back or sides of a lot the ROW may be five feet wide. Within the ROW the utility company manages vegetation and construction to maintain clearances to the lines. Incursions into the ROW are regularly checked and corrected to make sure there are no foreign objects near the power lines. In scenic, congested, or wealthy areas power lines may be buried, but undergrounding costs 4-14 times more than overhead lines. Currently 97% or more of power lines are above ground in the United States, and they connect the vast majority of houses. 
         [0003]    Delivering parcels and material by drone or unmanned aerial vehicles (UAV) is desirable since deliveries can be faster, cheaper, and more efficient. One challenge to widespread adoption of UAV delivery is routing to meet safety objectives and to avoid collisions between autonomous drones. In manned flight the available airspace is divided into layers with certain altitudes reserved for certain directions of flight. The layers are separated by about one thousand feet vertically and flights are tracked by air traffic control to ensure sufficient separation. However, the total available altitude under Federal Aviation Administration (FAA) small unmanned aerial system (sUAS) rules for UAVs is four hundred feet. This makes it difficult to keep enough space between drones in a layered system. 
         [0004]    Prior art reference US20160216304A1 discloses using the distinct magnetic signature of power lines for navigation of UAVs using power lines as roads and highways [0026]. It does not discuss airspace segmentation and regulation of UAV traffic. 
         [0005]    Prior art references U.S. Pat. No. 9,087,451, U.S. Pat. No. 9,359,074B2, and U.S. Pat. No. 9,494,937B2 disclose UAV routing over roadways and mention power lines only as obstacles. Roadways are crossed by bridges, trees, stoplights, power lines, and other obstructions to flight. The FAA also explicitly disallows flights over people not involved with the operation, so it would be more risky and currently not legal to fly over roadways with cars and pedestrians. 
         [0006]    High speed highways with multiple lanes in each direction use different lanes for different speeds; segmenting traffic by speed to maximize throughput and minimize traffic conflicts. 
       SUMMARY 
       [0007]    Using power line rights of way for UAV routing provides a direct, uninterrupted, aerially clear path to the vast majority of lots and buildings from nearby substations and generating stations. Segmenting or separating the UAV traffic by airframe glide ratio improves safety for people on the ground and utilization of the limited airspace. Further segmenting UAV traffic by airframe speed and size allows greater traffic throughput. 
       Advantages 
       [0008]    Utilities have had rights of way for overhead lines for more than a century. UAV routing and delivery is relatively new. Routing UAVs along utility rights of way is a novel and non-obvious approach to improving safety, enhancing efficiency, and improving utilization of an existing resource. Various aspects of the embodiments of my UAV routing method are superior because: 
         [0000]    Power line rights of way extend uninterrupted from generating stations to substations to each individual lot.
 
Power line companies currently have the right and obligation to maintain clearances above and around the power lines, so that airspace is free from obstructions to flight.
 
Larger power lines are generally located in remoter, quieter areas, away from people; and residential lines are often located at the back or sides of lots, away from most activity.
 
         [0009]    Additional unanticipated advantages include: 
         [0000]    The power lines provide a ready source of energy for recharging the UAV to extend its range. The UAV could either perch on the lines or dock at charging stations built on transformers mounted on the towers and poles.
 
The additional 400 feet of airspace allowed by the FAA adjacent to and above the power line structures provides a corridor free of manned airframes, eases congestion, and increases the altitude safety margin for the UAV.
 
Flying in linear directions beside and above the lines substantially reduces the number of angles a UAV has to check to sense and avoid other UAVs and obstructions. Instead of checking the full four Pi steradians all the time, it can focus on a cone in the forward direction most of the time, with sideways checks at branches or turn-offs.
 
Platforms built on towers can be used to transfer loads from large, long distance UAVs to smaller, more maneuverable local delivery UAVs.
 
The alternating 50/60 Hz field strength can be used as a hardware geofence failsafe shaped like a UAV Tunnel in case the UAV primary navigation fails or is jammed.
 
The alternating 50/60 Hz field strength and direction can be used for supplementary navigation input.
 
The known configuration and spacing of the conductors can be used with a camera to determine distance and angle from the lines to the UAV as another navigation input.
 
Power line companies already use avian repellents to keep birds away, so routing the UAVs along the lines is less likely to disturb or cause conflicts and collisions with birds.
 
Power meters can provide a landing spot, homing signal, and charging station for the UAV, as well as communicating with occupants that a delivery has arrived. Smart meters already have wireless technology installed.
 
         [0010]    Other advantages of one or more aspects will be apparent from a consideration of the drawings and ensuing description. 
     
    
     
       FIGURES 
         [0011]      1 . Perspective view of UAV routing along overhead lines. 
           [0012]      2 . Section view across right of way showing legal airspace and glide ratio lines 
           [0013]      3 . Section view across right of way showing additional virtual routing channels in different orientations and shapes. 
           [0014]      4 . Section view across right of way showing software and hardware geofence boundaries. 
           [0015]      5 . Section view along the right of way showing collision avoidance angle of view. 
           [0016]      6 . Perspective view of charging and transfer platform. 
           [0017]      7 . Perspective view of landing platform. 
           [0018]      8 . Flowchart for UAV routing between towers. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    This section describes several embodiments of the UAV routing method with reference to  FIGS. 1-8 . 
         [0020]      FIG. 1  is a perspective view of UAVs routed along a power line. Towers  10 ,  12 , and  14  support phase conductors  16 ,  18 , and  20 , as well as shield wires  22  and  24 . The utility owning the power line has an easement or right of way  50  that it must keep clear of encroachments. Virtual tunnel  2  contains a left virtual channel  4  and a right virtual channel  6  divided by a surface  5 . Multirotor UAV  26  supports autopilot  25  containing a processor and memory; wireless communication device  27 ; location sensor  28 ; payload  29 ; and camera  30  in flight along flight path  31 . On the other side of surface  5 , multirotor UAV  32  supports autopilot  8  containing a processor and memory; a wireless communication device  33 ; camera  34 , location sensor  35 ; and payload  36  in flight along flight path  37 . Fixed wing UAV  44  supports autopilot  48  containing a processor and memory; location sensor  45 ; wireless communication device  46 ; and payload  47  in flight along flight path  48 . Large scale fixed wing UAV  38  supports autopilot  42  containing a processor and memory; location sensor  39 ; wireless communication device  40 ; and payload  41  flying at much higher speed along flight path  43 . 
         [0021]      FIG. 1  illustrates flight of UAVs above and beside shield wires  22  and  24 , segmented by direction. In this representation UAVs  26 ,  32 ,  38 , and  44  fly on the right of surface  5  when facing the direction of travel (of course in the United Kingdom and other former Commonwealth countries they may fly on the left!). 
         [0022]      FIG. 2  is a much broader section at tower  10  across phase conductors  16 ,  18 , and  20  and shield wires  22  and  24 . An easement or right of way  50  is clear of trees, houses, poles, and other obstructions due to vegetation management and incursion detection by the utility company. Trees  52  may grow adjacent to right of way  50 , but the utility typically manages nearby trees as well so none can fall across phase conductors  16 ,  28 , and  20 . In urban areas taller buildings may obstruct flight adjacent to the right-of-way, so the UAVs will have to fly above them. 
         [0023]    In  FIG. 2  UAVs  32 ,  44 , and  38  are represented as bullseyes or the tips of an arrow to show their flight paths are coming out of the page with a diameter proportional to flight speed. UAVs  26 ,  54 , and  56  are represented with crosses or the feathers in an arrow to show their flight paths are into the page with a speed proportional to the size of the cross. Double dot dash lines  58  and  60  represent a 2:1 glide ratio from the top of tower  10  at the edge of right of way  50 . Dotted line  62  represents the 400 foot top of the legal airspace with current FAA sUAS regulations. The legal limit increases by the height of tower  10  within 400 feet of the tower  10 . Thus virtual tunnel  3  and virtual channels  7  and  8  divided by surface  5  are higher than 400 feet and much wider than right of way  50 . 
         [0024]    The utility company has the right and the obligation to manage incursions into right of way  50  to maintain clearances to phase conductors  16 ,  18 , and  20 . Right of way  50  and the airspace above it will be free of obstructions to flight, other than known towers like  10 . Human activity is typically limited to crossings at right angles, though occasionally there are trails along rights of way. Structures are not allowed in right of way  50 . In the event of a serious problem, such as a power loss with a UAV, it is unlikely to strike a person, vehicle, or structure if it lands in right-of-way  50 . 
         [0025]    Fixed wing UAVs, such as  38  and  44  may have a glide ratio of more than ten units horizontal for one unit vertical. Helicopter UAVs with autorotation may have a glide ratio of between two and four. Multirotor UAVs typically do not glide. To make sure UAVs land in right of way  50  in the event of problems, the airspace might be segmented by airframe glide ratio. Multirotors  26  and  32  are only permitted to fly directly over right of way  50 . Helicopter and fixed wing UAVs such as  44  and  38  can fly further to the sides, but still above their minimum glide ratio represented by lines  58  and  60 . This approach segments the available airspace laterally, first left/right by direction of flight and then by lateral distance based on UAV glide ratio. 
         [0026]    It may be desirable to also separate UAVs by their cruise speeds or size.  FIG. 2  shows the bigger, faster UAVs  38 ,  56 ,  54 , and  44  flying higher than the smaller multicopters  26  and  32 . 
         [0027]    The FAA sUAS rule generally limits flight altitude to 400 feet in class G airspace. Near a structure, such as tower  10 , UAV flight is allowed 400 feet from the structure. Hence the legal altitude limit  62  rises by the height of tower  10 , 400 feet to the left and right of tower  10 . This gives UAVs more airspace and a higher safety margin when flying along power lines. 
         [0028]    It is dangerous to fly low and slow. Helicopter manufacturers for manned flight publish charts of altitude versus airspeed and recommend either flying high or flying fast. The bottom corner of the chart at low altitude and slow flight is known as “dead man&#39;s corner”. In routing UAVs along power lines, the extra airspace allowed by the FAA not only eases congestion, but it also provides a bit more altitude for airframe recovery in the event of problems. A drop from 400 feet would take about five seconds to hit the ground. From 500 feet it would take 12% longer which may be enough extra time to manage a recovery. 
         [0029]    Near road, rail, and river crossings power line towers are often built higher to provide more clearance and/or longer spans. This is another unexpected benefit for UAV routing along power lines. Exactly where a larger safety margin will be required for safe flight, the towers are taller, and the legal airspace provides more altitude for flight. 
         [0030]      FIG. 3  is a section at tower  10  across phase conductors  16 ,  18 ,  20  and shield wires  22  and  24 . In utility right of way  50  and the airspace above it there are no obstructions to flight. The FAA legal altitude  62  rises by the height of tower  10  within 400 feet of tower  10 . Lines  58  and  60  represent glide ratios of 2:1 so that many airframes can manage to still land in right of way  50  in the event of problems. On the left, slow UAV  32 , medium speed UAV  44 , and fast UAV  38  are further separated into smaller virtual channels represented by vertical ellipses  64 ,  66 , and  68  respectively. On the right, slow UAV  26 , medium speed UAV  54 , and fast UAV  56  are separated into horizontal rectangular virtual channels  72 ,  74 , and  76  respectively. 
         [0031]    UAVs can select or be assigned different virtual channels based on airframe capabilities with minimum glide ratios and minimum and maximum speeds in each channel. The channels may be arranged vertically, horizontally, or on a diagonal. Likewise the virtual channels may have different shapes such as the ellipses and rectangles illustrated here. 
         [0032]      FIG. 4  is a section at tower  10  across phase conductors  16 ,  18 ,  20  and shield wires  22  and  24 . Utility right of way  50  and tower  10  height at shield wires  22  and  24  defines the base of clear airspace. Dash double dotted lines define a software geofence on the left  80  and right  82  aligned with virtual channels  7  and  8  in virtual tunnel  3 . Dash, long dash lines  84  and  86  represent approximate lines of equal 50/60 Hz electric field strength. An electric field strength meter could implement a hardware geofence to contain UAVs  26  and  32 . 
         [0033]    A geofence is a virtual boundary beyond which a UAV should not be able to fly. Most current autopilots implement geofences as vertical cylinders of a given height and radius around the takeoff location. If the autopilot is given incorrect waypoints, if it malfunctions, or if the wind is too strong, then UAV  26  may breach the geofence. Then the failsafe code should return he UAV to the launch point or immediately land UAV  26 . 
         [0034]    A software geofence shape more appropriate for routing along power lines is an elongated prism parallel to the ground for the left  80  and right  82  parts of the clear airspace. 
         [0035]    An unexpected benefit of flying near power lines is that the geofence can also be implemented in hardware. Antennas or sheets of a metal foil placed on three orthogonal sides of a cube mounted on UAV  26  will measure electric field strength, no matter the orientation of UAV  26 . A minimum field strength is set before the flight or early in the flight. Then the field strength measured during flight is compared to the preset minimum. If the current field strength ever falls below the preset minimum, UAV  26  can be forced to drop, land, deploy a parachute, or otherwise be stopped. This prevents flyaways, problems from GPS spoofing, loss of radio control, or bad guidance from someone impersonating the remote control as described in “UAV Constraint in Overhead Line Inspection”, U.S. Ser. No. 14/733,962 van Cruyningen and Van Wart, incorporated in full by reference. 
         [0036]    The electric field sensor can also be used as a location sensor for navigation. If the three orthogonal foil sheets are attached to separate analog to digital converters, then the strength and direction of the electric field in each direction can be detected in real time. The field along straight phase conductors is always zero due to symmetry. The field decreases roughly as the inverse radius away from the phase conductors. Thus if UAV  26  is flying with zero measured electric field in the fore-aft direction then it is flying parallel to the lines. The strength in the other two directions gives an indication how far UAV  26  is from phase conductors  16 ,  18 , and  20  if the voltage of the power line and geometry are known. 
         [0037]    Power lines tend to have a consistent configuration from tower to tower along the lines (except at transposition towers). This may be three across as shown in  FIG. 1 ; or three vertical; or three pairs of conductors vertically, etc. The clearances between phase conductors  16 ,  18 , and  20  are also kept constant because they are typically set to the minimum that meets leakage and noise goals. With a known conductor configuration and separation, a single camera can be used as a location sensor to detect the angle and distance to the lines in real time as described in “Aerial Photogrammetry of Overhead Lines” U.S. 61/940,371, incorporated in full by reference. 
         [0038]    The above paragraphs described location sensors based on GPS, the electric field sensor, and vision with triangulation. Other examples of location sensors include stereo cameras, LiDAR sensors, and radio beacon triangulation. Using more than one location sensor provides redundancy for much greater reliability in flight. 
         [0039]      FIG. 5  is a section along phase conductor  20  and shield wire  24  showing towers  10 ,  12 , and  14 . UAV  26  is flying below the FAA legal limit altitude  62 , using obstacle detection sensor  95  to scan in the forward direction in an angle  94  delimited by lines  90  and  92 . Server processors and memory  96  located in the Internet cloud  97  and communicating with wireless communication device  98  with the wireless communication device  26 ,  33 ,  40 , and  46  on the UAVs could also be used to direct UAV traffic. 
         [0040]    Sensing and avoiding other UAVs and obstacles is a challenging problem for completely free  3 D flight. LiDAR, SONAR, RADAR, stereo cameras, and other obstacle detection sensors are limited by how many samples they can measure from a multitude of different angles. To scan the entire four Pi steradians around a UAV takes time and power. By constraining the UAVs to linear flight along power lines and defining some “rules of the route” the problem can be greatly simplified. With two basic rules 
         [0000]    “fly on the right” as shown in  FIG. 1 , and
 
“overtaking UAV has to keep clear”,
 
         [0041]    a UAV primarily has to scan in a forward cone as shown by angle  94  between lines  90  and  92 . In this example the fifty four degree cone subtends about 5% of the four Pi solid angle of the whole hemisphere, thus simplifying the detection problem by about a factor of 20. 
         [0042]    If all the UAVs cooperate and broadcast their positions over wireless communication devices  27 ,  33 ,  40 , and  46  using ADS-B or the equivalent, then obstacle detection sensor  95  is no longer as critical in detecting UAVs. However it is still useful for other obstacles or non-cooperating or broken UAVs. 
         [0043]    An alternative to obstacle detection on each UAV is to use a system similar to air traffic control. Server processors and memory  96  located in the Internet cloud  97  would track each UAV  26 ,  32 ,  38 ,  44  and select flight paths for them based on the other traffic in the vicinity. 
         [0044]      FIG. 6  is a perspective view of a transfer and recharge platform. Distribution pole  96  supports transformer  100  with landing platform  102  supporting recharging contacts  104  for UAV  32 . These platforms provide convenient voltages up in the air to allow UAV  32  to recharge to extend its range. UAV  32  cannot be stolen, people cannot be electrocuted, and the location high on a pole makes it much less likely the charging station will be tampered with or vandalized. A transfer and recharge platform up on a pole could also be used to transfer payloads between long-distance UAVs and local delivery UAVs. 
         [0045]      FIG. 7  is a perspective view of a delivery platform with power meter  106 , wireless communication device  107 , landing platform  108  supporting payload  34  and recharging electrodes  110  for UAV  32 . A power meter is a reasonable place to land and drop off cargo as well as get a recharge. Enhancements would be a locking box to deposit the cargo and notifications to the occupants that the cargo had arrived. Smart meters already contain wireless communication devices. 
         [0046]      FIG. 8  is a flowchart for UAV navigation between towers  10 ,  12 , and  14 . Tower waypoints are stored in memory of autopilot  25  before the flight or received during flight through wireless communication device  27 . When the UAV is at a given tower it looks up the waypoint for the next tower  120 . It selects an altitude based on the tower height and its relative airframe speed  122 . It selects a lateral offset based on its glideslope  124 . If there are additional virtual channels defined like  64 ,  66 ,  68 ,  72 ,  74 , or  76 , then it will select a virtual channel that provides for its speed and glide ratio. Then it selects to fly to the left or right  126  based on direction of travel and embarks on the chosen flight path  128 . 
         [0047]    Alternatively, a UAV traffic control system using server processors and memory  96  located in the Internet cloud  97  and communicating wirelessly  98  with individual UAVs  26 ,  32 ,  38 ,  44 , could select flight paths for them to ensure there are no collisions. 
         [0048]    Autopilot  25  flies the selected flight path  130 , repeatedly checking for a number of conditions: 
         [0000]    if a geofence was breached  132 , then it drops, lands, or glides into the right of way  150 ;
 
if it detects loss of power  134 , then it glides into the right of way  152 ;
 
if the comparing detects a deviation from the planned flight path  136  using output of location sensor  28 , then it corrects the course  154  and keeps flying the selected flight path  130 ;
 
if it detects an obstacle  138 , then it selects a new flight path beside or above the obstacle  156  and flies the newly selected flight path  130 ;
 
if it is near the waypoint of its transfer point or low on power  140 , it selects a flight path to the nearest transfer and charging platform  158 ;
 
if it has to turn at an intersection of power lines  144 , then it descends, slows down, and turns  142  before finding the waypoint for the next tower  120 ;
 
if it is at its destination  146 , then it lands on the delivery platform  160 ;
 
otherwise if it is at the tower  148 , then it starts with the waypoint for the next tower  120 , or else keeps flying the selected flight path.
 
         [0049]    This section illustrated details of specific embodiments, but persons skilled in the art can readily make modifications and changes that are still within the scope. For example the discussion has focused on electric power lines, but all the same concepts apply to electrified railway rights of way.