Patent Publication Number: US-2019176974-A1

Title: Unmanned aerial vehicle

Description:
TECHNICAL FIELD 
     The present invention relates to a water take-off and landing technique of an unmanned aerial vehicle. 
     BACKGROUND ART 
     Conventional small-size unmanned aerial vehicles represented by industrial unmanned helicopters have had airframes too expensive to be affordable. Also, these vehicles used to require skillful pilotage for stable flight. In recent years, however, there have been considerable improvements in sensors and software used to control posture of unmanned aerial vehicles and to implement autonomous flight of unmanned aerial vehicles. This has led to considerable improvement in manipulability of unmanned aerial vehicles and availability of high-end airframes at lower prices. Under the circumstances, multi-copters, especially small size multi-copters, are currently not only used for hobbyist purposes but also applied to various missions in a wide range of fields, since multi-copters are simpler in rotor structure than helicopters and thus easier to design and maintain. In order to further enlarge the applicable range of multi-copters, there has been a need for a multi-copter with a structure that enables the multi-copter to take off from and land on water. 
     CITATION LIST 
     Patent Literature 
     PTL1: JP 11-334698 A 
     SUMMARY OF INVENTION 
     Technical Problem 
     Realizing a multi-copter capable of taking off from and landing on water naturally involves increasing the waterproof property of the airframe itself of the multi-copter. If, however, the airframe tilts after landing on water and part of a rotor sinks in water, it is difficult for the airframe to take off from water. In light of the above circumstances, in order to make the multi-copter take off from water without human intervention after landing on water, it is necessary to keep the airframe level on the water surface. 
     Also, with an airframe such as the one recited in, for example, patent literature 1, there is such a problem that a buoyant structure mounted on the bottom surface of the airframe becomes attached to the water surface, making it difficult for the airframe to take off from water smoothly. 
     An object of the present invention is to overcome the above-described problem in the background art and to provide an unmanned aerial vehicle that is capable of keeping the airframe level on the water surface and that is capable of taking off from and landing on water smoothly. 
     Solution to Problem 
     In order to solve the above-described problem, an unmanned aerial vehicle according to the present invention includes: a plurality of rotary wings; and a plurality of arms radially extending from an airframe center portion of the unmanned aerial vehicle. The arms include floating portions extending downward from the respective arms. The floating portions include air chambers in the respective floating portions, the air chambers each including a hollow and hermetic space. 
     Also, each floating portion of the floating portions may preferably have a tapering shape having an outer diameter that gradually decreases toward a lower end of the each floating portion. 
     Also, the each floating portion may have an vertically long shape, and the each floating portion may have the tapering shape at a lower side in a vertical direction of the each floating portion. 
     Also, the floating portions may preferably be located at leadings end of the respective arms, which include the respective floating portions, and the rotary wings may be located above the respective floating portions. 
     Also, each air chamber of the air chambers of the floating portions may include an air valve, and the air valve may preferably be configured to keep pressure in the each air chamber within a predetermined range by: releasing air out of the each air chamber when the pressure in the each air chamber has increased and exceeded a predetermined threshold; and taking the air into the each air chamber when the pressure in the each air chamber has decreased and fallen below a predetermined threshold. 
     Also, each floating portion of the floating portions further may include a leg storage chamber that includes a space vertically extending along a center in a radial direction of the each floating portion. The leg storage chamber may be partitioned from the air chamber and extends downward through the each floating portion. The leg storage chamber may contain an elastic member and a bar-shaped member energized downward by the elastic member. The bar-shaped member may have a lower end portion exposed downward through the leg storage chamber. 
     Also, the plurality of arms may include three or more arms circumferentially arranged at equal intervals around the airframe center portion. 
     Advantageous Effects of Invention 
     The unmanned aerial vehicle according to the present invention is capable of keeping the airframe level on the water surface and capable of taking off from and landing on water smoothly. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of an exterior of a multi-copter according to this embodiment. 
         FIG. 2  is an enlarged view of a float. 
         FIG. 3  is a cross-sectional view taken along B-B illustrated in  FIG. 2 . 
         FIG. 4  is a block diagram illustrating a functional configuration of the multi-copter. 
         FIG. 5  is a side sectional view of a modification of the float. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     An embodiment of the present invention will be described by referring to the accompanying drawings. The following embodiment is an example of a multi-copter, which is a kind of an unmanned aerial vehicle having a plurality of rotary wings. It is to be noted that in the following description and the present invention, the terms “up” and “down” refer to vertical directions as seen in  FIG. 1 . 
     [Outline of Configuration] 
       FIG. 1  is a perspective view of an exterior of a multi-copter  100  according to this embodiment. As illustrated in  FIG. 1 , the multi-copter  100  includes six arms  21  to  26 , which extend horizontally from an airframe center portion  10  of the multi-copter  100  (these arms will be hereinafter collectively referred to as “arms  20 ”). The arms  20  are circumferentially arranged at equal intervals around the airframe center portion  10  and extend radially from the airframe center portion  10 . 
     At the leading ends of the arms  20 , floats  41  to  46  are located. The floats  41  to  46  are floating portions extending downward from the respective arms  20  (these floats will be hereinafter collectively referred to as “floats  40 ”). Above the floats  40 , rotors  31  to  36  are located. The rotors  31  to  36  are rotary wings (these rotors will be hereinafter collectively referred to as “rotors  30 ”). 
     [Float Structure] 
     Each float  40  of the floats  40  has an air chamber  51  (described later) in the each float  40 . The air chamber  51  is a hollow and hermetic space. By having the air chamber  51 , the each float  40  serves as a floating member that makes the multi-copter  100  float on water surfaces. The floats  40  are mounted on the arms  20 , which support the respective rotors  30 . This prevents the rotors  30  on the arms  20  from sinking in water when the multi-copter  100  has landed on water. 
       FIG. 2  is an enlarged view of the each float  40 , and  FIG. 3  is a cross-sectional view taken along B-B illustrated in  FIG. 2 . As illustrated in  FIGS. 1 through 3 , the float  40  has an vertically long shape. The float  40  has an approximately hollow-cylindrical shape that extends upward from a center portion of the float  40  in its vertical direction, and has a tapering shape that extends downward from the center portion and that gradually decreases in outer diameter toward the lower end of the float  40 . The tapering shape of the float  40  is less resistant to the water surface when the float  40  lands on water perpendicularly to the water surface. The tapering shape also makes it difficult for the water surface to attach to the float  40  when the float  40  takes off from water. 
     The airframe center portion  10  according to this embodiment is approximately disk-shaped. The floats  40  protrude further downward than the bottom surface of the airframe center portion  10 . With this configuration, the floats  40  double as skids (legs) of the multi-copter  100 . With the floats  40  doubling as skids, the multi-copter  100  has a simplified airframe structure. 
     When the multi-copter  100  lands on water, it is preferable that the bottom surface of the airframe center portion  10  be out of contact with the water surface. This is for the purpose of preventing the water surface from attaching to the airframe center portion  10 , thereby minimizing the resistance against the multi-copter  100  when taking off from water. The floats  40  protrude further downward than the bottom surface of the airframe center portion  10 . This enables the floats  40  to keep the airframe center portion  10  out of contact with the water surface by adjusting the buoyancy of the floats  40 , the number of floats  40  to be installed, the lengths of the floats  40 , and other parameters in a desired manner. The floats  40  according to this embodiment have such a configuration that prevents the airframe center portion  10  from landing on water. This configuration enables the multi-copter  100  to take off from and land on water smoothly. 
     As described earlier, the arms  20  according to this embodiment are circumferentially arranged at equal intervals around the airframe center portion  10 , and the floats  40  are located at the leading ends of the respective arms  20 . That is, the floats  40  according to this embodiment are located at positions farthest away from the airframe center portion  10 , and, further, located at positions to which the weight of the airframe center portion  10  can be uniformly dispersed. This enables the multi-copter  100  to stably keep the airframe level on water surfaces. 
     Also, the floats  40  extend downward from the rotors  30 . Typically, the rotors  30  are located at positions at which the rotors  30  are able to more easily keep the airframe in balance in the air. The floats  40  are located at positions identical to the positions of the respective rotors  30 . This enables the multi-copter  100  to keep the airframe sufficiently level not only in the air but also on water surfaces. 
     As illustrated in  FIG. 3 , the air chamber  51 , which is a hollow and hermetic space, is located inside the float  40 . Further, an air valve  52  is mounted on the air chamber  51  of the float  40 . The air valve  52  according to this embodiment is made up of: a gasket  54 , which is fitted with an attachment hole  53  of the air chamber  51 ; and a pin  56 , which is mounted in a through hole  55  of the gasket by being inserted through the through hole  55 . It is to be noted that the gasket  54  and the pin  56  are made of a rubber material, a plastic material, or another material. At normal time, the air valve  52  is sealed, with the pin  56  in the gasket  54 . This prevents water from entering the air chamber  51  through the air valve  52  when the multi-copter  100  lands on water. 
     The air valve  52  is a mechanism that avoids damage to the float  40  when the air in the air chamber  51  expands or contracts. More specifically, the air valve  52  keeps the pressure in the air chamber  51  within a predetermined range by: releasing the air out of the air chamber  51  when the pressure in the air chamber  51  has increased and exceeded a predetermined threshold; and taking air into the air chamber  51  when the pressure in the air chamber  51  has decreased and fallen below a predetermined threshold. It is to be noted that the thresholds vary depending on the material of the gasket  54 , the size and shape of the pin  56 , and/or other characteristics. By changing these characteristics suitably, the thresholds are adjusted to optimum values for this embodiment. 
     [Modification of Float] 
       FIG. 5  is a side sectional view of a structure of a float  40 ′, which is a modification of the float  40 . The float  40 ′ has such a configuration that the skid function of the float  40  is expanded. It is to be noted that in the following description, configurations serving same or similar functions in the float  40 ′ and the float  40  will be denoted the same reference numerals, and these configurations will not be elaborated upon here. 
     The float  40 ′ includes a leg storage chamber  61 , which is a space vertically extending along the center in the radial direction of the float  40 ′. The leg storage chamber  61  is partitioned from the air chamber  51  and vertically extends through the float  40 ′. The leg storage chamber  61  contains: a coil spring  62 , which is an elastic member; and a leg  63 , which is a bar-shaped member energized downward by the coil spring  62 . The leg  63  has a lower end portion and a portion near the lower end portion. These portions are exposed downward through the leg storage chamber  61 . The leg  63  is supported by the elasticity force of the coil spring  62 . This enables the exposed portions of the leg  63  to be exposed or hidden within the range indicated by arrow S illustrated. 
     If the multi-copter  100  lands on the ground with the floats  40  directly contacting the ground, the floats  40  may be damaged when the weight of the airframe is a particular weight, when the descending speed of the airframe is a particular descending speed, and/or when the hardness of the ground is a particular hardness. In this modification, the multi-copter  100  lands on the leg  63 , which is cushioned by the coil spring  62 . This alleviates the landing impact on the float  40 ′, eliminating or minimizing the damage to the float  40 ′. 
     [The Rest of Airframe Configuration] 
     The configuration of the multi-copter  100  is similar to the configuration of a known multi-copter, except the configuration of the each float  40 .  FIG. 4  is a block diagram illustrating a functional configuration of the multi-copter  100 . The airframe of the multi-copter  100  mainly includes: a flight controller FC; six rotors  30 ; ESCs  141  (Electric Speed Controllers), which control rotation of the respective rotors  30 ; and a battery  190 , which supplies power to the foregoing elements. 
     Each rotor  30  of the rotors  30  includes: a motor  142 ; and a blade  143 , which is connected to the output shaft of the motor  142 . Each ESC  141  of the ESCs  141  is connected to the motor  142  of the rotor R and causes the motor  142  to rotate at a speed specified by the flight controller FC. 
     It is to be noted that there is no particular limitation to the number of rotors of the multi-copter  100 ; the number of rotors may be determined considering required flight stability, cost tolerated, and other considerations. As necessary, the multi-copter may be changed to: a tricopter, which has three rotors R; an octocopter, which has eight rotors R; and even a multi-copter having more than eight rotors. 
     The flight controller FC includes a controller  120 , which is a micro-controller. The controller  120  includes: a CPU  121 , which is a central processing unit; a memory  122 , which is a storage device such as ROM and RAM; and a PWM (Pulse Width Modulation) controller  123 , which controls the number of rotations of the motor  142  and the rotational speed of the motor  142  through the each ESC  141 . 
     The flight controller FC further includes a flight control sensor group  132  and a GPS receiver  133  (these will be hereinafter occasionally referred to as “sensors”). The flight control sensor group  132  and the GPS receiver  133  are connected to the controller  120 . The flight control sensor group  132  of the multi-copter  100  according to this embodiment includes a three-axis acceleration sensor, a three-axis angular velocity sensor, a pneumatic sensor (altitude sensor), and a geomagnetic sensor (direction sensor). 
     The controller  120  is capable of obtaining, from these sensors, how much the airframe is inclined or rotating, latitude and longitude of the airframe on flight, altitude, and position information of the airframe including nose azimuth. 
     The memory  122  of the controller  120  stores a flight control program FCP, in which an algorithm for controlling the posture of the multi-copter  100  during flight and controlling basic flight operations is described. In response to an instruction from an operator (transmitter  110 ), the flight control program FCP adjusts the number of rotations of each rotor R based on information obtained from the sensors so as to correct the posture and/or position of the airframe while the multi-copter  100  is making a flight. 
     The multi-copter  100  may be manipulated manually by the operator using the transmitter  110 . Another possible example is to: register a flight plan FP in an autonomous flight program APP in advance, the flight plan FP being a parameter such as the flight path, speed, or altitude of the multi-copter  100 ; and cause the multi-copter  100  to fly autonomously to the destination (this kind of autonomous flight will be hereinafter referred to as “autopilot”). 
     Thus, the multi-copter  100  according to this embodiment has high-level flight control functions. However, the unmanned aerial vehicle according to the present invention may be any other airframe that includes a plurality of rotors R and that controls the posture of the airframe and the flight operation of the airframe by adjusting the number of rotations of the rotor R. Other examples include: an airframe in which one or some of the sensors is omitted; and an airframe that is without an autopilot function and that is capable of flying by manual manipulation only. 
     While the embodiment of the present invention has been described hereinbefore, the present invention will not be limited to the above-described embodiment; various modifications are possible without departing from the scope of the present invention. For example, while the floats  40  according to the above embodiment are located at the leading ends of the respective arms  20 , the floating portions according to the present invention may be located at portions other than the leading ends of the arms. Also, the rotors  30  may not necessarily be located above the respective floats  40 . Further, the floating portions according to the present invention may not necessarily have tapering shapes in all applications insofar as the floating portions extend downward from the respective arms.