Abstract:
An unmanned aerial vehicle (UAV) and a landing method thereof are provided. The landing method includes the following steps. Firstly, a depth image of a scene is obtained. Next, a landing position is determined in accordance with the depth image. Next, a height information of the landing position is obtained. Next, a plurality of relative distances of the landing gears relative to the landing position are adjusted in accordance with the height information to make the relative distances substantially the same. Then, the UAV lands on the landing position.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This application claims the benefit of People&#39;s Republic of China application Serial No. 201610152609.X, filed Mar. 17, 2016, the disclosure of which is incorporated by reference herein in its entirety. 
       FIELD OF THE INVENTION 
       [0002]    The invention relates to an unmanned aerial vehicle and a landing method thereof, and more particularly to an unmanned aerial vehicle capable of landing steadily even on a relatively steep terrain and a landing method thereof. 
       DESCRIPTION OF THE RELATED ART 
       [0003]    The unmanned aerial vehicle (UAV) refers to an aerial vehicle without any pilot therein. The UAV can fly via control or fly automatically, and land on different environments to perform a number of tasks. However, if the place where the UAV is going to land belongs to a relatively steep terrain, such as a stairway, a bumpy ground, a steep cliff and so on that have a larger level drop, it is possible to cause the UAV to topple over or even drop and be broken when the UAV lands due to the level drop of the terrain. 
       SUMMARY OF THE INVENTION 
       [0004]    The invention is directed to a UAV and a landing method thereof. The UAV will first search for a suitable landing position before landing, so as to prevent itself from toppling over resulted from the larger level drop while being landing. 
         [0005]    According to one aspect of the present invention, a landing method of a UAV is provided. The method includes the following steps. Firstly, a depth image of a scene is obtained. Next, a landing position is determined in accordance with the depth image. Next, a height information of the landing position is obtained. Next, a plurality of relative distances of the landing gears relative to the landing position are adjusted in accordance with the height information to make the relative distances substantially the same. Then, the UAV lands on the landing position. 
         [0006]    According to another aspect of the present invention, a UAV is provided. The UAV includes a fuselage, a plurality of landing gears disposed on the fuselage, a 3D image recognition system disposed on the bottom of the fuselage for obtaining a depth image of a scene, a processing unit coupled to the 3D image recognition system for determining a landing position in accordance with the depth image, and a plurality of distance sensing units respectively disposed on the landing gears for obtaining a height information of the landing position. The processing unit adjusts a plurality of relative distances of the landing gears relative to the landing position in accordance with the height information to make the relative distances substantially the same, and lands the UAV on the landing position. 
         [0007]    The above and other aspects of the invention will become better understood with regard to the following detailed description of the preferred but non-limiting embodiment(s). The following description is made with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a perspective view of a UAV according to an embodiment of the present invention. 
           [0009]      FIG. 2  is a block diagram of the UAV according to an embodiment of the present invention. 
           [0010]      FIG. 3  is a flow chart of a landing method of the UAV according to an embodiment of the present invention. 
           [0011]      FIG. 4  is a part of flow chart of the landing method of the UAV according to another embodiment of the present invention. 
           [0012]      FIG. 5  is a schematic diagram of a 2D image according to another embodiment of the present invention. 
           [0013]      FIGS. 6A-6C  are schematic diagrams showing the landing of the UAV according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    Various embodiments are provided and described in detail as follow. The embodiments are merely described for being an example, but do not limit the scope of the present invention. In addition, in order to clearly show the technical features of the present invention, parts of elements are omitted in the drawings of the embodiments. 
         [0015]    Refer to  FIG. 1 .  FIG. 1  is a perspective view of a UAV  100  according to an embodiment of the present invention. 
         [0016]    The UAV  100  includes a fuselage  110 , a plurality of landing gears  121 ,  122 ,  123  and  124 , a plurality of whirl wing structures  130 , a 3D image recognition system  140  and a plurality of distance sensing units  150 . The 3D image recognition system  140  may be disposed on the bottom of the fuselage  110  for obtaining a depth image of a scene, and may be capable of capturing a 2D image of the scene. The landing gears  121 ,  122 ,  123  and  124  and the whirl wing structures  130  are assembled together and disposed on the fuselage  110 . Each of the landing gears  121 ,  122 ,  123  and  124  may respectively correspond to one of the whirl wing structures  130 . The distance sensing units  150 , such as the infrared sensors, are used to obtain a height information of the landing position and respectively disposed on the landing gears  121 ,  122 ,  123  and  124 . The landing gears  121 ,  122 ,  123  and  124  with a telescopic function may be specifically designed as screw rods, sleeves and so on, which are controlled to lengthen or shorten by an element such as a stepping motor. The numbers of the landing gears, the whirl wing structures and the distance sensing units of the UAV  100  as shown in  FIG. 1  are all four, but the present invention does not limit thereto. The numbers of the landing gears, the whirl wing structures and the distance sensing units may be three or more than four. 
         [0017]    Refer to  FIG. 2 .  FIG. 2  is a block diagram of the UAV  100  according to an embodiment of the present invention. 
         [0018]    The UAV  100  further includes a processing unit  202  and a storage unit  206 . The storage unit  206  is used to store the height information of the landing position obtained from the distance sensing units  150 , such as a memory. The processing unit  202  is coupled to the 3D image recognition system  140  and the storage unit  206  for determining a landing position in accordance with the depth image obtained from the 3D image recognition system  140 . In addition, the processing unit  202  may further control and adjust the length of each of the landing gears  121 ,  122 ,  123  arid  124  respectively in accordance with the height information stored in the storage unit  206 . The processing unit  202  may be, for example, a microprocessor or a microcontroller. 
         [0019]    Refer to  FIG. 3 .  FIG. 3  is a flow chart of a landing method of the UAV according to an embodiment of the present invention. In the present embodiment, the UAV  100  of  FIGS. 1-2  is exemplarily used for describing these steps of flow process. 
         [0020]    In step S 1 , the 3D image recognition system  140  obtains a depth image of a scene. The 3D image recognition system  140  may capture 2D images of different scenes, and perform processing to the 2D images to obtain a depth information of the 2D image, so as to obtain the depth image of the scene. 
         [0021]    Refer to  FIGS. 4 and 5 .  FIG. 4  is a part of flow chart of the landing method of the UAV according to another embodiment of the present invention.  FIG. 5  is a schematic diagram of a 2D image according to another embodiment of the present invention. 
         [0022]    For instance, in step S 11 , the image capturing unit in the 3D image recognition system  140  (such as a camera or a video camera) captures a 2D image I of the scene. The image capturing unit may capture the 2D image I of the scene in accordance with different shooting angles (e.g., swinging the lens of the image capturing unit) and shooting ranges (e.g., controlling the lens of the image capturing unit to zoom in or zoom out). 
         [0023]    Next, in step  512 , the 3D image recognition system  140  divides the 2D image I into a plurality of regions, such as region A 1 , region A 2 , region A 3  and region A 4 . In one embodiment, the number of the regions being divided may correspond to the number of the landing gears of the UAV. 
         [0024]    In step S 13 , the 3D image recognition system  140  obtains depth values of all pixels in each of the regions A 1 , A 2 , A 3  and A 4 . For example, in region A 1 , there are pixels A 11 , A 12 , . . . , A 1   n  contained therein. The 3D image recognition system  140  may depend on the color depth in each of the pixels A 11 , A 12 , . . . , A 1   n  to recognize and obtain corresponding depth values D 1   n  of all the pixels A 11 , A 12 , . . . , A 1   n,  wherein n is an integer equal to or larger than 1. 
         [0025]    In step S 14 , the 3D image recognition system  140  calculates average depth values respectively corresponding to each of the regions A 1 , A 2 , A 3  and A 4  to obtain the depth image. In case of region A 1  the 3D image recognition system  140  calculates average values of all the depth values D 1  n to obtain an average depth value D 1  of region A 1 . On this basis, the 3D image recognition system  140  respectively calculates average depth values D 2 , D 3  and D 4  of the regions A 2 , A 3  and A 4 , so as to obtain the depth image of the captured scene. 
         [0026]    Refer to  FIG. 3 . After the step S 1  of obtaining the depth image of the scene, the method proceeds to step S 2 . In step S 2 , the processing unit  202  determines a landing position in accordance with the depth image. 
         [0027]    Refer to  FIG. 4 . In step S 21 , the processing unit  202  obtains a maximum average depth value D MAX  and a minimum average depth value D MIN  from the average depth values D 1 , D 2 , D 3  and D 4  of the regions A 1 , A 2 , A 3  and A 4 , respectively. For instance, among the four regions A 1 , A 2 , A 3  and A 4 , the average depth value D 3  of the region A 3  is the maximum, while the average depth value D 1  of the region A 1  is the minimum. As a result, D 3  is the maximum average depth value D MAX , and D 1  is the minimum average depth value D MIN . 
         [0028]    In step S 22 , the processing unit  202  subtracts the minimum average depth value D MIN  from the maximum average depth value D MAX  to obtain a difference value D DIFF =D 3 −D 1 . 
         [0029]    In step S 23 , the processing unit  202  determines whether the difference value D DIFF  is smaller than a threshold value. When the processing unit  202  determines that the difference value D DIFF  is smaller than the threshold value, the method proceeds to step S 24 , that is, the processing unit  202  determines to land the UAV on the landing position. When the processing unit  202  determines that the difference value D DIFF  is larger than the threshold value, the processing unit  202  determines the 3D image recognition system  140  to re-obtain a depth image of a scene, that is, the method proceeds back to step S 1  to search for a suitable landing position. 
         [0030]    In one embodiment, the threshold value of step S 23  may be a maximum telescopic length of each of the landing gears  121 ,  122 ,  123  and  124 . That is, before landing, the UAV will first search for a suitable landing position where the UAV can land steadily. If the first found landing position has a level drop that is larger than a maximum telescopic length of each of the landing gears  121 ,  122 ,  123  and  124  so that the UAV cannot keep a balance or may even topple over, the UAV will continue to find another landing positions. 
         [0031]    Refer to  FIG. 2 . After the step S 2  of determining the landing position in accordance with the depth image, the method proceeds to step S 3 . In step S 3 , the distance sensing units  150  obtain a height information of the landing position, and store the height information in the storage unit  206 . 
         [0032]    In one embodiment, when determining to land the UAV on the landing position, the processing unit  202  orders the UAV to fly to the landing position, and aims each of the landing gears  121 ,  122 ,  123  and  124  to correspond to each of the regions A 1 , A 2 , A 3  and A 4 . In this embodiment, the distance sensing units  150  are, for example, infrared sensors for sensing distance. The distance sensing units  150  are respectively disposed in the landing gears  121 ,  122 ,  123  and  124  for obtaining a height information of the landing position corresponding to each of the regions A 1 , A 2 , A 3  and A 4 . The infrared sensor includes an emitting end for emitting an infrared light to the ground and a receiving end for receiving the infrared light reflected from the ground. During the traveling of the infrared light, an energy attenuation will be generated. The infrared sensors may respectively obtain current heights relative to the ground of each of the landing gears  121 ,  122 ,  123  and  124  according to the energy attenuation, so as to obtain the height information of the landing position, and store the height information in the storage unit  206 . 
         [0033]    Next, after the step S 3  of obtaining the height information of the landing position, the method proceeds to step S 4 . In step S 4 , the processing unit  202  adjusts a plurality of relative distances of the landing gears  121 ,  122 ,  123  and  124  relative to the landing position in accordance with the height information to make the relative distances substantially the same. 
         [0034]    In one embodiment, the processing unit  202  may lengthen or shorten the length of each of the landing gears  121 ,  122 ,  123  and  124  respectively in accordance with the height information stored in the storage unit  206  to make the relative distances of the landing gears  121 ,  122 ,  123  and  124  substantially the same. 
         [0035]    Next, after the step S 4  of adjusting the relative distances of the landing gears  121 ,  122 ,  123  and  124  relative to the landing position, the method proceeds to step S 5 . In step S 5 , the processing unit  202  orders the UAV  100  to land on the landing position. Because the relative distances of the landing gears  121 ,  122 ,  123  and  124  relative to the landing position have been adjusted substantially the same in the step S 4 , the processing unit  202  may order the UAV  100  to land in such a straightly downward way that the landing gears  121 ,  122 ,  123  and  124  can touch the ground simultaneously to keep the balance during landing. 
         [0036]      FIGS. 6A-6C  are schematic diagrams showing the landing of the UAV according to an embodiment of the present invention.  FIGS. 6A-6C  are exemplarily used for describing the landing process of the steps S 3  to S 5 . In the present embodiment, the UAV  100  of  FIGS. 1-2  is exemplarily used for describing these steps of landing process. 
         [0037]    Refer to  FIG. 6A . When the UAV  100  confirms a landing position  10 , the distance sensing units  150  respectively disposed on the landing gears  121 ,  122  (not shown),  123  and  124  obtain a height information of the landing gears  121 ,  122 ,  123  and  124  on the landing position  10 . For example, heights relative to the ground H 1 , H 3  and H 4  of each of the landing gears  121 ,  123  and  124  measured by the distance sensing units  150  on the landing gears  121 ,  123  and  124  are 140 cm, 200 cm and 160 cm, respectively. The heights relative to the ground H 1 , H 3  and H 4  are used as the height information of the landing position  10 . 
         [0038]    Refer to  FIG. 6B . After the distance sensing units  150  obtain the height information of the landing position  10 , the processing unit  202  depends on the height information to shorten the length L 1  of the landing gear  121  by 10 cm, and respectively lengthen the lengths L 3  and L 4  of the landing gears  123  and  124  by 50 cm and 10 cm. Therefore, the relative distances of the landing gears  121 ,  123  and  124  relative to the landing position  10  are adjusted to be equal to each other (i.e., 150 cm). 
         [0039]    Refer to  FIG. 60 . After adjusting the relative distances of the landing gears  121 ,  123  and  124  relative to the landing position  10 , the processing unit  202  controls the UAV  100  to fly downwards by 150 cm on the landing position  10 . Finally, the landing gears  121 ,  123  and  124  may touch the ground simultaneously without losing balance when the UAV  100  lands. 
         [0040]    In the landing method of the UAV disclosed in above embodiment of the present invention, the UAV will first search for a suitable landing position before landing, so as to prevent itself from toppling over resulted from the larger level drop while being landing. After finding the suitable landing position, the UAV of the present invention will obtain a height information of the landing position, and then adjust the landing gears in accordance with the height information, and finally land on the landing position. Therefore, the UAV can prevent from toppling over resulted from late calculation of gravity. Moreover, in the step of correspondingly adjusting the landing gears in accordance with the height information, the relative distances of the landing gears relative to the landing position are made all the same. Thus, when the UAV is controlled to land in a straightly downward way, the landing gears can not only touch the ground simultaneously to keep the balance, but also prevent itself from toppling over in the case that any landing gears have not touched the ground while being landing. 
         [0041]    While the invention has been described by way of example and in terms of the preferred embodiment(s), it is to be understood that the invention is not limited thereto. On the contrary, it is intended to cover various modifications and similar arrangements and procedures, and the scope of the appended claims therefore should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and procedures.