Patent Publication Number: US-2022213669-A1

Title: Display system for work vehicle and display method for work vehicle

Description:
TECHNICAL FIELD 
     The present disclosure relates to a display system for a work vehicle and a display method for a work vehicle. 
     Priority is claimed on Japanese Patent Application No. 2019-133074, filed Jul. 18, 2019, the content of which is incorporated herein by reference. 
     BACKGROUND ART 
     Patent Document 1 discloses a technique related to a periphery monitoring system that detects a person in the periphery of a work vehicle. According to the technique described in 
     Patent Document 1, the periphery monitoring system performs image processing to identify whether or not an image includes a person. 
     CITATION LIST 
     Patent Document 
     Patent Document 1 
     Japanese Unexamined Patent Application, First Publication No. 2017-151815 
     SUMMARY OF INVENTION 
     Technical Problem 
     In a process of detecting an obstacle such as a person, a plurality of obstacles may be detected from one region. At this time, when all the obstacles detected by the detection process are displayed on a screen, a large amount of detection results are displayed. Therefore, there is a possibility that necessary information cannot be immediately determined. 
     An object of the present disclosure is to provide a display system for a work vehicle and a display method for a work vehicle capable of reducing the possibility of overlooking necessary information related to detection of an obstacle. 
     Solution to Problem 
     According to the first aspect of the present disclosure, a display system for a work vehicle includes: an image acquisition unit configured to acquire a captured image of surroundings of a work vehicle; a detection unit configured to detect an obstacle around the work vehicle; and a display control unit configured to generate a signal for displaying an obstacle-identifying display at a position related to an obstacle having high detection accuracy among a plurality of obstacles detected in a region corresponding to the captured image when the plurality of obstacles are detected by the detection unit, the detection accuracy indicating a certainty of the obstacle. 
     Advantageous Effects of Invention 
     According to the above aspect, the display system can reduce the possibility of overlooking necessary information related to detection of an obstacle. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic view showing a configuration of a work vehicle according to a first embodiment. 
         FIG. 2  is a view showing imaging ranges of a plurality of cameras provided in the work vehicle according to the first embodiment. 
         FIG. 3  is a view showing an internal configuration of a cab according to the first embodiment. 
         FIG. 4  is a schematic block diagram showing a configuration of a control device according to the first embodiment. 
         FIG. 5  is a flowchart showing operation of the control device according to the first embodiment. 
         FIG. 6  is an example of a display image according to the first embodiment. 
         FIG. 7  is an example of a display image according to the first embodiment. 
         FIG. 8  is an example of a display image according to the first embodiment. 
         FIG. 9  is an example of a display image according to the first embodiment. 
         FIG. 10  is a flowchart showing operation of the control device according to another embodiment. 
         FIG. 11  is an example of a display image according to another embodiment. 
         FIG. 12  is an example of a display image according to another embodiment. 
         FIG. 13  is an example of correspondence between frame regions of a display image and captured images in another embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
     Hereinafter, embodiments will be described in detail with reference to the drawings. 
     Configuration of Work Vehicle 
       FIG. 1  is a schematic view showing a configuration of a work vehicle according to a first embodiment. 
     A work vehicle  100  operates at a construction site to construct a construction target such as earth. The work vehicle  100  according to the first embodiment is, for example, a hydraulic excavator. The work vehicle  100  includes an undercarriage  110 , a swing body  120 , work equipment  130 , and a cab  140 . 
     The undercarriage  110  supports the work vehicle  100  so as to be capable of traveling. The undercarriage  110  is, for example, a pair of right and left endless tracks. 
     The swing body  120  is supported by the undercarriage  110  so as to be swingable around a swing center. 
     The work equipment  130  is driven by hydraulic pressure. The work equipment  130  is supported by a front portion of the swing body  120  so as to be capable of driving in a vertical direction. The cab  140  is a space in which an operator gets to operate the work vehicle  100 . The cab  140  is provided on a left front portion of the swing body  120 . 
     Here, a portion of the swing body  120  to which the work equipment  130  is attached is referred to as a front portion. In addition, in the swing body  120 , with reference to the front portion, a portion on an opposite side is referred to as a rear portion, a portion on a left side is referred to as a left portion, and a portion on a right side is referred to as a right portion. 
     Configuration of Swing Body 
     The swing body  120  is provided with a plurality of cameras  121  that capture images of surroundings of the work vehicle  100 .  FIG. 2  is a view showing imaging ranges of the plurality of cameras provided in the work vehicle according to the first embodiment. Specifically, the swing body  120  is provided with a left rear camera  121 A that captures an image of a left rear range Ra around the swing body  120 , a rear camera  121 B that captures an image of a rear range Rb around the swing body  120 , a right rear camera  121 C that captures an image of a right rear range Rc around the swing body  120 , and a right front camera  121 D that captures an image of a right front range Rd around the swing body  120 . Incidentally, the imaging ranges of the plurality of cameras  121  may partially overlap each other. 
     The imaging ranges of the plurality of cameras  121  cover the entire periphery of the work vehicle  100  excluding a left front range Re visible from the cab  140 . Incidentally, the cameras  121  according to the first embodiment capture images of regions on left rear, rear, right rear, and right front sides of the swing body  120 , but is not limited thereto in another embodiment. For example, the number of the cameras  121  and the imaging ranges according to another embodiment may differ from the example shown in  FIGS. 1 and 2 . 
     Incidentally, as shown by the rear range Rb in  FIG. 2 , the left rear camera  121 A captures an image of a range of a left side region and a left rear region of the swing body  120 , but may capture an image of one region thereof. Similarly, as shown by the right rear range Rc in  FIG. 2 , the right rear camera  121 C captures an image of a range of a right side region and a right rear region of the swing body  120 , but may capture an image of one region thereof. Similarly, as shown by the right front range Rd in  FIG. 2 , the right front camera  121 D captures an image of a range of a right front region and the right side region of the swing body  120 , but may capture an image of one region thereof. 
     Configuration of Work Equipment 
     The work equipment  130  includes a boom  131 , an arm  132 , a bucket  133 , a boom cylinder  134 , an arm cylinder  135 , and a bucket cylinder  136 . 
     A base end portion of the boom  131  is attached to the swing body  120  via a boom pin P 1 . The arm  132  connects the boom  131  and the bucket  133 . A base end portion of the arm  132  is attached to a tip end portion of the boom  131  via an arm pin P 2 . 
     The bucket  133  includes blades to excavate earth, etc. and an accommodating portion to accommodate the excavated earth. A base end portion of the bucket  133  is attached to a tip end portion of the arm  132  via a bucket pin P 3 . 
     The boom cylinder  134  is a hydraulic cylinder that operates the boom  131 . A base end portion of the boom cylinder  134  is attached to the swing body  120 . A tip end portion of the boom cylinder  134  is attached to the boom  131 . 
     The arm cylinder  135  is a hydraulic cylinder that drives the arm  132 . A base end portion of the arm cylinder  135  is attached to the boom  131 . A tip end portion of the arm cylinder  135  is attached to the arm  132 . 
     The bucket cylinder  136  is a hydraulic cylinder that drives the bucket  133 . A base end portion of the bucket cylinder  136  is attached to the arm  132 . A tip end portion of the bucket cylinder  136  is attached to a link member connected to the bucket  133 . 
     Configuration of Cab 
       FIG. 3  is a view showing an internal configuration of the cab according to the first embodiment. 
     An operator&#39;s seat  141 , an operation device  142 , and a control device  143  are provided inside the cab  140 . 
     The operation device  142  is an interface that drives the undercarriage  110 , the swing body  120 , and the work equipment  130  according to a manual operation by the operator. The operation device  142  includes a left operation lever  1421 , a right operation lever  1422 , a left foot pedal  1423 , a right foot pedal  1424 , a left traveling lever  1425 , and a right traveling lever  1426 . 
     The left operation lever  1421  is provided on a left side of the operator&#39;s seat  141 . The right operation lever  1422  is provided on a right side of the operator&#39;s seat  141 . 
     The left operation lever  1421  is an operation mechanism that causes the swing body  120  to perform a swing operation and causes the arm  132  to perform a pulling or pushing operation. Specifically, when the operator of the work vehicle  100  tilts the left operation lever  1421  forward, the arm  132  performs pushing operation. In addition, when the operator of the work vehicle  100  tilts the left operation lever  1421  backward, the arm  132  performs pulling operation. In addition, when the operator of the work vehicle  100  tilts the left operation lever  1421  in a right direction, the swing body  120  swings rightward. In addition, when the operator of the work vehicle  100  tilts the left operation lever  1421  in a left direction, the swing body  120  swings leftward. Incidentally, in another embodiment, when the left operation lever  1421  is tilted in a front to back direction, the swing body  120  swings rightward or leftward, and when the left operation lever  1421  is tilted in a right to left direction, the arm  132  may perform a dumping operation or an excavating operation. 
     The right operation lever  1422  is an operation mechanism that causes the bucket  133  to perform an excavating or dumping operation and causes the boom  131  to perform a raising or lowering operation. Specifically, when the operator of the work vehicle  100  tilts the right operation lever  1422  forward, the lowering operation of the boom  131  is executed. In addition, when the operator of the work vehicle  100  tilts the right operation lever  1422  backward, the raising operation of the boom  131  is executed. In addition, when the operator of the work vehicle  100  tilts the right operation lever  1422  in the right direction, the dumping operation of the bucket  133  is performed. In addition, when the operator of the work vehicle  100  tilts the right operation lever  1422  in the left direction, the excavating operation of the bucket  133  is performed. 
     The left foot pedal  1423  is disposed on a left side of a floor surface in front of the operator&#39;s seat  141 . The right foot pedal  1424  is disposed on the left side of the floor surface in front of the operator&#39;s seat  141 . The left traveling lever  1425  is pivotally supported by the left foot pedal  1423  and is configured such that the inclination of the left traveling lever  1425  and the pressing down of the left foot pedal  1423  are linked. The right traveling lever  1426  is pivotally supported by the right foot pedal  1424  and is configured such that the inclination of the right traveling lever  1426  and the pressing down of the right foot pedal  1424  are linked. 
     The left foot pedal  1423  and the left traveling lever  1425  correspond to rotational drive of a left crawler belt of the undercarriage  110 . Specifically, when the operator of the work vehicle  100  tilts the left foot pedal  1423  or the left traveling lever  1425  forward, the left crawler belt rotates in a forward movement direction. In addition, when the operator of the work vehicle  100  tilts the left foot pedal  1423  or the left traveling lever  1425  backward, the left crawler belt rotates in a backward movement direction. 
     The right foot pedal  1424  and the right traveling lever  1426  correspond to rotational drive of a right crawler belt of the undercarriage  110 . Specifically, when the operator of the work vehicle  100  tilts the right foot pedal  1424  or the right traveling lever  1426  forward, the right crawler belt rotates in the forward movement direction. In addition, when the operator of the work vehicle  100  tilts the right foot pedal  1424  or the right traveling lever  1426  backward, the right crawler belt rotates in the backward movement direction. 
     The control device  143  is an input and output device and is capable of displaying, for example, as an overhead image, a situation around the work vehicle  100  acquired by the plurality of cameras  121 . Input means of the control device  143  according to the first embodiment is a hardware key. Incidentally, in another embodiment, a touch panel, a mouse, a keyboard, etc. may be used as the input means. 
     Configuration of Control Device 
       FIG. 4  is a schematic block diagram showing a configuration of the control device according to the first embodiment. 
     The control device  143  includes a processor  210 , a main memory  230 , a storage  250 , and an interface  270 . 
     The storage  250  is a non-transitory storage medium. Exemplary examples of the storage  250  include a hard disk drive (HDD), a solid state drive (SSD), a magnetic disk, a magneto-optical disk, a compact disc read only memory (CD-ROM), a digital versatile disc read only memory (DVD-ROM), a semiconductor memory, etc. The storage  250  may be an internal medium directly connected to a bus of the control device  143  or may be an external medium to be connected to the control device  143  via the interface  270  or a communication line. The storage  250  stores a program for realizing the monitoring of the surroundings of the work vehicle  100 . 
     The program may realize some of functions to be exhibited by the control device  143 . For example, the program may exhibit functions in combination with another program already stored in the storage  250  or in combination with another program installed in another device. 
     Incidentally, in another embodiment, the control device  143  may include a custom large scale integrated circuit (LSI) such as a programmable logic device (PLD) in addition to the above configuration or instead of the above configuration. Exemplary examples of the PLD include a programmable array logic (PAL), a generic array logic (GAL), a complex programmable logic device (CPLD), and a field programmable gate array (FPGA). In this case, some or all of the functions to be realized by the processor may be realized by the integrated circuit. 
     In addition, the storage  250  stores person dictionary data D 1  to detect a person. The person dictionary data D 1  is, for example, dictionary data of a feature quantity to be extracted from each of a plurality of known images in which persons are portrayed. As an example of the feature quantity, histograms of oriented gradients (HOG) or Co-occurrence HOG (CoHOG) can be used. 
     The processor  210  executes the program to function as an image acquisition unit  211 , a feature quantity extraction unit  212 , a detection unit  213 , an image generation unit  214 , a marker disposition unit  215 , a presence determination unit  216 , and a display control unit  217 . In addition, a storage region of a marker storage unit  231  is secured in the main memory  230  by executing the program. 
     The image acquisition unit  211  acquires images from the plurality of cameras  121 . The image acquired from each of the cameras  121  is a frame image to be updated at a predetermined frame rate. 
     The feature quantity extraction unit  212  extracts a feature quantity from the frame images acquired by the image acquisition unit  211 . Exemplary examples of the feature quantity to be extracted by the feature quantity extraction unit  212  include a HOG feature quantity, a CoHOG feature quantity, etc. 
     The detection unit  213  detects a person in the frame images based on the feature quantity extracted by the feature quantity extraction unit  212  and the person dictionary data D 1  stored in the storage  250 . Exemplary examples of a method for detecting a person include pattern matching, an object detection process based on machine learning, etc. A person is one example of an obstacle. Incidentally, in the first embodiment, the detection unit  213  detects a person using the feature quantity of the image but is not limited thereto. For example, in another embodiment, the detection unit  213  may detect a person based on a measured value of an infrared sensor, etc. The detection unit  213  specifies detection accuracy for each detected person. The detection accuracy is accuracy indicating a certainty of a person, and is expressed as, for example, the similarity or likelihood of a feature quantity. 
     The image generation unit  214  transforms and combines a plurality of the frame images acquired by the image acquisition unit  211 , to generate an overhead image in which a site viewed in a planar view from above and in which the work vehicle  100  is centered. Namely, the image generation unit  214  transforms each of the plurality of frame images into an overhead coordinate system and combines the transformed frame images to generate an overhead image. Incidentally, the image generation unit  214  may cut out a part of each of the transformed frame images and combine the cutout frame images to generate an overhead image. An image in which the work vehicle  100  is viewed in a planar view from above is affixed in advance to the center of the overhead image generated by the image generation unit  214 . 
     The marker disposition unit  215  disposes a marker indicating the position of a person at a position corresponding to the detection position of the person, such that the marker is superimposed on the overhead image generated by the image generation unit  214 . Incidentally, the marker disposition unit  215  according to another embodiment may dispose a marker within a predetermined range from the detection position. Exemplary examples of the shape of the marker include a circular shape, an elliptical shape, a regular polygon shape, a polygon shape, etc. Incidentally, the marker is one example of an obstacle-identifying display. In another embodiment, for example, the obstacle-identifying display may be any obstacle-identifying display such as a display of a text indicating a person, a change in the color of a person, and a change in the shape of a person. 
     The marker disposition unit  215  records the position of the disposed marker in the marker storage unit  231 . The marker storage unit  231  stores the position of the marker disposed in the overhead image. 
     The marker disposition unit  215  sets a different color for the marker according to a positional relationship between the detection position and a warning range set around the work vehicle  100 . For example, the marker disposition unit  215  sets the color of the marker to red when the detection position is within the warning range and sets the color of the marker to yellow color when the detection position is outside the warning range. The warning range may be set as, for example, a circle having the swing center of the work vehicle  100  as a center. 
     Incidentally, the color of the marker and the relationship between the position and the color of the marker are not limited thereto. For example, the marker disposition unit  215  according to another embodiment may set a color other than red and yellow colors for the marker. In addition, the marker disposition unit  215  according to another embodiment may set the color of the marker to red when the detection position is within the warning range, set the color of the marker to yellow color when the detection position is outside the warning range but within a caution range, and set the color of the marker to gray color when the detection position is outside the caution range. In addition, when the detection position is within the warning range or the caution range, the color of the marker may be set to red. In addition, the color of the marker may be set to red regardless of the detection position. The caution range may be set as, for example, a circle having the swing center of the work vehicle  100  as a center and a range outside the warning range. 
     In addition, the marker disposition unit  215  may highlight a region including the detection position of a person, together with the disposition of the marker in the overhead image. The region is determined by the imaging ranges of the plurality of cameras  121 . Incidentally, the region may be determined by an imaging range of one camera  121  or may be determined by imaging ranges of at least two cameras  121 . In addition, the region may be narrower than the imaging range. Exemplary examples of the highlighting include, for example, displaying a frame of the region as a thick red frame. Incidentally, the highlighting is not limited to the above example, and may be done with a color other than red color. In addition, the highlighting may be done by blinking the frame of the region. 
     In addition, only when the detection position is within the warning range or the caution range, the marker disposition unit  215  may highlight a region including the position. In this case, a marker is disposed on the detected person and a region corresponding to the detection position is highlighted, so that the operator can easily figure out the person to which caution has to be given, and a direction. Namely, the control device  143  is capable of encouraging the operator to exercise caution. 
     The presence determination unit  216  determines whether or not a person is present inside the caution range or the warning range set around the work vehicle  100 , based on the detection position in the overhead coordinate system. 
     The display control unit  217  attaches an icon corresponding to a determination result of the presence determination unit  216  to the overhead image in which the marker is disposed, to generate a monitoring image. The display control unit  217  outputs the generated monitoring image to a touch panel. The form of the icon is set differently between, for example, when a person is not present within the caution range, when a person is present within the caution range but outside the warning range, and when a person is present within the warning range. Exemplary examples of the form of the icon include color, transparency, size, etc. 
     Operation of Control Device 
       FIG. 5  is a flowchart showing operation of the control device according to the first embodiment. 
     When the control device  143  starts a process of monitoring the surroundings, the image acquisition unit  211  acquires frame images from the plurality of cameras  121  (step S 1 ). Next, the control device  143  executes a person detection process P 1  and a display control process P 2  in parallel based on the acquired frame images. 
     The person detection process P 1  is a process from step S 2  to step S 3  below. 
     The feature quantity extraction unit  212  extracts a feature quantity from the frame images acquired in step S 1  (step S 2 ). Next, the detection unit  213  reads the person dictionary data D 1  from the storage  250  and compares the extracted feature quantity with the person dictionary data D 1  to specify detection positions at which persons are present in the frame images (step S 3 ). The person detection process P 1  has a larger amount of calculation than the display control process P 2 . 
     The display control process P 2  is a process from step S 4  to step S 9  below. 
     The image generation unit  214  generates an overhead image based on the frame images acquired in step S 1  (step S 4 ). Next, the presence determination unit  216  determines whether or not the persons are inside the caution range or the warning range, based on the position of the marker stored in the marker storage unit  231  (step S 5 ). 
     The display control unit  217  draws a marker for the position and the size stored in the marker storage unit  231 , on the overhead image generated in step S 4 , and attaches an icon corresponding to a determination result in step S 7  at a position corresponding to the left front range Re in the overhead image to generate a monitoring image (step S 6 ). The display control unit  217  outputs the generated monitoring image to the touch panel (step S 7 ). 
     Next, the display control unit  217  determines whether or not the person detection process P 1  is completed (step S 8 ). When the person detection process P 1  is not completed (step S 8 : NO), the image acquisition unit  211  acquires next frame images from the plurality of cameras  121  (step S 9 ), and the process returns to step S 4 . 
     When the person detection process P 1  and the display control process P 2  are completed, the presence determination unit  216  determines whether or not persons are present inside the warning range in each of the frame images that have become detection targets in the person detection process P 1 , based on the detection positions related to the result of the detection process in step S 3  (step S 10 ). For a frame image in which persons are present inside the warning range (step S 10 : YES), the marker disposition unit  215  specifies one detection position within the warning range, the one detection position being related to a person with the highest detection accuracy indicated by the detection result (step S 11 ). 
     For a frame image in which persons are not present inside the warning range (step S 10 : NO), the presence determination unit  216  determines whether or not the persons are present inside the caution range, based on the detection positions related to the result of the detection process in step S 3  (step S 12 ). For a frame image in which persons are inside the caution range (step S 12 : YES), the marker disposition unit  215  specifies one detection position within the caution range, the one detection position being related to a person with the highest detection accuracy indicated by the detection result (step S 13 ). For a frame image in which persons are not present within the warning range and the caution range (step S 12 : NO), the marker disposition unit  215  specifies a person with the highest detection accuracy indicated by the detection result (step S 14 ). 
     Then, the marker disposition unit  215  disposes a marker at the detection position of the person specified in any one of step S 10  to step S 14  in each of the frame images that have become detection targets in the person detection process P 1 . Namely, the marker disposition unit  215  records information of the marker at a position corresponding to the detection position in the marker storage unit  231  (step S 15 ), and the control device  143  ends a periphery monitoring process. 
     Incidentally, the marker disappears when a certain period of time has elapsed from the disposition of the marker. Namely, the marker disposition unit  215  deletes information of the corresponding marker from the marker storage unit  231  when a certain period of time has elapsed from the disposition of the marker. Incidentally, the marker disposition unit  215  according to another embodiment may delete a marker when the marker reaches a predetermined size or larger. In addition, in this case, the marker disposition unit  215  may determine the color of the marker based on a relationship between the detection position and the warning range. Accordingly, the number of markers for each of regions corresponding to a plurality of frame images can be suppressed to  1  or less in an overhead image. 
     Incidentally, the person detection process P 1  may be executed on the plurality of frame images in parallel or may be executed on the frame images in order. In addition, when a marker related to a person extracted from other frame images is already at the detection position, the marker disposition unit  215  may not dispose a marker at the detection position. 
     Accordingly, the overlapping disposition of markers which makes it difficult to see the markers can be prevented. In addition, when the person detection process P 1  is executed on the frame images in order, a process from step S 10  to step S 15  is performed only on a frame image to be targeted by the person detection process P 1 . 
     Incidentally, the flowchart shown in  FIG. 5  is one example, and in another embodiment, all the steps may not be necessarily executed. For example, in another embodiment, any one of step S 2 , steps S 5  to S 9 , and steps S 10  to S 13  may not be executed. 
     Example of Display Image 
       FIGS. 6 to 9  are examples of display images according to the first embodiment. 
     According to  FIGS. 6 to 9 , in the display images, a monitoring image G 1  generated by the display control unit  217  and a single camera image G 2  are displayed. In addition, each of the display images include a work mode indicator G 32 , a service meter reading (SMR) indicator G 33 , a fuel level indicator G 34 , a hydraulic oil temperature indicator G 35 , and an engine coolant temperature indicator G 36 . The monitoring image G 1  includes an overhead image G 11 , a region frame G 12  indicating the caution range, a region frame G 13  indicating the warning range, a plurality of markers G 14 , and an icon G 15 . The single camera image G 2  is a frame image captured by one of the plurality of cameras  121 . 
     In addition,  FIGS. 6 to 9  show a detection position E that is not displayed in the display images but is not specified in a process from step S 10  to step S 14 . In addition,  FIGS. 6 to 9  show frame regions F 1 , F 2 , F 3 , and F 4  that are not displayed in the display images. The frame F 1  is a frame region corresponding to the left rear range Ra of which an image is to be captured by the left rear camera  121 A. The frame F 2  is a frame region corresponding to the rear range Rb of which an image is to be captured by the rear camera  121 B. The frame F 3  is a frame region corresponding to the right rear range Rc of which an image is to be captured by the right rear camera  121 C. The frame F 4  is a frame region corresponding to the right front range Rd of which an image is to be captured by the right front camera  121 D. Incidentally, the overhead image G 11  is not generated for a front and left front frame region F 0 . The reason is that the operator can directly see a region in front of and on a left front side of the cab  140 . 
       FIG. 6  shows a case where one or more persons are present within the warning range of the work vehicle and shows an example of a display image in which a frame image captured by the right front camera  121 D is displayed in the single camera image G 2 . According to  FIG. 6 , when one or more persons are detected within the warning range, the marker G 14  is attached only at a detection position related to a person with the highest detection accuracy. Accordingly, the operator can recognize the person to which special caution has to be given among persons in a short distance. Incidentally,  FIG. 6  shows an example in which one or more persons are present within the warning range, and even when no person is present within the warning range and one or more persons are present within the caution range, the same above result is obtained. Incidentally, the one or more persons may be one person or may be a plurality of persons. 
       FIG. 7  shows a case where one or more persons are present outside the caution range and shows an example of a display image in which a frame image captured by the right rear camera  121 C is displayed in the single camera image G 2 . According to  FIG. 7 , when one or more persons are detected outside the caution range, the marker G 14  is attached only at a detection position related to a person with the highest detection accuracy. Accordingly, when no person is present in a short distance, the operator can recognize the person to which special caution has to be given. Incidentally, the one or more person may be one person or may be a plurality of persons. 
       FIG. 8  shows a case where one or more persons are present within the caution range and objects are present within the caution range and outside the caution range, and shows an example of a display image in which a frame image captured by the left rear camera  121 A is displayed in the single camera image G 2 . According to  FIG. 8 , when one or more persons are detected within the caution range and a person is detected outside the caution range because of an object being falsely detected as a person, the marker G 14  is attached only at a detection position related to a person with the highest detection accuracy within the caution range. When a person and an object are compared with each other, generally, the detection accuracy of the person is higher, so that the marker G 14  is attached at the position of the person instead of the object. Accordingly, the operator can recognize the person to which special caution has to be given. 
     In addition, since the marker G 14  is attached only to the person with the highest detection accuracy among a plurality of the detected persons, the marker G 14  can be prevented from being attached at a position related to false detection. In addition, even when a person is detected outside the caution range, the marker G 14  is attached only to a person within the caution range, so that markers can be prevented from causing troublesomeness, and necessary information can be immediately determined. Incidentally,  FIG. 8  shows an example in which one or more persons and objects are present within the caution range, and even when one or more persons and objects are present within the warning range, the same above result is obtained. Incidentally, the one or more persons may be one person or may be a plurality of persons. 
       FIG. 9  shows a case where one or more persons are present within the warning range and one or more persons are present outside the caution range and shows an example of a display image in which a frame image captured by the right front camera  121 D is displayed in the single camera image G 2 . According to  FIG. 9 , when one or more persons are present within the warning range and one or more persons are present outside the caution range, the marker G 14  is attached only at a detection position related to a person with the highest detection accuracy within the warning range. Even if a person present outside the caution range has a higher detection accuracy than that of a person within the warning range, the marker G 14  is attached only to a person with the highest detection accuracy within the warning range. Accordingly, the operator can recognize the person to which special caution has to be given when a plurality of persons is detected. In addition, markers can be prevented from causing troublesomeness, and necessary information can be immediately determined. Incidentally, the one or more persons may be one person or may be a plurality of persons. 
     When the work vehicle is keyed on, a frame image captured by the rear camera  121 B is to be displayed as the single camera image G 2 . The single camera image G 2  can be switched to a frame image captured by another camera  121  by the input means of the control device  143 . Incidentally, a frame image captured by one of the cameras  121  other than the rear camera  121 B may be used as the single camera frame image G 2  to be displayed at key-on. In addition, when a person is detected, the single camera image G 2  may be automatically switched to a frame image of the camera  121  that captures an image of the person. 
     Effects 
     As described above, when a plurality of obstacles are detected in the process of detecting obstacles portrayed in captured images, the control device  143  according to the first embodiment causes a display image to be displayed, in which markers are disposed at positions related to a predetermined number of obstacles having the highest detection accuracy. Accordingly, the number of markers in the display image can be reduced, and a possibility that necessary information related to the detection of the obstacles is overlooked can be reduced. 
     In addition, when a plurality of obstacles is detected within a predetermined range around the work vehicle  100 , the control device  143  according to the first embodiment causes to display a display image in which markers are disposed at positions related to a predetermined number of obstacles having the highest detection accuracy within the range. Accordingly, even when an obstacle far away from an obstacle in the vicinity of the work vehicle has a higher detection accuracy, the obstacle in the vicinity can be notified with priority. Incidentally, in another embodiment, the invention is not limited thereto. For example, the control device  143  according to another embodiment may cause a display image to be displayed, in which markers are disposed at positions related to a predetermined number of obstacles having the highest detection accuracy regardless of the caution range and the warning range. 
     Other Embodiments 
     One embodiment has been described above in detail with reference to the drawings; however, the specific configuration is not limited to the above-described configuration, and various design changes, etc. can be made. In another embodiment, the order of the above-described processes may be appropriately changed. In addition, some of the processes may be executed in parallel. 
     In the above-described embodiment, the work vehicle  100  has been described as being a hydraulic excavator; however, in another embodiment, the invention is applicable to various work vehicles such as dump trucks and wheel loaders. For example, the invention is applicable to a display system for dump trucks, wheel loaders, or other work vehicles. 
     In addition, in the above-described embodiment, one control device  143  has been described as being installed in the work vehicle; however, in another embodiment, a part of the configuration of the control device  143  may be disposed in other control devices, and the invention may be realized by a display system formed of two or more control devices. 
     Incidentally, one control device  143  shown in the above-described embodiment is also one example of a display system. 
     The control device  143  according to the above-described embodiment has been described as being installed in the work vehicle; however, in another embodiment, a part or the entirety of the configuration of the control device  143  may be installed outside the work vehicle. 
     In addition, the control device  143  according to the above-described embodiment detects a person but may detect an obstacle other than a person. 
     In addition, the control device  143  according to the above-described embodiment does not include a left front camera that captures an image of the left front range Re but may include a left front camera that captures an image of the left front range Re in another embodiment. In this case, the control device  143  is capable of generating an overhead image in which the entire periphery around the work vehicle  100  is portrayed. On the other hand, also in this case, the control device  143  may not detect a person from a frame image of the left front camera in the person detection process P 1 . This technique aims to preventing an increase in overall calculation load by not performing the person detection process P 1  in a range in which the necessity for monitoring by the control device  143  is low, since the amount of calculation of the person detection process P 1  is large. 
     In addition, the control device  143  according to the above-described embodiment specifies one detection position having the highest detection accuracy for each frame image but is not limited thereto. For example, in another embodiment, a predetermined number of detection positions of two or more may be specified in descending order of detection accuracy. In addition, for example, in another embodiment, a predetermined number of detection positions with high detection accuracy may be specified for all frame images (the left rear range Ra, the rear range Rb, the right rear range Rc, and the right front range Rd), or a predetermined number of detection positions with high detection accuracy may be specified for each of combinations of frame images (for example, a combination of the left rear range Ra and the rear range Rb and a combination of the right rear range Rc and the right front range Rd). 
     In addition, the control device  143  according to the above-described embodiment causes a detection result to be displayed so as to encourage an operator to exercise caution; however, in another embodiment, the control device may control the work vehicle  100  based on a detection result of the control device  143 . For example, the control device may perform control to prohibit the travelling and swing of the work vehicle  100  and operation of the work equipment when a marker is disposed within a warning region. In this case, the number of markers is reduced as in the above-described embodiment, so that stop control of the work vehicle  100  caused by false detection can be prevented. 
     The control device  143  according to the above-described embodiment includes a display, and cause to display a display image on the display but is not limited thereto in another embodiment. For example, the control device  143  according to another embodiment may not include a display and may transmit a signal for displaying a display image on a display separate from the control device  143 . The signal is a signal for displaying a display image in which a marker is disposed at a position related to an obstacle. Incidentally, the invention may be realized by a display system formed of a display separate from the control device  143 , and two or more control devices each including a part of the configuration of the control device  143  described above. 
     In addition, in the above-described embodiment, each of the alarm range and the caution range has been described as being set as a circle having the swing center of the work vehicle as a center, but in another embodiment, may be a range other than a circle which has the swing center of the work vehicle  100  as a center. For example, each of the warning range and the caution range may be a range obtained by partially extending a circle in directions of a front portion, a rear portion, a left portion, and a right portion of the circle by a predetermined distance, the circle having the swing center of the work vehicle  100  as a center. In addition, each of the warning range and the caution range may be set as a circle having a portion other than the swing center of the work vehicle  100  as a center. In addition, each of the warning range and the caution range may be a range obtained from an operation range of the work equipment  130 . In addition, each of the warning range and the caution range may be a range formed of an ellipse, a polygon, or straight lines and curved lines. 
     In addition, in the above-described embodiment, the display has been described as being installed in the work vehicle  100 ; however, in another embodiment, the display may be installed outside the work vehicle  100 . For example, a display may be provided at a point away from a work site, and the control device  143  may transmit a signal for displaying a display image on the display via a network such as the Internet. 
     In addition, in the above-described embodiment, the warning range and the caution range have been described as being set; however, in another embodiment, one range of the warning range and the caution range may be set. In addition, three or more ranges may be set. 
     In addition, in the above-described embodiment, the marker G 14  is attached to the overhead image G 11  but is not limited thereto. For example, in another embodiment, the markers G 14  may be attached to both of the overhead image G 11  and the single camera image G 2 , or the marker G 14  may be attached only to the single camera image G 2 . At this time, the markers G 14  may be attached at a predetermined number of detection positions having high detection accuracy in both of the overhead image G 11  and the single camera image G 2 . In addition, the markers G 14  may be attached only at a predetermined number of detection positions having high detection accuracy in one image of the overhead image G 11  and the single camera image G 2 , and the markers G 4  may be attached at all detection positions in the other image. 
     In addition, in another embodiment, a display image may include only one of the overhead images G 11  and the single camera image G 2 . In this case, the marker G 14  is attached to the overhead image G 11  or the single camera image G 2  included in the display image. In addition, in another embodiment, the single camera images G 2  captured by the plurality of cameras  121  may be displayed side by side. In this case, the marker G 14  may be attached to one single camera image G 2 , or the markers G 14  may be attached to two or more single camera images. 
     Here, an example will be described in which the control device  143  generates a display image including the single camera image G 2  to which the marker G 14  is attached. 
       FIG. 10  is a flowchart showing operation of the control device according to another embodiment. In another embodiment, the control device  143  executes step S 104 , step S 106 , and step S 115  instead of step S 4 , step S 6 , and step S 15  in the first embodiment. 
     In step S 104 , the image generation unit  214  of the control device  143  generates a single camera image based on a frame image acquired in step S 1 . 
     In step S 106 , the display control unit  217  of the control device  143  draws a marker for the position stored in the marker storage unit  231 , on the single camera image generated in step S 104 , and attaches an icon corresponding to a determination result in step S 5  to the single camera image to generate a display image. The icon is disposed at a position at which the necessity for monitoring is low, such as a region in which a part of the work vehicle  100  is shown, in the single camera image, so that the icon can be prevented from covering a person present at a position at which the necessity for monitoring by the control device  143  Is high. In step S 115 , the marker disposition unit  215  of the control device  143  disposes a marker at a detection position related to a result of the detection process in step S 3 . Namely, the marker disposition unit  215  records information of the marker at the detection position in the marker storage unit  231 . 
       FIG. 11  is an example of a display image according to another embodiment. 
     According to  FIG. 11 , the display image includes two single camera images G 2  captured by different cameras  121 . One marker G 14  is attached to each of the single camera images G 2 . Incidentally, in the example shown in  FIG. 11 , for each of the two single camera images G 2 , a predetermined number of detection positions with high detection accuracy are specified, and the markers G 14  are attached at the detection positions; however, the invention is not limited thereto. For example, in another embodiment, for one of two single camera images G 2 , a predetermined number of detection positions with high detection accuracy may be specified and the markers G 14  may be attached at the detection positions, and for the other, the marker G 14  may not be attached. In addition, in another embodiment, for one of two single camera images G 2 , a predetermined number of detection positions with high detection accuracy may be specified and the markers G 14  may be attached at the detection positions, and for the other, the markers G 14  may be attached at all the detection positions. In addition, in another embodiment, a display image may include three or more single camera images G 2 . 
       FIG. 12  is an example of a display image according to another embodiment. 
     Imaging ranges may overlap each other in the frame regions F 1 , F 2 , F 3 , and F 4 . Hatched portions in  FIG. 12  are overlapping portions of the imaging ranges which are not to be displayed on an actual screen. For example, in the frame region F 3  and the frame region F 4 , a part of the imaging range of the right rear camera  121 C corresponding to the frame region F 3  and a part of the imaging range of the right front camera  121 D corresponding to the frame region F 4  may overlap each other. When the detection accuracy of a person detected in an overlapping portion of the frame regions F 3  and F 4  is higher than that of a person detected in a portion other than the overlapping portion, the marker G 14  may also be disposed at the position of the person detected in the portion other than the overlapping portion. 
     In addition, when the detection accuracy of persons detected in an overlapping portion of imaging ranges is higher than that of persons detected in a portion other than the overlapping portion, the markers G 14  may be disposed at a predetermined number of detection positions in descending order of detection accuracy among a plurality of the persons detected in adjacent frame regions, for example, in the frame region F 3  and the frame region F 4 . In this case, attaching the markers G 14  only to the persons detected in the overlapping portion can be prevented. 
     Incidentally, the case of the overlapping portion of the frame regions F 3  and F 4  has been described; however, the above process may be performed for any combination of adjacent frame regions among the frame regions F 1 , F 2 , F 3 , and F 4 . 
     Incidentally, a detection of a person in an overlapping portion can be determined, for example, by determining a portion where the imaging ranges of adjacent cameras overlap each other, for each frame image, and determining whether or not a person is detected in the overlapping portion. 
     In addition, the imaging ranges of the cameras  121  may be wider than the corresponding frame regions F 1 , F 2 , F 3 , and F 4 .  FIG. 13  is an example of correspondence between frame regions of a display image and captured images in another embodiment. 
     As shown in  FIG. 13 , when a plurality of persons is detected in a frame image of the rear camera  121 B, a person detected in an outside frame region OF are excluded, and a marker may be disposed at the position of a person having high detection accuracy in the frame image excluding the outside frame region OF. Accordingly, the marker G 14  can be prevented from being disposed on the person detected in the outside frame region OF, and the marker G 14  is attached to the specified region in which the necessity for monitoring is high, so that necessary information can be immediately determined. Incidentally, the outside frame region OF is a predetermined region in a frame image, and is, for example, a region other than a part of a frame image to be cut out when an overhead image is generated, namely, a region other than the region of the overhead image, which is not displayed in the overhead image. 
     In addition, when a plurality of persons is detected in a frame image, persons detected outside the caution range may be excluded, and a marker may be disposed at the position of a person having high detection accuracy in the frame image excluding a region outside the caution range. Accordingly, the marker G 14  can be prevented from being disposed on the person detected outside the caution range, and the marker G 14  is attached to the specified person within the caution range, so that necessary information can be immediately determined. In addition, in the above-described embodiment, lines of the frame regions F 1 , F 2 , F 3 , and F 4  have been described as not being displayed in a display image; however, the invention is not limited thereto. For example, in another embodiment, the lines of the frame regions F 1 , F 2 , F 3 , and F 4  may be displayed in a display image. 
     INDUSTRIAL APPLICABILITY 
     According to the above disclosure, the display system can reduce the possibility of overlooking necessary information related to the detection of an obstacle. 
     REFERENCE SIGNS LIST 
     
         
           100 : Work vehicle 
           110 : Undercarriage 
           120 : Swing body 
           121 : Camera 
           130 : Work equipment 
           140 : Cab 
           141 : Operator&#39;s seat 
           143 : Control device 
           211 : Image acquisition unit 
           212 : Feature quantity extraction unit 
           213 : Detection unit 
           214 : Image generation unit 
           215 : Marker disposition unit 
           216 : Presence determination unit 
           217 : Display control unit