Patent Publication Number: US-2021190934-A1

Title: Object-detecting device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is the U.S. bypass application of International Application No. PCT/JP2019/034987, filed on Sep. 5, 2019, which designated the U.S. and claims priority to Japanese Patent Application No. 2018-166853, filed on Sep. 6, 2018, the contents of both of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to a technology for determining axial misalignment of a search wave sensor that searches a detection region in the vicinity of a moving body with a search wave. 
     BACKGROUND 
     A search wave sensor is installed in a moving body such as a vehicle, and the search wave sensor performs irradiation of a detection region in the vicinity of the moving body around a detection axis with a search wave to detect a distance to an object present in the detection region and an orientation of the object relative to the moving body. Misalignment of the detection axis of the search wave sensor causes the orientation of the object to be incorrectly detected, so that it is necessary to determine whether the detection axis of the search wave sensor is misaligned. 
     SUMMARY 
     An object-detecting device in an aspect of the present disclosure includes a first detector, an object tracker, a second detector, and an axial misalignment determiner. 
     The first detector detects, based on detection information acquired from each of a plurality of detection sensors installed in a moving body and having different detection regions for detection targets in a vicinity of the moving body, a distance between the moving body and an object present in the detection region and an orientation of the object relative to the moving body, the detection sensors including at least one search wave sensor that searches the detection region around a detection axis with a search wave. 
     Based on the detection information, the object tracker tracks the same object that passes through the different detection regions as the moving body travels. Based on the detection information, the second detector detects at least either one of a height of the object tracked by the object tracker or a lateral distance between the moving body and the object in a lateral direction as object information. 
     Regarding the same object tracked by the object tracker, the axial misalignment determiner determines whether the detection axis of the search wave sensor is misaligned based on the distance and the orientation of the object detected by the first detector, which are based on the detection information from the search wave sensor and the object information detected in the detection region different from the detection region of the search wave sensor by the second detector. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above features and advantages of the present disclosure will be made clearer by the following detailed description, given referring to the appended drawings. In the accompanying drawings: 
         FIG. 1  is a block diagram showing an object-detecting device; 
         FIG. 2  is a schematic diagram showing a relationship between a detection region of a detection sensor and a position of an object; 
         FIG. 3  is a flowchart showing an axial misalignment determination process; 
         FIG. 4  is a schematic diagram showing determination of axial misalignment based on height information regarding the object; and 
         FIG. 5  is a schematic diagram showing determination of axial misalignment based on lateral distance information regarding the object. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     For example, JP 2015-78925 A describes a technology in which in a case where an object is present in an overlap region where detection regions of a plurality of search wave sensors that search a vicinity of a moving body with a search wave, such as a laser radar, a millimeter-wave radar, and a sonar, overlap, it is determined, based on a position of the object detected in the overlap region by each of the search wave sensors, whether a detection axis of the search wave sensor is misaligned. 
     In the technology described in JP 2015-78925 A, it is to be determined, based on a difference between a correct position of an object detected in the overlap region by a first search wave sensor among the plurality of search wave sensors and a position of the same object detected in the overlap region by a second search wave sensor, whether a detection axis of the second search wave sensor is misaligned. 
     However, as a result of detailed studies by the inventors, it has been found that the technology described in JP 2015-78925 A is disadvantageous in that if no object is present in the overlap region where the detection regions of the plurality of search wave sensors overlap, it cannot be determined whether the detection axis of the search wave sensor is misaligned. 
     An object of the present disclosure is to provide a technology in which axial misalignment of a search wave sensor is determined based on detection information regarding an object passing through non-overlapping detection regions of a plurality of detection sensors including the search wave sensor as a moving body travels. 
     An object-detecting device in an aspect of the present disclosure includes a first detector, an object tracker, a second detector, and an axial misalignment determiner. 
     The first detector detects, based on detection information acquired from each of a plurality of detection sensors installed in a moving body and having different detection regions for detection targets in a vicinity of the moving body, a distance between the moving body and an object present in the detection region and an orientation of the object relative to the moving body, the detection sensors including at least one search wave sensor that searches the detection region around a detection axis with a search wave. 
     Based on the detection information, the object tracker tracks the same object that passes through the different detection regions as the moving body travels. Based on the detection information, the second detector detects, at least either one of a height of the object tracked by the object tracker or a lateral distance between the moving body and the object in a lateral direction as object information. 
     Regarding the same object tracked by the object tracker, the axial misalignment determiner determines whether the detection axis of the search wave sensor is misaligned based on the distance and the orientation of the object detected by the first detector, which are based on the detection information from the search wave sensor and the object information detected in the detection region different from the detection region of the search wave sensor by the second detector. 
     By virtue of such a configuration, axial misalignment of the detection axis of the search wave sensor is determined based on, regarding the same object, the distance and the orientation of the object detected based on the detection information from the search wave sensor and the object information indicating at least either one of the height of the object and the lateral distance between the moving body and the object in the lateral direction detected based on the detection information from the detection sensor different in detection region from the search wave sensor. 
     In other words, an overlap between the detection region of the search wave sensor that detects the distance and the orientation of the object and the detection region of another detection sensor that detects the object information indicating at least either one of the height of the object and the lateral distance of the object is not necessary for determining whether the detection axis of the search wave sensor is misaligned. 
     Therefore, axial misalignment of a search wave sensor can be determined based on detection information regarding an object passing through non-overlapping detection regions of a plurality of detection sensors including the search wave sensor as the moving body travels. 
     An embodiment of the present disclosure will be described below with reference to the drawings. 
     [1. Configuration] 
     An object-detecting device  10  shown in  FIG. 1  is installed in a moving body such as a vehicle or a mobile robot to detect an object present in the vicinity of the moving body. Description will be made below with a vehicle taken as an example of the moving body. 
     The object-detecting device  10  mainly includes a known microcomputer including a CPU, a RAM, a ROM, and a semiconductor memory such as a flash memory, which are not shown. A variety of functions of the object-detecting device  10  are implemented when the CPU executes a computer program stored in a non-transitory tangible storage medium. 
     In the object-detecting device  10  of the present disclosure, the semiconductor memory corresponds to the non-transitory tangible storage medium in which the program is stored. Further, with the program executed, a method corresponding to the program is performed. It should be noted that object-detecting device  10  may include a single microcomputer or a plurality of microcomputers. 
     The object-detecting device  10  includes, as components for a function implemented when the CPU executes the program, a first detector  12 , an object tracker  14 , a second detector  16 , an axial misalignment determiner  18 , and a notification unit  20 . 
     Means for implementing these elements that constitute the object-detecting device  10  is not limited to software and a part or all of the elements may be implemented by a piece of or a plurality of pieces of hardware. For example, in a case where the above-described function is implemented by an electronic circuit, which is hardware, the electronic circuit may be implemented by a digital circuit including a number of logic circuits or an analog circuit or by a combination thereof. 
     The first detector  12  acquires detection information from five millimeter-wave radars  2 , a camera  4 , a LiDAR  6 , and a sonar  8 , that is, detection sensors detection targets of which are different detection regions in the vicinity of the vehicle. LiDAR is an abbreviation for Light Detection and Ranging. The different detection regions do not necessarily refer to regions that do not overlap each other at all and the regions may at least partly overlap. 
     Out of the detection sensors, the five millimeter-wave radars  2  applies electromagnetic waves as a search wave, the LiDAR  6  applies a laser as a search wave, and the sonar  8  applies an ultrasonic wave as a search wave. In other words, the millimeter-wave radars  2 , the LiDAR  6 , and the sonar  8  are search wave sensors. 
     As shown in  FIG. 2 , the five millimeter-wave radars  2  are located at, for example, a front-side middle, front-side right and left, and rear-side right and left of a vehicle  100 , respectively. Detection regions  110  in which the five millimeter-wave radars  2  search the vicinity of the vehicle around respective detection axes  112  partly overlap but are different regions. 
     Thus, in a case where the vehicle  100  travels forward as shown by an arrow  120  in  FIG. 2 , an object  200  present in front of the vehicle  100  passes through the respective detection regions  110  of the millimeter-wave radar  2  at the front-side middle, the millimeter-wave radar  2  at the front-side left, and the millimeter-wave radar  2  at the rear-side left in sequence, being detected by the millimeter-wave radars  2 . The object  200  is a stationary object. It should be noted that the camera  4 , the LiDAR  6 , and the sonar  8  are not shown in  FIG. 2 . 
     The first detector  12  detects a distance between the vehicle  100  and the object  200  present in the detection region  110  in the vicinity of the vehicle  100  and an orientation of the object  200  relative to the vehicle  100  based on the detection information acquired from the above-described various detection sensors. Further, the first detector  12  detects a relative speed of the object  200  relative to the vehicle  100  based on the detection information acquired from the millimeter-wave radars  2 . 
     The object tracker  14  tracks the object  200 , which can be identified as the same object based on the detection information from the detection sensors, with the travel of the vehicle  100 . For example, the object tracker  14  estimates a position of the object  200  reached after the elapse of predetermined time based on the distance to the object  200 , the orientation of the object  200 , and the relative speed, which includes a travel direction, of the object  200  relative to the vehicle  100 . The object tracker  14  then identifies the object  200  present at a position that matches the estimated position of the object  200  reached after the elapse of the predetermined time as the same object  200 . 
     The second detector  16  detects, based on the detection information acquired from the detection sensors, at least either one of a height of the object  200  tracked by the object tracker  14  or a lateral distance between the vehicle  100  and the object  200  in a lateral direction as object information. 
     The axial misalignment determiner  18  determines whether the detection axis of each of the search wave sensors is misaligned based on the distance and the orientation of the object  200  detected by the first detector  12  based on the detection information from the search wave sensor and the object information detected in another detection region different from the detection region of the search wave sensor by the second detector  16 . If an axial misalignment angle of the detection axis of the search wave sensor is equal to or larger than a predetermined angle, the axial misalignment determiner  18  determines that axial misalignment of the search wave sensor has occurred. 
     When the axial misalignment determiner  18  determines that the axial misalignment of the search wave sensor has occurred, the notification unit  20  performs notification of axial misalignment abnormality by showing the axial misalignment on a display, by voice, or the like. 
     [2. Process] 
     Next, description will be made below on an axial misalignment determination process to be performed by the object-detecting device  10  with reference to a flowchart in  FIG. 3 . 
     In S 400 , the axial misalignment determiner  18  determines whether conditions for determination of the axial misalignment of the search wave sensor are satisfied. For example, the axial misalignment determiner  18  determines whether conditions that the vehicle  100  travels straight at a predetermined vehicle speed or more on a road surface of a flat straight road are satisfied as the conditions for determination of the axial misalignment based on image data captured by the camera  4 , detection information acquired from an acceleration sensor, a vehicle speed sensor, and a yaw rate sensor, which are not shown, a current location of the vehicle  100  and map information acquired from a navigation device not shown, or the like. 
     If a determination result is No in S 400 , that is, the conditions for determination of the axial misalignment of the search wave sensor are not satisfied, the process proceeds to S 416 . 
     If the determination result is Yes in S 400 , that is, the conditions for determination of the axial misalignment of the search wave sensor are satisfied, the first detector  12  acquires detection information regarding detection of the different detection regions in the vicinity of the vehicle  100  from the five millimeter-wave radars  2 , the camera  4 , the LiDAR  6 , and the sonar  8  in S 402 . 
     The first detector  12  then, for example, detects a distance R 1  to the object  200  and an orientation θ of the object  200  relative to the vehicle  100  from the detection information from the millimeter-wave radars  2 . The first detector  12  further detects a relative speed Vr of the object  200  relative to the vehicle  100  from the detection information from the millimeter-wave radars  2 . 
     In S 404 , the second detector  16 , for example, detects a height H of the object  200  or a lateral distance L between the vehicle  100  and the object  200  in the lateral direction based on the detection information acquired from the millimeter-wave radar  2  located at the front-side middle of the vehicle  100  as shown in  FIG. 4  or  FIG. 5 . In this case, it is assumed that the axial misalignment of the millimeter-wave radar  2  located at the front-side middle of the vehicle  100  has not occurred. It should be noted that the height of the object  200  may represent either the height of the object  200  existing above the vehicle  100  or the lowness of the object  200  existing below the vehicle  100 . 
     It should be noted that in detecting the height H of the object  200  or the lateral distance L of the object  200 , the use of the detection information acquired from the millimeter-wave radar  2  located at the front-side middle of the vehicle  100  is preferable. This is because the millimeter-wave radar  2  located at the front-side middle of the vehicle  100  can detect the object  200  for an increased number of times by virtue of a long detection distance to the object  200  present in front of the vehicle  100 . 
     An increase in the number of times for which the object  200  can be detected improves accuracy of detection information when the detection information is averaged or the detection information is used with a maximum value and a minimum value excluded. 
     Further, with a plurality of millimeter-wave radars  2  located at the front-side middle of the vehicle  100 , the height H or the lateral distance L of the object  200  can be detected with a high accuracy by calculating an average of the heights H or the lateral distances L of the object  200  based on the detection information acquired from the plurality of millimeter-wave radars  2 . 
     In detecting the height H of the object  200 , it is preferable that the object  200  be present at a level as high as possible or a level as low as possible with respect to the vehicle  100 . This is because in determining whether axial misalignment of the millimeter-wave radar  2  in a vertical direction has occurred based on the height H of the object  200  in later-described S 410 , accuracy in estimating an angle of the object  200  in the vertical direction is improved when the object  200  is present at a level as high as possible or a level as low as possible with respect to the vehicle  100 . 
     Further, in detecting the height H of the object  200 , it is preferable that the object  200  be present within a vehicle width of the vehicle  100 . This is because a reduction in influence of the angle of the object  200  in the lateral direction on the vehicle  100  as much as possible results in an improvement in accuracy in estimating the angle of the object  200  in the vertical direction. 
     In view of the above, in detecting the height H of the object  200 , it is preferable that the object  200  be a guide sign or a manhole located on a road where the vehicle  100  travels. 
     The height H or the lateral distance L of the object  200  is calculated as follows. First, when Vr denotes the relative speed of the object  200  detected by the millimeter-wave radar  2 , V denotes the vehicle speed of the vehicle  100 , and θ1 denotes an angle in the vertical direction or the lateral direction as the orientation of the object  200  relative to the vehicle  100 , the relative speed Vr of the object  200  is represented by the following expression (1) and the angle θ1 is represented by the following expression (2). 
         Vr=−V  cos θ1  (1)
 
       θ1=cos −1 (− Vr/V )  (2)
 
     Further, when R 1  denotes the distance between the vehicle  100  and the object  200  detected by the millimeter-wave radar  2 , the height H of the object  200  is represented by the following expression (3) and the lateral distance L is represented by the following expression (4) from the distance R 1  and the angle θ1 represented by the expression (2). 
       H=R1 sin θ1  (3)
 
       L=R1 cos θ1  (4)
 
     In S 406 , the object tracker  14  estimates the position of the object  200  reached after the elapse of the predetermined time based on the distance to the object  200  and the orientation of the object  200  and the relative speed of the object  200  relative to the vehicle  100 . The object tracker  14  then identifies the object  200  present at a position matching the estimated position of the object  200  reached after the predetermined time as the same object  200 . The object  200  detected in the different detection region  110  by the different detection sensor with the travel of the vehicle  100  can be identified as the same object  200 . 
     Next, in S 408 , as shown in  FIG. 4  or  FIG. 5 , the axial misalignment determiner  18  estimates the orientation of the object  200  relative to the vehicle  100  based on the height H or the lateral distance L of the object  200  detected in S 404  and a distance R 2  to the object  200  detected by one of the millimeter-wave radars  2  that is different in detection region  110  from the millimeter-wave radar  2  that detects the height H or the lateral distance L of the object  200  in S 404  and in which axial misalignment has not occurred. 
     For example, as shown in  FIG. 4 , the axial misalignment determiner  18  estimates an angle θ2 of the object  200  in the vertical direction relative to the vehicle  100  by calculating it from the following expression (5) based on the height H of the object  200  determined from the detection information from the millimeter-wave radar  2  located at the front-side middle of the vehicle  100  by using the expression (3) and the distance R 2  to the object  200  detected from the detection information from the millimeter-wave radar  2  located at the rear-side left of the vehicle  100 . 
       θ2=sin 1 ( H/R 2)  (5)
 
     In the expression (5), the height H is calculated from the expression (3) with a high accuracy. Further, the millimeter-wave radar  2  located at the rear-side left of the vehicle  100  can correctly detect the distance R 2  irrespective of whether the detection axis  112  is misaligned. Therefore, the angle θ2 in the vertical direction estimated from the expression (5) is correct. 
     If the object  200  passes through the detection region  110  of the millimeter-wave radar  2  located at the front-side left, the distance R 2  to the object  200  detected from the detection information from the millimeter-wave radar  2  located at the front-side left of the vehicle  100  may be used in the expression (5). 
     Further, as shown in  FIG. 5 , the axial misalignment determiner  18  estimates an angle θ2 of the object  200  in the lateral direction relative to the vehicle  100  by calculating it from the following expression (6) based on the lateral distance L of the object  200  determined from the detection information from the millimeter-wave radar  2  located at the front-side middle of the vehicle  100  by using the expression (4) and the distance R 2  to the object  200  detected from the detection information from the millimeter-wave radar  2  located at the rear-side left of the vehicle  100 . 
       θ2=cos −1 ( L/R 2)  (6)
 
     In expression (6), the lateral distance L is calculated from the expression (4) with a high accuracy. Further, the millimeter-wave radar  2  located at the rear-side left of the vehicle  100  can correctly detect the distance R 2  irrespective of whether the detection axis  112  is misaligned. Therefore, the angle θ2 in the lateral direction estimated from the expression (6) is correct. 
     If the object  200  passes through the detection region  110  of the millimeter-wave radar  2  located at the front-side left, the distance R 2  to the object  200  detected from the detection information from the millimeter-wave radar  2  located at the front-side left of the vehicle  100  may be used in the expression (6). 
     In S 410 , the axial misalignment determiner  18  determines whether an axial misalignment angle β defined by a difference between the angle θ2 of the object  200 , which is estimated from the expression (5) or (6) and shown in  FIG. 4  or  FIG. 5 , and an angle α of an object detected from the detection information from the millimeter-wave radar  2  located at the rear-side left of the vehicle  100  is equal to or larger than a predetermined angle. In other words, the axial misalignment determiner  18  determines whether the detection axis  112  of the millimeter-wave radar  2  located at the rear-side left of the vehicle  100  is misaligned. 
     If a determination result is No in S 410 , that is, the detection axis  112  of the millimeter-wave radar  2  located at the rear-side left of the vehicle  100  is not misaligned, the process proceeds to S 416 . 
     If the determination result is Yes in S 410 , that is, the detection axis  112  of the millimeter-wave radar  2  located at the rear-side left of the vehicle  100  is misaligned, the axial misalignment determiner  18  determines whether axial misalignment of the millimeter-wave radar  2  located at the rear-side left of the vehicle  100  has occurred for a predetermined number of times or more in S 412 . 
     If a determination result is No in S 412 , that is, the number of times for which the axial misalignment of the millimeter-wave radar  2  located at the rear-side left of the vehicle  100  has occurred is less than the predetermined number of times, the process proceeds to S 416 . 
     If the determination result is Yes in S 412 , that is, the axial misalignment of the millimeter-wave radar  2  located at the rear-side left of the vehicle  100  has occurred for the predetermined number of times or more, the notification unit  20  records the fact that the axial misalignment of the millimeter-wave radar  2  located at the rear-side left of the vehicle  100  has occurred as diagnosis information and performs notification of axial misalignment abnormality by showing the axial misalignment on the display, by voice, or the like in S 414 . 
     The process from S 400  to S 414  is continued until an ignition switch or the like is turned off and termination of the axial misalignment determination process is determined in S 416 . 
     The object-detecting device  10  corrects an orientation of an object detected by the millimeter-wave radar  2  in which the detection axis  112  is misaligned with the axial misalignment angle β calculated in S 410 , thereby detecting the orientation of the object. 
     [3. Effects] 
     The above-described embodiment can achieve the following effects. 
     (1) The object-detecting device  10  estimates, based on the height H or the lateral distance L of the object  200  detected in the detection region  110  of a normal one of the millimeter-wave radars  2  in which axial misalignment has not occurred and the distance to the object  200  detected by another millimeter-wave radar  2  different in detection region  110  from the normal one of millimeter-wave radars  2 , the orientation of the object  200  in the vertical direction or the lateral direction relative to the other millimeter-wave radar  2 . The object-detecting device  10  determines whether axial misalignment of the other millimeter-wave radar  2  has occurred based on a difference between the estimated orientation and the orientation of the object  200  detected by the other millimeter-wave radar  2 . 
     This enables determining whether axial misalignment of the millimeter-wave radar  2  has occurred based on the detection information from the normal one of the millimeter-wave radars  2  in which axial misalignment has not occurred even in a case where there is no overlap between the detection regions of the plurality of millimeter-wave radars  2 . 
     (2) The axial misalignment determiner  18  determines whether axial misalignment of the millimeter-wave radar  2  has occurred when the vehicle  100  travels on a flat straight road at a predetermined vehicle speed or more, which makes it possible to reduce a variation in detection accuracy among the detection sensors including the millimeter-wave radars  2 . As a result, it is possible to determine whether axial misalignment of the millimeter-wave radar  2  has occurred with a high accuracy based on the detection information from the detection sensors with a less variation. 
     In the above-described embodiment, the millimeter-wave radars  2 , the camera  4 , the LiDAR  6 , and the sonar  8  correspond to the detection sensors, the millimeter-wave radars  2 , the LiDAR  6 , and the sonar  8  among the detection sensors correspond to the search wave sensors, and the vehicle  100  corresponds to the moving body. 
     Further, S 402  corresponds to a process of the first detector  12 , S 404  corresponds to a process of the second detector  16 , S 406  corresponds to a process of the object tracker  14 , S 408  to S 412  correspond to a process of the axial misalignment determiner  18 , and S 414  corresponds to a process of the notification unit  20 . 
     [4. Other Embodiments] 
     Although the embodiment of the present disclosure is described above, the present disclosure is not limited to the above-described embodiment and may be implemented with a variety of modifications. 
     (1) In the above-described embodiment, the height H or the lateral distance L of the object  200  is detected based on the detection information from normal one of the millimeter-wave radars  2  in which axial misalignment has not occurred. In this regard, the height H or the lateral distance L of the object  200  may be detected by any one of the normal camera  4 , LiDAR  6 , and the sonar  8 . 
     (2) A target for determining whether axial misalignment has occurred, i.e., the search wave sensor that searches the vicinity of the vehicle  100  with a search wave, is not limited to the millimeter-wave radar  2  and may be the LiDAR  6  or the sonar  8 . 
     (3) A plurality of functions of one component in the above-described embodiment may be implemented by a plurality of components and one function of one component may be implemented by a plurality of components. In addition, a plurality of functions of a plurality of components may be implemented by one component and one function implemented by a plurality of components may be implemented by one component. In addition, the configuration of the above-described embodiment may be partly omitted. In addition, at least a part of the configuration of the above-described embodiment may be added to or replaced with the configuration of another above-described embodiment. It should be noted that any mode included in a technical idea determined from wordings in claims should be an embodiment of the present disclosure. 
     (4) The present disclosure can be implemented in various forms such as, in addition to the above-described object-detecting device  10 , a system including the object-detecting device  10  as a component, a program for enabling a computer to function as the object-detecting device  10 , a non-transitory substantive recording medium storing the program, and an object detection method.