Abstract:
An autonomous moving machine system continuously maintaining moving machines thereof at higher reliability is provided. Each moving machine measures a self-location thereof with a sensor thereof, and autonomously moves to a target location by controlling a mover. Operations of the moving machine includes acquiring sensor information, estimating the self-location in accordance with the sensor information, calculating the reliability of the self-location, transmitting the reliability to the other moving machine. Operations of a particular moving machine further includes recording history information that associates the reliability, the self-location, and an identifier identifying each of the moving machines, selecting a moving machine to restore the reliability in accordance with the history information and moving the selected moving machine to a location where the reliability of the selected moving machine increases.

Description:
BACKGROUND 
     1. Technical Field 
       [0001]    The present disclosure relates to an autonomous moving machine system that includes multiple moving machines, each moving machine autonomously moving to a target location by measuring a self-location with a sensor thereof and by controlling a mover. 
       2. Description of the Related Art 
       [0002]    Moving machines are disclosed that autonomously and individually move to a target location while detecting a self-location thereof using a variety of sensors. Such a moving machine is unable to reach a predetermined location and then to accomplish a target job there if the moving machine fails to acquire the self-location. 
         [0003]    Japanese Unexamined Patent Application Publication No. 2014-149622 discloses an autonomous flying robot that independently and autonomously moves while acquiring a self-location in accordance with memorized map information including information concerning obstacles, such as buildings, and measurement results of a sensor. If a relatively large obstacle, such as a truck, appears, an ambient environment may greatly change, possibly causing the autonomous flying robot to be unable to acquire the self-location. In such a case, the autonomous flying robot re-acquires the self-location by increasing a flying height and then performs a target job. 
         [0004]    Japanese Unexamined Patent Application Publication No. 2006-300700 discloses another technique. According to the disclosure, multiple moving machines receive information related to self-locations through communication. The moving machines are divided by role. A first type of moving machine is able to acquire the absolutely accurate self-location thereof using satellites. A second type of moving machine acquires the self-location thereof, based on a relative positional relationship with the first type of moving machine. The second type of moving machine that is unable to directly acquire an absolute self-location is able to perform a job, based on the absolute self-location. 
         [0005]    The re-acquisition technique disclosed in Japanese Unexamined Patent Application Publication No. 2014-149622 is not applicable to a moving machine that runs on the ground. If there is a bridge or a power-transmission line in the air, it may be difficult to fly the moving machine high above. 
         [0006]    In accordance with the technique disclosed in Japanese Unexamined Patent Application Publication No. 2006-300700, if multiple moving machines are present in a wide area, multiple moving machines designed to acquire absolute self-locations may be needed. When an infrastructure inspection job is performed, the use of the moving machines that include a dedicated moving machine that is designed to acquire an absolute self-position leads to an inefficient job. Increasing the efficiency of the job using all moving machines is considered to be difficult. 
         [0007]    Even if these techniques are combined, it is still difficult to operate the multiple moving machines in an efficient way. 
       SUMMARY 
       [0008]    One non-limiting and exemplary embodiment provides an autonomous moving machine system that efficiently operates multiple moving machines. 
         [0009]    In one general aspect, the techniques disclosed here feature an autonomous moving machine system. The autonomous moving machine system includes multiple moving machines. Each moving machine autonomously moves to a target location by measuring a self-location thereof with a sensor and by controlling a mover. The moving machine includes a sensor information acquisition unit that acquires sensor information related to the self-location and including a relative positional relationship between the sensor and another moving machine, a position estimating unit that estimates the self-location in accordance with the sensor information acquired by the sensor information acquisition unit, a reliability calculating unit that calculates the reliability of the self-location estimated by the position estimating unit, a moving machine information communication unit that exchanges retention information stored thereon with other moving machines, a position reliability recording unit that records in an associated form the reliability calculated by the reliability calculating unit, the self-location estimated by the position estimating unit, and an identifier identifying each moving machine, a reliability restoring moving machine selecting unit that selects, based on information stored on the position reliability recording unit, the moving machine that takes a reliability restoring action, and a reliability restoring action control unit that controls the mover such that the moving machine selected by the reliability restoring moving machine selecting unit moves to a location having higher reliability. 
         [0010]    According to the disclosure, a moving machine that moves to a location where a self-location is acquired at higher reliability is selected from a group of multiple moving machines, and selection results are shared among the moving machines. The group of moving machines may thus autonomously move while stably acquiring the self-locations at high reliability. In this way, the moving machines are efficiently operated. 
         [0011]    Additional benefits and advantages of the disclosed embodiments will become apparent from the specification and drawings. The benefits and/or advantages may be individually obtained by the various embodiments and features of the specification and drawings, which need not all be provided in order to obtain one or more of such benefits and/or advantages. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a perspective view of a moving machine in an autonomous moving machine system of a first embodiment; 
           [0013]      FIG. 2  is a block diagram illustrating part of functional units of each moving machine in the autonomous moving machine system of the first embodiment together with part of mechanical units of the moving machine; 
           [0014]      FIG. 3  visually illustrates an example of data stored on a memory; 
           [0015]      FIG. 4  is a flowchart illustrating a process of a reliability restoring moving machine selecting unit; 
           [0016]      FIG. 5  is a perspective view three-dimensionally illustrating a positional distribution of reliability centered on a self-location; 
           [0017]      FIG. 6  is a block diagram illustrating functional units of the moving machine in an autonomous moving machine system of a second embodiment; 
           [0018]      FIG. 7  is a perspective view of the autonomous moving machine system that performs bridge inspection; and 
           [0019]      FIG. 8  is a block diagram illustrating functional units of the moving machine in an autonomous moving machine system of another embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    Autonomous moving machine systems of embodiments of the disclosure is described with reference to the drawings. The embodiments described below are examples of the moving machine of the disclosure. The embodiments are described for reference purposes, and the scope of the disclosure is not limited by the embodiments but is limited by the claims. Elements in the embodiment not described in an independent claim that indicates a generic concept are not necessarily needed to achieve the object of the disclosure but are used to form a more preferable configuration. 
         [0021]    The drawings are highlighted, partially omitted, and diagrammatically adjusted in size ratio to indicate the disclosure, and may be different from real shapes, positional relationship, and size ratio. 
       First Embodiment 
       [0022]    A first embodiment of the disclosure is described below. The first embodiment is related to an autonomous flying object, so-called drone, as a moving machine  100  in an autonomous moving machine system  110 . 
         [0023]      FIG. 1  is a perspective view of the moving machine  100  in the autonomous moving machine system  110  of the first embodiment. 
         [0024]      FIG. 2  is a block diagram illustrating part of functional units of each moving machine  100  in the autonomous moving machine system  110  of the first embodiment together with part of mechanical units of the moving machine. 
         [0025]    Referring to  FIG. 1  and  FIG. 2 , the moving machine  100  includes multiple rotors (propellers)  111  as the mover  101 , multiple motors  112  that respectively drive the rotors  111 , a sensor  103  that acquires the self-location thereof, and a control apparatus  104  that acquires a signal from the sensor  103  and controls autonomous movement by controlling the motors  112 . 
         [0026]    The drone-type moving machine  100  including the multiple rotors  111  individually control the rotational speeds of the rotors  111 , thereby moving the moving machine  100  in a variety of directions (left and right, up and down, back and forth), and adjusting the posture thereof. In accordance with the first embodiment, the control apparatus  104  also acquires from the mover  101 , as sensor information, information concerning a control state of the rotational speed of the rotor  111 , and uses the sensor information as part of information that is used to estimate the self-location of the moving machine  100 . 
         [0027]    Any particular device is acceptable as the sensor  103  as long as the device acquires information that estimates the self-location through measurement. More specifically, the sensor  103  may be an inertia measurement unit (IMU) that detects angles and speed thereof in three axial directions, and acceleration in the three axial directions, a pressure meter (altimeter), a flowmeter (anemometer), a global positioning system (GPS) receiver, a laser range finder (LRF), or a depth camera. The sensor  103  may also include a device that acquires, as the sensor information, information related to a relative positional relationship between the self-location and the location of another moving machine  100 . For example, the LRF may be used to acquire, as the sensor information, relative position information that indicates a relative positional relationship of the moving machine  100  with another moving machine  100  present in the ambient space. 
         [0028]    The moving machine  100  may include one or more of several types of sensors  103 . The sensor  103  that is to be mounted is selected depending on the type, purpose of movement, and target location of the moving machine  100 . 
         [0029]    The control apparatus  104  moves the host moving machine  100  by controlling the mover  101  in response to the information acquired from the sensor  103  or another moving machine  100  as illustrated in  FIG. 2 . In other words, the control apparatus  104  is a computer including a central processing unit (CPU) and performs a variety of processes by executing a program stored on a memory  140 . The control apparatus  104  includes, as processing units that are executed by executing the program, a sensor information acquisition unit  141 , a position estimating unit  142 , a position reliability calculating unit  143 , a position reliability recording unit  144 , a reliability restoring action control unit  145 , a reliability restoring moving machine selecting unit  147 , and a moving machine information communication unit  148 . 
         [0030]    In accordance with the first embodiment, each moving machine  100  includes the control apparatus  104 . The moving machine  100  is autonomously moved by the control apparatus  104 . The moving machine  100  also moves while recognizing a relative relationship with another moving machine  100 . 
         [0031]    The memory  140  may be an information storage device, such as a read-only memory (ROM), or a hard disk drive (HDD). The control apparatus  104  stores the self-location and a program corresponding to each process. The memory  140  also stores position information of a target location, and map information indicating a path and an obstacle. 
         [0032]    The sensor information acquisition unit  141  is a processor that acquires a signal t measured by the sensor  103  as the sensor information used to estimate the self-location. The sensor information acquisition unit  141  also acquires, as the sensor information, information acquired from the mover  101 , for example, control information such as the rotational speed of each of the rotors  111 . The sensor information acquisition unit  141  further acquires, as the sensor information, a relative positional relationship with the other moving machines  100 . 
         [0033]    The position estimating unit  142  is a processor that estimates as the self-location the present position of the moving machine  100 , based on at least a piece of sensor information and a relationship between the sensor information and the self-location of another moving machine  100  acquired from the other moving machine  100 . In accordance with the first embodiment, the position estimating unit  142  calculates a location as results that the sensor  103  has actually measured, based on multiple pieces of sensor information. The position estimating unit  142  acquires the self-location of the other moving machine  100  from the other moving machine  100 , calculates the measurement location from the sensor information indicating the relative position information related to the other moving machine  100 , and estimates the self-location by combining the measurement locations. 
         [0034]    The method of estimating the self-location is not limited to any particular one. For example, a Kalman filter may be used to estimate the self-location, based on a measurement location that is calculated from a signal received from GPS satellites, and a measurement location calculated from sensor information acquired from an inertial measurement device. Simultaneous localization and mapping (SLAM) may be used to estimate the self-location, based on a measurement location that is calculated by checking sensor information from a depth camera against the map information stored on the memory  140  and a measurement location that is calculated from the sensor information from the inertial measurement device. 
         [0035]    If the Kalman filter is used as the position estimating unit  142 , the self-location is represented as the normal distribution. The variance of the normal distribution increases in response to elapsed time or an amount of travel from last observation of an absolute position and decreases by observing the absolute position. More specifically, the reliability value increases in response to the elapsed time or the amount of travel from the last observation of the absolute position and decreases by observing the absolute position. The observation of the absolute position may be performed through position fixing using the GPS, or by observing a landmark whose position is known. 
         [0036]    The position reliability calculating unit  143  is a processor that calculates the reliability value of the self-location, based on the reliability value of the sensor  103  itself that performs measurement, the reliability value that decreases with time, and an error in the sensor information that is used to estimate the self-location. In accordance with the first embodiment, when the position estimating unit  142  estimates the self-location, based on the measurement location indicating the relative positional relationship with the other moving machine  100  and the self-location of the other moving machine  100 , the position reliability calculating unit  143  calculates the reliability value in combination with the reliability value of the other moving machine  100  that is acquired from the other moving machine  100  via the moving machine information communication unit  148 . 
         [0037]    The calculation method of the reliability value performed by the position reliability calculating unit  143  may include using a distribution (such as the normal distribution) that is used when the position estimating unit  142  estimates the self-location and calculating as the reliability value a reciprocal of the variance of the distribution. 
         [0038]    The moving machine information communication unit  148  transmits retention information stored thereon to another moving machine  100  included in the autonomous moving machine system  110 . 
         [0039]    The retention information includes the self-location, the reliability value of the self-location, the absolute location of the other moving machine  100 , the reliability value of the absolute location, the relative positional relationship between the self-location and the other moving machine  100 , and the reliability value of the relative positional relationship. The retention information, if retained by the moving machine  100 , may be the sensor information acquired by the sensor information acquisition unit  141 , or the signal from the sensor  103 . 
         [0040]    The following items of information may be combined as the retention information the moving machine information communication unit  148  transmits or receives. (1) Self-location and the reliability value thereof, (2) absolute location of the other moving machine  100  and the reliability value thereof, (3) relative position between the self-location and the other moving machine  100 , and the reliability value thereof. In accordance with the first embodiment, the moving machine information communication unit  148  transmits and receives signals via radio communication such that the moving machines  100  share with the other moving machine  100  the retention information including the self-locations and the reliability value thereof. 
         [0041]    The position reliability recording unit  144  is a processor that records on the memory  140  the self-location (coordinates) estimated by the position estimating unit  142  and the reliability value calculated by the position reliability calculating unit  143  with the self-location and the reliability value in association with each other. In accordance with the first embodiment as illustrated in  FIG. 3 , the position reliability recording unit  144  stores on the memory  140  time information in association with the self-location and the reliability. Furthermore, time information, the self-location (coordinates), and the reliability value, transmitted from another moving machine  100 , are stored in association with an identity (id) on the memory  140 . The time information is information indicating time when the position estimating unit  142  estimates the self-location. Referring to  FIG. 3 , an identification symbol is attached to information related to time and coordinates, other than the reliability, for identification. The identification symbol has no specific meaning, and different identification symbols could represent the same coordinates. 
         [0042]    The reliability restoring moving machine selecting unit  147  is a processor that selects a moving machine  100  that is to perform a reliability restoring action in response to information recorded by the position reliability recording unit  144 . In accordance with the first embodiment, each moving machine  100  in the autonomous moving machine system  110  includes the reliability restoring moving machine selecting unit  147 . If the host moving machine  100  satisfies a predetermined condition, the host moving machine  100  selects itself as a moving machine  100  to restore the liability of the whole autonomous moving machine system  110 . 
         [0043]      FIG. 4  is a flowchart illustrating a process of the reliability restoring moving machine selecting unit  147 . 
         [0044]    Referring to  FIG. 4 , the reliability restoring moving machine selecting unit  147  determines whether the reliability value of the whole autonomous moving machine system  110  satisfies a predetermined condition (S 101 ). The evaluation of the overall reliability is performed based on the reliability value of each moving machine  100  stored on the memory  140 . If the whole autonomous moving machine system  110  does not satisfy the predetermined condition (no branch from S 101 ), a standard job continues. The standard job includes a job of the moving machine  100  to move to a target location, and a job of performing an inspection operation at the target location. 
         [0045]    Examples (patterns) of a specific determination method that is performed when the overall reliability satisfies the predetermined condition are described below. 
         [0046]    1.1 The reliability restoring moving machine selecting unit  147  reads from the memory  140  the reliability value of the host moving machine  100  and the reliability value of another moving machine  100 , and performs a statistical operation on the read reliability values, and calculates the variance at each time point. If the calculated variance continues to be equal to or above a first threshold value for a first threshold duration of time, the reliability restoring moving machine selecting unit  147  proceeds to an operation (S 103 ) to select a moving machine  100  that is to perform the reliability restoring action. 
         [0047]    All the moving machines  100  are determined to be in a state that merely causing the moving machines  100  to mutually observe a positional relationship therebetween and to share observation results through communication is not sufficient to uniformly increase all reliability values. 
         [0048]    1.2 The reliability restoring moving machine selecting unit  147  proceeds to an operation (S 103 ) to select a moving machine  100  that is to take a reliability restoring action if a difference between a minimum value and a maximum value of the reliability values of all the moving machines  100  continues to be equal to or above a first threshold value for a first threshold duration of time. 
         [0049]    In such a case, the same is true, again. All the moving machines  100  are determined to be in a state that merely causing the moving machines  100  to mutually observe a positional relationship therebetween and to share observation results through communication is not sufficient to uniformly increase all reliability values. 
         [0050]    1.3 The reliability restoring moving machine selecting unit  147  statistically processes the reliability values of all moving machines  100 . If at least one of the maximum value, mean value, and median thus acquired is lower than a second threshold value, the reliability restoring moving machine selecting unit  147  proceeds to the operation (S 103 ) to select the moving machine  100  that is to take the reliability restoring action. 
         [0051]    All the moving machines  100  are determined to be in a state that all reliability values are not uniformly increased even if the moving machines  100  measure relative locations and communicate with each other. 
         [0052]    1.4 The reliability restoring moving machine selecting unit  147  statistically processes the reliability values of all moving machines  100 , and compares at least one of the resulting maximum value, mean value, and median with the corresponding type of value immediately preceding thereto. If the difference is equal to or above a third threshold value, the reliability restoring moving machine selecting unit  147  determines that all the reliability values sharply drop and then proceeds to the operation (S 103 ) to select a moving machine  100  that is take the reliability restoring action. 
         [0053]    In such a case, multiple moving machines  100  are determined to be losing track of the self-locations in response to a disturbance, such as a blast of wind. 
         [0054]    The moving machine  100  that is to take the reliability restoring action is selected in accordance with information recorded by the position reliability recording unit  144  (S 103 ). 
         [0055]    Listed below are examples (patterns) of selection conditions when the moving machine  100  that is to take the reliability restoring action is selected. In accordance with the first embodiment, each moving machine  100  including the reliability restoring moving machine selecting unit  147  determines whether the selection condition described below is satisfied. If the moving machine  100  determines that the selection condition is satisfied (yes branch from S 103 ), the moving machine  100  autonomously takes a reliability restoring action (S 104 ). If the moving machine  100  determines that the selection condition is not satisfied (no branch from S 103 ), the moving machine  100  continues a standard job. 
         [0056]    2.1 The reliability restoring moving machine selecting unit  147  selects the moving machine  100  that is to take the reliability restoring action in response to the reliability value. For example, the reliability restoring moving machine selecting unit  147  selects a moving machine  100  having a lowest reliability value as the moving machine  100  that is to take the reliability restoring action. The selection condition is applicable if the variance of the reliability values of all the moving machines  100  continues to be equal to or above a first threshold value for a first threshold duration of time, or if a difference between a minimum value and a maximum value of the reliability values of all the moving machines  100  continues to be equal to or above the first threshold value for the first threshold duration of time. 
         [0057]    In accordance with the first embodiment, the latest reliability values of the other moving machines  100  acquired by the moving machine information communication unit  148  are compared with the latest reliability value of the host moving machine  100 . If the reliability value of the host moving machine  100  is equal to or lower than the reliability values of the other moving machines  100 , the host moving machine  100  autonomously starts the reliability restoring action (S 104 ). 
         [0058]    2.2 The reliability restoring moving machine selecting unit  147  selects the moving machine  100  that is to take the reliability restoring action depending on battery remaining power of a battery that feeds power to the moving machine  100 . For example, a moving machine  100  having highest remaining battery power may be selected as the moving machine  100  that is to take the reliability restoring action. The selection condition is applicable if at least one of the maximum value, the mean value, and the median of all the reliability values of the moving machines  100  is lower than a second threshold value. Since this method makes battery remaining power values of the moving machines  100  uniform, a long operation time may be ensured. 
         [0059]    In accordance with the first embodiment, the moving machine information communication unit  148  communicates information indicating battery remaining power in addition to the self-location and the reliability value o the other moving machines  100  to share these pieces of information. Each moving machine  100  compares the latest battery remaining power thereof with the latest remaining power of the other moving machines  100 . If there is no other moving machine  100  having remaining battery power higher than the remaining battery power of the moving machine  100 , the moving machine  100  autonomously starts the reliability restoring action (S 104 ). 
         [0060]    2.3 The reliability restoring moving machine selecting unit  147  selects a moving machine  100  in accordance with the reliability value. For example, the reliability restoring moving machine selecting unit  147  selects a moving machine  100  having a highest reliability value as the moving machine  100  that is to take the reliability restoring action. The selection condition is applicable if at least one of the maximum value, the mean value, and the median of all the reliability values of the moving machines  100  is lower than the second threshold value. 
         [0061]    In accordance with the first embodiment, the moving machine information communication unit  148  compares the latest reliability value of the moving machine  100  with the latest reliability values of the other moving machines  100  acquired by the moving machine information communication unit  148 . If there is no other moving machine  100  having the reliability value higher than the reliability value of the moving machine  100 , the moving machine  100  autonomously starts the reliability restoring action (S 104 ). 
         [0062]    2.4 The reliability restoring moving machine selecting unit  147  selects a moving machine  100  closest to a region having the highest reliability value as the moving machine  100  that is to take the reliability restoring action. The selection condition is applicable if at least one of the maximum value, the mean value, and the median of all the reliability values of the moving machines  100  is lower than the second threshold value. In this case, an amount of energy for the reliability restoring action is minimized, and time for the reliability restoring action is shortened. 
         [0063]    In accordance with the first embodiment, each moving machine  100  collects the reliability values of all the moving machines  100  from the memory  140 , and searches for a region having the highest reliability value. The moving machine  100  calculates the Euclidean distance between coordinates of the region having the highest reliability value and the self-location of another moving machine  100 , and compares the calculated Euclidean distance with the Euclidean distance between the coordinates of the region having the highest reliability value and the self-location. If there is no Euclidean distance that is shorter than the Euclidean distance between the coordinates of the region having the highest reliability value and the self-location, the moving machine  100  autonomously starts the reliability restoring action (S 104 ). 
         [0064]    Examples (patterns) of specific control methods of the reliability restoration by the moving machine  100  selected by the reliability restoring moving machine selecting unit  147  are described below. 
         [0065]    The reliability restoring action control unit  145  is a processor that controls the mover  101  such that the moving machine  100  selected by the reliability restoring moving machine selecting unit  147  moves to a location having a higher reliability value in response to information recorded on the position reliability recording unit  144 . 
         [0066]    3.1 The reliability restoring action control unit  145  controls the mover  101  in response to the reliability value stored on the memory  140  such that the moving machine  100  successively moves along the self-locations recorded on the memory  140  until the reliability value is equal to or above a predetermined threshold value (S 104 ). 
         [0067]    The control method is described with reference to data of  FIG. 3 . It is assumed that the present time is 6, the threshold value is 0.8, and the identifier indicating the selected moving machine  100  is 1001. By controlling the mover  101 , the reliability restoring action control unit  145  moves the moving machine  100  such that the moving machine  100  is routed along G (reliability value of 0.3)=F (reliability value of 0.5)=E(reliability value of 0.6)→D(reliability value of 0.8). More specifically, the moving machine  100  changes back to the one that has selected the path that reaches coordinates having the reliability value equal to or above the threshold value. 
         [0068]    The self-location is then re-estimated at a coordinate location having a higher reliability value. Using the moving machine  100 , another moving machine  100  estimates the self-location thereof again, thereby increasing the reliability values of all the moving machines  100 . 
         [0069]    The reliability restoring action described above is effective when the moving machine  100  moves in a given space for the first time, or when the reliability values sharply drops because of an occurrence of sudden wind. 
         [0070]    3.2 The reliability restoring action control unit  145  controls the mover  101  such that the moving machine  100  moves to a location that is closest to the current location and where the reliability value stored on the memory  140  is equal to or above a predetermined threshold value. 
         [0071]    More specifically, as illustrated in  FIG. 5 , the memory  140  stores coordinate locations that are present in an ambient area centered on the self-location of the moving machine  100  selected when the reliability value satisfies the predetermined condition (present time  6 ) (at up and down, back and forth, and left and right positions) and that have the reliability value equal to or above the first threshold value (0.8). Those coordinate locations may be A, C, and D, for example, and extracted from the reliability values of all the moving machines  100  according to the information stored on the memory  140 . The Euclidean distance between each coordinate location and the current self-location is calculated. The mover  101  is controlled such that the moving machine  100  linearly moves to a coordinate location having the shortest Euclidean distance (D, for example). The moving machine  100  thus reaches the coordinate location D. 
         [0072]    The moving machine  100  reaches the coordinate location having the highest reliability value within a short period of time. The moving machine  100  estimates the self-location at the coordinate location again, and may shift to an action to perform a standard job within a short period of time. 
         [0073]    Such a reliability restoring action is effective when the moving machine  100  performs an inspection operation within a narrow area. 
         [0074]    3.3 The reliability restoring action control unit  145  controls the mover  101  such that the moving machine  100  moves to a location where a selected moving machine  100  has a past reliability value equal to or above a predetermined threshold value and that is associated with time information having time closest to the present time. 
         [0075]    The control method is described with reference to data of  FIG. 3 . It is assumed that the present time is 6, and the threshold value is 0.8. The reliability restoring action control unit  145  checks the reliability values at id 1001 along time series 6 (reliability value 0.3)→5 (reliability value 0.5)→4 (reliability value 0.6)→3 (reliability value 0.8), and controls the mover  101  such that the moving machine  100  moves to a coordinate location having a reliability value equal to or above the threshold value, namely, the coordinate location (D). The moving machine  100  thus moves to the coordinate location D. 
         [0076]    As described above, the moving machine  100  reaches the coordinate location having the highest reliability value within a short period of time. The moving machine  100  estimates the self-location at the coordinate location again, and may shift to an action to perform a standard job within a short period of time. 
         [0077]    Such a reliability restoring action is effective when the moving machine  100  moves within a wide space with a small number of obstacles. 
       Second Embodiment 
       [0078]    An autonomous moving machine system  110  of a second embodiment of the disclosure is described below. Elements identical in operation, function, shape, mechanism, and structure to those of the first embodiment are designated with the same reference numerals, and the discussion thereof is omitted. The following discussion focuses on a difference between the first embodiment and the second embodiment, and the same discussion is not repeated. 
         [0079]      FIG. 6  is a block diagram illustrating functional units of the moving machine in an autonomous moving machine system of the second embodiment. 
         [0080]    The autonomous moving machine system  110  of the second embodiment includes as moving machines  100  a master moving machine  100 M including a reliability restoring moving machine selecting unit  147  in control apparatus  104  and a slave moving machine  100 S that moves in response to a command from the master moving machine  100 M. 
         [0081]    The master moving machine  100 M collects the self-locations and reliability values of all the moving machines  100  via the moving machine information communication unit  148 . In a similar way to the first embodiment or in response to a determination result described below, the reliability restoring moving machine selecting unit  147  in the master moving machine  100 M selects a moving machine  100  that is to take the reliability restoring action. 
         [0082]    Described below are examples (patterns) of selection conditions according to which the moving machine  100  to perform a reliability restoring action different from the reliability restoring action of the first embodiment is selected. 
         [0083]    2.5 The reliability restoring moving machine selecting unit  147  selects at least one moving machine  100  that is to take the reliability restoring action from among the moving machines  100  present in a region where moving machines  100  having a lower reliability value aggregate. The master moving machine  100 M transmits through the moving machine information communication unit  148  information indicating that the moving machine  100  has been selected. The selection condition is applicable if the variance of the reliability values of all the moving machines  100  continues to be equal to or above a first threshold value for a first threshold duration of time, or if a difference between a minimum value and a maximum value of the reliability values of all the moving machines  100  continues to be equal to or above the first threshold value for the first threshold duration of time. 
         [0084]    In accordance with the second embodiment, coordinates associated with a reliability value equal to or below a predetermined threshold value are extracted from the latest reliability values and the coordinates of the self-locations of all the moving machines  100  collected by the moving machine information communication unit  148 . A specific unit region having the largest number of coordinates is identified as a region where moving machines  100  having lower reliability values aggregate. One moving machine  100  is selected from the moving machines  100  at the coordinates within the identified region. The moving machine information communication unit  148  transmits information indicating that the moving machine  100  has been selected. If the master moving machine  100 M is selected, transmitting the information concerning the master moving machine  100 M is not needed. 
         [0085]    2.6 The reliability restoring moving machine selecting unit  147  selects a moving machine  100 , in a region where moving machines  100  aggregate, as the moving machine  100  that is to take the reliability restoring action. Using the moving machine information communication unit  148 , the master moving machine  100 M transmits to the moving machine  100  information that the moving machine  100  has been selected. The selection condition of the moving machine  100  is applicable if at least one of the maximum value, the mean value, and the median of the reliability values of all the moving machines  100  is below a second threshold value. 
         [0086]    In accordance with the second embodiment, a specific unit region having the largest number of coordinates therewithin is identified as a region where moving machines  100  having lower reliability values aggregate by referencing the coordinates of the latest self-locations of all the moving machines  100  collected by the moving machine information communication unit  148 . One moving machine  100  is selected from the moving machines  100  at the coordinates within the identified region. The moving machine information communication unit  148  transmits information indicating that the selected moving machine  100  has been selected. 
         [0087]    The process workload on the control apparatus  104  of the slave moving machine  100 S is thus reduced by causing the master moving machine  100 M in a centralized fashion to evaluate the reliability values of all the moving machines  100  and to select the moving machine  100  that is to take the reliability restoring action. 
       EXAMPLES 
       [0088]    Specific examples of the autonomous moving machine system  110  are described below. 
         [0089]      FIG. 7  is a perspective view of the autonomous moving machine system  110  that performs a bridge inspection job. 
         [0090]    Referring to  FIG. 7 , in this example, the moving machine  100  is a drone, and the autonomous moving machine system  110  includes multiple drone-type moving machines  100 . The job performed of the autonomous moving machine system  110  is an inspection job to be performed on the underside of a bridge  200 . Each moving machine  100  having an inspection camera mounted on top thereof photographs the underside of the bridge  200 . The moving machines  100  perform this job on their respective portions of the underside of the bridge. Cracks on the structure of the bridge  200  may be detected by referencing a video captured by each moving machine  100  and the location of the captured video. 
         [0091]    Each moving machine  100  estimates the self-location and performs the job using the Kalman filter in accordance with the sensor information from the sensor  103 , such as IMU or GPS, and the relative positional relationship of the moving machine  100 . As the job is in progress, the reliability of the whole autonomous moving machine system  110  decreases. For example, the variance of the reliability values of the self-locations of all the moving machines  100  may continue to be equal to or above a first threshold value for a first threshold duration of time or longer. In such a case, each moving machine  100  communicates with the other moving machines  100  via the moving machine information communication unit  148  and selects a moving machine  100  that is closest to a region having a higher reliability value (in this example, the moving machine  100  having id  1002 ). 
         [0092]    In response to the information stored on the memory  140 , the reliability restoring action control unit  145  in the selected moving machine  100  controls the mover  101  such that the moving machine  100  moves to the region having the higher reliability value, for example, the region where signals from GPS satellites  210  are received. 
         [0093]    The moving machine  100  that moves by controlling the mover  101  restores the reliability value of the self-location and returns back to the location where the moving machine  100  starts the reliability restoring action, and then photographs the bridge  200 . 
         [0094]    The moving machine  100  increases the reliability value of the other moving machines  100  by transmitting the new self-location and reliability value to the other moving machines  100 . The overall reliability of the autonomous moving machine system  110  is thus increased. 
         [0095]    As described above, the autonomous moving machine system  110  may perform the job efficiently while keeping the system reliability at a higher level. 
         [0096]    The disclosure is not limited to the embodiments. For example, an embodiment of the disclosure may be configured by using some of the elements described in this specification in any combination, or by deleting some of the elements. The embodiments may be modified in a manner recognized by ordinarily skilled artisans within the scope of the disclosure, namely without departing from the scope of the disclosure defined by the claims. The modifications fall within the scope of the disclosure. 
         [0097]    In the above discussion, the master moving machine  100 M performs the standard job as the slave moving machine  100 S does. Alternatively, the master moving machine  100 M may only manage the slave moving machine  100 S without performing the standard job. 
         [0098]    As illustrated in  FIG. 8 , the autonomous moving machine system  110  may include a fixed apparatus  1006  that includes the position reliability recording unit  144 , the reliability restoring moving machine selecting unit  147 , and a communication unit  149  that is communicable with the moving machine information communication unit  148 . In this case, the moving machines  100  are all slave moving machines  100 S. The fixed apparatus  1006  acquires the self-locations and the reliability values from the slave moving machines  100 S via communication, selects in accordance with these pieces of information a slave moving machine  100 S whose reliability is to be restored, and transmits to the selected slave moving machine  100 S information indicating that the slave moving machine  100 S has been selected. In this case, as well, the slave moving machine  100 S may not necessarily have to include the position reliability recording unit  144  and the memory  140 . 
         [0099]    The fixed apparatus  1006  may collect the sensor information via the sensor information acquisition unit  141  and the moving machine information communication unit  148  in each slave moving machine  100 S, and may calculate the self-locations and the reliability values of all the moving machines  100 S. The reliability restoring moving machine selecting unit  147  in the fixed apparatus  100 B may select in accordance with the reliability values a slave moving machine  100 S that is to take the reliability restoring action. 
         [0100]    In accordance with the embodiments, the moving machine  100  is an autonomous flying object that freely and three-dimensionally moves, namely, is a drone flying in the air. The moving machine  100  is not limited to the drone. The moving machine  100  may be an autonomous vehicle running on the ground, or an autonomous ship cruising on the sea. 
         [0101]    The sensor  103  that acquires information contributing to estimating the self-location is not limited to any particular type. The sensor  103  may further include any sensor that has not been described herein. 
         [0102]    All processes are implemented by the control apparatus  104  alone. Alternatively, the processes may be distributed among multiple controllers, and information may be exchanged among the controllers via mutual communication. 
         [0103]    The self-location and the reliability value are successively calculated during the reliability restoring action, and the reliability restoring action may be ended when the acquired reliability value exceeds a predetermined value. Alternatively, the reliability restoring action may be ended when the self-location matches the target location. 
         [0104]    After the reliability is restored, the moving machine  100  may return back to the location where the reliability restoring action starts. Alternatively, the moving machine  100  may directly move to a target location from the location where the reliability is restored. 
         [0105]    The disclosure finds applications in vehicles, trains, ships, air planes, and vacuum cleaners, each of these moving in an autonomous fashion.