Patent Publication Number: US-2023152803-A1

Title: Control method for controlling delivery system

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese patent application No. 2021-185506, filed on Nov. 15, 2021, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND 
     The present disclosure relates to a delivery system, a control method therefor, and a control program. 
     Japanese Unexamined Patent Application Publication No. 2019-128801 discloses a delivery system including an autonomously-moving-type delivery vehicle configured to deliver an article(s) to a delivery destination and a transportation vehicle configured to carry and transport the delivery vehicle. A transportation vehicle that carries therein a delivery vehicle travels to the destination of the article(s) to be delivered (hereinafter also referred to as “delivery destination” of the article(s)), and then the delivery vehicle gets out of the transportation vehicle and delivers the article(s) to the delivery destination. 
     SUMMARY 
     The inventors have found the following problem in a delivery system in which a transportation vehicle that carries therein a delivery vehicle travels to the destination of the article(s) to be delivered, and then the delivery vehicle gets out of the transportation vehicle and delivers the article(s) to the delivery destination. 
     In such a delivery system, there is a problem that in the case where the delivery vehicle moves autonomously by electric power its battery is charged with, when the remaining amount of charge of the battery falls to zero while the delivery vehicle is delivering the article(s), the delivery vehicle cannot deliver the article(s) to the delivery destination or cannot return to the transportation vehicle after delivering the article(s). 
     The present disclosure has been made in view of the above-described circumstances, and an object thereof is to provide a delivery system in which it is possible to suppress a remaining amount of charge of a battery of a delivery vehicle from falling to zero while the delivery vehicle is delivering an article(s). 
     A first exemplary aspect is a delivery system including: 
     a plurality of autonomously-moving-type delivery vehicles each including a chargeable and dischargeable battery and configured to deliver an article to a delivery destination by electric power the battery is charged with; and 
     a transportation vehicle configured to carry and transport the plurality of the delivery vehicles, in which 
     for each of the plurality of the delivery vehicles, based on a respective route for delivering the article and a respective remaining amount of charge of the battery, a surplus or shortfall in the remaining amount of charge of the battery required for traveling along the respective route is calculated, and 
     based on the result of the calculation of the surplus or shortfall in the remaining amount of charge of the battery for each of the plurality of the delivery vehicles, surplus electric power is supplied from, among the plurality of the delivery vehicles, the battery of a delivery vehicle having a surplus remaining amount of charge to the battery of a delivery vehicle having a shortfall in the remaining amount of charge. 
     Further, another exemplary aspect is a control method performed by a computer for controlling a delivery system that includes: 
     a plurality of autonomously-moving-type delivery vehicles each including a chargeable and dischargeable battery and configured to deliver an article to a delivery destination by electric power the battery is charged with; and 
     a transportation vehicle configured to carry and transport the plurality of the delivery vehicles, 
     the control method including:
         calculating, for each of the plurality of the delivery vehicles, based on a respective route for delivering the article and a respective remaining amount of charge of the battery, a surplus or shortfall in the remaining amount of charge of the battery required for traveling along the respective route, and   supplying, based on the result of the calculation of the surplus or shortfall in the remaining amount of charge of the battery for each of the plurality of the delivery vehicles, surplus electric power from, among the plurality of the delivery vehicles, the battery of a delivery vehicle having a surplus remaining amount of charge to the battery of a delivery vehicle having a shortfall in the remaining amount of charge.       

     Further, another exemplary aspect is a control program for causing a computer to perform control of a delivery system that includes: 
     a plurality of autonomously-moving-type delivery vehicles each including a chargeable and dischargeable battery and configured to deliver an article to a delivery destination by electric power the battery is charged with; and 
     a transportation vehicle configured to carry and transport the plurality of the delivery vehicles, 
     the control program causing the computer to:
         calculate, for each of the plurality of the delivery vehicles, based on a respective route for delivering the article and a respective remaining amount of charge of the battery, a surplus or shortfall in the remaining amount of charge of the battery required for traveling along the respective route, and   supply, based on the result of the calculation of the surplus or shortfall in the remaining amount of charge of the battery for each of the plurality of the delivery vehicles, surplus electric power from, among the plurality of the delivery vehicles, the battery of a delivery vehicle having a surplus remaining amount of charge to the battery of a delivery vehicle having a shortfall in the remaining amount of charge.       

     As described above, according to an aspect of the present disclosure, for each of the plurality of the delivery vehicles, based on a respective route for delivering the article and a respective remaining amount of charge of the battery, a surplus or shortfall in the remaining amount of charge of the battery required for traveling along the respective route is calculated, and based on the result of the calculation of the surplus or shortfall in the remaining amount of charge of the battery for each of the plurality of the delivery vehicles, surplus electric power is supplied from, among the plurality of the delivery vehicles, the battery of a delivery vehicle having a surplus remaining amount of charge to the battery of a delivery vehicle having a shortfall in the remaining amount of charge. Therefore, it is possible to suppress the remaining amount of charge of a battery of a delivery vehicle from falling to zero while the delivery vehicle is delivering an article. 
     Further, another exemplary aspect is a delivery system including: 
     a plurality of autonomously-moving-type delivery vehicles each including a chargeable and dischargeable battery and configured to deliver an article to a delivery destination by electric power the battery is charged with; and 
     a transportation vehicle configured to carry and transport the plurality of the delivery vehicles, in which 
     for each of the plurality of the delivery vehicles, based on a respective route for delivering the article and a respective remaining amount of charge of the battery, a surplus or shortfall in the remaining amount of charge of the battery required for traveling along the respective route is calculated, and 
     based on the result of the calculation of the surplus or shortfall in the remaining amount of charge of the battery for each of the plurality of the delivery vehicles, the article carried by, among the plurality of the delivery vehicles, a delivery vehicle having a shortfall in the remaining amount of charge is transferred to a delivery vehicle having a surplus remaining amount of charge. 
     Further, another exemplary aspect is a control method performed by a computer for controlling a delivery system that includes: 
     a plurality of autonomously-moving-type delivery vehicles each including a chargeable and dischargeable battery and configured to deliver an article to a delivery destination by electric power the battery is charged with; and 
     a transportation vehicle configured to carry and transport the plurality of the delivery vehicles, 
     the control method including:
         calculating, for each of the plurality of the delivery vehicles, based on a respective route for delivering the article and a respective remaining amount of charge of the battery, a surplus or shortfall in the remaining amount of charge of the battery required for traveling along the respective route, and   transferring, based on the result of the calculation of the surplus or shortfall in the remaining amount of charge of the battery for each of the plurality of the delivery vehicles, the article carried by, among the plurality of the delivery vehicles, a delivery vehicle having a shortfall in the remaining amount of charge to a delivery vehicle having a surplus remaining amount of charge.       

     Further, another exemplary aspect is a control program for causing a computer to perform control of a delivery system that includes: 
     a plurality of autonomously-moving-type delivery vehicles each including a chargeable and dischargeable battery and configured to deliver an article to a delivery destination by electric power the battery is charged with; and 
     a transportation vehicle configured to carry and transport the plurality of the delivery vehicles, 
     the control program causing the computer to:
         calculate, for each of the plurality of the delivery vehicles, based on a respective route for delivering the article and a respective remaining amount of charge of the battery, a surplus or shortfall in the remaining amount of charge of the battery required for traveling along the respective route, and   transfer, based on the result of the calculation of the surplus or shortfall in the remaining amount of charge of the battery for each of the plurality of the delivery vehicles, the article carried by, among the plurality of the delivery vehicles, a delivery vehicle having a shortfall in the remaining amount of charge to a delivery vehicle having a surplus remaining amount of charge.       

     As described above, according to an aspect of the present disclosure, for each of the plurality of the delivery vehicles, based on a respective route for delivering the article and a respective remaining amount of charge of the battery, a surplus or shortfall in the remaining amount of charge of the battery required to travel along the route is calculated, and based on the result of the calculation of the surplus or shortfall in the remaining amount of charge of the battery, the article carried by, among the plurality of the delivery vehicles, a delivery vehicle having a shortfall in the remaining amount of charge is transferred to a delivery vehicle having a surplus remaining amount of charge. Therefore, it is possible to suppress the remaining amount of charge of a battery of a delivery vehicle from falling to zero while the delivery vehicle is delivering an article. 
     According to the present disclosure, it is possible to provide a delivery system in which it is possible to suppress the remaining amount of charge of a battery of a delivery vehicle from falling to zero while the delivery vehicle is delivering an article. 
     The above and other objects, features and advantages of the present disclosure will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a block diagram of a delivery system according to a first embodiment; 
         FIG.  2    is a perspective view showing a state in which a delivery vehicle  200  gets out of a transportation vehicle  100 ; 
         FIG.  3    is a side view showing a state in which the delivery vehicle  200  gets out of the transportation vehicle  100 ; 
         FIG.  4    is a block diagram of a delivery system according to the first embodiment; 
         FIG.  5    is a side view showing two delivery vehicles  200   a  and  200   b  inside the transportation vehicle  100 ; 
         FIG.  6    is a side view showing two delivery vehicles  200   a  and  200   b  inside the transportation vehicle  100 ; 
         FIG.  7    is block diagram of a delivery system according to a second embodiment; and 
         FIG.  8    is a side view showing two delivery vehicles  200   a  and  200   b  inside the transportation vehicle  100 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Specific embodiments will be described hereinafter in detail with reference to the drawings. The same or corresponding elements are denoted by the same reference numerals (or symbols) throughout the drawings, and redundant descriptions thereof are omitted as required for clarifying the explanation. 
     First Embodiment 
     &lt;Configuration of Delivery System&gt; 
     Firstly, a delivery system and its control method according to a first embodiment will be described with reference to  FIG.  1   .  FIG.  1    is a block diagram of a delivery system according to the first embodiment. As shown in  FIG.  1   , the delivery system according to this embodiment includes a transportation vehicle  100 , a delivery vehicle  200 , and a management server  300 . After the transportation vehicle  100  carrying the delivery vehicle  200  travels toward the delivery destination of an article(s), the delivery vehicle  200  gets out of the transportation vehicle  100  and delivers the article(s) to the delivery destination. 
     Firstly, the transportation vehicle  100  will be described. 
     The transportation vehicle  100  carries and transports the delivery vehicle  200 . Although the transportation vehicle  100  in this embodiment is an autonomous mobile vehicle (i.e., an autonomously-driven vehicle), it may be a vehicle driven by a human driver. As shown in  FIG.  1   , the transportation vehicle  100  includes a control unit  110 , a sensor unit  120 , a traveling mechanism  130 , and an unloading mechanism  140 . Further, the transportation vehicle  100  is wirelessly connected to the delivery vehicle  200  and the management server  300  so as to be able to communicate with them. 
     Note that when the management server  300  is disposed in the transportation vehicle  100 , the transportation vehicle  100  may be connected to the management server  300  through a cable(s). Further, although only one delivery vehicle  200  is shown in  FIG.  1   , the transportation vehicle  100  may carry a plurality of delivery vehicles  200 , as will be described later. 
     The control unit  110  controls the traveling mechanism  130  based on various types of information acquired from the sensor unit  120 . In this way, the transportation vehicle  100  autonomously travels. Further, the control unit  110  controls the unloading mechanism  140  for enabling the delivery vehicle  200  to get out of the transportation vehicle  100 . 
     The control unit  110  includes, for example, an arithmetic unit such as a CPU (Central Processing Unit), and a storage unit such as a RAM (Random Access Memory) and a ROM (Read Only Memory) in which various types of control programs, data, and the like are stored. That is, the control unit  110  has a function as a computer, and controls the traveling mechanism  130  and the unloading mechanism  140  based on the aforementioned various types of control programs and the like. 
     In the example shown in  FIG.  1   , the sensor unit  120  includes an obstacle sensor  121 , an acceleration sensor  122 , a speed sensor  123 , and a posture sensor  124 . 
     The obstacle sensor  121  detects an obstacle ahead of the transportation vehicle  100  in the traveling direction thereof. Further, the obstacle sensor  121  detects an obstacle at the time when the delivery vehicle  200  gets out of the transportation vehicle  100 . The obstacle sensor  121  is, for example, a radar sensor, a sonar sensor, an ultrasonic sensor, a LIDAR sensor, a camera, or the like. Examples of the obstacle include people such as pedestrians and animals as well as other vehicles and objects on the road that have accidentally fallen from other vehicles. 
     The acceleration sensor  122  detects the acceleration of the transportation vehicle  100 . It is possible to detect vibrations of the transportation vehicle  100  caused by irregularities or the like on the road surface by detecting the acceleration of the transportation vehicle  100 . 
     The speed sensor  123  detects the speed of the transportation vehicle  100 . 
     The posture sensor  124  detects the posture of the transportation vehicle  100 . It is possible to detect the gradient of the road on which the transportation vehicle  100  is traveling (hereinafter also referred to as the road gradient) by the posture sensor  124 . 
     The traveling mechanism  130  is a mechanism for moving the transportation vehicle  100  (i.e., making the transportation vehicle  100  travel). For example, the traveling mechanism  130  includes, in addition to the driving mechanism, such as a motor or an engine, for moving the transportation vehicle  100 , a braking mechanism for stopping the transportation vehicle  100 , and a steering mechanism for making the transportation vehicle  100  turn (i.e., making the transportation vehicle  100  change the traveling direction). 
     The unloading mechanism  140  is a mechanism for making the delivery vehicle  200  get out of the transportation vehicle  100  (or for enabling the delivery vehicle  200  to get out of the transportation vehicle  100 , or for unloading the delivery vehicle  200  from the transportation vehicle  100 ). Here, an example of the unloading mechanism  140  will be described with reference to  FIGS.  2  and  3   .  FIG.  2    is a perspective view showing a state in which the delivery vehicle  200  gets out of the transportation vehicle  100 .  FIG.  3    is a side view showing the state in which the delivery vehicle  200  gets out of the transportation vehicle  100 . 
     As shown in  FIGS.  2  and  3   , the unloading mechanism  140  according to this embodiment is a simple plate-like slope. In the example shown in  FIGS.  2  and  3   , the unloading mechanism  140  also functions as an opening/closing door provided in the rear part of the transportation vehicle  100 . The unloading mechanism  140  is connected to one side (e.g., a side at the lower edge) of the opening provided in the rear part of the transportation vehicle  100 . In the normal state, the unloading mechanism  140  serves as an opening/closing door and is closed. However, when the delivery vehicle  200  gets out of the transportation vehicle  100 , the unloading mechanism  140 , which serves as the opening/closing door, is opened and functions as a slope extending from the inside of the transportation vehicle  100  to the ground surface. 
     For example, when the delivery vehicle  200  gets out of the transportation vehicle  100  to delivery an item(s), as shown in  FIG.  1   , the control unit  110  of the transportation vehicle  100  instructs the control unit  210  of the delivery vehicle  200  to get out of the transportation vehicle  100 . At that time, the control unit  110  of the transportation vehicle  100  controls the unloading mechanism  140 . Specifically, as shown in  FIGS.  2  and  3   , the control unit  110  opens the unloading mechanism  140 , which functions as the opening/closing door, and makes the unloading mechanism  140  function as a slope extending from the inside of the transportation vehicle  100  to the ground surface. Then, as shown in  FIGS.  2  and  3   , the delivery vehicle  200  travels on the unloading mechanism  140  and thereby gets down onto the roadway. Further, the delivery vehicle  200  delivers the article(s) to the delivery destination, for example, by traveling from the roadway to the sidewalk and to the delivery destination. 
     Note that the unloading mechanism  140  shown in  FIGS.  2  and  3    may be provided separately from the opening/closing door provided in the rear part of the transportation vehicle  100  as long as it can function as a slope. In such a case, in the normal state, the unloading mechanism  140  is housed, for example, under the floor of the transportation vehicle  100 . 
     Further, the unloading mechanism  140  shown in  FIGS.  2  and  3    is just an example, and the mechanism is not limited to any particular mechanism as long as it can make the delivery vehicle  200  get out of the transportation vehicle  100 . The unloading mechanism  140  may be, for example, a conveyor or a crane. 
     Next, the delivery vehicle  200  will be described. 
     The delivery vehicle  200  is an autonomously-moving-type vehicle which, after being transported by the transportation vehicle  100 , gets out of the transportation vehicle  100  and delivers an article(s) to the delivery destination thereof. As shown in  FIG.  1   , the transportation vehicle  200  includes a control unit  210 , a sensor unit  220 , a traveling mechanism  230 , and a battery  240 . Further, the delivery vehicle  200  is wirelessly connected to the transportation vehicle  100  and the management server  300  so as to be able to communicate with them. Note that when the management server  300  is disposed in the delivery vehicle  200 , the delivery vehicle  200  may be connected to the management server  300  through a cable(s). 
     The traveling control unit  210  controls the traveling mechanism  230  based on various types of information acquired from the sensor unit  220 . That is, the delivery vehicle  200  autonomously travels as the control unit  210  controls the traveling mechanism  230 . Note that, similarly to the sensor unit  120  of the transportation vehicle  100 , the sensor unit  220  includes various types of sensors. 
     Similarly to the control unit  110  of the transportation vehicle  100 , the control unit  210  includes an arithmetic unit such as a CPU, and a storage unit such as a RAM and a ROM in which various types of control programs, data, and the like are stored. That is, the traveling control unit  210  has a function as a computer, and controls the traveling mechanism  230  based on the aforementioned various types of control programs and the like. 
     The control unit  210  acquires the delivery route for delivering an article(s) from the management server  300  and also acquires, from the battery  240 , information about the remaining amount of charge of the battery  240 . Then, the control unit  210  calculates, based on the delivery route and the information about the remaining amount of charge of the battery  240  acquired from the management server  300 , a surplus or shortfall in the remaining amount of charge of the battery  240  required for the delivery vehicle  200  to travel along the delivery route thereof. When the remaining amount of charge of the battery  240  required for the delivery vehicle  200  to travel along the delivery route thereof falls short, the control unit  210  requests another delivery vehicle  200  having a surplus remaining amount of charge of its battery  240  to supply the surplus electric power. 
     A method of controlling, by the control unit  210 , the remaining amount of charge of the battery  240  will be described later. 
     The traveling mechanism  230  is a mechanism for moving the delivery vehicle  200  (i.e., making the delivery vehicle  200  travel). For example, the traveling mechanism  230  includes, in addition to the driving mechanism, such as a motor or an engine, for moving the delivery vehicle  200 , a braking mechanism for stopping the delivery vehicle  200 , and a steering mechanism for making the delivery vehicle  200  turn (i.e., making the delivery vehicle  200  change the traveling direction). 
     The battery  240  is a secondary battery that can be charged and discharged, such as a lithium-ion battery. The battery  240  is a power supply device that supplies a source of power (electricity) to the control unit  210 , the sensor unit  220 , and the traveling mechanism  230 . That is, the delivery vehicle  200  delivers an article(s) to the delivery destination using the electric power its battery  240  charged with. 
     Next, the management server  300  will be described. 
     The management server  300  is a server for communicating with the transportation vehicle  100  and the delivery vehicle  200  and managing the delivery system. The management server  300  is, for example, a cloud server. As shown in  FIG.  1   , the management server  300  includes a route determination unit  310  and a storage unit  320 . 
     The route determination unit  310  is configured of, for example, an arithmetic unit such as a CPU. As shown in  FIG.  1   , the route determination unit  310  determines a delivery route from the place where the transportation vehicle  100  is currently present to a delivery destination based on map information stored in the storage unit  320 . Then, the route determination unit  310  transmits the determined delivery route to the control unit  110  of the transportation vehicle  100  and the control unit  210  of the delivery vehicle  200 . Further, the map information may include road-surface information. 
     The storage unit  320  is configured of, for example, RAM, ROM, and the like, and stores various control programs and data in addition to the map information. 
     That is, the management server  300  has a function as a computer, and controls the delivery system based on the aforementioned various types of control programs and the like. 
     &lt;Method for Controlling Remaining Amount of Charge of Battery  240 &gt; 
     Next, a method for controlling the remaining amount of charge of the battery  240  will be described with reference to  FIGS.  4  to  6   .  FIG.  4    is a block diagram of a delivery system according to the first embodiment.  FIGS.  5  and  6    are each a side view showing two delivery vehicles  200   a  and  200   b  inside the transportation vehicle  100 . 
     Note that in  FIG.  4   , the delivery system includes only two delivery vehicles  200   a  and  200   b  and the management server  300 , and the transportation vehicle  100  shown in  FIG.  1    is omitted. Further, the delivery vehicles  200   a  and  200   b  each has a configuration same as that of the delivery vehicle  200  shown in  FIG.  1   . Here, in  FIG.  4   , the delivery vehicles  200   a  and  200   b  include only the control unit  210  and the battery  240 , and the sensor unit  220  and the traveling mechanism  230  shown in  FIG.  1    are omitted. 
     As described above, the control unit  210  of each of the delivery vehicles  200   a  and  200   b  acquires the delivery route for delivering an article(s) from the management server  300  and also acquires, from the battery  240 , information about the remaining amount of charge of the battery  240 . Then, the control unit  210  of each of the delivery vehicles  200   a  and  200   b  calculates, based on the delivery route and the information about the remaining amount of charge of the battery  240  acquired from the management server  300 , a surplus or shortfall in the remaining amount of charge of the battery  240  required for traveling along the delivery route. 
     Here, the delivery vehicle  200   a  has a shortfall in the remaining amount of charge of the battery  240  required to travel along the delivery route thereof whereas the delivery vehicle  200   b  has a surplus remaining amount of charge of the battery  240  required to travel along the delivery route thereof. In this case, due to the shortfall in the remaining amount of charge of the battery  240  of the delivery vehicle  200   a , the control unit  210  of the delivery vehicle  200   a  requests the control unit  210  of the delivery vehicle  200   b  having a surplus remaining amount of charge of its battery  240  to supply its surplus electric power to the delivery vehicle  200   a . As a result, surplus electric power is supplied from the battery  240  of the delivery vehicle  200   b  to the battery  240  of the delivery vehicle  200   a.    
     Note that in  FIG.  4   , the result of the calculation of the surplus or shortfall in the remaining amount of charge of the battery  240  of the delivery vehicle  200   a  may be transmitted from the control unit  210  of the delivery vehicle  200   a  to the management server  300 . Similarly, the result of the calculation of the surplus or shortfall in the remaining amount of charge of the battery  240  of the delivery vehicle  200   b  may be transmitted from the control unit  210  of the delivery vehicle  200   b  to the management server  300 . Then, the management server  300  may instruct the control unit  210  of the delivery vehicle  200   b  to supply its surplus electric power from the battery  240  of the delivery vehicle  200   b  to the battery  240  of the delivery vehicle  200   a.    
     For example, as shown in  FIGS.  5  and  6   , the delivery vehicles  200   a  and  200   b  each includes a plug  241  and a socket  242  that are electrically connected to the respective batteries  240 . As shown in  FIG.  6   , the plug  241  of the delivery vehicle  200   b  and the socket  242  of the delivery vehicle  200   a  are fitted with each other and can be electrically connected. That is, as shown in  FIG.  6   , the battery  240  of the delivery vehicle  200   a  and the battery  240  of the delivery vehicle  200   b  are electrically connected with each other and surplus electric power is supplied from the battery  240  of the delivery vehicle  200   b  to the battery  240  of the delivery vehicle  200   a.    
     Note that although not shown in the drawings, the plug  241  of the delivery vehicle  200   a  and the socket  242  of the delivery vehicle  200   b  can be fitted with each other and can be electrically connected. Further, the plug  241  and the socket  242  shown in  FIGS.  5  and  6    are just an example and they may have any configuration as long as the battery  240  of the delivery vehicle  200   a  can be electrically connected with the battery  240  of the delivery vehicle  200   b.    
     As described above, in the delivery system according to this embodiment, for each of the plurality of the delivery vehicles  200   a  and  200   b , based on the delivery route for delivering the article(s) and the information about the remaining amount of charge of the battery  240 , a surplus or shortfall in the remaining amount of charge of the battery  240  required for traveling along the delivery route is calculated. Then, based on the result of the calculation of the surplus or shortfall in the remaining amount of charge of the battery, surplus electric power is supplied from the battery  240  of the delivery vehicle  200   b  having a surplus remaining amount of charge to the battery  240  of the delivery vehicle  200   a  having a shortfall in the remaining amount of charge. Therefore, in the delivery system according to this embodiment, it is possible to suppress the remaining amount of charge of the battery  240  of each of the delivery vehicles  200   a  and  200   b  from falling to zero while the delivery vehicles  200   a  and  200   b  are delivering articles. 
     As a matter of course, the transportation vehicle  100  may carry three or more delivery vehicles  200 . 
     Second Embodiment 
     Next, a delivery system and its control method according to a second embodiment will be described with reference to  FIGS.  7  and  8   .  FIG.  7    is a block diagram of a delivery system according to the second embodiment.  FIG.  8    is a side view showing two delivery vehicles  200   a  and  200   b  inside the transportation vehicle  100 . 
     As shown in  FIG.  7   , in the delivery system according to the second embodiment, the transportation vehicle  100  includes a manipulator  150 . Note that in  FIG.  7   , the delivery vehicle  100  includes only the control unit  110  and the manipulator  150 , and the sensor unit  120 , the traveling mechanism  130 , and the unloading mechanism  140  shown in  FIG.  1    are omitted. 
     As shown in  FIG.  7   , in the delivery system according to this embodiment too, the control unit  210  of each of the delivery vehicles  200   a  and  200   b  acquires the delivery route for delivering an article(s) from the management server  300  and also acquires, from the battery  240 , information about the remaining amount of charge of the battery  240 . Then, the control unit  210  of each of the delivery vehicles  200   a  and  200   b  calculates, based on the delivery route and the information about the remaining amount of charge of the battery  240  acquired from the management server  300 , a surplus or shortfall in the remaining amount of charge of the battery  240  required for traveling along the delivery route. 
     As shown in  FIG.  7   , the control unit  210  of the delivery vehicle  200   a  transmits the result of the calculation cr 1  of the surplus or shortfall in the remaining amount of charge of the battery  240  required for traveling along the delivery route of the delivery vehicle  200   a  to the control unit  110  of the transportation vehicle  100 . Similarly, the control unit  210  of the delivery vehicle  200   b  transmits the result of the calculation cr 2  of the surplus or shortfall in the remaining amount of charge of the battery  240  required for traveling along the delivery route of the delivery vehicle  200   b  to the control unit  110  of the transportation vehicle  100 . Here, the delivery vehicle  200   a  has a shortfall in the remaining amount of charge of the battery  240  required to travel along the delivery route thereof whereas the delivery vehicle  200   b  has a surplus remaining amount of charge of the battery  240  required to travel along the delivery route thereof. 
     In this case, in the delivery system shown in  FIG.  7   , the control unit  110  of the transportation vehicle  100  controls the manipulator  150  so that the article(s) carried by the delivery vehicle  200   a  having a shortfall in the remaining amount of charge of its battery  240  is transferred to the delivery vehicle  200   b  having a surplus remaining amount of charge of its battery  240 . 
       FIG.  8    illustrates a state in which the manipulator  150  transfers an article carried by the delivery vehicle  200   a  having a shortfall in the remaining amount of charge of its battery  240  to the delivery vehicle  200   b  having a surplus remaining amount of charge of its battery  240 . 
     Note that the manipulator  150  shown in  FIG.  8    is just an example, and it may have any configuration as long as the articles carried by the delivery vehicles  200   a  and  200   b  can be transferred. 
     In the example shown in  FIG.  8   , the manipulator  150  includes a base part  51 , a link base part  52 , a first link  53 , a second link  54 , and an end effector  55 . Each article is grasped by the end effector  55  and transferred. 
     The base part  51  is fixed to the floor surface of the transportation vehicle  100 . 
     The link base part  52  is connected to the base part  51  through a rotation shaft  52   a  so that the link base part  52  can rotate around the rotation shaft  52   a . The rotation shaft  52   a  of the link base part  52  is a shaft that is positioned perpendicular to the floor surface of the transportation vehicle  100 . The link base part  52  is rotationally driven by a motor or the like (not shown). 
     The first link  53  is rotatably connected to the link base part  52  through a first joint part  53   a  provided at the rear end of the first link  53 . Further, the second link  54  is rotatably connected to the tip of the first link  53  through a second joint part  54   a  provided at the rear end of the second link  54 . The end effector  55  is connected to the tip of the second link  54 . 
     Note that the rotation axis of the first joint part  53   a  and the second joint part  54   a  is an axis parallel to the floor surface of the transportation vehicle  100 . The height of the end effector  55  can be changed by rotating the first link  53  and the second link  54 . The first link  53  and the second link  54  are rotationally driven by a motor or the like (not shown). By the above-described configuration, each article can be grasped and transferred using the end effector  55 . 
     Note that the configuration of the end effector  55  is not particularly limited as long as each article can be transferred using the end effector  55 . For example, the end effector  55  may adsorb an article and transfer the article. Further, the link mechanism in the example shown in  FIG.  8    is configured of two links, i.e., the first link  53  and the second link  54 , but it may be configured of three or more links. 
     As described above, in the delivery system according to this embodiment, for each of the plurality of the delivery vehicles  200   a  and  200   b , based on the delivery route for delivering the article(s) and the information about the remaining amount of charge of the battery  240 , a surplus or shortfall in the remaining amount of charge of the battery  240  required for traveling along the delivery route is calculated. Then, based on the result of the calculation of the surplus or shortfall in the remaining amount of charge of the battery, an article(s) loaded on the delivery vehicle  200   a  having a shortfall in the remaining amount of charge of its battery  240  is transferred to the delivery vehicle  200   b  having a surplus remaining amount of charge of its battery  240 . 
     That is, the delivery vehicle  200   b  delivers the transferred article(s) instead of the delivery vehicle  200   a . Accordingly, the problem of shortfall in the remaining amount of charge of the battery  240  of the delivery vehicle  200   a  is solved. Therefore, in the delivery system according to this embodiment, it is possible to suppress the remaining amount of charge of the battery  240  of each of the delivery vehicles  200   a  and  200   b  from falling to zero while the delivery vehicles  200   a  and  200   b  are delivering article(s). The rest of the configuration is similar to that of the first embodiment, and therefore the description thereof is omitted. 
     In the above-described examples, the program includes instructions (or software codes) that, when loaded into a computer, cause the computer to perform one or more of the functions described in the embodiments. The program may be stored in a non-transitory computer readable medium or a tangible storage medium. By way of example, and not a limitation, non-transitory computer readable media or tangible storage media can include a random-access memory (RAM), a read-only memory (ROM), a flash memory, a solid-state drive (SSD) or other types of memory technologies, a CD-ROM, a digital versatile disc (DVD), a Blu-ray disc or other types of optical disc storage, and magnetic cassettes, magnetic tape, magnetic disk storage or other types of magnetic storage devices. The program may be transmitted on a transitory computer readable medium or a communication medium. By way of example, and not a limitation, transitory computer readable media or communication media can include electrical, optical, acoustical, or other forms of propagated signals. 
     From the disclosure thus described, it will be obvious that the embodiments of the disclosure may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the disclosure, and all such modifications as would be obvious to one skilled in the art are intended for inclusion within the scope of the following claims.