Patent Publication Number: US-2021175751-A1

Title: Charging system, charging station, movable body, and charging method

Description:
FIELD 
     The present invention relates to a charging system, a charging station, a movable body, and a charging method. 
     BACKGROUND 
     When performing patrol inspection work or the like using a movable robot, the robot is required to be self-propelled and thus is equipped with a battery. In this case, when the amount of charge of the battery is reduced through patrol inspection work or the like, the robot needs to run to a charging station for power supply. When patrol inspection work is performed at, for example, a petrochemical plant, if oil or the like leaks, the work environment of the robot will become an explosive atmosphere to cause a fire upon ignition with sparks generated at actuation of the robot. Thus, the robot needs to have an explosion-proof structure in this case. 
     For example, an explosion-proof structure of a conventional robot is disclosed in Patent Literature 1 below. An industrial robot disclosed in Patent Literature 1 includes a control device, a battery, and a motor that are disposed on a movable frame, and has an internal pressure explosion-proof structure in which air is supplied into the frame from an air supply device to maintain the inside the frame at a pressure higher than a predetermined pressure. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: JP 2015-036172 A 
     SUMMARY 
     Technical Problem 
     At power supply to the battery in the frame, the frame needs to be opened to connect the battery to a charging facility. However, when the frame is opened, the state in which the internal pressure is high is released, and thus it is needed to set the internal pressure to be high again after the charging is completed. Thus, a there is a need for a technology that enables appropriate charging without releasing the state in which the internal pressure in the frame is high. 
     The present invention has been made to solve the above-described problem, and an object of the present invention is to provide a charging system, a charging station, a movable body, and a charging method that enable appropriate charging without releasing a state in which the internal pressure in a frame is high. 
     Solution to Problem 
     To achieve the object described above, a charging system according to the present disclosure includes a movable body including a frame and a battery provided in the frame; and a charging station configured to charge the battery. The movable body includes a pressure detection unit configured to detect pressure in the frame, and a charging permission signal output unit configured to output a charging permission signal indicating that the pressure in the frame is detected to be equal to or higher than a threshold pressure. The charging station includes a charging permission signal acquisition unit configured to acquire the charging permission signal from the charging permission signal output unit, and a power transmission unit configured to execute non-contact charging of the battery when the charging permission signal is acquired by the charging permission signal acquisition unit. 
     Since the charging system performs non-contact charging when triggered by the charging permission signal, charging can be appropriately performed while the risk of ignition is reduced without releasing a state in which the internal pressure in the frame is high. 
     It is preferable that the charging permission signal output unit stops outputting the charging permission signal when the pressure in the frame is detected to be lower than the threshold pressure; and the power transmission unit stops the non-contact charging of the battery when the charging permission signal is not acquired by the charging permission signal acquisition unit. The charging system stops non-contact charging by stopping outputting of the charging permission signal when the internal pressure has been reduced. Thus, with the charging system, the risk of ignition due to charging can be reduced. 
     It is preferable that the movable body includes a movable body signal output unit configured to output a signal to a region that the movable body signal output unit faces; the charging station includes a station signal acquisition unit configured to acquire the signal from the movable body signal output unit; and the power transmission unit executes the non-contact charging of the battery when the signal from the movable body signal output unit is received by the station signal acquisition unit and the charging permission signal is acquired by the charging permission signal acquisition unit. With the charging system, the position of the movable body can be highly accurately checked by acquiring the signal from the movable body, and thus charging can be appropriately performed. 
     It is preferable that the charging station includes a station signal output unit configured to output a signal to a region that the station signal output unit faces; the movable body includes a movable body signal acquisition unit configured to acquire the signal from the station signal output unit when positioned in the region that the station signal output unit faces; and the movable body signal output unit outputs a signal when the signal from the station signal output unit is acquired by the movable body signal acquisition unit. With the charging system, both of the movable body and the charging station can check each other&#39;s positions, and thus charging can be appropriately performed. 
     It is preferable that the movable body includes a power reception coil connected with the battery; the power transmission unit of the charging station includes a power transmission coil configured to transmit power to the power reception coil in a non-contact manner, a movement unit configured to move the power transmission coil toward the power reception coil, and a power transmission control unit configured to cause the power transmission coil to perform power transmission; the movement unit moves the power transmission coil to a position facing the power reception coil; and the power transmission control unit causes the power transmission coil to perform power transmission when the power transmission coil is at the position facing the power reception coil and the charging permission signal is acquired by the charging permission signal acquisition unit. With the charging system, non-contact charging is performed based on results of positioning of the power transmission coil and the power reception coil. Thus, with the charging system, non-contact charging can be appropriately performed. 
     It is preferable that the charging station includes an interface position detection unit configured to detect whether the power transmission coil and the power reception coil are at appropriate positions; and the power transmission control unit causes the power transmission coil to perform power transmission when the power transmission coil and the power reception coil are at the appropriate positions. With the charging system, non-contact charging is performed when the power transmission coil and the power reception coil are at the appropriate positions. Thus, with the charging system, non-contact charging can be appropriately performed. 
     It is preferable that the frame of the movable body has an internal pressure explosion-proof structure. With the charging system, the battery of the movable body having the internal pressure explosion-proof structure can be excellently charged without releasing an internal pressure explosion-proof state. 
     To achieve the object described above, a charging station according to the present disclosure is for charging a movable body that includes a frame, a battery provided in the frame, and a pressure detection unit configured to detect pressure in the frame. The charging station includes: a charging permission signal acquisition unit configured to acquire, from the movable body, a charging permission signal indicating that the pressure in the frame is equal to or higher than a threshold pressure; and a power transmission unit configured to execute non-contact charging of the battery when the charging permission signal is acquired by the charging permission signal acquisition unit. With the charging station, charging can be appropriately performed while the risk of ignition is reduced without releasing the state in which the internal pressure in the frame is high. 
     To achieve the object described above, a movable body according to the present disclosure includes: a frame; a pressure detection unit configured to detect pressure in the frame; a charging permission signal output unit configured to output, to a charging station, a charging permission signal indicating that the pressure in the frame is detected, by the pressure detection unit, to be equal to or higher than a threshold pressure; and a power reception unit configured to be charged in a non-contact manner from the charging station having acquired the charging permission signal. With the movable body, charging can be appropriately performed while the risk of ignition is reduced without releasing the state in which the internal pressure in the frame is high. 
     To achieve the object described above, a charging method according to the present disclosure is performed by a charging device for charging a movable body that includes a frame and a battery provided in the frame. The charging method includes: a charging permission signal outputting step of outputting a charging permission signal from the movable body toward the charging device when the pressure in the frame is detected to be equal to or higher than a threshold pressure; and a charging step of executing non-contact charging of the battery when the charging permission signal is acquired by the charging device. With the charging method, charging can be appropriately performed while the risk of ignition is reduced without releasing the state in which the internal pressure in the frame is high. 
     Advantageous Effects of Invention 
     According to the present invention, charging is appropriately performed without releasing a state in which the internal pressure in the frame is high. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic diagram illustrating a movable body of the present embodiment. 
         FIG. 2  is a schematic block diagram of a charging station according to the present embodiment. 
         FIG. 3  is a schematic diagram for description of charging between the movable body and the charging station. 
         FIG. 4  is a flowchart for description of a charging method according to the present embodiment. 
         FIG. 5  is a schematic diagram illustrating positions at a time of charging of the movable body. 
         FIG. 6  is a flowchart for description of a process in which the movable body starts movement. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     A preferred embodiment of the present invention will be described below in detail with the accompanying drawings. The present invention is not limited by the embodiment. Components in the embodiment described below include those that could be replaced and easily thought of by the skilled person in the art or those identical in effect. 
     A charging system  1  of the present embodiment includes a movable body  10  (refer to  FIG. 1 ) and a charging station  100  (refer to  FIG. 2 ) configured to charge the movable body  10 . The charging system  1  is a system in which the movable body  10  is charged at the charging station  100 , for example, in a facility where the movable body  10  moves in a petrochemical plant and performs patrol inspection work. In the petrochemical plant, if oil or the like leaks, the work environment of the movable body becomes an explosive atmosphere. Thus, the movable body  10  has an explosion-proof structure. In the present embodiment, the movable body  10  is an industrial robot configured to perform work such as disaster prevention support work, building maintenance work, or patrol in an explosive atmosphere. The work environment in which the movable body  10  performs work includes a wide range of fields that may generate flammable gas, such as a petrochemical plant, a manufacturing-storage-management facility for dangerous substances such as flammable liquids, a coating facility, a solvent using facility, a high pressure gas facility, and a fuel battery related facility. 
     Configuration of Movable Body 
     The following first describes the movable body  10 .  FIG. 1  is a schematic diagram illustrating the movable body of the present embodiment. The movable body  10  is a robot, more specifically, an industrial robot. As illustrated in  FIG. 1 , the movable body  10  includes a frame  11 , a movement device  12 , a battery  13 , a control device  14 , an internal pressure explosion-proof device  15 , a camera  16 , and a communication device  17 . Although not illustrated, the movable body  10  may include, for example, a robotic arm. 
     The frame  11  has a hollow box shape and a sealing structure. The frame  11  is a container that prevents entry of explosive gas from the outside by maintaining the pressure of internal gas higher than the pressure of external gas by the internal pressure explosion-proof device  15  to be described later. In other words, the frame  11  is an internal pressure explosion-proof container having an internal pressure explosion-proof structure. The frame  11  can travel independently by being provided with the movement device  12  at the power part. The movement device  12  includes an electric motor  21 , a drive sprocket  22 , and a crawler  23 . The electric motor  21  is mounted in the frame  11 , the drive sprockets  22  are mounted at front and back lower parts on both sides of the frame  11 , and each crawler  23  is wound around the front and back drive sprockets  22  on the corresponding one of the right and left sides. The movement device  12  is not limited to the four drive sprockets  22  and the crawlers  23  but may include a plurality of drive wheels. 
     The battery  13  and the control device  14  are mounted in the frame  11 . The battery  13  can supply power to the control device  14  and the electric motor  21 . The control device  14  can control forward movement, backward movement, stopping of the frame  11 , that is, the movable body  10  through the movement device  12  by controlling drive of the electric motor  21 . 
     The internal pressure explosion-proof device  15  prevents external gas from entering the inside of the frame  11  by maintaining the pressure inside the frame  11  higher than the pressure outside the frame  11 . The internal pressure explosion-proof device  15  includes an air supply device  24  and an exhaust device  25 . The air supply device  24  is provided with an air supply line  28  extending from an air tank  26  provided outside the frame  11  to the inside through the frame  11 . The air supply line  28  is provided with a decompression valve  29  on the outside of the frame  11  and has an end part opened. Thus, normally, pressurized gas in the air tank  26  is supplied into the frame  11  through the air supply line  28 , and the pressure inside the frame  11  is maintained at a constant set pressure higher than the external pressure by the decompression valve  29 . 
     The exhaust device  25  includes an air discharge line  31  penetrating the frame  11  and extending to the inside, and the air discharge line  31  is provided with a relief valve  32  on the outside of the frame  11  and has an end part opened. Thus, when the temperature inside the frame  11  rises and the pressure inside the frame  11  becomes higher than the set pressure, the air inside the frame  11  is discharged to the outside through the air discharge line  31  by the relief valve  32 , thereby lowering the pressure inside the frame  11 . 
     The camera  16  is mounted at an upper part in the frame  11 . The camera  16  is controlled by the control device  14  to capture an image of the outside and output the captured image to the control device  14 . The communication device  17  can perform communication with an external administrative room (not illustrated) and the like. The communication device  17  transfers, to the control device  14 , information input from the outside and transfers information from the control device  14 , such as the captured image by the camera  16 , to the outside. 
     The movable body  10  also includes pressure detection units  40 A and  40 B, an internal pressure monitoring unit  42 , a power reception unit  44 , a charging permission signal output unit  46 , and a movable body position detection unit  48 . The pressure detection units  40 A and  40 B are devices (sensors) configured to detect the pressure inside the frame  11 . The pressure detection units  40 A and  40 B detect whether the pressure inside the frame  11  is equal to or higher than the threshold pressure. The threshold pressure is a pressure set in advance and equal to or higher than the pressure inside the frame  11 . For example, the threshold pressure may be set to be equal to or higher than atmospheric pressure. The pressure detection units  40 A and  40 B may include a pressure sensor configured to detect the pressure inside the frame  11  and a pressure sensor configured to detect the pressure outside the frame  11  and may detect pressures inside and outside the frame  11 . In this case, the pressure detection units  40 A and  40 B may detect whether the pressure inside the frame  11  is equal to or higher than the pressure outside the frame  11  as the threshold pressure. In the present embodiment, two pressure detection units are provided for improving safety, but one pressure detection unit may be provided or three or more pressure detection units may be provided. Hereinafter, the pressure detection units  40 A and  40 B are referred to as pressure detection units  40  when not distinguished from each other. 
     The internal pressure monitoring unit  42  is provided in the frame  11 . Based on detection results of the pressure detection units  40 , the internal pressure monitoring unit  42  switches between transmitting and stopping the signal to the power reception unit  44  and also switches between supplying and stopping the power to the movable body position detection unit  48 . When the pressure detection units  40  detect that the pressure inside the frame  11  is equal to or higher than the threshold pressure, the internal pressure monitoring unit  42  transmits, to the power reception unit  44 , a signal indicating that charging is possible, and power is supplied to the movable body position detection unit  48 . When the pressure detection units  40  detect that the pressure inside the frame  11  is lower than the threshold pressure, the internal pressure monitoring unit  42  does not transmit, to the power reception unit  44 , the signal indicating that charging is possible, and power supply is stopped to the movable body position detection unit  48 . Thus, the internal pressure monitoring unit  42  is a switch element configured to switch on and off the contacts to the power reception unit  44  and the movable body position detection unit  48  based on detection results of the pressure detection units  40 , which will be described in detail later. When the pressure inside the frame  11  is detected by the pressure detection units  40  to be equal to or higher than the threshold pressure, the internal pressure monitoring unit  42  may supply power to the movement device  12  (the electric motor  21 ), the control device  14 , the camera  16 , and the communication device  17 . When the pressure inside the frame  11  is detected by the pressure detection units  40  to be lower than the threshold pressure, the internal pressure monitoring unit  42  may stop power supply to the movement device  12  (the electric motor  21 ), the control device  14 , the camera  16 , and the communication device  17 . 
     The power reception unit  44  is a device (charger) connected with the battery  13  and configured to charge the battery  13  by receiving power from the charging station  100 . The configuration of the power reception unit  44  will be described later. 
     The charging permission signal output unit  46  outputs a charging permission signal L 0  based on detection results of the pressure detection units  40 . The charging permission signal output unit  46  outputs the charging permission signal L 0  when the pressure inside the frame  11  is detected by the pressure detection units  40  to be equal to or higher than the threshold pressure, and stops outputting the charging permission signal L 0  when the pressure inside the frame  11  is detected by the pressure detection units  40  to be lower than the threshold pressure. In the present embodiment, the charging permission signal output unit  46  outputs the charging permission signal L 0  when the signal indicating that charging is possible is transmitted from the internal pressure monitoring unit  42  to the power reception unit  44 . Details of the charging permission signal output unit  46  will be described later. 
     The movable body position detection unit  48  outputs a signal (a movable body signal L 2  to be described later) based on detection results of the pressure detection units  40  and based on whether a signal (a station signal L 1  to be described later) from the charging station  100  is acquired. When the pressure inside the frame  11  is detected by the pressure detection units  40  to be equal to or higher than the threshold pressure and the signal (the station signal L 1  to be described later) from the charging station is acquired, the movable body position detection unit  48  outputs the signal (the movable body signal L 2  to be described later). When at least one of two conditions is not satisfied, the movable body position detection unit  48  outputs no signal (the movable body signal L 2  to be described later). The two conditions are: a condition in which the pressure inside the frame  11  is detected by the pressure detection units  40  to be equal to or higher than the threshold pressure; and a condition in which the signal (the station signal L 1  to be described later) is acquired from the charging station. Details of the movable body position detection unit  48  will be described later. 
     The movable body  10  configured as described above can move forward, backward, and stop through control of the movement device  12  by the control device  14 . The movable body  10  can be steered by adjusting the speeds of the right and left crawlers  23  through control of the movement device  12  by the control device  14 . In the movable body  10 , the control device  14  stores a patrol map and determines a moving route based on this map information and distance information detected by a sensor mounted on the movable body  10 . The movable body  10  may determine a moving route in accordance with position signals from the GPS. 
     The movable body  10  needs to be subjected to power supply when the charged amount of the battery  13  has reduced through patrol inspection work or the like. Thus, in the present embodiment, the charging station  100  is provided in a patrol inspection work zone. Subsequently, the charging station  100  will be described. 
     Configuration of Charging Station 
     The charging station  100  is provided in a facility in which the movable body  10  performs work. Thus, the charging station  100  is provided in an explosive atmosphere. Thus, the charging station  100  has an explosion-proof structure, more specifically, a pressure-resistant explosion-proof structure. The charging station  100  charges the movable body  10  when the movable body  10  has moved into a charging region Po (refer to  FIG. 5 ) and conditions described below are satisfied. The charging region Po is set as a region in which the movable body  10  needs to be positioned in order to enable non-contact charging by the charging station  100 . The charging region Po is in a predetermined region facing the charging station  100 . The charging station  100  may replenish the movable body  10  with internal pressure gas in addition to charging of the movable body  10 . 
       FIG. 2  is a schematic block diagram of the charging station according to the present embodiment. As illustrated in  FIG. 2 , the charging station  100  includes a power source unit  102 , a power transmission unit  104 , a charging permission signal acquisition unit  105 , a station position detection unit  106 , an interface position detection unit  108 , and a light emission control unit  110 . The power source unit  102 , the power transmission unit  104 , the charging permission signal acquisition unit  105 , the station position detection unit  106 , the interface position detection unit  108 , and the light emission control unit  110  are disposed in the pressure-resistant explosion-proof structure of the charging station  100 . 
     The power source unit  102  is a power source capable of supplying power. The power transmission unit  104  is a device configured to charge the battery  13  of the movable body  10  with power from the power source unit  102 . The power transmission unit  104  charges the battery  13  of the movable body  10  by non-contact charging. The charging permission signal acquisition unit  105  can acquire a charging permission signal from the charging permission signal output unit  46  of the movable body  10  being positioned in the charging region Po. When having acquired a signal (the movable body signal L 2  to be described later) from the movable body position detection unit  48  of the movable body  10 , the station position detection unit  106  moves a power transmission coil  166  (refer to  FIG. 3 ) of the power transmission unit  104  toward a power reception coil  66  (refer to  FIG. 3 ) of the power reception unit  44  of the movable body  10 . The interface position detection unit  108  detects a relative position between the power transmission coil  166  and the power reception coil  66 . The light emission control unit  110  controls light emission of the station position detection unit  106  and the interface position detection unit  108 . The configuration of each component of the charging station  100  will be described below in detail based on  FIG. 3 . 
     Functional Configurations of Movable Body and Charging Station 
       FIG. 3  is a schematic diagram for description of charging between the movable body and the charging station.  FIG. 3  is a block diagram of components of the movable body  10  and the charging station  100 , which are used when charging is performed, illustrating functional configurations thereof. As illustrated in  FIG. 3 , in the movable body  10 , the pressure detection unit  40 A is connected with an internal pressure monitoring unit  42 A, and the pressure detection unit  40 B is connected with an internal pressure monitoring unit  42 B. In other words, one pressure detection unit  40  is connected with one internal pressure monitoring unit  42 . Detection results of the pressure inside the frame  11  detected by the pressure detection units  40  are converted into digital data by an AD converter (not illustrated). The internal pressure monitoring unit  42  acquires the detection results of the pressure detection units  40 , which is converted into the digital data. 
     The internal pressure monitoring unit  42 A is a switch element capable of operating a contact point D 1  that is connected with a signal line  52  to be described later and a contact point D 3  that is connected with an electrical line  54  to be described later. When the internal pressure of the frame  11  is equal to or higher than the threshold pressure based on the detection result of the pressure detection unit  40 A, the internal pressure monitoring unit  42 A puts the contact points D 1  and D 3  into closed states (connected states). When the internal pressure of the frame  11  is lower than the threshold pressure based on the detection result of the pressure detection unit  40 A, the internal pressure monitoring unit  42 A puts the contact points D 1  and D 3  into opened states (disconnected states). The internal pressure monitoring unit  42 B is a switch element capable of operating a contact point D 2  that is connected with the signal line  52  and a contact point D 4  that is connected with the electrical line  54 . When the internal pressure of the frame  11  is equal to or higher than the threshold pressure based on the detection result of the pressure detection unit  40 B, the internal pressure monitoring unit  42 B puts the contact points D 2  and D 4  into closed states (connected states). When the internal pressure of the frame  11  is lower than the threshold pressure based on the result of detection by the pressure detection unit  40 B, the internal pressure monitoring unit  42 B puts the contact points D 2  and D 4  into opened states (disconnected states). In this manner, the number of internal pressure monitoring units  42  is two in accordance with the number of pressure detection units  40 , but may be, for example, one when the number of pressure detection units  40  is one. In this case, the number of contact points is one for each of the signal line  52  and the electrical line  54 . When the number of pressure detection units  40  is equal to or larger than three, the number of internal pressure monitoring units  42 , the number of contact points of the signal line  52 , and the number of contact points of the electrical line  54  are each equal to or larger than three in accordance with the number of pressure detection units  40 . 
     As illustrated in  FIG. 3 , in the movable body  10 , the power reception unit  44  is connected with the signal line  52 . The power reception unit  44  includes a control unit  60 , a power reception control unit  62 , a smoothing circuit  64 , a capacitor  65 , and the power reception coil  66 . The control unit  60  is an arithmetic device, in other words, a central processing unit (CPU) configured to control the power reception unit  44 . The control unit  60  is connected with the signal line  52  and can receive, from the signal line  52 , a signal S 0  indicating that the movable body  10  is to be charged. More specifically, the signal line  52  is connected with, for example, a battery control unit (not illustrated) included in the battery  13 . The battery control unit checks the current charged amount (battery remaining amount) of the battery  13  and outputs the signal S 0  to the signal line  52  when charging is needed. In other words, the signal S 0  is a signal serving as a trigger for requesting charging. The signal line  52  is connected in series with the contact points D 1  and D 2 . When the internal pressure of the frame  11  is equal to or higher than the threshold pressure based on the detection results of the pressure detection units  40 A and  40 B, the contact points D 1  and D 2  become the closed states (connected states), so that the control unit  60  is connected with the signal line  52 . In other words, when the contact points D 1  and D 2  are both in the closed states (connected states), the control unit  60  receives the signal S 0  from the signal line  52 . When the internal pressure of the frame  11  is lower than the threshold pressure based on at least one of the detection results of the pressure detection units  40 A and  40 B, at least one of the contact points D 1  and D 2  becomes the opened state (disconnected state), so that the control unit  60  is not connected with the signal line  52 . In other words, when at least one of the contact points D 1  and D 2  is in the opened state, the control unit  60  stops receiving the signal S 0  from the signal line  52  (does not receive the signal S 0 ). 
     When having received the signal S 0  from the signal line  52 , the control unit  60  transmits a control signal to the power reception control unit  62 . The control signal is a signal for controlling charging of the battery  13  and is a signal that serves as a trigger for causing the power reception control unit  62  to start the charging. The control signal may include a signal instructing a charging scheme such as constant voltage (CV) charging or constant current (CC) charging. 
     The power reception control unit  62  is a control circuit configured to control charging of the battery  13 , in other words, a control circuit configured to control the amount of power received by the power reception coil  66 . The power reception control unit  62  is connected with the control unit  60  to acquire the control signal from the control unit  60 . The smoothing circuit  64  is connected with the power reception control unit  62 . The smoothing circuit  64  is a circuit configured to rectify and convert alternating current received by the power reception coil  66  into direct current and smooth the rectified direct current. The capacitor  65  and the power reception coil  66  are connected with the power reception control unit  62  through the smoothing circuit  64 . The capacitor  65  and the power reception coil  66  are connected in series with each other to form a series resonance circuit. The power reception control unit  62  controls power reception by the power reception coil  66  based on the control signal from the control unit  60 . The power reception coil  66  is connected with the battery  13  through the smoothing circuit  64  and the power reception control unit  62 . Power (alternating-current power) received by the power reception coil  66  is rectified by the smoothing circuit  64  into direct-current power and is output to the battery  13  to charge the battery  13 . 
     The control unit  60  is also connected with the charging permission signal output unit  46 . When having received the signal S 0  from the signal line  52 , the control unit  60  outputs, to the charging permission signal output unit  46 , a signal indicating that the charging permission signal is to be output. Having acquired, from the control unit  60 , the signal indicating that the charging permission signal is to be output, the charging permission signal output unit  46  outputs the charging permission signal L 0 . Specifically, the charging permission signal output unit  46  outputs the charging permission signal L 0  when the internal pressure of the frame  11  is equal to or higher than the threshold pressure based on the detection results of the pressure detection units  40 A and  40 B. The charging permission signal output unit  46  stops outputting the charging permission signal L 0  (does not output the charging permission signal L 0 ) when the internal pressure of the frame  11  is lower than the threshold pressure based on at least one of the detection results of the pressure detection units  40 A and  40 B. Thus, the charging permission signal L 0  is a signal indicating that the pressure inside the frame  11  has been detected to be equal to or higher than the threshold pressure, and is a signal indicating that the charging station  100  is permitted to perform charging. 
     The charging permission signal L 0  is a signal for permitting the charging station  100  to perform charging, and is a signal that serves as a trigger for starting charging by the charging station  100 . In the present embodiment, the charging permission signal output unit  46  outputs the charging permission signal L 0  as light. In other words, the charging permission signal output unit  46  is a light source configured to emit light of the charging permission signal L 0 . The charging permission signal L 0  is, for example, infrared light but may be visible light or the like. The charging permission signal L 0  is not limited to an optical signal as long as a signal does not cause ignition in a volatile atmosphere, and may be, for example, radio wave or ultrasonic wave. Specifically, the control unit  60  may output the charging permission signal L 0  to the charging station  100  through, for example, a wireless network using radio wave, such as Wi-Fi (registered trademark), Bluetooth (registered trademark), or specified low power radio, or ultrasonic wave communication using ultrasonic wave. 
     In the movable body  10 , the movable body position detection unit  48  is connected with the electrical line  54 . The movable body position detection unit  48  is a mechanism for detecting a relative position between the movable body  10  and the charging station  100 , in other words, a mechanism for detecting whether the movable body  10  is positioned in the charging region Po. The movable body position detection unit  48  includes a movable body signal acquisition unit  70  and a movable body signal output unit  72 . The movable body signal acquisition unit  70  acquires the station signal L 1  from a station signal output unit  140  of the charging station  100  to be described later. Since the station signal L 1  in the present embodiment is light, the movable body signal acquisition unit  70  in the present embodiment is a light receiving element. Specifically, the movable body signal acquisition unit  70  detects that the station signal L 1  has been acquired when the station signal L 1  has entered the movable body signal acquisition unit  70 , and does not detect that the station signal L 1  has been acquired when the station signal L 1  has not entered the movable body signal acquisition unit  70 . 
     The movable body signal output unit  72  outputs a movable body signal L 2  when the station signal L 1  is received by the movable body signal acquisition unit  70 . When the station signal L 1  is not received by the movable body signal acquisition unit  70 , the movable body signal output unit  72  stops outputting the movable body signal L 2  (does not output the movable body signal L 2 ). In the present embodiment, the movable body signal output unit  72  outputs the movable body signal L 2  as light. In other words, the movable body signal output unit  72  is a light source configured to emit light of the movable body signal L 2 . The movable body signal L 2  is, for example, visible light, and the movable body signal output unit  72  is a laser emitting diode (LED). The movable body signal output unit  72  emits, for example, visible light of red as the movable body signal L 2 . However, the movable body signal L 2  is not limited to visible light but may be, for example, infrared light. The movable body signal L 2  is not limited to an optical signal as long as the signal does not cause ignition in an explosive atmosphere, and may be, for example, ultrasonic wave or radio wave. 
     The movable body signal acquisition unit  70  and the movable body signal output unit  72  are each connected with the electrical line  54  to operate upon reception of power P from the electrical line  54 . The electrical line  54  is connected with, for example, the battery  13  to supply the power P from the battery  13 . The electrical line  54  has the contact points D 3  and D 4  connected in series. The movable body signal acquisition unit  70  and the movable body signal output unit  72  are connected with the electrical line  54  when the contact points D 3  and D 4  are both in the closed states (connected states), in other words, when the internal pressure of the frame  11  is equal to or higher than the threshold pressure based on the detection results of the pressure detection units  40 A and  40 B. When the contact points D 3  and D 4  are both in the closed states (connected states), the movable body signal acquisition unit  70  and the movable body signal output unit  72  receive the power P from the electrical line  54  and perform operation, in other words, light reception and light emission. When at least one of the contact points D 3  and D 4  is in the opened state (disconnected state), in other words, when the internal pressure of the frame  11  is lower than the threshold pressure based on at least one of the detection results of the pressure detection units  40 A and  40 B, the movable body signal acquisition unit  70  and the movable body signal output unit  72  are not connected with the electrical line  54 . When at least one of the contact points D 3  and D 4  is in the opened state (disconnected state), the movable body signal acquisition unit  70  and the movable body signal output unit  72  stop operation, in other words, light reception and light emission because supply of the power P from the electrical line  54  is stopped. 
     The movable body  10  is also provided with a reflection unit  74 . The reflection unit  74  is a mechanism for detecting whether the power reception coil  66  of the movable body  10  and the power transmission coil  166  (to be described later) of the charging station  100  are at appropriate positions, in other words, is a mechanism for positioning the power reception coil  66  and the power transmission coil  166 . The reflection unit  74  receives a signal (interface signal L 3 ) from an interface signal output unit  150  of the charging station  100  to be described later and reflects the received signal. Since the interface signal L 3  is light in the present embodiment, the reflection unit  74  is a member capable of reflecting light. 
     As illustrated in  FIG. 3 , the light emission control unit  110  of the charging station  100  is connected with the power source unit  102  through an electrical line  130  to receive supply of the power P from the power source unit  102 . A converter may be provided between the power source unit  102  and the light emission control unit  110 . In this case, for example, alternating-current power from the power source unit  102  is converted into direct-current power by the converter, and the power P converted into direct-current power is supplied to the light emission control unit  110 . The light emission control unit  110  is a device configured to control operation of the station position detection unit  106  and the interface position detection unit  108 , in other words, light emission. 
     In the charging station  100 , the station position detection unit  106  is connected with the light emission control unit  110  through an electrical line  132 . The station position detection unit  106  is a mechanism for detecting a relative position between the movable body  10  and the charging station  100 , in other words, is a mechanism for detecting whether the movable body  10  is positioned in the charging region Po. The station position detection unit  106  includes the station signal output unit  140 , a station signal acquisition unit  142 , and a switch unit  144 . The station signal output unit  140  outputs the station signal L 1 . In the present embodiment, the station signal output unit  140  outputs the station signal L 1  as light. In other words, the station signal output unit  140  is a light source configured to emit light of the station signal L 1 . The station signal L 1  is, for example, visible light, and the station signal output unit  140  is a laser emitting diode (LED). The station signal output unit  140  emits, for example, visible light of red as the station signal L 1 . However, the station signal L 1  is not limited to visible light but may be, for example, infrared light. The station signal L 1  is not limited to an optical signal as long as the signal does not cause ignition in an explosive atmosphere, and may be, for example, ultrasonic wave or radio wave. 
     The station signal output unit  140  continuously outputs the station signal L 1 , in other words, emits light. However, as will be described later, the station signal output unit  140  stops outputting the station signal L 1  during a predetermined time when the movable body  10  departs after charging is completed. 
     The station signal acquisition unit  142  acquires the movable body signal L 2  from the movable body signal output unit  72  of the movable body  10 . Since the movable body signal L 2  in the present embodiment is light, the station signal acquisition unit  142  in the present embodiment is a light receiving element. Specifically, the station signal acquisition unit  142  detects that the station signal L 1  has been acquired when the movable body signal L 2  has entered the station signal acquisition unit  142 , and does not detect that the station signal L 1  has been acquired when the movable body signal L 2  has not entered the station signal acquisition unit  142 . 
     The switch unit  144  is connected with the station signal acquisition unit  142 . The switch unit  144  is a switch element capable of operating a contact point D 6  that is connected with a signal line  136  to be described later. When the movable body signal L 2  is acquired (light thereof is received) by the station signal acquisition unit  142 , the switch unit  144  puts the contact point D 6  into a closed state (connected state). When the movable body signal L 2  is not acquired (light thereof is not received) by the station signal acquisition unit  142 , the switch unit  144  puts the contact point D 6  into an opened state (disconnected state). 
     The station signal output unit  140  and the station signal acquisition unit  142  perform operation, in other words, light emission and light reception upon reception of supply of the power P from the light emission control unit  110 . Specifically, the light emission control unit  110  controls the operation, in other words, light emission and light reception of the station signal output unit  140  and the station signal acquisition unit  142  by controlling power supply to the station signal output unit  140  and the station signal acquisition unit  142 . The light emission control unit  110  operates the station signal output unit  140  and the station signal acquisition unit  142  by supplying power to the station signal output unit  140  and the station signal acquisition unit  142 , and stops the operation of the station signal output unit  140  and the station signal acquisition unit  142  by stopping power supply to the station signal output unit  140  and the station signal acquisition unit  142 . 
     In the charging station  100 , the interface position detection unit  108  is connected with the light emission control unit  110  through an electrical line  134 . The interface position detection unit  108  is a mechanism for detecting whether the power reception coil  66  of the movable body  10  and the power transmission coil  166  (to be described later) of the charging station  100  are at appropriate positions, in other words, is a mechanism for positioning the power reception coil  66  and the power transmission coil  166 . The interface position detection unit  108  includes the interface signal output unit  150 , an interface signal acquisition unit  152 , and a switch unit  154 . 
     The interface signal output unit  150  outputs the interface signal L 3 . In the present embodiment, the interface signal output unit  150  outputs the interface signal L 3  as light. In other words, the interface signal output unit  150  is a light source configured to emit light of the interface signal L 3 . The interface signal L 3  is, for example, visible light, and the interface signal output unit  150  is an LED. The interface signal output unit  150  emits, for example, visible light of red as the interface signal L 3 . However, the interface signal L 3  is not limited to visible light but may be, for example, infrared light. The interface signal L 3  is not limited to an optical signal as long as the signal does not cause ignition in an explosive atmosphere. In other words, the interface signal output unit  150  is not limited to a device configured to detect whether the power reception coil  66  and the power transmission coil  166  are at appropriate positions using the light signal. The interface signal output unit  150  may be, for example, a limit switch configured to output a contact point signal, a proximity sensor, a magnetic sensor configured to output a magnetic signal, or an ultrasonic wave sensor configured to output an ultrasonic wave signal. 
     When the power reception coil  66  and the power transmission coil  166  are at appropriate positions, the interface signal L 3  from the interface signal output unit  150  is output toward the reflection unit  74  of the movable body  10 . The reflection unit  74  reflects the interface signal L 3  as a reflection signal L 3   a . The reflection signal L 3   a  is reflected light of the interface signal L 3 . The interface signal acquisition unit  152  acquires the reflection signal L 3   a  from the reflection unit  74 . Since the reflection signal L 3   a  is light, the interface signal acquisition unit  152  in the present embodiment is a light receiving element. Specifically, the interface signal acquisition unit  152  detects that the reflection signal L 3   a  has been acquired when the reflection signal L 3   a  has entered the interface signal acquisition unit  152 . 
     The switch unit  154  is connected with the interface signal acquisition unit  152 . The switch unit  154  is a switch element capable of operating a contact point D 5  that is connected with the signal line  136  to be described later. When the reflection signal L 3   a  acquired (light thereof received) by the interface signal acquisition unit  152  satisfies a predetermined condition, the switch unit  154  puts the contact point D 5  into a closed state (connected state). When the reflection signal L 3   a  acquired (light thereof received) by the interface signal acquisition unit  152  does not satisfy the predetermined condition, the switch unit  154  puts the contact point D 5  into an opened state (disconnected state). The predetermined condition is such that, for example, the intensity of the reflection signal L 3   a  is in a threshold intensity range. Specifically, when the intensity of the reflection signal L 3   a  is in the threshold intensity range, the interface position detection unit  108  determines that the power reception coil  66  and the power transmission coil  166  are at appropriate positions and the reflection signal L 3   a  is appropriately reflected on the interface signal L 3 , and puts the contact point D 5  into the closed state (connected state). When the intensity of the reflection signal L 3   a  is out of the threshold intensity range, the interface position detection unit  108  determines that the reflection signal L 3   a  is not appropriately reflected on the interface signal L 3  because the power reception coil  66  and the power transmission coil  166  are not at appropriate positions or a foreign object is interposed between the power reception coil  66  and the power transmission coil  166 , and puts the contact point D 5  into the opened state (disconnected state). The case in which the intensity of the reflection signal L 3   a  is out of the threshold intensity range includes a case in which the intensity of the reflection signal L 3   a  is too high or too low as well as a case in which light of the reflection signal L 3   a  cannot be received. 
     In the charging station  100 , the signal line  136  is connected with a switch unit  138 . For example, a signal S 1  is output to the signal line  136  from a control unit (not illustrated) in the charging station  100 . The signal S 1  is a signal that serves as a trigger for causing the power transmission unit  104  to start charging. The signal line  136  is provided with the contact points D 5  and D 6 . The switch unit  138  is a switch element configured to operate a contact point D 7  that is connected with an electrical line  160  to be described later. When the contact points D 5  and D 6  are both in the closed states (connected states), the switch unit  138  receives the signal S 1 . When the contact points D 5  and D 6  are both in the closed states, the switch unit  138  receives the signal S 1  and puts the contact point D 7  into a closed state (connected state). Specifically, when the movable body signal L 2  is acquired (light thereof is received) by the station signal acquisition unit  142  and the reflection signal L 3   a  acquired by the interface signal acquisition unit  152  satisfies the predetermined condition, the switch unit  138  puts the contact point D 7  into the closed state (connected state). When at least one of the contact points D 5  and D 6  is in the opened state (disconnected state), the switch unit  138  stops receiving the signal S 1  (does not receive the signal S 1 ) and puts the contact point D 7  into an opened state (disconnected state). Specifically, when at least one of two cases is not satisfied, the switch unit  138  puts the contact point D 7  into the opened state (disconnected state). The two cases are: a case in which the movable body signal L 2  (reception of light thereof) is acquired by the station signal acquisition unit  142 ; and a case in which the reflection signal L 3   a  acquired by the interface signal acquisition unit  152  satisfies the predetermined condition. 
     In the charging station  100 , the power transmission unit  104  is connected with the power source unit  102  through the electrical line  160 . The electrical line  160  is provided with the contact point D 7  and supplied with the power P from the power source unit  102 . When the contact point D 7  is in the closed state (connected state), in other words, when the movable body signal L 2  is acquired (light thereof is received) by the station signal acquisition unit  142 , and the reflection signal L 3   a  acquired by the interface signal acquisition unit  152  satisfies the predetermined condition, the power transmission unit  104  receives power supply from the power source unit  102 . When the contact point D 7  is in the opened state (disconnected state), in other words, when at least one of two cases is not satisfied, the power supply from the power source unit  102  to the power transmission unit  104  is stopped. The two cases are: a case in which the movable body signal L 2  is acquired (light thereof is received) by the station signal acquisition unit  142 ; and a case in which the reflection signal L 3   a  acquired by the interface signal acquisition unit  152  satisfies the predetermined condition. 
     The power transmission unit  104  includes a power transmission control unit  162 , a capacitor  164 , and the power transmission coil  166 . The power transmission control unit  162  is a control circuit configured to control charging of the battery  13 , in other words, is a control circuit configured to control the amount of power transmitted by the power transmission coil  166 . The power transmission control unit  162  is connected with the power source unit  102  through the electrical line  160 . The capacitor  164  and the power transmission coil  166  are connected with the power transmission control unit  162 . The capacitor  164  and the power transmission coil  166  are connected in series with each other to form a series resonance circuit. The power transmission coil  166  is supplied with the power P from the power source unit  102  through the power transmission control unit  162 . The power transmission coil  166  can transmit power to the power reception coil  66  in a non-contact manner when the power reception coil  66  is provided at a position facing the power transmission coil  166 . 
     In the charging station  100 , the charging permission signal acquisition unit  105  is connected with the power transmission control unit  162 . The charging permission signal acquisition unit  105  acquires the charging permission signal L 0  from the charging permission signal output unit  46  of the movable body  10 . Since the charging permission signal L 0  is light in the present embodiment, the charging permission signal acquisition unit  105  is a light receiving element capable of receiving light of the charging permission signal L 0 . Specifically, the charging permission signal acquisition unit  105  detects that the charging permission signal L 0  has been acquired when the charging permission signal L 0  is incident thereon, and does not detect that the charging permission signal L 0  has been acquired when the charging permission signal L 0  is not incident thereon. When the charging permission signal L 0  is acquired by the charging permission signal acquisition unit  105  while the power P is supplied from the power source unit  102 , the power transmission control unit  162  supplies the power P to the power transmission coil  166  and causes the power transmission coil  166  to perform power transmission. 
     The power transmission unit  104  includes a movement unit  168 . The movement unit  168  is a mechanism configured to move the power transmission coil  166  toward the power reception coil  66  side. The movement unit  168  moves the power transmission coil  166  toward the power reception coil  66  side when the movable body signal L 2  is acquired (light thereof is received) by the station signal acquisition unit  142 . 
     The functional configurations of the movable body  10  and the charging station  100  are as described above. Subsequently, a method of charging the movable body  10  will be described below. 
     Charging Method 
       FIG. 4  is a flowchart for description of a charging method according to the present embodiment.  FIG. 5  is a schematic diagram illustrating positions at a time of charging of the movable body. As illustrated in  FIG. 4 , in the charging station  100 , the station signal output unit  140  emits light of the station signal L 1  (step S 10 ). The station signal output unit  140  continuously emits light of the station signal L 1  during a period other than a predetermined period when the movable body  10  departs. When having determined that charging is needed, the movable body  10  moves to a position facing the charging station  100  in such a state. 
     More specifically, as illustrated in  FIG. 5 , the movable body  10  moves to the charging region Po, which is a region facing the charging station  100 . As illustrated in  FIG. 5 , the charging region Po is set at a position where the power reception coil  66  faces the power transmission coil  166  at a predetermined distance, the reflection unit  74  faces the interface signal output unit  150  and the interface signal acquisition unit  152  at a predetermined distance, the charging permission signal output unit  46  faces the charging permission signal acquisition unit  105  at a predetermined distance, the movable body signal output unit  72  faces the station signal acquisition unit  142  at a predetermined distance, and the movable body signal acquisition unit  70  faces the station signal output unit  140  at a predetermined distance. Accordingly, when the movable body  10  is positioned in the charging region Po, the power reception coil  66  faces the power transmission coil  166 , the reflection unit  74  faces the interface signal output unit  150  and the interface signal acquisition unit  152 , the charging permission signal output unit  46  faces the charging permission signal acquisition unit  105 , the movable body signal output unit  72  faces the station signal acquisition unit  142 , and the movable body signal acquisition unit  70  faces the station signal output unit  140 . The distance (predetermined distance) between the charging permission signal output unit  46  and the charging permission signal acquisition unit  105 , the distance (predetermined distance) between the movable body signal output unit  72  and the station signal acquisition unit  142 , and the distance (predetermined distance) between the movable body signal acquisition unit  70  and the station signal output unit  140  are set to be lengths with which each light receiving element (the charging permission signal acquisition unit  105 , the station signal acquisition unit  142 , or the movable body signal acquisition unit  70 ) can receive light from the corresponding unit that faces the corresponding light receiving element when the movable body  10  is positioned in the charging region Po. 
     In this manner, when the movable body  10  has arrived at the charging region Po, the movable body signal acquisition unit  70  faces the station signal output unit  140 . The station signal output unit  140  emits light of the station signal L 1  to a region that the station signal output unit  140  faces. Thus, when the movable body  10  is positioned in the charging region Po, the movable body signal acquisition unit  70  receives the light of the station signal L 1  from the station signal output unit  140 . Specifically, when having arrived at the charging region Po, the movable body  10  determines whether the light of the station signal L 1  is received by the movable body signal acquisition unit  70  (step S 12 ) as illustrated in  FIG. 4 . When the light of the station signal L 1  is not received by the movable body signal acquisition unit  70  (No at step S 12 ), the movable body  10  returns to step S 12  and continues the determination of whether the light of the station signal L 1  is received. For example, when the light of the station signal L 1  is not received, the movable body  10  determines that the movable body  10  has not appropriately arrived at the charging region Po, and moves again to park in the charging region Po. When the light of the station signal L 1  is received by the movable body signal acquisition unit  70  (Yes at step S 12 ), the movable body  10  performs light emission (outputting) of the movable body signal L 2  through the movable body signal output unit  72  under condition that the internal pressure of the frame  11  is equal to or higher than the threshold pressure (step S 14 ). Specifically, the movable body signal output unit  72  emits light of the movable body signal L 2  when the light of the station signal L 1  is received by the movable body signal acquisition unit  70  and the internal pressure of the frame  11  is equal to or higher than the threshold pressure, in other words, the internal pressure of the frame  11  is equal to or higher than the threshold pressure based on both detection results of the pressure detection units  40 A and  40 B. The movable body signal output unit  72  does not emit the light of the movable body signal L 2  when the light of the station signal L 1  is not received by the movable body signal acquisition unit  70 . In addition, the movable body signal output unit  72  does not emit the light of the movable body signal L 2  when the internal pressure of the frame  11  is lower than the threshold pressure, in other words, the internal pressure of the frame  11  is lower than the threshold pressure based on at least one of the detection results of the pressure detection units  40 A and  40 B. 
     In the following processing as well, the pressure detection units  40 A and  40 B constantly continues detection of whether the internal pressure of the frame  11  is equal to the threshold pressure. When the internal pressure of the frame  11  has become lower than the threshold pressure, the movable body  10  puts, at least one of the contact points D 1  and D 2  and at least one of the contact points D 3  and D 4 , which are illustrated in  FIG. 3 , into the opened states (disconnected states). Thus, when the internal pressure of the frame  11  has become lower than the threshold pressure, the movable body  10  stops emitting light of the movable body signal L 2  and outputting the charging permission signal L 0  to be described later and stops non-contact charging, in other words, charging work at steps described with reference to  FIG. 4 . 
     The movable body signal output unit  72  emits light of the movable body signal L 2  to a region that the movable body signal output unit  72  faces. Thus, when the movable body  10  is positioned in the charging region Po, the charging station  100  receives the light of the movable body signal L 2  from the movable body signal output unit  72  through the station signal acquisition unit  142 . The charging station  100  determines whether the light of the movable body signal L 2  has been received by the station signal acquisition unit  142  (step S 16 ), and when the light of the movable body signal L 2  has been received (Yes at step S 16 ), the charging station  100  causes the movement unit  168  to move the power transmission coil  166  toward the power reception coil  66  (step S 18 ). As illustrated in  FIG. 5 , when the movable body  10  is positioned in the charging region Po, the power transmission coil  166  and the power reception coil  66  face each other while being separated from each other at a distance longer than a distance at which non-contact charging is possible. In this state, the movement unit  168  moves the power transmission coil  166  toward the power reception coil  66 , so that the power transmission coil  166  and the power reception coil  66  are brought close to each other to a distance at which non-contact charging is possible while maintaining the state of being separated from each other. The movement unit  168  is attached to the interface signal output unit  150  and the interface signal acquisition unit  152  in addition to the power transmission coil  166 . Accordingly, the movement unit  168  moves the power transmission coil  166 , the interface signal output unit  150 , and the interface signal acquisition unit  152  to the movable body  10  side. The movement unit  168  moves the interface signal output unit  150  and the interface signal acquisition unit  152  toward the reflection unit  74  as the power transmission coil  166  moves. The movement unit  168  brings the interface signal output unit  150  and the interface signal acquisition unit  152  close to the reflection unit  74 , so that the reflection unit  74  can receive light of the interface signal L 3  from the interface signal output unit  150  and the interface signal acquisition unit  152  can receive light of the reflection signal L 3   a  from the reflection unit  74 . In the present embodiment, the interface signal output unit  150  and the interface signal acquisition unit  152  are attached to the movement unit  168  and moved integrally with the movement unit  168  in this manner. However, the station signal output unit  140 , the station signal acquisition unit  142 , and the charging permission signal acquisition unit  105  may be attached to the movement unit  168  in the charging station  100 , and these units may be moved integrally with the movement unit  168 . 
     In this manner, when the light of the movable body signal L 2  from the movable body signal output unit  72  is received, the charging station  100  determines that the movable body  10  is appropriately positioned in the charging region Po, and causes the movement unit  168  to move the power transmission coil  166  to a position at which non-contact charging is possible. When the light of the movable body signal L 2  is not received by the station signal acquisition unit  142  (No at step S 16 ), the charging station  100  returns to step S 16  and continues the determination of whether the light of the movable body signal L 2  is received. In other words, when the light of the movable body signal L 2  is not received, the charging station  100  determines that the movable body  10  is not appropriately positioned in the charging region Po, and does not move the power transmission coil  166 . 
     After having moved the power transmission coil  166 , the charging station  100  causes the interface signal output unit  150  to emit light of the interface signal L 3  (step S 20 ). The interface signal output unit  150  and the interface signal acquisition unit  152  have been brought close to the reflection unit  74  as the power transmission coil  166  has moved. Thus, when the power transmission coil  166  and the power reception coil  66  are at appropriate positions, in other words, at positions where non-contact charging is possible, the interface signal L 3  from the interface signal output unit  150  is reflected as the reflection signal L 3   a  by the reflection unit  74 . Then, the light of the reflection signal L 3   a  from the reflection unit  74  is received by the interface signal acquisition unit  152 . The interface signal output unit  150  may continuously emits light of the interface signal L 3  or may be controlled to emit light of the interface signal L 3  by the light emission control unit  110 , triggered by movement of the power transmission coil  166 . The interface signal output unit  150  is separate from the reflection unit  74  before movement of the power transmission coil  166 . Thus, even when light of the interface signal L 3  is continuously emitted, acquisition of the reflection signal L 3   a  by the interface signal acquisition unit  152  does not occur before step S 20 . 
     The charging station  100  determines whether the power transmission coil  166  and the power reception coil  66  are at appropriate positions, based on the reflection signal L 3   a  from the reflection unit  74  (step S 22 ). When the light of the reflection signal L 3   a  received by the interface signal acquisition unit  152  satisfies the predetermined condition, in other words, the intensity of the reflection signal L 3   a  is in the threshold intensity range, the interface position detection unit  108  of the charging station  100  determines that the power transmission coil  166  and the power reception coil  66  are at appropriate positions. When the light of the reflection signal L 3   a  received by the interface signal acquisition unit  152  does not satisfy the predetermined condition, in other words, the intensity of the reflection signal L 3   a  is not in the threshold intensity range, the charging station  100  determines that the power transmission coil  166  and the power reception coil  66  are not at appropriate positions. 
     When the power transmission coil  166  and the power reception coil  66  are at appropriate positions (Yes at step S 22 ), the charging station  100  sets the power transmission coil  166  to a charging possible state (step S 24 ). The charging possible state is a standby state in which power transmission from the power transmission coil  166  to the power reception coil  66  is not started but can be started. Specifically, when the light of the movable body signal L 2  is received by the station signal acquisition unit  142  and the power transmission coil  166  and the power reception coil  66  are at appropriate positions, the charging station  100  puts the contact points D 5  and D 6  illustrated in  FIG. 3  into the closed states (connected states) and puts the contact point D 7  into the closed state through the switch unit  138 . Accordingly, the power P from the power source unit  102  is ready to be supplied to the power transmission coil  166 . In other words, in the present embodiment, the charging possible state can also be a state in which the power P from the power source unit  102  is ready to be supplied to the power transmission coil  166 . When the power transmission coil  166  and the power reception coil  66  are not at appropriate positions (No at step S 22 ), the charging station  100  does not set the power transmission coil  166  to the charging possible state but returns to step S 22  and continues the appropriate-position determination. Alternatively, the charging station  100  may return to step S 18  and move the power transmission coil  166  again when the coils are not at appropriate positions. 
     When the charging possible state is set by the charging station  100 , the movable body  10  causes the charging permission signal output unit  46  to output (emit light of) the charging permission signal L 0  under condition that the internal pressure of the frame  11  is equal to or higher than the threshold pressure (step S 26 ). When the internal pressure of the frame  11  is equal to or higher than the threshold pressure, in other words, when both detection results of the pressure detection units  40 A and  40 B indicate that the internal pressure of the frame  11  is equal to or higher than the threshold pressure, the charging permission signal output unit  46  outputs the charging permission signal L 0 . When the internal pressure of the frame  11  is lower than the threshold pressure, in other words, when at least one of the detection results of the pressure detection units  40 A and  40 B indicates that the internal pressure of the frame  11  is lower than the threshold pressure, the charging permission signal output unit  46  does not output the charging permission signal L 0 . 
     The movable body  10  stands by for a predetermined time after the light of the movable body signal L 2  is emitted at step S 14 , and after the standby, outputs the charging permission signal L 0  under condition that the internal pressure of the frame  11  is equal to or higher than the threshold pressure. Specifically, the movable body  10  outputs the charging permission signal L 0  triggered by elapse of a predetermined time, without acquiring information indicating that the charging possible state is set from the charging station  100 . Alternatively, the movable body  10  may output the charging permission signal L 0 , triggered by acquisition of information indicating that the charging possible state is set from the charging station  100 . 
     The charging permission signal output unit  46  outputs (emits light of) the charging permission signal L 0  to a region that the charging permission signal output unit  46  faces. Thus, when the movable body  10  is positioned in the charging region Po, the charging station  100  causes the charging permission signal acquisition unit  105  to acquire (receive light of) the charging permission signal L 0  from the charging permission signal output unit  46 . The charging station  100  determines whether the charging permission signal L 0  is acquired by the charging permission signal acquisition unit  105  (step S 28 ), and when the charging permission signal L 0  is acquired (Yes at step S 28 ), the charging station  100  causes the power transmission control unit  162  to supply power to the power transmission coil  166 , thereby performing power transmission from the power transmission coil  166  to the power reception coil  66  (step S 30 ). In other words, the charging station  100  executes non-contact charging of the battery  13  when the movable body signal L 2  from the movable body signal output unit  72  is received by the station signal acquisition unit  142  and the charging permission signal L 0  is acquired by the charging permission signal acquisition unit  105 . More specifically, the charging station  100  executes non-contact charging of the battery  13  when the power transmission coil  166  and the power reception coil  66  are at appropriate positions (the power transmission coil  166  and the power reception coil  66  face each other) and the charging permission signal L 0  is acquired by the charging permission signal acquisition unit  105 . When the charging permission signal L 0  is not acquired (No at step S 28 ), the charging station  100  does not perform power transmission from the power transmission coil  166  to the power reception coil  66  but returns to step S 28  and waits for acquisition of the charging permission signal L 0 . 
     The battery  13  of the movable body  10  is charged through power transmission from the power transmission coil  166  to the power reception coil  66 . Thereafter, the movable body  10  determines whether to end the charging based on, for example, the charged amount of the battery  13  (step S 32 ). When the charging is not to be ended (No at step S 32 ), the movable body  10  returns to step S 26  and continues outputting the charging permission signal L 0 , thereby continuing the charging. When the charging is to be ended (Yes at step S 32 ), the movable body  10  stops outputting the charging permission signal L 0  (step S 34 ). After outputting of the charging permission signal L 0  is stopped, the charging permission signal acquisition unit  105  of the charging station  100  stops acquisition of the charging permission signal L 0  (step S 36 ). After acquisition of the charging permission signal L 0  is stopped, the charging station  100  stops power transmission from the power transmission coil  166  to the power reception coil  66  (step S 38 ) and ends the charging processing. 
     After charging is ended in this manner, the movable body  10  may stand by in the charging region Po while the charging possible state is maintained. In other words, the charging station  100  maintains the charging possible state at step S 24  after charging is ended. When charging is needed again during the standby, the movable body  10  outputs the charging permission signal L 0  again at step S 26  and performs charging again. After charging, the movable body  10  may move out of the charging region Po to resume work in some cases. Subsequently, a process when the movable body  10  moves after charging will be described below. 
       FIG. 6  is a flowchart for description of a process in which the movable body starts movement. As illustrated in  FIG. 6 , after charging, the movable body  10  determines whether the movable body  10  needs to move out of the charging region Po (step S 50 ). When the movable body  10  needs to move (Yes at step S 50 ), the movable body  10  stops light emission of the movable body signal L 2  by the movable body signal output unit  72  (step S 52 ). Specifically, the movable body  10  stands by in the charging region Po in the charging possible state of step S 24  in  FIG. 4  and continues light emission of the movable body signal L 2  during the standby. However, when the movable body  10  needs to move, the movable body  10  stops light emission of the movable body signal L 2 . The movable body  10  is stopping outputting of the charging permission signal L 0  since charging is not being performed. When the movable body  10  does not need to move (No at step S 50 ), the movable body  10  returns to step S 50  and stands by while continuing light emission of the movable body signal L 2  (while in the charging possible state) until the movable body  10  needs to move. 
     When light emission of the movable body signal L 2  is stopped, the station signal acquisition unit  142  of the charging station  100  stops light reception of the movable body signal L 2  (step S 54 ). In addition, the charging station  100  is stopping acquisition of the charging permission signal L 0  since outputting of the charging permission signal L 0  is being stopped as well. When light reception of the movable body signal L 2  is stopped while acquisition of the charging permission signal L 0  is stopped, the charging station  100  releases the charging possible state (step S 56 ). Specifically, when light reception of the movable body signal L 2  is stopped in the charging station  100 , the contact point D 6  as well as the contact point D 7  in  FIG. 3  become the opened states (disconnected states) so that power supply from the power source unit  102  to the power transmission coil  166  is impossible. In addition, when light reception of the movable body signal L 2  is stopped, the charging station  100  causes the movement unit  168  to move the power transmission coil  166  farther away from the power reception coil  66 . Specifically, the charging station  100  returns the power transmission coil  166  to a position at which non-contact power supply to the power reception coil  66  is impossible, in other words, a position before movement of the power transmission coil  166  at step S 18  in  FIG. 4 . Accordingly, the charging possible state is released. 
     Having released the charging possible state, the charging station  100  temporarily stops light emission of the station signal L 1  by the station signal output unit  140  (step S 58 ). Specifically, triggered by the release of the charging possible state, the station signal output unit  140  stops light emission of the station signal L 1  only for a predetermined time. When light emission of the station signal L 1  is stopped, the movable body signal acquisition unit  70  of the movable body  10  stops light reception of the station signal L 1  (step S 60 ). When having stopped light reception of the station signal L 1 , the movable body  10  determines that movement preparation is completed, and starts movement (step S 62 ). Accordingly, the present processing ends. 
     As described above, the charging system  1  according to the present embodiment includes the movable body  10  including the frame  11  and the battery  13  provided in the frame  11 , and the charging station  100  configured to charge the battery  13 . The movable body  10  includes the pressure detection unit  40  and the charging permission signal output unit  46 . The pressure detection unit  40  detects the pressure inside the frame  11 . The charging permission signal output unit  46  outputs the charging permission signal L 0  indicating that the pressure inside the frame  11  is detected to be equal to or higher than the threshold pressure. The charging station  100  includes the charging permission signal acquisition unit  105  and the power transmission unit  104 . The charging permission signal acquisition unit  105  acquires the charging permission signal L 0  from the charging permission signal output unit  46 . When the charging permission signal L 0  is acquired by the charging permission signal acquisition unit  105 , the power transmission unit  104  executes non-contact charging of the battery  13 . 
     A movable body having an internal pressure explosion-proof structure includes a battery inside a frame having an internal pressure explosion-proof structure. Thus, when the frame is opened to charge the battery, the pressure inside the frame reduces and the internal pressure cannot be maintained. Thus, in this case, it is needed to close the frame after charging and raises the internal pressure again. However, in the charging system  1  according to the present embodiment, since the battery  13  is charged by non-contact charging, it is possible to perform the charging without opening the frame  11 . Thus, according to the charging system  1 , the charging can be performed without releasing a state in which the internal pressure is high. In addition, since the movable body  10  is charged in an explosive atmosphere, it is important to reduce the risk of ignition at the charging. The charging system  1  transmits the charging permission signal L 0  toward the charging station  100  when the internal pressure of the frame  11  is equal to or higher than the threshold pressure. The charging station  100  performs non-contact charging of the battery  13 , triggered by acquisition of the charging permission signal L 0 . Specifically, through the acquisition of the charging permission signal L 0 , the charging station  100  starts the non-contact charging after having determined that the state in which the internal pressure is high is maintained, in other words, the internal pressure explosion-proof structure is maintained and charging of the battery  13  would cause no problem. Thus, according to the charging system  1 , charging can be appropriately performed while the risk of ignition is reduced without releasing the state in which the internal pressure of the frame  11  is high. 
     The charging permission signal output unit  46  stops outputting of the charging permission signal L 0  when the pressure inside the frame  11  is detected to be lower than the threshold pressure. The power transmission unit  104  stops the non-contact charging of the battery  13  when the charging permission signal L 0  is not acquired by the charging permission signal acquisition unit  105 . The charging system  1  stops the non-contact charging by stopping outputting the charging permission signal L 0  when the internal pressure of the frame  11  has reduced, in other words, internal pressure explosion proof potentially cannot be maintained. Thus, according to the charging system  1 , the risk of ignition by charging can be reduced. 
     The movable body  10  includes the movable body signal output unit  72 . The movable body signal output unit  72  outputs a signal (the movable body signal L 2 ) to a region that the movable body signal output unit  72  faces. The charging station  100  includes the station signal acquisition unit  142  capable of acquiring light of the movable body signal L 2  from the movable body signal output unit  72 . The power transmission unit  104  executes non-contact charging of the battery  13  when light of the movable body signal L 2  from the movable body signal output unit  72  is received by the station signal acquisition unit  142  and the charging permission signal L 0  is acquired by the charging permission signal acquisition unit  105 . The movable body signal output unit  72  outputs the movable body signal L 2  to the region that the movable body signal output unit  72  faces. The station signal acquisition unit  142  acquires the movable body signal L 2  when positioned in the region that the movable body signal output unit  72  faces, in other words, when the movable body  10  is positioned in the charging region Po. The power transmission unit  104  executes the non-contact charging when the movable body signal L 2  is received. Specifically, the charging station  100  executes the charging when having checked that the movable body  10  is positioned in the charging region Po based on the movable body signal L 2  and having checked that the internal pressure explosion-proof structure is maintained based on the charging permission signal L 0 . Thus, according to the charging station  100 , the movable body  10  can be appropriately charged. In particular, the charging station  100  checks the position of the movable body  10  through acquisition of the movable body signal L 2  from the movable body  10 , thereby highly accurately checking the position of the movable body  10 . 
     The charging station  100  further includes the station signal output unit  140  configured to output a signal (the station signal L 1 ) to a region that the station signal output unit  140  faces. The movable body  10  includes the movable body signal acquisition unit  70  capable of acquiring the station signal L 1  from the station signal output unit  140  when positioned in the region that the station signal output unit  140  faces. The movable body signal output unit  72  outputs the movable body signal L 2  when the station signal L 1  from the station signal output unit  140  is acquired by the movable body signal acquisition unit  70 . The movable body  10  receives the station signal L 1  from the station signal output unit  140  when the station signal output unit  140  is positioned in the region facing the station signal output unit  140 , in other words, is positioned in the charging region Po. When having received the station signal L 1 , the movable body signal output unit  72  outputs the movable body signal L 2 . Thus, the charging system  1  determines that the movable body  10  is positioned in the charging region Po when the station signal L 1  from the charging station  100  is received by the movable body  10  and the movable body signal L 2  from the movable body  10  is received by the charging station  100 , and then performs non-contact charging. Thus, according to the charging system  1 , the movable body  10  and the charging station  100  can each check the position of the other, and thus the position of the movable body  10  can be more highly accurately checked. 
     The movable body  10  includes the power reception coil  66  connected with the battery  13 . The power transmission unit  104  of the charging station  100  includes the power transmission coil  166  configured to transmit electricity to the power reception coil  66  in a non-contact manner, the movement unit  168  configured to move the power transmission coil  166  toward the power reception coil  66 , and the power transmission control unit  162  configured to cause the power transmission coil  166  to perform power transmission. The movement unit  168  moves the power transmission coil  166  to a position facing the power reception coil  66 , in other words, a position where non-contact charging is possible. The power transmission control unit  162  causes the power transmission coil  166  to perform power transmission when the power transmission coil  166  is at the position facing the power reception coil  66  and the charging permission signal L 0  is acquired by the charging permission signal acquisition unit  105 . The charging system  1  performs positioning of the power transmission coil  166  and the power reception coil  66  by checking whether the power transmission coil  166  is at the position facing the power reception coil  66 . Then, non-contact charging is performed when a result of the positioning of the power transmission coil  166  and the power reception coil  66  is appropriate. Thus, according to the charging system  1 , non-contact charging can be appropriately performed. 
     The charging station  100  includes the interface position detection unit  108  configured to detect whether the power transmission coil  166  and the power reception coil  66  are at appropriate positions. The power transmission control unit  162  causes the power transmission coil  166  to perform power transmission when the power transmission coil  166  and the power reception coil  66  are at appropriate positions. The charging system  1  performs non-contact charging when the power transmission coil  166  and the power reception coil  66  are at predetermined appropriate positions. Thus, according to the charging system  1 , non-contact charging can be appropriately performed. 
     The frame  11  of the movable body  10  has an internal pressure explosion-proof structure. The charging system  1  can excellently charge the battery  13  of the movable body  10  having the internal pressure explosion-proof structure without releasing an internal pressure explosion-proof state. 
     The charging station  100  according to the present embodiment charges the movable body  10  including the frame  11 , the battery  13  provided in the frame  11 , and the pressure detection unit  40  configured to detect the pressure inside the frame  11 , and includes the charging permission signal acquisition unit  105  and the power transmission unit  104 . The charging permission signal acquisition unit  105  acquires the charging permission signal L 0  indicating that the pressure inside the frame  11  is equal to or higher than the threshold pressure from the movable body  10 . The power transmission unit  104  executes non-contact charging of the battery  13  when the charging permission signal L 0  is acquired by the charging permission signal acquisition unit  105 . According to the charging station  100 , charging can be appropriately performed while the risk of ignition is reduced without releasing the state in which the internal pressure of the frame  11  is high. 
     The movable body  10  according to the present embodiment includes the frame  11 , the pressure detection unit  40  configured to detect the pressure inside the frame  11 , the charging permission signal output unit  46 , and the power reception unit  44 . The charging permission signal output unit  46  outputs, to the charging station  100 , the charging permission signal L 0  indicating that the pressure inside the frame  11  is detected by the pressure detection units  40  to be equal to or higher than the threshold pressure. The power reception unit  44  is charged in a non-contact manner from the charging station  100  having acquired the charging permission signal L 0 . According to the movable body  10 , charging can be appropriately performed while the risk of ignition is reduced without releasing the state in which the internal pressure of the frame  11  is high. 
     In the charging method according to the present embodiment, the movable body  10  including the frame  11  and the battery  13  provided in the frame  11  is charged by a charging device (the charging station  100 ). The charging method includes a charging permission signal outputting step of outputting the charging permission signal L 0  from the movable body  10  toward the charging device when the pressure inside the frame  11  is detected to be equal to or higher than the threshold pressure, and a charging step of executing non-contact charging of the battery  13  when the charging permission signal L 0  is acquired by the charging device. According to the charging method, charging can be appropriately performed while the risk of ignition is reduced without releasing the state in which the internal pressure of the frame is high. 
     The embodiment of the present invention is described above but not limited to the content of the present embodiment. The above-described components include those easily thought of by the skilled person in the art, those identical in effect, and equivalents. The above-described components may be combined as appropriate. The components may be omitted, replaced, and changed in various kinds of manners without departing from the scope of the above-described embodiment. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  charging system 
               10  movable body 
               11  frame 
               13  battery 
               40  pressure detection unit 
               44  power reception unit 
               46  charging permission signal output unit 
               48  movable body position detection unit 
               66  power reception coil 
               70  movable body signal acquisition unit 
               72  movable body signal output unit 
               74  reflection unit 
               100  charging station 
               104  power transmission unit 
               105  charging permission signal acquisition unit 
               106  station position detection unit 
               108  interface position detection unit 
               140  station signal output unit 
               142  station signal acquisition unit 
               150  interface signal output unit 
               152  interface signal acquisition unit 
             L 0  charging permission signal 
             L 1  station signal 
             L 2  movable body signal 
             L 3  interface signal