Abstract:
A plug is provided that includes: at least two electrodes; a housing that supports the electrodes; an electrode cover which covers the electrodes when not connected with a plug receptacle, and which is accommodated in the housing and exposes the electrodes when connected with the plug receptacle; and a lock mechanism which inhibits the electrode cover from being accommodated in the housing when not connected with the plug receptacle, and which allows the electrode cover to be accommodated in the housing when connected with the plug receptacle.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a plug, a plug receptacle and an electric power supplying system. 
       BACKGROUND ART 
       [0002]    Many electronic devices, such as personal computers and game consoles, use an AC adapter that inputs alternating current (AC) electric power from a commercial power source and outputs electric power in accordance with the device, in order to operate and charge the device. Normally, electronic devices are operated using direct current (DC), and voltage and current are different according to each device. Therefore, a specification of the AC adapter to output electric power in accordance with the device also differs with each device. Thus, even if an AC adapter has a same kind of shape, there are problems with a lack of compatibility and an increase in a number of the AC adapters in line with an increase in the devices. 
         [0003]    With respect to these kind of problems, a power source bus system has been proposed in which a power source supply block, which supplies electric power to a device such as a battery or an AC adapter, and a power consumption block, which is supplied with the electric power from the power source supply block, are connected to a single common direct current bus line (as disclosed, for example, in Patent Literature 1). In this power source bus system, direct current is flowing through the bus line. Further, in the power source bus system, each block itself is described as an object and each of the block objects mutually transmits and receives information (status data) via the bus line. In addition, each of the block objects generates information (status data) based on a request from another of the block objects, and transmits the status data as response data. Then, the block object that has received the response data can control the electric power supply and consumption based on the content of the received response data. 
       CITATION LIST 
     Patent Literature 
       [0004]    Patent Literature 1: Japanese Patent Application Publication No. JP-A-2001-306191 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0005]    In this type of power source bus system, the power supply block and the power consumption block are connected using a bus line and a plug to which electric power is supplied. In known electronic devices that receive supply of AC electric power, when the electronic devices are consuming electric power and are also in the vicinity of an AC peak value, if the plug is removed from an outlet (a plug receptacle), a spark occurs between the outlet and the plug. It is conceivable that the occurrence of spark constantly occurs in the power source bus system to which DC electric power or low frequency AC electric power is supplied. The occurrence of spark leads to a problem of deterioration of the plug and the outlet. Therefore, in electronic devices in the electric power supplying system in which an information signal is superimposed on electric power and is supplied, it is necessary to allow a user to safely remove or insert the plug into the outlet. 
         [0006]    The present invention is made in view of the above-mentioned issue, and aims to provide a plug, a plug receptacle into which the plug is inserted, and a power source bus system which are novel and improved and which are capable of being safely connected to a bus line or disconnected from the bus line in the power source bus system, by providing a structure in which electrodes are not exposed when disconnected from the bus line. 
       Solution to Problem 
       [0007]    According to an aspect of the present invention in order to achieve the above-mentioned object, there is provided a plug that includes at least two electrodes, a housing that supports the electrodes, an electrode cover which covers the electrodes when not inserted in a plug receptacle, and which is accommodated in the housing and exposes the electrodes when inserted in the plug receptacle, and a lock mechanism which inhibits the electrode cover from being accommodated in the housing when not inserted in the plug receptacle, and which allows the electrode cover to be accommodated in the housing when inserted into the plug receptacle. 
         [0008]    The lock mechanism may be depressed when connected with the plug receptacle and allows the electrode cover to be accommodated in the housing. 
         [0009]    The housing may include a reverse insertion inhibition portion that inhibits connection with a different polarity. 
         [0010]    According to another aspect of the present invention in order to achieve the above-mentioned object, there is provided a plug receptacle that includes a cover that protects electrodes, and a lock release mechanism that releases inhibition of accommodation of an electrode cover into a housing by a lock mechanism, when a plug is inserted that includes at least two electrodes, the housing that supports the electrodes, the electrode cover which covers the electrodes when not inserted and which is accommodated in the housing and exposes the electrodes when inserted, and the lock mechanism which inhibits the electrode cover from being accommodated in the housing when not inserted and which allows the electrode cover to be accommodated in the housing when inserted. 
         [0011]    The lock release mechanism may depress the lock mechanism and thereby releases the inhibition of accommodation into the housing by the lock mechanism. 
         [0012]    The cover may include a reverse insertion inhibition portion that inhibits connection of the plug with a different polarity. 
         [0013]    According to another aspect of the present invention in order to achieve the above-mentioned object, there is provided an electric power supplying system that includes a bus line which is formed by at least two conductors and on which an information signal representing information is superimposed on electric power, at least one power supply server which is connected to the bus line and which supplies the electric power, and at least one client which is connected to the bus line and which receives the supply of the electric power from the power supply server. At least one of the power supply server and the client may be provided with a plug that includes at least two electrodes, a housing that supports the electrodes, an electrode cover which covers the electrodes when not inserted in a plug receptacle and which is accommodated in the housing and exposes the electrodes when inserted in the plug receptacle, and a lock mechanism which inhibits the electrode cover from being accommodated in the housing when not inserted in the plug receptacle, and which allows the electrode cover to be accommodated in the housing when inserted into the plug receptacle. The bus line may be provided with the plug receptacle that includes a cover that protects electrodes and a lock release mechanism that, when the plug is inserted, releases the inhibition, by the lock mechanism, of accommodation of the electrode cover into the housing. 
       ADVANTAGEOUS EFFECTS OF INVENTION 
       [0014]    According to the present invention described above, there is provided a plug, a plug receptacle into which the plug is inserted, and a power source bus system which are novel and improved and which are capable of being safely connected to a bus line or disconnected from the bus line in the power source bus system to which DC electric power or low frequency AC electric power is supplied, by providing a structure in which electrodes are not exposed when disconnected from the bus line. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0015]      FIG. 1  is an explanatory diagram illustrating a structure of an electric power supplying system according to an embodiment of the present invention. 
           [0016]      FIG. 2  is an explanatory diagram illustrating a structure of a power supply server  100  according to the embodiment of the present invention. 
           [0017]      FIG. 3  is an explanatory diagram illustrating a structure of a client  200  according to the embodiment of the present invention. 
           [0018]      FIG. 4A  is an explanatory diagrams illustrating the structure of the outlet  170  according to the embodiment of the present invention. 
           [0019]      FIG. 4B  is an explanatory diagrams illustrating the structure of the outlet  170  according to the embodiment of the present invention. 
           [0020]      FIG. 5A  is an explanatory diagrams illustrating the structure of the plug  171  according to the embodiment of the present invention. 
           [0021]      FIG. 5B  is an explanatory diagrams illustrating the structure of the plug  171  according to the embodiment of the present invention. 
           [0022]      FIG. 5C  is an explanatory diagrams illustrating the structure of the plug  171  according to the embodiment of the present invention. 
           [0023]      FIG. 6  is an explanatory diagram showing a state of a cross section when the plug  171  is inserted partway into the outlet  170 . 
           [0024]      FIG. 7  is an explanatory diagram showing a state of a cross section when the plug  171  is completely inserted into the outlet  170 . 
           [0025]      FIG. 8  is an explanatory diagram illustrating electric power supply processing by the electric power supplying system  1  according to the embodiment of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0026]    Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the appended drawings. Note that, in this specification and the drawings, elements that have substantially the same function and structure are denoted with the same reference signs, and repeated explanation is omitted. 
         [0027]    Note that the preferred embodiment of the present invention will be described in detail in the following order: 
         [0028]    [1] Structure of electric power supplying system 
         [0029]    [2] Structure of power supply server 
         [0030]    [3] Structure of client 
         [0031]    [4] Electric power supply processing by the electric power supplying system 
         [0032]    [5] Structure of outlet (plug receptacle) according to embodiment of the present invention 
         [0033]    [6] Structure of plug according to embodiment of the present invention 
         [0034]    [7] Change in shape of plug when plug is inserted into outlet 
         [0035]    [10] Conclusion 
         [0036]    [1] Structure of Electric Power Supplying System 
         [0037]    First, a structure of an electric power supplying system using plug according to an embodiment of the present invention will be described.  FIG. 1  is an explanatory diagram illustrating the structure of the electric power supplying system according to the embodiment of the present invention. Hereinafter, the structure of the electric power supplying system according to the embodiment of the present invention will be explained with reference to  FIG. 1 . 
         [0038]    As shown in  FIG. 1 , an electric power supplying system  1  according to the embodiment of the present invention includes a power supply server  100  and clients  200 . The power supply server  100  and the clients  200  are connected via a bus line  10 . 
         [0039]    The power supply server  100  supplies direct current electric power to the clients  200 . Further, the power supply server  100  transmits and receives information signals to and from the clients  200 . In the present embodiment, the bus line  10  is commonly used both for the supply of direct current electric power and the transmitting and receiving of information signals between the power supply server  100  and the clients  200 . A structure of the power supply server  100  will be explained below. 
         [0040]    The clients  200  receive the supply of direct current electric power from the power supply server  100 . Further, the clients  200  transmit and receive the information signals with the power supply server  100 . A structure of the client  200  will be explained below. 
         [0041]    Note that the single power supply server  100  and two of the clients  200  are exemplified in the electric power supplying system  1  shown in  FIG. 1 , but it is needless to say that in the present invention, a number of the power supply servers and a number of the clients are not limited to this example. 
         [0042]    Above, the structure of the electric power supplying system according to the embodiment of the present invention is explained using  FIG. 1 . Next, a structure of the power supply server  100  according to the embodiment of the present invention will be explained. 
         [0043]    [2] Structure of Power Supply Server 
         [0044]      FIG. 2  is an explanatory diagram illustrating the structure of the power supply server  100  according to the embodiment of the present invention. Hereinafter, the structure of the power supply server  100  according to the embodiment of the present invention will be explained with reference to  FIG. 2 . 
         [0045]    As shown in  FIG. 2 , the power supply server  100  according to the embodiment of the present invention includes an AC/DC converter  110 , a server controller  120 , a modem  130 , an inductor  140 , a switch  150  and a plug  171 . 
         [0046]    The AC/DC converter  110  is an alternating current/direct current converter portion that converts alternating current electric power supplied from a commercial power source  160  to direct current electric power such that it can be supplied to the client  200 . The electric power that has been converted from alternating current to direct current by the AC/DC converter  110  is supplied to the client  200  via the bus line  10 . Note that the inductor  140  and the switch  150  are provided between the AC/DC converter  110  and one of the bus lines  10 , as shown in  FIG. 2 . The inductor  140  is provided such that impedance on a communication path is not lowered by a bypass condenser that is normally provided in an output portion of the AC/DC converter  110 . Further, the switch  150  is provided in order that electric power is not suddenly output from the power supply server  100  to the bus line  10 . 
         [0047]    The server controller  120  is a control portion to execute various functions in order to supply electric power by the power supply server  100 . The server controller  120  is formed, for example, of a micro processor and peripheral circuits to operate the micro processor. Controls executed by the server controller  120  include, for example, control of whether or not to connect electric power supplied from the AC/DC converter to the bus line  10  and control of a communication protocol for communication with the client  200 . In addition, controls executed by the server controller  120  include, for example, control of transmission and reception of information signals to and from the client  200 . Furthermore, the server controller  120  is provided with a storage portion (not shown in the figures), which stores, as internal information, the electric power specification (a server profile), a protocol for the information signals, and information of the client  200  acquired by communication and so on. 
         [0048]    The modem  130  makes possible the transmission and reception of information signals between the power supply server  100  and the client  200  via the bus line  10 . In the electric power supplying system  1  according to the present embodiment, information signals and electric power share a same pair of conductors. Thus, so that electrical interference does not occur, it is necessary to separate the information signals and the electric power through frequency division. In the electric power supplying system  1  according to the present embodiment, the transmission and reception of the information signals between the power supply server and the client  200  is performed via the bus line  10 . The transmission and reception of the information signals is performed using a sufficiently high frequency bandwidth, such that electrical interference does not occur with a frequency bandwidth that is used to deliver the electric power (a low frequency bandwidth of around 400 Hz or below, for example). The modem  130  performs signal modulation and demodulation in the transmission and reception of the information signals, which are performed using the sufficiently high frequency bandwidth. 
         [0049]    The plug  171  connects the power supply server  100  and the bus line  10  by being inserting into an outlet  170  provided on the bus line  10 . The structure of the outlet  170  and the plug  171  will be described later. 
         [0050]    The structure of the power supply server  100  according to the embodiment of the present invention is explained above. Next, a structure of the client  200  according to the embodiment of the present invention will be explained. 
         [0051]    [3] Structure of Client 
         [0052]      FIG. 3  is an explanatory diagram illustrating the structure of the client  200  according to the embodiment of the present invention. Hereinafter, the structure of the client  200  according to the embodiment of the present invention will be explained with reference to  FIG. 3 . 
         [0053]    As shown in  FIG. 3 , the client  200  according to the embodiment of the present invention includes a DC/DC converter  210 , a client controller  220 , a modem  230 , an inductor  240 , switches  250  and  260 , a battery  270 , an outlet  290  and a plug  291 . 
         [0054]    The DC/DC converter  210  converts the direct current electric power supplied from the power supply server  100  to an electric current and voltage required by a load  280  that is connected to the client  200 . Further, as shown in  FIG. 3 , the inductor  240  and the switches  250  and  260  are provided between the DC/DC converter  210  and one of the bus lines  10 . The inductor and switches function similarly to the inductor  140  and the switch  150  of the above-described power supply server  100 . 
         [0055]    The client controller  220  executes various functions in order for the client  200  to receive the electric power supply. Similarly to the above-described server controller  120 , the client controller  220  is formed, for example, of a micro processor and peripheral circuits to operate the micro processor. The client controller  220 , for example, determines how to consume the electric power supplied from the power supply server  100  and performs control of a protocol used in communication of information signals to and from the power supply server  100 . Further, the client controller  220  is provided with a storage portion (not shown in the figures), which stores, as internal information, a protocol for the transmission and reception of the information signals, client information relating to the specification of the client  200  (a client power profile) and so on. 
         [0056]    The modem  230  makes possible the transmission and reception of information signals between the power supply server  100  and the client  200  via the bus line  10 . In a similar manner to the above-described modem  130 , the modem  230  performs signal modulation and demodulation in the transmission and reception of the information signals, which are performed using the sufficiently high frequency bandwidth. 
         [0057]    Note that when the consumed electric power of the load  280  is zero or is low, the client  200  can accumulate the electric power supplied by the power supply server  100  in the battery  270 . 
         [0058]    The plug  291  connects the power supply server  100  and the bus line  10  by being inserting into the outlet  290  provided on the bus line  10 . 
         [0059]    The structure of the client  200  according to the embodiment of the present invention is explained above. Next, an electric power supply processing by the electric power supplying system  1  according to the embodiment of the present invention will be explained, and subsequently the structure of the outlet  170 ,  290  and the plug  171 ,  291 , which are used for the power supply server  100  and the clients  200  will be explained. 
         [0060]    [4] Electric Power Supply Processing by the Electric Power Supplying System 
         [0061]    In the electric power supplying system  1  according to the embodiment of the present invention, the electric power supply processing from the power supply server  100  to the client  200  is performed based on synchronous packets that are periodically output from the power supply server  100  to the bus line  10 . The client  200  is aware of the existence of the power supply server  100  by the synchronous packets delivered through the bus line  10 , and can access the power supply server  100 . When the power supply server  100  receives access from the client  200 , the power supply server  100  transmits its own address to the client  200 . When the client  200  receives the address of the power supply server  100 , the client  200  transmits to the power supply server  100 , addressed to the received address, an information signal that requests the supply of electric power. When the power supply server  100  receives the information signal requesting the supply of electric power from the client  200 , the power supply server  100  supplies the electric power to the client  200 . 
         [0062]      FIG. 8  is an explanatory diagram illustrating the electric power supply processing by the electric power supplying system  1  according to the embodiment of the present invention. Hereinafter, the electric power supply processing of the electric power supplying system  1  according to the embodiment of the present invention will be explained in more detail with reference to  FIG. 8 . Regarding the electric power supply processing of the electric power supplying system  1  according to the embodiment of the present invention, it would be helpful to refer to an invention disclosed in JP2008-123051A1 described by the same inventor of this application. 
         [0063]    As shown in  FIG. 11 , the power supply server  100  periodically outputs synchronous packets A 1 , A 2 , A 3  and so on to the bus line  10 . Further, in order to supply electric power to the client  200 , the power supply server  100  outputs information packets B 1 , B 2 , B 3  and so on, which are information signals transmitted and received to and from the client  200 , and also outputs electric power packets C 1 , C 2 , C 3  and so on, which are packetized electric power energy. Meanwhile, in order to receive the supply of electric power from the power supply server  100 , the client  200  outputs information packets D 1 , D 2 , D 3  and so on, which are information signals transmitted and received to and from the power supply server  100 . 
         [0064]    The power supply server  100  outputs the synchronous packets A 1 , A 2 , A 3  and so on at a start time of a time slot of a predetermined interval (a one second interval, for example). The time slot is formed of an information slot in which an information packet is transmitted, and an electric power slot in which an electric power packet is transmitted. Information slots IS 1 , IS 2 , IS 3  and so on are intervals during which exchange of the information packets is performed between the power supply server  100  and the client  200 . Further, power supply slots PS 1 , PS 2 , PS 3  and so on are intervals in which the electric power packets C 1 , C 2 , C 3  and so on supplied from the power supply server  100  to the client  200  are output. The information packets are packets that can only be output in the intervals of the information slots IS 1 , IS 2 , IS 3  and so on. Therefore, when it is not possible to complete transmission and reception of the information packet during one of the information slots, the information packet is transmitted over a plurality of the information slots. Meanwhile, the electric power packets are packets that can only be output in the intervals of the power supply slots PS 1 , PS 2 , PS 3  and so on. 
         [0065]    The power supply server  100  has one, or two or more, server power profiles that indicate an electric power specification at which the power supply server  100  itself can supply electric power. The client  200  receives the supply of electric power from the power supply server  100  that is able to supply the electric power that matches a specification of the client  200 . At this time, the client  200  acquires the server power profiles from the power supply server  100  and decides the specification of the power supply server  100  (the server power profile) for itself. At that time, first, the client  200  detects the synchronous packet A 1  output by the power supply server  100  and acquires the address of the power supply server  100  that is included in the synchronous packet A 1 . The address can be, for example, a MAC address. Next, the client  200  transmits the information packet D 1  to the power supply server  100  to request transmission of a number of the server power profiles that the power supply server  100  has. 
         [0066]    When the power supply server  100  receives the information packet D 1 , the power supply server  100  transmits, in the information packet B 1 , a server power profile number that is the number of server power profiles that the power supply server  100  has. When the client  200  receives the information packet B 1 , the client  200  acquires, from the power supply server  100 , content of the server power profiles for the number of server power profiles of the power supply server  100 . For example, when the power supply server  100  has two server power profiles, the client  200  first acquires an initial one of the server power profiles. When the client  200  acquires the initial one of the server power profiles, the client  200  transmits to the power supply server  100 , as the information packet D 2 , a request to use electric power. 
         [0067]    When the power supply server  100  receives the information packet D 2 , the power supply server  100  transmits to the client  200 , as the information packet B 2 , a first server power profile that is stored in the storage portion (not shown in the figures) of the server controller  120 . When the client  200  receives the information packet B 2  from the power supply server  100 , the client  200  transmits an information packet in order to acquire a second server power profile. However, at this point in time, the information slot IS 1  ends, and the power supply slot PS 1  to transmit a power supply packet starts. Thus, the information packet is transmitted in the next information slot IS 2 . Further, in the power supply slot PS 1 , as the client  200  has not confirmed the electric power supply specification to receive the supply from the power supply server  100 , electric power supply is not carried out. 
         [0068]    When the power supply slot PS 1  ends, the synchronous packet A 2  indicating the start of the next time slot is output from the power supply server  100 . After that, when the client  200  receives the information packet B 2  from the power supply server  100 , the client  200  transmits, as the information packet D 3 , information to acquire the second server power profile. 
         [0069]    When the power supply server  100  receives the information packet D 3 , the power supply server  100  transmits to the client  200 , as the information packet B 3 , the second server power profile that is stored in the storage portion (not shown in the figures) of the server controller  120 . When the client  200  receives the information packet B 3  and acquires the two server power profiles that the power supply server  100  has, the client  200  selects the server power profile of the power supply specification that is compatible with itself. The client  200  then transmits, to the power supply server  100 , an information packet D 4  that causes the selected server power profile to be confirmed. 
         [0070]    When the power supply server  100  receives the information packet D 4 , in order to notify the client  200  that the first server power profile has been confirmed, the power supply server  100  transmits, as an information packet B 4  to the client  200 , information representing a response that indicates that the electric power supply specification has been confirmed. After that, when the information slot IS 2  ends and the power supply slot PS 2  starts, the power supply server  100  outputs the power supply packet C 1  to the client  200  and performs supply of electric power. Note that, with respect to a transmission timing of the electric power packet, an electric power supply start time can be specified from the client  200  to the power supply server  100  by using information representing a transmission start time setting request. 
         [0071]    The electric power supply processing by the electric power supplying system  1  according to the embodiment of the present invention is described above. Next, the structure of the plugs  171  and  291  will be explained, which are used for the power supply server  100  and the clients  200  in the electric power supplying system  1  according to the embodiment of the present invention. Note that, in the description below, although only the outlet  170  and the plug  171  will be explained as an example, the structure that will be explained below can also be applied to the outlet  290  and the plug  291 . 
         [0072]    [5] Structure of Outlet (Plug Receptacle) According to Embodiment of the Present Invention 
         [0073]      FIG. 4A  and  FIG. 4B  are explanatory diagrams illustrating the structure of the outlet  170  according to the embodiment of the present invention.  FIG. 4A  is an explanatory diagram showing a cross section of the outlet  170  according to the embodiment of the present invention when viewed from a direction of a right side surface.  FIG. 4B  is an explanatory diagram when the outlet  170  is viewed from an electrode direction. Hereinafter, the structure of the outlet  170  according to the embodiment of the present invention will be explained using  FIG. 4A  and  FIG. 4B . 
         [0074]    As shown in  FIG. 4A  and  FIG. 4B , the outlet  170  according to the embodiment of the present invention is structured such that it includes a pair of electrodes  181 , a cover  182  formed of an insulator, lock release mechanisms  183   a  and  183   b,  and inclined portions  184 . 
         [0075]    The electrodes  181  are female electrodes that are structured such that they can be in contact with plug electrodes, which will be described later. The electrodes  181  are similar to female electrodes that are currently in widespread use and that are used in an outlet that supplies AC electric power. The electrodes  181  are connected to the bus line  10 . However, a method for connecting the electrodes  181  with the bus line  10  and a method for insulating a connection point do not have a direct relationship with the present invention, and a detailed explanation thereof is therefore omitted. The cover  182  is formed of an insulator as described above. The inclined portions  184 , which are an example of a reverse insertion inhibition portion of the present invention, are formed on the cover  182  in order to inhibit plug insertion with a reverse polarity. Note that, although the two inclined portions  184  are provided in  FIG. 4B , it is needless to mention that, in the present invention, the shape of the outlet is not limited to that shown in  FIG. 4B  as long as it inhibits plug insertion with a reverse polarity. For example, in place of the inclined portions  184 , the outlet may be formed to have a stair shape or an arc shape as the reverse insertion inhibition portion. 
         [0076]    The lock release mechanisms  183   a  and  183   b  are formed integrally with the cover  182 , and they release a lock of a cover that inhibits exposure of the electrodes in the plug  171 , which will be described later, when the plug  171  is inserted into the outlet  170 . 
         [0077]    The structure of the outlet  170  according to the embodiment of the present invention is explained above. Next, the structure of the plug, which is used by being inserted into the outlet  170  according to the embodiment of the present invention, will be explained. 
         [0078]    [6] Structure of Plug According to Embodiment of the Present Invention 
         [0079]      FIG. 5A ,  FIG. 5B  and  FIG. 5C  are explanatory diagrams illustrating the structure of the plug  171  according to the embodiment of the present invention.  FIG. 5A  is an explanatory diagram showing a cross section of the plug  171  according to the embodiment of the present invention when viewed from a direction of a right side surface.  FIG. 5B  is an explanatory diagram when the plug  171  is viewed from an electrode direction. In  FIG. 5C , the plug  171  is shown as a perspective view. Hereinafter, the structure of the plug  171  according to the embodiment of the present invention will be explained using  FIG. 5A ,  FIG. 5B  and  FIG. 5C . 
         [0080]    As shown in  FIG. 5A  and  FIG. 5B , the plug  171  according to the embodiment of the present invention is structured such that it includes a housing  191 , a pair of electrodes  192 , protruding portions  193 , an electrode protection cover  194 , lock mechanisms  195   a  and  195   b,  recessed portions  196   a  and  196   b,  cutaway portions  197  and electrode holes  198 . 
         [0081]    The housing  191  is formed such that it can accommodate the electrode protection cover  194 , which will be described later, when the plug  171  is inserted into the outlet  170 . The housing  191  is formed in such a shape that it can be engaged with the cover  182  of the plug  171 . Further, in order to inhibit insertion into the outlet  170  with a reverse polarity, the housing  191  is provided with the cutaway portions  197 , which are an example of the reverse insertion inhibition portion of the present invention. Note that it is desirable that the shape of the cutaway portions  197  is formed to match the shape of the inclined portions  184  in the outlet  170 . Note that it is needless to mention that, in the present embodiment, the shape of the cutaway portions is not limited to that shown in  FIG. 5A  and so on. 
         [0082]    The electrodes  192  are knife-shaped electrodes that are structured such that they can be in contact with the above-described electrodes  181  of the outlet  170 , and they are similar to knife-shaped electrodes that are currently in widespread use and that are used in a plug that is supplied with AC electric power. The protruding portions  193  are formed inside the housing  191  as shown in  FIG. 5A  and  FIG. 5B . The protruding portions  193  inhibit the electrode protection cover  194  from moving into the housing  191 , and exposure of the electrodes  192  from the electrode holes  198  can be inhibited by the protruding portions  193 . 
         [0083]    The electrode protection cover  194  is formed of an insulating material and it protects the electrodes  192 . When the plug  171  is not engaged with the outlet  170 , the electrodes  192  are covered as shown in  FIG. 5A  so that the electrodes  192  are not exposed. Further, as described above, the electrode protection cover  194  is inhibited from moving into the housing  191  by the protruding portions  193  that are formed inside the housing  191 . Note that it is desirable that, when the plug  171  is not engaged with the outlet  170 , the electrodes  192  are covered, and when the plug  171  is engaged, the electrode protection cover  194  is coupled with the housing  191  using a spring or another elastic body in order to expose the electrodes  192 . 
         [0084]    The lock mechanisms  195   a  and  195   b  are provided inside the electrode protection cover  194  as shown in  FIG. 5A  and  FIG. 5B . When the plug  171  is not engaged with the outlet  170 , even when the electrode protection cover  194  is pressed from the electrode side, the electrode protection cover  194  does not slide to the inside of the housing  191  due to the lock mechanisms  195   a  and  195   b.  Then, when the plug  171  is inserted into the outlet  170 , the lock mechanisms  195   a  and  195   b  are depressed to the inside of the electrode protection cover  194  by the lock release mechanisms  183   a  and  183   b  provided in the outlet  170 . Because the lock mechanisms  195   a  and  195   b  are depressed to the inside of the electrode protection cover  194 , the electrode protection cover  194  can move to the inside of the housing  191 . The recessed portions  196   a  and  196   b  are spaces that are provided so that the lock mechanisms  195   a  and  195   b  are depressed by the lock release mechanisms  183   a  and  183   b.  The recessed portions  196   a  and  196   b  are provided so as to correspond to the positions of the lock release mechanisms  183   a  and  183   b  when the plug  171  is inserted into the outlet  170 . The recessed portions  196   a  and  196   b  are provided in the housing  191  and the electrode protection cover  194 , respectively. The electrode holes  198  are holes to expose the electrodes  192 . When the electrode protection cover  194  slides to the inside of the housing  191 , it is possible to expose the electrodes  192  from the electrode holes  198 . 
         [0085]    The structure of the plug  171  according to the embodiment of the present invention is explained above. Next, a change in the shape of the plug  171  when the plug  171  is inserted into the outlet  170  according to the embodiment of the present invention will be explained. 
         [0086]    [7] Change in Shape of Plug When Plug is Inserted Into Outlet 
         [0087]      FIG. 6  is an explanatory diagram showing a state of a cross section when the plug  171  is inserted partway into the outlet  170  according to the embodiment of the present invention. 
         [0088]    As shown in  FIG. 6 , when the plug  171  is inserted partway into the outlet  170 , the lock release mechanisms  183   a  and  183   b  come in contact with the lock mechanisms  195   a  and  195   b  because the recessed portions  196   a  and  196   b  are provided in the electrode protection cover  194 . 
         [0089]    As shown in  FIG. 6 , in a state where the lock release mechanisms  183   a  and  183   b  are in contact with the lock mechanisms  195   a  and  195   b,  the plug  171  is further pressed into the outlet  170 . As a result of this, the lock mechanisms  195   a  and  195   b  are depressed to the inside of the electrode protection cover  194  by the lock release mechanisms  183   a  and  183   b.  Because the lock mechanisms  195   a  and  195   b  are depressed to the inside of the electrode protection cover  194 , the lock of the electrode protection cover  194  by the protruding portions  193  is released, and it is possible to cause the electrode protection cover  194  to slide to the inside of the housing  191 . 
         [0090]      FIG. 7  is an explanatory diagram showing a state of a cross section when the plug  171  is completely inserted into the outlet  170 . 
         [0091]    When the lock mechanisms  195   a  and  195   b  are depressed to the inside of the electrode protection cover  194  by the lock release mechanisms  183   a  and  183   b,  the electrode protection cover  194  is caused to slide to the inside of the housing  191  as shown in  FIG. 7 , and the electrodes  192  are exposed from the electrode holes  198 . Because the electrode protection cover  194  is caused to slide to the inside of the housing  191  and the electrodes  192  are exposed from the electrode holes  198 , the electrodes  181  and the electrodes  192  are connected, and the power supply server  100  having the plug  171  can be connected to the bus line  10 . 
         [0092]    On the other hand, when the plug  171  is removed from the outlet  170 , the plug  171  is removed from the outlet  170  while holding the housing  191 . In this case, when the plug  171  is partially removed from the outlet  170 , the depression of the lock mechanisms  195   a  and  195   b  by the lock release mechanisms  183   a  and  183   b  is released. When the depression of the lock mechanisms  195   a  and  195   b  by the lock release mechanisms  183   a  and  183   b  is released, a state is achieved in which the electrodes  192  are accommodated in the electrode protection cover  194 , as shown in  FIG. 6 . 
         [0093]    The change in the shape of the plug  171  when the plug  171  is inserted into the outlet  170  according to the embodiment of the present invention is explained above. 
         [0094]    [8] Conclusion 
         [0095]    By structuring the outlet  170  and the plug  171  in this manner, the electrodes of the plug  171  are not exposed until immediately before insertion into the outlet  170 . Therefore, by structuring the outlet  170  and the plug  171  in this manner, it is possible to insert the plug  171  into the outlet  170  safely and to remove  170  from the outlet. 
         [0096]    The preferred embodiments of the present invention have been described above with reference to the accompanying drawings, whilst the present invention is not limited to the above examples, of course. A person skilled in the art may find various alternations and modifications within the scope of the appended claims, and it should be understood that they will naturally come under the technical scope of the present invention. 
       REFERENCE SIGNS LIST 
       [0097]      1  electric power supplying system 
         [0098]      10  bus line 
         [0099]      100  power supply server 
         [0100]      110  AC/DC converter 
         [0101]      120  server controller 
         [0102]      130  modem 
         [0103]      140  inductor 
         [0104]      150  switch 
         [0105]      160  commercial power source 
         [0106]      170  outlet 
         [0107]      171  plug 
         [0108]      181  electrode 
         [0109]      182  cover 
         [0110]      183   a,    183   b  lock release mechanism 
         [0111]      184  inclined portion 
         [0112]      191  housing 
         [0113]      192  electrode 
         [0114]      193  protruding portion 
         [0115]      194  electrode protection cover 
         [0116]      195   a,    195   b  lock mechanism 
         [0117]      196   a,    196   b  recessed portion 
         [0118]      197  cutaway portion 
         [0119]      198  electrode hole 
         [0120]      200  client 
         [0121]      210  DC/DC converter 
         [0122]      220  client controller 
         [0123]      230  modem 
         [0124]      240  inductor 
         [0125]      250 ,  260  switch 
         [0126]      270  battery 
         [0127]      280  load 
         [0128]      290  outlet 
         [0129]      291  plug