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CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the priority of Korean Patent Application No. 10-2009-0024908, filed on Mar. 24, 2009, in the KIPO (Korean Intellectual Property Office), the disclosure of which is incorporated herein in their entirety by reference. Further, this application is the National Phase application of International Application No. PCT/KR2010/001817, filed Mar. 24, 2010, which designates the United States and was published in Korean. Each of these applications is hereby incorporated by reference in their entirety into the present application. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates, in general, to an electric door lock and an electric door having the same and, more particularly, to an electric door lock which has a simple structure, ensures the reliability of a locking function, reduces a danger of a failure and an operation error, and is easy to fabricate and maintain, saving the cost for the fabrication and maintenance relative to the cost taken in the related art, and an electric door having the same. 
     2. Description of the Related Art 
     In case of a railway train, a currently available electric door (auto door) is operated such that when a train arrives at a station, the door is opened and closed for boarding or alighting of passengers following the driver&#39;s manipulation of an actuation switch, which is performed by the driver who is seeing the passengers boarding on or alighting from the railway train. 
     Here, if a passenger or an object gets caught in the door during the closing of the electric door, the electric door cannot be completely closed. In this case, the driver is informed of such situation or information through a display or an alarm means, and the driver who recognized the state of the door being not completely closed repeatedly manipulates the actuation switch to open and close the electric door until the electric door is completely closed. 
     In the meantime, if the railway train is stopped to run owing to a fire, a failure, etc. of the train, or passengers should escape from the train because an emergency situation occurs in the train, the driver should directly manipulate the actuation switch to open the door after checking the state of the railway tracks, or otherwise the passengers should directly manually manipulate a manual opening/closing means, which was mounted in the proximity of the electric door, to open the door. 
     However, if the situation is that the railway train is running, or the state of the railway tracks is dangerous, or otherwise if nevertheless the situation is not an emergency state, the passengers can open the electric door even with their less effort, a very dangerous situation can be caused. Thus, there is a need for an electric door lock providing a reliable locking operation. 
     In order to provide a reliable locking function, a conventional electric door lock, which was disclosed in U.S. Pat. No. 5,077,938, includes a locking roller, a locking finger member, a guide finger member, a locking roller slide channel, a roller keeper, a carriage, and the like. 
     However, the conventional electric door lock having the above-mentioned configuration has a problem of increased cost of fabrication and maintenance because of numerous, complex parts. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention has been made keeping in mind the above problems occurring in the related art, and the present invention is intended to propose to an electric door lock which has a simple structure, ensures the reliability of a locking function, reduces a danger of a failure and an operation error, and is easy to fabricate and maintain, saving the cost for the fabrication and maintenance relative to the cost taken in the related art, and an electric door having the same. 
     In order to achieve the above object, according to one aspect of the present invention, there is provided an electric door lock including: a locking switch provided in a door frame for checking the locking state of a door body when the door body is closed, the door frame slidably supporting at least one door body; a pair of screws capable of rotating forwards and rearwards and disposed parallel with each other in one side of the door frame in the direction towards which the door body slides; a locking roller guide provided in the door frame in the proximity of the screws; and a slide unit wherein one end thereof is rotatably connected to the screw and the other end thereof is connected to the door body, the slide unit including a locking switch-pressing plate actuated to operate the locking switch when the door body is closed, such that a locking signal is generated by the locking switch, and a locking roller acting in combination with the locking roller guide. 
     The locking roller guide includes: a guide body; an inclined section provided at a certain angle on one surface of the guide body to define a path along which the locking roller rolls, the angle being defined in the direction towards which the door body is closed; and a vertical end formed at the utmost position of the inclined section such that the vertical end extends in the direction that intersects the direction in which the door body slides. 
     According to the electric door lock of the present invention, when the door body is closed, the locking switch-pressing plate is actuated to operate the locking switch in response to the interaction between the locking roller and the locking roller guide. When the locking roller that is moving on the inclined section of the locking roller guide passes through the utmost position of the inclined section of the locking roller guide, it falls down towards the vertical end so that the locking roller comes into contact with or confronts the vertical end of the locking roller guide. In the state of the locking roller being brought into contact with or confronting the vertical end, even if force is exerted to manually open the door, the door cannot be opened because the motion of the locking roller is resisted by the vertical end of the locking roller guide. 
     The locking roller is elastically biased towards the direction against which the locking roller approaches the locking roller guide. 
     The sliding unit may include: a screw nut that is rotatably screw-coupled to the screw such that it is movable in the longitudinal direction of the screw; a screw nut lump that surrounds and supports the screw nut and to which the locking switch-pressing plate and the locking roller are connected at one side; and a screw nut lump housing that partially surrounds and supports the screw nut lump such that the screw nut lump can be rotated at a certain angle. 
     The screw nut lump housing may include: a housing body; an opening that is formed to one side of the housing body such that the locking switch-pressing plate is open towards the locking switch; and a through-passage that is formed in one side of the housing body to allow a support for the locking roller, which connects and supports the locking roller and screw nut lump, to move therethrough. 
     The through-passage may be composed of a long hole through which the locking switch-pressing plate reciprocates between the switch-off position where the door body is opened so that the locking switch is not actuated and the switch-on position where the door body is closed so that the locking switch is actuated. 
     The sliding unit may further include: a hanger connected with the door body; a guide roller connected to one side of the hanger and coupled to a guide rail formed on the door frame such that it is able to roll along the guide rail; and a link that connects and supports the other side of the hanger and the screw nut lump housing. 
     The sliding unit may further include a hinge pin that is coupled to the screw nut lump housing and the link such that it rotatably supports the screw nut lump housing in connection with the link. 
     The door body, the locking switch, the screw, the locking roller guide, and the sliding unit may be respectively provided in a single unit or a pair unit, in which both elements are symmetric with each other, on the door frame. If they are respectively provided in a pair unit, the opposite screws may respectively have threads extending opposite to each other. 
     The electric door lock may further include a closing switch provided in the door body so as to generate a signal indicative of the locked state of the door body when the door body was closed. 
     A space in which the screw nut lump can move in the sliding direction of the door body or in the direction that intersects the sliding direction in connection with the screw nut lump housing may be further provided between the screw nut lump and the screw nut lump housing. 
     In another aspect of the present invention, there is provided an electric door having the electrical door lock having the above-mentioned configuration. 
     As set forth before, the electric door lock has a simple structure, ensures the reliability of a locking function, reduces a danger of a failure and an operation error, and is easy to fabricate and maintain, saving the cost for the fabrication and maintenance relative to the cost taken in the related art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a partially enlarged perspective view of an embodiment of an electric door lock that is viewed from upside; 
         FIG. 2  is a partially enlarged perspective view of a major part of the electric door lock that is viewed in the direction A of  FIG. 1 ; 
         FIG. 3  is a front view of the electric door lock; 
         FIG. 4  is a view of the electric door lock that is viewed in line B-B of  FIG. 3 ; and 
         FIG. 5  is a view that is partially cut from  FIG. 3  to explain the operation of a locking roller of the electric door lock. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in greater detail to a preferred embodiment of the invention, an example of which is illustrated in the accompanying drawings. Wherever possible, the same reference numerals will be used throughout the drawings and the description to refer to the same or like parts. 
       FIG. 1  is a partially enlarged perspective view of an embodiment of an electric door lock that is viewed from upside,  FIG. 2  is a partially enlarged perspective view of a major part of the electric door lock that is viewed in the direction A of  FIG. 1 ,  FIG. 3  is a front view of the electric door lock,  FIG. 4  is a view of the electric door lock that is viewed in line B-B of  FIG. 3 , and  FIG. 5  is a view that is partially cut from  FIG. 3  to explain the operation of a locking roller of the electric door lock. 
     As shown in  FIGS. 1 to 5 , the electric door lock includes a locking switch  10  provided in a door frame  2  for checking the locking state of a door body  1  when the door body is closed, wherein the door frame slidably supports the door body, a pair of screws  15  capable of rotating forwards and rearwards and disposed parallel with each other in one side of the door frame  2  in the direction towards which the door body  1  slides, a locking roller guide  20  provided in the door frame  2  in the proximity of the screws  15 , and a slide unit  30  having a locking switch-pressing plate  40  and a locking roller  50  wherein one end thereof is rotatably connected to the screw  15  and the other end thereof is connected to the door body  1 . Here, when the electric door body  1  is closed, the locking roller  50  interacts with the locking roller guide  20  to drive the locking switch-pressing plate  40 , thereby actuating the locking switch  10 . 
     According to the electric door lock, when the electric door body  1  is being closed in response to the forward or rearward rotation of the screw  15 , as shown in  FIG. 5 , the locking roller  50  moves along an inclined section  22  of the locking roller guide  20  (see the dotted line of  FIG. 5 ) so that when the locking roller  50  falls down towards a vertical end  23  (downwards in  FIG. 5 ) at the utmost position of the inclined section  22 , a screw nut lump  32  rotates at a certain angle in a screw nut lump housing  33 , thereby rotating the locking switch-pressing plate  40  from the position of the dotted line to the position of the solid line of  FIG. 4 . With the actuation of the locking switch  10  by the rotation of the locking switch-pressing plate  40  from the position of the dotted line to the position of the solid line, the locking switch  10  generates a locking signal. In this case, since the locking roller  50  has been disposed against and been engaged with the vertical end  23 , even though passengers intend to open the electric door body  1 , the electric door body  1  can be held in the locked state. 
     As shown in  FIG. 4 , the locking switch  10  is coupled to a connection block  11 , which is connected to the upper portion of the door frame  2 . Since the locking switch  10  may be adapted to a pressure-sensitive sensor that is actuated by the operation, i.e. the pressing of the locking switch-pressing plate  40 , thereby generating the locking signal, it may preferably be rotatably coupled to the connection block  11 . 
     The screw  15  is an element that transmits a practical driving force from a motor to the electric door body  1  in order to open or close the electric door body  1 . 
     In the present embodiment, since a pair (set) of electric door bodies  1  is provided, a pair of screws  15  is also provided. Here, sine the pair of electric door bodies  1  is opened or closed in opposite directions to each other, the pair of screws  15  has threads that extend in opposite directions to each other. That is, in  FIGS. 2 and 3 , the left side screw  15  has the right-side thread, whereas the right side screw  15  has the left-side thread. Since such screws  15  transmit a practical driving force to the electric door body  1 , they are connected to a drive shaft (not shown) of the motor in order to rotate forwards or rearwards. For reference, opening/closing of the door may be manually controlled by a user, or otherwise may be automatically controlled. 
     The sliding unit  30  is a unit wherein one end thereof is rotatably connected to the screw  15  and the other end thereof is connected to the door body  1 , serving to open/close the door body  1  following the transmission of the rotating power of the screw  15  that is rotating to the door body  1 . 
     The sliding unit  30  includes a screw nut  31  that is rotatably screw-coupled to the screw  15  such that it is movable in the longitudinal direction of the screw  15 , a screw nut lump  32  that surrounds and supports the screw nut  31 , a screw nut lump housing  33  that partially surrounds and supports the screw nut lump  32  such that the screw nut lump can be rotated at a certain angle, a link  37 , and a hanger  34 . 
     The screw nut  31  is an element that is screw-coupled to the screw  15 . Thus, as the screw  15  rotates, the screw nut  31  connected to the side of the door body  1  can be move along the longitudinal direction of the screw  15 . As such, the screw nut  31  can move along the longitudinal direction of the screw  15 , so that the door body  1  connected to the screw nut  31  can also be actuated. 
     The screw nut lump  32  is an element that surrounds and supports the screw nut  31  and to which the locking switch-pressing plate  40  and the locking roller  50  are connected. 
     Between the screw nut lump  32  and the screw nut lump housing  33 , there is further provided a space (not shown) in which the screw nut lump  32  can move in the sliding direction of the door body  1  or in the direction that intersects the sliding direction in connection with the screw nut lump housing  33 . Thus, when the door body  1  is operated to slide, the screw nut lump  32 , to which the locking switch-pressing plate  40  and the locking roller  50  are connected, can be smoothly operated without interruption. This helps securing reliability of a locking function. Here, the space is not greatly formed, but may suffice if it is of the size that the screw nut lump  32  can freely move in the screw nut lump housing  33 . 
     The sliding unit  30  of the present embodiment advantageously has a very simple configuration because in addition to detailed elements described below, the locking switch-pressing plate  40  that actuates the locking switch  10  and the locking roller  50  that interacts with the locking roller guide  20  are formed into a single piece. 
     More specifically, according to the present embodiment, since most parts other than the locking switch  10 , the screws  15 , and the locking roller guide  20  are integrated with the sliding unit  30 , the door lock may have a simple structure, ensure the reliability of a locking function, reduce a danger of a failure and an operation error, and be easy to fabricate and maintain, saving the cost for the fabrication and maintenance relative to the cost taken in the related art. 
     Then a description will be made of the operation of the locking switch-pressing plate  40  actuated by the interaction between the locking roller guide  20  and the locking roller  50 . 
     Referring to  FIG. 4 , it is noted that when the locking switch-pressing plate  40  pushes the locking switch  10  from the position of the dotted line to the position of the solid line, the locking switch  10  is pushed at a certain angle on the connection block  11 , generating a single. 
     Naturally, this is only one embodiment. That is, while the present embodiment has illustrated the configuration in which when the door body  1  is closed, the locking switch-pressing plate  40  is concurrently rotated to actuate the locking switch  10 , alternative embodiment is possible in which the locking switch  10  is disposed as a proximity sensor at the position closer to the door frame  2  than the position of  FIG. 4 , so that when the locking switch-pressing plate  40  rotates and approaches the locking switch  10 , the locking switch can then only generate a locking signal. However, so long as when the door body  1  is closed, the reliability of the locking function can be secured, any method may be adapted. 
     The locking roller guide  20  interacts with the locking roller  50  such that when the door body  1  is closed, the locking switch-pressing plate  40  actuates the locking switch  10  in response to the rotation of the screw  15 . 
     As described before, the locking switch-pressing plate  40  serves to actuate the locking switch  10  when the door body  1  is closed, generating the locking signal, and the locking roller  50  interacts with the locking roller guide  20  to allow the locking switch-pressing plate  40  to actuate the locking switch  10 . In this case, the locking roller  50  may be configured such that it is elastically biased towards the direction in which it moves towards the locking roller guide  20 . Since the structure for this configuration is simply provided so that an elastic spring (not shown), which can be mounted to the screw nut lump  32 , is disposed to be actuated to allow the locking roller  50  to be elastically actuated against the locking roller guide  20 , the structure will be omitted in the figures. 
     The screw nut lump housing  33  is an element that partially surrounds and supports the screw nut lump  32 . Here, since the screw nut lump  32  and the locking roller  50  are operated, i.e. rotated in the state of being connected to the screw nut lump housing so as to actuate the locking switch  15  or interact with the locking roller guide  20 , the screw nut lump housing  33  is provided such that it does not interfere with the operation of the screw nut lump  32  and the locking roller  50 . 
     The screw nut lump housing  33  includes a housing body  33   a , an opening  33   b  that is formed to one side of the housing body  33   a  such that the locking switch-pressing plate  40  is open towards the locking switch  10 , and a through-passage  33   c  that is formed in one side of the housing body  33   a  to allow a support  51  for the locking roller, which connects and supports the locking roller  50  and screw nut lump  32 , to move therethrough. 
     As shown in  FIG. 4 , the side of the screw nut lump housing  33  may have the shape of a substantially Y form. Particularly, the through-passage  33   c  is composed of a long hole  33   c  through which the locking switch-pressing plate  40  reciprocates between the switch-off position (dotted line in  FIG. 4 ) where the door body  1  is opened so that the locking switch  10  is not actuated and the switch-on position (solid line in  FIG. 4 ) where the door body  1  is closed so that the locking switch  10  is actuated. 
     That is, the length or size of the long hole  33   c  can be determined within a range by which the locking switch-pressing plate  40  can reciprocate between the switch-off position (dotted line in  FIG. 4 ) and the switch-on position (solid line in  FIG. 4 ). 
     In order for the locking switch-pressing plate  40  to actuate the locking switch  10  when the door body  1  is closed, the screw nut lump  32 , to which the locking switch-pressing plate  40  is connected, should be rotated at a certain angle in the screw nut lump housing  33 . To this end, the locking roller  50  and the locking roller guide  20  are provided wherein the locking roller  50  is a simple circular roller connected to the support  51  for the locking roller, whereas the locking roller guide  20  has a structural characteristic as follows. 
     As shown in  FIG. 5 , the locking roller guide  20  includes a guide body  21 , an inclined section  22  provided at a certain angle on one surface of the guide body  21  to define a path along which the locking roller  50  rolls, the angle being defined in the direction towards which the door body  1  is closed, and a vertical end  23  formed at the utmost position of the inclined section  22  such that the vertical end extends in the direction that intersects the direction in which the door body  1  slides. In order to allow the locking roller  50  to smoothly interact with the locking roller guide  20 , the boundary between the inclined section  22  and the vertical end  23  may be formed into a round. 
     Thus, when the electric door body  1  is being closed in response to the forward or rearward rotation of the screw  15 , as shown in  FIG. 5 , the locking roller  50  moves along an inclined section  22  of the locking roller guide  20  (see the dotted line of  FIG. 5 ) so that when the locking roller  50  falls down towards a vertical end  23  (downwards in  FIG. 5 ) at the utmost position of the inclined section  22 , a screw nut lump  32  rotates at a certain angle in a screw nut lump housing  33 , thereby rotating the locking switch-pressing plate  40  from the position of the dotted line to the position of the solid line of  FIG. 4 . 
     With the actuation of the locking switch  10  by the rotation of the locking switch-pressing plate  40  from the position of the dotted line to the position of the solid line, the locking switch  10  generates a locking signal. In this case, since the locking roller  50  has been disposed against the vertical end  23 , even though passengers intend to manually open the electric door body  1 , the electric door body  1  can be held in the locked state. 
     In order to open the electric door body  1 , the screw  15  is actuated such that it rotates rearwards. In this case, due to strong torque initially occurring upon reverse rotation of the screw  15 , the locking roller  50  disengages from the vertical end  23  and in turn moves along the inclined section  22 , so that the electric door body  1  can be opened without interference. 
     In addition to the above-mentioned construction, the sliding unit  30  may further include a hanger  34  connected with the door body  1 , a guide roller  35  connected to one side of the hanger  34  and coupled to a guide rail  36  formed on the door frame  2  such that it is able to roll along the guide rail  36 , a link  37  that connects and supports the other side of the hanger  34  and the screw nut lump housing  33 , and a hinge pin  38  that is coupled to the screw nut lump housing  33  and the link  37  such that it rotatably supports the screw nut lump housing  33  in connection with the link  37 . 
     When the electric door body  1  is opened/closed, while the electric door body  1  moves along an axis of the screw  15 , the guide roller  35  rolls along the guide rail  36  formed on the door frame  2 , so that the electric door body  1  can be smoothly opened/closed. 
     In addition, the hinge pin  38  serves to partially compensate for vibrations of the door body  1  when the door body  1  is opened/closed particularly in the state of  FIG. 4 . That is, since the guide roller  50  and the screw nut lump housing  33  are rotatably connected to each other by the hinge pin  38 , even when the door body  1  shakes with vibrations in the state shown in  FIG. 4 , the door body  1  can be smoothly opened/closed. 
     In the present embodiment, the door frame  2  is an attachment plate that fixes the door body  1  such that the door body can be slidably moved. The door frame  2  may be made from a metal frame for securing certain hardness. 
     Referring to  FIGS. 3 and 5 , the electric door body  1  further includes a closing switch  60  that is provided in order to generate a signal indicative of the locked state of the door body  1  when the door body  1  has been closed. The closing switch  60  is a sensor that only generates a signal that is indicative of the locked state of the door body  1  and the closing switch generates the signal before the locking signal is generated by the locking switch  10 , and transmits it to the user. Consequently, the user receives both the signal indicative of the locked state and generated by the closing switch  60  and the locking signal generated by the locking switch  10 , and then the motor is stopped to actuate the screw  15  to rotate, thereby completing the closing stroke. 
     Subsequently, a description will be made of the operation of the electric door lock having the above-mentioned configuration with reference to  FIGS. 4 and 5 . Here, the description will be performed by exemplifying a railway train. 
     When the screw  15  rotates forwards or rearwards by the driving force from the motor, the door body  1  is concurrently opened/closed. 
     That is, as shown in  FIG. 5 , when the locking roller  50 , which is moving along the door body  1  such that it moves along the inclined section  22  of the locking roller guide  20  in the region of the locking roller guide  20  (see the dotted line of  FIG. 5 ), then only falls down towards and engages with the vertical end  23  at the utmost position of the inclined section  22 , the screw nut lump  32  rotates at a certain angle in the screw nut lump housing  33 . 
     Thus, the locking switch-pressing plate  40 , which is connected to the screw nut lump  32 , rotates from the position of the dotted line to the position of the solid line of  FIG. 4  in the direction in which the screw nut lump  32  rotates, thereby allowing the locking switch-pressing plate  40  to actuate the locking switch  10 . Thus, the locking switch  10  generates a locking signal, which in turn is transmitted to a user, making the locking stroke of the door completed. 
     Of course, this stage is a stage that finally checks the locked state, so that the signal indicative of the locked state and generated by the closing switch  60  was already transmitted to the user before the locking signal is generated. 
     When the signal indicative of the locked state and generated by the closing switch  60  and the locking signal generated by the locking switch  10  are transmitted to a user&#39;s control system, the closing stroke of the door is then only completed. Here, since the locking roller  50  is already in the state of being disposed towards the vertical end  23 , even though the passengers intend to open the door body  1 , the door body  1  is still held in the locked state so that the door body  1  cannot be opened. 
     In the meantime, in order to open the door, the screw  15  is actuated such that it rotates rearwards following the rearward rotation of the motor shaft. In this case, due to rearward torque occurring upon reverse rotation of the screw  15 , the locking roller  50  disengages from the vertical end  23  and in turn moves along the inclined section  22 , so that the electric door body  1  can be opened without interference. 
     As set forth before, according to the present embodiment, the electric door lock can have a simple structure, ensure the reliability of a locking function, reduce a danger of a failure and an operation error, and be easy to fabricate and maintain, saving the cost for the fabrication and maintenance relative to the cost taken in the related art. 
     In an embodiment of the present invention, the locking switch  10 , the screw  15 , the locking roller guide  20 , and the sliding unit  30  may be respectively provided in a pair unit, in which both elements are symmetric with each other, on the door frame. This is because the door body  1  is provided in a pair unit such that both elements are opened/closed by being moved apart from or close to each other. 
     However, the scope of the present invention is not limited thereto, so a single door body  1  can be provided in the door frame  2 . In the case that the single door body  1  is provided, it may suffice if the locking switch  10 , the screw  15 , the locking roller guide  20 , and the sliding unit  30  respectively are concurrently provided in a single piece. Of course, even through the single door body  1  is provided on the door frame  2 , the embodiment can also implement the same performance as the present embodiment. 
     The electric door lock according to the above embodiments of the present invention may be adapted to electric doors of railway trains, screen doors of subway stations, etc. 
     Although a preferred embodiment of the present invention has been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Summary:
The present invention provides an electric door-locking apparatus, and an electric door comprising same. The electric door-locking apparatus according to the present invention comprises: a locking switch arranged at a door frame to check the locked status of an electric door body when the electric door body is closed; a screw rotatable in the forward and backward directions; a locking roller guide arranged at the door frame in the vicinity of the screw; and a sliding unit, one end of which is rotatably connected to the screw and the other end of which is connected to the electric door body. The electric door-locking apparatus according to the present invention has a structure which enables simple and easy operation, improves the reliability of the locking function, reduces the risk of failure and erroneous operation, and enables easy manufacture and maintenance to reduce manufacturing costs and maintenance costs as compared to conventional apparatuses.