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BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT 
     The present invention relates to a door apparatus for opening and closing side doors of a train. 
     A mechanism for opening and closing a door of a train is an essential part for the safety of passengers on the train. Once the door of the train is closed, the door should not be opened accidentally regardless of moving or stationary. Further, the doors must always be held closed with a specific force to prevent rain or wind from entering, and to suppress vibrations. However, when an emergency such as a power failure happens to stop the train and the passengers need to evacuate from the train, it must be possible for a passenger to manually open the door relatively easily. Thus, a train door apparatus must be able to work very reliably. The inventor has already developed a train door apparatus that meets these requirements and applied for a patent (see Japanese Patent Publication (KOKAI) No. 2000-142392). 
     FIGS. 14 to  17  show a train door apparatus according to Japanese Patent Publication (KOKAI) No. 2000-142392. This apparatus is briefly described below. FIG. 14 is a front view showing an entire train door apparatus. FIG. 15 is an enlarged view of an essential part of the train door apparatus. In FIGS. 14 and 15, two doors  1  and  2  are movably suspended from and supported by a door rail  3  horizontally mounted along a side of a train. The two doors move in opposite directions (left and right in the figure) to open or close the train doorways. The door  1 , shown at left in the figure, is driven by a linear motor  5  as an actuator connected to a moving member  4  of the door  1 . 
     As shown in FIG. 15, a moving unit  5   a  of the linear motor  5  engages the moving member  4  to be able to slide for a predetermined distance ‘x’ in an opening or closing direction (to the right or left in the figure). A compression spring  6  is interposed between the moving unit  5   a  and the moving member  4 , as shown in the figure. Thus, the linear motor  5  is connected to the door  1  so that the door can move by the distance ‘x’ in the opening direction thereof. 
     The right door  2  moves in cooperation with the door  1  via a direction conversion mechanism  7 . As shown in FIG. 15, the direction conversion mechanism  7  is composed of a lower rack  9  connected to the moving member  4  of the door  1  via a connection rod  8 , an upper rack  11  connected to the moving member  4  of the door  2  via a connection plate  10 , and a pinion  12  that simultaneously engages these racks  9  and  11 . The lower rack  9  and the upper rack  11  are guided to be able to slide within a unit case  7   a  fixed to the train in the opening or closing direction, and the pinion  12  is supported by a shaft fixed to the unit case  7   a . The opening or closing movement of the door  1  driven by the linear motor  5  is transferred to the door  2  by changing the direction by the direction conversion mechanism  7 . 
     FIGS. 16 and 17 are detailed views showing a locking mechanism  13  (in FIG. 14) attached to the direction conversion mechanism  7  and pushing/pulling attachments (members)  14  and  15  for locking and unlocking the locking mechanism  13 . FIG. 16 shows a locked state, while FIG. 17 shows an unlocked state. In FIGS. 16 and 17, the pushing attachment  14  and the pulling attachment  15  are attached to a tip of the moving unit of the actuator  5 . 
     The pushing attachment  14  has a rod-like shape and one end horizontally fixed to the actuator  5 . The pulling attachment  15  with a key-shaped tip is placed on a top surface of the pushing attachment  14 , and has one end joined to the actuator  5  by a pin to rotate and move along the vertical axis. The pulling attachment  15  is urged upward by a compression spring  16  interposed between the pulling attachment  15  and the pushing attachment  14 . A pin  17  with a head is screwed into the pulling attachment  15  while loosely passing through the pushing attachment  14 , and limits an upward rotational range of the pulling attachment. A guide fixture  18  contacts a top surface of the pulling attachment  15  and is attached to a tip of a fixed portion of the linear motor  5  to stop the pulling attachment from rotating upwardly. 
     The locking mechanism  13  has a slider  19  guided to be able to slide in the directions in which the doors  1  and  2  move; a back spring  20  composed of a compression spring to urge the slider  19  toward the door  2 ; a latch  21  guided to be able to slide vertically; and a locking spring  22  composed of a tension spring to urge the latch  21  downward. The slider  19  has a cam surface  19   a  disposed on a top surface thereof having an oblique stage surface, and an engaging protruding portion  19   b  provided at a tip thereof. Although not shown in detail, the latch  21  is composed of a vertical latch rod  24  guided to be able to move up or down inside a guide cylinder  23  fixed to a unit case  7   a , and a frame  25  integrated with the latch rod  24 . A roller  26  is rotatably attached to the frame  25  to contact the cam surface  19   a  of the slider  19 . The locking spring  22  for urging the latch  21  downward is provided between the frame  25  and the unit case  6   a . As described later, the latch  21  advances or retracts in concert with the opening and closing operations of the doors. 
     In the door apparatus described above, FIG. 16 shows a state in which the doors  1  and  2  are closed and locked. In this state, a tip of the latch rod  24  advances into an engaging hole  27  in the upper rack  11 , which constitutes an engaging portion of the direction conversion mechanism  7 , thereby locking the sliding motion of the upper rack  11 . Thus, the doors  1  and  2 , linked to the upper rack  11 , will not move. 
     In this state, the pushing attachment  14  abuts against the engaging protruding portion  19   b  of the slider  19 , and the key-shaped portion of the pulling attachment  15  engages the engaging protruding portion  19   b . When a signal is sent to open the door, the moving unit  5   a  of the linear motor  5  moves to the left. With the door  1  staying at its closed position, the moving unit  5   a  initially moves to the left by a predetermined distance ‘x’ while pushing the compression spring  6 . The pulling attachment  15  pulls the slider  19  via the engaging protruding portion  19   b . At this time, the pulling attachment  15  tries to move upwardly, but it can not open, as it is pressed by the guide attachment  18 . 
     When the slider  19  is pulled and moved to the left, the roller  26  is pushed onto an upper surface of the cam surface  19   a  via the inclined surface thereof as shown in FIG.  17 . Thus, the latch  21  is lifted to withdraw the latch rod  24  from the engaging hole  27  to unlock the upper rack  11 , thereby unlocking the doors  1  and  2 . Once the moving unit  5   a  moves by the distance ‘x’, the guide attachment  18  stops pushing the pulling attachment  15 . As a result, the pulling attachment  15  rotates upward by the compression spring  16  and is released from the engaging protruding portion  19   b  of the slider  19 . Although the pulling attachment  15  is released, the slider  19  remains at its forward position due to a spring force of the back spring  20 , thereby keeping the roller  26  pushed up. 
     Subsequently, the moving unit  5   a  moves the door  1  leftward to its predetermined open position. Correspondingly, the door  2  linked to the door  1  via the direction conversion mechanism  7  moves to the right to open the doors  1  and  2 . Thereafter, a signal is sent to move the door  1  to the right, and the door  1  moves to its closed position, shown in FIG.  16 . Then, the moving unit  5   a  pushes the slider  19  via the pushing attachment  14 . As a result, the roller  26  falls from the upper surface of the cam surface  19   a , and the latch rod  24  advances through the engaging hole  27  in the upper rack  11  to lock the doors again. When the doors need to be opened in an emergency, a handle  28 , shown in FIG. 14, is rotated by 90 degree to pull up the latch  21  via a wire  29 , thereby forcibly unlocking the doors. 
     In a state where the doors are closed, and the latch is engaged to lock the doors, if a hand or a cloth of a passenger is caught between the doors, the locked doors can not be manually opened. Thus, there is a safety problem associated with the train door apparatus described above. 
     It is thus an object of the present invention to improve the safety of a train door apparatus in an emergency when the train door apparatus has locked the door while in a closed state. 
     Further objects and advantages will be apparent from the following description of the invention. 
     SUMMARY OF THE INVENTION 
     To attain the above objects, the present invention provides a door apparatus. The door apparatus keeps a door in a semi-locked state rather than a fully locked state, even when the doors are closed, so that the door can be opened manually in a certain extent for a while after the train has left a station. For this purpose, in the present invention, a direction conversion mechanism transmits a movement of one door driven by an actuator to the other door in a converted direction. The direction conversion mechanism has a two-stage engagement portion with a latch. When the latch moves down to the first stage of the engagement portion, the doors become in a semi-locked state so that the door can be opened manually in a predetermined distance. When the latch moves further down to the second stage of the engagement portion, the door is completely locked. A stopper mechanism is provided to stop the latch during the operation. When the door is closed, the stopper mechanism stops the latch at the first stage of the engaging portion. Then, when the train reaches a specified speed or higher, the latch is released and moves through the engaging portion down to the second stage. 
     As a way for moving the latch in connection with the opening and closing operations of the doors, the actuator is connected to one of the doors to be able to move to open the door in a predetermined distance, as shown in Japanese Patent Application (KOKAI) No. 2000-142392. The apparatus is provided with the slider supported to be able to slide in a door moving direction and having a stage cam surface on a top surface; a back spring for urging the slider toward one of the doors; a roller connected to the latch and contacting the cam surface of the slider; a locking spring for urging the latch toward an engaging portion of the direction conversion mechanism; and pushing/pulling attachments (members) attached to the actuator. 
     When the doors are closed, the actuator pushes the slider via the pushing attachment. The roller is pushed down from an upper stage of the cam surface by the locking spring, and the latch advances into the engaging portion, thereby locking the doors in a closed state. When the doors are opened, the actuator moves in the predetermined distance in the opening direction to pull the slider via the pulling attachment. The roller is pushed onto the upper stage of the cam surface, thereby withdrawing the latch from the engaging portion to unlock the door. 
     As another means for moving the latch in connection with the opening and closing operations of the doors, the apparatus may be provided with a locking spring for urging the latch toward the engaging portion of the direction conversion mechanism and a solenoid for driving the latch against a force of the locking spring. In this case, to close the doors, the latch is moved into the engaging portion by the locking spring to lock the doors, whereas to open the doors, the solenoid moves the latch from the engaging portion to unlock the doors. 
     As yet another means for moving the latch in connection with the opening and closing operations of the doors, the apparatus may be provided with a solenoid for driving the latch to advance into the engaging portion of the direction conversion mechanism or retracts therefrom. In this case, to close the doors, the solenoid moves the latch to enter into the engaging portion to lock the doors, whereas to open the doors, the solenoid moves the latch to withdraw from the engaging portion to unlock the doors. 
     The stopper mechanism is constituted of a slide piece for abutting against the latch when the latch advances into the engaging hole and a solenoid for moving the slide piece into or out in a latch moving path. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front view showing an essential part of a train door apparatus in a semi-locked state, according to an embodiment of the present invention; 
     FIG. 2 is a front view showing an essential part of the door apparatus in FIG. 1 in a state where the doors are manually opened; 
     FIG. 3 is a front view showing an essential part of the door apparatus in FIG. 1 in a fully locked state; 
     FIG. 4 is a front view showing an unlocking operation of the door apparatus in FIG. 1; 
     FIG. 5 is a front view showing an emergency opening operation of the door apparatus in FIG. 1; 
     FIG. 6 is a front view showing an essential part of a train door apparatus in a semi-locked state according to the second embodiment of the present invention; 
     FIG. 7 is a front view showing the door apparatus in FIG. 6 in a fully locked state; 
     FIG. 8 is a front view showing an unlocking operation of the door apparatus in FIG. 6; 
     FIG. 9 is a front view showing an emergency opening operation of the door apparatus in FIG. 6; 
     FIG. 10 is a front view showing an essential part of a train door apparatus in a semi-locked state, according to the third embodiment of the present invention; 
     FIG. 11 is a front view showing the door apparatus in FIG. 10 in a fully locked state; 
     FIG. 12 is a front view showing an unlocking operation of the door apparatus in FIG. 10; 
     FIG. 13 is a front view showing an emergency opening operation of the door apparatus in FIG. 10; 
     FIG. 14 is a front view showing an entire construction of a conventional door apparatus; 
     FIG. 15 is an enlarged view showing an essential part of the door apparatus in FIG. 14; 
     FIG. 16 is a front view showing a locking operation of the door apparatus in FIG. 14; and 
     FIG. 17 is a front view showing an unlocking operation of, the door apparatus in FIG.  14 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Hereunder, preferred embodiments of the present invention will be explained with reference to the accompanied drawings. In these figures, the same reference numbers denote the parts corresponding to those in the prior art (FIGS. 14 to  17 ). 
     First, FIGS. 1 to  5  show the first embodiment in which the present invention has been applied to the conventional apparatus of FIG.  16 . FIGS. 1 to  5  is partially sectional front views of a locking mechanism portion (the compression spring  16  and the pin with a head  17  shown in FIG. 16 are omitted). FIG. 1 shows a semi-locked state, FIG. 2 shows a state in which the doors in FIG. 1 are manually opened in a specified distance, FIG. 3 shows a fully locked state, FIG. 4 is an unlocked state, and FIG. 5 shows an emergency unlocked state. 
     A difference in FIG. 1 from the prior art is that the engaging hole  27 , that engages the latch rod  24  of the direction conversion mechanism  7 , is formed of two stages. The latch rod  24  has an elliptical cross-section, with a larger diameter in the transverse direction in FIG.  1 . The engaging hole  27  engages the latch rod  24  with an appropriate gap, and has a semi-elliptical recess along an outer peripheral surface of the latch rod  24  formed at an upper left of the elliptical through-hole, shown in FIG.  1 . The engaging hole  27  is formed of two stages, namely the first stage  27   a  and the second stage  27   b.    
     A unit case  7   a  of the direction conversion mechanism  7  has a stopper mechanism  33  installed thereon. The stopper mechanism  33  is composed of a block-shaped slide piece  31  guided by a slide base  30  to be able to slide in the transverse direction of FIG. 1 and a solenoid  32  for moving the slide piece  31 . The solenoid  32  is composed of a bi-stable polarized electric magnet containing a permanent magnet to generate a stroke in the transverse direction of FIG.  1 . Whenever a switch signal is input, a plunger  34  is reversed and held at the end of the stroke by the permanent magnet. The slide piece  31  slides in and out from a moving path of the latch  21  (the vertical direction in FIG.  1 ). When the slide piece  31  slides in the path, the slide piece  31  abuts against the frame  25  to stop the latch  21  (the frame  25 ) in the middle of advancement, as shown in FIG.  1 . The locking spring  22  is installed on the frame  25  between the latch rod  24  and the stopper mechanism  33 . The other configurations are substantially the same as those of the conventional apparatus in FIG.  16 . 
     In the door apparatus according to this embodiment, when the actuator  5  drives the doors (see FIG. 5) into the closed position upon a close instruction from a vehicle, the roller  26  falls from the cam surface  19   a , and the latch rod  24  is pulled toward the engaging hole  27  by the spring force of the locking spring  22 . When the close instruction is sent, the stopper mechanism  33  has already moved the slide piece  31  into the moving path of the latch  21 . As shown in FIG. 1, the latch  21  is stopped at a distance ‘a’ from the fully locked position, with the frame.  25  abutting against the slide piece  31  and pressed by the locking spring  22 . At this time, the tip of the latch rod  24  has already entered the engaging hole  27  down to the first stage  27   a , as shown in FIG. 1 (a semi-locked state). The actuator  5  has an encoder for detecting a position of the moving unit  5   a , so that a thrust of the moving unit  5   a  can be reduced to, for example, about one-tenths of its normal value before the doors are completely closed. 
     In the semi-locked state, the doors are pushed in the closing direction with this small force. In this state, the doors can be opened with a hand. When the doors are pushed, the doors open with the upper rack  11  moving to the right in FIG.  1 . The doors are then locked when the latch rod  24  engages the first stage  27   a  of the engaging hole  27 . FIG. 2 shows the state where the door can be opened manually. The distance ‘b’ (FIG. 1) in which the upper rack  11  can move may be set, for example, to be 15 to 20 mm. This setting allows the doors to be opened by a double distance (b×2), for example, 30 to 40 mm. Accordingly, when a cloth or a hand of a passenger is caught between the doors, the passenger can pull it free from the doors by pushing the doors. 
     The semi-locked state in FIG. 1 is maintained while the train is not moving or is moving within a low-speed range, for example, 5 km/hour, after starting. Once the train reaches a specific speed, a switch signal based on a speed signal from the vehicle is sent to the solenoid  32 . The solenoid  32  is reversed to retract the slide piece  31 , i.e. move to the right in FIG.  1 . As a result, the latch  21  is released from the slide piece  31  and further moved down by the spring force of the locking spring  22 . The latch rod  24  moves in the engaging hole  27  from the first stage  27   a  to the second stage  27   b , thereby bringing the apparatus into the state shown in FIG. 3 (the fully locked state). In the fully locked state, the upper rack  11  is fully locked by engaging the latch rod  24 , thereby fully locking the doors. 
     FIG. 4 shows a state where the train has stopped and the doors start to open from the closed state as shown in FIG.  3 . When the doors open, the moving unit  5   a  of the actuator  5  moves by the specific distance ‘x’ (see FIG. 17) with the doors closed state, while the pulling attachment  15  pulls the slider  19  to push the roller  26  onto the cam surface  19   a , as described in the prior art. The latch rod  24 , integrated with the roller  26  via the frame  25 , is pushed upward by a distance ‘c’ to push from the engaging hole  27  to unlock the doors as shown in FIG.  4 . Then, the actuator  5  opens the doors. Once the moving unit  5   a  of the actuator  5  reaches its fully opened position, the above-described encoder sends a fully opened signal, which is then transmitted to the solenoid  32 . The solenoid  32  is reversed from the state shown in FIG. 3 to move the slide piece  31  to a position corresponding to the state shown in FIG. 1 to be ready for the next operation. 
     FIG. 5 shows an emergency unlocking operation. In the fully locked state in FIG. 3, the handle  28  is rotated from a position shown by a broken line in FIG. 5 to a position shown by a solid line in FIG. 5 to pull up the frame  25  via the unlocking cable  29 . This causes the latch rod  24  to withdraw from the engaging hole  27  to allow the doors to be fully opened manually. 
     FIGS. 6 to  9  shows the second embodiment using a solenoid as an unlocking device. FIG. 6 shows a semi-locked state, FIG. 7 shows a fully locked state, FIG. 8 shows an unlocked state, and FIG. 9 shows an emergency unlocking operation. In this embodiment, a solenoid  35  is installed opposite to the frame  25  of the latch  21  instead of the slider  19 , the roller  26 , the pushing attachment  14 , the pulling attachment  15 , and other parts in the embodiment shown in FIG.  1 . The solenoid  35  is also composed of a bi-stable polarized electromagnet so that a plunger  36  moves in the vertical direction of FIG.  6  and is held at the end of the stroke by a permanent magnet. 
     In the fully locked state of FIG. 7, the plunger  36  of the solenoid  35  is at a retracted position. Upon an open instruction, the plunger  36  pushes up the frame  25  of the latch  21 . As shown in FIG. 8, the latch rod  24  is withdrawn from the engaging hole  27  to unlock the doors. Then, the actuator  5  opens the doors. Once the doors are fully opened, with a fully open signal from the encoder, the stopper  33  is driven to move the slide piece  31  into the moving path of the latch  21 . Subsequently, when a close instruction is sent to close the doors, with a fully close signal from the encoder, the solenoid  35  is switched to move the plunger  36  to retract. Thus, the latch  21  is lowered by the spring force of the locking spring  22 , abuts against the slide piece  31 , and is stopped, thereby bringing the apparatus into the semi-locked state shown in FIG.  6 . The other parts of the construction and operation are the same as those in the embodiment shown in FIGS. 1 to  5 , and the description is thus omitted. 
     FIGS. 10 to  13  shows the third embodiment. FIG. 10 shows a semi-locked state, FIG. 11 shows a fully locked state, FIG. 12 shows an unlocked state, and FIG. 13 shows an emergency unlocked state. In this embodiment, the locking spring in the second embodiment is omitted. As shown in FIG. 10, the plunger  36  of the solenoid  35  is connected to the frame  25  of the latch  21  via a joining attachment  37 . When the doors are closed, the plunger  36  of the solenoid  35  retracts to pull down the latch  21  to move the latch rod  27  through the engaging hole  27 . Accordingly, the locking spring  22  is not required. Other aspects of the configuration and operation are the same as those in the second embodiment, and the description is thus omitted. 
     As described above, according to the present invention, the semi-locked state is maintained for some time after the train has left from the station. Accordingly, the door safety function is added to the apparatus in addition to the conventional closing function so that a cloth or a hand of the passenger caught between the doors can be easily released therefrom, thereby improving the passenger safety. 
     While the invention has been explained with reference to the specific embodiments of the invention, the explanation is illustrative and the invention is limited only by the appended claims.

Summary:
A door apparatus for opening and closing two doors supported on a horizontal door rail includes an actuator connected to one of the two doors for driving the same, a direction conversion mechanism connected to the other of the two doors for transmitting a movement of the actuator to the other door to move the same and having an engaging portion formed of a first stage and a second stage, and a locking mechanism having a latch engaging the direction conversion mechanism for locking the two doors and non-engaging the direction conversion mechanism for allowing the two doors to open. The latch engages the first stage of the engaging portion to semi-lock the doors to be able to open manually, and engages the second stage of the engaging portion to lock the doors completely.