Abstract:
An elevator safety system ( 10 ) includes a limit switch ( 32 ) coupled to a first elevator car ( 14 ) and an actuator plate ( 30 ) coupled to a governor rope ( 24 ) of a second elevator car ( 16 ). The actuator plate trips ( 30 ) the limit switch ( 32 ) when a distance between the first elevator car ( 14 ) and the second elevator car ( 16 ) goes below a safety threshold distance to stop the first and second elevator cars ( 14, 16 ).

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to an elevator safety system, and more particularly to a system and method for maintaining adequate spacing between multiple cars in an elevator hoistway. 
         [0002]    Conventional elevator systems include a single elevator car and a counterweight disposed in a hoistway, a plurality of ropes that interconnect the car and counterweight, a drive machine having a drive pulley wheel engaged with the ropes to drive the car, and a brake to mechanism to stop the movement of the car and counterweight. 
         [0003]    Multiple cars can now be controlled within the same elevator hoistway, with one car operating above the other. The cars are controlled by a common controller that determines the most efficient ways of getting people to their appropriate destinations. 
         [0004]    Although various safety systems have been designed to maintain an adequate distance between a single elevator car and the top or bottom of the hoistway, additional safety measures are needed to maintain an adequate distance between multiple elevator cars operating within the same hoistway. 
       BRIEF SUMMARY OF THE INVENTION 
       [0005]    A multiple car elevator safety system includes a limit switch coupled to a first elevator car and an actuator plate coupled to a governor rope of a second elevator car. The actuator plate trips the limit switch when a distance between the first elevator car and the second elevator car goes below a safety threshold distance, causing a brake mechanism to engage and stop the first and second elevator cars. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a block diagram of an elevator including an elevator safety system. 
           [0007]      FIG. 2  is a block diagram of the elevator illustrating the operation of the elevator safety system including an actuator plate and a limit switch. 
           [0008]      FIG. 3  is a block diagram of the elevator after actuation of the limit switch. 
           [0009]      FIG. 4  is a perspective view of the actuator plate and the limit switch. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]      FIG. 1  is a block diagram of elevator  10  including elevator safety system  28 . Elevator  10  is located in or around a building, and operates to transport people or objects from one location of the building to another location of the building. The elevator includes elevator hoistway  12 , elevator car  14 , elevator car  16 , ropes  18 , drive machines  20 , brakes  21 , elevator controller  22 , governor rope  24 , governor  26 , and elevator to safety system  28 . Elevator cars  14  and  16  are located within elevator hoistway  12 , and elevator car  14  operates above elevator car  16 . Both elevator cars  14  and  16  are capable of servicing all floors of the building. More than two elevator cars may be present within hoistway  12 . 
         [0011]    Elevator cars  14  and  16  are moved between floors by drive machines  20  under the control of elevator controller  22 . Elevator cars  14  and  16  are suspended by ropes  18 , which are also connected to counterweights (not shown). Drive machines  20  adjusts ropes  18  to move elevator cars  14  and  16  independently within elevator hoistway  12 . Brakes  21  are used by elevator controller  22  to stop elevator cars  14  and  16  at the appropriate locations. 
         [0012]    Governor rope  24  is connected to elevator car  16  and extends adjacent to elevator cars  14  and  16 , parallel with hoistway  12 . Governor rope  24  loops around governor  26 , which spins as elevator car  16  moves up or down within hoistway  12 . Governor  26  is a mechanical speed control mechanism that utilizes governor rope  24  to monitor the speed of elevator car  16 . If governor  26  detects that elevator  16  is moving too quickly, it initiates a car safety device (not shown) to slow or stop the movement of the elevator car. Elevator car  14  also has a governor rope, not shown in  FIG. 1 . 
         [0013]    When two elevator cars share the same hoistway, measures must be taken to ensure that an adequate spacing is maintained between elevator car  14  and elevator car  16 . One way of maintaining adequate spacing is through elevator controller  22 . Elevator controller  22  monitors the location of the elevator cars  14  and  16  at all times, and controls the movement of each elevator car in hoistway  12 . Elevator controller  22  operates elevator cars  14  and  16  to maintain adequate spacing between them at all times. 
         [0014]    However, it is desirable to have additional safety measures in place in case of a malfunction in some component of elevator  10 . Therefore, elevator safety system  28  is provided. Elevator safety system  28  includes actuator plate  30  and limit switch  32 . In one embodiment, actuator plate  30  is a round plate with a hole in the middle, where it is clamped to governor rope  30 . Limit switch  32  includes switch actuation to rod  34  and switch box  36 . Limit switch  32  is attached to a lower portion of elevator car  14 . Switch actuation rod  34  extends out from switch box  36 , adjacent to governor rope  34 . Limit switch  32  is located near governor rope  34 , such that actuator plate  30  will trip switch actuation rod  34  if elevator car  14  and elevator car  16  get closer than the safety threshold distance. Actuator plate  30  and limit switch  32  are described in more detail with reference to  FIG. 4 . 
         [0015]    When limit switch  32  is tripped by actuator plate  30 , an electrical stop signal is sent to elevator controller  22 . In one embodiment, limit switch  32  is normally closed, and opens to stop the flow of electricity when tripped by actuator plate  30 . In another embodiment, limit switch  32  is normally open, and closes to allow the flow of electricity when tripped by actuator plate  30 . However, it is recognized that any type of electrical stop signal could be used to communicate with elevator controller  22 , including digital communication signals. Furthermore, the stop signal could be communicated from limit switch  32  to elevator controller  22  using radio frequency communications, or other known communication methods. 
         [0016]    Once the stop signal from limit switch  32  has been received by elevator controller  22 , drive machines  20  are deactivated and brakes  21  are engaged to stop the movement of elevator cars  14  and  16  within hoistway  12 . 
         [0017]      FIGS. 1-3  illustrate the method of stopping elevator cars  14  and  16  in more detail. In the example shown in  FIG. 1 , elevator cars  14  and  16  are moving toward each other, such that elevator car  14  is moving down and elevator car  16  is moving up within hoistway  12 . As elevator cars  14  and  16  approach each other, limit switch  32  and actuator plate  30  also approach each other. 
         [0018]    When elevator cars  14  and  16  get too close to each other, as shown in  FIG. 2 , actuator plate  30  hits actuation rod  34 , causing switch actuation rod  34  to pivot, tripping limit switch  32 . Limit switch  32  then sends stop signal to elevator controller  22 , to inform elevator controller  22  that elevator car  14  and elevator car  16  are no longer adequately spaced from each other. Elevator controller  22  then deactivates drive machines  20  and activates brakes  21  to stop elevator car  14  and elevator car  16 . Elevator cars  14  and  16  continue to move toward each other momentarily until coming to a complete stop as shown in  FIG. 3 . 
         [0019]      FIG. 3  illustrates the desired location of actuator plate  30 . After limit switch  32  has been tripped by actuator plate  30 , elevator cars  14  and  16  will each continue moving toward each other for a distance referred to as a “stopping distance.” The stopping distance depends upon various factors, including: the speed of elevator cars  14  and  16  at the time limit switch  30  is tripped, the amount of time it takes for limit switch  32  to communicate to elevator controller  22 , the amount of time it takes for elevator controller  22  to disengage drive machines  20  and engage brakes  21 , and the length of time it takes for brakes  21  to bring elevator cars  14  and  16  to a complete stop. 
         [0020]    To avoid a collision between elevator cars  14  and  16 , it is desirable to maintain at least a minimum clearance distance between elevator cars  14  and  16  after they have come to a complete stop. The minimum clearance distance may be determined by building code, such as the American Society of Mechanical Engineers (ASME) A17.1 safety code for elevators and escalators. The location of actuator plate  30  on governor rope  24 , however, should be greater than the minimum clearance distance away from elevator car  16 . The distance between the top of elevator car  16  and actuator plate  30  (referred to as the safety threshold distance) should be at least the sum of the minimum clearance distance and maximum stopping distances of each of elevator cars  14  and  16 , where the maximum stopping distance is calculated by considering the factors listed above or by experimental testing. The safety threshold distance will vary for every elevator system. 
         [0021]      FIG. 4  is a perspective view of actuator plate  30  and limit switch  32 . In one embodiment, actuator plate  30  is a doughnut-shaped plate constructed of two semi-circular disks  40 . Semi-circular disks  40  contain notch  42  sized to fit around governor rope  24 . Semi-circular disks  40  are bolted together around governor rope  24  to clamp governor rope  24 . Actuator plate  30  extends out from governor rope  24  in a plane perpendicular to governor rope  24 . Due to the tension on governor rope  24 , actuator plate  30  remains within the vertical path of switch actuation rod  34  at all times. Actuator plate  30  can also be constructed in any other desired shape, such as a square plate, a cube, or a sphere. 
         [0022]    Limit switch  32  includes switch box  36  and switch actuation rod  34 . Switch box  36  contains an electrical switch and wires, and is connected to a lower portion of elevator car  14 . Switch box  36  may be fastened directly to the lower portion of elevator car  14 , adjacent governor rope  24 , or can be connected by a rigid member, such as an angle bracket extending out and/or down from elevator car  14 . Switch actuation rod  34  extends out from switch box  36 , and is positioned a distance away from the governor rope that is less than a radius of the actuator plate, to ensure that actuator plate  30  will contact switch actuation rod  34  when the safety threshold distance is reached. It is recognized that other types of switches, sensors, or detectors could also be used to perform substantially the same function as limit switch  32  and actuator plate  30 . 
         [0023]    Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. For example, the elevator safety system could be reversed with respect to elevator cars  14  and  16 , such that limit switch  32  is connected to a top portion of elevator car  16 , and actuator plate  30  is connected to the governor rope of elevator car  14 . As another example, limit switch  32  could be wired directly to drive machines  20  and brakes  21 , rather than being wired to elevator controller  22 . Many other modifications will also be apparent.