Abstract:
A method of detecting a stuck car or a stuck counterweight in an elevator system having a machine for imparting motion to the car and counterweight includes sensing a car side suspension member tension, T 1 ; sensing a counterweight side suspension member tension, T 2 ; determining a traction ratio in response to a relationship between T 1  and T 2 ; and determining a stuck car or a stuck counterweight if the traction ratio violates a limit.

Description:
BACKGROUND 
       [0001]    The subject matter disclosed herein relates to elevator systems. More specifically, the subject disclosure relates to detection of a stuck elevator car or a stuck counterweight. 
         [0002]    In order to assure safety, codes require that the car or counterweight must not be lifted, if the counterweight or car becomes stuck in the hoistway, for example on the rails or buffer. Codes prescribe a loss of traction test which must be passed to demonstrate that the car or counterweight will not be lifted if the counterweight or car is stuck. This loss of traction test puts an upper limit on the value of friction or traction between the machine sheave and a suspension member. To meet the loss of traction requirement, one solution includes using friction modifier(s) in the suspension member, which may adversely affect other performance parameters of the suspension member. Another solution includes adding weight to the car to assure that the test can be passed. Both of these solutions add cost and limit performance. 
       BRIEF DESCRIPTION 
       [0003]    In one embodiment, a method of detecting a stuck car or a stuck counterweight in an elevator system having a machine for imparting motion to the car and counterweight includes sensing a car side suspension member tension, T 1 ; sensing a counterweight side suspension member tension, T 2 ; determining a traction ratio in response to a relationship between T 1  and T 2 ; and determining a stuck car or a stuck counterweight if the traction ratio violates a limit. 
         [0004]    Additionally or alternatively, in this or other embodiments, determining if the traction ratio violates the limit includes determining that the counterweight is stuck when T 1 /T 2  exceeds an upper limit or T 2 /T 1  goes below a lower limit. 
         [0005]    Additionally or alternatively, in this or other embodiments, determining if the traction ratio violates the limit includes determining that the car is stuck when T 1 /T 2  goes below a lower limit or T 2 /T 1  exceeds an upper limit. 
         [0006]    Additionally or alternatively, this or other embodiments include stopping the machine in response to the traction ratio violating the limit. 
         [0007]    Additionally or alternatively, this or other embodiments include stopping the machine in response to the traction ratio violating the limit for more than a predetermined time. 
         [0008]    In another embodiment, an elevator system includes a car; a counterweight; a suspension member suspending the car and the counterweight; a machine having a traction sheave, the suspension member positioned about the traction sheave; a car side suspension member load sensor sensing a car side suspension member tension, T 1 ; a counterweight suspension member load sensor sensing a counterweight side suspension member tension, T 2 ; and a controller determining a traction ratio in response to a relationship between T 1  and T 2 , the controller determining a stuck car or a stuck counterweight if the traction ratio violates a limit. 
         [0009]    Additionally or alternatively, this or other embodiments include the controller determining that the counterweight is stuck when T 1 /T 2  exceeds an upper limit or when T 2 /T 1  goes below a lower limit. 
         [0010]    Additionally or alternatively, this or other embodiments include the controller determining that the car is stuck when T 1 /T 2  goes below a lower limit or T 2 /T 1  exceeds an upper limit. 
         [0011]    Additionally or alternatively, this or other embodiments include the controller stopping the machine in response to the traction ratio violating the limit. 
         [0012]    Additionally or alternatively, this or other embodiments include the controller stopping the machine in response to the traction ratio violating the limit for more than a predetermined time. 
         [0013]    Additionally or alternatively, this or other embodiments include the car side suspension member load sensor positioned at a car side termination of the suspension member and the counterweight side suspension member load sensor positioned at a counterweight side termination of the suspension member. 
         [0014]    Additionally or alternatively, this or other embodiments include a bed plate for supporting the machine, the bed plate rotatable about an axis; the car side suspension member load sensor being coupled to the bed plate and the counterweight side suspension member load sensor being coupled to the bed plate. 
         [0015]    Additionally or alternatively, this or other embodiments include the controller adjusting the car side suspension member tension, T 1 , and the counterweight side suspension member tension, T 2 , prior to determining the traction ratio. 
         [0016]    Additionally or alternatively, this or other embodiments include the controller adjusting the car side suspension member tension, T 1 , and the counterweight side suspension member tension, T 2 , by subtracting a portion of machine weight from at least one of the car side suspension member tension, T 1 , and the counterweight side suspension member tension, T 2 , prior to determining the traction ratio. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  depicts an elevator system in an exemplary embodiment; 
           [0018]      FIG. 2  depicts a process of detecting a stuck car or stuck counterweight in an exemplary embodiment; and 
           [0019]      FIG. 3  depicts a machine in an exemplary embodiment. 
       
    
    
       [0020]    The detailed description explains the invention, together with advantages and features, by way of examples with reference to the drawings. 
       DETAILED DESCRIPTION 
       [0021]    Shown in  FIG. 1  is an exemplary traction elevator systems  10 . Features of the elevator system  10  that are not required for an understanding of the present invention (such as the guide rails, safeties, etc.) are not discussed herein. The elevator system  10  includes an elevator car  12  operatively suspended or supported in a hoistway  14  with one or more suspension members  16 . Suspension member  16  may comprise a belt (e.g., a coated steel belt), rope or other member. Further, multiple suspension members  16  may be arranged in parallel. 
         [0022]    Suspension member  16  interacts with one or more deflector sheaves  18  to be routed around various components of the elevator system  10 . Suspension member  16  is coupled to a counterweight  22 , which is used to help balance the elevator system  10  and reduce the difference in suspension member tension on both sides of the traction sheave  24  during operation. Embodiments of the invention may be used on elevator systems having suspension member configurations other than the exemplary type shown in  FIG. 1 . 
         [0023]    A machine  26  drives the traction sheave  24 . Movement of the traction sheave  24  by the machine  26  imparts motion (through traction) to suspension member  16  routed around the traction sheave  24 . Machine  26  responds to drive signals from a controller  28 . Controller  28  may be implemented using a general-purpose microprocessor executing a computer program stored on a storage medium to perform the operations described herein. Alternatively, controller  28  may be implemented in hardware (e.g., ASIC, FPGA) or in a combination of hardware/software. Controller  28  may also be part of an elevator control system. 
         [0024]    A first end of suspension member  16  is terminated at a car side termination  30 . A car side suspension member load sensor  32  monitors tension on suspension member  16  at the car side termination  30 . Suspension member  16  may be terminated to the car side suspension member load sensor  32 , which is connected to the car side termination  30 . Alternatively, suspension member  16  may be terminated to car side termination  30 , and the car side suspension member load sensor  32  coupled to suspension member  16  (e.g., a strain sensor positioned on the suspension member). 
         [0025]    A second end of suspension member  16  is terminated at a counterweight side termination  34 . A counterweight side suspension member load sensor  36  monitors tension on suspension member  16  at the counterweight side termination  34 . Suspension member  16  may be terminated to the counterweight side suspension member load sensor  36 , which is connected to the counterweight side termination  34 . Alternatively, suspension member  16  may be terminated to counterweight side termination  34 , and the counterweight side suspension member load sensor  36  coupled to suspension member  16  (e.g., a strain sensor positioned on the suspension member). 
         [0026]    Car side suspension member load sensor  32  generates a car side suspension member tension signal that is provided to controller  28 . The car side suspension member tension signal may be a non-discrete voltage (e.g., analog signal), a discrete signal produced by multiple sensors or a digital signal. The resolution of the car side suspension member tension signal is sufficient to accurately determine a traction ratio without failing to detect a stuck car/counterweight or generate a false positive. Counterweight side suspension member load sensor  36  generates a counterweight side suspension member tension signal that is provided to controller  28 . The counterweight side suspension member tension signal may be a non-discrete voltage (e.g., analog signal), a discrete signal produced by multiple sensors or a digital signal. The resolution of the counterweight side suspension member tension signal is sufficient to accurately determine a traction ratio without failing to detect a stuck car/counterweight or generate a false positive. Controller  28  executes a process to detect whether car  12  or counterweight  22  is stuck. If either the car  12  or counterweight  22  is stuck, then operation of the elevator system  10  is stopped and a rescue operation may be initiated. 
         [0027]      FIG. 2  is a flowchart of a process for determining if car  12  or counterweight  22  is stuck. At  100 , elevator system  10  is placed into operation. At  102 , car side suspension member load sensor  32  generates the car side suspension member tension signal, T 1 , indicative of tension on the suspension member  16  at the car side termination  30 . If multiple suspension members  16  are used, T 1  represents a sum of the tension on the suspension members  16  terminated at the car side termination  30 . At  104 , counterweight side suspension member load sensor  36  generates the counterweight side suspension member tension signal, T 2 , indicative of tension on the suspension member  16  at the counterweight side termination  34 . If multiple suspension members  16  are used, T 2  represents a sum of the tension on the suspension members  16  terminated at the counterweight side termination  30 . 
         [0028]    At  106 , controller  28  determines a first traction ratio by deriving T 1 /T 2 . At  108 , controller  28  determines a second traction ratio by deriving T 2 /T 1 . At  110 , controller  28  determines if either the first traction ratio or the second traction ratio violates a limit. The limit may represent an upper limit or lower limit. For example, if car  12  is traveling upwards and the counterweight  22  becomes stuck, then T 2  will decrease, causing T 1 /T 2  to increase and T 2 /T 1  to decrease. If T 1 /T 2  exceeds an upper limit or T 2 /T 1  goes below a lower limit, controller  28  determines that counterweight  22  is stuck. When the counterweight  22  is traveling up and car  12  becomes stuck, T 1  will decrease, causing T 1 /T 2  to decrease and T 2 /T 1  to increase. If T 1 /T 2  goes below a lower limit or T 2 /T 1  exceeds an upper limit, controller  28  determines that car  12  is stuck. The upper limits and lower limits may be established based on the weight of suspension member(s)  16 , the number of floors in the building, etc. 
         [0029]    If at  110 , the first traction ratio T 1 /T 2  or the second traction ratio T 2 /T 1  exceeds an upper limit or goes below a lower limit, then flow proceeds to  112  where controller  28  stops the car. At  110 , the violation of the limit may need to be present for a predetermined amount of time, in order to filter out spurious increases or decreases in suspension member tension that are not indicative of a stuck car or stuck counterweight. Block  112  may also include a initiating a rescue operation where machine  26  attempts to move the stuck car  12  or counterweight  22  by reversing direction. If at  110  no limits are violated, flow returns to  102  where the process continues. 
         [0030]      FIG. 3  depicts the car side suspension member load sensor  32  and counterweight side suspension member load sensor  36  positioned under a bed plate  50  that supports machine  26  and traction sheave  24  As described above with reference to  FIGS. 1 and 2 , the car side suspension member load sensor  32  generates a car side suspension member tension signal, T 1 , that is provided to controller  28 . Counterweight side suspension member load sensor  36  generates a counterweight side suspension member tension signal, T 2 , that is provided to controller  28 . If one side of suspension member  16  traversing traction sheave  24  loses tension, then the bedplate  50  will rotate about an axis away from that side due to the tension imbalance across traction sheave  24 . Controller  28  executes the process of  FIG. 2  to detect whether car  12  or counterweight  22  is stuck. The tension signals T 1  and T 2  may be compensated to account for the weight of machine  26 . For example, the car side suspension member load sensor  32  may generate a signal corresponding to the car side suspension member tension signal, T 1 , plus a portion of the weight of the machine  26  (e.g., ½ the machine weight). Similarly, the counterweight side suspension member load sensor  36  may generate a signal corresponding to the counterweight side suspension member tension signal, T 2 , plus a portion of the weight of the machine  26 . Controller  28  can adjust the car side suspension member tension signal, T 1 , and the counterweight side suspension member tension signal, T 2 , by subtracting the portion of the machine weight from each signal prior to computing the traction ratio. 
         [0031]    Embodiments described above depict the car side suspension member tension signal and the counterweight side suspension member tension signal being provided to a controller  28  for processing. In exemplary embodiments, controller  28  is part of a standalone safety system, and not a component of the elevator system  10  for processing elevator calls and driving machine  26 . In such embodiments, controller  28  would initiate stopping the car (e.g., breaking a safety chain to apply a brake). 
         [0032]    Embodiments of the invention eliminate the upper limit on suspension member traction in order to pass the loss of traction test. Embodiments allow for the use of light weight cars, which reduces cost and sizing demands on machine  26 . 
         [0033]    While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.