Abstract:
A rope sway mitigation device for an elevator system includes a rope tension adjuster connected to a plurality of ropes operably connected to an elevator car. The rope tension adjuster is configured to adjust a tension of at least one individual rope of the plurality of ropes thereby mitigating excitation of natural frequencies of the plurality of ropes during sway of at least one component of the elevator system and or a building in which the elevator system is located. Further disclosed is an elevator system including a rope sway mitigation device and a method of rope sway mitigation in an elevator system.

Description:
This is a U.S. national stage application of International Application No. PCT/US2009/052054, filed on 29 Jul. 2009, the disclosure of which is also incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     The subject matter disclosed herein relates to elevator systems. More specifically, the subject matter relates to sway mitigation of ropes of elevator systems. 
     During periods of, for example, high velocity winds, buildings tend to sway laterally. As a building sways, lateral motion of the building typically translates into lateral motion of ropes and cables of elevator systems installed in the building. The lateral motion of the ropes and cables can result in noise, wear, and/or damage to elevator system equipment and/or the building. 
     Typically, one of several approaches are utilized to mitigate rope sway issues. The first uses mechanical means to restrain the ropes to limit rope sway. Such devices include cab followers and swing arms as described, for example, in U.S. Pat. No. 5,947,232. Such mechanical devices are potentially effective to limit rope sway, but are costly and take up space in the hoistway. 
     A second approach typically involves limiting elevator car operations during periods of building sway. This involves a sensor added to the elevator system which detects building sway. When sway exceeds a preset limit, a set of alternate control instructions are placed on the elevator system to, for example, reduce operating speed of the elevator and/or to restrict parking access of the elevator car at floors where rope sway is likely to occur. 
     BRIEF DESCRIPTION OF THE INVENTION 
     According to one aspect of the invention, an elevator system includes an elevator car connected to a plurality of ropes and a sway detection sensor configured to detect sway of at least one component of the elevator system and/or a building in which the elevator system is located. A rope tension adjuster is connected to the sway detection sensor and is configured to adjust a tension of at least one individual rope of the plurality of ropes to mitigate excitation of natural frequencies of the plurality of ropes when the sway detection sensor detects sway of the building. 
     According to another aspect of the invention, a rope sway mitigation device for an elevator system includes a rope tension adjuster connected to a plurality of ropes operably connected to an elevator car. The rope tension adjuster is configured to adjust a tension of at least one individual rope of the plurality of ropes thereby mitigating excitation of natural frequencies of the plurality of ropes during a sway of at least one component of the elevator system and/or a building in which the elevator system is located. 
     According to yet another aspect of the invention, a method of rope sway mitigation in an elevator system includes detecting sway of at least one component of the elevator system and/or a building in which the elevator system is located. A tension of a plurality of ropes connected to the elevator car is adjusted in response to detection of the sway to mitigate excitation of natural frequencies of the plurality of ropes thereby preventing sway of the plurality of ropes. 
     These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is an illustration of an embodiment of an elevator system; and 
         FIG. 2  is an illustration of an embodiment of a rope tension adjuster. 
     
    
    
     The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Shown in  FIG. 1  is an illustration of an elevator system  10  disposed in a building  12 . An elevator car  14  is positioned in a hoistway  16  by a plurality of ropes including a plurality of suspension ropes  18  extending substantially upward from the elevator car  14  and, in some embodiments, by a plurality of compensation ropes  20  extending substantially downward from the elevator car  14  connected to a counterweight  22 . The hoistway  16  includes a plurality of landing locations  24  for the elevator car  14 . In some embodiments, the elevator system  10  includes a sway detection sensor  26  which may be, for example, a pendulum switch, accelerometer, anemometer, or the like configured to detect, directly (from, for example, building motion) and/or indirectly (from, for example, wind speed), sway of the building  12  and/or sway of the plurality of suspension ropes  18  and/or the plurality of compensation ropes  20 . Sway of the plurality of suspension ropes  18  and/or the plurality of compensation ropes  20  depends on the proximity of the building  12  sway frequency to a natural frequency of the pluralities of ropes  18 ,  20 . The building  12  sway frequency is fairly constant and can be estimated for a particular building  12  based on its structural design. The building  12  sway frequency typically is in the range of 0.1-0.2 Hz. One or more modes of rope  18 ,  20  frequency, when the rope  16  frequency modes are integer multiples of the building  12  sway frequency, can be excited by the building  12  sway frequency. Given a layout of an elevator system  10  in a building  12 , it is possible to determine at which landing locations  24  the pluralities of ropes  18 ,  20  will have frequency modes which will be excited by the building  12  sway frequency. 
     When the sway detection sensor  26  detects building  12  sway which may excite one or more modes in the plurality of suspension ropes  18  and/or the plurality of compensation ropes  20 , a signal is sent from the sway detection sensor  26  to a control system  28  which determines a course of action. One course of action is to change tensions in individual ropes of the plurality of suspension ropes  18  and/or the plurality of compensation ropes  20  to place at least one individual rope above building  12  sway frequency and at least one individual rope below building  12  sway frequency. The total tension of the plurality of ropes is T. In normal conditions, the tension on each individual rope is approximately equal. For example, is an elevator system  10  utilizing five suspension ropes  18 , individual suspension rope tensions, T i , are approximately T/5 in normal operation. When tension T i  produces vibratory frequencies close to the building  12  sway frequency, tensions in individual suspension ropes  18   a  through  18   e  are adjusted, for example, as shown in equations 1-5.
 
 T   a =( T/ 5)−Δ T   1   (1)
 
 T   b =( T/ 5)+Δ T   2   (2)
 
 T   c =( T/ 5)−Δ T   1   (3)
 
 T   d =( T/ 5)+Δ T   2   (4)
 
 T   e =( T/ 5)−Δ T   1   (5)
 
     In this example, ΔT 1  equals ⅔ times ΔT 2  so that the resultant total tension, T, remains constant. While this example illustrates an elevator system  10  including five suspension ropes  18 , it is to be appreciated that elevator systems  10  utilizing other quantities of suspension ropes  18  and/or compensation ropes  20 , for example between 2 and 12 or more suspension ropes  18  or compensation ropes  20 , and/or tension adjustment values are contemplated within the present scope. 
     In operation, when the sway detection sensor  26  detects a building  12  sway event, a signal is sent from the sway detection sensor  26  to the control system  28 . The control system  28  determines if the elevator car  14  is parked at a landing location  24  where the suspension rope  18  sway frequency or compensation rope  20  sway frequency will be excited by the building  12  sway, and if so communicates with a rope tension adjuster  30  to adjust the tension of the suspension ropes  18  and/or compensation ropes  20  accordingly. When the building  12  sway event has passed, the tensions of the suspension ropes  18  are returned to equal. In some embodiments, the sway detection sensor  26  may be configured to detect sway of individual suspension ropes  18  or groups of suspension ropes  18 . When a sway of the suspension ropes  18  is detected, the tension adjuster  30  adjusts the tension of the swaying suspension ropes  18  until the sway is reduced by a desired amount. 
     Each suspension rope  18  of the plurality of suspension ropes  18  is connected to a rope tension adjuster  30  disposed at the elevator car  14  Likewise, in some embodiments, each compensation rope  20  of the plurality of compensation ropes is connected to a rope tension adjuster  30  disposed at, for example, a bottom  36  of the elevator car  14 . Embodiments of the rope tension adjuster  30  connected to the plurality of suspension ropes  18  will now be described by way of example, but it is to be appreciated that the same embodiments may be utilized in connection with the plurality of compensation ropes  20 . As shown in  FIG. 1 , the plurality of suspension ropes  18  is connected to the rope tension adjuster  30  disposed at a top  32  of the elevator car  14 , but in some embodiments the rope tension adjuster  30  may be disposed at other locations, for example a side  34  or a bottom  36  of the elevator car  14  or in the hoistway  18 . Referring now to  FIG. 2 , a more detailed view of a rope tension adjuster  30  is illustrated. Each suspension rope  18  of the plurality of suspension ropes  18  are connected a termination  38  which passes through a hitch plate  40  and is connected to a plurality of hydraulic cylinders  42 . The hydraulic cylinders  42  are connected to a pump  44  which is, in turn, connected to the control system  28 . When activated, the pump  44  pumps additional fluid, for example, from a first group  46  of the hydraulic cylinders  42  into a second group  48  of the hydraulic cylinders  42 . Increasing the fluid in the second group  48  of hydraulic cylinders  42  increases the tension of the suspension ropes  18  connected to the second group  48  of hydraulic cylinders  42  while decreasing the tension of the suspension ropes  18  connected to the first group  48  of hydraulic cylinders  42 . The first group  46  and the second group  48  of hydraulic cylinders  42  may be separated by a one-way check valve  50  which is configured to allow fluid to be pumped from the first group  46  to the second group  48  but prevents fluid from flowing backward from second group  48  to the first group  46 . In some embodiments, sway of the suspension ropes  18  may be detected via, for example, a pressure sensor (not shown) disposed at each hydraulic cylinder  42 . A pressure variation at a particular hydraulic cylinder  42  would indicate sway of the corresponding suspension rope  30  and adjustment of the tension of the suspension rope  18  would be initiated. 
     Some embodiments of rope tension adjusters  30  include a solenoid valve  52  connected to the control system  28 . The solenoid valve  52  is disposed between the first group  46  and second group  48  at, for example, a return conduit  54 . Opening the solenoid valve  52  allows excess fluid to pass from the second group  48  to the first group  46  to equalize the pressure among the hydraulic cylinders  42  thus equalizing the tension on the plurality of suspension ropes  18 . In some embodiments, the solenoid valve  52  is normally open during non-sway conditions. During a sway event, the solenoid valve is energized and closed. The pump  44  is switched on to pump fluid into the hydraulic cylinders  48  thereby increasing tension of the ropes  18  connected to the hydraulic cylinders  48 . When the sway event is over, the solenoid valve  52  is reopened allowing the pressure to reequalize. 
     Some embodiments of the rope tension adjuster  30  may include a pressure sensor  56  connected to the hydraulic cylinders  42 . The pressure sensor may be utilized to weigh a load on the elevator car  14  ( FIG. 1 ) which may be utilized by the control system  28  to determine elevator car  14  operational settings. Further, some embodiments may include an accumulator  58  connected to the hydraulic cylinders  42 . The accumulator  58  may be utilized to distribute fluid during normal operation to aid in damping vibration of the elevator car  14 . 
     The embodiments of rope tension adjusters  30  described above are merely exemplary. While the embodiments utilize hydraulic cylinders  42  to adjust the tension of the plurality of suspension ropes  18  and/or the plurality of compensation ropes  20 , other means, for example, mechanical linkage could be used to move the hitch plate  40  over a group of suspension ropes  18  and/or compensation ropes  20  thus effectively changing the tension on the suspension ropes  18  and/or compensation ropes  20 . 
     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.