Abstract:
A method of wear detection of a coated belt or rope includes measuring an initial electrical resistance of one or more cords, strands or wires of the coated belt or rope. The initial electrical resistance is calibrated by repeating the measuring of initial electrical resistance and populating a database with the measured initial electrical resistance values. A true initial resistance is determined from the population of initial electrical resistances and subsequent measured values of electrical resistance of the one or more cords, strands or wires of the coated belt or rope.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The subject matter disclosed herein relates to coated belts or ropes used, for example, in elevator systems. More specifically, the subject disclosure relates to wear detection (e.g. detection of corrosion, fretting, etc.) of coated belts or ropes used for elevator suspension and/or driving. 
         [0002]    Elevator systems utilize ropes or belts operably connected to an elevator car, and routed over one or more sheaves, also known as pulleys, to propel the elevator car along a hoistway. Coated steel belts in particular include a plurality of wires located at least partially within a jacket material. The plurality of wires is often arranged into one or more strands and the strands are then arranged into one or more cords. In an exemplary belt construction, a plurality of cords is typically arranged equally spaced within a jacket in a longitudinal direction. 
         [0003]    During normal elevator operation, coated steel belts are subjected to a large number of bending cycles as the belt travels over drive sheaves and deflector sheaves of the elevator system. These bending cycles cause a degradation of the breaking strength of the wires or cords within the coated steel belt via the mechanism of wire fretting or fatigue. Such fatigue is a major contributor to reduction in service life of the coated steel belt. While the service life of the coated steel belt can be estimated through calculation, a more accurate estimation of remaining life of the coated steel belt is often obtained by utilizing a life-monitoring system. 
         [0004]    One such system is called resistance-based inspection (RBI). An RBI system is secured to the coated belt or rope at a fixed point of the elevator system and monitors a change in electrical resistance of one or more of the cords in the belt or rope. Since the electrical resistance of each cord is proportional to its cross-sectional area, changes is electrical resistance can be correlated to reduction in cross-sectional area of the cord, indicating an amount of fretting of the cord, and a corresponding remaining service life. The changes in electrical resistance are determined relative to a baseline resistance, typically taken at installation of the system. This initial reading compensates for cord temperature by measuring temperature at the monitoring unit, and then assumes the relationship between cord and monitoring unit temperature to be fixed over the life of the cord. Cord temperature has a significant effect on cord resistance, and therefore inaccuracy in cord temperature could lead to false alarms or false indications of adequate remaining cord life. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0005]    According to one aspect of the invention, a method of wear detection of a coated belt or rope includes measuring an initial electrical resistance of one or more cords, strands or wires of the coated belt or rope. The initial electrical resistance is calibrated by repeating the measuring of initial electrical resistance and populating a database with the measured initial electrical resistance values. A true initial resistance is determined from the population of initial electrical resistances and subsequent measured values of electrical resistance of the one or more cords, strands or wires of the coated belt or rope. 
         [0006]    Alternatively in this or other aspects of the invention, the true initial resistance is determined by computing an average of the population of initial electrical resistances. 
         [0007]    Alternatively in this or other aspects of the invention, the initial resistance measurement is repeated hourly. 
         [0008]    Alternatively in this or other aspects of the invention, the initial resistance measurement is repeated over a period of about six months. 
         [0009]    Alternatively in this or other aspects of the invention, the method further includes measuring an initial belt temperature at the time of measuring the initial electrical resistance one or more cords, strands or wires of the coated belt or rope and repeating the initial temperature measurement along with repeating the measuring of initial resistance. The database is populated with the measured initial temperatures correlated to the measured initial resistance values. 
         [0010]    Alternatively in this or other aspects of the invention, electrical resistance of the one or more cords, strands or wires of the coated belt or rope and temperature are subsequently measured. The threshold is determined by using the measured temperature to determine the true initial electrical resistance at that measured temperature by querying the database and calculating the threshold as a percentage change from the true initial electrical resistance. 
         [0011]    Alternatively in this or other aspects of the invention, action is taken if the threshold is exceeded. 
         [0012]    According to another aspect of the invention, a monitoring system for a coated belt or rope having one or more cords, strands and/or wires includes a wear detection unit for engaging the one or more cords, strands or wire of the coated belt or rope and capable of measuring electrical resistance thereof and a temperature sensor capable of measuring temperature. A database is utilized to store electrical resistance and corresponding temperature measurements. The wear detection unit repeatedly measures an initial electrical resistance, and the temperature sensor repeatedly measures an initial temperature, the initial electrical resistance measurements and initial temperatures are utilized to determine a true initial electrical resistance. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1A  is a schematic of an exemplary elevator system having a 1:1 roping arrangement; 
           [0014]      FIG. 1B  is a schematic of another exemplary elevator system having a different roping arrangement; 
           [0015]      FIG. 1C  is a schematic of another exemplary elevator system having a cantilevered arrangement; 
           [0016]      FIG. 2  is a cross-sectional view of an elevator belt; 
           [0017]      FIG. 3  is a schematic of an elevator belt wear detection unit; 
           [0018]      FIG. 3A  is a schematic of a wear detection unit in conjunction with a coated rope; 
           [0019]      FIG. 4  is an illustration of a method for calibrating a wear detection unit; and 
           [0020]      FIG. 5  is an illustration of another method for calibrating a wear detection unit. 
       
    
    
       [0021]    The detailed description explains the invention, together with advantages and features, by way of examples with reference to the drawings. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    Shown in  FIGS. 1A ,  1 B and  1 C are schematics of exemplary traction elevator systems  10  that could utilize the present invention. 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 belts  16 . The one or more belts  16  interact with one or more sheaves  18  to be routed around various components of the elevator system  10 . The one or more belts  16  could also be connected to a counterweight  22 , which is used to help balance the elevator system  10  and create traction. 
         [0023]    The sheaves  18  each have a diameter  20 , which may be the same or different than the diameters of the other sheaves  18  in the elevator system  10 . At least one of the sheaves  18  could be a drive sheave. A drive sheave is driven by a machine  50 . Movement of the drive sheave by the machine  50  drives, moves and/or propels (through traction) the one or more belts  16  that are routed around the drive sheave. 
         [0024]    At least one of the sheaves  18  could be a diverter, deflector or idler sheave. Diverter, deflector or idler sheaves are not driven by a machine  50 , but help guide the one or more belts  16  around the various components of the elevator system  10 . Further, one or more of the sheaves  18 , such as the diverter, deflector or idler sheaves, may have a convex shape or crown along its axis of rotation to assist in keeping the one or more belts  16  centered, or in a desired position, along the sheaves  18 . 
         [0025]    In some embodiments, the elevator system  10  could use two or more belts  16  for suspending and/or driving the elevator car  12 . In addition, the elevator system  10  could have various configurations such that either both sides of the one or more belts  16  engage the one or more sheaves  18  (such as shown in the exemplary elevator systems in  FIG. 1A ,  1 B or  1 C) or only one side of the one or more belts  16  engages the one or more sheaves  18 . 
         [0026]      FIG. 1A  provides a 1:1 roping arrangement in which the one or more belts  16  terminate at the car  12  and counterweight  22 .  FIGS. 1B and 1C  provide different roping arrangements. Specifically,  FIGS. 1B and 1C  show that the car  12  and/or the counterweight  22  can have one or more sheaves  18  thereon engaging the one or more belts  16  and the one or more belts  16  can terminate elsewhere, typically at a structure within the hoistway  14  (such as for a machineroomless elevator system) or within the machine room (for elevator systems utilizing a machine room). The number of sheaves  18  used in the arrangement determines the specific roping ratio (e.g., the 2:1 roping ratio shown in  FIGS. 1B and 1C  or a different ratio).  FIG. 1C  also provides a cantilevered type elevator. The present invention could be used on elevator systems other than the exemplary types shown in  FIGS. 1A ,  1 B and  1 C. 
         [0027]      FIG. 2  provides a schematic of an exemplary belt construction or design that could utilize the present invention. The present invention is also capable of use with coated rope. Each belt  16  can be constructed of one or more cords  24  in a jacket  26 . As seen in  FIG. 2 , the belt  16  can have an aspect ratio greater than one (i.e. belt width is greater than belt thickness). The belts  16  can be constructed to have sufficient flexibility when passing over the one or more sheaves  18  to provide low bending stresses, meet belt life requirements and have smooth operation, while being sufficiently strong to be capable of meeting strength requirements for suspending and/or driving the elevator car  12 . The jacket  26  could be any suitable material, including a single material, multiple materials, two or more layers using the same or dissimilar materials, and/or a film. In one arrangement, the jacket  26  could be a polymer, such as an elastomer, applied to the cords  24  using, for example, an extrusion or a mold wheel process. In another arrangement, the jacket  26  could be a woven fabric that engages and/or integrates the cords  24 . As an additional arrangement, the jacket  26  could be one or more of the previously mentioned alternatives in combination. 
         [0028]    The jacket  26  can substantially retain the cords  24  therein. The phrase substantially retain means that the jacket  26  has sufficient engagement with the cords  24  to transfer torque from the machine  50  through the jacket  26  to the cords  24  to drive movement of the elevator car  12 . The jacket  26  could completely envelop the cords  24  (such as shown in  FIG. 2 ), substantially envelop the cords  24 , or at least partially envelop the cords  24 . 
         [0029]    Referring to  FIG. 3 , a wear detection unit  52  is electrically connected to one or more cords  24  of the belt  16 . Although described below with respect to cords, the unit  52  could alternatively be electrically connected to one or more strands of the belt or rope, or to one or more wires of the belt or rope. The wear detection unit  52  is connected to belt  16  at a suitable location, for example, at an end of the belt  16  located at an upper end of the hoistway  14  (e.g. the 2:1 roping arrangements shown in  FIGS. 1B and 1C ). It is to be appreciated, though, that this location is merely exemplary and other locations for connecting the wear detection unit  52  to the belt  16  are contemplated within the present scope. For example, in the  1 : 1  roping arrangement shown in  FIG. 1A , the unit  52  would need to engage the end(s) of the belt  16 . During operation, an electrical current is applied through the cords  24 . A resulting voltage allows for determination of an electrical resistance of the cord  24 . This measured resistance is compared to an initial resistance of the cord measure during initial installation of the belts  16 . A change in the electrical resistance of the cord  24 , typically an increase in resistance, indicates wear of the cord  24 . The change in resistance is compared to one or more thresholds, and when the threshold is exceeded, action may be taken by the elevator system  10 , including but not limited to, notifying the maintenance provider, sounding of an alarm and/or stopping operation of the elevator system  10 . To return the signal transmitted through the cords  24  to the wear detection unit  52 , another wear detection unit  52 , or other device such as a shunt connector is provided to transmit the return signal. Referring to  FIG. 3A , the wear detection unit  52  may be utilized with a coated rope  78  including a plurality of cords  24  coated with a jacket  26  in a manner similar to that described herein regarding the belt  16 . 
         [0030]    In the wear detection unit  52 , the threshold is determined or set, based on an initial measured resistance of the belt  16 , and may be a percent change of the measured resistance from the initial measured resistance. The wear detection unit  52  further includes a temperature sensor  54  to measure a temperature at the wear detection unit  52  to which the initial measured resistance correlates. To more accurately determine the threshold, and thereby more accurately determine a level of wear in the cord  24 , the determination of the initial measured resistance is made based upon repeated resistance measurements made periodically over an initial time period after installation. The sampling of the resistance measurements should be frequent enough to capture the normal temperature variations that occur during the course of a day, for example once per hour. The length of the initial time period used for determining the initial resistance should be long enough to capture typical variations that occur, for example six months. However, the length of the initial time period needs to be chosen so that degradation of the cord  24  is not experienced during the process. Stated differently, the time period is chosen so that the coated belt or rope still exhibits characteristics of a new coated belt or rope. An exemplary method is shown in  FIG. 4 . 
         [0031]    The process begins at step  56  with installation of the coated belt or rope in elevator system  10  in the hoistway  14 . The installation could be the initial coated belt or rope used in the elevator system  10  or a replacement belt or rope installed at a later time in the life of the elevator system  10 . At step  58 , the initial cord resistance is measured and an initial temperature is also measured by the temperature sensor  54 . The initial cord resistance and initial temperature are stored in the wear detection unit  52  or other suitable location, such as in memory located off-site at the maintenance provider of the elevator system  10  at step  60 . The measurement of temperature and resistance are repeated periodically as part of a calibration routine as shown at step  62 . This results in a set of calibration resistances and calibration temperatures which, along with the initial cord resistance and initial temperature, populate a database of temperatures and corresponding resistances at step  64 . Because the calibration routine is performed early in the service life of the belt  16 , no deterioration of the belt  16  has yet occurred, so the database is, in effect, a collection of initial cord resistance values at various temperatures. 
         [0032]    In some embodiments, the resistance values in the database are averaged at step  66  to determine a calibrated initial resistance used in calculation of a threshold at step  68 . As an example, the threshold could be 80% of calibrated initial resistance. In other embodiments, as shown in  FIG. 5 , the threshold is determined each time an inspection is performed at step  70 . After the calibration routine is completed, an inspection temperature and an inspection resistance are measured at step  70 . At step  72 , the database is queried, and a calibration resistance for that particular temperature is determined at step  74 . The calibration resistance is used in calculation of the threshold at step  76 , to which the inspection resistance is compared. 
         [0033]    Performing the calibration routine and utilizing temperature measurements in determination of the threshold provides a more accurate initial resistance value for determining the threshold thereby providing a more accurate determination of belt  16  condition. Further, the calibration routine allows for a better understanding of the effects of cord temperature on measured belt resistance. 
         [0034]    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.