Abstract:
A method of fault detection of a belt or rope includes interconnecting a plurality of cords of the belt or rope, the cords including a plurality of wires, to form a bridge circuit. A fault detection bridge circuit is subjected to a voltage excitation and outputs a voltage which is indicative of the belt or rope damage but remaining insensitive to other environmental noises.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The subject matter disclosed herein relates to belts or ropes used, for example, in elevator systems. More specifically, the subject disclosure relates to fault detection (e.g. of corrosion, fatigue, wear, etc.) of 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 pulleys, also known as sheaves, 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 and ropes are subject to various failures due to fatigue, wear and corrosion over the time of their service which could progressively lead to a catastrophic consequence. It is desirable to have an online health monitoring system for early warning of structural compromise at low cost. The prevalent technology for real time health monitoring of ferromagnetic rope is magnetic flux leakage (MFL) based inspection which could provide adequate detection of minor rope damage but the system is complex, bulky and costly to elevator industry. Resistance based inspection (RBI) is a low cost and popular method for steel cord reinforced belt inspection. However, it lacks of sensitivity for early warning and ability to detect all the common failure modes of the ropes and belts. Dynamic measurement of extremely low resistance multi-strand cords subject to electromagnetic interference or “noise” and/or thermal or mechanical variations presents major challenges relative to interference resistance and signal to noise ratio of the system. A method of continuous monitoring elevator for early warning of wire rope or steel belt damage with low cost is highly desirable. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0004]    According to one aspect of the invention, a method of fault detection of a belt or rope includes interconnecting a plurality of cords of the belt or rope, the cords including a plurality of wires, to form a bridge circuit. The bridge circuit is subjected to an excitation voltage and outputs a signal voltage, the bridge circuit structure suppressing environmental noise to increase signal to noise ratio of the signal voltage. The signal voltage is monitored to detect a fault condition of the rope. 
         [0005]    According to this or other aspects of the invention, the method includes comparing a profile of the measured electrical impedance to a baseline electrical impedance profile and determining a fault condition of the belt or rope via the comparison. 
         [0006]    According to this or other aspects of the invention, each leg of the bridge circuit includes at least one cord of the belt or rope. 
         [0007]    According to this or other aspects of the invention, each leg of the bridge circuit includes two or more cords of the belt or rope. 
         [0008]    According to this or other aspects of the invention, fault conditions include wire breakage, fretting and/or birdcaging. 
         [0009]    According to this or other aspects of the invention, the method further includes switching the interconnection of the plurality of cords via a switching mechanism operably connected to the plurality of cords. 
         [0010]    According to this or other aspects of the invention, the belt or rope is a coated belt or rope. 
         [0011]    According to this or other aspects of the invention, at least one leg of the bridge circuit is a fixed resistor. 
         [0012]    According to this or other aspects of the invention, two legs of the bridge circuit each comprise at least one cord and two legs of the bridge circuit each comprise a fixed resistor. 
         [0013]    According to another aspect of the invention, an elevator system includes an elevator car and one or more sheaves. A belt or rope having a plurality of wires arranged into a plurality of cords for supporting and/or driving the elevator car is routed across the one or more sheaves and is operably connected to the elevator car. The plurality of cords are interconnected to form a bridge circuit. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a schematic of an exemplary elevator system; 
           [0015]      FIG. 2  is a schematic of another exemplary elevator system; 
           [0016]      FIG. 3  is a cross-sectional view of an embodiment of an elevator belt; 
           [0017]      FIG. 4  is a cross-sectional view of an embodiment of a cord or rope; 
           [0018]      FIG. 5  is a schematic of an embodiment of an elevator belt fault detection unit; and 
           [0019]      FIG. 6  is schematic circuit diagram for elevator belt fault detection; 
           [0020]      FIG. 7  is a schematic of another embodiment of an elevator belt fault detection unit; 
           [0021]      FIG. 8  is another schematic circuit diagram for elevator fault detection; 
           [0022]      FIG. 9  is yet another embodiment of an elevator belt fault detection unit. 
           [0023]      FIG. 10  is still another embodiment of an elevator belt fault detection unit; 
           [0024]      FIG. 11  is a schematic circuit diagram of the embodiment of  FIG. 10 ; 
           [0025]      FIG. 12  is another embodiment of an elevator belt fault detection unit; 
           [0026]      FIG. 13  is a schematic circuit diagram of the embodiment of  FIG. 12 ; 
           [0027]      FIG. 14  is still another embodiment of an elevator belt fault detection unit; and 
           [0028]      FIG. 15  is a schematic circuit diagram of the embodiment of  FIG. 14 ; 
       
    
    
       [0029]    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 
       [0030]    Shown in  FIGS. 1 and 2  are schematics of 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 belts  16  or ropes. 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 reduce the difference in belt tension on both sides of the traction sheave during operation. It is to be appreciated that while the embodiments herein are described as applied to coated steel belts, it is to be appreciated that the disclosure herein may similarly be applied to steel ropes, either coated or uncoated. 
         [0031]    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 (not shown). Movement of the drive sheave by the machine drives, moves and/or propels (through traction) the one or more belts  16  that are routed around the drive sheave. 
         [0032]    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, 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 . 
         [0033]    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. 1  or  2 ) or only one side of the one or more belts  16  engages the one or more sheaves  18 . 
         [0034]      FIG. 1  illustrates an elevator system  10  in which the elevator car  12  includes a sheave  18  around which the belt  16  is routed to support the elevator car  12 . Similarly, the counterweight  22  includes a sheave  18  around which the belt  16  is routed to support the counterweight  22 . Each end  24   a  and  24   b  of the belt  16  is terminated at a fixed location such as a support  26  or other fixed location of the elevator system  10 .  FIG. 2  illustrates an embodiment of an elevator system  10  in which, as in  FIG. 1 , the elevator car  12  includes a sheave  18  around which the belt  16  is routed to support the elevator car  12 . In this embodiment, however, a first end  24   a  of the belt  16  is terminated at the support  26 , while a second end  24   b  of the belt  16  is terminated at the counterweight  22  and is movable with the counterweight  22 . 
         [0035]      FIG. 3  provides a schematic of a belt construction or design. Each belt  16  is constructed of a plurality of wires  28  (e.g. twisted into one or more strands  30  and/or cords  32  as shown in  FIG. 4 ) in a jacket  34 . As seen in  FIG. 3 , the belt  16  has an aspect ratio greater than one (i.e. belt width is greater than belt thickness). The belts  16  are 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  34  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  32  using, for example, an extrusion or a mold wheel process. In another arrangement, the jacket  34  could be a woven fabric that engages and/or integrates the cords  32 . As an additional arrangement, the jacket  34  could be one or more of the previously mentioned alternatives in combination. 
         [0036]    The jacket  34  can substantially retain the cords  32  therein. The phrase substantially retain means that the jacket  34  has sufficient engagement with the cords  32  to transfer torque from the machine  50  through the jacket  34  to the cords  32  to drive movement of the elevator car  12 . The jacket  34  could completely envelop the cords  32  (such as shown in  FIG. 3 ), substantially envelop the cords  32 , or at least partially envelop the cords  32 . 
         [0037]    Referring to  FIG. 5 , a fault detection unit  52  is electrically connected to a plurality of cords  32  of the belt  16 . The fault detection unit  52  is connected to a terminated portion of the belt  16 , for example, at an end  24   a  and/or  24   b  of the belt  16  located at the support  26  (shown in  FIG. 1 ). The cords  32  are electrically connected to the fault detection unit  52  in a Wheatstone bridge configuration. In one embodiment, as shown in  FIG. 5 , each cord  32   a,    32   b,    32   c  and  32   d  of a four-cord  32  arrangement forms each leg of the Wheatstone bridge. Cord ends  32 A and  32 B are connected are connected via input leads  54 , while cord ends  32 C and  32 D are connected via input leads  54 . Other ends of cords  32   a  and  32   b , referred to as  32 A′ and  32 B′ are connected via output lead  56 , while ends of cords  32   c  and  32   d,  referred to as  32 C′ and  32 D′ are also connected by an output lead  56 . The resulting bridge circuit  58  is shown in  FIG. 6 . Each leg  60  of the bridge circuit  58  is an LCR circuit allowing for measurement of complex impedance of the legs  60  or alternatively resistance of the legs  60 . An excitation voltage is applied across the bridge circuit  58  via the input leads  54  from the fault detection unit  52  in the form of an AC voltage, or alternatively a DC voltage source, and the bridge circuit  58  outputs a signal voltage via output leads  56  to the fault detection unit  52 . The fault detection unit  52  compares the excitation voltage to the signal voltage and evaluates an electrical impedance and/or electrical resistance of the belt  16 . The measurements are dynamic such that changes in complex impedance or electrical resistance are evaluated by the detection unit  52  and are indicative of wear, fretting and wire breakage in the cords  32  of the belt  16 . Configuring the cords  32  as a bridge circuit  58  suppresses noise from electromagnetic interference (EMI), temperature variation along a length of the cords  32 , and tensile load variation along each cord  32 . The connection scheme increases the total resistance of the circuit  58  and reduced the interrogating current through the cords  32 , thus improving signal to noise ratio. Further, since the cords  32  are all interconnected in the circuit  58 , all of the cords  32  are monitored simultaneously, thus reducing a number of required measurement channels. 
         [0038]    In another embodiment, as shown in  FIG. 7 , the belt  16  includes 8 cords  32 , with adjacent cords  32  arranged in cord-pairs  64 A,  64 B,  64 C and  64 D. The configuration of  FIG. 7  is utilized when, for example, the first end  24   a  of the belt  16  is fixed and the second end  24   b  is not fixed, as in the elevator system  10  of  FIG. 2 . In this embodiment, the individual cords  32  of each cord-pair  64 A,  64 B,  64 C,  64 D are connected at the second end  24   b  by jumper wires  66 . At the first end  24   a,  the cord pairs  64 A,  64 B,  64 C,  64 D are interconnected to form the bridge circuit  58 . For example, as shown in  FIG. 7  and  FIG. 8 , cord-pair  64 A is connected to cord-pair  64 B, cord-pair  64 B is connected to cord-pair  64 C, cord-pair  64 C is connected to cord-pair  64 D, and cord-pair  64 D is connected to cord-pair  64 A. As in the embodiment of  FIG. 6 , voltage is applied across the bridge circuit  58  via the input leads  54  and output leads  56  from the fault detection unit  52  measures an electrical impedance and/or electrical resistance of the belt  16 . Specifically, an output voltage at the output leads  56  indicates a difference in impedance of cord-pairs  64 A and  64 D from cord-pairs  64 B and  64 C, or inner cords  32  of the belt  16  compared to outer cords  32  of the belt  16 . While the cords  32  of cord-pairs  64 A,  64 B,  64 C and  64 D are illustrated as connected external to the jacket  34 , in some embodiments, the cords  32  are connected internal to the jacket  34 . Further, while embodiments of belts  16  having 4 or 8 cords  32  are illustrated, it is to be appreciated that in other embodiments, belts  16  having any number of cords  32  four or greater may be utilized, with select cords  32  connected as bridge circuit  58  at any one time. 
         [0039]    In another embodiment, as shown in  FIG. 9 , the cords  32  are connected to a switch array  68  including one or more relays or other switching elements. In this embodiment, the cords  32  are selectably connected fault detection unit  52 . In belts  16  having greater than 4 cords  32 , this allows for selection of cords  32  or multiples of cords  32  for assessment. Further, with the selective connection of a single cord  32 , the fault detection unit  52  may assess the condition of the single cord  32  via, for example, a traditional resistance-based inspection process. 
         [0040]    Referring now to  FIGS. 10-15 , a combination of cords  32  and fixed resistors  70  may be used to define the bridge circuit  58 . As shown in  FIGS. 10 and 11 , two cords, in this embodiment  32   c  and  32   d  are used in combination with two resistors  70 , for example, two low inductance resistors  70 , to form the bridge circuit  58 . Output leads  56  are connected between cords  32  and resistors  70  and the fault detection unit  52  essentially compares the complex impedance of the cords  32   c  and  32   d  to the impedance of the fixed resistors  70 . The impedance of the fixed resistors  70  is stable, while the impedance of cords  32   c  and  32   d  is variable, so change in impedance of the cords  32   c,    32   d  is more easily detectable. In some embodiments, the resistor  70  legs are low inductance and may also be temperature matched utilizing thermocouples and heaters (not shown). Further, the resistors  70  are matched to the cord impedance within 0.5 to 10× of the cord impedance. 
         [0041]    In another embodiment, as shown in  FIGS. 12 and 13 , cord pairs  64 A and  64 B are connected to form two legs of the bridge circuit  58 , while resistors  70  for the other two legs. The behavior of this bridge circuit  58  is similar to that of the circuit in  FIGS. 10-11 , but with higher levels of cord impedance. Additional cords  32  may be connected in series to form legs  64 A and  64 B. 
         [0042]    Referring to  FIGS. 14 and 15 , in some embodiments, the cords  32  and resistors  70  are interconnected such that the bridge circuit  58  is formed with cords  32  at opposing legs, and likewise resistors  70  at opposing legs, as opposed to at adjacent legs as in other embodiments. In this embodiment, an increase in complex impedance in the cords  32  will unbalance the bridge in opposite directions, resulting in approximately double the measurable signal at the fault detection unit  52 . Thus a smaller change in impedance in the cords  32  is detectable. 
         [0043]    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.