Elevator cord health monitoring

A method of fault detection of a belt or rope includes connecting a fault detection unit to at least a portion of a belt or rope including a plurality of wires arranged in a plurality of strands and/or cords. At least the portion of the belt or rope is subjected to an AC voltage of high frequency range and an electrical impedance of the portion of the belt or rope is measured via the fault detection unit. Using at least the measured electrical impedance of the portion of the belt or rope, a fault condition of the belt or rope is determined.

BACKGROUND OF THE INVENTION

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.

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.

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 defect all the common failure modes of the ropes and belts. It is also less reliable for continuous online inspection in an electrometrically and mechanically noisy environment. 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

According to one aspect of the invention, a method of fault detection of a belt or rope includes connecting a fault detection unit to at least a portion of a belt or rope including a plurality of wires arranged in a plurality of strands and/or cords. At least the portion of the belt or rope is subjected to an AC voltage and a complex (real and imaginary) electrical impedance of the portion of the belt or rope is measured via the fault detection unit. Using at least the measured electrical impedance of the portion of the belt or rope, a fault condition of the belt or rope is determined.

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.

According to this or other aspects of the invention, the method includes extracting components of electrical impedance from the measured electrical impedance and determining a fault condition of the belt or rope from the components of the measured electrical impedance.

According to this or other aspects of the invention, the components of electrical impedance include inductance, capacitance and/or resistance.

According to this or other aspects of the invention, the fault condition includes wire breakage, fretting and/or birdcaging.

According to this or other aspects of the invention, the method includes measuring the electrical impedance over a range of frequencies.

According to this or other aspects of the invention, the portion of belt or rope is at least one cord of the belt or rope.

According to this or other aspects of the invention, the electrical impedance is measured substantially periodically.

According to another aspect of the invention, an elevator system includes an elevator car, one or more sheaves and a belt or rope having a plurality of wires arranged into a plurality of strands and/or cords for supporting and/or driving the elevator car. A fault detection unit is operably connected to the belt or rope to measure an electrical impedance of at least a portion of the belt or rope.

According to this or another aspect of the invention, the fault detection unit measures electrical impedance of one or more cords of the belt or rope.

According to this or another aspect of the invention, the fault detection unit is configured as an LCR meter in a bridge circuit format.

According to this or another aspect of the invention, the elevator system further includes an AC voltage source operably connected to the belt or rope.

According to this or another aspect of the invention, the belt or rope is a coated belt or rope.

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

Shown inFIGS. 1A, 1B and 1Care schematics of exemplary traction elevator systems10. Features of the elevator system10that are not required for an understanding of the present invention (such as the guide rails, safeties, etc.) are not discussed herein. The elevator system10includes an elevator car12operatively suspended or supported in a hoistway14with one or more belts16. The one or more belts16interact with one or more sheaves18to be routed around various components of the elevator system10. The one or more belts16could also be connected to a counterweight22, which is used to help balance the elevator system10and 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.

The sheaves18each have a diameter20, which may be the same or different than the diameters of the other sheaves18in the elevator system10. At least one of the sheaves18could be a drive sheave. A drive sheave is driven by a machine50. Movement of the drive sheave by the machine50drives, moves and/or propels (through traction) the one or more belts16that are routed around the drive sheave.

At least one of the sheaves18could be a diverter, deflector or idler sheave. Diverter, deflector or idler sheaves are not driven by a machine50, but help guide the one or more belts16around the various components of the elevator system10. Further, one or more of the sheaves18, 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 belts16centered, or in a desired position, along the sheaves18.

In some embodiments, the elevator system10could use two or more belts16for suspending and/or driving the elevator car12. In addition, the elevator system10could have various configurations such that either both sides of the one or more belts16engage the one or more sheaves18(such as shown in the exemplary elevator systems inFIG. 1A, 1B or 1C) or only one side of the one or more belts16engages the one or more sheaves18.

FIG. 1Aprovides a 1:1 roping arrangement in which the one or more belts16terminate at the car12and counterweight22.FIGS. 1B and 1Cprovide different roping arrangements. Specifically,FIGS. 1B and 1Cshow that the car12and/or the counterweight22can have one or more sheaves18thereon engaging the one or more belts16and the one or more belts16can terminate elsewhere, typically at a structure within the hoistway14(such as for a machineroomless elevator system) or within the machine room (for elevator systems utilizing a machine room). The number of sheaves18used in the arrangement determines the specific roping ratio (e.g., the 2:1 roping ratio shown inFIGS. 1B and 1Cor a different ratio).FIG. 1Calso provides a cantilevered type elevator. The present invention could be used on elevator systems other than the exemplary types shown inFIGS. 1A, 1B and 1C.

FIG. 2provides a schematic of a belt construction or design. Each belt16is constructed of a plurality of wires28(e.g. twisted into one or more strands30and/or cords24as shown inFIG. 3) in a jacket26. As seen inFIG. 2, the belt16has an aspect ratio greater than one (i.e. belt width is greater than belt thickness). The belts16are constructed to have sufficient flexibility when passing over the one or more sheaves18to 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 car12. The jacket26could 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 jacket26could be a polymer, such as an elastomer, applied to the cords24using, for example, an extrusion or a mold wheel process. In another arrangement, the jacket26could be a woven fabric that engages and/or integrates the cords24. As an additional arrangement, the jacket26could be one or more of the previously mentioned alternatives in combination.

The jacket26can substantially retain the cords24therein. The phrase substantially retain means that the jacket26has sufficient engagement with the cords24to transfer torque from the machine50through the jacket26to the cords24to drive movement of the elevator car12. The jacket26could completely envelop the cords24(such as shown inFIG. 2), substantially envelop the cords24, or at least partially envelop the cords24.

Referring toFIG. 4, a fault detection unit52is electrically connected to one or more cords24of the belt16. The fault detection unit52is connected to a terminated portion of the belt16, for example, at an end of the belt16located at an upper end of the hoistway14. It is to be appreciated, though, that this location is merely exemplary and other locations for connecting the fault detection unit52to the belt16are contemplated within the present scope. During operation of the fault detection unit52, one or more of the cords24are subjected to an AC excitation voltage provided by the detection unit52in a frequency range of about 100 kilo Hertz to about 10 mega Hertz. A signal voltage from the cords24is received at the fault detection unit52and is compared to the excitation voltage at the fault detection unit52to determine an electrical impedance of the cord24. In some embodiments, the fault detection unit52is configured as an LCR meter as a bridge circuit to detect electrical impedance across the cord24. The fault detection unit52compares the excitation voltage to the signal voltage and evaluates an electrical impedance and/or electrical resistance of the belt16. The measurements are dynamic such that changes in complex impedance or electrical resistance are evaluated by the detection unit52and are indicative of wear, fretting and wire breakage in the cords24of the belt16.

The measurement of complex impedance of the cords24may occur during any one of several operating states of the elevator system10. First, the elevator car12and belt16position may be static, with position in the hoistway14unknown, with the cords24subjected to variable voltage, AC current as stated above, or a current pulse. The measurement may be taken when the elevator car12is moving in the hoistway14, and the cords are subjected to AC current, a variable voltage or a current pulse. Further, it may be useful to correlate an impedance of the cords24to a particular position in the hoistway14. In such cases, the measurements may be taken when the elevator car12is in a known position in the hoistway14, either moving or static, so the measurement may be correlated to or adjusted for particular conditions (such as temperature or tension) at that particular location.

Referring toFIG. 5, the output of the impedance measurement involves three variables, the magnitude, phase and frequency of the excitation defining a measured impedance profile34resulting from the measurement. In some embodiments, the electrical impedance is measured continuously or intermittently (such as 1 measurement per hour) or periodically (such as one measurement per day) during operation of the elevator system. The measured impedance profile34is compared to an initial or baseline impedance profile36with differences indicative of wear of or damage to the cord24. The measured impedance profile34may be correlated to specific faults, damage or failure modes of the cord24, such as wire breakage, fretting and/or birdcaging of one or more wires28of the cord24. The correlation may be established by modeling or testing or other accepted method. The measured impedance profile may be then compared to known or established failure mode profiles to diagnose the measures profiles. In some embodiments, the components of electrical impedance: inductance, capacitance and resistance are extracted from the measured impedance profile34as indicators of cord24failure modes and specific properties or feature of the measured impedance profile indicate specific failure modes of the cord24.

For example, shown inFIG. 5are measured impedance profiles34a,34b, and34ccompared with baseline impedance profile36. InFIG. 5, impedance is plotted relative to frequency. Further for reference, DC resistance38of the cord24is shown. In this example, a first peak40aof a first measured impedance profile34ais indicative of one wire28broken in the cord24. Similarly, second peak40bof second measured impedance profile34band third peak40cof third measured impedance profile34care indicative of two wires28broken and three wires28broken, respectively, in the cord24. As shown, the measured impedance profiles34a,34band34cvary to a great degree over varying frequencies, while the DC resistance38remains substantially constant. Thus, the measured impedance34has an increased sensitivity versus DC resistance38to damage of the cord24and can indicate minor and more subtle structural defects of damage of the cord24than purely resistance-based damage assessment.