WO2010071607A1 - Procédé et système pour surveiller les charges s'exerçant sur une attache - Google Patents

Procédé et système pour surveiller les charges s'exerçant sur une attache Download PDF

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Publication number
WO2010071607A1
WO2010071607A1 PCT/SG2009/000476 SG2009000476W WO2010071607A1 WO 2010071607 A1 WO2010071607 A1 WO 2010071607A1 SG 2009000476 W SG2009000476 W SG 2009000476W WO 2010071607 A1 WO2010071607 A1 WO 2010071607A1
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WO
WIPO (PCT)
Prior art keywords
fastener
piezoelectric sensor
piezoelectric
monitoring
standing wave
Prior art date
Application number
PCT/SG2009/000476
Other languages
English (en)
Inventor
Narasimalu Srikanth
Original Assignee
Vestas Wind System A/S
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Vestas Wind System A/S filed Critical Vestas Wind System A/S
Publication of WO2010071607A1 publication Critical patent/WO2010071607A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L5/00—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes
    • G01L5/0028—Force sensors associated with force applying means

Definitions

  • the present invention relates broadly to a method and system for monitoring fastener loads, to a fastener, to a method of fabricating a fastener sensor, and to a wind turbine.
  • Tensioned bolts under cyclic loads such as vibration, thermal variation and the like have been known to stretch and thus loosen over time. Looseness will result in reduction of the joint stiffness and the overall load carrying capacity of the bolted joint. It is thus required to monitor bolt loads.
  • bolt sensors may be employed instead.
  • bolt sensors may be of a washer-type and are sandwiched between the bolt and the joint.
  • this affects the stiffness of the joint as it directly affects the force path between the bolt and the joint.
  • external bolt sensors may be employed and brought into contact with, for example, the bolt head during manual monitoring.
  • this is oftentimes cumbersome and may not be suitable for applications where space constraint is a critical factor.
  • a fastener comprising a head for abutting a mounting surface of a medium; a shaft for engaging the medium; and a piezoelectric sensor integrated into the head; for monitoring loads on the fastener.
  • Said piezoelectric sensor may be disposed in a cavity within the head.
  • Said piezoelectric sensor in use, may generate a longitudinal standing wave in the shaft.
  • Said piezoelectric sensor may comprise a piezoelectric material sandwiched between a pair of electrodes.
  • ⁇ aid fastener may further comprise a preload element for compressing the piezoelectric material.
  • Said fastener may further comprise a plurality of wires integrated into the head for contacting the piezoelectric sensor.
  • Said fastener may further comprise a backing material disposed between the piezoelectric material and the preload element for facilitating acoustic coupling.
  • Said fastener may further comprise a matching layer disposed between the piezoelectric material and a bulk of the bolt for facilitating acoustic coupling.
  • a method of monitoring fastener loads comprising the steps of generating a longitudinal standing wave in a shaft of the fastener using a piezoelectric sensor; and determining a load to which a fastener has been subjected from a change in the frequency of the longitudinal standing wave.
  • the method may further comprise integrating the piezoelectric sensor into a head of the fastener.
  • the change in the frequency of the longitudinal standing wave may be measured by performing a frequency response function measurement of the piezoelectric sensor.
  • the frequency of the longitudinal standing wave may be determined based on a minimum impedance measurement.
  • the frequency of the longitudinal standing wave may be determined based on a phase difference measurement between the input and output signals of the piezoelectric sensor.
  • the phase difference measurement may comprise using a phase lock loop circuit.
  • a method of fabricating a fastener comprising forming a piezoelectric sensor integrated into a head of the fastener for generating a longitudinal standing wave in a shaft of the fastener using the piezoelectric sensor.
  • a system for monitoring fastener loads comprising one or more fasteners as defined in the first aspect; wherein the fasteners are connected to an apparatus for performing frequency response function measurements of the piezoelectric sensors of the respective fasteners for monitoring loads on the fasteners.
  • the fasteners may be connected to the apparatus through wired or wireless connections.
  • a wind turbine comprising one or more fasteners as defined in the first aspect.
  • a wind turbine comprising a system for monitoring fastener loads as defined in the fourth aspect.
  • Figure 1 shows a cross-sectional view of a bolt sensor according to an embodiment of the invention.
  • Figure 2 shows a cross-sectional view of a bolt sensor according to an alternate embodiment of the invention.
  • Figure 3 shows an example of a frequency response function plot from a bolt with integrated sensor according to an example embodiment.
  • Figure 4 is a flow chart illustrating one method of monitoring bolt loads according to an example embodiment.
  • Figure 5 shows a schematic exploded view drawing of a sensor structure according to an example embodiment.
  • Figure 6 is a flowchart illustrating another method of monitoring fastener loads according to an example embodiment.
  • Figure 7 shows a schematic diagram illustrating a wind turbine comprising a system for monitoring bolt loads according to an example embodiment.
  • Embodiments of the present invention may monitor bolt loads, non- destructively, without affecting the overall stiffness of a bolted joint, by means of a sensor and in addition, provides a means for real-time monitoring.
  • Figure 1 illustrates one embodiment of the present invention, which comprises of a sensor 101 that is physically integrated into a bolt head 100 of a bolt
  • the bolt 102 may be any type of threaded fastener, comprising a head and a shaft; and in the example embodiment is designed to be used in conjunction with a threaded portion 108a of one of the joint components 108. It will be appreciated that the present invention can also be applied to other fasteners, including, but not limited to screws, rivets, nails, etc.
  • the sensor 101 is positioned within the bolt head 100 such that, it will not affect the bolt's load capacity, strength and stiffness. More particular, in the example embodiment the cavity for r
  • receiving the sensor 101 is positioned such that it lies outside of a force path, schematically indicated at 104 in Figure 1 , between bolt 102 and a joint structure between two joint components 106, 108 to be secured by the bolt 102.
  • the sensor 101 comprises a preload element, here in the form of a screw 105 with an Allen key notch 103, which may be screwed into the bolt 100 by means of threads 106.
  • the sensor 101 further comprises a backing material 107; a pair of electrodes 109,113; a piezoelectric element 111 ; a matching layer 115 and +ve and - ve electrode wires 117,1 19.
  • the electrode wires 117, 119 are accommodated in one or two grooves or recesses formed along a perimeter of the cavity for receiving the screw 105, backing material 107, electrodes 109, 113, piezoelectric element 11 1 , and matching layer 115, using for example drilling or forging techniques.
  • the preload screw 105 is screwed down in order to compress the other components of the sensor 101.
  • the piezoelectric element 111 is preferably compressed between the pair of electrodes 109,113 in order to have a preload for enhanced fatigue life.
  • the Allen key notch 103 with the threads 106 may facilitate the fastening of the preload screw 105 in order to ensure compression of the sensor's components.
  • the various components of the sensor are simply fixed in position by the compressional force applied by the preload screw.
  • the various components of the sensor 101 are assembled layer-by- layer within the cavity.
  • the piezoelectric element 111 may be of any piezoelectric material.
  • the piezoelectric material could be quartz, lead zirconium titanate (PZT), etc.
  • the thickness of the element 111 is such that it may operate in a thickness mode matched with a frequency of interest, for example about 2OkHz to 50OkHz.
  • the longitudinal frequency (/) chosen is inversely proportional to the wavelength (A) 1 as the speed of sound (v) is a constant for a particular material.
  • a mechanical longitudinal wave is generated, which reflects back from the free end 121 of the bolt 102.
  • a mechanical longitudinal standing wave can be formed between the free end 121 and the top surface 122 of the screw 105.
  • the frequency of a standing wave is related to the length of the bolt by: f - v - v (l + 0
  • the sensor 102 configuration is preferably chosen such that for a given overall dimension of the bolt 102, the frequency of the standing wave of interest is substantially matched to a thickness mode of the piezoelectric element 111 , such that the sensor 101 can advantageously operate with minimal energy loss.
  • the piezoelectric deformation of the piezoelectric 111 is preferably purely a longitudinal deformation, or the other modes, i.e. radial and flextual modes, are at least minimised. In addition to facilitating operation at minimal energy loss, this can also advantageously minimise damage to/fatigue of the piezoelectric element 111 under operation.
  • the matching to the thickness mode takes into account the compression of the piezoelectric element 111 exerted by the preload screw 105.
  • a balancing between different factors can be performed. For example, for higher resonance modes, the sensivity to structural defects such as cracks forming in the bolt 102 along the force path 104 is increased, due to the shorter wavelength of the standing wave. At the same time, energy damping increases with increasing frequency, resulting in losses which reduce the energy efficiency of the sensor 101 , and effectively heat the bolt 102. Thus can be additionally disadvantageous as it can contribute to fatigue of the bolt 102, and/or changing of material parameters of ⁇ the bolt 102, for example.
  • the longitudinal resonance frequency may be obtained from the zero point 300 of a Frequency Response Function (FRF) plot 302 illustrated in Figure 3, which shows the magnitude of the FRF as a function of frequency.
  • FRF Frequency Response Function
  • the plot 302 may be generated from a sine sweep of the piezoelectric element 111 ( Figure 1).
  • the change in length ⁇ /Of the bolt 102 ( Figure 1) can be measured from slifts in the zero point 300 and the axial load, P, can be derived:
  • A is the cross sectional area of the bolt 102 ( Figure 1 ) along the force path 104 ( Figure 1), and E is the elastic modulus.
  • the FRF which measures the output over the input of the piezoelectric element 111 ( Figure 1), includes both magnitude and phase information.
  • additional information may be obtained with reference to the phase information, including information for determining location of crack(s) along the bolt, which can be associated with occurrence of different set(s) of longitudinal resonance mode(s).
  • the electronics coupled to the sensor 101 ensures to observe that the operating frequency is matching with the longitudinal resonant frequency of the overall bolt system.
  • the benefits to operate at that resonant frequency point include that the monitoring can provide infromation not only about the change in bolt dimension, but advantageously also inromation about the presence of bolt damage (like crack, elongation, etc). Such damage can result in at leats partial reflection of the wave, and an associated resonance frequency can be detected. Also energy wastage is low and so no or littel heat up and corresponding fatigue or softening effects to the bolt material are encountered.
  • monitoring for operating at a resonance condition does not require complex circuitry or processing.
  • the circuit applies a sinusoidal voltage and observes the current waveform. Two example methods that can be be used, but the invention is not limited to, are described below. _ o
  • the circuit uses the ratio of the voltage and current seen as impedence and is analysed for different frequencies. To find, indirectly, a resonance frequency, one can adopt a frequency sweep from a low frequency to high frequency and observe the minimal impedence condition.
  • a phase lock loop (PLL) concept is used to ensure that the circuitry looks only at the resonance frequency.
  • vibration modes such as flexural modes, twisting modes, etc and they may get exited during the sensing measurements.
  • Using a PLL concept in may be preferred over using other types such as proportional control, etc.
  • the phase difference between the input and output signal to the piezo electric element 111 is a useful information to locate the resonance.
  • a phase difference between 0° and -90° corresponds to a driving frequency below resonance, while a phase difference between -90° and -180° implies operation above resonance.
  • the relevant frequency of operation can be taken down as the resonant frequency and the impedence magnitude value can be taken down.
  • Figure 4 is a flow chart illustrating one method of monitoring bolt forces according to an example embodiment.
  • the method begins 400 with applying a sinusoidal voltage on the piezoelectric element 111 , as shown at reference numeral 402.
  • the following step involves conducting a sine sweep 404 of the piezoelectric element 11 1.
  • a FRF plot is obtained from the sine sweep, as shown at reference numeral 406.
  • the longitudinal frequency of the standing wave is extracted from the FRF plot, as shown at reference numeral 408.
  • the change in bolt length is then derived 410.
  • the next step 412 determines if the bolt length is within tolerance. If it is, the next step will determine if monitoring is to be done continuously 418. If it is, the system will go back to step 402.
  • monitoring ends 420. Should the bolt length fall out of the tolerance range, the subsequent step 414 will derive the axial load and thereafter determine the looseness of the bolt 416. Once completed, the monitoring process ends 420.
  • Figure 5 shows a schematic exploded view drawing illustrating the layer-by- layer built-up of a sensor structure 500 for incorporation into a bolt head (not shown) according to an example embodiment.
  • a matching layer in the form of a sheet material 502 is provided, with the material chosen to provide good acoustic coupling/matching without reflection of energy at the interface to the bulk bolt material, in the assembled configuration.
  • the sheet material 502 is further chosen to be electrically insulating. It will be appreciated that in different embodiments, a separate insulating layer may additionally be provided.
  • the next layer comprises the bottom electrode layer, here in the form of a metallic sheet material 504, for example BeCu alloy.
  • the sheet material 504 includes a tail portion 506, to which a contact wire 506 is connected, in the example embodiment through a solder connection.
  • a piezoelectric material here in a form of a disc 510 is provided, followed by the upper electrode, here in the form of a conducting material sheet 512, for example Be.
  • the sheet material 512 includes a tail portion 513, to which a contact wire 515 is connected, in the example embodiment through a solder connection.
  • a packing material here in the form of another sheet material 514, chosen for providing good acoustic coupling/matching to the material of the preload screw 516, which in this example embodiment is formed from the same material as the bolt (not shown).
  • the wires 506, 515 are arranged for assembly in recesses or channels formed in the bolt head (not shown) along a cavity for receiving the sensor structure 500.
  • the wires 506, 515 can e.g. be terminated in suitable connector structures such as multi-pin co-axial cable connectors, for connection to external measurement equipment (not shown) via corresponding plugs.
  • Figure ' 2 shows an alternate embodiment of the present invention, a sensor
  • a preload element in the form of a screw 205, is in a cylindrical T shape.
  • the preload screw 205 is screwed into the bolt 201 by means of an Allen key notch 203 and suitable threads 206.
  • the threads 206 are formed at a bottom portion 204 of the cavity for receiving the sensor 201.
  • the components of the sensor 201 further comprise a backing material 207; a piezoelectric element 211 ; a pair of electrodes 209, 213; a matching layer 215 and a +ve and -ve electrode wires 217, 219.
  • the backing material 207; piezoelectric element 211 ; pair of electrodes 209, 213 and matching layer 215 are of a cylindrical ring shape and surround the stem portion 210 of the preload screw 205.
  • FIG. 6 is a flowchart 600 illustrating another method of monitoring fastener loads according to an example embodiment.
  • a longitudinal standing wave is generated in a shaft of the bolt using a piezoelectric sensor.
  • a load to which a fastener has been subjected is determined from a change in the frequency of the longitudinal standing wave.
  • a method of fabricating a fastener comprises forming a piezoelectric sensor integrated into a head of the fastener for generating a longitudinal standing wave in a shaft of the fastener using the piezoelectric sensor.
  • the embodiments described can be applied in many different application environments, where monitoring of tension and/or damage to fasteners is a critical issue.
  • the example embodiments are individually connected to the relevant measurement equipment for performing the frequency response function measurements in an ad-hoc basis, for example conducted by a service engineer.
  • one or more fasteners according to example embodiments are "permanently" electrically interconnected to a suitable measurement equipment or system, for continued, real-time measurements or centralized ad-hoc measurements.
  • interconnection between the fasteners according to example embodiments and the relevant measurement equipment can take many forms, including wired or wireless connections for performing of the FRF measurements.
  • Figure 7 shows a schematic diagram illustrating a wind turbine 700 comprising a system for monitoring bolt loads according to an example embodiment.
  • the wind turbine 700 comprises numerous bolts the loads of which may be desired to be monitored.
  • example bolts 704 to 706 are shown in Figure 7, representing bolts used to interconnect the respective tower segments e.g. 708, 710.
  • the bolts 704 to 706 would typically be used in conjunction with nuts to secure the segments e.g. 708, 710 via adjacent inner flanges (not shown) of adjoining segments 708, 710.
  • the fasteners 704 to 707 are each connected to an apparatus for performing FRF measurements of the integrated piezoelectric sensors of the respective bolts 704 to 707 for monitoring loads on the bolts 704 to 706, here in the form of a spectrum analyzer 712 with PLL function located at a base station 714 of the wind turbine 700.
  • the bolts 704 to 706 are connected to the spectrum analyzer 712 using wireless interconnections, using an RF transceiver 716 coupled to the spectrum analyzer 712, and corresponding transceivers (not shown) mounted at or near the heads of the bolts 704 to 706, and coupled to the piezoelectric sensors integrated in the respective heads of the bolts 704 to 706.

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  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Force Measurement Appropriate To Specific Purposes (AREA)

Abstract

La présente invention concerne un procédé et un système pour surveiller les charges s'exerçant sur une attache, une attache, un procédé de fabrication d'un capteur d'attache et une éolienne. L'attache comprend une tête butant contre une surface de fixation d'un support ; un arbre pour emboîter le support ; et un capteur piézoélectrique intégré dans la tête pour surveiller les charges s'exerçant sur l'attache.
PCT/SG2009/000476 2008-12-17 2009-12-11 Procédé et système pour surveiller les charges s'exerçant sur une attache WO2010071607A1 (fr)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
US13817408P 2008-12-17 2008-12-17
DKPA200801793 2008-12-17
US61/138,174 2008-12-17
DKPA200801793 2008-12-17

Publications (1)

Publication Number Publication Date
WO2010071607A1 true WO2010071607A1 (fr) 2010-06-24

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Cited By (12)

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Publication number Priority date Publication date Assignee Title
US8434996B2 (en) 2011-12-06 2013-05-07 General Electric Company System and method for detecting and/or controlling loads in a wind turbine
US8538667B2 (en) 2011-07-28 2013-09-17 International Business Machines Corporation Evaluating road conditions using a mobile vehicle
US8706325B2 (en) 2011-07-27 2014-04-22 International Business Machines Corporation Evaluating airport runway conditions in real time
US8788222B2 (en) 2011-07-25 2014-07-22 International Business Machines Corporation Detection of pipeline contaminants
US8990033B2 (en) 2011-07-27 2015-03-24 International Business Machines Corporation Monitoring operational conditions of a cargo ship through use of sensor grid on intermodal containers
US9146112B2 (en) 2011-10-04 2015-09-29 International Business Machines Corporation Mobility route optimization
US9207089B2 (en) 2011-10-04 2015-12-08 International Business Machines Corporation Mobility route optimization
US9322657B2 (en) 2011-10-04 2016-04-26 International Business Machines Corporation Mobility route optimization
CN105986963A (zh) * 2015-02-11 2016-10-05 赤峰华源新力科技有限公司 风电机组的连接螺栓松动监测系统
DK201570840A1 (en) * 2015-12-21 2017-07-10 Kk Wind Solutions As Ultrasonic bolt monitoring
US9897127B1 (en) 2017-05-02 2018-02-20 General Electric Company Fastening device with integrated sensor
CN113286944A (zh) * 2019-12-16 2021-08-20 远景能源有限公司 一种用于监测叶根紧固件的健康状态的方法及系统

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Publication number Priority date Publication date Assignee Title
US4846001A (en) * 1987-09-11 1989-07-11 Sps Technologies, Inc. Ultrasonic load indicating member
EP0459068A1 (fr) * 1990-05-31 1991-12-04 K.K. Holding Ag Palpeur de force à disque mince
DE19831270A1 (de) * 1998-07-13 2000-01-27 Peter Haug Anordnung zur Bestimmung und Überwachung des Spannungszustandes eines Befestigungselementes

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4846001A (en) * 1987-09-11 1989-07-11 Sps Technologies, Inc. Ultrasonic load indicating member
EP0459068A1 (fr) * 1990-05-31 1991-12-04 K.K. Holding Ag Palpeur de force à disque mince
DE19831270A1 (de) * 1998-07-13 2000-01-27 Peter Haug Anordnung zur Bestimmung und Überwachung des Spannungszustandes eines Befestigungselementes

Cited By (17)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9182314B2 (en) 2011-07-25 2015-11-10 International Business Machines Corporation Detection of pipeline contaminants
US8788222B2 (en) 2011-07-25 2014-07-22 International Business Machines Corporation Detection of pipeline contaminants
US8706325B2 (en) 2011-07-27 2014-04-22 International Business Machines Corporation Evaluating airport runway conditions in real time
US8990033B2 (en) 2011-07-27 2015-03-24 International Business Machines Corporation Monitoring operational conditions of a cargo ship through use of sensor grid on intermodal containers
US8538667B2 (en) 2011-07-28 2013-09-17 International Business Machines Corporation Evaluating road conditions using a mobile vehicle
US8731807B2 (en) 2011-07-28 2014-05-20 International Business Machines Corporation Evaluating road conditions using a mobile vehicle
US9207089B2 (en) 2011-10-04 2015-12-08 International Business Machines Corporation Mobility route optimization
US9146112B2 (en) 2011-10-04 2015-09-29 International Business Machines Corporation Mobility route optimization
US9322657B2 (en) 2011-10-04 2016-04-26 International Business Machines Corporation Mobility route optimization
US8434996B2 (en) 2011-12-06 2013-05-07 General Electric Company System and method for detecting and/or controlling loads in a wind turbine
CN105986963A (zh) * 2015-02-11 2016-10-05 赤峰华源新力科技有限公司 风电机组的连接螺栓松动监测系统
CN105986963B (zh) * 2015-02-11 2019-08-20 赤峰华源新力科技有限公司 风电机组的连接螺栓松动监测系统
DK201570840A1 (en) * 2015-12-21 2017-07-10 Kk Wind Solutions As Ultrasonic bolt monitoring
DK179021B1 (en) * 2015-12-21 2017-08-28 Kk Wind Solutions As Ultrasonic bolt monitoring
US9897127B1 (en) 2017-05-02 2018-02-20 General Electric Company Fastening device with integrated sensor
CN113286944A (zh) * 2019-12-16 2021-08-20 远景能源有限公司 一种用于监测叶根紧固件的健康状态的方法及系统
CN113286944B (zh) * 2019-12-16 2022-06-10 远景能源有限公司 一种用于监测叶根紧固件的健康状态的方法及系统

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