WO2020223769A1

WO2020223769A1 - Method and apparatus for estimating tension in a bolt or stud

Info

Publication number: WO2020223769A1
Application number: PCT/AU2020/050456
Authority: WO
Inventors: Andrew Duncan Mcphee
Original assignee: Nord-Lock Switzerland Gmbh
Priority date: 2019-05-09
Filing date: 2020-05-08
Publication date: 2020-11-12

Abstract

A bolt tension monitor for estimating tension in an elongate fastening member, said monitor comprising: a transducer for converting a vibration of the elongate fastening member into an electrical signal; a frequency detection assembly arranged to determine a frequency of the vibration from the electrical signal; and a tension value assembly responsive to the frequency detection assembly and arranged to produce a signal representing a tension value of the elongate fastening member.

Description

METHOD AND APPARATUS FOR ESTIMATING TENSION IN A BOLT OR

STUD

The present disclosure generally relates to elongate fasteners such as bolts and studs and to apparatus for estimating tension in an elongate fastener.

BACKGROUND

Any references to methods, apparatus or documents of the prior art are not to be taken as constituting any evidence or admission that they formed, or form part of the common general knowledge.

The stress, i.e. the tension divided by cross sectional area, in an elongate fastening member, such as a bolt or stud, and thus its elongation under that stress is an important parameter because the fitness for purpose of a bolted joint depends on the clamping force across the joint which in turn depends on the tension apphed to each bolt of the joint. For example, FIG. 1 is a partially cutaway side view of a joint 1 that is comprised of first and second workpieces in the form of flanges 3a, 3b that are held together by an elongate fastening member in the form of a bolt 5 having a shank 7 that extends through holes of the flanges 3a, 3b. The shank 7 terminates at one end in a head 11 that abuts an outside of flange 3b, and at an opposite end in a threaded point 13. A nut in the form of a multi-jack-tensioner (MJT) 15, including a nut body 17 with jackbolts 19 and a hardened washer 21 is attached to the threaded point. As the jackbolts 19 of the MJT 15 are torqued the nut body 17 is displaced from the washer 21 thereby tensioning shank 7 which stretches in response. It will be reahzed that the nut could be a standard single piece nut rather than an MJT.

There are several ways of estimating the tension in an elongate fastener such as a bolt or a stud. One common way is to derive a value for the tension based on the level of torque used to tighten a nut, or each jackbolt of an MJT, attached to the bolt.

However, particularly where an ordinary nut, rather than an MJT, is used such a method is prone to inaccuracies due to friction of the nut against a bearing surface such as a washer causing the torque to be due to factors other than the pitch of the thread and the stress in the bolt.

In more recent years ultrasonic bolt tension monitors have become available.

Ultrasonic bolt tension monitors are microprocessor based devices that are coupled to an ultrasonic transducer, such as a piezo-electric crystal. The transducer is attached to one end of the bolt and operated by the device to transmit a pulse of ultrasonic sound through the bolt. The ultrasonic sound travels axially down the bolt and is reflected back from its far end thereby causing an echo that is sensed by the transducer. The time between transmitting an ultrasonic pulse and the receipt of its echo back at the transducer is used to determine the length of the bolt. Thus the change in length of the bolt as the bolt is tensioned can be measured. The change in length can then be used to determine a value for the tension in the bolt. The ultrasonic bolt tension monitor is unsuited for use with bolts that have ends which are not cut square or which are unduly rough since in that case either the transmitted pulse and/ or the echo will be caused to be internally reflected from side to side thereby increasing the echo time and overestimating the bolt length.

Other approaches to determining the tension in a bolt are also known. For example, in a Master's Thesis entitled A Novel Ultrasonic Method to Quantify Bolt Tension (January 2012, University of South Florida) by Jairo Andres Martinez Garcia there is described a sophisticated method for estimating bolt tension using surface acoustic waves (SAWs). In the method that is described the tension is estimated by observing the points of interaction between SAWs and the bolt head and thus the area of reflective boundaries, which increase as torque is apphed to the nut so that the bolt head to bearing surface contact area (e.g. an adjacent flange or washer) increases as the bolt tension is increased.

It will be reahzed that although these prior art methods have their merits they tend to be either too inaccurate, as in the case of the torque-to-tension estimation, are intolerant to variations in the ends of the bolts, as in the case of the ultrasonic bolt tension monitor, or are susceptible to variations in surface contact properties of the bolt head and bearing surface, as in the case of the SAW method.

It is an object of the present invention to provide a method and apparatus for estimating the tension in an elongate fastener such as a bolt or stud which is a useful alternative to those that are presently known in the prior art. SUMMARY

According to a first aspect of the present invention there is provided a tension monitor for estimating tension in an elongate fastening member tensioned to secure one or more workpieces, said monitor comprising:

a transducer for converting a vibration ehcited from the elongate fastening member into an electrical signal;

a frequency detection assembly arranged to determine a frequency of the vibration from the electrical signal; and

a tension value assembly responsive to the frequency detection assembly and arranged to produce a signal representing a tension value of the elongate fastening member.

In an embodiment the frequency detection assembly includes an analog to digital converter for digitizing the electrical signal and a fast Fourier transform (FFT) assembly responsive thereto.

In an embodiment the frequency detection assembly includes a Harmonic Product Spectrum (HPS) assembly responsive to the FFT assembly for determining the frequency as a fundamental frequency of the vibration.

The relationship between the tension in a string (bolt), its size (in terms of mass per unit length) and its length that is based on Mersenne's laws may be:

where T is the tension (in Newtons), m is the hnear density (that is, the mass per unit length), and L is the length of the vibrating part of the elongate fastener.

In an embodiment the tension value assembly is arranged to produce the signal representing the tension value of the elongate fastening member according to a relationship of tension-to-frequency based on Mersenne's laws. In an embodiment the bolt tension monitor includes or remotely accesses an electronic memory containing tension values for a plurality of frequencies of vibration for each of a number of bolts of different dimensions and/ or masses.

In an embodiment the bolt tension monitor includes a memory containing length and mass per unit length values for a number of elongate fastening members.

In an embodiment the tension monitor includes a user interface for selecting one of said number of elongate fastening members.

In an embodiment the tension monitor includes an actuator assembly for interacting with the elongate fastening member to thereby elicit the vibration.

In an embodiment the actuator assembly comprises a rotatable member.

In an embodiment the rotatable member is arranged to strike the elongate fastening member to thereby elicit the vibration.

In another embodiment the actuator assembly includes a striker and a biasing member arranged to bias the striker against the elongate fastening member. For example the biasing member may comprise a spring.

In an embodiment an arc of a path of a peripheral portion of the rotatable member interferes with the striker for forcing the striker against the biasing member.

In an embodiment the actuator comprises a transducer for producing vibrations across a range of frequencies to sympathetically elicit the vibration of the elongate fastening member.

In an embodiment the tension monitor includes a tensioning assembly for tensioning the elongate fastener to adjust tension therein wherein the tensioning assembly is responsive to the tension value assembly for attaining a desired tension in the elongate fastening member. According to a further aspect of the present invention there is provided a system for monitoring tensions in each of a plurahty of elongate fastening members, the system comprising:

a plurality of actuators each one arranged to elicit a vibration from a corresponding one of said elongate fastening members;

a processing assembly coupled to the plurahty of actuators for operation thereof;

the processing assembly being responsive to vibrations elicited from each of the plurahty of elongate fastening members by said actuator;

wherein the processing assembly is configured to estimate a tension of each of the elongate fastening members based on its corresponding vibration.

In an embodiment the processing assembly comprises a portable electronic device including:

a microprocessor;

a digital memory in communication with the microprocessor;

an analog to digital converter (ADC) assembly in communication with the microprocessor; and

an electronic interface under control of the microprocessor for receiving user input and displaying information to a user; wherein the digital memory stores a software product comprised of instructions for execution by the microprocessor, including:

instructions for processing a digitized signal from the ADC assembly to determine a characteristic frequency thereof;

instructions for processing the characteristic frequency to thereby estimate a corresponding tension of a predetermined elongate fastening member.

In an embodiment the digital memory stores instructions for a user to select the predetermined elongate fastening member by use of the electronic interface.

In an embodiment the digital memory stores instructions for operating the electronic interface to prompt the user to enter physical parameters of an elongate fastening member. In an embodiment the digital memory stores instructions for operating the electronic interface to prompt the user to enter one or more of mass, length and material of the elongate fastening member.

According to another aspect of the present invention there is provided a method for estimating tension in an elongate fastening member comprising:

operating an electronic processor to analyze a vibration from the elongate fastening member to determine a characteristic frequency thereof; and

operating the electronic processor to estimate the tension based on the characteristic frequency and one or more physical properties of the elongate fastening member.

In an embodiment the characteristic frequency comprises a fundamental frequency of vibration.

In an embodiment the one or more physical properties include, mass per unit length of the fastener and vibrational length of the fastener.

In an embodiment operating the electronic processor to analyze the vibration from the elongate fastening comprises applying a fast Fourier transform (FFT) to the vibration.

In an embodiment the method includes operating the electronic processor to form a Harmonic Product Spectrum from an output of the FFT to thereby determine the characteristic frequency as a fundamental frequency of the vibration.

In an embodiment the method includes operating the electronic processor to estimate the tension based on a relationship between tension and frequency according to Mersenne's law.

In an embodiment the method includes operating the electronic processor to cause an actuator assembly responsive to said processor to elicit the vibration from the elongate fastening member by striking. In an embodiment the actuator assembly comprises a transducer and the method includes operating the electronic processor to cause the transducer to sweep through a range of range of frequencies for eliciting a sympathetic vibration from the elongate fastening member.

In an embodiment the method includes operating the electronic processor to cause a tensioning assembly to tension the elongate fastener to acquire a desired tension with reference to the estimated tension.

According to another aspect of the present invention there is provided a method of estimating tension in an elongate fastener by analyzing a vibration elicited from the elongate fastener.

According to one aspect of the present invention there is provided a system for determining tension in an elongate fastening member comprising:

an actuator arranged to elicit a vibration from the elongate fastening member; and

a processing assembly configured to process the vibration and estimate the tension therefrom.

According to a final aspect of the present invention there is provided an apparatus that is configured to estimate tension in an elongate fastener by analyzing a vibration elicited from the elongate fastener.

DESCRIPTION OF FIGURES

Preferred features, embodiments and variations of the invention may be discerned from the following Detailed Description which provides sufficient information for those skilled in the art to perform the invention. The Detailed Description is not to be regarded as limiting the scope of the preceding Summary of the Invention in any way. The embodiments described herein may be better understood by reference to the accompanying figures, in which: FIG. 1 depicts a joint comprised of two adjacent workpieces in the form of flanges interconnected by an elongate fastening member in the form of a bolt that has a nut in the form of a Multi-Jack Tensioner (MJT).

FIG. 2 is a block diagram of a bolt tension monitor according to a first embodiment of the present invention, shown in use determining the tension in a bolt by processing an acoustic vibration from the bolt ehcited by it being struck.

FIG. 3 is a block diagram of a further embodiment of a bolt tension monitor according to the present invention.

FIG. 4 is a flowchart of a method according to a preferred embodiment of the present invention, which the bolt tension monitor of FIG. 3 implements.

FIG. 5 depicts a first striker assembly for eliciting a vibration from a stud/bolt.

FIG. 6 depicts a second striker assembly.

FIG. 7 illustrates a system for automatically tensioning a stud/bolt to a desired level.

FIG. 8 depicts a system for remotely checking the tension of each of a plurahty of bolts/ studs.

DETAILED DESCRIPTION

The Inventor has observed that an audible tone, i.e. a vibration in the range of human hearing, which is typically 20Hz to 20kHz, can be heard when a tensioned elongate fastener is struck. The tone changes in frequency, becoming higher and lower as the tension in the fastener is increased and decreased. Consequently the Inventor has conceived that it is possible to estimate tension in an elongate fastening member such as a stud or bolt by analyzing vibration elicited by striking the stud or bolt.

Referring now to FIG. 2, in a first embodiment of the invention there is provided a bolt tension monitor 25 for estimating tension in an elongate fastening member such as bolt 5. The bolt tension monitor 25 is a handheld device that includes a transducer in the form of microphone 27. Upon a worker 4 striking a surface of the bolt 5, or a surface securely fastened thereto, with a striker, such as mallet 6, shank 7 of bolt 5 vibrates thereby causing an audible tone or "ringing" to propagate as an acoustic wave 29 through the surrounding air. The acoustic wave 29 is picked up by the microphone 27, which is located proximal to the bolt 5 e.g. within a few centimeters, and converted into an electrical signal 31. A frequency detection assembly 33 is coupled to the microphone 27 and is arranged to determine a frequency of the vibration of the shank 7 of bolt 5 from the electrical signal 31. There are a number of possible methods for determining a fundamental frequency of vibration of the electrical signal 31. In the present embodiment the frequency detection assembly 33 includes an anti-aliasing filter 33a, that provides an analog, low pass filtered version of signal 31 to an Analog-to-Digital Converter (ADC) 33b. The digital output from ADC 33b is passed to a Fast-Fourier-Transform assembly 33c which produces magnitude values for a number of frequency bins that are passed to a Harmonic Product Spectrum (HPS) assembly 33d. The output from the HPS assembly 33d is a signal that represents the value of the fundamental frequency f₀35 of the signal 31. HPS assembly 33d is arranged to determine the fundamental frequency using a Harmonic Product Spectrum, in which the signal is repeatedly multiplied with down-sampled copies of itself, causing a large peak to occur in the frequency spectrum corresponding to the fundamental frequency. Harmonic Product Spectrum is described, for example, in. "Pitch determination of human speech by the harmonic product spectrum, the harmonic sum spectrum and a maximum likelihood estimate" in Noll, A. M. (1970) Proc. SCPC, the disclosure of which is hereby incorporated in its entirety by reference. Other methods for determining the fundamental frequency are possible too.

For example, an alternative method that does not require HPS 33d is simply to assume that the center frequency of the bin with the highest magnitude value corresponds to the fundamental frequency. However, use of the HPS may be preferable since it is not susceptible to errors caused by high magnitude harmonics. Autocorrelation may also be used as an alternative method to HPS for determining the fundamental frequency. Other methods for detecting a characteristic frequency, such as the fundamental frequency of a vibration are also known and may be used such as autocorrelation and the previously mentioned method of deeming the center frequency of the output frequency bin of the FFT with the greatest magnitude to correspond to the fundamental frequency. An autocorrelation based method for estimating fundamental frequency is described in Cheveigne and Kawahara "YIN, a fundamental frequency estimator for speech and music" in 2002 J. Acoust. Soc. Am. Vol. Ill, No. 4 April 2002, the disclosure of which is hereby incorporated in its entirety by reference. Time domain methods, for example zero crossing counting methods are also known though less preferred to frequency domain methods. In other embodiments a characteristic frequency of the elicited vibration, other than the fundamental frequency might be used for determining the tension. For example in some embodiments the characteristic frequency may be a harmonic frequency other than the fundamental frequency which is correlated to tension in the elongate fastening member.

The bolt tension monitor 25 also includes a tension value assembly 37 that is responsive to the frequency detection assembly 33 and which is arranged to process the fundamental frequency signal 35. In one embodiment of the invention the tension value assembly 37 comprises an arithmetic calculation assembly that is configured to calculate the tension T using a rearrangement of Mersenne's law. Mersenne's law is set out by the following equation:

where T is the tension (in Newtons), L is the length of the vibrating part of the elongate fastener and m is the hnear density (that is, the mass per unit length) of the length L of the vibrating part. A rearrangement of Mersenne's law that makes tension T the subject of the equation is:

T = 1m1y

As indicated in FIG. 2, the length of the vibrating part is typically the distance along shank 7 between the head 11 of the bolt 5 and the nut body 17. For example, if the length L is 0.3m, mass per meter is 10kg/ m and the vibration is 650Hz, then the tension value assembly 37 will calculate the tension T to be 4 x 10 (kg/ m) x 0.09 (m2) x 2.25xlOE6 (/ s/ s) = 425kN. For a bolt with a shank of radius 2cm (i.e. 0.02m) the cross sectional area is PI x 0.02 x 0.02 = 0.001256 square meters and thus the stress is 8.1MN/0.001256 (m2) = 338MPa.

Values such as the length of the vibrating part of the fastener, the mass per meter, and the diameter of the vibrating part, if the stress is to be calculated from the determined tension, may be input by means of user interface assembly 39. Assembly 39 typically includes a touchscreen that prompts for and receives user input for the values and passes them to the tension value assembly 37 for use in the necessary calculations that have been described. The bolt tension monitor may include a memory 41 containing length and mass per unit length values for a number of elongate fastening members. In that case the user interface assembly 39 presents screens for a user to select one of a number stored stud/bolt models and then passes the associated vibration length, mass/length and diameter parameters to the tension value assembly 37.

The tension value assembly 37 generates a signal 42 representing the calculated tension value T of the elongate fastening member at a particular time f, which may be expressed in terms of stress if the cross sectional area of the elongate fastening member has been calculated.

Finally the calculated tension or stress value is displayed on tension value display 43, which is typically an LCD screen.

In another embodiment an alternative approach to determining the tension value, which does not rely on a rearrangement of Mersenne's law is used by the tension value assembly 37. In this alternative embodiment tension values for a plurahty of frequencies of vibration for each of a number of bolts of different dimensions and/ or mass/unit length are stored in memory 41. The tension value assembly 37, on receiving the selection of the bolt/ stud model from the user interface assembly 39 then looks up the tension value that corresponds to the frequency that has been determined and the parameters for the selected bolt that have been retrieved from the memory 41.

Referring to FIG. 3, another embodiment of a bolt tension monitor 100 is depicted. The bolt tension monitor 100 comprises a specially programmed portable computational device such as a smartphone.

The bolt tension monitor 100 includes a microprocessor 103 that accesses an electronic memory 105. The electronic memory 105 includes an operating system 108 such as the Android operating system or the Apple iOS operating system, for example, for execution by the microprocessor 103.

The electronic memory 105 also includes a bolt tension software product or "App" 106 according to a preferred embodiment of the present invention. The bolt tension App 106 includes instructions that are executable by the microprocessor 103 in order for the bolt tension monitor 100 to process a vibration or "ringing" from a struck elongate fastener and present a tension or stress value to worker 4 via touchscreen interface 113. The App 106 includes a lookup table 122 of bolt/stud parameters for each of a number of bolt/ stud models. The microprocessor 103 uses the lookup table 122 to look up parameters, such as diameter and mass/unit length for a particular bolt or stud as specified by worker 4 by means of touchscreen interface 113.

The microprocessor 103 is in data communication with a plurahty of peripheral assembhes 109 to 123, as indicated in FIG. 3, via a data bus 107. The peripherals include:

A camera in the form of Lens & Capacitive Charge/ Discharge (CCD) Assembly 109 for capturing images, such as images of the fastener;

a Bluetooth communications assembly 110 for establishing paired short range radio communications with other devices;

a touchscreen interface 113 for presenting information to a human and receiving commands;

a power adaptor port and battery management assembly 119 for providing electrical power to the overall system; an audio interface 121 which includes suitable circuitry for interfacing between microphone 125 and microprocessor 103 and similarly speaker 127 and microprocessor 103;

a GPS module 117 for ascertaining geographical location; and

a WAN/ WLAN assembly 123 for establishing wireless telecommunications via antenna 129.

Consequently, the bolt tension monitor 100 is able to estabhsh voice and data communication with the voice and/ or data communications network 131 via WAN/WLAN assembly 123 and radio frequency antenna 129.

Although the bolt tension monitor 100 that is illustrated in FIG. 3 is provided in the form of a smartphone it might equally be some other computational device such as a laptop, or tablet that is programmed with App 106.

In some embodiments the bolt tension monitor 100 collects metadata, such as GPS coordinates from GPS assembly 117 at the site where it makes the tension determination. For example, the tension monitor 100 may be configured by App 106 to log the determined tension values or transfer them over the Internet to cloud server 133 along with GPS information identifying where the measurement was made and possibly images captured by Lens & CCD assembly 109, when/ if network 131 is available.

Referring now to FIG.4, there is shown a flowchart of a method according to a preferred embodiment of the present invention, which the bolt tension monitor 100 implements under the control of the instructions that are coded into the bolt tension monitor App 106.

At box 135, the microprocessor 103 operates the touch screen 113 to prompt for the worker 4 to input a unique identifier for the model of bolt/ stud or physical parameters of the bolt/ stud, i.e. vibration length, mass/ unit length and diameter. If the worker 4 inputs a unique identifier for the model of bolt/ stud then the microprocessor 103 looks up the corresponding physical parameters from the fastener lookup tables 122 in memory 105. The worker is also required to input the vibrational length L of the shank of the stud/bolt or alternatively that information or an estimate of it may be pre-stored in memory 105.

At box 137 of FIG. 4, the microprocessor 103 operates the touch screen 113 to display a prompt for a user, e.g. worker 4, to indicate that the elongate fastener is about to be struck. The worker 4 then strikes the elongate fastening member to produce the acoustic tone which is picked up by microphone 125, filtered and then digitized by audio interface 121 and recorded into memory 105.

At box 139 the microprocessor 103 processes the recorded digitized audio by performing a Fast Fourier Transform and Harmonic Product Spectrum analysis to find the fundamental frequency associated with the audio recording.

Whilst the characteristic frequency is preferably the fundamental frequency in another embodiment the characteristic frequency that is determined may be a harmonic frequency that is subsequently used to find an associated tension / stress of the elongate fastening member.

At box 141 the microprocessor 103 uses the fundamental frequency value that has been calculated at box 139 to determine the tension, or if the bolt diameter (and thus the cross sectional area) is available, the stress, in the bolt. The tension/ stress may be calculated using the rearrangement of Mersenne's law that has previously been discussed. Alternatively, it may also be calculated by extrapolating between tension values stored in a look up table in memory 105 that relate the tension for a selected bolt/ stud model to ringing frequency. At box 143 the calculated tension/ stress value is presented to worker 4 by means of touchscreen interface 113.

The bolt tension monitor may be include one or more actuators that interact with corresponding bolts/ studs to thereby elicit the vibration so that the worker 4 does not have to manually strike the bolt with mallet 6. For example, with reference to FIG. 5, an actuator 150 may comprise a rotatable member 151, driven by a motor 153. A number of spherical strikers 155 are attached to the rotatable member 151 for striking the elongate fastening member, e.g. bolt or stud 5, to thereby elicit the vibration 29 in response to a control signal 152, such as a short range wireless communications signal such as a Bluetooth protocol signal from Bluetooth Comms assembly 110, or a wired communication signal. Alternatively, FIG. 6 depicts an alternative actuator assembly in the form of a striking actuator 160 that locates above bolt/ stud 5 and which includes an actuator 161. Actuator 161 rotates an elongate fastening member in the form of flipper 162 so that a peripheral portion of the flipper follows a circular path as indicated by the arcuate arrow. The flipper, at position "a", wherein its peripheral portion interferes with the striker, hits the striker in the form of ball 163 upwardly in channel 167 of housing 169 (as indicated by the vertical arrow) so that it compresses biasing spring 165. As the flipper rotates it comes to a position "b" clear of the striker so that the striker is released and urged by spring 165 down to strike the bolt/ stud 5 to which the ball 163 is attached to thereby elicit acoustic wave 29.

Alternatively, the actuator assembly may comprise a transducer, for example a piezo electric transducer which may be coupled to audio interface 121 and which, produces vibrations that microprocessor 103 is programmed to sweep across a range of frequencies to sympathetically elicit the vibration of the elongate fastening member.

A further alternative is that the actuator may comprise a rotatable wheel with a surface, for example a ribbed surface, which rubs against the elongate fastening member to thereby ehcit the vibration.

With reference to FIG. 7, the bolt tension monitor 100 may be provided in combination with a torqueing assembly 170 for torqueing a nut 15 of the elongate fastener 5 to adjust tension therein. For example the torqueing assembly 170 may be a remotely controllable power driver for driving an ordinary nut or, if an MJT is used, the torqueing assembly may be specially designed to simultaneously apply torque to a plurahty of jackbolts of an MJT as described in international patent apphcation No. PCT/US2018/057923 to the present applicant. In either case the torqueing assembly 170 is responsive to the tension monitor 100 for attaining a desired tension in the elongate fastening member. For example, as shown in FIG. 7, torqueing assembly 170 is attached to the MJT and placed in communication, either wirelessly or with a cable, with the tension monitor 100. A striking actuator 160 is also attached to the nut 15 and similarly placed in communication with the tension monitor 100. The tension monitor then operates the striking actuator 160 to elicit an acoustic wave 29 in the form of a ringing vibration from the bolt/ stud 5. The tension monitor 100 determines the tension in the bolt from the vibration as previously explained. If the determined tension is less than a desired value then the tension monitor operates the torqueing assembly 170 to tighten the nut (e.g. by torqueing the jackbolts) and thus increase the tension in the bolt 5. The monitor 100 repeats the process until the desired tension is achieved.

Referring now to FIG. 8 there is illustrated a system 200 for monitoring tensions in each of a plurality of elongate fastening members 5a,...,5n. Tension monitoring system 200 comprises a plurality of striking actuators 201a,..,201n each one arranged to elicit a vibration from a corresponding one of the elongate fastening members 5a,.. ,5n. A processing assembly in the form of a server 260 that executes a software program 244 is coupled to the plurality of wi-fi enabled actuators 201a,...,201n via wireless router 220. The software program 244 includes instructions for server 260 to command each of the actuators 201a,...,201n to operate in order to elicit a vibration from its associated elongate fastening member 5a,.. ,5n. Each actuator 201a,.. ,201n is paired with a corresponding transducer assembly 203a,.. ,203n that is able to sense the elicited vibration, convert it into an electrical signal and transmit it, for example by wi-fi to the central router 220.

The server 260, which is in data communication with router 220 via data network 212, is therefore able to periodically check the tension in each of the elongate fasteners 5a,...,5n based on the tension that is determined from the vibration signal received back from the transducers 201a,...,201n. If the tension in an elongate fastener 5 is outside of a preset range then the server 260 can send an alarm message to an administrator 216 and/ or directly to worker 4 via his/her smartphone running App 6 and configured as tension monitor 100. The bolt/ stud 5 can then be checked for correct tension by worker 4 and tightened as necessary.

Alternatively, in some embodiments wi-fi enabled torqueing assemblies, such as torqueing assembly 170 of Figure 7, may be attached to the nuts/MJTs of the bolts/ studs 5 so that the server 260 can remotely command the torqueing assemblies to operate until the required level of tension is attained in each bolt/ stud 5. The tension values and other information that is collected can be stored in database 214. Actual recordings of the vibrations can be stored in file storage repository 218 if desired. Any documents cited herein are incorporated herein by reference, but only to the extent that the incorporated material does not conflict with existing definitions, statements, or other documents set forth herein. To the extent that any meaning or definition of a term in this document conflicts with any meaning or definition of the same term in a document incorporated by reference, the meaning or definition assigned to that term in this document shall govern. The citation of any document is not to be construed as an admission that it is prior art with respect to this apphcation.

While particular embodiments have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, numerous equivalents to the specific apparatuses and methods described herein, including alternatives, variants, additions, deletions, modifications and substitutions. This apphcation including the appended claims is therefore intended to cover all such changes and modifications that are within the scope of this application.

Claims

CLAIMS:

1. A tension monitor for estimating tension in an elongate fastening member tensioned to secure one or more workpieces, said monitor comprising:

a transducer for converting a vibration elicited from the elongate fastening member into an electrical signal;

2. The tension monitor of claim 1, wherein the frequency detection assembly includes an analog to digital converter for digitizing the electrical signal and a fast Fourier transform (FFT) assembly responsive thereto.

3. The tension monitor of claim 2, wherein the frequency detection assembly includes a Harmonic Product Spectrum (HPS) assembly responsive to the FFT assembly for determining the frequency as a fundamental frequency of the vibration.

4. The tension monitor of any one of claims 1 to 3, wherein the tension value assembly is arranged to produce the signal representing the tension value of the elongate fastening member according to a relationship of tension-to-frequency based on Mersenne's laws.

5. The tension monitor of any one of claims 1 to 3, wherein the bolt tension monitor includes, or is arranged to remotely access, an electronic memory containing tension values for a plurality of frequencies of vibration for each of a number of bolts of different dimensions and/ or masses.

6. The tension monitor of any one of claims 1 to 3, wherein the bolt tension monitor includes a memory containing length and mass per unit length values for a number of elongate fastening members.

7. The tension monitor of any one of the preceding claims including an actuator assembly for interacting with the elongate fastening member to thereby elicit the vibration.

8. The tension monitor of claim 7, wherein the actuator assembly comprises a rotatable member.

9. The tension monitor of claim 8, wherein the rotatable member is arranged to strike the elongate fastening member to thereby elicit the vibration.

10. The tension monitor of claim 8, wherein the actuator assembly includes a striker and a biasing member arranged to bias the striker against the elongate fastening member.

11. The tension monitor of claim 10, wherein an arc of a path of a peripheral portion of the rotatable member interferes with the striker for forcing the striker against the biasing member.

12. The tension monitor of claim 8, wherein the actuator comprises a transducer for producing vibrations across a range of frequencies to sympathetically elicit the vibration of the elongate fastening member.

13. The tension monitor of any one of the preceding claims including a tensioning assembly for tensioning the elongate fastener to adjust tension therein wherein the tensioning assembly is responsive to the tension value assembly for attaining a desired tension in the elongate fastening member.

14. A system for monitoring tensions in each of a plurality of elongate fastening members, the system comprising:

a processing assembly coupled to the plurality of actuators for operation thereof; the processing assembly being responsive to vibrations ebcited from each of the plurahty of elongate fastening members by said actuator;

15. The system of claim 14, wherein the processing assembly comprises a portable electronic device including:

a microprocessor;

a digital memory in communication with the microprocessor;

16. The system of claim 15, wherein the digital memory stores instructions for a user to select the predetermined elongate fastening member by use of the electronic interface.

17. The system of claim 15 or claim 16, wherein the digital memory stores instructions for operating the electronic interface to prompt the user to enter physical parameters of an elongate fastening member.

18. The system of claim 17, wherein the digital memory stores instructions for operating the electronic interface to prompt the user to enter one or more of mass, length and material of the elongate fastening member.

19. A method for estimating tension in an elongate fastening member comprising: operating an electronic processor to analyze a vibration from the elongate fastening member to determine a characteristic frequency thereof; and

20. The method of claim 19, wherein the characteristic frequency comprises a fundamental frequency of vibration.

21. A method according to claim 19, wherein the one or more physical properties include, mass per unit length of the fastener and vibrational length of the fastener.

22. The method of one of claims 19 to 21 wherein operating the electronic processor to analyze the vibration from the elongate fastening comprises applying a fast Fourier transform (FFT) to the vibration.

23. The method of claim 22, including operating the electronic processor to form a Harmonic Product Spectrum from an output of the FFT to thereby determine the characteristic frequency as a fundamental frequency of the vibration.

24. The method of any one of claims 19 to 23, operating the electronic processor to estimate the tension based on a relationship between tension and frequency according to Mersenne's law.

25. The method of any one of claims 19 to 24, including operating the electronic processor to cause an actuator assembly responsive to said processor to elicit the vibration from the elongate fastening member by striking.

26. The method of claim 25 wherein the actuator assembly comprises a transducer and wherein the method includes operating the electronic processor to cause the transducer to sweep through a range of range of frequencies for eliciting a sympathetic vibration from the elongate fastening member.

27. The method of any one of claims 19 to 26 including operating the electronic processor to cause a tensioning assembly to tension the elongate fastener to acquire a desired tension with reference to the estimated tension.