WO2013057283A1

WO2013057283A1 - Force monitoring for jetting equipment

Info

Publication number: WO2013057283A1
Application number: PCT/EP2012/070807
Authority: WO
Inventors: Willem Griffioen
Original assignee: Plumettaz Holding SA
Current assignee: Plumettaz Holding SA
Priority date: 2011-10-21
Filing date: 2012-10-19
Publication date: 2013-04-25
Anticipated expiration: 2014-04-21

Abstract

A method for monitoring an axial force Fp in a strand, whereby the axial force is applied along an axial direction of the strand, the method comprising: - guiding the strand through an Ω-Ιοορ, whereby the strand is first guided at a first location, the strand is secondly guided through a measuring site located at a second location, and the strand is thirdly guided at a third location, the Ω-Ιοορ being defined between the first location and the third location, the Ω-Ιοορ corresponding to a curved trajectory connecting the first location and the third location, - measuring a transversal force Fs that the strand exerts at the measuring site, - calculating a value of the axial force (Fp) as a function of the measured transversal force (Fs).

Description

Force monitoring for jetting equipment

Technical field

Background

Cable jetting

Cable jetting is a commonly known technology for installing a cable, typically of the kind as used in telecommunications, in a duct, as is for example described in patent publication US 4.850.569, wherein the cable is installed into the duct by means of combined pushing and blowing with a jetting equipment. Although forces exerted on the cable are much lower than with winch pulling, there is still a risk that the cable buckles excessively (this is also known as "kinking") when being pushed with the jetting equipment, especially for a small and flexible cable.

Cable floating

Cable floating is another commonly known technique for installing a cable in a duct. Instead of air, now water is used. This technique is not only used for cables used in telecommunication, but also for energy cables. In the latter situation, also a piston, powered by the pressurised water, is often used in combination with floating. Forces exerted on the cable can be very high here, and many users would like to record the pushing force during installation of the cable.

Buckling detection in blown fibre tools

A blown fibre tool for use in a blown fibre method may typically comprise a mechanical drive and a pressure chamber, whereby the mechanical drive may or may not be inside the pressure chamber. The pressure chamber is positioned at an extremity of the duct or tube. In the blown fibre method such as the one described in patent publication EP 0108590, a flexible fibre unit is fed and introduced into the tube with the help of an air flow. Specifically for the use with the blown fibre tool, devices have been developed for detecting buckling of the fibre, which are for example described in patent publication EP 0253636 A1 in the name of British Telecom wherein the fibre adopts a "banana-shape", in patent publication EP 1015928 A1 to British Telecom wherein the fibre adopts a more pronounced convex curve that can be qualified as "u-shape", and in International publication WO 2010/020656 A1 to Plumettaz wherein the fibre also adopts a "u- shape". These devices output a signal that may be used to trigger a braking of the feeding of the fibre unit when buckling is detected and keep a pushing (or compressive) force on these fibre units in the detector zone below zero. The feeding force is applied along an axial direction of the fibre unit. The feeding force is needed to pull the fibre unit typically from a reel and pull or push the fibre unit into a pressure chamber, whereby the pulling occurs when the mechanical drive is placed inside the pressure chamber, and the pushing occurs when the mechanical drive is placed outside the pressure chamber.

Further issues concerning cables

Returning now to specific issues concerning cables, it shall be noted that the aforementioned jetting, as described in patent publication US 4.850.569, is a synergy of blowing and pushing, still active in the duct, which considerably increases the length that can be installed with respect to blowing only. For this the cable must possess some stiffness, which is the case for most cables.

It appears that installers or operators of a cable find it more convenient to work with a specification of the maximum force, i.e., the pushing force that may be experienced by the cable under installation, even rather monitoring or a recording this force as a function of installed length.

Various manners of maintaining the pushing force of the jetting equipment below the maximum specified pushing force are known, and 3 examples are briefly discussed here under.

In a first example the installers or operators determine a maximum value of the pushing force as it is produced by a specific setting of their jetting equipment, at the start of an installation, e.g., by performing a so-called "crash test" whereby the maximum value is exceeded and thus the specific setting determined. Thereafter the installation is done with the settings of the jetting equipment remaining below the specific setting which corresponds to the maximum value.

In a second example, the information from the power consumption of the motor which drives the feeding of the cable in the jetting equipment is used as an estimate of the pushing force on the cable. The pushing force is maintained below the maximum value by controlling the power consumption of the motor.

In a third example a force monitoring device built on a jetting equipment as described in patent publication US 5.813.658 to Arnco is used. The cable feeder of the jetting equipment uses tractor type drive belts and compressed air to propel cable through a conduit. As described in the abstract of this publication, the axial force applied to the cable is sensed with a strain gauge near the conduit or a pressure detector in a hydraulic system powering the drive belts. The latter is used to propel cable through a conduit. The radial force applied to the cable is limited by a calibrated spring.

Problems encountered in prior art

The buckle detectors described in previously mentioned EP 0253636 A1 , EP 1015928 A1 and WO 2010/020656 A1 detect buckling only, the detection being made at about zero force on the cable. The buckle detectors do not allow to detect the axial and/or any other forces applied on the cable as is the case in real life with jetting equipment when the cable is being pushed. Furthermore the pushing force is the parameter which the installers or operators of a cable wish to work with while the cable is under installation. In these prior art buckle detectors, the buckling occurs when the axial force in the cable in the detector zone just starts becoming compressive (pushing).

In the first example described in the previous section here above, setting the pushing force of the jetting equipment to a maximum value, or in the second example where the pushing force is obtained as a feedback from the pushing motor power consumption, problems occur when a relatively large force is needed to pull the cable from the reel. In that case much of the force produced in the jetting equipment is used for the pulling and becomes less available for inserting the cable. As the force to pull the cable from the reel may vary a lot, this makes the methods from the first and the second examples very inaccurate. A similar problem occurs when considering the force required to insert the cable into the pressure chamber of the jetting equipment. This force may be relatively high compared to the maximum allowed pushing force, especially for flexible cables (or microducts) and bundles of cables (or microducts). As the force to insert the cable into the pressure chamber varies with pressure, it is difficult to select a proper maximum drive force on the equipment, that is constant.

In the third example, i.e., the Arnco patent, the force monitor only measures the axial force on the cable, not when it buckles. Also the described system is inaccurate because the moveable part that gives the force signal is attached to the duct. It will only work accurately when the duct makes a flexible loop or when the jetting equipment is placed on wheels on a horizontal and smooth floor.

Summary of invention

The invention provides a solution to the problems encountered in prior art as described hereafter.

In a first aspect the invention provides a method for monitoring an axial force (Fp) in a strand, whereby the axial force is applied along an axial direction of the strand. The method comprises guiding the strand through an Ω-Ιοορ, whereby the strand is first guided through an entrance guide located at a first location, the strand is secondly guided through a measuring site located at a second location, and the strand is thirdly guided through an exit guide located at a third location, the Ω-Ιοορ being defined between the first location and the third location, the Ω-Ιοορ corresponding to a curved trajectory that departs from a straight line connecting the first location and the third location and returns to the straight line, the second location is defined on the Ω-Ιοορ as being an extremum of the Ω-Ιοορ. The method further comprises measuring a transversal force (F_s) that the strand exerts at the measuring site, a direction of the transversal force being perpendicular to a tangential line to the Ω-Ιοορ passing through the second location, and calculating a value of the axial force (F_p) as a function of the measured transversal force (F_s).

In a first preferred embodiment of the invention the axial force is a pushing force.

In a second preferred embodiment of the invention the axial force is a pulling force.

In a third preferred embodiment of the invention, the relationship between the measured transversal force and the pushing force is defined in following formula:

wherein F^, is the transversal force, F_pmh is the pushing force, B is a stiffness of the strand, h is a value of the distance between the second location and the straight line connecting the first location and the third location, h is a base distance separating the first location from the third location.

In a fourth preferred embodiment the relationship between the measured transversal force and the pushing force is defined in following formula:

F = /r 8/L

71 b wherein F_s is the transversal force, F_push is the pushing force, h is a value of the distance between the second location and the straight line connecting the first location and the third location, b is a base distance separating the first location from the third location and F₀ is a transversal force when the pushing force is zero.

In a fifth preferred embodiment the relationship between the measured transversal force and the pulling force is defined in following formula:

wherein F, is the transversal force, F_puU is the pulling force, B is a stiffness of the strand, h is a value of the distance between the second location and the straight line connecting the first location and the third location, b is a base distance separating the first location from the third location.

In a sixth preferred embodiment the relationship between the measured transversal force and the pulling force is defined in following formula:

1 p - p. + A i p„

π b wherein F, is the transversal force, F_puU is the pulling force, h is a value of the distance between the second location and the straight line connecting the first location and the third location, b is a base distance separating the first location from the third location and F₀ is a transversal force when the pulling force is zero.

In a second aspect, the invention provides a device for monitoring an axial force (F_p) in a strand, whereby the axial force is applied along an axial direction of the strand. The device comprises a guiding means for guiding the strand through a Ω-shaped loop, whereby the guiding means comprises a first guiding means for firstly guiding the strand through an entrance guide located at a first location, a second guiding means for secondly guiding the strand through a measuring site located at a second location, and a third guiding means for thirdly guiding the strand through an exit guide located at a third location. The Ω-Ιοορ is defined between the first location and the third location, the Ω-Ιοορ corresponding to a curved trajectory that departs from a straight line connecting the first location and the third location and returns to the straight line. The second location is defined on the Ω-Ιοορ as being an extremum of the Ω-Ιοορ. The device further comprises a force measuring means for measuring a transversal force that the strand exerts at the measuring site, a direction of the transversal force being perpendicular to a tangential line to the Ω-Ιοορ passing through the the second location, and a calculating means for calculating a value of the axial force as a function of the measured transversal force.

In a third aspect, the invention provides a device for monitoring an axial force ( F_p) in a strand, whereby the axial force is applied along an axial direction of the strand in order to push the strand into a duct which may be connected to an output opening of the device. The device comprises a guiding means for guiding the strand through a banana-shaped-loop, whereby the guiding means comprises a first wall, a second wall which is positioned relative to the first wall to make an angle with the first wall which has a value that lies in the range between 90° and 180°, and positioned inside the device such that it is substantively parallel to an axial direction of the duct at the output opening of the device, and an entrance guiding means for guiding the strand through an entrance opening of the device such that the strand may be directed to slide against the first wall in direction towards the second wall and towards the output opening of the device. The banana-shaped-loop being defined between the entrance opening and the output opening, the banana-shaped-loop corresponding to a curved trajectory. The device further comprises an optical array sensor to measure a change of the banana-shape inside the device, and a calculating means for calculating a value of the axial force as a function of at least the measured change of the banana- shape and a stiffness of the strand.

In a seventh preferred embodiment of the invention, the calculated value of the axial force is recorded. In an eighth preferred embodiment of the invention each of the first guiding means and the third guiding means comprises a double set of wheels which force the strand to align on parts of the Ω-Ιοορ which respectively pass at the first location and the third location.

In an ninth preferred embodiment the first guiding means and the third guiding means further comprise springs that are mounted in a manner that each double set of wheels presses on the strand.

In a tenth preferred embodiment the first guiding means and the third guiding means further comprise means that have an effect to press on the strand by pneumatic, hydraulic, electric, magnetic, or gravity action.

In a fourth aspect, the invention provides a pulling equipment for installing a strand, comprising the device according to the second or the third aspect.

In a fifth aspect, the invention provides a pushing equipment for installing a strand, comprising the device according to the second or the third aspect.

In a sixth aspect, the invention provides a jetting equipment for installing a strand, comprising the device according to the second or the third aspect.

In a seventh aspect, the invention provides a floating equipment for installing a strand, comprising the device according to the second or the third aspect.

Brief description of the figures

Figure 1 is a schematic illustration of a preferred embodiment of the invention; Figure 2 schematically illustrates an example of the value F_s of the transversal force calculated as a linear function of the value F_p of the pushing force;

Figure 3 and 4 schematically illustrate a device for monitoring a pushing force in a strand according to a further preferred embodiment of the invention;

Figure 4a schematically illustrates a device for monitoring a pushing force in a strand according to an other preferred embodiment of the invention;

Figure 5 schematically illustrates the device from figure 3 or 4 as used together with a jetting equipment for a cable installation;

Figure 6 schematically illustrates an alternative preferred embodiment of a device for monitoring a pushing force in a strand with a jetting equipment for a cable installation.

Description of preferred embodiments

The invention will be better understood through the description of preferred embodiments that will be given in the present section with reference to the figures 1 -6, whereby same reference numbers are used throughout the description to refer to similar features that are illustrated in more than one figure.

In the following the term strand will be used to designate in a generic manner a relatively thin length of something such as for example a cable, an optical fibre, without being limited thereto.

Also in the following examples of preferred embodiments mention will be made of a jetting equipment used to introduce the strand into a tube. However the invention is not limited to be used with a jetting equipment and may well be used for other types of installations than a jetting equipment. Also in the following the preferred embodiments relate to devices for monitoring an axial force in a strand. This axial force may in fact be either a pushing force or a pulling force. For reasons of simplicity the description mainly refers to the pushing force F_P . It is however understood that this can be read to an axial force or a pulling force too (F_P will be negative as compared to the pushing force, when in fact F_P is a pulling force).

Figure 1 is a schematic representation of a device 101 for monitoring a pushing force F_P in a strand 100 in form of a buckle sensor, according to the invention. The device is preferably placed in the pressure chamber of the jetting equipment (both chamber and jetting equipment are not shown), but could in a different embodiment also be used in other parts of the jetting equipment.

The strand 100 is guided through a Ω-Ιοορ, which is fixed at its ends and has a fixed amplitude, i.e., parts of the strand at extremities of the Ω-Ιοορ are kept aligned on a straight line, but are free to move axially. In order to guide the strand 100 in this manner, it is first guided through an entrance guide 102 located at a first location 103 of the device 101 . The strand 100 is secondly guided through a measuring site 104 located at a second location 105, and thirdly guided through an exit guide 106 located at a third location 107 of the device 101 .

The Ω-Ιοορ through which the strand evolves is further defined between the first location 103 and the third location 107, and corresponds to a curved trajectory that departs from the straight line, i.e., the trajectory departs from the x- axis that connects the first location and the third location, and the trajectory then returns to the straight line.

Although for the present invention the name "Ω-Ιοορ" is used, this in fact is a similar shape as the "u-shape" known from prior art, especially when considering the loop in the measuring site 104. However, in the present invention, i.e, for the "Ω-Ιοορ", the guiding at the first location 103 and at the third location 107 results in the extremities of the loop being aligned on the straight line, more in the fashion of an "Ω" than for the prior art methods. The device 101 is enabled to measure a value of the transversal force F_s that is exerted by the strand 100 at the measuring site 104. The second location 105 at which the measuring site 104 is positioned corresponds to an extremum in the Ω-Ιοορ. If for the sake of discussion we consider the x-axis as a lower horizontal reference and define that the Ω-Ιοορ is located above with respect to the x-axis, then the second location 105 may also be called for most of the cases the top of the Ω-Ιοορ.

The transversal force F_s has a direction which is perpendicular to a tangential line (not shown in figure 1 ) to the Ω-Ιοορ passing through the second location.

Once the value F_s of the transversal force has been measured, it may be used to calculate a value F_p of the pushing force.

In the embodiment of figure 1 , the equation binding the value F_s of the transversal force and the value F_p of the pushing force is as follows:

. . _P _ 3hB 48/? p

equation 1 ^{Fl ~} i/if ^~ Wb ^Fp wherein B is a stiffness of the strand, h is a value of the distance between the second location and the straight line connecting the first location and the third location, h is a base distance separating the first location from the third location. The values h and b may typically be understood as parameters of the Ω- loop.

The stiffness B of the strand may either be known, or perhaps obtained from a calibration measurement to be made at zero pushing force, i.e., when

Fp = 0 , when closing the device 101 at the beginning of the installation. The device 101 is closed after preparation for the installation has been made, including for example a positioning of the strand 100 inside the open device 101 . Note that as already mentioned herein above, also a pulling force can be measured. For this purpose, the same equation 1 can be used, whereby the pulling force appears as a negative pushing force F_p.

The value F), of the pushing force may then obtained by simply reorganising equation 1 in order to have F_p alone on one side of the equal sign, and using the measured values and parameters of the Ω-Ιοορ in the equation.

A simplified approach which completely eliminates the need of determining the stiffness B is just to use the following formula in equation 2, wherein F_Q = F, when F_p = 0 , when closing the device 101 at the beginning of the installation: n 48/?

equation 2 _s - ₀ - ^ ^'Ί

(Again it is noted that also a pulling force can be measured. For this purpose, the same equation 2 can be used, whereby the pulling force appears as a negative pushing force F_p)

Figure 2 schematically illustrates an example of the value F_s of the transversal force calculated as a linear function of the value F_p of the pushing force according to equation 1 . The resulting line is represented as a solid line.

Both s and F_p are given on the respective y and x axis in Newton. In this example the strand is a 4 mm diameter unitube cable with stiffness

B = 0, 03 Nm² in a Ω-Ιοορ with b = 150 mm and h = 2 mm . The graph in figure 2 further illustrates with the dashed line a curve obtained through numerical simulation. This curve represents values which are closer to the real values but requires more computational power to obtain than the linear function approximation.

The linear function approximation allows to calculate the value F_p of the pushing force from the value F_s of the transversal force. It can be integrated in software programmed in the jetting equipment to provide the value F_p of the pushing force at all times. Also a cable stiffness calibration measurement procedure as mentioned herein above may be integrated in the software to easily determine the stiffness B of the cable.

The software may easily be provided with further functions such as for example a capability to make decisions about what the maximum pushing force will be for pushing the cable into the duct, based on cable diameter, cable stiffness and duct diameter.

To be very precise, it should be noted that equation 1 constitutes an approximation, which for the example in figure 2 is good within 8% of the full scale, on the range between -200 N and 200 N pushing force. However a sensor on the measuring site is normally not intended to be used over that full range for this type of relatively small and flexible cable. In practice the range between -50 N and 50 N pushing force will be used for this cable, and the approximation will be good within 1 %. For larger cables and larger forces, the same quality of approximation remains.

Figures 3 and 4 schematically illustrate a device 303 for monitoring a pushing force in a strand 100 according to a preferred embodiment of the invention.

In figure 3 the strand 100 is a cable having a diameter of 4 mm. In figure 4 the strand 100 is a cable having a diameter of 16 mm. In the following the terms strand and cable will be used to designate the same feature with the reference 100.

In figure 3 the device 303 is shown in a side view 300, a right end view 302 and a bottom view 301 .

In figure 4 the device 303 is shown in a side view 400 and a right end view

402. In both figures 3 and 4 the device 303 is located inside a pressure chamber

305.

Further, in both figures 3 and 4 a first guiding means 102 and a third guiding means 106 comprise each a double set of wheels which force the cable 100 to be straight when guiding the cable through the device 303. This has a beneficial effect on the measurement of the stiffness in the calibration measurement procedure. The double set of wheels also enable to work with a cable having an intrinsic curvature.

As can be seen by comparing figure 3 and figure 4, the overall design of the device 303 is made such that the cable 100 remains substantively on a same curved trajectory, the Ω-Ιοορ, whereby a straight line (not shown in figures 3 and 4) passing through the centre of the cable 100 at the first guiding means 102 and the centre of the cable 100 at the third guiding means 106 remains positioned in a centred manner in the device 303 for different cable diameters. Springs 304 that keep the cable 100 pressed between the wheels supply more force for cables with a larger diameter, i.e., the cable having 16 mm diameter experiences a higher pressing force than the cable having 4 mm diameter. This is beneficial because cables with a larger diameter have also a larger stiffness and require more force to being bent in the Ω-Ιοορ. Since cables with a larger diameter are usually specified to withstand higher sidewall forces than the cable with smaller diameter, the former can withstand the higher pressing force without being damaged.

It shall be noted that the present invention can also be used with other means to keep the cable pressed between the wheels, e.g., pneumatic, hydraulic, electric or magnetic means. It is even possible to just use a weight for this. The magnitude of the pressing force shall again be sufficiently large to keep the cable in the required Ω-shape, and not exceeding the maximum sidewall forces specified for the cables. In figures 3 and 4, the arrows departing from the circumference of the wheels in a direction perpendicular to the straight line are representative of normal forces exerted from the respective wheels on the cable. When comparing the length of the arrows, a longer arrow indicates a higher force exerted.

Figures 3 and 4 also each show the second guiding means 104 which is combined with a force measuring means for measuring the transversal force that the cable exerts in a direction perpendicular to the straight line.

The value of the transversal force as measured is fed to calculating means (not shown in figures 3 and 4) that calculates the value of the pushing force as explained herein above in connexion with figures 1 and 2.

In the preferred embodiment, the parameters of the Ω-curve are selected such that, for the range of cables used in the device and the range of axial forces applied to those cables, the cable is always pressing down on the wheel at the second guiding means 104, i.e. resulting in a counter-acting transverse force Fs from the force sensor, as shown in Figures 3 and 4. However, it is also possible that aforementioned parameters cannot be selected. In Figure 4a the situation is shown that the pushing force becomes such large that the cable has crossed to the upper part of the second guiding means 104. For this reason here another wheel and a force sensor have been mounted at said upper part. Here the transverse force points in the other direction, and appears as a negative number in the formulas. This situation can also be recognised in Figure 2, right of the point where the line has passed the x-axis.

Figure 5 schematically illustrates the device from figure 3 or 4 as used together with a jetting equipment for a cable installation. The cable 100 is provided from roll 500 and jetted into duct 501. The pushing force F,. is exerted on the cable by cable drive belt 502, together with pressure chamber 305, called cable jetting means. The device 303 is positioned inside pressure chamber 305 between the cable drive belt 502 and the entrance of the duct 501 . In the preferred embodiments, the force sensor is placed inside the pressure chamber, when used with jetting (or floating) equipment. In this case the axial force experienced by the cable is measured at the location where it matters most: it is inside the duct that the cable can buckle; buckling outside the pressure chamber can be avoided when placing the pressure chamber sufficiently close to the drive mechanism of the pusher. However, the present invention is not limited to such use alone. The force sensor can also be placed outside said pressure chamber. In such a case an estimate of the axial force experienced by the cable inside the pressure chamber can be made by correcting for the pressure drop over the cross-sectional area of the cable.

Alternatively a further preferred embodiment of a device 600 for monitoring a pushing force in a strand / cable 100 is schematically illustrated together with a jetting equipment in figure 6. In device 600, the cable 100 is guided on a banana- shaped-loop through the device 600. A sidewall force of the cable 100 on the inner curve of the "banana" may be used, but is not required here. Again the pushing force F,> is exerted on the cable 100 by cable jetting means. The device 600 is positioned between the cable drive belt 502 and the entrance of the duct 501 , the latter being connected to an output opening 504 of the device 600. The device 600 comprises guiding means including a first wall 505 and a second wall 506. The second wall 506 is positioned relative to the first wall 505 to make an angle 507 with the first wall, which has a value that lies in the range between 90° and 180°. Furthermore the second wall 506 is positioned inside the device 600 such that it is substantively parallel to an axial direction of the duct 501 at the output opening 504 of the device 600. An entrance guiding means 508 for guiding the cable 100 through an entrance opening of the device 600 allows the cable 100 to be directed to slide against the first wall 505 in direction towards the second wall 506 and towards the output opening 504. Hence the banana-shaped- loop is defined between the entrance opening and the output opening, and corresponds to a curved trajectory. An optical array sensor 503 measures the change in position of the cable 100 inside the device 600. The change of position may be calculated to the pushing force and integrated in software programmed in the jetting equipment (calculating means not illustrated in figure 6). The calculation may require the value of the cable stiffness as a parameter. In this embodiment, if the cable stiffness is not known, it must be measured in a separate test, e.g., with a 3-point bending test from IEC 60794-1 -2 ed.2/FDIS OPTICAL FIBRE CABLES - Part 1 -2: Generic specification - Basic optical cable test procedures".

Also, the software can make an estimate, based on cable diameter. Furthermore the cable stiffness can be obtained by calibration of the equipment. For this, the equipment can be run at known maximum pushing force while stopping the cable close to the equipment, e.g. by closing the duct. Also a known counterforce can be given to the cable close to the equipment with the mechanical drive set to a stop. To make the banana frictionless, guide wheels with ball bearings can be used.

Compared to the buckling sensors from prior art, which buckle whenever the pushing force becomes larger than zero, the method of the present invention supplies information of the pushing force, which can also be larger than zero (and shall be larger than zero for effective jetting). In the embodiment of figure 5, also the pulling force is measured.

Compared to the method disclosed in the prior art to Arnco, the method of the present invention not only measures the relevant force more accurately, avoiding systematic errors, but also buckling is recognised and can be related to cable diameter, duct (inner) diameter and cable stiffness. With the method an easy calibration of the cable stiffness can be carried out, just when closing the equipment. The equipment can give a warning or even a stop when applicable.

Claims

Clai ms

1 . A method for monitoring an axial force (F ) in a strand, whereby the axial force is applied along an axial direction of the strand, the method comprising:

- guiding the strand through an Ω-Ιοορ, whereby

the strand is first guided through an entrance guide located at a first location, the strand is secondly guided through a measuring site located at a second location, and

the strand is thirdly guided through an exit guide located at a third location, the Ω-Ιοορ being defined between the first location and the third location, the Ω-Ιοορ corresponding to a curved trajectory that departs from a straight line connecting the first location and the third location and returns to the straight line, with the extremities of the Ω-Ιοορ at the first location and the third location aligned on the straight line,

the second location is defined on the Ω-Ιοορ as being an extremum of the Ω- loop,

- measuring a transversal force (F. ) that the strand exerts at the measuring site, a direction of the transversal force being perpendicular to a tangential line to the Ω-Ιοορ passing through the second location,

- calculating a value of the axial force (F_p) as a function of the measured transversal force (F_s),

wherein if the axial force (F_p) is a pushing force (F_push), the relationship between the measured transversal force (F_s) and the pushing force (F_push) is defined in following formula:

F 3hB ASh

(b/AY n²b ^push

wherein F_s is the transversal force, F_push is the pushing force, B is a stiffness of the strand, h is a value of the distance between the second location and the straight line connecting the first location and the third location, b is a base distance separating the first location from the third location, and wherein, if the axial force (F_p) is a pulling force (F_pun), the relationship between the measured transversal force (F_s) and the pulling force (F_pun) is defined in following formula:

wherein F_s is the transversal force, F_pun is the pulling force, B is a stiffness of the strand, h is a value of the distance between the second location and the straight line connecting the first location and the third location, b is a base distance separating the first location from the third location.

2. A method for monitoring an axial force (F ) in a strand, whereby the axial force is applied along an axial direction of the strand, the method comprising:

guiding the strand through an Ω-Ιοορ, whereby

the strand is thirdly guided through an exit guide located at a third location, the Ω-Ιοορ being defined between the first location and the third location, the Ω-Ιοορ corresponding to a curved trajectory that departs from a straight line connecting the first location and the third location and returns to the straight line,

the second location is defined on the Ω-Ιοορ as being an extremum of the Ω- loop, measuring a transversal force (F_s ) that the strand exerts at the measuring site, a direction of the transversal force being perpendicular to a tangential line to the Ω-Ιοορ passing through the second location,

calculating a value of the axial force (F_p) as a function of the measured transversal force (F_s),

wherein F_s is the transversal force, F_push is the pushing force, h is a value of the distance between the second location and the straight line connecting the first location and the third location, b is a base distance separating the first location from the third location, F₀ is a transversal force when the pushing force is zero, and wherein, if the axial force (F_p) is a pulling force (F_pun), the relationship between the measured transversal force (F_s) and the pulling force (F_pun) is defined in following formula:

wherein F_s is the transversal force, F_pun is the pulling force, h is a value of the distance between the second location and the straight line connecting the first location and the third location, b is a base distance separating the first location from the third location, F₀ is a transversal force when the pushing force is zero.

3. A device for monitoring an axial force (F_p) in a strand (100), whereby the axial force is applied along an axial direction of the strand, the device comprising:

- a guiding means for guiding the strand through a Ω-shaped loop, whereby the guiding means comprises

a first guiding means (102) for firstly guiding the strand through an entrance guide located at a first location,

a second guiding means (104) for secondly guiding the strand through a measuring site located at a second location, and

a third guiding means (106) for thirdly guiding the strand through an exit guide located at a third location,

the Ω-Ιοορ being defined between the first location and the third location, the Ω-Ιοορ corresponding to a curved trajectory that departs from a straight line connecting the first location and the third location and returns to the straight line,

- a force measuring means (104) for measuring a transversal force that the strand exerts at the measuring site, a direction of the transversal force being perpendicular to a tangential line to the Ω-Ιοορ passing through the second location,

- a calculating means for calculating a value of the axial force as a function of the measured transversal force.

4. A device for monitoring an axial force (F_p) in a strand (100), whereby the axial force is applied along an axial direction of the strand in order to push the strand into a duct (501 ) which may be connected to an output opening (504) of the device, the device comprising:

- a guiding means for guiding the strand through a banana-shaped-loop, whereby the guiding means comprises

a first wall (505);

a second wall (506) which is positioned relative to the first wall to make an angle (507) with the first wall which has a value that lies in the range between 90° and 180°, and positioned inside the device such that it is substantively parallel to an axial direction of the duct at the output opening of the device; an entrance guiding means (508) for guiding the strand through an entrance opening of the device such that the strand may be directed to slide against the first wall in direction towards the second wall and towards the output opening of the device,

the banana-shaped-loop being defined between the entrance opening and the output opening, the banana-shaped-loop corresponding to a curved trajectory, - an optical array sensor (503) to measure a change of the banana-shape inside the device,

- a calculating means for calculating a value of the axial force as a function of at least the measured change of the banana-shape and a stiffness of the strand.

5. The device of claim 3 or 4, wherein the calculated value of the axial force is recorded.

6. The device of claim 3, wherein each of the first guiding means (102) and the third guiding means (106) comprises a double set of wheels which force the strand (100) to align on parts of the Ω-Ιοορ which respectively pass at the first location and the third location.

7. The device of claim 6, wherein the first guiding means and the third guiding means further comprise springs (304) that are mounted in a manner that each double set of wheels presses on the strand (100).

8. The device of claim 6, wherein the first guiding means and the third guiding means further comprise means that have an effect to press on the strand by pneumatic, hydraulic, electric, magnetic, or gravity action.

9. A device according to any one of claims 3, 6 or 7, wherein the axial force is a pushing force.

10. A device according to any one of claims 3, 6 or 7, wherein the axial force is a pulling force.

1 1 . The device of claim 9, wherein the relationship between the measured transversal force and the pushing force is defined in following formula:

wherein F_s is the transversal force, F_push is the pushing force, B is a stiffness of the strand, h is a value of the distance between the second location and the straight line connecting the first location and the third location, b is a base distance separating the first location from the third location.

12. The device of claim 9, wherein the relationship between the measured transversal force and the pushing force is defined in following formula:

wherein F_s is the transversal force, F_push is the pushing force, h is a value of the distance between the second location and the straight line connecting the first location and the third location, b is a base distance separating the first location from the third location, F₀ is a transversal force when the pushing force is zero.

13. The device of claim 10, wherein the relationship between the measured transversal force and the pulling force is defined in following formula:

14. The device of claim 10, wherein the relationship between the measured transversal force and the pulling force is defined in following formula:

Γ7 Γ7 I 48 Z 7

r_s — Γο ^ ^rr _puii

n^{^}b

15. A pulling equipment for installing a strand, comprising the device according to any one of claims 3 to 14.

16. A pushing equipment for installing a strand, comprising the device according to any one of claims 3 to 14.

17. A jetting equipment for installing a strand, comprising the device according to any one of claims 3 to 14.

18. A floating equipment for installing a strand, comprising the device according to any one of claims 3 to 12.