Method and system for checking the tension in at least one elongate body

Abstract

The invention relates to a method for checking the tension in at least one taut elongate body (105), comprising the steps of: vibrating the at least one elongate body (105), acquiring one or more images of the at least one elongate body (105) as it is vibrating by means of a camera (5), transmitting the image(s) acquired to a data processing unit, analyzing the image(s), for determining a variation in the movement of the at least one elongate body (105) over time, and calculating a tension in the at least one elongate body (105) from the determined variation over time and on the basis of at least one of the following parameters of the at least one elongate body (105): a diameter, a length, a density, a linear density, a Young's modulus. The invention also relates to a corresponding checking system (1).

Description

Method and system for controlling the tension of at least one elongated body

[0001] The invention relates to a method for controlling the tension of at least one elongated body, as well as a corresponding control system. An elongated body is understood to mean any body, wire-like, long, or thread-like, whether single-strand or multi-strand, made of any natural or artificial material, used alone or in combination; for example, any elongated body (or wire, cable, or rope) made of metal, plastic, or textiles. The invention can be applied in particular to a spoke of a spoked wheel, notably for a cycle such as a bicycle. Technical background

[0002] A spoked wheel, particularly on a bicycle, comprises a hub in its central section. The hub has a transverse shaft defining a transverse axis. A rim surrounds the central hub, and a number of spokes connect the central hub and the rim. A tire is attached to the outer circumference of the rim. The number of spokes varies depending on the type of wheel. The spokes may, for example, be arranged in two sets that connect the rim to one end of the central hub.

[0003] The spokes structurally connect the peripheral rim and the central hub, which gives the wheel rigidity and resistance to stress.

[0004] When spoke tensions are not properly adjusted, particularly in the case of uneven spoke tension, this impacts the wheel's stiffness, and can also impact the parameters of jump (radial runout), sag (axial runout), offset (centering relative to the fixings), stiffness and these parameters being crucial for the quality of the spoked wheel.

[0005] For a spoked wheel to be "properly" rigid, that is, meeting the rigidity criteria defined for use, the spokes must not be excessively tensioned, and primarily their tension must be uniform.

[0006] Contrary to the mistaken belief that the tighter the spokes, the stiffer the spoked wheel, excessive spoke tension can weaken the spoked wheel; for example, the rim can crack.

[0007] Conversely, insufficient tension on one spoke can create excessive tension on the opposite spoke, or even generate noise while pedaling due to spoke clashing. Spoke tension must be sufficient to prevent a spoke from loosening during normal use of the spoked wheel, which could lead to a localized loss of stiffness. A lack of stiffness in the spoked wheel can be particularly noticeable when pedaling hard (uphill).

[0008] The target spoke tension can vary and depends on factors such as its position on the wheel (e.g., chain or disc), the number of spokes, the angle between the spoke plate and the cross axis, the material, and the spoke's shape. For example, the closer the angle of the spoke plate to the cross axis is to 90°, the tighter the spoke tension should be.

[0009] One challenge with spoked wheels lies in applying the correct, and not excessive, spoke tension. To achieve this, spoke tension must be measured. However, this measurement is made difficult by the different spoke positions, particularly depending on the type of spoked wheel (front, rear, hub type).

[0010] One known solution is to measure beam tension using a vibro-acoustic method. However, this technology is incompatible with a production environment, as the vibro-acoustic method can be disrupted by ambient noise.

[0011] To enable application in production, a commonly used solution is to perform sampling and manual measurement with mechanical tools, such as a strain tensiometer.

[0012] Document EP2161558A1 describes a device and method for measuring the tension of the spokes of a wheel, employing a laser beam and a distance sensor or a CCD camera, to detect the vibration of a mechanically excited spoke.

[0013] However, the teaching presented in this document considers a single harmonic frequency for a beam, without taking into account the reality of the beam's vibrational frequency spectrum, which includes a fundamental frequency and several harmonics. Furthermore, this document lacks information on signal processing methods and the optical specifications that guarantee reliable measurements. Distance sensors or CCD cameras are indeed limited by their acquisition rate, processing time, and the amount of data to be processed.

[0014] An objective of the present invention is to resolve at least partially one or more of the aforementioned drawbacks by proposing an alternative solution for controlling the tension of at least one elongated body, such as a spoke of a spoked bicycle wheel.

[0015] Another objective is to enable reliable and rapid measurement of the tension in a plurality of elongated bodies, such as spokes in a spoked wheel, after the wheel has been mounted. The invention also aims to achieve the ability to control multiple elongated bodies in a timeframe compatible with production rates, for example, of spoked wheels. Yet another objective is to provide a solution that can be quickly adapted to any spoked wheel model.

[0016] To this end, the invention relates to a method for controlling the tension of at least one elongated body stretched between two fixing points, characterized in that the control method comprises the following steps: vibrating the at least one elongated body, acquiring at least one image of the at least one elongated body while it vibrates by means of a line camera, for a predefined period, the image being formed by a stacking of lines acquired by means of said camera, transmitting the at least one acquired image to a data processing unit, analyzing the at least one image, by the data processing unit, to determine a temporal evolution of a displacement of the at least one elongated body, and calculating, by the data processing unit, a tension of the at least one elongated body from the determined temporal evolution of the displacement of the at least one elongated body and on the basis of at least one parameter of the at least one elongated body among a diameter,a length, a density, a linear mass density, a Young's modulus.

[0017] This is a visual control or measurement process based on the vibrational resonance of a stretched, elongated body, for example, following an impact. The vibration is recorded visually and then analyzed, thus eliminating interference from methods such as analyzing a sound emitted by the vibration, as ambient noise could disrupt the measurement.

[0018] Such a control process can be industrialized / automated. Positioning accuracy like that required with a laser sensor, for example, is not necessary.

[0019] Precise alignment is not required for the acquisition of one or more images, which allows working on a moving system unlike an acquisition that would be done using a laser sensor, for example.

[0020] The invention also relates to a system for controlling the tension of at least one elongated body. The control system is configured to implement, at least in part, the method for controlling the tension of at least one elongated body as defined above.

[0021] The control system includes at least one element to vibrate at least one elongated body.

[0022] The control system includes at least one line camera, configured to acquire at least one image of at least one elongated body when it vibrates, for a predefined period, the image being formed by a stack of lines acquired by means of said camera.

[0023] The control system includes at least one data processing unit.

[0024] The data processing unit can be configured to receive at least one image acquired by said camera.

[0025] The data processing unit can be configured to analyze at least one image in order to determine a temporal evolution of a displacement of at least one elongated body.

[0026] The data processing unit can be configured to calculate a tension of at least one elongated body from the determined time evolution of the displacement of at least one elongated body and on the basis of at least one parameter of at least one elongated body among a diameter, a length, a density, a linear mass, a Young's modulus.

[0027] The control process and / or control system may also include one or more of the following characteristics described below, taken separately or in combination.

[0028] The control method can be implemented to measure the tension of elongated bodies forming spokes mounted in a spoked wheel, particularly for a bicycle.

[0029] This process has the advantage of being able to be automated when spoked wheels are mounted on the cycle.

[0030] Image acquisition, for example, is at a fixed frequency.

[0031] Alternatively, a variable acquisition frequency can be considered.

[0032] The process may include at least one step of acquiring lines using a line camera, for example at a fixed frequency, the image being formed by stacking the lines.

[0033] The predefined period for image acquisition(s) can be less than 1s, for example on the order of 0.1s.

[0034] The data processing unit can deduce, from the determined time evolution of the displacement of at least one elongated body, a fundamental resonance frequency and / or a harmonic frequency.

[0035] The data processing unit can calculate the voltage of at least one elongated body as a function of said inferred frequency and at least one parameter of at least one elongated body.

[0036] A frequency spectrum can be calculated from the position of an edge of at least one elongated body on at least one acquired image.

[0037] The frequency spectrum can be calculated by Fourier transform.

[0038] The fundamental resonance frequency can be obtained as the x-coordinate of the first non-zero frequency peak in the spectrum.

[0039] The data processing unit can calculate the tension of at least one elongated body according to the following formula (A): (A): , with T the voltage, f the deduced fundamental resonance frequency, d the diameter, µ the linear mass, L the free length of at least one elongated body, E the Young's modulus.

[0040] Alternatively, the data processing unit can calculate the tension of at least one elongated body according to the following formula (A'): (A') : , with T the voltage, f the deduced fundamental resonance frequency, d the diameter, µ the linear mass, L the free length of at least one elongated body, E the Young's modulus, n the rank of the harmonic.

[0041] The vibration of at least one elongated body whose tension is to be calculated is, for example, within a frequency range of approximately 100 Hz to 1 kHz.

[0042] At least one elongated body can be mounted on a support.

[0043] The said process may include at least one additional step of setting the support in motion at a constant speed, for example a rotation of the spoked wheel forming a support for elongated bodies.

[0044] At least one image acquisition step(s) can be performed while the medium is in motion.

[0045] A drift in the position of at least one elongated body in the image can be corrected by image processing.

[0046] The control process may include at least one additional image acquisition step when the medium is static.

[0047] At least one lighting element can be arranged opposite said camera.

[0048] Image acquisition can be implemented when at least one elongated body is located on a light path between said camera and the lighting element.

[0049] When the moving support is a spoked wheel, image acquisition steps can be performed over one or more revolutions of the spoked wheel.

[0050] At least one elongated body can vibrate under the effect of an element arranged near said camera, so as to strike at least one elongated body when it is between said camera and the lighting element.

[0051] The control process may include at least one step of identifying at least one elongated body whose tension is to be calculated.

[0052] The control method can be applied to a spoked wheel comprising a peripheral rim, a central hub and individual connecting spokes stretched between the peripheral rim and the central hub, the spokes being able to be distributed according to two layers which connect the peripheral rim to a respective end of the central hub.

[0053] The spoked wheel can be set in motion.

[0054] When the spoked wheel is set in rotation, each spoke can be struck successively.

[0055] The rays of the two layers can vibrate alternately.

[0056] The steps of image acquisition(s) of each spoke when it vibrates, transmission and analysis of the image(s) acquired, and calculation of the tension of each spoke can be implemented for the spokes of both sheets in one turn of the spoke wheel.

[0057] At least one lighting element can be arranged opposite said camera.

[0058] Preferably, the camera can be telecentric. For example, a linear camera has a telecentric lens.

[0059] The lighting element can be telecentric.

[0060] Thus, said camera with a telecentric lens is sensitive almost exclusively to rays emitted by telecentric lighting and very little to ambient lighting.

[0061] The element used to vibrate at least one elongated body can be arranged to strike the elongated body or bodies when it is located between the camera and the lighting element. For example, it could be a metal rod.

[0062] Other advantages and features of the invention will become clearer upon reading the following description, given by way of illustrative and non-limiting example, and the accompanying drawings, among which:

[0063] shows a tension control system as well as a spoked wheel mounted on a support for measuring spoke tension by the control system.

[0064] is a partial view of the control system and the spoked wheel according to another perspective.

[0065] shows an example of an image of a vibrating spoke of the spoked wheel acquired by means of a linear camera of the control system of Figures 1 and 2.

[0066] In these figures, identical elements bear the same reference numbers.

[0067] The following embodiments are examples. Although the description refers to one or more embodiments, this does not necessarily mean that each reference relates to the same embodiment, or that the features apply only to a single embodiment. Simple features of different embodiments can also be combined or interchanged to provide other embodiments, without departing from the scope of the invention as defined by the claims. Detailed description

[0068] Lamontre provides an example of a 100-spoke wheel, specifically for a cycle, such as a bicycle. Examples of bicycles are known but not illustrated.

[0069] The spoked wheel 100 comprises a peripheral rim 101, a central hub 103 and individual connecting spokes 105, tensioned between the peripheral rim 101 and the central hub 103.

[0070] The peripheral rim 101, for example, has a hollow structure defining a channel for receiving a tire. This peripheral rim 101 generally includes at least one valve hole (or bore) through which a valve must be able to pass.

[0071] The spokes 105 are each formed by an elongated or long-lined body, which defines for each spoke 105, a longitudinal direction and two opposite attachment ends, by which the spokes 105 are attached on one side to the central hub 103 and on the other to the peripheral rim 101.

[0072] The central hub 103 may have two axial ends. As shown in the example, the spokes 105 are arranged in two layers, with the spokes 105 of each layer attached on one side to the peripheral rim 101 and on the other side to a respective axial end of the central hub 103, forming two attachment points. By way of non-limiting example, the spoked wheel 100 may have from 24 to 32 spokes 105, for example, 28 spokes 105, arranged in two layers.

[0073] The 100 spoked wheel forms a support for the 105 spokes. According to an example embodiment, each 105 spoke can be indexed according to its positioning relative to the valve hole.

[0074] Such a spoked wheel 100 can in turn be mounted on a support 200. The support 200 allows, for example, the spoked wheel 100 to be held by its central hub 103. The support 200 notably allows the spoked wheel 100 to be rotated.

[0075] Control system

[0076] The invention relates to a control system 1 for the tension of at least one stretched elongated body, which can be applied to the measurement of the tension of one or more spokes 105 of a spoked wheel 100 as represented in the example of the.

[0077] The control system 1 can be intended to be used to measure or determine the tension of one or more spokes 105 of a spoked wheel 100, when the latter is stationary, static or on the contrary in motion.

[0078] Any other example can be considered, namely that the control system 1 can be intended to be used to measure the tension of any type of elongated, stretched body between two fixing points. The elongated body is, for example, a wire, a cable, a spoke 105 of a 100 spoked bicycle wheel, or even a rope, or any other element of generally elongated, wire-like, threadlike, or long-slender shape.

[0079] The elongated body can be single-stranded or multi-stranded. In a multi-stranded wire, such as a cable, with several parallel strands, the strands react differently due to the interaction between them. Another example of a multi-strand assembly is a guitar or piano string, typically consisting of a core wire and another wire tightly wound around the core to increase linear density. In this case, only the core contributes to the string's stiffness.

[0080] The elongated body can be made of any natural or artificial material

[0081] The control system 1 includes at least one element for vibrating at least one elongated body, such as a radius 105.

[0082] This refers, for example, to a metal rod 3, visible in the diagram, which strikes the elongated body, such as the radius 105, whose tension must be controlled. The rest of the description refers to such a rod 3. Of course, the description can be applied to any other element used to strike the elongated body, or radius 105.

[0083] The rod 3 can be intended to strike several spokes 105 successively during a rotation of the spoked wheel 100.

[0084] The control system 1 allows measurement or control of the tension of an elongated body or stretched radius 105, without contact, by vision.

[0085] The control system 1 includes for this purpose a camera 5 and at least one associated lighting element 7.

[0086] The camera 5 and the associated lighting element 7 form an optical device for acquiring one or more images. Advantageously, this is a telecentric optical device.

[0087] The element or rod 3 can be designed to strike the elongated body or each radius 105 when it is located between the camera 5 and the associated lighting element 7. This element, such as the rod 3, is therefore positioned close to the camera 5.

[0088] The relative arrangement of the optical device 5, 7 and the elongated body or radius 105 can be adapted. For example, the camera 5 can be positioned opposite a central portion of the elongated body or radius 105. As another example, the camera 5 can be positioned closer to one end, for example, at the rim of the spoked wheel. The lighting element 7 is positioned on the other side of the elongated body or radius 105, opposite the camera 5.

[0089] Camera 5 is configured to acquire one or more images of the elongated body or radius 105 when it vibrates for a predefined period.

[0090] Camera 5 is notably a linear camera 5.

[0091] Such a linear camera can be configured to film / capture at least one image at a fixed frequency.

[0092] Camera 5 can be telecentric. In this embodiment, the linear camera 5 has a telecentric lens. The telecentric lens may have a diaphragm at one of its focal points. It is configured so that the light rays are parallel to the optical axis in front of and behind the lens.

[0093] The lighting element 7 is arranged opposite the associated camera 5.

[0094] Lighting element 7 can be telecentric. Lighting element 7 is configured to emit light beams parallel to each other.

[0095] The telecentric optical device (camera 5 and lighting element 7) allows for a very focused light, with an exposure time that can be on the order of a few microseconds.

[0096] The camera 5 with a telecentric lens is sensitive almost exclusively to the rays emitted by the telecentric lighting element 7 and very little to ambient lighting.

[0097] The control system 1 further includes a data processing unit (not shown in the figures), such as a computer or an electronic card, comprising one or more controllers or microcontrollers or processors and a memory.

[0098] One or more parameters of the elongated body or radius 105 can be stored in memory. These may include, for example, a diameter, a linear mass, a length, including a free length of the elongated body or radius 105, and / or one or more material-related characteristics such as a Young's modulus, a density of the elongated body / radius 105.

[0099] One or more formulas can also be saved in memory. This could be a formula for the linear mass density µ of an elongated body / radius 105: ; with ρ the density of the elongated body / radius 105, d the diameter of the elongated body / radius 105.

[0100] Another example of a formula saved in memory could be a formula (A) for calculating a tension T of an elongated body / radius 105,(A): ;with µ the linear mass of the elongated body / radius 105, L the length, in particular the free length, of the elongated body / radius 105, f the fundamental resonance frequency, E the Young's modulus of the elongated body / radius 105, d the diameter of the elongated body / radius 105.

[0101] Camera 5 can exchange data with the data processing unit via a computer link, wired or wireless.

[0102] The data processing unit includes one or more processing means configured to: receive one or more images acquired by the camera, and / or analyze the image or images, and / or calculate a tension of at least one elongated body or radius 105.

[0103] The processing means can be configured to analyze the image or images in order to determine a temporal evolution of a displacement of the elongated body or radius 105. This may include an image processing module such as image processing software.

[0104] The processing means, or another processing means, can calculate the tension from the determined time evolution of the displacement of the elongated body or radius 105. This processing means can also take into account at least one parameter of the elongated body or radius 105, including the diameter, length (including free length), density, linear mass density, and Young's modulus. These parameters, one or more of which can be stored in the memory of the data processing unit, can be stored.

[0105] Finally, the control system 1 can be configured to implement, at least in part, a method for controlling the tension of at least one elongated body stretched between two fixing points. Such a control method is described in more detail below.

[0106] Control method

[0107] The control method can be implemented to measure / determine the tension of any type of elongated body, wire, cable, or rope. As a specific example, the control method can be implemented to measure / determine the tension of at least one elongated body forming a radius 105 mounted in a spoked wheel 100, particularly for a bicycle.

[0108] Other applications can be considered, for example, but not limited to, winding to regulate cable tension. Yet another application could be in the context of a string on a musical instrument, for instance.

[0109] The control procedure may include at least one preliminary step to mount at least one elongated body on a support.

[0110] In the case of a 105 spoke, the support corresponds to a 100 spoked wheel. This 100 spoked wheel can in turn be mounted on its 200 support during the preliminary step.

[0111] The method for controlling the tension of at least one elongated body, such as a radius 105, stretched between two fixing points includes at least one step for vibrating the elongated body or each 105 radius.

[0112] For this step, the elongated body / radius 105 whose tension is to be measured can be struck with the metal rod 3 to create a vibration of the elongated body / radius 105. Thus, a wave is created in the or each elongated body or radius 105 under the effect of the mechanical shock.

[0113] The impact may have a minimal amplitude allowing the vibration to be observed. This vibration is generally within a frequency range of approximately 100 Hz to 1 kHz.

[0114] For each elongated body with a radius of 105, when vibrating, one or more images can be acquired during a predefined period. This predefined period can be less than 1 second, for example, on the order of 0.1 seconds. The acquired image(s) can optionally be saved, for example, in the memory of the data processing unit.

[0115] The vibration of the or each elongated body / radius 105 can be acquired and recorded, by means of the linear camera 5, and preferably having a telecentric lens.

[0116] Image acquisition is implemented when the vibrating elongated body / radius 105 is located on a light path between the camera 5 and the lighting element 7.

[0117] An example of an image acquired by the linear camera 5 is shown on the graph. This image shows the evolution of the position P (in arbitrary units ua) of an edge of an elongated body with a radius of 105 as a function of time t (in ms). On the graph, the scales for position P and time t are given for illustrative purposes only and are not exhaustive.

[0118] Image acquisition can be done at a fixed frequency. Alternatively, a variable acquisition frequency can be considered.

[0119] As a specific example, a line scan camera can acquire lines at a fixed frequency, for example around 20kHz. The acquisition frequency can be high, in particular around 50kHz, or even 100kHz, or even higher than 100kHz.

[0120] The time interval is regular, for example 50µs between each line acquisition. Each line is acquired at a specific time. In this example, an image is formed by stacking several lines to obtain a pixel matrix.

[0121] At least one image acquisition step can be performed statically, that is, when the support for the elongated bodies, such as a spoked wheel 100, is static and stationary. In this case, the elongated bodies or spokes 105 whose tension is to be measured can be placed successively between the camera 5 and the lighting element 7 for image acquisition.

[0122] Advantageously, at least one image acquisition step can be performed dynamically, that is, while the support for the elongated bodies is in motion. The control process then includes a preliminary step of setting the support for the elongated bodies in motion, preferably at a constant speed.

[0123] When the control process is applied to a 100 spoked wheel, image acquisition can be done after the 100 spoked wheel has been rotated, notably thanks to the support 200 of the latter.

[0124] In particular, for a wheel 100 with spokes distributed according to two layers, after rotation, the spokes 105 of the two layers vibrate alternately, for example under the effect of the strike of the rod 3.

[0125] The vibration of the elongated body / radius 105 used for measurement is independent of the movement of the support, such as the spoked wheel 100. This movement of the support manifests as a constant displacement, a drift, of the trace of the elongated body, such as a radius 105, on the image from one time acquisition line to the next.

[0126] Furthermore, acquiring images during the movement of the support, such as the spoked wheel 100, avoids stopping in front of the camera 5, thus saving considerable time. Indeed, the movement of the support (spoked wheel 100) ensures the successive positioning of the elongated bodies / spokes 105 within the field of view of the camera 5.

[0127] For example, when the moving support is a 100-spoke wheel, image acquisition steps can be performed on one or more revolutions of such a 100-spoke wheel.

[0128] These so-called dynamic image acquisition steps can be done continuously.

[0129] In particular, when the support for elongated bodies, such as the spoked wheel 100, is in motion, each elongated body or spoke 105 whose tension must be calculated can be identified during an identification step.

[0130] When the control procedure is applied to the measurement of the tension of the spokes 105 of a spoked wheel 100, in particular for a cycle, the identification of the spokes 105 can be done in particular by the location of the valve hole and according to the positioning of each spoke 105 in relation to the located valve hole.

[0131] The control method may optionally combine static (stationary support) and dynamic (moving support) steps for image acquisition. Initially, image acquisition may be static, for example by successively placing each of the elongated bodies, such as spokes 105 of a spoked wheel 100, between the lighting element 7 and the camera 5. One or more dynamic image acquisition steps may be implemented subsequently.

[0132] Then, the acquired image(s), depending on whether they are static or dynamic, can be transmitted, notably to the data processing unit for analysis. Data / image transmission can be carried out, for example, via a wired or wireless computer link from the camera 5 to the data processing unit.

[0133] The acquired image or images can then be processed.

[0134] At least one image processing technique can potentially be implemented, for example, to remove / correct the drift of the elongated body's trace, such as a 105 ray, in at least one image acquired while the elongated body / 105 ray support is moving. The vibration signal can thus be recovered. The displacement of the ray's edge can then be observed at a constant speed in the image.

[0135] Furthermore, at least one image processing can be implemented in order to obtain one or more data points necessary to calculate the tension of the or each elongated body / radius 105.

[0136] For example, the data processing unit (e.g. more precisely an image processing module such as image processing software) can analyze the image or images to determine a time evolution of a displacement of the or each elongated body / radius 105.

[0137] In a given image, a line can be compared with the next and / or the previous one. Each image is processed independently. Multiple images of the same elongated body can improve measurement accuracy, for example, by averaging the values ​​obtained for each image.

[0138] The processing time for an image can, for example, be less than 200ms, corresponding to an image acquisition time of 20,000 lines per second, in the specific case of acquisition using a line scan camera. Thus, the processing of one or more images can be performed in the background.

[0139] More specifically, the control method may include a step to calculate or deduce a fundamental resonance frequency from the determined time evolution of the displacement of the elongated body (or bodies) with a radius of 105. Alternatively or in addition, harmonic frequencies may also be used. When used in conjunction with other methods, harmonic frequencies can, for example, improve measurement accuracy.

[0140] In one embodiment, the frequency is obtained from the position P of the ray edge on the acquired image, and the frequency spectrum can be calculated. The frequency spectrum can be calculated using a Fourier transform.

[0141] The fundamental resonance frequency is obtained as the abscissa of the first non-zero frequency peak in the spectrum.

[0142] The control process further includes one or more steps to calculate the tension of the or each elongated body / radius 105. The calculation step or steps may be implemented at least in part by the data processing unit.

[0143] The tension can be calculated through the determined time evolution of the displacement of the or each elongated body / radius 105, more precisely, the fundamental resonance frequency which is deduced from it and which can be related to the tension of the or each elongated body / radius 105 by a calculation formula.

[0144] In addition to the fundamental resonance frequency f, the voltage can also be calculated on the basis of at least one parameter of the or each elongated body / radius 105. The parameter(s) can be chosen from the diameter, the length in particular the free length, the density, the linear mass, the Young's modulus.

[0145] For example, the tension T of each elongated body or radius 105 is calculated as a function of the fundamental resonance frequency, as well as the diameter d, the linear mass density µ, the free length L, and the Young's modulus E, according to the following formula (A): (A): .

[0146] When harmonic frequencies are used, due to the stiffness effect of the stretched elongated body, the harmonic frequencies are not exact multiples of the fundamental resonance frequency: this is called the inharmonicity effect, according to formula (A') modified from the previous formula (A), as follows: (A'): , with n being the rank of the harmonic.

[0147] The process may include a preliminary step of calculating the linear mass µ, as a function of the diameter d and the density ρ according to the following formula (B):(B): .

[0148] Thus, the corresponding method and control system make it possible to measure or determine the tension of any stretched elongated body, by sight, based on the vibratory resonance of stretched elongated bodies after an impact and at least one known characteristic of the elongated body.

[0149] This visual measurement method eliminates potential interference that could occur, for example, during the analysis of the sound emitted by the vibration. Such interference can originate from ambient noise disrupting the measurement. The proposed solution has the advantage of being insensitive to ambient noise.

[0150] The use of a telecentric optical device (linear camera 5 and facing lighting element 7) prevents image blurring. Ambient lighting has little or no impact because the telecentric optics used are highly directional.

[0151] Furthermore, since the measurement is also a function of known characteristics of the elongated body (material, diameter, free length), the result obtained does not depend on any calibration.

[0152] When applied to measuring the tension of the 105 spokes of a 100 spoked wheel, the control method makes it possible to measure / determine the tension of all the 105 spokes of a spoked wheel in a time compatible with the production rates of these 100 spoked wheels, for example less than 30s.

[0153] When the spokes 105 are divided into two layers, both layers can be measured simultaneously. When the spoked wheel 100 is rotated, the spokes 105 of the two layers vibrate alternately, and the steps of acquiring an image of each spoke 105 as it vibrates, transmitting and analyzing the acquired image(s), and calculating the tension of each spoke 105 are performed for the spokes of both layers in one revolution of the spoked wheel 100. The measurement can take, for example, approximately 5 to 6 seconds for one complete revolution of the spoked wheel 100.

[0154] Finally, the control process can be automated when 100 spoked wheels are mounted on a cycle.

Claims

A method for controlling the tension of at least one elongated body (105) stretched between two fixing points, characterized in that the control method comprises the following steps: vibrating the at least one elongated body (105), acquiring at least one image of the at least one elongated body (105) while it vibrates by means of a linear camera (5), for a predefined period, the image being formed by a stacking of lines acquired by means of said camera (5), transmitting the at least one acquired image to a data processing unit, analyzing the at least one image by the data processing unit to determine a time evolution of the displacement of the at least one elongated body (105), and calculating, by the data processing unit, a tension of the at least one elongated body (105) from the determined time evolution of the displacement of the at least one elongated body (105) and based on at least one parameter of the at least one elongated body (105) among a diameter,a length, a density, a linear mass density, a Young's modulus. Control method according to the preceding claim, implemented to measure the tension of elongated bodies forming spokes (105) mounted in a spoked wheel (100), in particular for a cycle. A control method according to any one of the preceding claims, wherein the acquisition of at least one image is at a fixed frequency. Control method according to any one of the preceding claims, wherein the data processing unit deduces, from the determined time evolution of the displacement of at least one elongated body (105), a fundamental resonance frequency (f) and / or a harmonic frequency, and calculates the tension of at least one elongated body as a function of said deduced frequency (f) and at least one parameter of at least one elongated body (105). A control method according to the preceding claim, wherein the data processing unit calculates the tension of at least one elongated body (105) according to formula (A) or formula (A'):(A): ,(HAS') : ,with T the voltage, fla the fundamental resonance frequency deduced, d the diameter, µ the linear mass, L the free length of at least one elongated body (105), E the Young's modulus, n the rank of the harmonic. A control method according to any one of the preceding claims, wherein the vibration of at least one elongated body (105) whose tension is to be calculated is within a frequency range of approximately 100 Hz to 1 kHz. A control method according to any one of the preceding claims, wherein at least one elongated body (105) is mounted on a support (100), said method comprising at least one additional step of setting the support (100) in motion at a constant speed, and wherein at least one step of acquiring at least one image is carried out while the support (100) is in motion. Control method according to the preceding claim, comprising at least one additional step of acquiring at least one image when the support (100) is static. A control method according to any one of the preceding claims, wherein: at least one lighting element (7) is arranged opposite said camera (5), and wherein the acquisition of at least one image is carried out when at least one elongated body (105) is on a light path between said camera (5) and the lighting element (7). A control method according to the preceding claim, wherein at least one elongated body (105) vibrates under the effect of an element (3) arranged near said camera (5), so as to strike at least one elongated body (105) when it is between said camera (5) and the lighting element (7). Control method according to any one of the preceding claims, comprising at least one step of identifying at least one elongated body (105) whose tension is calculated. A control method according to claims 2 and 7 in combination with any one of the preceding claims, wherein: the spoked wheel (100) comprises a peripheral rim (101), a central hub (103) and individual connecting spokes (105) tensioned between the peripheral rim (101) and the central hub (103), the spokes (105) being distributed in two layers which connect the peripheral rim (101) to a respective end of the central hub (103), and wherein the spoked wheel (100) is rotated, the spokes (105) of the two layers vibrate alternately, and the steps of acquiring at least one image of each spoke (105) when it vibrates, of transmitting and analyzing the at least one acquired image, and of calculating the tension of each spoke (105) are carried out for the spokes of the two layers in one revolution of the spoked wheel (100). Control system (1) for the tension of at least one elongated body (105), the control system (1) being configured to implement at least in part a method for controlling the tension of at least one elongated body (105), the control system (1) comprising at least: an element (3) for vibrating the at least one elongated body (105), a linear camera (5), configured to acquire at least one image of the at least one elongated body (105) when it vibrates, for a predefined period, the image being formed by a stacking of lines acquired by means of said camera (5), a data processing unit configured to receive the at least one image acquired by said camera (5) and to analyze the at least one image so as to determine a temporal evolution of a displacement of the at least one elongated body (105),and to calculate a tension of at least one elongated body (105) from the determined time evolution of the displacement of at least one elongated body (105) and on the basis of at least one parameter of at least one elongated body (105) among a diameter, a length, a density, a linear mass density, a Young's modulus. Control system (1) according to the preceding claim, wherein at least one lighting element (7) is arranged opposite said camera (5). Control system (1) according to any one of claims 13 or 14, wherein said camera (5) has a telecentric lens and / or the lighting element (7) is telecentric.

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