Tension control system for a fastener in an assembly and associated control method

Abstract

Tension control system for a fastener in an assembly and associated control method. The present invention relates to a tension control system (10) for a fastener (12) in an assembly (36), said fastener (12) comprising a rod (14) and an assembly member (16), the control system (10) comprising: - a first measuring device (44), the first measuring device (44) being adapted to measure a first parameter representative of the time response of the rod (14) to an ultrasonic excitation, - a second measuring device (46) adapted to measure a second parameter representative of the frequency response of the rod (14) to an ultrasonic excitation, and - a calculator (48), the calculator (48) being adapted to determine a value of the tension of the rod (14) as a function of at least said first parameter and said second parameter. Figure for the abstract: Figure 1

Description

Title of the invention: System for controlling the tension of a fastener in an assembly and associated control method

[0001] The present invention relates to a system for controlling the tension of a fastener in an assembly. It also relates to a corresponding control method.

[0002] The invention applies particularly, but not exclusively, to the control of the tightening of aircraft fasteners.

[0003] In the aeronautical field, it is useful to know the preload of an installed fastener, particularly a screw / nut type fastener. The preload of a fastener is the mechanical tension initially created in the fastener when it tightens an assembly of parts, for example, during the manufacturing of an aircraft. Accurate knowledge of the installed tension is essential to ensure the long-term durability of the assembly under the effect of external stresses. Indeed, excessive tightening can damage the screw or the part into which it is screwed, and insufficient tightening can lead to the screw becoming detached from the assembly.

[0004] In particular, it is useful to be able to monitor the evolution of said tension over time in order to plan maintenance operations. One known method for determining the tension in a screw is to measure the screw's elongation using ultrasonic waves. However, this method requires two measurements: one in the unconstrained free state and one in the tightened state. Furthermore, it is not possible to measure the tension by measuring the elongation, for example during a maintenance operation, if the measurement of the fastener in the free state during aircraft manufacturing is not saved in a database, which is then made available to a third party performing the maintenance operation.

[0005] Techniques are known for determining the tension in a screw already installed in its nut even if the initial state is not known.

[0006] In particular, a method based on exploiting the propagation of longitudinal (along the axis of the screw) and transverse (at normal incidence to the axis of the screw) ultrasonic waves can be used. For example, by knowing the time of flight of each of the two types of waves, it is possible to determine the tension of the screw.

[0007] However, in practice, the transmission of transverse waves is limited, so complex and bulky sensors are used.

[0008] Moreover, this method gives very dispersive measurements for titanium alloy screws, an alloy massively used in aircraft, and the measurements are very sensitive to temperature variations.

[0009] There is therefore a need for a tension control system for a rod of a fastener in an assembly that is easier to implement and usable for any type of rod.

[0010] To this end, the description describes a system for controlling the tension of a fastener in an assembly, said fastener comprising a rod and an assembly member, the control system comprising:

[0011] - a first measuring device, the first measuring device being specific to to control a first parameter representative of the temporal response of the rod to ultrasonic excitation,

[0012] - a second measuring device, the second measuring device being specific to to control a second parameter representative of the frequency response of the rod to ultrasonic excitation, and

[0013] - a calculator, the calculator being capable of determining a value of the voltage of the rod as a function of at least said first parameter and said second parameter.

[0014] According to particular embodiments, the control system has one or more of the following characteristics, taken individually or in all technically possible combinations:

[0015] - a first parameter is the time of flight of a longitudinal ultrasonic wave or transverse in the stem.

[0016] - a second parameter is a frequency interval between two frequencies of resonance of the stem.

[0017] - the calculator also determines the value of the rod tension as a function of a parameter relating to the stem.

[0018] - the calculator calculates the value F of the rod tension by applying the formula next:

[0020] where:

[0021] K denotes the parameter relating to the rod,

[0022] denotes the time of flight of an ultrasonic excitation in the rod under stress, and

[0023] f1 denotes the frequency interval between two resonance frequencies of the rod under duress.

[0024] - the first measuring device comprises:

[0025] - a first ultrasonic probe arranged to generate an ultrasonic excitation of the rod and collect a response signal from the rod to the generated excitation,

[0026] - a first acquisition device, the first acquisition device being suitable for controlling the first ultrasonic probe according to a first law of command and receive the response signal, the first control law being an impulse law, and

[0027] - a first computing device, the first computing device being suitable for processing the response signal to extract the first parameter.

[0028] - a main axis is defined for the rod, the first ultrasonic probe being arranged to generate an ultrasonic excitation propagating along the main axis of the rod.

[0029] - the second measuring device comprises:

[0030] - a second ultrasonic probe arranged to generate an ultrasonic excitation of the rod and collect a plurality of rod response signals to the generated excitation,

[0031] - a second acquisition device, the second acquisition device being suitable for controlling the second ultrasonic probe according to a second control law and for receiving the plurality of response signals, the second control law comprising a pulse train at different frequencies, and

[0032] - a second computing device, the second computing device being specific to process the plurality of response signals to extract the second parameter.

[0033] - the second computing device is suitable for performing a frequency analysis of the plurality of response signals.

[0034] - the first ultrasonic probe and the second ultrasonic probe are confused and include an ultrasonic transducer made of lead titano-zirconates.

[0035] The description also describes a method for controlling the tension of a fastener in an assembly, said fastener comprising a rod and an assembly member, the control method comprising the steps of:

[0036] - measurement of a first parameter of the temporal response of the rod to an excitation ultrasound,

[0037] - measurement of a second parameter of the frequency response of the rod to a ultrasonic excitation, and

[0038] - determination of the value of the tension of the rod as a function of at least said first parameter and said second parameter.

[0039] In this description, the expression "specific to" means interchangeably "suitable for", "adapted to" or "configured for".

[0040] Some features and advantages of the invention will become apparent from the following description, given solely by way of non-limiting example, and made with reference to the accompanying drawings, in which:

[0041] - [Fig. 1] [Fig. 1] is a schematic representation of a control system of the the tension of a screw, the control system comprising a first measuring device and a second measuring device,

[0042] - [Fig.2] [Fig.2] is a block diagram of the first control device of [Fig.1],

[0043] - [Fig.3] [Fig.3] is a schematic representation of several control laws that the first measuring device of [Fig.2] is suitable for use,

[0044] - [Fig.4] [Fig.4] is a schematic representation of a signal backscattered by the see that the first measuring device of [Fig.2] is suitable for receiving,

[0045] - [Fig.5] [Fig.5] is a block diagram of the second measuring device of the [Fig.l],

[0046] - [Fig.6] [Fig.6] is a schematic representation of a control law that the The second measuring device [Fig. 5] is suitable for use,

[0047] - [Fig.7] [Fig.7] is a schematic representation of a signal obtained by the second measuring device after processing the signals backscattered by the screw in the presence of an excitation corresponding to the control law of [Fig.6], and

[0048] - [Fig.8] [Fig.8] is a flowchart of an example of the implementation of a voltage control method.

[0049] A control system 10 is illustrated in [Fig.1].

[0050] The control system 10 is designed to control the tension of a fastener 12, also visible in [Fig.1].

[0051] The fastener 12 comprises a rod 14 and an assembly member 16. The rod 14 and the assembly member 16 are shown in cross-section.

[0052] The rod 14 extends along a first axis 20 between a first end and a second end. The rod 14 includes a flat face 22, perpendicular to the first axis 20, forming said first end.

[0053] The rod 14 further includes an assembly element 30, disposed on a radial surface of said rod 14. The assembly element 30 is able to cooperate with the assembly member 16, so as to form the fastener 12 from the rod 14 and the assembly member 16.

[0054] In the embodiment shown, the rod 14 is a screw and the assembly element is a threaded portion 30 of said screw 14. The screw 14 further comprises a smooth shank 32, aligned with the threaded portion 30 along the first axis 20.

[0055] In the embodiment shown, the screw 14 further comprises an enlarged head 34, adjacent to the smooth shank 32. The head 34 forms a radial projection relative to said shank 32.

[0056] In the embodiment shown, the flat face 22 of the screw 14 is formed by the head 34.

[0057] As specified above, the assembly member 16 is suitable for assembling with the assembly element 30 of the screw 14 to form the fastener 12.

[0058] In the embodiment shown, the assembly member 16 is a threaded nut 16, suitable for assembly with the threaded portion 30 of the screw 14.

[0059] In particular, the fastener 12 is suitable for forming an assembly 36 with structural elements 38, superimposed so as to present a first 40 and a second 42 opposite faces. In the assembly 36, the shank 32 of the screw 14 is disposed in a hole (not shown) in the structural elements 38; the head 34 bears against the first face 40; and the nut 16 is assembled to the threaded portion 30 of the screw 14 and bears against the second face 42. A clamping tension is applied in the screw 14 by tightening the nut 16.

[0060] The control system 10 is suitable for controlling the tension of a fastener 12 by determining a tension value of the rod 14.

[0061] The control system 10 comprises a first measuring device 44, a second measuring device 46 and a computer 48.

[0062] The first measuring device 44 is suitable for measuring at least a first parameter representative of the time response of the screw 14 to an ultrasonic excitation.

[0063] The time response is the variation of the backscattered signal (or echo) by the screw 14 with time.

[0064] According to the example described, the first parameter that the first measuring device 44 is suitable for measuring is the time of flight of a longitudinal ultrasonic excitation in the screw 14.

[0065] The time of flight is the propagation time of the ultrasonic excitation. The time of flight thus corresponds to the time elapsed between the instant of emission of the ultrasonic excitation by a transducer and the reception of the echo of the excitation by the same transducer. Hereafter, the time of flight is denoted L.

[0066] Ultrasonic excitation can also, alternatively, be transverse ultrasonic excitation.

[0067] Another example of a first parameter is the time shift of the resonance frequency of the screw 14 induced by the injected ultrasonic wave(s).

[0068] As can be seen in [Fig.2], the first measuring device 44 comprises a first ultrasonic probe 50, a first acquisition device 52 and a first calculation device 54.

[0069] The first ultrasonic probe 50 is arranged to generate an ultrasonic excitation of the screw 14 and collect a response signal from the screw 14 to the generated excitation.

[0070] More specifically, the first ultrasonic probe 50 is an axial probe in the sense that the first ultrasonic probe 50 is arranged to generate an ultrasonic excitation propagating along the main axis of the screw 14.

[0071] According to the example described, the first ultrasonic probe 50 is a transducer comprising a piezoelectric sensor 56.

[0072] As its name indicates, the sensor 56 is made of a piezoelectric material, that is to say a material capable of converting an electrical signal into an acoustic signal and vice versa an acoustic signal into an electrical signal.

[0073] Advantageously, the piezoelectric material is a lead titano-zirconate, for example PZT-4 or PZT-8 corresponding respectively to types I and III of the MIL-STD-1376B standard.

[0074] The use of such materials makes it possible to obtain a transducer exhibiting a high mechanical quality factor: such a material will tend to resonate for a long time in response to an excitation.

[0075] The first acquisition device 52 is an electronic control circuit for the first ultrasonic probe 50.

[0076] The first acquisition device 52 is suitable for controlling the first ultrasonic probe 50 according to a first control law and for receiving the backscattered signal.

[0077] Examples of first control law are shown in [Fig.3].

[0078] Each first control law is an impulse law, that is to say that it includes only electrical impulses (in volts) as a function of time (for example in seconds).

[0079] More specifically, in the case of [Fig.3], each first control law includes at least one pulse, either half-periodic or periodic.

[0080] The first case shown at the top of [Fig.3] corresponds to a half-periodic negative unipolar rectangular pulse, the second case shown in the middle of [Fig.3] to a periodic bipolar rectangular pulse (two half-periodic pulses of opposite sign) and the third case at the bottom of [Fig.3] to a bipolar sinusoidal pulse (two half-periodic pulses of opposite sign).

[0081] The first acquisition device 52 comprises a first transmitter 58, a first receiver 60 and a first isolation unit 62.

[0082] The first emitter 58 is suitable for emitting the electrical signal corresponding to the first control law.

[0083] The first transmitter 58 is connected to the first ultrasonic probe 50 by an electrical track 64 through which the first control law passes.

[0084] The first receiver 60 is suitable for receiving the electrical signal corresponding to the backscattered signal captured by the first ultrasonic probe 50.

[0085] The first isolation unit 62 is suitable for isolating the first receiver 60 from the first emitter 58.

[0086] Thus, the first insulation unit 62 is suitable for protecting the first receiver to prevent an excessively high electrical voltage input emission.

[0087] The first computing device 54 is suitable for processing the response signal to extract at least one first parameter, here the time of flight k.

[0088] Figure 4 illustrates the backscattered signal received by the first receiver where the initial pulse is highlighted by an arrow.

[0089] The gap between the echoes corresponds to the desired flight time.

[0090] Depending on the case, the difference can be measured directly or by using an average.

[0091] For example, one can measure the difference for three echoes and divide by three or measure the difference with the first echo, the difference between the first echo and the second echo and the difference between the second echo and the third echo and average the three values ​​to obtain the flight time k.

[0092] As can be seen in [Fig.5], the second measuring device 46 comprises a second ultrasonic probe 65, a second acquisition device 66 and a second computing device 68.

[0093] The second measuring device 46 is suitable for measuring at least one second parameter representative of the frequency response of the screw 14 to an ultrasonic excitation.

[0094] The frequency response is a reconstruction of the backscattered signals for each excitation frequency according to a second control law, for example described in [Fig. 6]. An example of such a reconstruction is shown in [Fig. 7].

[0095] According to the example described, the second parameter that the second measuring device 46 is suitable for measuring is a frequency interval y1 between two or more consecutive resonance frequencies of the screw 14.

[0096] The second parameter is, according to a similar variant, a set of resonance frequencies of the screw 14.

[0097] The same remarks as for the first ultrasonic probe 50 apply to the second ultrasonic probe 68.

[0098] Advantageously, the first ultrasonic probe 50 and the second ultrasonic probe 68 are confused.

[0099] The first measuring device 44 and the second measuring device 46 therefore use the same ultrasonic probe, which makes it possible to reduce the compactness of the control system 10.

[0100] The second acquisition device 66 is an electronic control circuit for the second ultrasonic probe. The second acquisition device 66 is adapted to control the second ultrasonic probe 65 according to a second control law and to receive the plurality of response signals.

[0101] An example of a second control law is shown in [Fig.6].

[0102] As can be seen in this figure, the second control law comprises a pulse train at different frequencies.

[0103] More precisely, it is a series of sinusoidal pulses of the same amplitude but of different frequencies (here fl, f2, f3 and f4 but this number is not limiting).

[0104] The second acquisition device 66 includes a second transmitter 70, a second receiver 72, a third receiver 74, a second protection unit 76, a third protection unit 78 and a calibrated resistor 80.

[0105] The second emitter 70 is suitable for emitting the electrical signal corresponding to the second control law.

[0106] The second transmitter 70 is connected to the second ultrasonic probe 65 by an electrical track 82 through which the second control law passes.

[0107] The second receiver 72 is suitable for receiving the electrical signal corresponding to the backscattered signal captured by the second ultrasonic probe 65 after passing through the calibrated resistor 80. The calibrated resistor 80 here forms a shunt.

[0108] The second isolation unit 76 is suitable for isolating the second receiver 72 from the second emitter 70.

[0109] Thus, the second isolation unit 76 is suitable for protecting the second receiver 72 to prevent an excessively high electrical voltage input emission.

[0110] The same remarks apply to the third receiver 74 and the third isolation unit 76.

[0111] The only difference is that the third receiver 74 is directly connected to the second ultrasonic probe 65 (no shunt).

[0112] The presence of the two receivers 72 and 74 arranged thus and of the calibrated resistance 80 makes it possible to analyze the variation of impedance related to the pulse trains.

[0113] The second acquisition device 46 thus acts as an impedance analyzer. The second acquisition device 46 can be a vector network analyzer, commonly referred to by the abbreviation VNA.

[0114] The second computing device 68 is suitable for processing the response signal to extract at least one second parameter, here the frequency interval y1 between two resonance frequencies of the screw 14.

[0115] For this purpose, the second computing device 68 performs a reconstructed frequency analysis from the collected signals, for example by a Fourier transform of the collected signals.

[0116] Figure [Fig. 7] illustrates an example of a curve that may result from such an analysis. More specifically, [Fig.7] represents the variation of the phase of the impedance of the second ultrasonic probe 65 as a function of the frequency of the applied pulse.

[0117] The curve has peaks, each peak corresponding to a resonance frequency of the screw 14. The gap between two peaks corresponds to the frequency interval y1 sought.

[0118] The calculator 48 is an electronic circuit designed to manipulate and / or transform data represented by electronic or physical quantities in registers of the calculator and / or memories into other similar data corresponding to physical data in register memories or other types of display devices, transmission devices or storage devices.

[0119] As specific examples, the computer 48 includes a single-core or multi-core processor, such as a central processing unit (CPU), a graphics processing unit (GPU), a microcontroller and a digital signal processor (DSP), a programmable logic circuit, such as an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), a programmable logic device (PLD) and programmable logic arrays (PLAs), a state machine, a logic gate and discrete hardware components.

[0120] The calculator 48 is suitable for determining the value of the tension of the screw 14 as a function of at least the first parameter and the second parameter.

[0121] For this purpose, the calculator 48 uses a function having the said first and second parameters as input variables, and gives as output a calculated value of the tension of the screw 14.

[0122] Depending on the embodiments, the function is more or less complex.

[0123] For example, the function is a table that the calculator 48 consults to obtain the desired value.

[0124] According to another example, the function can be a function that the calculator 48 applies to obtain, after calculation, the value sought.

[0125] In this perspective, the function can be a numerical function or a more elaborate function, in particular a neural network that has been previously learned.

[0126] The function can also take more input parameters, such as other measurements or predefined values.

[0127] According to the example described, the function takes as input another parameter which is a parameter dependent on the geometry of the screw 14 and the material of the screw 14. The parameter dependent on the screw 14 is here a constant K.

[0128] The constant K is, for example, obtained by measuring the tension F of the screw 14 by preliminary tests on the screw 14, for example on a tensile test bench or an instrumented clamping test bench, and by measuring either the resonance frequency to exploit a first relation, or the propagation time to exploit a second relation.

[0129] The first relation is written:

[0130] -gf^F

[0131] Where: • g / ” is the frequency variation of the nth resonance frequency of the screw 14, between an initial state at rest and a state under stress; • denotes the nth resonance frequency of screw 14 in an initial state at rest, and • F designates the tension of screw 14.

[0132] The second relation is written:

[0133] 5t = KJ(yF

[0134] Where: • 5t is the variation in the wave propagation time in the screw, between an initial state at rest and a state under stress, • A) denotes the wave propagation time in the screw in an initial state at rest, and • F denotes the screw tension.

[0135] From one of these two test campaigns, it is possible to deduce the value of the constant K. It is obviously possible to carry out both test campaigns, in order to refine the value of the constant K.

[0136] It is advantageous to carry out the tests on a screw - or a set of screws - and to consider that the value found for the constant K is valid for all screws of the same type, for example having the same material, the same diameter and the same length, from the same manufacturing batch or from different manufacturing batches.

[0137] By repeating these preliminary tests on different types of screws, the calculator 48 has a database giving a value of the constant K for a set of screw types, the screw types differing for example by the material, the diameter of the screw and the length of the screw.

[0138] In the example described, the calculator 48 uses only the constant K, the time of flight L and the interval between two resonance frequencies of the screw 14 for J (J Calculate the tension F in screw 14, by applying the following formula:

[0140] The calculator 48 thus obtains the value of the tension of the screw 14, without knowing its initial state, or its previous tension state if the tension has already been measured, for example during a maintenance operation.

[0141] The operation of the control system 10 is now described with reference to [Fig.8] which illustrates an example of the implementation of a method for controlling the tension of the screw 14.

[0142] The voltage control method comprises a first measurement step E100, a second measurement step E102 and a determination step E104.

[0143] During the first measurement step E100, the first ultrasonic probe 50 emits an ultrasonic excitation in the form of a pulse.

[0144] This pulse propagates in the screw 14 and is reflected towards the first ultrasonic probe 50.

[0145] By collecting and analyzing the reflected signal, the first measuring device 44 obtains the value of at least one first parameter of the time response of the screw 14 to an ultrasonic excitation, namely, in the example described, the time of flight U.

[0146] During the second measurement step El02, the second ultrasonic probe emits an ultrasonic excitation in the form of a pulse train.

[0147] Each pulse propagates in the screw 14 and is reflected towards the first ultrasonic probe 50.

[0148] The second measuring device 46 collects and analyzes the signals thus reflected.

[0149] The second measuring device 46 thus obtains the second parameter of the frequency response of screw 14 to ultrasonic excitation, for example here the frequency interval y1 between two resonance frequencies of screw 14.

[0150] During the determination step E104, the calculator 48 applies the following formula: 101511

[0152] The result of this formula gives the value of the tension F of the screw 14.

[0153] The control system 10 thus makes it easy to obtain the voltage of the fixing 12.

[0154] Indeed, it is not the initial state of stress in the screw 14 to obtain the desired value.

[0155] An operator performing this check can then decide, based on the voltage value indicated by the calculator 48, whether the fastener needs to be tightened so that the tension in the fastener 12 is within the recommended voltage range. The operator can verify using the same method whether the tightening has achieved the recommended voltage range.

[0156] In addition, it is usable for all types of screws, including small or already installed screws.

[0157] Furthermore, it is possible to implement the invention with only longitudinal waves and using a single transducer.

[0158] Other embodiments benefiting from the previous advantages are also conceivable.

[0159] For example, the first measuring device 44 and the second measuring device 46 are grouped together in the same housing.

[0160] Alternatively or in addition, the calculator 48, the first calculating device 54 and the second calculating device 56 can be confused.

[0161] Advantageously, only one computer, for example computer 48, will implement the processing carried out by the first computing device 54 and the second computing device 56.

[0162] The invention has been described for a fastener comprising a threaded rod and a nut. The invention also applies to any type of fastener, including, for example, a threaded rod and a crimping ring, a rivet and a crimping ring, or a blind fastener that is crimped, screwed, or pulled-screwed. To determine the tension of a blind fastener, the first and second measuring devices 44 and 46 will then be brought into contact with the accessible surface of the fastener, that is, generally the head of the fastener, the surface of the opposite end generally being inaccessible.

Claims

Demands

1. Control system (10) for the tension of a fastener (12) in an assembly (36), said fastener (12) comprising a rod (14) and an assembly member (16), the control system (10) comprising: - a first measuring device (44), the first measuring device (44) being adapted to measure a first parameter representative of the time response of the rod (14) to an ultrasonic excitation, - a second measuring device (46), the second measuring device (46) being adapted to measure a second parameter representative of the frequency response of the rod (14) to an ultrasonic excitation, and - a calculator (48), the calculator (48) being adapted to determine a value of the tension of the rod (14) as a function of at least said first parameter and said second parameter.

2. Control system according to claim 1, wherein the first parameter is the time of flight of a longitudinal or transverse ultrasonic wave in the rod (14).

3. Control system according to claim 1 or 2, wherein the second parameter is a frequency range between two resonance frequencies of the rod (14).

4. Control system according to any one of claims 1 to 3, wherein the calculator (48) determines the value of the tension of the rod (14) also as a function of a parameter (c) relating to the rod (14).

5. Control system according to claim 4, wherein the computer (48) calculates the value F of the tension of the rod (14) by applying the following formula: where: K denotes the parameter relating to the rod (14), denotes the time of flight of an ultrasonic excitation in the rod (14), and f1 denotes the frequency range between two resonance frequencies of the rod (14).

6. Control system according to any one of claims 1 to 5, wherein the first measuring device (44) comprises: - a first ultrasonic probe (50) arranged to generate an ultrasonic excitation of the rod (14) and collect a response signal from the rod (14) to the generated excitation, - a first acquisition device (52), the first acquisition device (52) being adapted to control the first ultrasonic probe (50) according to a first control law and to receive the response signal, the first control law being an impulse law, and - a first calculation device (54), the first calculation device (54) being adapted to process the response signal to extract the first parameter.

7. Control system according to claim 6, wherein a principal axis is defined for the rod (14), the first ultrasonic probe (50) being arranged to generate an ultrasonic excitation propagating along the principal axis of the rod (14).

8. Control system according to any one of claims 1 to 7, wherein the second measuring device (46) comprises: - a second ultrasonic probe (65) arranged to generate an ultrasonic excitation of the rod (14) and collect a plurality of response signals from the rod (14) to the generated excitation, - a second acquisition device (66), the second acquisition device (66) being adapted to control the second ultrasonic probe (65) according to a second control law and to receive the plurality of response signals, the second control law comprising a pulse train at different frequencies, and - a second computing device (68), the second computing device (68) being adapted to process the plurality of response signals to extract the second parameter.

9. Control system according to claim 8, wherein the second computing device (68) is suitable for performing a frequency analysis of the plurality of response signals.

10. Control system according to claims 6 and 8, wherein the first ultrasonic probe (50) and the second ultrasonic probe (65) are combined and comprise an ultrasonic transducer made of lead titano-zirconates.

11. Method for controlling the tension of a fastener (12) in an assembly (16), said fastener comprising a rod (14) and an assembly member (16), the control method comprising the steps of: - measuring a first parameter of the time response of the rod (14) to an ultrasonic excitation, - measuring a second parameter of the frequency response of the rod (14) to an ultrasonic excitation, and - determining the value of the tension of the rod (14) as a function of at least said first parameter and said second parameter.

Images