EP3387422A1

EP3387422A1 - Method for ultrasonic inspection of an object

Info

Publication number: EP3387422A1
Application number: EP16819150.0A
Authority: EP
Inventors: Hervé STOPPIGLIA; Pascale POMMIER
Original assignee: Constellium Issoire SAS
Current assignee: Constellium Issoire SAS
Priority date: 2015-12-07
Filing date: 2016-12-02
Publication date: 2018-10-17
Also published as: CN108369214A; FR3044770A1; US20180372688A1; WO2017098117A1

Abstract

The invention relates to a method for ultrasonic inspection of an object wherein a multi-element ultrasonic probe comprising a plurality of basic transducers is applied to the object. The method comprises: consecutive activation of the basic transducers such that when activated each transducer emits an ultrasonic wave incident on said object; following each activation of a basic transducer, acquisition, by a plurality of basic transducers, of a detection signal representative of a wave reflected by the object during propagation of said ultrasonic wave in the latter. The object is divided into points referred to as mesh points. Each acquired detection signal is subsequently used to calculate, at each mesh point, a parameter representative of the object that is to reflect an incident ultrasonic wave. The method comprises, during this calculation, a selection of a group of transducers from among the basic transducers of the probe.

Description

METHOD FOR CONTROLLING AN ULTRASONIC OBJECT

DESCRIPTION

TECHNICAL AREA

The technical field of the invention is the non-destructive testing of objects, in particular mechanical parts, by ultrasound. The invention is particularly applicable to the detection of defects in rooms or structures.

PRIOR ART

The use of ultrasound allows non-destructive testing in the medical and industrial fields. One known application in the industry is the control of the integrity or quality of objects, in order to detect defects. The main method used is ultrasound, whose principle is to have a probe on the surface of an object, the probe emitting an ultrasonic impulse wave from this surface. During its propagation in the object, the ultrasonic wave interacts with any defects present in the object. When the wave encounters a defect, a reflected wave is formed, causing echoes that can be detected on the surface of the object, from which a position of one or more defects in the object can be established. .

It is currently common to use so-called multi-element probes, formed by elementary transducers distributed side by side, in a single or two-dimensional arrangement. Each elementary transducer is formed of a piezoelectric material, capable of producing and / or detecting an ultrasonic wave, in a frequency range generally between 100 kHz and 50 MHz. Each elementary transducer is then able to be used as a transmitter and as a receiver.

During the control of an object, each elementary transducer of a multi-element probe is successively activated, so as to form a transmitter. During each activation of an elementary transducer, the elementary transducers of the probe are used, as detectors, to detect an echo coming from the object. If the probe has N elementary transducers, at each activation of one of these elementary transducers, N detected signals are collected. After successively activating the N transducers of the probe, N ² detected signals are collected, each detected signal corresponding to a transmitter / detector pair. Algorithms have been developed, making it possible, from these detected signals, to determine a position of one or more defects in the object. This type of check is up and running. However, when the probe is applied in contact with an object to be inspected, in particular a metallic object, the control is assigned a zone, called a dead zone, extending from the surface of the object against which it is applied the probe, in a shallow depth, in which the quality of the control is not optimal, Also, at present, it is considered that a multi-element probe is not completely adapted to a quality control carried out on objects of small thickness, or on the first millimeters of the thickness of an object.

The inventors have sought to solve this problem, by improving the quality of the results obtained, in particular in the first millimeters or centimeters deep in an object,

SUMMARY OF THE INVENTION

A first object of the invention is a control method of an object, in particular an industrial object, comprising the following steps:

a) application of a multi-element probe facing said object, said probe comprising a plurality of elementary transducers, each elementary transducer being able to emit an ultrasonic wave towards said object and / or to detect an ultrasonic wave reflected in said object;

b) activation of one of said elementary transducers, said transmission transducer, so that the latter transmits an ultrasonic wave, said incident wave, to said object;

c) acquisition, by a plurality of said elementary transducers, said detection transducer, a detection signal representative of a wave reflected in the object under the effect of said incident wave propagating in the object, each signal of detection being associated with said transmit transducer and with one of said detection transducers; d) repeating steps b) and c) by successively activating several elementary transducers of the probe, so as to acquire detection signals associated with different transmission transducers;

e) from the detection signals acquired during each step c), meshing of the object according to several points, said points of the mesh, and calculating, at each point of the mesh, a parameter, representing an aptitude of the object to reflect an incident wave at said mesh point.

the method being characterized in that, step e) comprises the following substeps: i) selecting, for at least one point of the mesh, a number of elementary emission transducers less than the number of elementary transducers constituting the multi-element probe;

ii) calculating said parameter at said mesh point by considering the detection signals associated with the transmission transducers thus selected.

Preferably, the substeps i) and ii) are implemented for each point of the mesh, or for each point of the mesh located at a depth, vis-à-vis the said multielement probe, less than a so-called limit depth this limit depth can be predetermined.

Preferably, during the sub-step ii), the calculation of the parameter at said point of the mesh is performed by considering only the detection signals detected by the transducers selected in the sub-step i).

The method may comprise any of the following features, taken alone or in technically feasible combinations:

The object is a metal object, which can be especially intended for an aeronautical application. It may be a parallelepiped plate or a cylinder or having any other form adapted to be placed in contact with said multi-element probe. The invention is particularly applicable to materials in which the speed of an ultrasonic wave emitted by said elementary transducers is greater than 5000 m. s ^{' 1} ,, and in particular between 5000 and 7000 m. ^"1 .

During step i), the number of elementary transducers selected for said mesh point depends on a depth of said point relative to said multi-element probe. This depth corresponds to a distance between said point and the probe rnuitiéiément.

During step i), the number of elementary transducers selected for said mesh point depends on a mean depth of a region of interest previously determined in the object.

The emission limit angle is defined according to a main emitting lobe of a transmitting transducer. Such a lobe is present in an angular distribution of the amplitude of an ultrasonic wave emitted by said emission transducer. The emission limit angle can be determined by calculating a ratio between a speed of the wave in the object on a product of the frequency of the wave by a dimension of the transducer, this ratio corresponding to a tangent of this emission limit angle. The multi-element probe defines a detection plane, along which the elementary transducers extend. The transducers selected during the sub-step i) are included in a cone, said selection cone, defined for each point of the mesh, this selection cone:

extending between a vertex, corresponding to said mesh point, and said detection plane, at a half-angle corresponding to the emission limit angle; having a height, joining said vertex to the detection plane, this height being orthogonal to said detection plane.

The multi-element probe defines a pitch, corresponding to a distance between the centers of two adjacent elementary transducers. In the sub-step i), the selection is carried out, for a point, or even for each point of the mesh, by:

an estimate of an emission limit angle associated with an elementary transducer; determining a depth of said point of the mesh with respect to the probe; a determination of the elementary transducer closest to said point, said proximal transducer;

calculating a product of the tangent of said emission limit angle by said depth;

determining a number of selected elementary transducers around said proximal transducer by dividing said calculated product by said step of said multi-element probe.

Step e) comprises the following substeps:

for each point of the mesh, determining a travel time of an incident wave emitted by a transmission transducer, then reflected at said point, before being detected by a detection transducer, said transmission transducers and detector forming a transmitter / detector pair with which said travel time is associated;

for each point of the mesh, summation of the amplitude of each detection signal associated with a transmission transducer / receiving transducer pair, at said travel time associated with the same emitter / detector pair, so as to obtain a so-called cumulative amplitude point; the cumulative amplitude, obtained at each point of the mesh, representing an ability of the object, at said point, to reflect an incident wave.

The method comprises a step f) of locating a defect in the object, from the parameters determined at each point, during step e), and in particular from an image formed with the aid of each parameter calculated during step e).

At each point of the mesh corresponds a depth with respect to the multi-element probe, the sub-steps t) and ii) being implemented for a plurality of points of maiiiage whose depth is less than a limit depth, less than 2 cm, even 1 cm.

The multi-element probe is applied against said surface of the object, a thin thickness of a coupling fluid, in particular in a form of gel or liquid, which can be interposed between said probe and said surface of the object, so as to improve a transmission ^of a uitrasonore wave between each elementary transducer and the object.

A second object of the invention is an information recording medium, comprising instructions for executing the method described in the present application, these instructions being able to be executed by a microprocessor.

A third subject of the invention is a multi-element ultrasound probe, comprising a plurality of elementary transducers, each elementary transducer being able to emit and / or detect an ultrasonic wave, said probe being characterized in that it comprises a calculator, by example a microprocessor, able to implement the method described in this application.

The invention will be better understood in the description of a detailed exemplary embodiment given below, without limitation, this description being based on the figures listed below.

FIGURES

FIG. 1A represents an ultrasonic wave, emitted by an elementary transducer of a multi-element probe, propagating in an object. FIG. 1B represents an ultrasonic wave, reflected by a defect present in an object, propagating towards elementary transducers of a multi-element probe. FIG. 1C illustrates two signals respectively detected by two adjacent elementary transducers, each signal representing a detection of the reflected wave evoked in connection with FIG. 1B. FIG. 1D shows two adjacent transducers of the multi-element probe, these transducers defining a pitch of said probe. FIG. 2 represents the main steps of a method of controlling an object according to the prior art.

Figures 3A and 3B show two images of a defect in the object respectively located at a depth of 10 mm and 3 mm of the ultrasonic phased array probe. The gray scale is represented as a horizontal bar.

FIGS. 4A and 4B show an emission diagram of elementary transducers, this diagram comprising a main lobe and two secondary lobes. These figures respectively represent a configuration according to which, the object being meshed at different mesh points, a mesh point of the object is and is not positioned in the main lobe of an elementary transducer.

FIG. 5A represents a selection cone, associated with a mesh point of the object, under which said mesh point sees elementary transducers of the multi-element probe, in the first transmission lobe of which said mesh point is located.

FIG. 5B represents selection cones associated with different mesh points of the object, distributed at different depths.

Figure 6 shows the main steps of a method according to the invention.

FIGS. 7A and 7B are images respectively obtained with and without implementation of the method according to the invention. The gray scale is represented as a horizontal bar.

DESCRIPTION OF PARTICULAR EMBODIMENTS

FIGS. 1A and 1B show a multi-element ultrasound probe 1, comprising N elementary transducers li at 1 _N arranged side by side, extending in a direction D in a plane, called detection plane Pi. Each elementary transducer comprises a material piezoelectric, allowing the emission and detection of an ultrasonic wave. The probe is applied against an object 2 in order to control it. In this example, the examined object is a plate formed of a first material, for example an aluminum alloy, likely to include a defect 3, in this case an air cavity. The objective of the control is to detect and locate the defect 3. In other applications, the defect may be a presence of corrosion, a local variation of the porosity or, more generally, any local singularity resulting in a variation of the acoustic impedance in the object. Thus, in general, the object is an object intended for industrial use. It is in particular a metalic object. One of the elementary transducers 1 ,, said transmission transducer, can be activated, so as to emit an ultrasonic wave 10, said incident wave, propagating in the object 2. As indicated in connection with the prior art, the frequency This incident wave can range from 100 kHz to 50 MHz. Preferably, this frequency is between 1 and 15 MHz. In this example, it is 5 MHz.

In the presence of a defect in the object, a reflected ultrasonic wave 12 is formed, and propagates through the object, at the same frequency / as the emission wave 10. This reflected wave 12 is formed at the same time. fault interface. It is due to a local variation of the acoustic impedance at this interface. The reflected wave 12 propagates towards the multi-element probe 1 and can then be detected by several elementary transducers 1j, called detection transducers, including by the elementary transducer 1, having emitted the incident wave 10. In this example, it is possible to N = 64 elementary transducers. The reflected wave 12 is detected by the N elementary transducers, each forming a detection signal Sj j, the index i denoting the emission transducer and the index j denoting the detection transducer. FIG. 1C shows the signals S ₁ and S _1, respectively detected by two adjacent transducers _I ₁ and _I _1-1 , as a function of time. The detection of the reflected wave 12 is manifested on each of these signals by a characteristic variation of the amplitude, or pattern of detection, constituting a signature of the defect. The time shift of the signature between these two signals is due to the travel time, or flight time, of the reflected wave 12 between the defect 3 and each detection transducer.

1D shows two adjacent transducers l _n, l _n -i. These transducers have, in a direction D according to which the transducers of the multi-element probe 1 are aligned, a dimension a, corresponding here to a width. They are spaced apart from an intertransducer space e. The sum of the dimension a and of the inter-transducer space e forms a step Δ of the multi-element probe 1. This step Δ corresponds to a distance between the centers of two adjacent elementary transducers, or at an edge-to-edge distance of two adjacent transducers.

The multi-element probe 1 is preferably applied in contact with the object and rests on a surface of the object, called the support surface. This does not exclude the possible presence of a coupling fluid, in particular under the effect of a gel or a liquid, interposed between the multielement probe 1 and the object 2, so as to improve a transmission of 'a wave uitrasonore between each elementary transducer and the object, whether it is a sncsdenie wave or a reflected wave.

We will now describe a conventional method of controlling an object, in connection with Figure 2. This process is known under the name of FMC-TFM, meaning "Full Matrix Capture - Total Focusing Method".

According to a first step 100 of application, the probe 1 is applied vis-à-vis the object 2, and preferably in contact with a face of the latter or in contact with a wedge resting on the object .

According to an acquisition step 120, each transducer 1 is successively activated, and then becomes an emission transducer. During the activation of a transducer 1 ,, detection signals Sj j are acquired, which are detected by the N transducers of the multi-element probe 1. Also, at each activation of a transducer 1 ,, N is acquired. . After the successive activation of the N elementary transducers 1I ... 1N, there are N ² detection signals Sj j, each corresponding to a transmitter 1, - detector lj.

According to a step 140, the analyzed object 2 is discretized according to a mesh comprising K points said points of the mesh M _k , with 1 <k <K. The index k represents for example a coordinate of the mesh point M _k in the object. At each point M _k of the mesh, it is possible to calculate a travel time tfj of an acoustic wave, of frequency /, propagating between a transmission transducer 1, and the point M _k , then between this point and a transducer reception lj. The travel times can be obtained, for each point of the mesh M _k , considering the N ² pairs transmitter / detector previously mentioned. We can then constitute, for each point of the mesh M _k , a matrix T ^k , with T ^k = tfj, the dimension of this matrix being (N, N). This calculation step of each travel time tfj can be performed before or after the acquisition step 120. Each travel time tfj corresponds to the instant at which a wave 12, reflected consecutively to the emission of an incident wave 10 by a transmission transducer 10i, reaches a detection transducer 10j, the instant at which the incident wave is transmitted corresponding to the instant t = 0.

The next step 160, called the focusing step, consists in summing, for each point M _k of the mesh, the amplitudes of the signals Sy respectively at each instant tfj, or in a time interval θfj located around this instant. We can then calculate, for each point M _k of the mesh, a sum, called coherent sum A (k, (or cumulative amplitude), of the amplitude of each signal Sy at each instant tfj, so that:

This coherent sum represents a reflectivity of the object at each point M _k of the mesh. By reflectivity is meant a parameter representing the ability to form a reflected wave from an incident wave propagating in the object. During a step 180 of interpretation, the amplitudes associated with the different points M _k of the mesh can be combined to form a matrix A representing a spatial distribution of the cumulative amplitude A (k) in the object. Such a matrix may be represented in the form of an image / reconstruction, assigning a color code to each cumulative amplitude A (k) This method makes it possible to detect, as well as locate, the presence of defects 3 in the object 2 .

The multi-element probe 1 also comprises a computing unit, or processor 20, for example a microprocessor, capable of processing each detection signal Sy detected by the transducers 1j. In particular, the processor is a microprocessor connected to a programmable memory 22 in which is stored a sequence of instructions for performing the spectral processing operations and calculations described in this description. These instructions can be saved on a recording medium, readable by the processor, hard disk type, CD OM or other type of memory. The processor may be connected to a display unit 24, for example a screen.

FIGS. 3A and 3B show images obtained by implementing an ultrasonic phased array probe connected to a portable electronic acquisition system of the "Gekko" type, marketed by M2M. This probe has in particular 64 elementary transducers, of frequency 5 Hz, width equal to 0.8 mm aligned in a direction D, the spacing e between two adjacent transducers amounting to 0.2 mm.

FIGS. 3A and 3B respectively correspond to the result of the control of an aluminum plate, comprising an air cavity 3 with a diameter of 0.8 mm located respectively at a depth of 10 mm and 3 mm with respect to a bearing surface. , against which is applied the probe 1. This cavity is obtained by practicing a flat bottom hole in the aluminum plate.

The defect 3 is detected on these two images but it appears more clearly when it is located in depth, (image 3A) due to a more favorable signal-to-noise ratio. When located at Shallow depth (image 3B), the signal-to-noise ratio is mediocre. Thus, a fault located at a shallow depth may not be correctly identified.

The inventors have established a link between this problem and the emission diagram of an elementary transducer. Indeed, the emission of an acoustic wave by a piezoelectric transducer is not isotropic. The acoustic pressure field has a main lobe and several side lobes 10p 10 _s, as shown in Figures 4A and 4B. In other words, the amplitude of an acoustic wave emitted by a transducer is spatially distributed according to a main lobe and one or more secondary lobes.

The main lobe is even thinner as the depth relative to the array probe is low. Thus, a mesh point Mk may be located inside the main lobe of an elementary transducer, as shown in FIG. 4A, but may not be located inside the main lobe of another elementary transducer of the probe, as shown in Figure 4B.

An emission limit angle Θ can be assigned to each transducer, this angle delimiting the main lobe previously mentioned. This emission limit angle is, for example, defined by determining the position of the first local minimum on either side of the main lobe. This emission limit angle is shown in FIGS. 4A and 4B. In a reciprocal manner, as represented in FIG. 5A, at each point Mk of the mesh of the object 2 can be associated a cone Qk, called selection cone, of half-angle Θ, delimiting the elementary transducers in the main lobe of which Mk. One of the basic principles of the invention is then to select, among the elementary transducers of the probe, those for which the point Mk is placed in the main lobe 10 _p .

The emission limit angle Θ is considered to be known, for example on the basis of preliminary experimental tests, manufacturer data or a theoretical calculation. In this example, we consider that this angle Θ is such that:

tan (0) = - (2),

f.a

OR

/ denotes the frequency of the wave 10 emitted in the object 2;

a represents the dimension of each elementary transducer in the direction D according to which the transducers extend, referred to in connection with FIG. 1D;

c denotes the velocity of an ultrasonic wave in the object at the frequency of the wave emitted in the object; Preferably, the invention applies to objects consisting of materials in which the speed c of the ultrasonic wave is between 5000 and 7000 m, s ^"1. The dimension a of each elementary transducer is generally between 0.5 mm. and 2 mm.

Considering an aluminum plate [c-6200 ms ^"1 }, a frequency / of 5 MHz and a dimension equal to 0.8 mm, we obtain tan (#)" 1.5, which corresponds to an emission limit angle Θ about 57 ^".

In this example, it is assumed that the emission limit angle Θ is the same for all the elementary transducers of the multi-element probe 1.

At each point of the mesh M _k , it is possible to determine a so-called proximal transducer l _p closest to said point. It is also possible to associate, at each point of the mesh M _k , a depth z _k with respect to the multi-element probe 1, which corresponds to the shortest distance between said point and the multi-element probe 1. The selection of the transducers consists in defining a number

S of elementary transducers li _s ls, extending on either side of the proximal transducer l _p , so that the point of the mesh M _k is located in the main lobe 10 _p of each transducer thus selected. This selection can be undertaken for all or part of the points of the mesh M _k of the object.

As can be seen in FIG. 5A, it is possible to associate, at each point of the mesh M _k , a selection cone Q _k , whose vertex corresponds to the point M _k , whose half-opening angle corresponds to emission limit angle Θ. This cone has a height h perpendicular to the plane Pi along which the transducers extend. This height passes through the proximal transducer 1 _p . The S transducers selected (lis .... ls) are those extending within this selection cone. These transducers are shown in gray in Figure 5A. Note that at each point M _k of the mesh corresponds to a different selection cone. The selected transducers constitute a selection group G _s , represented by a brace in Figures 5A and 5B.

In the case of a one-dimensional probe, as shown in FIG. 5A, the number of selected transducers S is such that: S ≤ ^{2, Zfc, tan} ^^ (3)

^ a + e ¹ '

In this example, tan (0) is obtained according to (2), hence:

S <^^ (4)

fa (a + e) ^v '

or : z _k denotes a depth of the mesh point M _k in the object;

/ denotes the transmission frequency of the wave emitted in the object;

a represents the width of each elementary transducer, here equal to 0.8 mm;

e represents a spacing between two adjacent transducers, here equal to 0.2 mm; the sum a + e corresponds to the pitch Δ of the multi-element probe, previously defined, here equal to 1 mm.

Thus, the number of selected transducers S can be such that:

_S = a - ^ - (5)

f.a. (a + e) '

being a reduction factor such that 0 <≤ 1. Preferably 0.8 <≤. 1, so as to maximize the number of selected transducers, to improve the quality of the reconstruction.

The velocity of the ultrasonic wave c in the object 2 depends on the nature of the material constituting the object. Also this speed c is preferably estimated on the examined object. For example, when the object is a plate of known thickness, the velocity of the ultrasonic wave emitted by a transducer can be determined by affixing the probe to one side of the plate and analyzing the detected signals corresponding to a reflected wave. by the opposite side.

Compared to the prior art, the control method comprises, in the step of calculating the weighted sum A (k) associated with each point M _k , a selection of the transmission transducers to be considered, as described herein below. above. The calculation of the weighted sum is performed only on the basis of signals detected subsequent to the activation of the selected transducers, the latter being included in the selection cone associated with the point M _k . Thus, from one point of the mesh to another, the weighted sum A (k) is using detection signals Sy corresponding to emitter / detector pairs that may be different.

As can be seen in Figure 5B, the S number of transducers defined by the selection cone associated with a point of the mesh depends on the depth z _k of this mesh point. When the depth z _k is less than a limiting depth z, the number S of selected transducers is smaller than the number N of transducers of the probe. The invention therefore has the effect of reducing the number of transmitter / detector pairs to be considered when calculating the weighted sum A (k), considering only the emitters or even the detectors included in the selection cone. This goes against a prejudice that the quality of the measurement is all the higher as the number of transmitter-detector pairs is high. Beyond said limiting depth z _is the selection cone. encompasses all the transducers of the multi-element probe and the invention has no effect for calculations performed on points of the mesh placed beyond this limit depth. This limiting depth is obtained by using equation (5) considering S = N, ie: N _¾ ^ (6)

a + e ¹ 'd or: z _f ÎK --- {,')

¹ . tarife)

Considering N = 64, Δ = (a + e) = 1 mm, tan (0) ~ 2.48, z ₍ ¾ 5 mm is obtained Thus, the invention applies particularly to the part of the object located between the bearing surface, on which is placed the probe, and the first 5 millimeters of the object.In general, the limiting depth z _t is generally less than 3 cm or even 2 cm. at 1 cm.

We will now describe, in connection with Figure 6, the main steps of a method according to the invention. The steps 100, 120 and 140 are similar to those described with reference to FIG. 2. The calculation step 160 comprises:

a sub-step 160a for selecting, for each point of the mesh Mk, a group G _s of elementary transducers, comprising transducers located in the selection cone. associated with the said point of the mesh, this cone depending on the depth z _k of this point and the emission limit angle Θ.

a calculation sub-step 160b in which only Sy signals detected subsequent to the activation of a transducer selected in step 160a are considered. In other words, during step 160b, only detected signals Sy corresponding to a transmitter / detector pair whose emitter or detector is considered to be one of the selected transducers are considered.

According to one embodiment, during the sub-step 160b, only the signals detected by the transducers selected during the step 160a are considered. Also, the cumulative amplitude A (k) calculated at each point of the mesh Mk is:

According to another embodiment, during the sub-step 160b, the signals detected by the set of transducers constituting the probe 1 are considered. Also, the cumulative amplitude A (k) calculated at each point of the mesh Mk is: According to a variant, the number S of transducers is predefined and applies regardless of the depth z _k of the mesh point M _k . It is smaller than the number N of elementary transducers constituting the probe 1. The number of selected transducers can be determined by considering a region of interest of the object ROI, in which an increased control accuracy is desired. The selection is made by considering an average depth z _R0I of the points of the mesh present in the region of interest. This region of interest may have been defined on the basis of a preliminary control, or by implementing a method of the prior art, as described with reference to FIG.

The selection step 160a may be applied to all or part of the points M _k of the mesh. When these points are located at a depth z _k of the probe 1 less than the z-limit depth previously mentioned, the calculation of the cumulative amplitude is made on the basis of a number of emission transducers S less than the number of transducers. N component phased array probe.

A comparative test was carried out by controlling the object described with reference to FIG. 3B, comprising a defect located at a depth of 3 mm. In a first step, a method according to the prior art, described with reference to FIG. 2, was implemented. In a second step, a method according to the invention, represented in FIG. selecting, at each point of the mesh, 16 elementary transducers. FIGS. 7A and 7B respectively represent the results obtained by implementing the invention and the prior art. It is observed that Figure 7A is less noisy than Figure 7B, which attests the effectiveness of the invention.

Although described in relation to a one-dimensional probe, in which the transducers extend along a line, the invention applies to two-dimensional probes, for example matrix probes, in which the transducers are distributed according to a matrix in the detection plane Pi. On the other hand, the invention has been described in connection with a determination of a defect in an industrial part, in this case an aluminum plate. This application is not limiting and the invention can be applied to the detection of singularities in other types of applications concerning the control of industrial objects.

Claims

1. A method for controlling an object (2) for industrial use comprising the following steps: a) application of a multi-element probe (1) facing said object (2), said probe comprising a plurality of elementary transducers (li .. .l _N ), each elementary transducer being able to emit an ultrasonic wave towards said object and / or to detect an ultrasonic wave (12) reflected in said object;

b) activating one of said elementary transducers (1,), said transmission transducer, so that it transmits an ultrasonic wave, said incident wave (10), to said object;

c) acquisition, by a plurality of said elementary transducers (lj), said detection transducers, of a detection signal (Sy) representative of a reflected wave (12) by the object under the effect of said incident wave, each detection signal being associated with said transmitting transducer (1,) and with one of said detecting transducers (lj); d) repeating steps b) and c) by successively activating several elementary transducers of the probe, so as to acquire detection signals (Sy) associated with different transmission transducers (1,);

e) from the detection signals (Sy) acquired during each step c), meshing the object according to several points (M _k ) and calculating, at each point of the mesh (M _k ), a parameter (A (k)) representing an aptitude of the object, at said point of the mesh, to reflect an incident ultrasonic wave;

the method being characterized in that,

o step e) comprises the following substeps:

i) selecting, for at least one point of the mesh (M _k) of a number (S) of emission transducers (li ... _s l _s) less than the number (N) of transducer elements constituting said phased array probe (1);

ii) calculating said parameter (A (k)) at said mesh point (M _k ) by considering the detection signals (Sy) associated with the transmission transducers (li _s ... l _s ) thus selected; the multi-element probe defines a step (Δ), corresponding to a distance between the centers of two adjacent elementary transducers (l _n , ln-i), and during the sub-step i), the selection is carried out, for each point of the mesh M _k , by: an estimate of an emission limit angle (Θ) associated with an elementary transducer (li), said emission limit angle (Θ) delimiting the main lobe (10 _p ) of the sound pressure field of the elementary transducer (1, );

determining a depth (z _k ) of said point with respect to the multi-element probe;

a determination of the elementary transducer (l _p ) closest to said point, said proximal transducer;

calculating a product of the tangent of said emission limit angle (Θ) by said depth (z _k );

a determination of a number (S) of selected elementary transducers around said proximal transducer, by dividing said product by said step (Δ) of said multi-element probe (1).

2. Method according to claim 1, wherein during step i), the number of transmission transducers (S) selected for said mesh point (Mk) depends on a depth (z _k ) of said point relative to said multi-element probe (1), said depth corresponding to a distance between said mesh point and said multi-element probe;

3. Control method according to the preceding claim, wherein the substeps i) and ii) are performed for each point of the mesh (Mk) of the object.

4. Control method according to any one of the preceding claims, wherein in the sub-step i), the selection is carried out according to an emission limit angle (Θ), according to which a transmission transducer ( 1,) emits an incident wave (10).

5. The method of claim 4, wherein said emission limit angle (Θ) is defined according to a main lobe (10 _p ) of emission of a transmission transducer (1,).

6. Control method according to any one of claims 4 or 5, wherein the multielement probe (1) defining a detection plane (Pi), which extend the elementary transducers (li ... l _N ), the transducers selected during the sub-step i) are included in a cone, said selection cone (Ωι <), defined for each point of the mesh (Mk), this selection cone:

extending between a vertex, corresponding to said mesh point (Mk), and the detection plane, at a half-angle corresponding to the emission limit angle (Θ); having a height (h), joining said vertex to the detection plane (Pi), this height being orthogonal to said detection plane.

7. Control method according to any one of the preceding claims, wherein step e) comprises the following sub-steps:

for each point (Mk) of the mesh, determining a travel time (tfj) of an incident wave emitted by a transmission transducer (1,), then reflected at said point (Mk), before being detected by a detection transducer (l _j ), said transmission and detection transducers forming a transmitter / detector pair to which said travel time (tfj) is associated;

for each point of the mesh (Mk), summation of an amplitude of each detection signal (Sy) associated with a transmission transducer / detection transducer pair, at said travel time (tf) associated with the same transmitter / detector pair , so as to obtain, at said point, a so-called cumulated amplitude (A (k)) such that:

NN

the cumulative amplitude (A (k)), obtained for each point of the mesh (Mk), representing an ability of the object, at said point, to reflect an incident wave.

8. Control method according to any one of the preceding claims, comprising a step f) of locating a defect in the object, from the parameters (A (k)) determined at each point, during the step e).

9. Control method according to any one of the preceding claims, wherein said multielement sensor (1) is disposed in contact with said object (10).

10. Control method according to claim 9, wherein a liquid or a coupling gel is interposed between said probe and said object, so as to improve transmission of an ultrasonic wave between each transducer and the object.

11. Control method according to any one of the preceding claims wherein the velocity of an ultrasonic wave emitted by each elementary transducer in the object is between 5000 and 7000 ms ^-1 .

12. Control method according to any one of the preceding claims, wherein at each mesh point corresponds a depth (z _k ) with respect to the multi-element probe (1), and in which the substeps i) and ii) of step e) are implemented for a plurality of mesh points (Mk) whose depth is less than 2 cm or less than 1 cm.

A computer-readable recording medium on which a computer program is recorded, comprising program code instructions for executing the steps of the method according to any of the preceding claims, which instructions are adapted to be performed by a microprocessor (20).

14. ultrasonic array probe (1), comprising a plurality of elementary transducers (li ... l _N ), each elementary transducer being able to emit and / or detect an ultrasonic wave (10, 12), said probe being characterized in that it comprises a microprocessor (20) adapted to implement the control method according to any one of claims 1 to 12.