EP1687804B1 - Ultrasonic contact transducer comprising multiple emitting elements and means for pressing said elements - Google Patents

Description

TECHNICAL AREA

The present invention relates to an ultrasonic contact transducer with multiple ultrasound emitting elements.

It applies in particular to medicine and non-destructive testing of mechanical parts, in particular parts having a complex shape or an irregular surface condition, for example due to local grinding or adding of material.

STATE OF THE PRIOR ART

During the examination of certain parts by ultrasound, it is necessary to place an ultrasonic transducer on a material whose shape (geometric) superficial evolves according to the relevant area of the material.

In this case, the acoustic coupling between the materials and the front face of the transducer is not optimal and the acoustic characteristics of transmitted ultrasonic beams are no longer conserved. The quality of the inspections is then degraded.

Classical techniques do not allow to completely control parts whose geometry varies.

For example, geometric variations such as bends or taps are common on piping systems. However, it is often the parts with strong geometric variations that are subject to the highest mechanical constraints and therefore require the most frequent controls.

In order to optimize the control of such areas, an ultrasonic transducer has been developed, capable of adapting to any shape of parts.

It was first sought to ensure optimal coupling between this transducer and the surface of a room. To do this, a monolithic transducer has been replaced by a set of independent elementary transducers, this assembly being capable of deforming in contact with the surface of the part. This has improved the contact of the transducer with the surface of the test piece.

It should be noted that elementary transducers constitute a multi-element array ("array") whose various acoustic characteristics must be determined.

Then, ultrasonic waves having the characteristics (refraction angle and depth of focus in the room) required for the control must be transmitted in the controlled room. Transmit delays are then imposed on the transducer elements by appropriate electronic means to form the desired ultrasonic beam.

Then we sum the electrical signals provided by ultrasonic sensors which are provided with the transducer, these sensors may be the elements mentioned above, which are then used as elementary ultrasonic receivers.

To calculate the delays, which depend on the geometry and the constituent material of the controlled part and on the characteristics sought for the ultrasonic beam, and to reconstruct the excitation signal of the elementary emitters, simulation software is used which is integrated into the electronic means for controlling the transducer.

It is also necessary to know the shape of the surface of the piece (which is a priori unknown). To do this, the transducer is equipped with means capable of providing data that make it possible to know the local geometry of the controlled part. These data are injected in real time into the control means of the transducer and the corresponding delay laws are recalculated. This provides an adaptive transducer that can be considered "intelligent".

1. [1] WO 00/33292 A , « Transducteur ultrasonore de contact, à éléments multiples », correspondant à US 6 424 597 A .

Such a transducer is known from the following document to which reference will be made:

1. [1] WO 00/33292 A , "Multi-element ultrasonic contact transducer", corresponding to US 6,424,597 A .

• [2] US 5 913 825 A , « Ultrasonic probe and ultrasonic survey instrument », correspondant à JP 10 042 395 A
• [3] US 5 680 863 A , « Flexible ultrasonic transducers and related systems ».

Flexible ultrasonic transducers are also known from the following documents:

• [2] US 5,913,825 A , "Ultrasonic probe and ultrasonic survey instrument", corresponding to JP 10,042,395 A
• [3] US 5,680,863 A , "Flexible ultrasonic transducers and related systems."

US 4,437,468 A discloses an ultrasonic scanning system with a network of semi-independent transducers.

However, the transducers known from documents [1] to [3] do not allow to maintain an optimal coupling between them and complex parts, especially when these transducers are moved to the surface of such parts.

STATEMENT OF THE INVENTION

The present invention aims to overcome this disadvantage.

To do this, the present invention provides an ultrasonic transducer according to claim 1. Preferred embodiments are covered by the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

• la figure 1 est une vue schématique d'un mode de réalisation particulier du transducteur objet de l'invention, utilisant des photo-émetteurs et des photo-détecteurs,
• la figure 2 est une vue schématique et partielle d'un autre mode de réalisation particulier, utilisant des fibres optiques, et
• la figure 3 est une vue en coupe schématique d'un transducteur ultrasonore matriciel conforme à l'invention.

The present invention will be explained on reading the description of exemplary embodiments given below, purely by way of indication and in no way limiting, with reference to the appended drawings in which:

• the figure 1 is a schematic view of a particular embodiment of the transducer which is the subject of the invention, using photo-emitters and photo-detectors,
• the figure 2 is a schematic and partial view of another particular embodiment, using optical fibers, and
• the figure 3 is a schematic sectional view of a matrix ultrasonic transducer according to the invention.

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

The ultrasound transducer according to the invention, which will be described with reference to the figure 1 , is a flexible transducer with instrumentation that is suitable for controlling compact, complex-shaped parts that are difficult to access.

This transducer incorporates plating means and profile measuring means (relief sensor).

The plating means provide a permanent acoustic coupling of the emitter elements of the transducer with the part to be inspected, during the scanning thereof, while individual optical sensors measure the positions of spring pistons which is provided with the transducer. These measurements make it possible to deduce the profile of the part to determine laws of delay adapted to this part.

In order to minimize the size of the transducer and to make it grippable, the plating means and the means for measuring the deformation of all the emitting elements in contact with the workpiece are grouped together. The coupling of these means makes it possible to integrate, in the restricted volume of the transducer, a sufficient number of optical sensors and adaptive electronic means.

The figure 1 is compared to Figure 4 of document [1] to which we will refer.

In the example of the figure 1 , a linear bar-type transducer is used, which only corrodes deformations in the plane of incidence of the ultrasound, namely the plane (x, z) of the figure 1 .

This transducer comprises ultrasonic transceiver elements 2 forming a flexible assembly and connected, for this purpose, by elastic and flexible means 4.

• un câble, dans le cas d'un transducteur flexible à deux dimensions, ou
• un substrat en résine polymère, dans le cas d'un transducteur flexible à trois dimensions.

These means 4, which ensure the mechanical cohesion of the elements 2 and the flexibility of all of them, can for example be

• a cable, in the case of a flexible two-dimensional transducer, or
• a polymer resin substrate, in the case of a flexible three-dimensional transducer.

• une lame de polymère piézoélectrique souple et un réseau d'électrodes juxtaposées, obtenues par dépôt métallique, ou
• un ensemble d'éléments piézoélectriques rigides, coulés dans un substrat souple, inerte vis-à-vis des ultrasons, ou
• un ensemble d'éléments ultrasonores rigides, assemblés mécaniquement de façon à obtenir une structure articulée.

More generally, as mentioned in document [1], it is possible to use

• a flexible piezoelectric polymer plate and an array of juxtaposed electrodes, obtained by metal deposition, or
• a set of rigid piezoelectric elements, cast in a flexible substrate, inert with respect to ultrasound, or
• a set of rigid ultrasound elements, mechanically assembled so as to obtain an articulated structure.

In the example of the figure 1 using a known linear and deformable multi-element strip, the piezoelectric elements 2 of which have a trapezoidal shape.

To keep these piezoelectric elements 2 pressed against the part to be controlled 6, the transducer comprises spring pistons 8 and a metal foil 10 which constitutes a leaf spring. The latter is placed on all the rear faces of the elements 2, each of these having a front face, or active face, which is in contact with the surface of the workpiece 6, the set of active faces constituting a deformable emitting surface.

The metal foil 10 distributes the vertical forces exerted by the spring pistons and also allows the elements 2 to tilt transversely without being blocked by the pistons 8.

The transducer of the figure 1 also comprises a rigid housing 12 whose multi-element bar is secured. This housing 12 comprises a set of parallel holes 14 whose axes are coplanar and whose number is equal to the number of spring pistons.

Each spring piston 8 comprises a movable part 16, which is able to slide in the corresponding hole, and a spring 18 which is traversed by this movable part 16 and between the housing 12 and the end 20 of this moving part, which is closest to the elements 2.

This end 20 is wider than the rest of the moving part, to retain the spring 18. In addition, this end 20 is rounded, preferably hemispherical, as seen on the figure 1 , to optimize the pressure exerted on the rear faces of the elements 2 by means of the metal foil 10.

When the transducer is applied against the workpiece 6, the springs 18 are compressed and therefore tend to move the ends 20 away from the housing 12, so that the elements 2 are permanently held pressed against the workpiece 4.

In each hole 14 is placed a ball bushing 22, which has the same axis as this hole and in which slides the movable portion 16 of the piston corresponding to this hole. This ball bushing 22 is intended to improve the displacement of this part moving in the hole, to reduce the friction during this movement and to eliminate the clearance between this movable part and the hole.

The positions of the elements 2 relative to the part 6, during the displacement of the transducer, are determined by means of the spring pistons.

To do this, the upper part of the housing 12 comprises a plate (rigid) 24 which closes the upper ends of the holes 14 and which constitutes a geometrical reference for the measurements of the positions of the elements 2. In each hole 14, it is fixed to this plate 24 a light-emitting diode 26 and a photodetector 28 in an area 29 of the plate, located opposite the other end 30 of the movable portion 16 of the piston corresponding to this hole.

This other end 30 is perpendicular to the axis X which is common to the hole 14 and to this movable part 16 and is polished or made reflective, for example polished, to form a mirror. This mirror reflects a fraction of a light beam emitted by the light-emitting diode 26. The quantity of reflected light energy is a decreasing function of the distance of the moving part from the light-emitting diode 26.

The light beam reflected by the mirror is captured by the photodetector 28 which is placed next to the diode 26. This photodetector then provides a photo-current which is a function of the distance between the end 30 of the part 16 and the photodetector (and therefore the plate 24) and Therefore, the position of the elements 2 relative to the rigid portion 12 (knowing the length of the moving parts 16).

Programmable electronic means 32 are provided for controlling the light-emitting diodes 26, for digitizing the photo-current from each photodetector 28 and for converting this photocurrent into a displacement.

However, the curve of the displacement variations as a function of the photo-current is not linear so that a calibration is necessary.

This calibration is performed during an acquisition step during which the photocurrent is measured for several calibrated positions of the movable part 16 of each piston 8, over the entire extent of this piston, that is to say say all the possible move for the latter.

After having calibrated each photodetector, it is therefore possible to convert the measured photocurrent into a displacement.

The respective positions of the photodetectors with respect to the rear faces of the elements 2 being known, the profile described by these rear faces of the elements is reconstructed by interpolation methods. Then projection operations provide the coordinates of the surface of the part 6.

More specifically, the means 32 are furthermore provided for determining the positions of the rear faces of the elements 2 with respect to the rigid housing 12.

Auxiliary processing means 34 determine the positions of the active faces of the elements 2 relative to the housing, as a function of the positions of the rear faces thus determined (see document [1]).

An articulated mechanical arm 36 makes it possible to obtain the position and the orientation of the transducer in the fixed reference of the part to be controlled 6. Sensors 38, of which the arm 36 is provided, make it possible to locate this transducer in space and to measure its orientation during its movement relative to the part 6, as indicated in the document [1].

On the figure 1 Means 40 are also seen which, depending on the positions provided by the means 34 and depending on the position and the orientation provided by the sensors 38, determine the positions of the transducer relative to the part 6.

• engendrer des impulsions d'excitation des éléments 2,
• établir, à partir des positions ainsi déterminées, des lois de retard permettant aux éléments 2 d'engendrer un faisceau ultrasonore focalisé F, dont les caractéristiques sont maîtrisées par rapport à la pièce 2, et
• appliquer ces lois de retard aux impulsions d'excitation.

We also see control and processing means 42 provided for

• generate excitation pulses of the elements 2,
• establishing, from the positions thus determined, delay laws allowing the elements 2 to generate a focused ultrasound beam F, whose characteristics are controlled with respect to the part 2, and
• apply these delay laws to excitation pulses.

The elements 2 then provide signals to the means 42 also provided for forming, at from these signals, images relating to the part 6.

These images are displayed on a screen 44. As explained in document [1], it is also possible to use inertial sensors to obtain the position and the orientation of the transducer.

The light-emitting diodes may be controlled so as to emit continuous or, on the contrary, discontinuous light beams, in particular light pulses.

The means 32 may be provided for interrogating the desired photodetector 28 by controlling the corresponding light emitting diode.

The figure 2 is a schematic and partial view of a variant of the transducer of the figure 1 . In this variant, optical fibers are used to transmit the light to the respective second ends of the moving parts of the pistons and to transmit the lights respectively reflected by these second ends.

In the example of the figure 2 , the means 32 control a light source 46 whose light is sent to the ends of optical fibers 48, whose number is equal to that of the pistons, via an optical coupler 50. The other ends of the fibers 48 open respectively in the holes 14, as we see on the figure 2 , to be able to "illuminate" the reflective ends 30 of the moving parts 16.

It is also possible to use an optical fiber light source.

It can be seen that each of the other ends of the fibers is fixed to the zone 29 of the plate 24, facing the corresponding end 30.

Other optical fibers 52, the number of which is equal to that of the fibers 48 and whose ends open into the holes 14, next to the ends of the fibers 48, and are respectively fixed to the zones 29 opposite corresponding ends.

The fibers 52 make it possible to recover the lights reflected by the reflective ends 30 of the moving parts 16 and transmit these lights respectively to photodetectors 54. These latter then generate photocurrents which are transmitted to the means 32.

In the examples of the invention, which has just been described, the distance measuring means, in particular for detecting displacements of the pistons, are optical means, thus allowing optical detection of these displacements.

However, these optical means can be replaced by magnetic means.

In an example not shown, each diode 26-photodetector assembly 28 is replaced by figure 1 by a Hall effect sensor and a magnet is fixed on the end 30 of the movable part of the corresponding piston.

The Hall effect sensor is thus able to provide a signal that is a function of the distance between this sensor and this magnet. By replacing the means 32 of the figure 1 by appropriate means of controlling the sensor and signal processing provided by it, one is thus still able to measure the desired distance.

In a variant (not shown) of this example, the magnet is attached to the plate 24, next to the Hall effect sensor, in the corresponding hole 14, and at least the end 30 of the movable part of each piston is made of a magnetic material such as steel.

The magnetic field detected by each sensor is then disturbed by the corresponding end 30 and the sensor further provides a signal which is a function of the distance between this end 30 and this sensor.

In addition, the examples of the invention that have been given use elements that are both transmitters and receivers of ultrasound. Those skilled in the art can adapt these examples to the case of transducers comprising elements only intended to emit ultrasound and other elements only intended to receive ultrasound.

In addition, in these examples, transducers comprising a linear array of ultrasonic elements are used, but the invention is not limited to such transducers. As in the document [1], those skilled in the art can adapt the given examples to matrix transducers.

It is then necessary to associate parallel rows of spring pistons with such a matrix transducer, these rows being of the type described with reference to FIG. figure 1 , and provide a metal foil on the rear faces of the elements that includes the transducer.

We give below, with reference to the figure 3 , another example of the invention which is more particularly usable in the case where the ultrasonic elements form not a row but a matrix.

The transducer according to the invention, which is seen in section on the figure 3 , comprises a matrix of ultrasonic transceiver elements 56 which are trapped in a flexible resin substrate 58, this substrate being ultrasonic passive.

To maintain the piezoelectric elements 56 pressed against a part to be controlled 60, which is convex in the example of the figure 3 , the transducer comprises a spring piston piston assembly 62 and a rigid housing 64 whose flexible substrate 58 is secured in a manner to be explained later.

The housing 64 comprises a matrix assembly of parallel holes 66 which are respectively associated with the spring pistons. Each spring piston comprises a movable part 68, which is able to slide in the corresponding hole, and a spring 70 which is traversed by this movable part and between the housing 64 and the end 72 of this movable part, which is the closer to the elements 56. This end is rounded, preferably hemispherical, as in the case of the figure 1 .

Ball bushings 74 are still provided to improve the movement of the parts movable 68 in the corresponding holes 68 as seen on the figure 3 .

In the example of this figure 3 , the positions of the elements 56 relative to the part 60, during the displacement of the transducer, are determined by means of the spring pistons and, for this purpose, each piston is associated with a position sensor 76 as in the example of the figure 1 .

In the example of the figure 3 it is also an optical sensor, comprising a light emitter in the direction of the piston and a receiver of the light reflected by the rear end of the movable portion 68 of the piston, made reflective for this purpose.

Preferably, strips 78 are fixed to the upper surface of the flexible substrate 58, respectively facing the hemispherical ends 72 of the pistons, and thus form a matrix assembly. These slats make it possible to distribute the vertical forces exerted by the spring pistons. These slats preferably form thin metal discs whose diameter is equal to that of the hemispherical ends.

The transducer of the figure 3 also comprises four supports 80, which for example form angles and are at 90 ° to each other, only two of these supports being visible on the figure 3 . Each of these supports is secured to the flexible substrate 58 via a rod 82 which is articulated relative to this support. This rod 82 is slidable in an insert 84 which is embedded in the flexible resin substrate 58.

Each of these supports 80 is furthermore fixed at one end of an axis 86. The other end of these axes is able to slide in a hole 88 which passes through the rigid casing, as can be seen in FIG. figure 3 . This hole is parallel to the holes 66 in which the moving parts of the pistons slide.

The use of rods 82 sliding in the inserts 84 prevents the appearance of lateral tensions that could tear the substrate 58.

In addition, the mechanical system comprising the supports 80, the rods 86, the inserts 84, and the pins 82 makes it possible to prevent any rotation of the flexible substrate 58, and thus of all the elements 56.

If desired, the movement of the flexible substrate 58 relative to the housing 64 can be measured by means of position detectors 90, of the kind of the detectors 76, and making it possible to measure the stroke of the axes 86 which make it possible to maintain the flexible substrate.

On the figure 3 , we also see springs 91 through which the rods 86 and which are between the supports 80 and the rigid casing 64.

We can also associate with each of these rods 86 another rod 92 slidable in the rigid housing 64, through a ball bushing 94, and attached to the corresponding support 80. As can be seen on the figure 3 a spring 96 is then provided between this support 80 and the rigid casing 64 and traversed by this other rod 92.

The rigid casing 64 can be made integral with an electronic box 98 which can also serve as a handle for the transducer. To the party superior of this electronic unit 98, we see elements 100 allowing electrical cables (not shown) out of this housing. These cables allow the transport of signals provided by the transducer and by the position sensors 76.

At the base of this electronic box 90, there is a base 102 provided to receive electrical connectors (not shown) from the various ultrasonic elements 56 and to connect these connectors to electronic means contained in the housing 98 and to control these elements 56 and to process the signals provided by them.

The rods 92, which are associated with the ball bushings 94 and the springs 96 could be replaced by simple brackets fixed to the supports 80 and slidable in holes provided for this purpose in the rigid housing 94.

For the sake of clarity, the various electrical connections that are necessary to the transducer of the figure 3 are not represented.

Likewise, the various control and signal processing means, which are necessary for the operation of this transducer, are not represented. These means, which correspond to a matrix transducer, can be determined by those skilled in the art, from the means of the same kind which have been described with reference to the figure 1 , about a linear transducer.

Claims (10)

1. Ultrasonic contact transducer with multiple elements (2), this transducer being characterised in that it comprises means (8, 10) of bringing the elements into contact with the surface of an object to be checked (6) and means (26, 28, 34, 36, 38, 40) of determining the positions of the elements relative to the object, using the means of bringing the elements into contact, and in that each element (2) is at least an ultrasonic emitter and the emitting elements (2) are rigid and are assembled to each other mechanically so as to form an articulated structure, the transducer being characterized in that the emitting elements are rigid piezoelectric elements trapped in a flexible substrate that is passive with regard to ultrasounds,in which the transducer can be moved relative to the object to be checked (6) and has a deformable emitting surface formed by first faces of the elements and that will be brought into contact with the surface of this object and starting from which ultrasounds are emitted towards the object, control means (42) being provided to generate excitation pulses of the emitting elements, the determination means (26, 28, 34, 36, 38, 40) being designed to define positions of the ultrasound emitting elements relative to the object during displacement of the transducer,
   processing means being provided to

   - determine, starting from the positions thus determined, delay laws that emitting elements use to generate a focused ultrasonic beam (F) for which the characteristics are controlled with respect to the object, and

   - apply these delay laws to the excitation pulses,

   ultrasound receiving elements, possibly composed of the emitting elements (2), being designed to supply signals used to form images related to the object,
   the means (8, 10) for bringing into contact being provided to bring the emitting elements into contact with the surface of the object and the determination means being provided to determine the positions of the emitting elements relative to the object through the means bringing the emitting elements into contact, in which the means for bringing the emitting elements into contact with the surface of the object comprise mechanical elements (8), each mechanical element including a portion (16) that is free to move relative to a rigid portion (12) of the transducer, a first end of this moving portion being capable of pressing emitting elements into contact with the surface of the object,
   and the means of determining the positions of the emitting elements relative to the object comprise

   - first means (26, 28, 34, 48, 52) provided to determine the positions of the emitting elements (2) relative to the rigid portion (12) of the transducer, by measuring the deformation of the emitting surface, and to output signals representative of the positions thus determined, the first means comprising

   • distance measurement means (26, 28, 48, 52), provided to measure the distance between a second end (30) of the moving portion (16) of each mechanical element (8) and an area (29) of the rigid portion (12) of the transducer and

   • auxiliary processing means (34) provided to determine the positions of the emitting elements with respect to the rigid portion of the transducer, using the distances thus determined,

   - second means (36, 38) provided to determine the position and orientation of this rigid portion (12) with respect to the object and to output signals representative of the position and the orientation thus determined and

   - third means (40) provided to output the positions of the emitting elements with respect to the object using signals output by the first and second means,

   in which the distance measurement means (26, 28, 48, 52) are provided to optically measure the distance between the second end (30) of the moving portion (16) of each mechanical element (8) and an area (29) of the rigid portion, and comprise

   - light emission means (26, 48) fixed to the rigid portion and designed to emit light towards this second end, this second end being capable of reflecting this light, and

   - light reception means (28, 52) fixed to the rigid portion and provided to receive the light thus reflected, these reception means being capable of outputting signals representative of the distance between this second end and the corresponding zone.
2. Transducer according to claim 1, in which the first end (20) of each moving portion (16) is rounded.
3. Transducer according to any one of claims 1 and 2, in which the rigid portion (12) of the transducer comprises parallel holes (14) in which the moving portions (16) are respectively free to slide, and each mechanical element also includes elastic means (18) capable of separating the first end of the moving portion corresponding to this mechanical element, from the rigid portion.
4. Transducer according to claim 3, in which each mechanical element also comprises a means (22) in the hole corresponding to it, in which the moving portion of this mechanical element is free to slide with low friction.
5. Transducer according to one of claims 1 to 4, in which the light emission means and the light reception means include a photo-emitter (26) and a photo-detector (28) respectively, fixed to the rigid portion (12) facing the second end (30).
6. Transducer according to claim 5, in which the light emission means include a first optical fibre (48) to transmit light and send the light to the second end (30), and the light reception means include a second optical fibre (52) to transmit light reflected by this second end.
7. Transducer according to any one of claims 1 to 6, in which the optical distance measurement means (26, 28, 48, 52) use continuous light beams.
8. Transducer according to any one of claims 1 to 7, in which the optical distance measurement means (26, 28, 48, 52) use discontinuous light beams and particularly trains of light waves.
9. Transducer according to any one of claims 1 to 8, in which the means of bringing the emitting elements into contact also include a blade (10) that covers second faces of the emitting elements, the first end of the moving portion of each mechanical element (8) being capable of pressing emitting elements in contact with the surface of the object (6) through the blade, this blade being capable of distributing forces applied by the moving elements on the emitting elements through the blade.
10. Transducer according to one of claims 1 to 9, also comprising strips, the number of which is equal to the number of emitting elements and that are fixed to the face of the flexible substrate that is located facing the mechanical elements, each strip facing the moving portion of one of these mechanical elements, the first end of this moving portion being capable of pressing the emitting elements in contact with the surface of the object through the strip facing it.

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