The present invention concerns a method for dimensional inspection of a machine part, in particular turbomachine.

machine parts, including parts rotating turbomachinery such as blades that can be impacted by foreign bodies, degrade as you use the machine. This is particularly true of the areas reinforced by depositing a layer of Stellite (very hard material) that degrade because of strong friction they experience.

To comply with safety standards parts, especially areas Stellite, should have a maximum level of wear on pain of needing replacement. Thus, during maintenance operations, the parts are examined to determine if their level of wear is acceptable or not. If unacceptable level of wear, the part must be replaced.

A known method to control the level of wear of turbomachine parts consists of an operator:

- dismantled parts;

- measuring the thickness of the parts by means of coordinate measuring machines by contact;

- compares these measurements with tolerances ranges, and

- defines whether the parts can be lifts on the turbo or must be replaced.

This method does not achieve an accurate measurement of the thickness of the pieces. Indeed, several parameters affect negatively on the extent of the parts.

First, the operations performed by the operator, are repetitive. Thus, and this is particularly the case for measuring and comparing the measurements, the visual ability of the operator decreases progressively during a working day and the operator can, in the late afternoon misinterpret a measure . This may be the case for the last part of a series of identical parts.

Second, three-dimensional contact measuring machines use elements such as scale as readers or sensors that can become misaligned or worn over time. It is then necessary to calibrate, repeatedly, these elements or replace. These calibrations or such replacements require temporary immobilization of the machine and generates significant operating cost.

Third, the sensors commonly used include a rod terminated by a ball coming into contact with the part to be measured. Although fairly accurate measurements can be obtained, some areas of the room, including inaccessible areas or very small may not be achieved by the sensor. Thus, measurement of the play can not be performed optimally.

Finally, mounting the workpiece on a bench of the measuring machine and the wear of said bench influence on the quality and the result of the measurement. Thus, the repeatability of the measurement is not optimal.

The invention particularly aims to provide a simple, efficient and economical to this problem.

To this end, the invention proposes, firstly, a method for dimensional inspection without contact of the wear of a turbomachine component, the method comprising steps in which, via a computer:

- defining a reference plane having a first repository;

- it acquires, by measurement on said workpiece to control, a model of at least a portion of said workpiece in the form of a three-dimensional control mesh with a second reference, the first and second repositories being each oriented in a predetermined manner by respect to a third own repository to the turbine engine;

- one control room, in a common area in three-dimensional mesh and the reference plane by means of a dedicated algorithm using a projection points and wherein:

o to said common area, the reference plane comprises a field theoretical points which are projected in a projection perpendicular to said reference plane from said reference plane to the three-dimensional control mesh;

o for each projected point, a projection distance is calculated between the reference plane from which said point is projected and said intersection point with the three-dimensional control mesh;

o comparing projection distances of the points, so as to identify a maximum distance from said projection distances, and the projected point of maximum wear corresponding thereto,

o determining a minimum wear of the part thickness, measured between the projection onto the three-dimensional mesh of said projected point of maximum wear, and a fourth own repository to the workpiece and oriented relative to the second reference,

o said minimum thickness is compared with a predetermined wear tolerance range, and

- if the result of the comparison is within said predetermined wear tolerance range is defined as the part conforms, if the result of the comparison is not included in said predetermined wear tolerance range, the is defined piece improper.

Preferably, the minimum thickness is measured perpendicularly to the fourth repository.

Advantageously, the points of the point field are uniformly distributed on the reference plane.

This method allows one hand to use digital technology to overcome the decline in visual ability of operators and achieve precise control regardless of the time at which these measurements are made.

In addition, this method allows better repeatability control operations since all parts are oriented in control in the repository of the engine. Thus, the entire workpiece positioning error control is avoided since the position of all parts to be inspected is predetermined.

Finally, the control accuracy is increased relative to the known method, since even the less accessible areas can be modeled and therefore controlled.

In one aspect, in the comparing step, a first selection of points is performed in which the projected points are excluded not meeting the three-dimensional mesh.

Advantageously, in the comparison step, from the non-excluded point, a specific area is determined in said room defined among the set of points intersecting the three-dimensional control mesh.

Similarly, in the comparison step, a second selection of points can be carried out, wherein we exclude points that are not part of the specific area.

During the second selection points can be for each projected point:

- measuring an angle between the projection of said projected point and a normal to a tangent to the three-dimensional control mesh at the intersection of the projection of said point with the three-dimensional control mesh, and

- compare said angle with a predetermined angular tolerance range,

and, if the angle is within said angular tolerance range, then the point is considered to set the compliance of the workpiece, if the angle is not within said angular tolerance range, then the point n is not taken into account by the dedicated algorithm to determine the compliance of the room.

The angular tolerance range may be between 0 ° and

15°.

These selections are intended to delineate the specific study area, whose topology can vary significantly depending on its degradation during its use in the turbine engine.

Advantageously, the workpiece can comprise a coating that covers and whose minimum wear thickness is to be determined.

It is proposed, secondly, a dimensional control facility without contacting a turbomachine part for the implementation of the control method as described above, the installation comprising:

- a three-dimensional acquisition unit adapted to perform a three-dimensional mesh Workpiece control to control;

- a calculator adapted to implement said dedicated algorithm, and - a communication interface between an operator and installation.

The invention will be better understood and other details, features and advantages of the invention will become apparent from reading the following description given by way of non-limiting example with reference to the accompanying drawings in which:

- Figure 1 is a schematic sectional view of a turbomachine;

- Figure 2 is a perspective view of a turbine blade of the turbine engine of Figure 1;

- Figure 3 is a detailed view of a turbomachine blade control according to inset III of Figure 2;

- Figure 4 is a detailed view of a mesh of a scanning of the part of Figure 3, this figure comprising an enlarged detail inset showing the mesh;

- Figure 5 is a detail view showing one step of the control method which consists of a projection points on the digitized model to determine if the test piece is consistent or not;

- Figure 6 is a diagram showing a step of projecting points of the control method;

- Figure 7 is a section view showing the determination of the minimum thickness of the test piece;

- Figure 8 is a partly schematic diagram showing the determination of an area of ​​Figure 2 wherein the mesh wear control to be performed, and

- Figure 9 is a schematic view showing a dimensional inspection system of a turbomachine part.

While other parts that blade 4 below could be controlled by the method presented here, we hereafter refers to the case of the control of a blade. Also does one shown in Figure 1, a turbine engine 1 comprising a high pressure turbine 2 and a low pressure turbine 3. The impellers 2, 3 each comprise several parts, including blades 4 which may be circumferentially butted and form part of a turbine stage.

As and extent of use of the turbine engine 1, the blades wear out and control their wear is necessary so that defective blades should be replaced to protect the turbine engine 1.

2 shows, in perspective, a detail of a blade 4, the dimensions of which must be checked to determine whether the workpiece is adapted to be installed on a turbine engine or, alternatively, whether it should be replaced by a compliant piece . More specifically it is desired to control the thickness of a layer or coating of mechanical reinforcement which covers, at least in part, the blade 4 and allows the

protection, such as stellite layer. Stellite is a very durable material which can protect the blades 4 of friction, including heating.

The compliance of a blade 4 can therefore be understood as the ability of said blade 4 as to have a relatively thick backing layer to withstand the friction, in particular the increase in temperature.

The control method comprises a first step wherein one has a reference plane 5, shown in Figures 2 and 6. This reference plane 5 comprises a first repository 6. The first reference 6 is oriented in a predetermined manner, c ' is to say so as to be positioned according to a specific reference to the turbomachine, called third repository 7 (Figure 1), in which is mounted the blade to control.

In a second step of the control method, shown in Figure 4, the blade 4 to control (meaning the coated blade) is scanned using a three-dimensional scanner, for example in the form of a point cloud, to obtain a three-dimensional mesh 8 control, hereinafter referred to as mesh 3 control. 3 the control grid comprises a second reference system 9 (Figure 2).

Recall that a mesh is a surface reconstruction of an outer contour of an object by means of triangles of different sizes, i.e. of surfaces formed of three points, each triangle being connected to several other triangles so that the surface reconstruction obtained is devoid of holes, that is to say free from lack of surface.

Preferably, only a portion of the blade 4 to be inspected is scanned. However, all of the blade 4 can be modeled as a function of the extent of control of the blade 4.

The mesh control 8 is then also positioned with respect to the turbomachine. Specifically, the second reference frame 9 is predeterminedly oriented relative to the third reference 7. The expression "in a predetermined manner" is meant that the mesh 8

control is oriented in the same way that the part 4 is actually oriented in the turbomachine 1.

Thus, the reference plane 5 and 8 control grid have a common reference, by the third repository 7. This common repository enables notably to ensure a third step of the control method of determining the wear of vane 4 in a common area of ​​the reference plane 5 and 8 mesh control to determine whether the blade 4 may or may not be used, particularly on turbomachine 1.

In this third step, a dedicated control algorithm wear of the blade 4 to be tested by projection points from the reference plane 2, as described below and shown in Figures 5 and 6.

First, a point field 10 (referenced 10.1, 10.2, 10. n in Figure 6) is projected in a projection P perpendicular to said reference plane 5, therefrom, to the mesh 8 of control until that said points 10; 10.1, 10.2, 10. No 8 meet the mesh control. Advantageously, points 10.1, 10.2, 10. n are uniformly distributed on the reference plane 5, for example according to a constant pitch.

Then, for each point 10; 10.1, 10.2, 10. n projected, a distance d1, d2, dn, ... is calculated between the reference plane 5 from which said point 10; 10.1, 10.2, 10. n is projected and said intersection point 10; 10.1, 10.2, 10. 8 n with the mesh control.

Then, the dedicated algorithm compares therebetween projection distances d1, d2, dn, ..., so as to identify, among them, a maximum distance dm.

Figure 6 shows, schematically, the projection points 10; 10.1, 10.2, 10. n from the reference plane 5 to the mesh 8 of control, and determining the maximum distance dm.

Then, from point 10 specifies the maximum projected distance dm, dedicated algorithm determines a minimum thickness e of the blade 4, the intersection between said projected point 10 with the three-dimensional mesh 8 and a fourth repository own piece 9a 4 and oriented relative to the second reference frame 9 of 8 three-dimensional mesh. The minimum thickness e and the fourth reference frame are shown in Figure 6 and 7.

Figures 6 and 7, the reference 8a designates diagrammatically the projection of the point 10 of maximum wear on the three-dimensional mesh 8, corresponding to the maximum distance dm.

Preferably, the minimum thickness is measured perpendicularly to the fourth repository. The dedicated algorithm then compares the minimum thickness with a predetermined wear tolerance range.

If the result of the comparison is within said predetermined tolerance range wear, the blade 4 is defined in conformity, in contrast, if the result of the comparison is not included in said predetermined wear tolerance range, the blade 4 is non-compliant.

A blade 4 having excessive wear is rejected to ensure a good safety of use of the machine. Indeed, excessive wear of the blade 4 may cause it to malfunction or to break.

In order to define a specific zone 1 1 for control of a blade 4, a number of selection levels 10 projected points can be made in the comparing step.

In a first level, a first selection of points 10 is performed in which the 10 projected points not meeting the mesh 8 of control are excluded exclusion represented by an area 12 surrounded by dashed short lines in Figure 5. This exclusion is justified by the fact that it is unnecessary, particularly impossible to calculate a distance between the origin point 10 of projection, that is to say the reference plane 5, and the intersection of the projection with P 8 the mesh control.

This selection may be achieved by dedicated algorithm when it detects that for a determined point 10, the projection thereof did not meet the mesh 8 of control or calculation of the distance between the origin and the intersection is too long to realize or that a value can not be determined.

In a second level, from the points 10 not excluded after the first selection, the dedicated algorithm determines the zone 1 1 Specific to said blade 4 is defined among the set of points 10 intersecting the mesh 8 control. This selection allows the exclusion of the method points 10 that are not included in zone 1 1 Specific previously determined. Zone 1 1 Specific is represented in Figure 5 by an area surrounded by long dashed lines.

8 illustrates in part determining the zone 1 1 Specific during a second selection points, that is to say in the second level.

In the second selection of points, for each point 10; 10.1, 10.2, 10. No projected:

- measuring an angle a between the direction of projection of said point P 10; 10.1, 10.2, 10. n projected and a normal N to a tangent T to the three-dimensional mesh 8 crossing the control of said projected point with the mesh 8 three-dimensional control, and

- comparing said angle a with a predetermined angular tolerance range,

if a is in said angular tolerance range then the point 10; 10.1, 10.2, 10. n is taken into account to determine the wear of the blade 4 on the other hand, if a is outside of said angular tolerance range, then the point 10; 10.1, 10.2, 10. n is not taken into account for determining the wear of the blade 4.

Preferably, the angle tolerance range a is between 0 ° and 15 °, the angle value being an absolute value.

Finally, in a third level, a new selection is performed wherein are excluded points 10 located in a so-called discharge portion, that is to say a non-existing portion of the blade 4 to control its origin and wherein the material to creep as the use of the turbomachine 1.

Thus, only the zone 1 1 Specific will be analyzed by the method, typically a region of the blade 4 wherein concentrate mechanical stresses when the machine is in use. These selections are intended to delineate the specific study area, whose topology can vary significantly depending on its degradation during use in the machine.

Around the zone 1 1 Specific, various points 10 not taken into account are listed. A first zone 13 includes items 10 that are out of the area for which it is sought to control wear. However, unlike the zone 12 described above, the points of the zone 10 intersect the mesh 8 control. A second zone 14 comprises the points outside of the selection of the second level. The points 10 of the area 13 could also be considered as belonging to the second zone 14, that is to say, they could be excluded in the second selection. Finally, a third area 15 is intentionally excluded, this sone 15 comprising items 10 located in said discharge portion, that is to say a non-existing portion of the blade 4 to control its origin and wherein the flue material as and measuring the use of the turbomachine 1. This region 15 corresponds to the exclusion of the points 10 when selecting the third level.

It is, however, that in Figure 5, the angle of view used makes it difficult to distinguish between certain points 10 of the second region 14 and those of zone 1 1 Specific. It will be noted, however, that the orientation of the arrow points 10 are shorter in the specific zone 1 1 that the arrow points 10 of the second zone 14, which shows that the angle of the normal N with the projections respective points 10 of the area 14 is greater than the predetermined angular tolerance.

For applying a method such as that just described, was used an installation control 16, shown in Figure 9, which comprises:

- a unit 17 for acquiring three-dimensional models, typically a three-dimensional scanner;

- a calculator 18, and

- a communication interface 19, typically a computer. The acquisition unit 17 allows to obtain a blade the representative point cloud 4 to control. More specifically, the acquisition unit 17 allows to obtain an accurate three-dimensional numerical mesh of the blade 4 to be tested wherein all surfaces, however small they are reproduced.

Advantageously, the acquisition unit 17 includes a mounting table having locking members and holding in position of the blades 4 to be controlled, these members being movable to accommodate the blades 4 of different sizes and different geometries. Preferably, positioning of the planes of these locking members and position holding will be carried out so that for all the blades of the same range, and the reference position are the same in the scanner.

The computer 18 enables to implement the dedicated algorithm which, as we have seen, generates the mesh 8 control determines the maximum wear of the blade 4, and provides information relating to the dimensional compliance the area of ​​the blade 4 to be tested.

Finally, the communication interface 19 allows an operator, on the one hand follow in real time the progress of the control of the blade 4 and, on the other hand, interact with the computer 18 for modifying or new instructions for the implementation of the algorithm.

In addition, the communication interface 19 to inform the operator of the result of the check so that the operator instructs that the blade 4 can be wound on the turbine engine 1 or on the contrary, it must be replaced by a new blade 4.

The control method and installation of 16 control that just described have several advantages.

First, the quality control is higher compared to a control carried out only by an operator using machinery mechanical measures whose reliability decreases over time. Indeed, the use of digital means contactless eliminates the deterioration of the mechanical elements and provides results accurate control even in difficult to reach areas by mechanical measuring machine.

Then correct repeatability check can be made for several similar parts.

Finally, the control of a blade 4 is accelerated relative to a conventional method in that all measurements and comparisons are performed by a computer 18.

CLAIMS

dimensional control method without contacting the wear of a part (4) of a turbomachine, the method comprising steps in which, via a computer (18):

- defining a reference plane (5) having a first repository;

- it acquires, by measurement on said workpiece (4) to be controlled, a model of at least a portion of said workpiece (4) in the form of a mesh (8) three-dimensional control having a second repository, the first and second repository each being predeterminedly oriented relative to a clean third repository to the turbomachine;

- on the control piece (4) in a common area to the mesh (8) three-dimensional and the reference plane (5) by means of a dedicated algorithm using a projection of points (10) and wherein:

o to said common area, the reference plane (5) comprises a scatter field (10; 10.1, 10.2, ..., 10. n) Theoretical which are projected in a projection (P) perpendicular to said reference plane (5 ) from said reference plane, to the mesh (8) three-dimensional control;

o for each point (10; 10.1, 10.2, 10. n) projected, a projection distance is calculated between the reference plane (5) and the intersection of said projected point (10; 10.1, 10.2, 10.n) with the mesh (8) three-dimensional control;

o comparing projection distances of the points, so as to identify a maximum distance (dm) of said projection distances, and the point (10) projected maximum wear corresponding thereto,

o determining a thickness (e) Minimum wear of the part as measured between the projection onto the three-dimensional mesh of said projected point of maximum wear (10) and a fourth repository (9a), the fourth repository (9a) being adapted to the workpiece (4) and oriented with respect to the second reference (9), o comparing said thickness (e) with a minimum of wear predetermined tolerance range, and

- if the result of the comparison is included in the predetermined wear tolerance range, the part (4) is defined as compliant, if the result of the comparison is not included in said predetermined wear tolerance range, we define the part (4) to be improper.

2. Control method according to claim 1 wherein the thickness (e) minimum is measured perpendicular to the fourth repository (9a).

3. Control method according to claim 1 or 2, characterized in that the points (10; 10.1, 10.2, ..., 10. n) are distributed uniformly over the reference plane (5).

4. Control method according to any one of the preceding claims, characterized in that in the comparing step, a first selection of points (10) is carried out, wherein we exclude points (10; 10.1, 10.2, 10. n) projected not meeting the mesh (8) three-dimensional control.

5. Control method according to claim 4, characterized in that in the comparing step, from the points (10) not excluded, an area is determined (1 1) to said specific part (4) defined among the set of points (10; 10.1, 10.2, 10. n) intersecting the mesh (8) three-dimensional control.

6. Control method according to claim 5, characterized in that in the comparing step, a second selection of points is

performed in which we exclude points that are not part of the zone (1 1) specific.

7. Control method according to claim 6, characterized in that, during the second selection points, for each point (10; 10.1, 10.2, 10.n) Proposed:

- measuring an angle (a) between the projection (P) of said point (10; 10.1, 10.2, 10. n) projected and a normal (N) to a tangent (T) to the mesh (8) of three-dimensional control, passing the projection (P) of said point with the mesh (8) three-dimensional control, and

- comparing said angle (a) with a predetermined angular tolerance range,

and if the angle (a) is within said angular tolerance range, then the point (10; 10.1, 10.2, 10.n) is taken into account by the dedicated algorithm to set the compliance of the workpiece (4 ), if the angle (a) is not within said angular tolerance range, then the point (10; 10.1, 10.2, 10.n) is not taken into account when defining the compliance of the workpiece ( 1).

8. Control method according to claim 7, characterized in that the tolerance range is between 0 ° and 15 °.

9. Control method according to any one of the preceding claims, characterized in that the part (4) comprises a coating which covers and whose thickness (e) Minimum wear is to be determined.

10. Installation (16) Dimensional inspection without contact of a part (4) of a turbomachine, for the implementation of the control method according to any preceding claim, the device (16) comprising:

- a unit (1 1 17) of three-dimensional acquisition adapted to perform a mesh (8) three-dimensional workpiece control (4) to be inspected; - a computer (18) adapted to implement said dedicated algorithm, and an interface (19) for communication between an operator device (16).