NON-INVASIVE METHOD FOR WEARING A TURBOMACHINE BLADE

Abstract

Non-invasive method for monitoring wear on a turbomachine blade. The method comprises the steps of: a) acquiring, using an optical sensor (54), a three-dimensional point cloud of a reference surface (56), b) defining a projection direction (Z) from the point cloud of the reference surface (56), c) acquiring a three-dimensional point cloud of a control portion (32) of the blade (10), d) calculating a three-dimensional skin area of ​​the control portion (32) and scanning it to determine a lowest point (72), e) projecting onto said projection direction (Z) a first point (70) belonging to the control portion (32), and the point (72), f) determining a height (H') between the first point (70) and the second point (72), g) applying a comparison criterion of said height (H') to a predetermined value (C, C') quantifying an acceptable level of wear of said control portion (32).Figure to be published with the abbreviation: [Fig. 6].

Description

Title of the invention: METHOD FOR NON-INVASIVE WEAR CONTROL OF A TURBOMACHINE BLADE

[0001] DOMAIN

[0002] The present invention relates to a non-invasive method for inspecting the wear of a turbomachine blade, in particular an aircraft turbomachine blade. It also relates to an installation for implementing the method of inspecting a turbomachine blade.

[0003] CONTEXT

[0004] In an aircraft turbomachine, blades are arranged radially around an axis, and each blade has a cutting edge extending between a blade root near the axis and a blade tip opposite the axis. The blade has a first concave side called the lower surface (intrados) and a second convex side called the upper surface (extrados). Generally, the cutting edges of two consecutive blades are in close contact and have friction areas that can wear down over flight hours.

[0005] It is known to reinforce friction zones with metallic deposits, particularly those made of stellite. Such a metallic deposit wears unevenly over flight hours, giving it an irregular and complex shape that makes measuring wear difficult.

[0006] As part of the maintenance of such turbomachinery, blades are regularly removed for inspection. One of these inspections involves measuring the wear of the metal deposit located in a friction zone, as mentioned above. To do this, the blade to be inspected is placed on a support, and a manual dial indicator with a pendulum rod is used to measure, for each metal deposit, the height of the worn metal deposit between a reference point and the deepest point of the deposit. This height is then compared to the height of the metal deposit on a new blade. If the measured height is less than a predefined value, called the criterion, for at least one of the metal deposits, the blade is rejected. If the measured height is greater than or equal to a predefined value, called the criterion, for each metal deposit, the blade is retained. However, such an inspection is tedious and time-consuming because it involves numerous manual and repetitive tasks..

[0007] There is therefore a need to automate the turbomachine blade control process in order to reduce manual tasks and to make it faster.

[0008] To this end, the present disclosure relates to a non-invasive method for monitoring the wear of a turbomachine blade comprising a blade extending between a blade head and a blade root, the blade head comprising at least one monitoring portion, each control part comprising a notch having an outer surface and a metallic deposit having an outer surface and being adjacent to the notch, the method comprising the steps of, for each control part of the blade head:

[0009] a) acquire, using an optical sensor having an acquisition field and an optical axis, a three-dimensional point cloud of a reference surface,

[0010] b) define a projection direction from the point cloud of the reference surface,

[0011] c) acquire using the optical sensor a three-dimensional point cloud of the control part, the control part of the blade head being arranged close to the reference surface so that the acquisition field of the optical sensor includes both the control part and the reference surface,

[0012] d) calculate a three-dimensional skin surface of the control part of the blade head from the point cloud of the control part acquired in step c), and scan said three-dimensional skin surface of the control part to determine a lowest point of the outer surface of the metallic deposit along the projection direction, said second point,

[0013] e) project onto said projection direction a first point belonging to the outer surface of the notch of the control part of the blade head and the second point determined in step d) preceding,

[0014] f) determine from the projection of step e) a height between the first point and the second point taken along the direction of projection,

[0015] g) apply a comparison criterion of said height to a predetermined value quantifying an acceptable level of wear of said control part of the blade head.

[0016] The reference surface is acquired with each measurement of the wear of the metallic coating. This surface allows the measurements to be recalibrated with respect to this single, stable reference at each check, thus guaranteeing the quality and repeatability of the measurements. Measurement variations due to non-uniform deformation of the blades are eliminated. Thanks to the method according to the invention, the wear inspection of a metallic coating on a blade tip can therefore be carried out automatically and digitally. The method according to the invention also saves time and provides better traceability of measurements compared to the prior art.

[0017] According to other features of the process, taken individually or in any technically feasible combination:

[0018] - the reference surface is perpendicular to the acquisition field of the sensor optical, and the projection direction is perpendicular to said reference surface;

[0019] - the first point defined in step e) is the cusp point of the bottom of the notch in the control part, and the second point defined in step d) is a point maximum depth of the outer surface of the metallic deposit according to the direction of projection;

[0020] - the criterion for comparison to a predetermined value quantifying a level of wear acceptable uses one of the following two predetermined values:

[0021] - a. a first predetermined value quantifying an acceptable level of wear under the form of the remaining permissible thickness of the metallic deposit, to be compared to the aforementioned determined height of the metallic deposit in question,

[0022] - b. a second predetermined value quantifying an acceptable level of wear, which is compared to a difference between a reference height value corresponding to an unworn metallic deposit and said determined height of the metallic deposit considered;

[0023] - the reference surface has an area between 10 mm2 and 50 mm2;

[0024] - the reference surface is arranged at a distance of less than 10 mm, in particular less than or equal to 4 mm, of the control part and in the extension thereof;

[0025] - the blade to be controlled is a turbine blade of said turbomachine;

[0026] - the metallic deposit of each control part is in stellite;

[0027] - steps b), d), e), f), and g) are implemented by a processing unit data ;

[0028] - the reference surface is flat.

[0029] The invention also relates to an installation for implementing the method of controlling a turbomachine blade, comprising: - a support configured to hold said vane, - a blade to be inspected, placed on said support, the blade comprising a blade extending between a dawn head and a dawn foot, the dawn head comprising at least one control section, - an optical sensor having an optical axis and an acquisition field, configured to visualize a control portion of the blade head, said control portion comprising an adjacent notch and metallic deposit, - installation in which the support includes a reference surface arranged near and in line with the control part of the blade head so that the acquisition field of the optical sensor includes said control part of the blade head and said reference surface.

[0030] Depending on other characteristics of the installation, taken individually or in any technically feasible combination:

[0031] - the optical sensor is an optical microscope with a chromatic confocal sensor, in particular a white light microscope;

[0032] - the resolution of the optical sensor along the optical axis is between 0.1 and 0.5 microns, in particular equal to 0.3 microns;

[0033] - the installation further includes a data processing unit connected to the optical sensor, the data processing unit including in particular a processor, a memory and a display device.

[0034] 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. BRIEF DESCRIPTION OF THE FIGURES

[0035] [Fig.1] [Fig.1] is a schematic perspective view of a turbine blade comprising a blade root, a blade and a blade head to be inspected according to the non-invasive wear inspection method according to the invention, the blade head comprising an inspection part having a metallic deposit and a notch,

[0036] [Fig.2] [Fig.2] is a side view of the control part of the blade head of [Fig.1] where the metal deposit is new,

[0037] [Fig.3] [Fig.3] is an enlarged view of the control part of the blade head of [Fig.1] where the metallic deposit is worn,

[0038] [Fig.4] [Fig.4] is a schematic view of the blades of [Fig.1] positioned on a disk,

[0039] [Fig.5] [Fig.5] is a schematic view of an installation for implementing the control method according to the invention,

[0040] [Fig.6] [Fig.6] is a schematic side view of the control part of the blade head of [Fig.1]. DETAILED DESCRIPTION OF THE INVENTION

[0041] Figure 1 represents a turbomachine blade 10. For example, blade 10 is a turbine blade.

[0042] The turbomachine blade 10 has, in a known manner, a blade 12 extending along a longitudinal direction L between a blade root 14 intended to be engaged in a groove of a turbomachine disk and a blade tip 16 intended to be positioned opposite a turbomachine casing. The blade 12 has a first concave side 18 called the lower surface 18 and a second convex side 20 called the upper surface 20.

[0043] The blade head 16 has a first intrados portion 22 and a second extrados portion 24 having a complementary shape to the first portion 22. The blade head 16 has, for example, a general Z shape.

[0044] Each portion 22, 24 of blade head 16 has a notch 26 having an outer surface 27 and a metallic deposit 28 adjacent to the notch 26, visible on [Fig.2] in the case of a new blade head.

[0045] The notch 26 advantageously presents a complementary shape of a cylinder.

[0046] The metallic deposit 28 is, for example, made of stellite. The external surface 30 of the metallic deposit 28 is, for example, equal to 4 mm * 2 mm.

[0047] When blades 10 are in place in a turbomachine, the first intrados portion 22 of a blade head 16 comes into contact with the second extrados portion 24 of an adjacent blade head 16, as can be seen in [Fig.4]: the metallic deposit 28 on the first intrados portion 22 of a blade head thus faces the metallic deposit 28 on the second extrados portion 24 of the adjacent blade head 16, leading, as the turbomachine is used, to wear of the facing metallic deposits by friction.

[0048] We want to monitor this level of wear on each metal deposit 28 of the blade heads.

[0049] The outer surface 30 of the metal deposit 28 defines a plane devoid of protrusions when the blade 10 is new. The outer surface 30 exhibits asperities, and therefore protrusions, as flight hours accumulate, due to the wear of the metal deposit 28, as shown in [Fig. 3].

[0050] An object of the present invention relates to an installation 50 for implementing the method of controlling a turbomachine blade 10 shown in [Fig. 5], and more particularly to the method of controlling each control part on the lower surface 22 and the upper surface 24 of the blade head 16, referenced 32 in [Fig. 4]. Each control part 32 comprises the notch 26 and the metal deposit 28, on the corresponding part of the lower surface 22 or the upper surface 24. In particular, the outer surface 27 of the notch 26 and the outer surface 30 of the metal deposit 28 constitute the control part 32 for the method of controlling the blade 10.

[0051] The installation 50 includes a support 52 configured to hold said blade 10, a blade 10 to be controlled placed on said support 52, an optical sensor 54 having an optical axis A and an acquisition field, configured to view a control part 32 of the blade head 16 as defined above, and the support 52 including a reference surface 56.

[0052] The support 52, for example, has a flat, horizontal platform 58 carrying a receiving piece 60 for a blade head 16, and a receiving piece 62 for a blade foot 14, these two pieces being designed to allow for repeatable positioning of the blade to be inspected. In one example, the receiving piece 60, or 62 respectively, has a shape complementary to that of the blade head, or blade foot respectively. A support is generally provided for each side (intrados and extrados), but the invention is not limited to such a practical implementation.

[0053] The receiving part 60 is such that when the blade head 16 is placed on the support, a control portion 32 (intrados or extrados) is visible to the optical sensor. In particular, the outer surface 30 of the metallic coating 28 of the control portion 32 visible to the optical sensor is parallel to the platform 58 when the blade 10 is new, and perpendicular to the acquisition field of optical sensor 54.

[0054] The reference surface 56 of the support 52 is positioned near the receiving part 60 of a blade head 16. Thanks to this arrangement, the optical sensor 54 can view both the reference surface 56 and the control portion 32 of the blade head 16 within its acquisition field. The measurement is thus more reliable and saves time, since the acquisition only covers a very small area. In particular, the reference surface 56 is positioned at a distance of less than 10 mm, specifically less than or equal to 4 mm, from the control portion 32 of the blade head 16.

[0055] Preferably, the reference surface 56 is arranged to be perpendicular to the acquisition field of the optical sensor 54.

[0056] Preferably, the reference surface 56 is flat. In particular, the reference surface 56 has perfect submicron flatness.

[0057] The reference surface 56 typically has an area between 10 mm2 and 50 mm2, in particular equal to 25 mm2, i.e. 5 mm x 5 mm.

[0058] The reference surface 56 is preferably made of a robust, rustproof, and stable material that does not deform at ambient operating temperatures between 0°C and 40°C or storage temperatures between -20°C and 70°C. Examples of possible materials are a 36% nickel and 64% iron alloy, or hardened ASP60 steel with a Rockwell hardness of 60 HRC and a titanium nickel coating.

[0059] The optical sensor 54 is preferably an optical microscope with a chromatic confocal sensor, in particular a white light microscope. Preferably, the optical sensor 54 is arranged so that the acquisition field of said optical sensor 54 is perpendicular to the reference surface 56 of the support 52.

[0060] The operating principle of such an optical sensor 54 is to send white light onto a surface to be analyzed. When the light reaches the surface, a wave is reflected back to the optical sensor 54. The analysis of the reflected light makes it possible to obtain, with great precision, the distance, or height, between the surface and the optical sensor 54. The optical sensor 54 allows the acquisition of a point cloud with a very fine mesh. It is then possible to create a point-by-point image of the surface to be analyzed and to obtain the height of each of these points.

[0061] The resolution of the optical sensor 54 along the optical axis A is between 0.1 and 0.5 microns, in particular equal to 0.3 microns.

[0062] The optical sensor 54 enables high-precision, reliable and repeatable measurements.

[0063] When a blade 10 to be inspected is placed on the support 52, the acquisition field of the optical sensor 54 includes one of the two inspection parts 32 of the blade head 16, for example the one on the lower surface and the reference surface 56, as is visible in [Fig.5].

[0064] The optical sensor 54 is preferably connected to a data processing unit 66 comprising, in particular, a processor 67, a memory 68, and a display device 69. The memory 68 of the data processing unit 66 is typically configured to store the measurement data (point clouds) collected by the optical sensor 54. The processor 67 of the data processing unit 66 is typically configured to use the data stored in the memory to perform certain steps of the control process described below. The display device 69 of the data processing unit 66 is typically configured to display the raw data or the data processed by the processor.

[0065] The data processing unit 66 is specifically configured to define a projection direction Z from the point cloud of the reference surface 56.

[0066] The data processing unit 66 is configured in particular to calculate a three-dimensional skin surface of the control part 32 from the point cloud of the control part 32 acquired by the optical sensor 54. The skin surface is calculated by triangulation between the points of the point cloud. The results are obtained, for example, in the form of an STL file.

[0067] The processing unit 66 can also be configured to scan said skin surface and determine a lowest point along the projection direction Z, or second point 72, of the outer surface 30 of the metallic deposit 28.

[0068] The processing unit 66 can also be configured to project onto said projection direction Z a first point 70 belonging to the outer surface of the notch 26 of the control part 32 of the blade head 16 and the second point 72.

[0069] The processing unit 66 can further be configured to determine from said projection a height H' between the first point 70 and the second point 72 taken along the projection direction Z.

[0070] The processing unit 66 can further be configured to apply a comparison criterion of said height H' to a predetermined value quantifying an acceptable level of wear of the control part 32 of the blade head 16, as will be explained below.

[0071] A first embodiment of a non-invasive wear control method for a turbomachine blade 10 according to the invention will now be described. It should be specified that this control method applies in the same way to the control portion of the lower surface and the upper surface of the blade that is to be controlled.

[0072] For the implementation of the control method, an installation 50 as described above is provided. The blade 10 is installed on the support 52 so that the blade foot 14 is held by the blade foot receiving piece 62, and the blade head 16 is held by the blade head receiving piece 60.

[0073] One of the control parts 32 (intrados or extrados) of the blade head 16 is left visible to an optical sensor 54. Said control part 32 of the blade head is placed in the vicinity of the reference surface 56.

[0074] In a first step of the control process according to the invention, the optical sensor 54 acquires a three-dimensional point cloud of the reference surface 56.

[0075] In a second step of the control process, a projection direction Z is defined from the image of the reference surface 56, as can be seen in [Fig. 6]. In particular, the projection direction Z is perpendicular to the reference surface 56 and parallel to the optical axis A. The projection direction Z is determined, for example, using the processing unit 66.

[0076] This projection direction Z serves as a reference direction for projecting specific points on the control portion 32 of the blade head 16, as will be explained later. This projection direction Z is therefore independent of the measurement and depends only on the reference surface 56, which remains unchanged over time. This ensures the reliability and repeatability of the measurement.

[0077] In a third step of the inspection process, the optical sensor 54 acquires a three-dimensional point cloud of the inspection portion 32 of the blade head 16 of the blade 10 to be inspected. To do this, the optical sensor 54 scans the outer surface 27 of the notch 26 and the outer surface 30 of the metal deposit 28. Thanks to the proximity of the reference surface 56 and the inspection portion 32, the acquisition field of the optical sensor 54 includes both the reference surface 56 and the inspection portion 32. It is not necessary to move the optical sensor 54 after acquiring the image of the reference surface to acquire the image of the inspection portion 32. This allows for the most accurate measurement possible.

[0078] In a fourth step of the inspection process, a three-dimensional skin surface of the inspection part 32 is calculated from the three-dimensional point cloud acquired in the previous step. The skin surface is typically calculated by triangulation between the points of the point cloud, making it possible to obtain a three-dimensional representation, i.e., a three-dimensional image, of the inspection part 32. More precisely, the skin surface is a three-dimensional image that very accurately represents the outer surface 27 of the notch 26 and the outer surface 30 of the metal deposit 28. The three-dimensional skin surface is preferably calculated using the processing unit 66.

[0079] In a fifth step of the inspection process, from the skin surface calculated in the previous step, a first point 70 belonging to the outer surface 27 of the notch 26 of the inspection portion 32 of the blade head 16 is projected onto the projection direction Z. In particular, this first point 70 is the cusp point of the bottom of the notch 26. In other words, the first point 70 is the The lowest point of the notch 26 when the metallic deposit 28 of a new blade 10 is parallel to the horizontal with its outer surface 30 facing upwards. This first lowest point 70 of the bottom of the notch 26 is a reference point for measuring the wear of the blade 10, the notch 26 remaining unchanged during flight hours.

[0080] To find this lowest point 70 along the Z projection direction belonging to the outer surface 27 of the notch 26, the reconstructed skin surface part corresponding to the outer surface 27 of the notch is swept with profile sections in the Z projection direction to find the lowest point of the notch 26 along the Z projection direction of the reconstructed surface once it has been put back into the Z projection direction reference frame.

[0081] Alternatively, the first point 70 can be determined using a virtual cylinder of known radius R which coincides with the outer surface 27 of the notch 26. The radius R of the virtual cylinder is in particular between 1.0 mm and 1.2 mm.

[0082] From the skin surface, a second point 72 belonging to the outer surface 30 of the metal deposit 28 of the control part 32 of the blade head 16 is also projected onto said projection direction Z. This second point 72 is the point of maximum depth of the outer surface 30 of the metal deposit 28, or the least salient, of the outer surface 30 of the metal deposit 28, that is to say the lowest point along the projection direction Z.

[0083] To find this second point 72, the reconstructed skin surface area corresponding to the outer surface 30 of the metallic deposit 28 is swept with profile sections in the Z projection direction to find the lowest point of the reconstructed surface once placed back in the Z projection direction reference frame.

[0084] The fifth step of the process is preferably carried out using the processing unit 66.

[0085] In a sixth step of the control process, a height H' is determined between the first point 70 and the second point 72 along the projection direction Z. The height H' obtained is a determination of the remaining thickness of the metallic deposit 28 at point 72. The sixth step of the process is preferably carried out using the processing unit 66.

[0086] In a seventh step of the inspection process, a comparison criterion is applied to the height H' obtained in the previous step, to a predetermined value quantifying an acceptable level of wear in the form of a first predetermined value C defining a minimum permissible thickness (or remaining permissible thickness). This first predetermined value C is, in practice, a value defined at the factory for each type of blade and stored in the processing unit 66.

[0087] Comparing the values ​​of H' and C makes it possible to discriminate between a criterion An acceptability criterion and an unacceptability criterion are defined. The acceptability criterion corresponds to verifying the inequality H' > C (H' greater than or equal to C): the state of the metal deposit 28 (its remaining thickness) is then considered acceptable. The unacceptability criterion corresponds to verifying the inequality H' < C (H' strictly less than C): the state of the metal deposit 28 (its remaining thickness) is then considered unacceptable. A blade 10 is retained if, for each of its two metal deposits 28 (on the first intrados portion 22 and the second extrados portion 24 of the blade), the acceptability criterion H' greater than or equal to C is verified. If, for at least one of the metal deposits 28, the unacceptability criterion H' < C is verified, the blade is rejected.

[0088] The seventh step of the process is preferably carried out using the processing unit 66.

[0089] These seven steps of the process are applied, for each blade 10 to be inspected, first to check the condition of the metallic deposit 28 on one side, for example the lower surface (intrados) of the blade 10; then a second time to check the condition of the metallic deposit 28 on the other side, the upper surface (extrados) in this example. Then, based on the results of the comparison with the first predetermined value C, the blade is rejected if at least one of the two metallic deposits 28 is outside the acceptable range. Note that the inspection can be applied interchangeably to the lower surface (intrados) or the upper surface (extrados) first for each blade 10 to be inspected.

[0090] In one embodiment, if it is determined that the condition of the metallic deposit 28 on the first side checked (in the example, intrados) meets the acceptability criterion, then the same procedure is applied to check the condition of the metallic deposit on the other side, in the example extrados, of the blade

[0091] A second embodiment of the seven-step process according to the invention is now described, which applies a seventh step using a different comparison criterion. This comparison criterion uses a second predetermined value C' of an acceptable wear level, which is compared to the difference between a reference height value H when the blade 10 is new and the measured height H'.

[0092] In one example, the value H corresponds to a factory value, which is a manufacturing constant for the controlled blades. This value is stored or provided to the processing unit 66 for the implementation of the process.

[0093] Alternatively, a reference height value H can be determined from the determination of a virtual reference plane P corresponding to a new metallic deposit. This plane P is perpendicular to the projection direction Z and passes through a third point 73 of minimum depth on the outer surface 30 of the metallic deposit 28. In other words, the virtual reference plane P passes through the most salient point, that is to say, the highest point on the projection direction Z, of the external surface 30 of the metal deposit 28.

[0094] To find this third point of minimum depth 73, we sweep the entire reconstructed skin surface, with profile sections in the Z projection direction to find this highest point of the reconstructed surface once placed back in the Z projection direction reference frame.

[0095] The reference height value H is then measured on the projection line Z, between the first point 70 determined above, and the point of intersection 76 between the virtual reference plane P and the projection direction Z. This seventh step of the method is preferably carried out using the processing unit 66.

[0096] In this embodiment, with H the factory value or measured relative to a virtual reference plane P as described above, the acceptance or rejection of the blade 10 is based on comparing a measurement H” of the current value of the metal deposit thickness 28, given by the difference H-H', to the second predetermined value C'. The acceptability criterion then becomes H” < C'. In other words, if the difference between the reference height H and the measured height H' is less than the second predetermined value C', which quantifies a maximum permissible wear level, the condition of the metal deposit 28 is then considered acceptable. Thus, a blade will be retained if, for each of its two metal deposits 28 (on the first intrados portion 22 and the second extrados portion 24 of the blade), the acceptability criterion H-H' < C' is met. Conversely, if the unacceptability criterion H-H' > C' is met for at least one of its metallic deposits 28, the blade will be rejected.

[0097] With regard to the reference height value H of the metallic deposits 28, the variant of the seventh step described above makes it possible to monitor over time an evolution between a reference height which would be measured on the controlled blade, between the first point 70 determined above, and the point of intersection 76 between the virtual reference plane P and the projection direction Z, as defined above (via the determination of the third point 73), and a reference factory value, for each side intrados, extrados, of the blade.

[0098] The implementation of a method according to the invention may include carrying out the seventh step according to the first embodiment, or according to the second embodiment, or even according to both embodiments. All measured values ​​are advantageously stored in the processing unit at each blade control step.

Claims

Claims

1. A method for non-invasive wear monitoring of a turbine engine blade (10) comprising a blade (12) extending between a blade head (16) and a blade root (14), the blade head (16) comprising at least one monitoring portion (32), each monitoring portion (32) comprising a notch (26) having an outer surface (27) and a metal deposit (28) having an outer surface (30) and being adjacent to the notch (26), the method comprising the steps of, for each monitoring portion (32) of the blade head (16): a) acquiring, using an optical sensor (54) having an acquisition field and an optical axis, a three-dimensional point cloud of a reference surface (56), b) defining a projection direction (Z) from the point cloud of the reference surface (56), c) acquiring at using the optical sensor (54) a three-dimensional point cloud of the control part (32),the control portion (32) of the blade head (16) being arranged close to the reference surface (56) so that the acquisition field of the optical sensor (54) comprises both the control portion (32) and the reference surface (56), d) calculating a three-dimensional skin surface of the control portion (32) of the blade head (16) from the point cloud of the control portion (32) acquired in step c), and scanning said three-dimensional skin surface of the control portion (32) to determine a lowest point (72) of the outer surface (30) of the metal deposit (28) along the projection direction (Z), called the second point (72), e) projecting onto said projection direction (Z) a first point (70) belonging to the outer surface of the notch (26) of the control portion (32) of the blade head (16), and the second point (72) determined in step d) above,f) determining from the projection of step e) a height (H') between the first point (70) and the second point (72) taken along the projection direction (Z), g) applying a criterion for comparing said height (H') to a predetermined value (C, C') quantifying an acceptable level of wear of said control part (32) of the blade head (16).,

2. The method of claim 1, wherein the reference surface (56) is perpendicular to the acquisition field of the optical sensor (54), and the projection direction (Z) is perpendicular to said reference surface (56).

3. Method according to claim 1 or 2, in which the first point (70) defined in step e) is the turning point of the bottom of the notch (26) of the control part (32), and the second point (72) defined in step d) is a point of maximum depth of the outer surface of the metal deposit (28) in the projection direction (Z).

4. Method according to any one of claims 1 to 3, in which the criterion for comparison with a predetermined value quantifying an acceptable level of wear uses one of the following two predetermined values: a. a first predetermined value (C) quantifying an acceptable level of wear in the form of an authorized remaining thickness of the metal deposit (28), to be compared to said determined height (H') of the metal deposit (28) considered; b. a second predetermined value (C') quantifying an acceptable level of wear, which is compared to a difference between a reference value of height (H) corresponding to an unworn metal deposit and said determined height (H') of the metal deposit (28) considered.

5. A method according to any one of claims 1 to 4, wherein the reference surface (56) has an area of between 10 mm2 and 50 mm2.

6. Method according to any one of claims 1 to 5, wherein the reference surface (56) is arranged at a distance of less than 10 mm, in particular less than or equal to 4 mm, from the control part (32) and in the extension thereof.

7. Method according to any one of claims 1 to 6, in which the blade (10) to be controlled is a turbine blade of said turbomachine.

8. Method according to one of the preceding claims, in which the metal deposit (28) of each control part (32) is made of stellite.

9. Installation (50) for implementing the method for controlling a turbomachine blade (10) according to any one of the preceding claims, the installation comprising: a support (52) configured to hold said blade (10), a blade (10) to be controlled placed on said support, the blade (10) comprising a blade (12) extending between a blade head (16) and a blade root (14), the blade head (16) comprising at least one control portion (32), an optical sensor (54) having an optical axis and an acquisition field, configured to visualize a control portion (32) of the blade head (16), said control portion (32) comprising an adjacent notch (26) and metal deposit (28), installation in which the support (52) comprises a reference surface (56) arranged close to and in the extension of the control part (32) of the blade head (16) so that the acquisition field of the optical sensor (54) comprises said control part (32) of the blade head (16) and said reference surface.

10. Installation (50) according to claim 9, wherein the optical sensor (54) is an optical microscope with a chromatic confocal sensor, in particular a white light microscope.

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