Method for the non-invasive monitoring of wear of a turbine engine blade

Abstract

The invention relates to a method comprising the steps of: a) acquiring, by means of an optical sensor (54), a three-dimensional point cloud of a reference surface (56); b) defining a projection direction (Z) on the basis of the point cloud of the reference surface (56); c) acquiring a three-dimensional point cloud of a test portion (32) of the blade (10); d) calculating a three-dimensional skin surface of the test portion (32) and scanning it to determine a lowest point (72); e) projecting, in the projection direction (Z), a first point (70) belonging to the test portion (32) and point (72); f) determining a height (H') between the first point (70) and the second point (72); g) applying a criterion for comparing the height (H') with a predetermined value (C, C') that quantifies an acceptable level of wear of the test portion (32).

Description

[0001] NON-INVASIVE METHOD FOR MONITORING WEAR OF A TURBOMACHINE BLADE

[0002]

[0001] DOMAIN

[0003]

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

[0004]

[0003] CONTEXT

[0005]

[0004] In an aircraft turbomachine, blades are arranged radially around an axis and each blade has a blade extending between a blade root in the vicinity of the axis and a blade tip opposite the axis. The blade has a first concave side called the intrados and a second convex side called the extrados. Generally, the blade tips of two consecutive blades are placed in close contact and have friction zones likely to wear over the hours of flight.

[0006]

[0005] It is known to reinforce friction zones with metal deposits, in particular made of stellite. Such a metal deposit wears non-uniformly over the hours of flight, thus giving it an irregular and complex shape generating difficulties in measuring wear.

[0007]

[0006] As part of the maintenance of such turbomachines, blades are regularly removed in order to be checked. Among these checks, one of them consists of measuring the wear of the metal deposit located in a friction zone mentioned above. To do this, the blade to be checked is placed on a support and a manual comparator 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 and compare the height obtained with the height of the metal deposit of a new blade. If the measured height is less than a predefined value called a 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 a criterion for each metal deposit, the blade is kept. However, such a check is tedious and time-consuming because it involves many 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]

[0008] For this purpose, the present disclosure relates to a method for non-invasive wear control of a turbomachine blade comprising a blade extending between a blade head and a blade root, the blade head comprising at least one control part, each control part comprising a notch having an outer surface and a metal deposit having an outer surface and being adjacent to the notch, the method comprising the steps consisting of, for each control part of the blade head: a) acquiring using an optical sensor having an acquisition field and an optical axis a three-dimensional point cloud of a reference surface, b) defining a projection direction from the point cloud of the reference surface, c) acquiring 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, d) calculating 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 scanning said three-dimensional skin surface of the control part to determine a lowest point of the outer surface of the metal deposit along the projection direction, called the second point, e) projecting 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 the preceding step d), f) determining from the projection of step e) a height between the first point and the second point taken along the projection direction,(g) applying a criterion for comparing said height to a predetermined value quantifying an acceptable level of wear of said control portion of the blade head.,

[0009]

[0009] The reference surface is acquired at each wear measurement of the metal deposit. Said surface thus makes it possible to recalibrate the measurements at each check with respect to this unique and stable reference, and to guarantee the quality and repeatability of the measurements. Measurement variations due to non-uniform deformation of the blades are avoided. Thanks to the method according to the invention, the wear control of a metal deposit of a blade head can therefore be carried out automatically and digitally. The method according to the invention also allows time savings and better traceability of the measurements compared to the prior art.

[0010]

[0010] According to other characteristics of the process, taken in isolation or in any technically conceivable combination:

[0011] - the reference surface is perpendicular to the acquisition field of the optical sensor, and the projection direction is perpendicular to said reference surface;

[0012] - the first point defined in step e) is the turning point of the bottom of the notch of the control part, and the second point defined in step d) is a point of maximum depth of the outer surface of the metal deposit according to the projection direction;

[0013] - the comparison criterion to a predetermined value quantifying an acceptable level of wear uses one of the following two predetermined values:

[0014] - a. a first predetermined value quantifying an acceptable level of wear in the form of an authorized remaining thickness of the metal deposit, to be compared to said determined height of the metal deposit considered,

[0015] - 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 metal deposit and said determined height of the metal deposit considered;

[0016] - the reference surface has an area between 10 mm 2 and 50 mm 2 ;

[0017] - the reference surface is arranged at a distance of less than 10 mm, in particular less than or equal to 4 mm, from the control part and in the extension thereof;

[0018] - the blade to be checked is a turbine blade of said turbomachine;

[0019] - the metal deposit of each control part is made of stellite;

[0020] - steps b), d), e), f), and g) are implemented by a data processing unit;

[0021] - the reference surface is flat.

[0011] The invention also relates to an installation for implementing the method for controlling a turbomachine blade comprising:

[0022] - a support configured to hold said blade,

[0023] - a blade to be controlled placed on said support, the blade comprising a blade extending between a blade head and a blade root, the blade head comprising at least one control part,

[0024] - 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 metal deposit,

[0025] - installation in which the support comprises a reference surface arranged close to and in the extension of the control part of the blade head so that the acquisition field of the optical sensor comprises said control part of the blade head and said reference surface.

[0026]

[0012] According to other characteristics of the installation, taken in isolation or in any technically conceivable combination:

[0027] - the optical sensor is an optical microscope with a chromatic confocal sensor, in particular a white light microscope;

[0028] - 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;

[0029] - the installation further comprises a data processing unit connected to the optical sensor, the data processing unit comprising in particular a processor, a memory and a display device.

[0030]

[0013] The invention will be better understood and other details, characteristics and advantages of the invention will appear on reading the following description given by way of non-limiting example with reference to the appended drawings.

[0031]

[0014] BRIEF DESCRIPTION OF THE FIGURES

[0032]

[0015] [Fig. 1] Figure 1 is a schematic perspective view of a turbomachine blade comprising a blade root, a blade and a blade head to be checked according to the non-invasive wear checking method according to the invention, the blade head comprising a checking part comprising a metal deposit and a notch,

[0016] [Fig. 2] Figure 2 is a side view of the checking part of the blade head of Figure 1 where the metal deposit is new,

[0033]

[0017] [Fig. 3] Figure 3 is an enlarged view of the control portion of the blade head of Figure 1 where the metal deposit is worn,

[0034]

[0018] [Fig. 4] Figure 4 is a schematic view of blades of Figure 1 positioned on a disc,

[0035]

[0019] [Fig. 5] Figure 5 is a schematic view of an installation for implementing the control method according to the invention,

[0036]

[0020] [Fig. 6] Figure 6 is a schematic side view of the control portion of the blade head of Figure 1.

[0037]

[0021] DETAILED DESCRIPTION OF THE INVENTION

[0038]

[0022] Figure 1 shows a turbomachine blade 10. For example, the blade 10 is a turbine blade.

[0039]

[0023] The turbomachine blade 10 has, in a known manner, a blade 12 extending in a longitudinal direction L between a blade root 14 intended to be engaged in a groove of a turbomachine disk and a blade head 16 intended to come opposite a casing of the turbomachine. The blade 12 has a first concave side 18 called intrados 18 and a second convex side 20 called extrados 20.

[0040]

[0024] The blade head 16 has a first intrados portion 22 and a second extrados portion 24 having a shape complementary to the first portion 22. The blade head 16 has, for example, a general Z shape.

[0041]

[0025] Each portion 22, 24 of blade head 16 comprises a notch 26 having an outer surface 27 and a metal deposit 28 adjacent to the notch 26, visible in FIG. 2 in the case of a new blade head.

[0042]

[0026] The notch 26 advantageously has a shape complementary to a cylinder.

[0027] The metal deposit 28 is for example made of stellite. The outer surface 30 of the metal deposit 28 is for example equal to 4 mm * 2 mm.

[0043]

[0028] When blades 10 are in place in a turbomachine, the first intrados portion 22 of a blade head 16 comes opposite the second extrados portion 24 of an adjacent blade head 16, as can be seen in FIG. 4: the metal deposit 28 on the first intrados portion 22 of a blade head thus faces the metal deposit 28 on the second extrados portion 24 of the adjacent blade head 16, leading, as the turbomachine is used, to wear of the metal deposits facing each other, by friction.

[0044]

[0029] We want to monitor this level of wear of each metal deposit 28 of the blade heads.

[0045]

[0030] The outer surface 30 of the metal deposit 28 defines a plane free of salient points when the blade 10 is new. The outer surface 30 has asperities, and therefore salient points, over the hours of flight, due to the wear of the metal deposit 28, as shown in FIG. 3.

[0046]

[0031] An object of the present invention relates to an installation 50 for implementing the method for controlling a turbomachine blade 10 shown in FIG. 5, and more particularly the method for controlling each control part on the intrados 22 and the extrados 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 intrados 22 or extrados 24. In particular, the outer surface 27 of the notch 26 and the outer surface 30 of the metal deposit 28 considered form the control part 32 for the method for controlling the blade 10.

[0047]

[0032] The installation 50 comprises 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 visualize a control part 32 of the blade head 16 as defined above, and the support 52 comprising a reference surface 56.

[0048]

[0033] The support 52 has for example a flat and horizontal platform 58 carrying a part 60 for receiving a blade head 16, and a part 62 for receiving a blade root 14, these two parts being designed to allow repeatable placement of the blade to be checked. In one example, the receiving part 60, respectively 62, has a shape complementary to that of the blade head, respectively of the blade root. A support is generally provided per intrados, extrados side, but the invention is not limited to such a practical implementation.

[0049]

[0034] The receiving part 60 is such that when the blade head 16 is placed on the support, a control part 32 (intrados or extrados) is visible to the optical sensor. In particular, the outer surface 30 of the metal deposit 28 of the control part 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 the optical sensor 54.

[0050]

[0035] The reference surface 56 of the support 52 is placed in the vicinity of the part 60 for receiving a blade head 16. Thanks to this arrangement, the optical sensor 54 can visualize in its acquisition field the reference surface 56 and the control part 32 of the blade head 16. The measurement is thus more reliable, and allows a saving of time since the acquisition only concerns a very restricted zone. In particular, 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 of the blade head 16.

[0051]

[0036] Preferably, the reference surface 56 is arranged to be perpendicular to the acquisition field of the optical sensor 54.

[0052]

[0037] Preferably, the reference surface 56 is flat. In particular, the reference surface 56 has perfect submicron flatness.

[0053]

[0038] The reference surface 56 has an area typically between 10 mm 2 and 50 mm 2 , in particular equal to 25 mm 2 , or 5 mm x 5 mm.

[0054]

[0039] The reference surface 56 is preferably made of a robust, stainless and stable material over time and which does not deform with the ambient operating temperature between 0°C and 40°C or the storage temperature between -20°C and 70°C. Examples of possible materials are an alloy of 36% Nickel and 64% Iron, or hardened ASP60 steel having a Rockwell hardness of 60 HRC with a Titanium Nickel coating.

[0055]

[0040] 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.

[0056]

[0041] The operating principle of such an optical sensor 54 is to send a 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 wave makes it possible to obtain very precisely 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 tight mesh. It is then possible to produce a point-to-point image of the surface to be analyzed and to obtain the height of each of these points.

[0057]

[0042] 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.

[0058]

[0043] The optical sensor 54 makes it possible to carry out high-precision, reliable and repeatable measurements.

[0059]

[0044] When a blade 10 to be controlled is placed on the support 52, the acquisition field of the optical sensor 54 comprises one of the two control parts 32 of the blade head 16, for example that on the intrados side and the reference surface 56, as can be seen in FIG. 5.

[0060]

[0045] 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) recorded 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 in order to carry out certain steps of the control method described below. The display device 69 of the data processing unit 66 is typically configured to display the raw data or data processed by the processor.

[0061]

[0046] The data processing unit 66 is notably configured to define a projection direction Z from the point cloud of the reference surface 56.

[0062]

[0047] The data processing unit 66 is in particular configured 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 for example obtained in the form of an STL file.

[0063]

[0048] 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 metal deposit 28.

[0064]

[0049] 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.

[0065]

[0050] 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.

[0066]

[0051] 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.

[0067]

[0052] A first embodiment of a method for non-invasively monitoring the wear of a turbomachine blade 10 according to the invention will now be described. It should be noted that this monitoring method applies in the same way to the monitoring part of the intrados and to that of the extrados of the blade that is to be monitored.

[0068]

[0053] 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 root 14 is held by the part 62 for receiving a blade root, and the blade head 16 is held by the part 60 for receiving a blade head.

[0069]

[0054] One of the control parts 32 (intrados or extrados) of the blade head 16 is left visible for an optical sensor 54. Said control part 32 of the blade head is placed in the vicinity of the reference surface 56.

[0070]

[0055] In a first step of the control method according to the invention, the optical sensor 54 acquires a three-dimensional point cloud of the reference surface 56.

[0071]

[0056] In a second step of the control method, 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 for example determined using the processing unit 66.

[0072]

[0057] This projection direction Z serves as a reference direction in order to project particular points of the control part 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 guarantees reliability and repeatability of the measurement.

[0073]

[0058] In a third step of the control method, the optical sensor 54 acquires a three-dimensional point cloud of the control portion 32 of the blade head 16 of the blade 10 to be controlled. For this, the optical sensor 54 performs a scan of 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 control portion 32, the acquisition field of the optical sensor 54 includes the reference surface 56 and the control portion 32. It is not necessary to move the optical sensor 54 after having acquired the image of the reference surface to acquire the image of the control portion 32. This makes it possible to obtain the most accurate measurement possible.

[0074]

[0059] In a fourth step of the control method, a three-dimensional skin surface of the control portion 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 control portion 32. More precisely, the skin surface is a three-dimensional image which very precisely 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.

[0075]

[0060] In a fifth step of the control method, 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 control part 32 of the blade head 16 is projected onto the projection direction Z. In particular, this first point 70 is the turning point of the bottom of the notch 26. In other words, the first point 70 is the lowest point of the notch 26 when the metal deposit 28 of a new blade 10 is parallel to the horizontal with its outer surface 30 facing upwards. This first point 70, the lowest of the bottom of the notch 26, is a reference point for measuring the wear of the blade 10, the notch 26 not being modified during the flight hours.

[0076]

[0061] To find this lowest point 70 along the projection direction Z belonging to the outer surface 27 of the notch 26, the reconstructed skin surface portion corresponding to the outer surface 27 of the notch is scanned, with profile sections in the projection direction Z to find the lowest point of the notch 26 along the projection direction Z of the reconstructed surface once placed in the projection direction Z reference frame.

[0077]

[0062] 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.

[0078]

[0063] 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 protruding point of the outer surface 30 of the metal deposit 28, that is to say the lowest point along the projection direction Z.

[0079]

[0064] To find this second point 72, the reconstructed skin surface portion corresponding to the outer surface 30 of the metal deposit 28 is scanned, with profile sections in the projection direction Z to find the lowest point of the reconstructed surface once placed in the projection direction reference frame Z.

[0080]

[0065] The fifth step of the method is preferably implemented using the processing unit 66.

[0081]

[0066] In a sixth step of the control method, 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 metal deposit 28 at the point 72. The sixth step of the method is preferably implemented using the processing unit 66.

[0082]

[0067] In a seventh step of the control method, a criterion for comparing the height H' obtained in the previous step is applied to a predetermined value quantifying an acceptable level of wear in the form of a first predetermined value C defining a minimum authorized thickness (or authorized remaining thickness). This first predetermined value C is in practice a value defined in the factory for each type of blade, and stored in the processing unit 66.

[0083]

[0068] Comparing the values ​​H' and C makes it possible to discriminate between an acceptability criterion and an unacceptability criterion. The acceptability criterion corresponds to the verification of 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 the verification of 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.

[0084]

[0069] The seventh step of the method is preferably implemented using the processing unit 66.

[0085]

[0070] These seven steps of the method are applied, for each blade 10 to be checked, a first time to check the condition of the metal deposit 28 on one side, for example the intrados, of the blade 10; then a second time to check the condition of the metal deposit 28 on the other side, the extrados in the example. Then, according to the results of the comparison with the first predetermined value C, the blade is rejected if at least one of the two metal deposits 28 is outside the acceptability criterion. Note that the verification can be applied indifferently first to the intrados side, or first to the extrados side, for each blade 10 to be checked.

[0086]

[0071] In a variant, if it is determined that the state of the metal deposit 28 on the first side checked (in the example, intrados) meets the acceptability criterion, then the same method is applied to check the state of the metal deposit on the other side, in the example extrados, of the blade.

[0087]

[0072] A second embodiment of the seven-step method according to the invention is now described, which applies a seventh step using another 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 value of height H when the blade 10 is new and the measured height H'.

[0073] In one example, the value H corresponds to a factory value, which is a manufacturing constant of the blades being checked. This value is stored or supplied to the processing unit 66 for implementing the method.

[0088]

[0074] Alternatively, it is possible to provide for a determination of a reference value of height H from the determination of a virtual reference plane P corresponding to a new metal deposit. This plane P is perpendicular to the projection direction Z and passes through a third point 73 of minimum depth of the outer surface 30 of the metal deposit 28. In other words, the virtual reference plane P passes through the most salient point, in other words, the highest in the projection direction Z, of the outer surface 30 of the metal deposit 28.

[0089]

[0075] To find this third point of minimum depth 73, the entire reconstructed skin surface is scanned, with profile sections in the projection direction Z to find this highest point of the reconstructed surface once placed in the projection direction reference frame Z.

[0090]

[0076] 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 implemented using the processing unit 66.

[0091] In this variant, with H being 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 the comparison of a measurement H” of the current value of the thickness of the metal deposit 28, given by the difference H-H', with 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' quantifying a maximum permitted wear level, the state 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 verified. Conversely, if for at least one of its metallic deposits 28, the unacceptability criterion H-H' > C' is verified, the blade will be rejected.Regarding the reference value of height H of the metal 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 blade being checked, 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 intrados and extrados side of the blade.

[0092] The implementation of a method according to the invention may comprise implementing the seventh step according to the first embodiment, or according to the second embodiment, or even according to both embodiments.

[0093] All measured values ​​are conveniently stored in the processing unit at each stage of blade control.

Claims

CLAIMS 1. A method for non-invasive wear monitoring of a turbomachine 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 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. Method according to 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, wherein 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 mm 2 and 50 mm 2 .

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 view 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 portion (32) of the blade head (16) so that the acquisition field of the optical sensor (54) comprises said control portion (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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