Device and method for estimating the displacements of an object

Abstract

A device for estimating the displacements of an object having an external surface comprising a first electrode (31) and a second electrode (32), intended to form two capacitors with the object's external surface, the capacitance of which varies during an axial displacement of the object. The device further comprises a processing module configured to measure the respective capacitances of the two capacitors formed, calculate a voltage from each measured capacitance, estimate an air gap of a capacitor from the calculated voltages, the air gap constituting a distance in a projection direction, and estimate an axial displacement of the object relative to the device in the axial direction from the calculated voltages. Figure for the abstract: Fig. 2

Description

Title of the invention: Device and method for estimating the displacements of an object. Technical field

[0001] This disclosure relates to the general field of measuring devices and, in particular, to capacitive sensors for measuring the displacement of an object. PRIOR TECHNOLOGY

[0002] When a new propulsion system is developed, numerous tests must be carried out as part of a certification process to comply with applicable regulations, monitor the engine, and verify that operational objectives have been met. In particular, actual tests are performed on a turbomachine test bench using a set of instruments and measurements.

[0003] More specifically, clearance and displacement measurements between the various parts of the turbomachine, particularly rotor parts (e.g., discs or blades) and stator parts (e.g., the casing or distributors), are implemented to characterize the thermomechanical behavior of the engine during operation. Indeed, axial displacements, i.e., parallel to the engine's axis of rotation, can occur simultaneously with radial displacements, i.e., in a plane normal to the engine's axis of rotation. It is crucial to control and manage the clearances between rotor and stator parts and therefore to quantify these displacements, particularly to improve the overall performance of the engine.

[0004] Since technological research efforts have already made it possible to significantly improve the environmental performance of aircraft, it is necessary to take into consideration the factors impacting all phases of design and development in order to obtain propulsion systems that are less energy-intensive, more environmentally friendly and whose integration and use in civil aviation have more moderate environmental impacts.

[0005] Conventionally, these displacement or distance measurements between parts are performed using capacitive sensors that measure the distance separating them from an opposing mechanical part along a specific direction. The simultaneous characterization of axial and radial clearances and displacements therefore requires integrating two orthogonal eigendirection sensors into the test bench.

[0006] However, it is sometimes complex or even impossible to integrate two separate sensors into the test bench, due to the severe operating conditions and the low available spaces. In particular, the integration of self-direction sensors parallel to the engine's axis of rotation is often intrusive and risks disturbing the behavior of the test turbomachine, and therefore reducing the relevance of the measurements taken.

[0007] Furthermore, with such instrumentation assemblies, axial displacements of the rotor parts can induce significant measurement biases in radial displacement measurements, and vice versa. Indeed, capacitive sensors provide a voltage dependent on the distance to be measured and on a common surface area between the capacitive sensor electrode and the rotor part. This common surface area depends on the relative position of the sensor and the rotor part, along the direction orthogonal to the sensor's natural direction. Thus, displacements of the rotor part in the direction orthogonal to the natural direction corresponding to the measurement direction induce a significant measurement bias.

[0008] An alternative method for estimating axial and radial displacements is to use an X-ray radiography method. However, this method requires placing the test turbomachine in a dedicated test bench and taking several X-rays of the engine while it is running. Such a specific test bench is expensive to develop and maintain. Furthermore, the use of X-rays presents health and safety risks for operators. Finally, the measurements obtained in this way are less precise than local measurements obtained with capacitive sensors. Description of the invention

[0009] One objective of this disclosure is to measure the displacements of an object in different directions more simply, while limiting measurement uncertainties and without risk to an operator near the object. This objective is achieved by a device for estimating the displacements of an object having an external surface, the device comprising

[0010] a first electrode having a first surface,

[0011] a second electrode having a second surface,

[0012] the device being suitable for being placed in a measurement position in which:

[0013] the first electrode forms a first capacitor with the object, and the second electrode forms a second capacitor with the object,

[0014] A projection of the external surface onto the first surface in a projection direction has a first area, and a projection of the external surface onto the second surface in the projection direction has a second area, the projection direction being normal to the first surface or to the second surface,

[0015] the first electrode and the second electrode are further adapted so that a translation of the object in an axial direction along a first direction, relative to the device placed in the measurement position, causes a decrease in the first area and an increase in the second area, and for a translation of the object in the axial direction in a second direction opposite to the first direction with respect to the device placed in the measurement position to cause an increase in the first area and a decrease in the second area, the axial direction being perpendicular to the direction of projection,

[0016] the device further comprising a processing module configured for • measure the initial capacitance of the first capacitor, • calculate a first voltage from the first capacitance; • measure the second capacitance of the second capacitor, • calculate a second voltage from the second capacitance; • Estimate the air gap of the first or second capacitor from the first and second voltages, the air gap constituting a distance in the direction of projection, • estimate an axial displacement of the object relative to the device in the axial direction from the first tension and the second tension.

[0017] The use of capacitive sensors presents no risk to the operator when obtaining measurements. Such sensors allow for measurements with sufficient accuracy. Furthermore, taking into account the two voltages calculated from the different electrodes reduces measurement uncertainty, in particular by minimizing the impact of a measurement error at the level of one of the electrodes or the electrical circuit connecting the electrode to the device's processing module.

[0018] The presence of two electrodes in the common cross-section with the object—that is, the projection of the object's external surface onto the surface of each electrode varies inversely during the object's axial displacement—allows the axial displacement to be estimated based on the two calculated voltages. The presence of a single electrode, or of several electrodes whose common cross-section does not vary differently, would not provide two distinct pieces of information enabling the device to estimate the axial displacement. Furthermore, the estimation does not require the presence of chevrons, so the method for estimating the object's displacement does not require modifying the object's shape.

[0019] The invention is advantageously complemented by the following features, taken individually or in any of their technically possible combinations: - the air gap is estimated from a sum of the first voltage and the second voltage, and the axial displacement is estimated from a difference between the first voltage and the second voltage; - the first surface and the second surface are adapted so that a sum of the first area and the second area is constant during the translation of the object in the axial direction; - the first electrode and the second electrode are coplanar; - the first surface and the second surface are centrally symmetric with respect to an axis parallel to the direction of projection; - the first surface is triangular and has a first hypotenuse, and the second surface is triangular and has a second hypotenuse, the first hypotenuse being parallel to the second hypotenuse; - the device further includes a mass electrically connected to the first electrode and the second electrode, the mass being arranged between the first electrode and the second electrode.

[0020] According to another aspect, an assembly is proposed comprising a turbomachine rotor having an external surface, and a device as described above for estimating displacements of the object.

[0021] According to another aspect, a method for estimating the displacements of an object having an external surface is proposed, implemented by a device as described above, the method comprising the following steps: • Measurement of the first capacitance of the first capacitor while the device is placed in the measurement position, • calculation of the first voltage from the first capacitance; • Measurement of the second capacitance of the second capacitor while the device is placed in the measurement position, • calculation of the second voltage from the second capacitance; • Estimation of the air gap of the first or second capacitor from the first and second voltages, • estimation of the axial displacement of the object relative to the device from the first and second voltages.

[0022] The measurement steps of the method described above can be implemented while the object is rotating relative to the device around an axis parallel to the axial direction. DESCRIPTION OF THE FIGURES

[0023] Other features, objectives and advantages of the invention will become apparent from the following description, which is purely illustrative and not limiting, and which should be read in conjunction with the accompanying drawings on which:

[0024] Fig. 1 schematically represents an object and a device according to the invention in a measuring position.

[0025] Fig. 2 is a perspective view of the device in one embodiment of the invention.

[0026] Fig. 3 schematically illustrates a measurement surface of the device shown in Fig. 2.

[0027] Fig. 4 schematically represents a projection of the external surface of the object onto the surfaces of the electrodes of the device in Fig. 2.

[0028] The [Fig.5] is a flowchart of steps of a displacement estimation process according to an embodiment of the invention.

[0029] Throughout the figures, similar elements bear identical references. DETAILED DESCRIPTION OF THE INVENTION

[0030] Generally, an aircraft is propelled by a propulsion system comprising a turbomachine generating thrust through an airflow passing through it, and a nacelle surrounding the turbomachine.

[0031] The turbomachine comprises a rotor part and a stator part. The rotor part is a movable body rotating about an axis of rotation X extending in an axial direction corresponding to the airflow, and the stator part is fixed.

[0032] Typically, the turbomachine comprises, from upstream to downstream in the direction of the airflow, a blower, a compression section comprising a low-pressure compressor and a high-pressure compressor, a combustion chamber, an expansion section comprising a high-pressure turbine and a low-pressure turbine, and an exhaust casing.

[0033] Each of the low-pressure compressor, high-pressure compressor, high-pressure turbine, and low-pressure turbine comprises a rotor and a stator. The rotor is designed to be driven in rotation relative to the stator about the axis of rotation X, while the stator is fixed. For example, turbines are conventionally formed by rotating wheels and fixed distributors, arranged alternately along the axial direction. The rotor and stator generally comprise blades extending radially from a disk around a mechanical shaft. In operation, vibrations can cause displacement of the rotor and stator along the axial direction.

[0034] The compression and expansion sections are enclosed by a fixed engine casing, to which the stator parts of the compressors and turbines are connected. The engine casing defines a primary channel allowing the flow of a primary gas stream.

[0035] In order to maximize the thrust provided by the propulsion system to the aircraft, the entire primary gas flow should contribute to rotating the rotor parts. Therefore, the clearance between the tips of the rotor and stator blades and the engine casing must be reduced. Typically, the blade may include one or more radially extending flaps to prevent airflow from passing between the engine casing and the blade tip.

[0036] The proposed device 1 is particularly well-suited for integration into a turbomachine. In particular, device 1 can enable displacement estimation for turbomachine components under normal operating conditions, including tests on partial or complete machines, both on the ground and in flight. The proposed estimation method can be implemented on any test bench and does not require a specific test bench or modifications to the turbine rotor components.

[0037] As will be illustrated later, the proposed device allows the characterization of the simultaneous axial and radial displacements of a rotor part of a turbomachine presenting a target with a constant cross-section continuously present in front of the device 1, when the latter is in a measurement position.

[0038] Typically, the device 1 is fixed to the engine casing, opposite an external surface of the rotor part whose displacements are to be estimated. For example, the device 1 can be used to characterize the displacements of a low-pressure turbine disk by integrating the sensor at the base of a distributor. The device 1 can also be used to characterize the displacements of the tips of low-pressure turbine blades. The device 1 can be integrated into the sealing sector fixed to the engine casing surrounding the turbine, opposite the blades.

[0039] Device 1 can also be used to characterize the displacements of blade tips without a platform, for example, fan, booster, or compressor blades, particularly high-pressure compressor blades. Device 1 can then be integrated into an abradable part on the engine casing or nacelle.

[0040] Device 1 enables the estimation of displacements along two orthogonal directions (axial and radial) simultaneously, accurately, and in real time. It is not necessary to integrate several separate sensors into the test machine, thereby reducing both the costs and the complexity of integrating the instrumentation into the machine.

[0041] Presentation of the device

[0042] With reference to [Fig. 1], a device 1 is proposed configured to estimate the displacements of an object 4. As explained previously, the object 4 is, for example, a rotor part of a turbomachine with axis of rotation X. The object 4 is thus a moving body rotating about the axis X, and can also move in translation. along the X axis over a small amplitude. Object 4 has an external surface 41, here forming a protrusion along a radial direction parallel to the Y axis.

[0043] The device 1 comprises a body 2 and a sensing face 3. As illustrated, the device 1 is suitable for being placed in a measuring position, in which it can be used to measure an axial displacement Pax of the object 4 along the X-axis and a distance E between the sensing face 3 and the external surface 4L. Typically, the device 1 in the measuring position is oriented so that the sensing face 3 extends opposite the external surface 4L of the object 4. It is held fixed in position, for example attached to a frame, typically the engine casing of the turbomachine. The body 2 of the device 1 extends here along the radial Y-axis.

[0044] Device 1 is a capacitive sensor. The device is designed to operate by creating an electrostatic field and detecting changes in this field caused by the external surface 41 moving near the sensing face 3. More specifically, when the external surface 41 is opposite the sensing face, a capacitance is formed. This capacitance can be converted into an analog voltage and depends, among other things, on the distance E separating the sensing face from the external surface 41 and the common area between the sensing face 3 and the external surface 41, as will be detailed later. Device 1 thus allows the distance E to be estimated. A change in the distance E allows the radial displacement to be determined, that is, a displacement of the object 4 along the radial axis Y.

[0045] With reference to [Fig.2], the device 1 comprises a first electrode 31 having a first surface, and a second electrode 32 having a second surface.

[0046] A first area SI is introduced corresponding to the common surface between the first electrode 31 and the external surface 4L. In other words, the projection of the external surface 41 onto the first surface along a projection direction normal to the first surface presents the first area SL. A second area S2 is also introduced corresponding to the common surface between the second electrode 32 and the external surface 4L. In other words, the projection of the external surface 41 onto the second surface along the projection direction presents the second area S2.

[0047] Preferably, the first electrode 31 and the second electrode 32 have the same shape, apart from variations in design and manufacture. This allows, among other things, for the simplification of calculations carried out by the device 1 to estimate the displacement of the object 4, as will be detailed later.

[0048] In the illustrated embodiment, the body comprises a cylindrical electrode holder 22 extending along a radial axis Y and a cylindrical outer casing 21 extending over the circumference of the electrode holder 22. The outer casing 21 protects the electrode holder 22 and the electronic components of device 1 and the mechanical strength of the various components of device 1.

[0049] The outer casing 21 preferably includes a means of fixing suitable for fixing the device 1 on a support, for example the engine casing, and for orienting it in the measuring position, opposite the object 4.

[0050] Preferably, the device 1 comprises a first mass forming an outer layer of the electrode support 22. The electrode support 22 can be connected to the first mass. The first mass is separated from the outer casing 21 by an insulator, for example, air. Typically, the device 1 comprises an electrically insulating layer extending between the outer casing 21 and the electrode support 22. This prevents electrical interference in the device 1.

[0051] The electrode holder 22 comprises a base forming a support face 23 on which the first electrode 31 and the second electrode 32 are arranged. Alternatively, the first electrode 31 may belong to a first plane, and the second electrode 32 may belong to a second plane distinct from the first plane. Typically, the first plane is normal to the radial axis Y and the second plane is normal to the radial axis Y, and the two planes are separated by a predetermined distance along the radial axis Y.

[0052] Since the two electrodes 31, 32 are arranged on the same support face 23 of the device 1 or on parallel supports, they share the same eigendirection. The proposed device 1 is thus less bulky because it does not require the presence of two capacitive sensors with orthogonal eigendirections.

[0053] The first electrode 31 and the second electrode 32 are further adapted so that a translation of the object 4 relative to the device 1 placed in the measurement position along the axial direction results in opposite variations of the first area SI and the second area S2. In other words, a translation of the object 4 along the axial direction in a first direction results in a decrease in the first area SI and an increase in the second area S2, while a translation of the object 4 in a second direction opposite to the first direction results in an increase in the first area SI and a decrease in the second area S2.

[0054] Preferably, the first electrode 31 and the second electrode 32 are electrically connected to a common ground 24. The common ground 24 is arranged between the two electrodes 31,32. For example, the common ground 24 is substantially rectangular in shape, and extends between the first and second electrodes 31,32 along a diameter of the circular support face 23.

[0055] Device 1 also includes a processing module (not shown). The processing module is configured to estimate the displacements of object 4 according to an estimation method detailed later. The processing module includes a A processor for performing calculations, and memory for storing data, instructions or commands, and measurements, for example. The processing module may also include electronic circuits, for example an oscillator, a signal rectifier, a filtering circuit, and an output circuit.

[0056] More specifically, the processing module may include a first capacitive line associated with the first electrode 31. The first capacitive line includes a first conditioner configured to convert a measured capacitance into a first analog voltage T1. Similarly, the processing module may include a second capacitive line associated with the second electrode 32, with a second conditioner configured to convert a capacitance into a second analog voltage T2.

[0057] The device includes electrical cables for transmitting electrical signals between the various components of the processing module and the electrodes 31, 32. Preferably, the device includes a first guarded cable with a core connecting the first electrode 31 to the first conditioner, so as to provide the first conditioner with a signal representative of the capacitance of the first electrode 31. The presence of a guard allows for the observation of very small variations in capacitance, for example, on the order of tens of picofarads, compared to the overall line capacitance, on the order of a few nanofarads. Similarly, the device may include a second guarded cable with a core connecting the second electrode 32 to the second conditioner, so as to provide the second conditioner with a signal representative of the capacitance of the second electrode 32.

[0058] A detailed embodiment will now be described.

[0059] In this embodiment, the electrodes 31, 32 are coplanar. With reference to [Fig. 3], the circular support face 23 has central symmetry with respect to the radial axis Y passing through the center of the support face 23.

[0060] The first electrode 31 is triangular. More precisely, the first surface is a right triangle comprising a right angle from which extend two perpendicular sides and a first hypotenuse. Similarly, the second electrode 32 is triangular, and the second surface comprises a right angle from which extend two perpendicular sides and a second hypotenuse.

[0061] The two electrodes 31,32 are of substantially identical shape. The first and second surfaces can thus be determined by a transverse dimension Le, corresponding to the base of the triangle, and by an axial dimension le, corresponding to the length of the adjacent side, greater than the transverse dimension Le.

[0062] In the illustrated embodiment, the transverse dimension Le corresponds to the side adjacent to the shortest right angle, i.e., a base of the right triangles formed by the electrodes 31, 32, or substantially to the width of the rectangle formed by the first surface and the second surface. The axial dimension corresponds to the side adjacent to the longest right angle, that is to say the height of the right triangles formed by the electrodes 31,32 associated with the aforementioned base, or substantially to the length of the rectangle formed by the first surface and the second surface.

[0063] The first hypotenuse is parallel to the second hypotenuse. Mass 24 is arranged between the first and second hypotenuses.

[0064] With reference to figure 4, when the device 1 is in the measuring position, the axially dimensioned sides extend along the axial direction, i.e. parallel to the X axis.

[0065] Object 4 has a substantially rectangular shape and extends along the axial direction along an axial dimension Lc, or thickness. It is assumed that object 4 can translate along the axial direction between a first position PI and a second position P2 (represented by hatching). When the external surface 41 translates in the positive direction, towards position P2, the first area SI (hatched) decreases and the second area S2 increases. Conversely, when the external surface 41 translates in the negative direction, towards position PI, the first area SI increases and the second area S2 decreases.

[0066] The device is not limited to the embodiment shown in the figures. In particular, the first electrode 31 and the second electrode 32 may have different geometric shapes, for example, trapezoidal shapes. The electrodes 31 and 32 may not be flat, so as to be able to adapt to the confined environment. The dimensions of the first surface may differ from the dimensions of the second surface. The device 1 may also comprise more than two electrodes.

[0067] It will be understood that the dimensions of the electrodes depend on the displacements to be measured. In particular, the axial dimension is greater than or equal to the amplitude of axial displacement envisaged, and greater than or equal to the axial dimension of object 4.

[0068] Method for estimating displacements

[0069] With reference to [Fig.5], a method for estimating the displacements of object 4 by device 1 will now be described.

[0070] When the external surface 41 of the object 4 is opposite the first electrode 31, a first capacitance Cl forms across the terminals of the first electrode 31. Thus, the first electrode 31 forms a first capacitor with the object 4. During a step Bl, the processing module measures the first capacitance Cl of the first capacitor. The device 1 is then in the measuring position, so that the first surface forms the first capacitor with the external surface 41. The processing module can charge the first electrode 31 to create an electrostatic field and detect changes in the electric field.

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[0082] In simplified terms, the first tension Tl depends on a first area SI and a distance El according to the following relationship: m _ erXerXS, T1 = K1xC p C x = with the permittivity of free space, er the relative permittivity of the dielectric, i.e., of the first electrode 31, and Kj a conditioning factor applied by the conditioner of the first capacitive line. The distance El corresponds to the air gap of the first capacitor, i.e., the distance separating the first surface from the external surface 41, measured along the projection direction. We then have, with G^ = a first gain characterizing the first electrode 31. More generally, the relationship between the first voltage Tl and the distance El is non-linear. From the first capacitance Cl, the processing module calculates the first voltage Tl during a step B2. For example, the processing module multiplies the first measured capacitance by the conditioning factor Kl determined during a calibration process as described below. Similarly, when the external surface 41 is opposite the second electrode 32, a second capacitance C2 is formed across the terminals of the second electrode 32. Thus, the second electrode 32 forms a second capacitor with the object 4. During step B3, the device 1 is in the measurement position, and the processing module measures the second capacitance C2 of the second capacitor. In simplified terms, the second voltage T2 depends on a second area S2 and the distance E2, or air gap of the second capacitor, separating the second surface from the external surface 41 along a projection direction normal to the second surface, according to the following relationship: t" _F yrf* — ^2^2^2- c2— B, with K2 a conditioning factor applied by the conditioner of the second conditioning line. We then have 77 _ S2 , with G? = ■^2“ T2 G2 £06rK2 a second gain characterizing the second electrode 32. As before, the relationship between the second voltage T2 and the distance E2 is non-linear. Thus, from the second capacitance C2, the processing module calculates the second voltage T2 during a step B4. In the embodiment where the first electrode 31 and the second electrode 32 are coplanar, and in which the external surface 41 is substantially flat, the air gap E is defined as the distance separating the external surface 41 from the electrodes 31,32. the support face 23, along the projection direction common to both surfaces. We then have E = El = E2. The device 1 comprises two electrodes 31, 32; the air gap E can be obtained from two separate measurements taken from the two independent electrodes 31, 32. This increases the accuracy of the measurement of the radial distance separating the external surface 41 from the device 1, and therefore reduces the uncertainties in estimating the radial displacement of the object 4.

[0083] More generally, given that the radial distance separating the first surface from the second surface is fixed and assumed to be known, the air gap E can be defined with respect to a reference plane, for example, a plane containing the first surface or the second surface, or an intermediate plane. Thus, the air gap E depends directly on E1 and E2, for example, E is the average of E1 and E2. Therefore, the first voltage T1 and the second voltage T2 depend on both the air gap E and the areas S1, S2 corresponding to the common surfaces between the respective electrodes and the external surface 41 of the object 4.

[0084] During a step B5, the processing module estimates the air gap E of the first capacitor or the second capacitor from the first voltage T1 and the second voltage T2.

[0085] We assume that there exists a function f 1 such that = T^' modulus of The processing can store the function f1 as a lookup table and perform interpolations to estimate the air gap E from the measurements, or store an analytical expression of fp. As will be explained later, the function can be obtained analytically or approximated in a prior calibration step.

[0086] Preferably, the air gap E is estimated from the sum of the first voltage T1 and the second voltage T2. In this case, the established relationship corresponds to the definition of a function Fj such that — F^T] + T^' function Fx can be obtained as before and stored in the memory of the processing module.

[0087] Preferably, the sum of the first area SI and the second area S2 is constant during the translation of the object 4 along the axial direction. This advantageously ensures that a translation of the object 4 does not disturb the estimation of the air gap E by the device 1, the common section between the two electrodes 31,32 and the external surface being constant.

[0088] During a step B6, the processing module estimates the axial displacement Pax relative to the device in the axial direction from the first voltage T1 and the second voltage T2.

[0089] It is assumed that there exists a function / 2 such that PBX = f 2( 1' -^2' As before, the processing module can store the function / 2 in the form of a a lookup table and perform interpolations to estimate the axial displacement Pax from the tension measurements and the air gap E estimated in step B5, or store an analytical expression of f2. As will be explained later, the function f2 can be obtained analytically or approximated during a preliminary calibration step.

[0090] Preferably, there exists a function F2 allowing the estimation of the axial displacement Pax from the difference between the first tension T1 and the second tension T2 and the air gap E, that is to say a function F2 with two variables such that Pqx = F^Ty - TE^- The use of a model comprising only two variables allows for a more precise estimation of the axial displacement during the tests, once the air gap E is estimated.

[0091] Thus, the device 1 can also be used to estimate the axial displacement of the object 4 from the voltage variations T1,T2 resulting from the capacitance variations C1,C2 due to the variations of the common sections or areas S1,S2 during the axial displacement of the object.

[0092] Obtaining the functions by calibrating the device

[0093] As explained previously, the processing module is configured to measure the first capacitance Cl of the first capacitor and to calculate the first voltage Tl from the first capacitance Cl.

[0094] The relationship between the first voltage Tl and the distance El can be obtained experimentally, before testing, by calibrating the device 1.

[0095] For example, object 4 is placed in a reference position. Device 1 is fixed in the measurement position, opposite the external surface 4L. Object 4 is moved in translation along the axial direction, and the first voltage Tl is recorded by an operator. During calibration, a radial sensor can be used to provide a reference displacement. Typically, the radial sensor can be an optical sensor or a laser sensor with its own direction parallel to the radial axis Y and positioned close to the device. This allows the evolution of the air gap E to be obtained as a function of the voltage TL.

[0096] Typically, in the context of turbomachinery, calibration is carried out under conditions representative of the integration on the test turbomachine and the theoretical operating conditions of the machine.

[0097] The value of the conditioning factor Kl can be determined from the calibration curve obtained. The conditioning factor Kl is a gain that allows a first voltage Tl to be within a satisfactory range, for example on the order of 1 V, for the displacements observed under real conditions.

[0098] Similarly, the processing module is configured to measure the second capacitance C2 of the second capacitor and calculate the second voltage T2 from the second capacitance C2. As before, the relationship between the second voltage T2 and the distance E2 can be established by a calibration method, and the value of the conditioning factor K2 can be determined.

[0099] Thus, since the air gap E can be directly deduced from the respective air gaps E1, E2, the function fx such that = f can be defined from the curves of calibration results are obtained. The function f can be approximated from measurements of the voltages T1 and T2 performed by device 1 and the air gap values ​​E measured by the radial sensor and recorded by an operator during calibration. Typically, the function f can be obtained by the operator using interpolation methods. A lookup table can also be stored in the memory of device 1.

[0100] In a manner similar to the calibration carried out to establish the non-linear relationship between the air gap E (or more generally the distance between an electrode 31,32 and the external surface 41) and the voltages T1,T2, a calibration process can be carried out upstream to establish the relationship between the axial displacement Pax of the object and the voltages T1,T2.

[0101] For example, during calibration, object 4 is placed in the reference position, for which the axial displacement Pax is considered to be zero. Object 4 is moved in translation along the axial direction, and the first voltage T1 and the second voltage T2 estimated by device 1 are recorded by the operator. An axial sensor can be used to provide a reference axial displacement. The axial sensor can also be an optical sensor or a laser sensor with its own direction parallel to the X-axis and arranged orthogonally. Furthermore, the operator can also vary the value of the air gap E and perform a plurality of calibrations of the axial displacement Pax for each value of air gap E.

[0102] This allows us to obtain the evolution of the axial displacement Pax relative to the reference position as a function of the tensions T1, T2, and the air gap E.

[0103] Thus, we can define a function f2 such that Pqx = f°ncti°n can be approximated from measurements of the voltages T1,T2 made by device 1, the air gap values ​​E measured by the radial sensor, and the displacement values ​​measured by the axial sensor and recorded by an operator during calibration.

[0104] Preferably, during calibration, a relationship is established between the axial displacement Pax and the difference between the first voltage T1 and the second voltage T2. In other words, the calibration makes it possible to obtain a plurality of functions tc"c that

[0105] r>^v— (t1 t- X each function 2 depending on the value of the air gap E, or — y 1”1 2 More generally, the two-variable function F2 such that p^x = F^T^- T2, E^- Thus, the functions f^Fj and F2 representing the tensions T1,T2 calculated at the displacements E,Pax to be estimated can be defined experimentally before testing, by calibrating device 1 under suitable conditions and varying both the air gap E and the axial position of object 4 along the axial direction. The processing module can then obtain the estimates using the functions stored in memory.

[0106] Analytical determination of functions

[0107] Preferably, the air gap E can be further estimated from the dimensions of the first electrode 31 and the second electrode 32, and the axial dimension of the object 4. The dimensions can be stored in the memory of the processing module. For example, the processing module calculates the common area between the first surface and the external surface and the gain Gl, and determines the value of the air gap El from the formula given above.

[0108] In the illustrated embodiment, the air gap E depends more precisely on the transverse dimension Le of the first electrode and the second electrode, and on the axial dimension Lc of the object 4.

[0109] More precisely, in this simple configuration we can obtain an analytical expression of the function F Indeed, the total surface covered by the first and second electrodes 31,32 is equal to Sj+ S2 = Lc X Le, and this regardless of the axial displacement P according to the axial direction, within the limit of the axial dimension or length of the device 1.

[0110] Thus, according to the formulas above, we have [YES] 77 / , F j / ç 1 ç \ > E —---- [} G,+¾

[0112] As explained previously, the conditioning factors Kp K2 can be chosen arbitrarily upstream of the measurement procedure. Preferably, they are substantially equal and the electrodes 31,32 have the same relative permittivity, so that the first gain G and the second gain G2 are substantially equal. This allows for a simple analytical expression of the air gap E and the axial displacement Pax as a function of the voltages T1, T2.

[0113] By defining the conditioning factors K1, K2 to have G^ = G2 = G, we then have [0'14] E = ^^, i.e. Fl :x^LcLeGxi-

[0115] The processing module can be configured to estimate the air gap E using such a formula stored in memory.

[0116] The axial displacement Pax is further estimated from the dimensions of the first electrode 31 and the second electrode 32, and the axial dimension of the object 4. More precisely, the axial displacement Pax can be further estimated from the axial dimension le of the first electrode, of the second electrode, and the transverse dimension Le of the first electrode, of the second electrode, and the axial dimension Lc of the object 4.

[0117] The processing module can estimate the axial displacement according to the following formula:

[0118] p _ FL 1 rt / d Lç \ F 4 1 - [ 2LeLc Jne-^c\ 1 [ 2LeLc S^yG^ G2)

[0119] The expression for T\~ E) can be directly deduced for G^ = G2 = G, then we have

[0120] p [ 4 jtt / d G \ y_ F le 1 r 2 • X' y L 2LeLc J Le^c[ ~ ie / G [ 2LeLc XX

[0121] The estimation formulas given above correspond to the geometry illustrated in [Fig.4]. Similar formulas could be obtained for other electrode geometries 31,32.

[0122] The present invention is not limited to an external surface of constant axial dimension along the axial direction, as shown in all the figures. In particular, the device 1 can be used for objects 4 having a variable axial dimension. Specifically, the device 1 can be used with a rotor with continuous targets and a variable cross-section.

[0123] More generally, the proposed device and estimation method can be implemented in all fields requiring a combined estimation of displacements in two orthogonal directions of an object.

[0124] In particular, the measurement steps can be carried out while the object 4 is rotating relative to the device 1 around the X-axis parallel to the axial direction. The device 1 is thus particularly suitable for estimating displacements of a rotor part of the turbomachine relative to a static part such as the engine casing.

Claims

1. Demands Device for estimating displacements of an object (4) having an external surface (41), the device (1) comprising a first electrode (31) having a first surface, a second electrode (32) having a second surface, the device being suitable for being placed in a measurement position in which: The first electrode (31) forms a first capacitor with the object (4), and the second electrode (32) forms a second capacitor with the object (4). a projection of the external surface (41) onto the first surface in a projection direction has a first area (SI), and a projection of the external surface (41) onto the second surface in the projection direction has a second area (S2), the projection direction being normal to the first surface or to the second surface, the first electrode (31) and the second electrode (32) are further adapted so that a translation of the object (4) in an axial direction in a first direction, with respect to the device (1) placed in the measuring position, results in a decrease in the first area (SI) and an increase in the second area (S2), and so that a translation of the object (4) in the axial direction in a second direction opposite to the first direction with respect to the device (1) placed in the measuring position results in an increase in the first area (SI) and a decrease in the second area (S2),with the axial direction being perpendicular to the projection direction, the device also includes a processing module configured for, • measure a first capacitance (Cl) of the first capacitor, • calculate a first voltage (Tl) from the first capacitance (Cl); • measure a second capacitance (C2) of the second capacitor, • calculate a second voltage (T2) from the second capacitance (C2); • estimate an air gap (E) of the first or second capacitor from the first voltage (Tl) and the second voltage (T2), the air gap (E) constituting a distance in the direction of projection, • estimate an axial displacement (Pax) of the object relative to the device in the axial direction from the first voltage (Tl) and the second voltage (T2).

2. Device according to claim 1, wherein the air gap (E) is estimated from a sum of the first voltage (T1) and the second voltage (T2), and wherein the axial displacement (Pax) is estimated from a difference between the first voltage (T1) and the second voltage (T2).

3. Device according to any one of claims 1 and 2, wherein the first surface and the second surface are adapted so that a sum of the first area (S1) and the second area (S2) is constant during the translation of the object (4) in the axial direction.

4. Device according to any one of claims 1 to 3, wherein the first electrode (31) and the second electrode (32) are coplanar.

5. Device according to any one of claims 1 to 4, wherein the first surface and the second surface are centrally symmetric with respect to an axis (Y) parallel to the projection direction.

6. Device according to any one of claims 1 to 5, wherein the first surface is triangular and has a first hypotenuse, and wherein the second surface is triangular and has a second hypotenuse, the first hypotenuse being parallel to the second hypotenuse.

7. Device according to any one of claims 1 to 6, further comprising a mass (24) electrically connected to the first electrode (31) and to the second electrode (32), the mass (24) being arranged between the first electrode (31) and the second electrode (32).

8. Assembly comprising a turbomachine rotor (4) having an external surface (41), and a device (1) according to any one of claims 1 to 7 for estimating displacements of the object (4).

9. A method for estimating the displacements of an object (4) having an external surface (41), implemented by a device (1) according to any one of claims 1 to 7, the method comprising the following steps: • B1: measuring the first capacitance (C1) of the first capacitor while the device (1) is placed in the measuring position, • B2: calculating the first voltage (T1) from the first capacitance; • B3: measuring the second capacitance (C2) of the second capacitor while the device (1) is placed in the measuring position, • B4: calculating the second voltage (T2) from the second capacitance (C2);• B5: estimation of the air gap (E) of the first capacitor or the second capacitor from the first voltage (T1) and the second voltage (T2), • B6: estimation of the axial displacement (Pax) of the object (4) relative to the device (1) from the first voltage (T1) and the second voltage (T2).

10. A method according to claim 9, wherein the measurement steps are carried out while the object (4) is rotating relative to the device (1) around an axis (X) parallel to the axial direction.

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