Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
  • G01M13/00—Testing of machine parts
  • G01M13/02—Gearings; Transmission mechanisms
  • G01M13/028—Acoustic or vibration analysis

Definitions

• DESCRIPTION TITLE Device for monitoring the state of damage of a power transmission
• TECHNICAL FIELD OF THE INVENTION The technical field of the invention is that of monitoring the state of health of mechanical components used for power transmission.
• the present invention relates to a method and a device for monitoring the state of health of an epicyclic gear train.
• TECHNOLOGICAL BACKGROUND OF THE INVENTION Shaft lines integrated into rotating machines, for example an aircraft engine, are equipped, in a conventional manner, with different mechanical parts or components, such as bearings and gears.
• epicyclic gear trains also called planetary gearboxes, are mechanical parts comprising several concomitant gears.
• An example of an epicyclic train comprising 4 planetary gears 13 and a solar 14 is shown in Figure 1.
• the operation of an epicyclic gear train generates complex vibration signals subject to modulation overlap. Monitoring the state of health of such a component, to detect excessive and premature degradation, is therefore not easy to implement. However, it is essential to ensure good mechanical strength and the lifespan of the shaft line equipped with it in order to avoid operating anomalies of the systems in which they are integrated.
• the modulation phenomenon is already known for gears with parallel axes. This phenomenon is linked to the amplitude and/or phase modulation of the fault frequency by the meshing frequency. In the case of an epicyclic train, the modulation is much more complex due to the presence of several elements within the same train.
• modulation overlap we mean the phenomenon by which a frequency of a defect on a gear appears, in the spectrum of the associated vibration signal, at an erroneous location due to the fact that the modulation frequency of the gear is higher than the frequency of the fault.
• these approaches take into account neither the interactions between the natural modulations of the train and the modulations linked to its damage, nor the masking of gear modulations by noise.
• the vibration signals of an epicyclic gear train there are not only specific frequencies linked to damage to the gear but also frequencies modulating the meshing, for example: the rotation frequencies of the satellite carrier, the frequencies of a fault, the interaction between the fault and the variation in position of the fault relative to the fixed sensor, etc.
• these approaches are not suitable for the case where the operating regime of one of the connected shafts of the epicyclic gear train is non-stationary, which is nevertheless the case in aeronautical applications.
• the invention offers a solution to the problems mentioned above, by making it possible to monitor the health of epicyclic gear trains equipped on a high-power transmission system, for example on a rotating machine.
• a first aspect of the invention relates to a method of monitoring the state of health of an epicyclic gear train equipped on a rotating machine and adapted to carry out power transmission on a line of shafts of said rotating machine, the method comprising the following steps: - Acquisition by a vibration sensor of a vibration signal from the rotating machine, the vibration signal comprising vibrations generated during the transmission of power by the planetary gear train; - Construction of a measurement vector and a transition matrix of a phenomenological vibration model, this model being based on a Fourier series decomposition of the vibration signal taking into account interactions of vibration sources different from the epicyclic train; - Estimation of a possible fault vibration signature from the measurement vector, the transition matrix and the acquired vibration signal, the possible fault vibration signature taking into account a modulation overlap effect; - Determination of a distance by comparison of the vibration signature of a possible defect with a reference signature.
• the invention it is possible to determine with reliability and robustness the presence of a defect on one or more elements of the planetary gear train. Indeed, thanks to the phenomenological modeling of the vibration signal of the gear and the recursive estimation of the parameters of the constructed model, it is possible to estimate the different modulation components carrying information on the state of health of the gear. a gear as well as their mutual interaction. The modulations are thus estimated using a deterministic approach using the phenomenological vibration model and a priori knowledge of the kinematics of power transmission, contained in the measurement vector and the transition matrix.
• the modeling takes into account the interactions between the modulations generated by the transmission of power within the epicyclic train, coming from the various vibration sources which are the different elements of the epicyclic train (planets, planet carrier, solar and crown), making the Robust approach to modulation overlap.
• the proposed solution is valid for both a stationary and non-stationary regime of the rotating machine.
• taking into account the different modulation sources makes it possible to be robust to noise and peaks not linked to power transmission.
• the method can be used in real time, it can be used to monitor the progression of damage, for example the propagation of a crack from a tooth through the gear.
• the measurement vector is constructed from kinematic data of the planetary gear train and of the shaft to which the planetary gear train is connected and from parameters of the phenomenological vibration model.
• the transition matrix is an identity matrix whose size depends on the parameters of the phenomenological vibration model.
• the step of estimating the vibration signature of a possible fault comprises the following two sub-steps: - Recursive estimation of an estimated vector of the parameters of the model of the acquired signal, the estimation being a recursive estimation carried out by means of a Kalman filter, the Kalman filter taking as input the acquired vibration signal, the transition matrix and the measurement vector; - Reconstruction of the vibration signature of possible fault from the estimated vector of the parameters of the acquired signal model.
• a second aspect of the invention relates to a device for monitoring the state of health of an epicyclic gear train, the device comprising: - An acquisition module comprising at least the vibration sensor and configured to implement the step acquisition of the method; - A processing module configured to implement the steps of constructing a measurement vector and a transition matrix, estimating a vibration signature of a possible fault, determining a distance and transmitting of an alert.
• This second aspect according to the invention makes it possible to easily implement the method according to the first aspect by means of a simple device.
• a third aspect of the invention relates to a computer program product comprising instructions which, when the program is executed on a computer, cause it to implement the steps of the method according to the first aspect.
• a fourth aspect of the invention relates to a computer-readable medium comprising instructions which, when executed by a computer, cause it to implement the steps of the method according to the first aspect.
• - Figure 3 is a vibration signal of the epicyclic train acquired during execution of the method.
• - Figure 4 is a spectrum of the acquired vibration signal.
• - Figure 5 is a spectrum of an estimate around the fundamental meshing.
• - Figure 6 is a spectrum of the signature of a solar without taking into account the modulation effect by a planet carrier.
• - Figure 7 is the spectrum of the estimation of the solar signature with an meshing effect and a modulation effect of harmonic 1 of the planet carrier.
• - Figure 8 is the spectrum of the signature taking into account the effect of modulating harmonic 4 of the planet carrier.
• - Figure 9 is a graph representing an evolution of a possible fault indicator. DETAILED DESCRIPTION Unless otherwise specified, the same element appearing in different figures presents a unique reference.
• a first aspect of the invention relates to a method for monitoring the state of health of an epicyclic gear train equipped on a rotating machine.
• the planetary gear train is adapted to transmit power on a line of shafts of said rotating machine.
• rotating machine we mean a motor which transforms the energy supplied to it into a rotary movement, for example through a shaft line.
• this concerns in particular aircraft such as planes or helicopters, but it can also involve wind turbine engines, rolling vehicle engines, etc.
• Figure 1 is a schematic representation of the epicyclic gear train 10. This comprises several elements: a crown 11, a planet holder 12, four planets 13 and a solar 14. Each element of the epicyclic gear train 10 is connected to one of the shafts of the rotating machine.
• the stress on the planetary gear train 10 by the rotation of one of its elements generates vibrations coming from each of the elements and possible defects. These vibrations can be captured by a vibration sensor which will produce a vibration signal comprising the vibrations produced by each of the aforementioned sources as well as noise. This may be noise coming from other parts of the rotating machine or noise linked to the environment of said machine.
• defect is meant a discontinuity in the properties of the material making up a part or object inspected, in this case the planetary gear train 10. This discontinuity results from an anomaly present in the material. This anomaly can have diverse origins and be of varied nature. These anomalies are mainly the consequence of hazards that occur during the manufacturing of the part.
• the material may, for example, have been weakened during the manufacturing process and its use, generating strong local stresses at the level of the weakened area, or following an impact, causes a defect.
• the term “defect” therefore covers all forms of anomalies that may undergo the material: material defect, inclusion, crack, porosity, corrosion, alteration of the material properties, etc.
• the case of a tooth defect is considered here.
• the epicyclic gear train 10 includes ⁇ ⁇ planets 13 with ⁇ ⁇ teeth, the planet carrier 12, the solar 14 with ⁇ ⁇ teeth and the crown 11 with ⁇ ⁇ teeth.
• the vibration signal of the epicyclic train 10 comprises two components: - A natural component linked to the engagement of the teeth of the planets with those of the crown or between those of the solar; - An abnormal component linked to the presence of the defect on one of the elements.
• the amplitude associated with each of the components is modulated due to the mobility of the gear members.
• the amplitude of each component in the vibration signal is therefore more or less strong depending on the relative position of the point of contact between the teeth, which are mobile, with the sensor, which is fixed.
• the meshing signal ⁇ in the presence of the defect can be modeled using a phenomenological model, in discrete time, in the form ⁇ ⁇ [ Math.1] ⁇ ⁇ ⁇ , ⁇ ! ⁇
• - ) is a number of harmonics of the meshing, defined by an operator according to the precision of the desired model
• - ⁇ ⁇ is a weighting function resulting from the position of the contact point of the *-th planet relative to the position of the fixed sensor
• - ⁇ ⁇ , ⁇ is the signal generated by the fault in contact with the *-th planet
• - ⁇ ⁇ , ⁇ ,%& ⁇ ' is the +-th meshing harmonic generated by the *-th planet
• - And ⁇ is the index of the discrete time or that of the sample of the signal.
• the weighting function ⁇ ⁇ is zero and the planetary gear train 10 is treated as a gear with parallel axes.
• the weighting function is considered to be periodic to the rotation period of the planet holder - ⁇ Therefore, the function ⁇ ⁇ can be approximated by a trigonometric series with coefficients [Math.
• this signal can be expressed in the form of a trigonometric series such that ⁇ , - [Math. 5b] S ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ Q ⁇ R, ⁇ ⁇ QR, ⁇ A ⁇ C .RG ⁇ , - And T is the harmonic number of the characteristic signal of the fault, defined by the operator according to the desired precision of the model.
• ⁇ In vector form, this signal is written [Math.7] ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ⁇ ? A ⁇ where: and In a compact writing, the vibration signal ⁇ can thus be written [Math.9] ⁇ ⁇ ? A ⁇ W ⁇ ⁇ ( ⁇ , with: - [Math. 9a]?
• the vector of model parameters W implicitly contains information related to the state of health of the gear components. Given the slow variation of the parameters of the vector W, it is possible to apply a smoothing constraint to the vector of model parameters.
• the smoothing constraint is of order greater than or equal to 1.
• the smoothing constraint is of order 1, and its explicit writing is [Math.10] W ⁇ ⁇ 1 ⁇ ⁇ W ⁇ ⁇ [ ⁇ ⁇ , with - [ a Gaussian white noise vector with covariance matrix ⁇ ; the size of the white noise vector is the same as that of the model parameters vector.
• the transition matrix ] is the identity matrix of size 2) ⁇ ⁇ ⁇ 1 ⁇ 2 ⁇ T ⁇ 9 ⁇ ⁇ 4T9 ⁇ G 2) ⁇ ⁇ ⁇ 1 ⁇ 2 ⁇ T ⁇ 9 ⁇ ⁇ 4T9 ⁇ .
• the size of the transition matrix ] may be different if the order of the smoothing constraint is greater than 1. For example, for a smoothing constraint of order 2, the equation [Math. 10] becomes W ⁇ ⁇ 1 ⁇ ⁇ 2W ⁇ ⁇ W ⁇ ⁇ 1 ⁇ ⁇ [ ⁇ and the transition matrix ⁇ ⁇ 0 1
• the equations [Math. respectively the measurement equation and the equation of state for the vibration signal ⁇ .
• the above phenomenological model can be applied to epicyclic trains as well as to gears with parallel axes, which are explicitly integrated into this vibration model.
• the challenge of the present invention is therefore to produce an estimate of the vector of the parameters of the model of the acquired signal, denoted Wc, from the construction of the transition matrix] of said signal and a determination of the measurement vector?.
• Wc the vector of the parameters of the model of the acquired signal
• the interest is then to extract one or more vibrational signatures of possible defects then to compare and analyze these vibrational signatures to one or more reference signatures of e& ⁇ in order to detect the presence of the possible defect(s) on one or more elements of the epicyclic gear train 10.
• the method 100 for monitoring the state of health of an epicyclic gear train is schematized in Figure 2.
• the method 100 comprises five steps numbered from 101 to 105.
• the first step 101 is a step of acquiring the vibration signal ⁇ by means of a vibration sensor.
• the vibration sensor is, for example, a displacement sensor, a speed sensor or an accelerometer.
• the vibration sensor is an accelerometer based on piezoelectric technology.
• the vibration signal is acquired at the sampling frequency; ⁇ .
• the sampling frequency is at least twice as high as the maximum number of meshing harmonics considered for the epicyclic gear train.
• the duration of acquisition of the vibration signal is at least as long as a duration corresponding to a predetermined number of rotation cycles of a shaft of the rotating machine connected to the epicyclic gear train 10.
• the predetermined number of rotation cycles of the tree is greater than 1 and can be an integer or real.
• the predetermined number of rotation cycles of the shaft is chosen so as to cover sufficient rotation cycles to guarantee robust and reliable analysis of the signal and to limit the size of the signal, thus allowing rapid analysis of said signal and monitoring in real time of the epicyclic train 10.
• the acquisition duration is therefore advantageously short to allow the repetition of the implementation of the method 100 at a real time rate.
• the acquisition duration is at least as long as the duration corresponding to the predetermined number of rotation cycles of the shaft connected to the planetary gear train 10 which has the slowest rotation speed.
• the duration of the signal can, moreover, be fixed by a maximum number of samples - to be acquired, at the sampling frequency; ⁇ .
• the vibration sensor is placed on or near the rotating machine.
• the vibration sensor is placed near the shaft connected to the planetary gear train 10, for example on a frame of said shaft.
• the acquisition step 101 may also concern the measurement of a rotation speed of the shaft connected to the epicyclic gear train 10.
• the rotation speed is denoted ⁇ " .
• the rotation speed of the shaft can be obtained directly at by means of a speed sensor, for example a tachometer It is also possible to use another type of speed sensor, providing a square, sinusoidal or series of pulses speed signal.
• the second step 102 is a step of constructing the measurement vector? and the transition matrix].
• the point of constructing the measurement vector? is to model the frequency location of the frequencies of interest, in particular the meshing frequency, the frequencies of the gear and those of a possible fault.
• the transition matrix ] is constructed according to the smoothing constraint chosen for the model.
• the transition matrix ] is the identity matrix of size 2) ⁇ ⁇ ⁇ 1 ⁇ 2 ⁇ T ⁇ 9 ⁇ ⁇ 4T9 ⁇ G 2) ⁇ ⁇ ⁇ 1 ⁇ 2 ⁇ T ⁇ 9 ⁇ 4T9 ⁇ , as described above.
• the measurement vector? is constructed from known data on the kinematics of the shaft and the epicyclic gear train 10, according to equations Math.1 to 9. In this case, the measurement vector?
• the weighting function ⁇ ⁇ is constructed from: - the number 9 of harmonics contained in the weighting function ⁇ ⁇ , - the number T of harmonics of the signal characteristic of the fault, - the number ) of harmonics of the meshing, - the speed angle of the defect - the sampling period ⁇ ⁇ - the time lag ⁇ ⁇ between the vibration of the i-th planet and that of the (i-1)-th planet, - the weighting function ⁇ ⁇ , - the frequencies of rotation of the crown, solar, planets and planet holder; ⁇ , ; ⁇ , ⁇ , and ; ⁇ respectively.
• Step 103 is then a step of estimating the fault vibration signature(s). possible
• the defect may correspond to a tooth defect of one of the elements of the planetary gear train 10.
• Step 103 of estimating vibration signatures of possible defect comprises two sub-steps 103a and 103b.
• Sub-step 103a is. a step of estimating the estimated vector c W of the parameters of the model of the acquired signal. The estimation is preferably carried out recursively using a Kalman filter, for example according to the Rauch–Tung–Striebel variant.
• Kalman filter uses the transition matrix ], the measurement vector ? and the acquired signal ⁇ .
• the Kalman filter provides the estimatec W of the vector of model parameters of the acquired signal.
• the Kalman filter uses as parameter the initialization of the estimated vector Wc ⁇ 1 ⁇ , a covariance matrix s ⁇ 1 ⁇ of an initialization error, the covariance ⁇ of the state noise and the variance , of the measurement noise .
• substep 103b is a step of reconstructing the vibration signature(s) of possible fault t d.
• the reconstruction is carried out using the equations [Math. 1 to 9] above and from the estimate Wc of the vector of parameters of the model of the acquired signal.
• Each vibrational signature of possible defect t d is a matrix constructed such that d t ⁇ - - - wx ⁇ , ⁇ w?
• the vectors uc, wx ⁇ , wx ⁇ ,%& ⁇ ' wx ⁇ f ⁇ &e ⁇ hf are of sizes - or have a number of samples equal to -.
• ⁇ expresses the estimate of the vibration signature of the possible defect.
• the vector wx ⁇ f ⁇ &e ⁇ hf expresses the interaction between the defect and the weighting function due to the fixed position of the sensor compared to the variable position of each planet.
• Step 104 is then a step of comparing the vibration signature(s) of possible defect t d with the reference signature d ⁇ z . If no reference signature d ⁇ z is available, the or at least one of the vibration signatures of possible defect t d then becomes the reference signature(s) d ⁇ z .
• ⁇ is ⁇ & ⁇ ⁇ ⁇ ⁇ that wx z ⁇
• the distance is between the standard deviation of the effective value of the vibration signature of possible defect t d and the standard deviation of the effective value of the reference signature d ⁇ z .
• Step 105 is, finally, a step of issuing an alert based on the distance calculated in the previous step. The alert is triggered when the absolute value of the distance is greater than or equal to an alert threshold.
• This alert threshold may be an integer or real multiple of the standard deviation of the reference indicator.
• a second aspect according to the invention relates to a device for monitoring the state of health of the planetary gear train 10.
• the device comprises software and hardware means for implementing method 100.
• the monitoring device comprises an acquisition module comprising the vibration sensor , a signal conditioner, an analog-to-digital converter, a volatile and/or non-volatile memory and a processor. Instructions are included in the memory of the acquisition module which, when executed by the processor, allow the implementation of step 101 of acquisition of method 100, for the acquisition of the vibration signal and, if necessary , of the rotation speed of the shaft connected to the planetary gear train 10.
• the monitoring device also includes a processing module, comprising a processor and a volatile or non-volatile memory.
• the memory of the processing device includes instructions which, when executed by the processor, allow the implementation of steps 102 to 105 of method 100.
• the processing module can also include display means, such as a screen and a graphical interface, to translate monitoring into graphical form.
• the acquisition module and the processing module can be implemented in two different devices. Two examples are proposed below to demonstrate the performance and usefulness of method 100.
• the first example concerns the monitoring of an epicyclic gear train on a measuring bench.
• the second example involves monitoring the progression of damage.
• the crown 11 has ⁇ ⁇ ⁇ 96 teeth and is fixed.
• the input of the gear is the 14 planetary gear with ⁇ 34 teeth and the output is the 12 planetary gear carrier with ⁇ 5 planetary gear 13 of ⁇ 31 teeth.
• the vibration signal is acquired at a sampling frequency; ⁇ ⁇ 51.2 kHz.
• a seizure on solar 14 was noted.
• Method 100 is therefore applied to extract the signature of the defect of the solar 14, the period of which is equal to the rotation period of said solar 14.
• Figure 3 is an extract of the vibration signal ⁇ acquired as well as the rotation frequency; ⁇ of planet carrier 12, expressed as a function of time t.
• Figure 4 is represented the spectrum ⁇ of the vibrational signal ⁇ as a function of the machine orders ⁇ T whose reference here is the planet carrier 12.
• Method 100 makes it possible to extract the signature of the damage of the solar 14 from the vibrational signal without take into account the modulation induced by the planet carrier 12.
• Figure 5 shows the spectrum of the raw signal as well as the solar signature determined from the estimation of the parameter vector of the associated model.
• FIG 6 is represented the spectrum of the signature of the solar 14 without taking into account the effect of the modulation by the planet carrier 12.
• the prominence of the peaks linked to the order of the defect of the solar, which is at 2.8235, and its harmonics, are clearly distinguishable. However, this estimate does not take into account the effect of the modulation generated by the planet carrier 12.
• figure 7 is shown the spectrum of the estimation of the signature of the solar 14 with the effect of the meshing and the effect of modulation of harmonic 1 of the planet carrier 12.
• Figure 8 is represented the spectrum of the signature with taking into account the effect of the modulation of the planet carrier 12 when the first harmonic of the frequency of the solar 14 is considered, and that the latter is modulated by the harmonic 4 of the planet carrier 12.
• method 100 is applied to vibration data of damage to the planetary gear train 10 with propagation of the damage.
• a crack was detected in the tooth root of a planet 13, which then spread across the entire width of the gear body.
• the following parameters are chosen: + ⁇ 1, T ⁇ 4, 9 ⁇ 0, , ⁇ 10, ⁇ ⁇ 10 ⁇ G ⁇ , ⁇ being the identity matrix of appropriate size.
• the initializations for the Kalman filter are made by random selection following a Gaussian law.
• the possible fault indicator here is the effective RMS value (in English, “root-mean-square”), applied to the signature of the fault whose fundamental frequency is that of the fault of planet 13.
• the evolution of the possible fault indicator is displayed in Figure 9.
• the threshold is here set, in an illustrative manner, at 2 times the standard deviation (indicated by the notation ⁇ ⁇ 2 ⁇ where ⁇ is the average value of the indicator and ⁇ is the standard deviation) of the same indicator in the absence of damage to the gear, which is the case before the 350th measurement. It is possible to observe a clear increase in the effective value, reflecting a propagation of the damage over the entire body of the gear, as was observed during the test.

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• 2022
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