RU2356021C2 - Method of rotor system vibration diagnostics - Google Patents

Abstract

FIELD: physics, measurement.

SUBSTANCE: invention relates to machine building and is intended for diagnosing equipment. The proposed method of rotor system vibration diagnostics comprises measuring the parametres of a running unit vibration and comparing the results with the vibration parametres measured at the equipment initial state. Note here that vibration characteristics are recorded in two directions, i.e. vertical and horizontal relative to the rotor sense of rotation. The data obtained are stored in computer in digital. Note also that the cepstral analysis of vibration process is performed consisting in obtaining the vibration speed cepstrum in the envelope of rotor RPM, followed by lift rationing in vertical direction. Mind that the number of peaks allows judging on endurance crack origination and on its depth.

EFFECT: higher accuracy of diagnostics, expanded performances of estimating technical state and pinpointing other defects in rotor systems.

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Description

The invention relates to the field of engineering, namely to the study of equipment and can be used to diagnose the technical condition of rotor systems, in particular to identify fatigue cracks in general engineering equipment or building structures, and relates to methods and means for vibration diagnostics of the technical condition of such systems.

Most methods for diagnosing incipient defects in mechanisms are based on the same diagnostic model: the development of a defect causes an increase in amplitudes and a change in the shape of the vibration signal.

The task is to use the optimal signal processing method, which minimizes the influence of interference and allows you to unambiguously correlate the obtained signal characteristic with the type of defect. In order to solve the diagnostic problem by the totality of the vibrational characteristics of the system, it is necessary to select the diagnostic signs that are most sensitive to changes in the technical condition of machines. Since vibration causes fatigue failure of parts, when fatigue cracks appear, the nature of vibrations, stiffness and damping of parts begin to change, leading to significant nonlinear effects in the system. The sudden nature of the occurrence and growth of a fatigue crack makes it difficult to diagnose them at an early stage of occurrence. In most works devoted to this problem, informative diagnostic features are associated with the energy spectrum of the signal: the amplitude, duration and time of the appearance of the pulse, frequency and phase of the harmonic signal [Vibroacoustic diagnosis of incipient defects. Under the general ed. M.D. Genkina. - M .: Nauka, 1984; Genkin M.D., Sokolova A.G. Vibroacoustic diagnostics of machines and mechanisms. M .: Engineering, 1988].

The disadvantages of these diagnostic signs is their connection with several different defects of the aggregate at once, and their manifestation at rather late stages of the development of the defect.

A known method for diagnosing the integrity of a metal column, based on the identification of cracks, including determining and measuring the spectrum of noise over time before starting work, when the column string [patent No. 2295639, ЕВВ 47/00, publ. March 20, 2007, BI No. 8]. The disadvantage of this method is the impossibility of separation in the noise spectrum of column faults and environmental influences.

There is a method of bench tests of natural samples of rods and models of rods for fatigue strength when applying simultaneously constant and / or variable loads, the direction of which coincides with the axis of the rod. Diagnosis is carried out to identify and develop fatigue cracks [patent No. 32284494, G01M 15/00, publ. September 27, 2006, BI No. 27]. The disadvantage of this method is the inability to control the state of vibration in two mutually perpendicular directions.

A known method for diagnosing an engine by determining the location of a defect, based on measuring vibration of a running engine, spectral analysis of vibration and comparing the received data with data in the initial state. Localization of the defect is carried out in a wide range of frequencies [application. No. 2005113946/06, G01M 15/00, publ. November 20, 2006, BI No. 32]. The disadvantage of this method is that the detection of a defect is not always possible in the early stages of its appearance and development.

Since the time between the appearance of a fatigue crack and a sudden failure of the mechanism depends on the crack initiation site and on the general vibration level and an avalanche-like crack growth is often observed over a relatively short period of time, it is necessary to unambiguously relate the informative characteristic to the appearance of a fatigue crack. It is also necessary that the totality of the features makes it possible to detect a defect at the earliest stages of development.

The invention is based on a technical problem, which consists in increasing the accuracy of diagnostics, expanding the functionality of a method for evaluating the parameters of a technical condition and early detection of other defects in rotor systems.

This problem is solved in that in a method for diagnosing rotary systems based on measuring the parameters of the vibration process of a working unit, comparing the obtained parameters with the same values measured in the initial state, according to the invention, the characteristics are recorded in two directions: vertical and horizontal with respect to the axis of rotation rotor, the obtained data is stored in a computer in a digitalized form and conduct a cepstral analysis of the vibration process, which consists in obtaining a cepstrum vibration velocities in the vicinity of the rotor speed, and then its lift in the vertical direction, and by the number of peaks in the cepstrum, the appearance of a fatigue crack and its depth is judged.

With the help of cepstras, it is possible to isolate harmonic families from a single vibration source, and when logarithmic of the initial complex spectrum of vibration velocities, weak harmonics are amplified and strong harmonics peaks are weakened, thus, an optimal signal processing method is used that minimizes the influence of noise and allows you to unambiguously correlate the obtained signal characteristic with a kind of defect. From a physical point of view, the spectrum is aligned according to the amplitudes of the harmonics and in the vibration velocity cepstrum, weak pulses from the nascent crack are amplified and separated from pulses caused by other malfunctions in the rotor system: imbalance, misalignment, and defects in bearing assemblies that occur at frequencies that are multiples of the rotor system speed. The invention is illustrated by the following drawings, in which Fig. 1 shows a change in the cepstrum of vibration velocity in the vicinity of the rotor speed with increasing crack depth (% of the cross-sectional area of the shaft), Fig. 2 shows a block diagram for diagnosing a rotor system.

Figure 1 shows the change in the cepstrum of the vibration velocity of the signal in the vicinity of the rotor speed with increasing depth of the crack. For samples with a crack of up to 5%, there are only two peaks in the vibration signal cepstrum; with an increase in the crack depth, the number of peaks increases and the cepstrum gamnitude grows. Elevation (anagram of the word filtration) of a cepstrum in the vicinity of the rotational speed and its doubled component enhances the manifestation of pulses from different excitation sources: technological malfunctions of the rotor system are collected in one ragmonic (anagram of the word harmonica),

A fundamentally new characteristic was found for the first time, which allows one to diagnose the appearance of a fatigue crack with a depth of 5-7% of the shaft cross-sectional area. Using this informative characteristic, one can identify a fatigue crack: by the number of ragmonics in a cepstrum (the more ragmonics, the more sources of excitation, and therefore the impulses from the crack); by the distance between the ragmonics (the closer they are located to each other, the closer the manifestation of these pulses is in time, thus, the smaller the crack, the more its collapse will be closer in time with the rotation frequency - the first ragmonica); the height of the ragmonics (the higher the ragmonics, the stronger the source of excitation, that is, with increasing depth of the crack, the energy of the “collapse” mechanisms inside the crack increases).

The essence of the invention lies in the fact that the method of vibration diagnostics of rotor systems, in which the parameters of the vibration process are removed from the housing of the bearing assemblies as close as possible to the stress concentrators of the part from which a fatigue crack can occur, while the vibration characteristics are recorded using vibration sensors in two mutually perpendicular directions : vertical and horizontal with respect to the axis of rotation of the rotor; The characteristics are stored in a computer in the form of an amplitude-time dependence in digital form and processed using a fast Fourier transform to obtain a cepstrum of vibration velocity in the vicinity of the rotor speed and then lift it in the vertical direction. One of the possible ways to implement the method of vibration diagnostics is illustrated in the drawing, where Fig. 2 shows the housing 1 of the bearing assemblies, vibration sensors 2 connected to a vibration measuring complex 3, which transmit the measured vibration signal through the ADC 4 to the computer 5.

This invention is aimed at expanding the technical capabilities of vibration diagnostics of rotor systems in operating modes, and, unlike the existing ones, it is intended not only to analyze the effect of defects on vibration characteristics, but also to solve the inverse problem: to evaluate the technical state parameters based on the results of vibration measurements and separation of the effects of various defects to vibration signals. This method can also be used to detect other defects in rotor systems that manifest themselves at other excitation frequencies, as well as the degree of their development.

Claims (1)

The method of vibration diagnostics of rotor systems, including measuring the parameters of the vibration process of the operating unit and comparing the obtained parameters with the same values measured in the initial state, while the vibration characteristics are recorded in two directions: vertical and horizontal with respect to the axis of rotation of the rotor, the received data is stored in computer in digital form, characterized in that a cepstral analysis of the vibration process is carried out, which consists in obtaining a cepstrum vibration spine in the vicinity of rotor speed and then liftratsii in the vertical direction and the number of peaks in the cepstrum judge the occurrence of the fatigue crack and its depth.

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