KR101482511B1 - Diagnosis System and Method of Bearing Defect by Phase Lag and Data Dispersion Shape Factor - Google Patents

Abstract

The present invention relates to a system and a method thereof to diagnose a bearing fault by analyzing a phase delay and a data distribution form index based on a vibration signal generated on the bearing of a rotational facility. The system to diagnose a bearing fault in the rotational facility is formed of a sensor part measuring the vibration signal of the bearing, and a signal processing part includes: a filter extracting a phase delay signal for the measured vibration signal and a signal processing device setting an envelope in accordance to the data distribution of the phase delay signal and the vibration signal, and determining whether the bearing has a fault or not by extracting a monitoring factor based on a distance from a main shaft and a sub shaft to the envelope; and a warning display part including a display device displaying whether the bearing has fault or not, and a warning device generating a warning when the bearing has fault.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bearing defect diagnosis system using a phase delay and a data distribution shape index,

The present invention relates to a method for diagnosing a bearing defect, and more particularly, to a system and method for diagnosing a bearing defect by analyzing a phase delay and a data distribution shape index based on a vibration signal generated in a bearing of a rotating facility .

In general, Rolling Element Bearing is a basic component required for the operation of various machinery. It can be subjected to high pressure during operation and cause serious failure of machinery due to small defects on the surface. These bearings are used as an essential element in various industrial machinery, and the first anomaly occurs when the machinery is operated under abnormal conditions. Therefore, continuous monitoring of the condition of the bearings is required for stable operation of the mechanical device, and a recent Condition Monitoring System essentially includes a function for monitoring and diagnosing the defects of the bearings.

The most commonly used methods for diagnosing bearing defects are the envelope spectrum method and the trend monitoring method.

The envelope spectral method is to obtain the envelope from the vibration signal of the bearing and analyze the frequency through FFT (Fast Fourier Transform). This method can be compared with the defect frequency determined according to the specification of the bearing, which is a highly reliable method, and a new method may be derived by combining with other signal processing methods (see Prior Art 1).

However, in the above method, the frequency spectrum obtained from the actually measured vibration signal is influenced by factors such as (i) resolution used in the frequency analysis process, (ii) calculation error occurring in the frequency analysis process, and (iii) nonlinearity included in the vibration signal The failure frequency calculated theoretically from the specification of the bearing does not coincide with the defect frequency. If these factors are taken into consideration, reliability of bearing diagnosis by frequency spectrum can be secured. For example, using high-specification data analysis hardware that can handle large amounts of data to increase frequency resolution can improve accuracy when compared to the theoretical calculated fault frequencies.

On the other hand, the tendency monitoring method monitors the degree of variation of the measured vibration signal with time to determine the presence or absence of a defect, and it is based on accumulated vibration data through continuous monitoring. That is, the magnitude of the vibration data at the steady state with respect to the bearing and the magnitude of the vibration data to be newly measured are compared, and when the difference is greater than or equal to a predetermined magnitude, it is determined that a defect exists in the bearing.

This method can be applied only if there is vibration data accumulated for a certain period of time. If the same facility is installed at another position, vibration characteristics are different. Therefore, . As a result, the above-described method needs to individually manage the vibration monitoring standard customized for each equipment, which causes a problem in that all costs associated with the maintenance of the equipment are increased.

Therefore, in order to monitor the defects of the bearings more efficiently, it is necessary to (1) require no comparison with the defect frequency, (2) do not require high-specification hardware for the monitoring of bearing defects, (3) ④ It is required to build a system with low cost through this.

[Prior Art 1] United States Patent No. 7,602,985 B2

The present invention has been proposed in order to solve the above problems. The present invention defines a monitoring factor for monitoring a bearing defect from a vibration signal measured by a sensor, and determines whether the bearing is defective or not, And to provide a bearing defect diagnosis system and method therefor.

In addition, the present invention provides a bearing defect diagnosis system which can be performed with a simple system and does not require steady state vibration data in the process of determining whether a bearing is defective, And to provide such a method.

According to an aspect of the present invention, there is provided a system for diagnosing a defect occurring in a bearing of a rotating facility, the system comprising: a sensor unit for measuring a vibration signal of a bearing; A filter for extracting a phase delay signal with respect to the measured vibration signal; an envelope setting unit for setting an envelope according to the data distribution of the vibration signal and the phase delay signal, and extracting a monitoring factor based on the distance from the main axis and the auxiliary axis to the envelope; A signal processing unit including a signal processing unit for determining whether a bearing is defective or not; And an alarm display unit including a display device for indicating whether or not the bearing is defective and an alarm device for generating an alarm when a defect is generated in the bearing.

According to another aspect of the present invention, there is provided a method of diagnosing a defect occurring in a bearing of a rotating facility, the method comprising the steps of: (a) measuring a vibration signal of a bearing in a sensor unit installed in a housing of the bearing; (b) generating a phase delay signal for the vibration signal; (c) extracting a monitoring factor (Z) from the vibration signal and the phase delay signal; And (d) determining whether or not the bearing is defective based on the extracted monitoring factor (Z).

Here, the step (b) for generating a phase delay signal is characterized by generating a phase delay signal whose phase is delayed by 90 ° with respect to the vibration signal.

The step (c) of extracting the monitoring factor (Z) includes: (c1) displaying the data distribution by assigning the vibration signal and the phase delay signal to the horizontal axis and the vertical axis of the two-dimensional plane; (c2) setting an envelope including the displayed data; (c3) an envelope distance in the range of ± 22.5 ° around the main axis and the auxiliary axis, with respect to the auxiliary axis defined by the main axis defined by the vibration signal axis and the phase delay signal axis and the axis rotated by 45 ° with respect to the main axis D1 (i), D2 (i)); (c4) extracting a ratio of the sum of the envelope distance D2 (i) to the sub axis and the sum of the envelope distance D1 (i) to the main axis.

The step (d) of judging whether or not the bearing is defective is judged to be an outer ring defect when the monitoring factor Z is 0 or more and less than 0.5, and is judged to be an inner ring defect when it is 0.3 or more and less than 1.0. State.

The present invention having such a configuration can be applied easily and conveniently to any facility since it uses only the vibration signal measured in real time in the present time as judgment data on the presence or absence of bearing defects and does not need the accumulated data required in general tendency monitoring There is an advantage.

In addition, since the present invention defines a monitoring factor indicating a defect state to determine whether there is a bearing defect, it is not necessary to compare with a theoretical calculated defect frequency, and the system can be configured with simple hardware. That is, it does not require a high-end frequency analyzer for obtaining a high frequency resolution, and thus is cost-effective.

1 is a block diagram showing a configuration of a bearing defect diagnosis system according to an embodiment of the present invention;
2 is a flowchart illustrating a process for diagnosing bearing defects according to an embodiment of the present invention.
FIG. 3 is a graph illustrating a main axis and a sub axis according to an embodiment of the present invention,
4 is a graph illustrating distance measurement of an envelope according to an embodiment of the present invention,
FIG. 5 is a graph showing the probability of a bearing condition for a monitoring factor according to an embodiment of the present invention,
6 is a graph showing steady-state data distribution and its envelope in the bearing defect diagnosis system of the present invention,
7 is a graph showing the data distribution of the inner-ring defect state and its envelope in the bearing defect diagnosis system of the present invention, and Fig.
8 is a graph showing the data distribution of the outer ring defect state and the envelope thereof in the bearing defect diagnosis system of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects, features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: FIG. Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a block diagram illustrating a configuration of a bearing defect diagnosis system according to an embodiment of the present invention. 1, the bearing defect diagnosis system of the present invention comprises a sensor unit 10, a signal processing unit 20, and an alarm display unit 30.

The sensor unit 10 is for detecting a vibration signal of the bearing and is constituted by a vibration detection sensor 11. The vibration detection sensor 11 detects vibrations occurring in the bearing in real time.

The signal processing unit 20 uses the vibration signal of the bearing sensed by the sensor unit 10 to determine whether the bearing is defective or not. That is, the vibration signal of the bearing is filtered, and predetermined data is extracted by using the vibration signal values before and after filtering to determine whether or not the defect is defective. As shown in the figure, the signal processing unit 20 includes a sensor interface 21 for acquiring a vibration signal measured by the vibration sensor 11, and an apparatus for filtering and processing the obtained vibration signal, An analog to digital (A / D) converter 23 for data sampling, a temporary data storage 24 for redundancy of data storage, a digital filter 25 and a signal processing device 26 for signal processing . In this signal processing section 20, the presence or absence of a defect in the base ring and the type of defect (inner ring defect or outer ring defect) are determined from the received vibration signal.

The alarm display unit 30 includes a display device 31, an alarm device 32 and a data storage device 33 for displaying whether or not the bay ring is defective, informing an alarm, and storing data . That is, the alarm display unit 30 displays the presence or absence of a defect and the type of a defect on a screen, and generates an alarm when there is a defect in the bearing.

In the above configuration, the sensor unit 10 is installed in a bearing housing of the bearing, and the signal processing unit 20 and the alarm display unit 30 are installed in a cab of a facility of interest.

FIG. 2 is a flowchart illustrating a process for diagnosing bearing defects according to an embodiment of the present invention. FIG. 3 is a graph illustrating a main axis and a sub axis according to an embodiment of the present invention. And FIG. 5 is a graph showing a probability of a bearing state with respect to a monitoring factor according to an embodiment of the present invention.

As shown in FIG. 2, in the bearing defect diagnosis of the present invention, a vibration signal generated in a bearing is measured and a phase delay signal is generated therefrom (S11, S12). From the data distribution of the vibration signal and the phase delay signal, (S13), and a monitoring factor is extracted from the envelope distance (S14, S15) to determine whether the bearing is defective or not (S16). In addition, an alarm is generated or a maintenance work is performed according to the determination result (S17, S18). Hereinafter, each of the above processes will be described in detail.

1. Vibration signal measurement step ( S11 )

Rotating equipments generate vibration regardless of the state. In steady state bearings, there is no constant periodicity. Generally, it shows the characteristic of white noise and shows a very low flat spectrum in all frequency bands. On the other hand, in the case of a defective bearing, the periodicity associated with the bearing defect is shown, and in the frequency spectrum too much energy is concentrated in a specific frequency band. This specific frequency band is defined as the frequency corresponding to the natural frequency of the bearing.

[Formula 1]

Where fn is the natural frequency of the bearing, k is the stiffness of the bearing, and m is the mass of the bearing. Therefore, in the measuring step, a measurement can be made in a sufficiently wide frequency range including the natural frequency of the bearing.

2. Signal processing step ( S12 ~ S16 )

The present invention defines a monitoring factor (Z) capable of determining the presence or absence of a defect in a bearing from a vibration signal of a bearing, and determines whether the bearing is defective or not according to the value of the monitoring factor (Z). In the process of defining the monitoring factor Z, an envelope is set from the data distribution of the vibration signal x (t) and its phase delay signal x '(t), and the envelope distance D1 ( i) and the envelope distance D2 (i) with respect to the minor axis.

end. Phase Delay Signal Generation ( S12 )

In the process of measuring the vibration signal (x (t)) of the bearing, the frequency band should be selected to include the natural frequency of the bearing as described above. A signal (x '(t) = x (t + 90 °)) in which the phase of 90 ° is delayed from the measured vibration signal x (t) of the bearing.

I. Envelope setting ( S13 )

The measured vibration signal x (t) and the phase delay signal x '(t) generated therefrom are assigned to the horizontal axis and the vertical axis of the two-dimensional plane, respectively, and the data distribution is displayed. At this time, the data distribution is concentrated to a specific shape, and an envelope including most of the displayed data is set as shown in FIG.

All. Extraction of envelope distance S14 )

The envelope distance is calculated for the axial direction defined by the major axis and the minor axis. The envelope distance is the distance from the origin of the main axis to the point where the envelope is located. 3, the main axis is defined as a transverse axis and a longitudinal axis to which the vibration signal x (t) or the phase delay signal x '(t) is allocated, and the sub axis is rotated by 45 degrees with respect to the main axis Axis. Therefore, the distance of the envelope is divided into a distance existing within the range of ± 22.5 ° around the main axis and a distance existing within the range of ± 22.5 ° around the auxiliary axis. As shown in FIG. 4, the distance of the envelope (i)) and the distance (D2 (i)) of the envelope to the minor axis. At this time, i = 1, 2, ... , N, and N represents the number of data constituting the envelope existing within the range of ± 22.5 ° around the main axis and the auxiliary axis.

la. Suppression factor extraction S15 )

The Z value for determining the state of the bearing is calculated by using the envelope shape index D2 (i) using the envelope distance D1 (i) for the main axis and the envelope distance D2 (i) factor.

[Formula 2]

The monitoring factor (Z) represents the ratio of the sum of the distances from the center of the sub-axis to the envelope and the sum of distances from the center of the main axis to the envelope. Accordingly, the monitoring factor (Z) has a value between 0 and 1. For example, if a sine function is assigned to a horizontal axis and a sine function with a 90 ° phase delay is assigned to a vertical axis, the envelope is drawn in a circle, and the monitoring factor (Z), defined as the shape index of the envelope, .

hemp. Judgment of presence or absence of defect ( S16 )

In order to perform the determination of the state of the bearing from the defined monitoring factor Z, a probability graph of the bearing state for each monitoring factor (Z) as shown in FIG. 5 is used. This is due to the difference in the characteristics of the vibration signal generated by the defect state of the bearing. The steady-state bearing vibration signal has a uniform distribution without distinguishing between the main axis and the auxiliary axis (see FIG. Therefore, the monitoring factor Z in the steady state has a value close to 1.0.

However, if there is a defect in the inner or outer ring, the amplitude of the main axis becomes larger than the amplitude of the auxiliary axis. Also, when there is a defect in the bearing, the magnitude of the monitoring factor (Z) value for the outer ring defect and inner ring defect is different for the following reasons.

In general, the frequency factors that make up the bearing drive signal can be divided into the following three categories.

① fr: Rotation number of axis

② fb: Bearing defective frequency (inner ring / outer ring)

③ fc: Frequency of vibration corresponding to natural frequency of bearing

The magnitudes of the three frequencies are fr <fb << fc, which causes a difference between the vibration signal having the inner ring defect and the vibration signal having the outer ring defect.

In the case of a vibration signal having an inner ring defect, a change in the load applied to the inner ring occurs as the inner ring rotates, which is proportional to the shaft rotational speed fr. That is, a modulation phenomenon occurs between the shaft rotation frequency fr and the defect frequency fb of the bearing, and the amplitude of the vibration signal is also affected by the modulation. As a result, the difference in the envelope distance between the main shaft and the auxiliary shaft becomes unclear (see FIG. 7).

A bearing with an outer ring defect is given a constant load without any change in the load applied to the outer ring by the outer ring fixed irrespective of the rotation of the shaft. Therefore, in the case of a vibration signal having an outer ring defect, the influence of the shaft rotation speed fr can be neglected and is mainly influenced by the bearing failure frequency fc. That is, the difference in the envelope distance between the main axis and the auxiliary axis is conspicuous (see FIG. 8).

The distribution of the monitoring factor (Z) according to the bearing condition can be summarized as shown in [Table 1].

Outer ring defect

Inner ring defect
Steady state
Monitoring factor (Z)

that
medium
The

Prob (Z (Z)) corresponding to the monitoring factor (Z) is calculated by using the graph shown in FIG. 5, reflecting characteristics as shown in [Table 1]. That is, when the value of the monitoring factor Z is approximately 0 or more and less than 0.5, it can be judged as an outer ring defect. If it is 0.5 or more and less than 1.0, it can be judged as an inner ring defect. However, since the states of the bearings and the corresponding vibration signals are difficult to distinguish clearly, they define areas where the states of the respective bearings overlap. That is, when the monitoring factor (Z) is between 0.3 and 0.5, the outer ring defect and the inner ring defect overlap each other, and between 0.8 and 1.0, the inner ring defect and the normal state overlap each other.

3. Judgment and follow-up steps ( S17 ~ S18 )

The state of the bearing is determined based on the probability corresponding to the monitoring factor (Z) defined above. The probability of one or two bearing states is given according to the monitoring factor (Z). The probability is expressed as a value between 0 and 1. When the probability of two bearing states is obtained, the bearing state having a large probability value is determined as the current bearing state.

When it is judged that there is a defect in the bearing according to the calculated monitoring factor (Z) value, the kind of defect (inner ring defect or outer ring defect) is displayed and an alarm is generated and a maintenance plan for subsequent processing is established . If it is determined that there is no defect in the bearing, the vibration signal is repeatedly measured, and the state of the bearing is continuously monitored through the signal processing step shown in the present invention.

Experimental Example

According to the above procedure, the performance of the vibration signal of the bearing having the steady state and the bearing having the inner or outer ring defect is verified. FIG. 6 is a graph showing steady-state data distribution and its envelope in the bearing defect diagnosis system of the present invention. FIG. 7 is a graph showing the data distribution of the inner-ring defect state and its envelope in the bearing defect diagnosis system of the present invention And FIG. 8 is a graph showing the data distribution of the outer ring defect state and its envelope in the bearing defect diagnosis system of the present invention.

3 is a graph showing a vibration signal x (t) and a phase delay signal x '(t) of a steady state bearing measured through an experiment, and the envelope is indicated by a solid line. As shown, the vibration signal of the steady state bearing shows that the envelope distance ratio to the major axis and the minor axis is not large. The calculated monitoring factor (Z) is 1.03, and the corresponding probability has a probability 1.0 value of the normal state (Healthy) from FIG. 5, so that the state of the bearing is determined as a normal state. The actual calculated monitoring factor (Z) value will have a value greater than 1.0, which can be understood to be due to the non-linearity of the facilities existing in the actual environment.

7 and 8 show vibration signals of a bearing having an inner ring defect and an outer ring defect, and it can be seen that the shape of the envelope with respect to the main shaft and the auxiliary shaft is significantly different. The calculated monitoring factor (Z) sms is 0.68 for inner ring defects and 0.37 for outer ring defects.

The probability of this can be summarized as shown in [Table 2], and it can be seen that the given bearing condition is accurately determined as shown in [Table 2].

bearing
flaw
Monitoring factor
(Z value)
Probability for Z value
Judgment result OR
(paddle) IR
(Inner ring) Healthy
(normal) Maximum probability 6 normal 1.03 0.0 0.0 1.0 1.0 normal 7 Inner ring 0.68 0.0 1.0 0.0 1.0 Inner ring 8 paddle 0.37 0.7 0.3 0.0 0.7 paddle

(OR: Out Race, IR: Inner Race, Healthy: Normal state)

Table 3 summarizes the results of the determination of the bearing condition using vibration signals for six cases to test the conformity of the present invention. As shown in Table 3, it can be seen that the method using the monitoring factor (Z) defined by the present invention and the probability according to the present invention for all cases accurately determines the state of the bearing.

bearing
flaw

Monitoring factor
(Z value) Probability for Z value
Judgment result OR
(paddle) IR
(Inner ring) Healthy
(normal) Maximum probability One normal 1.02 0.0 0.0 1.0 1.0 normal 2 Inner ring 0.60 0.0 1.0 0.0 1.0 Inner ring 3 Inner ring 0.48 0.1 0.9 0.0 0.9 Inner ring 4 Inner ring 0.58 0.0 1.0 0.0 1.0 Inner ring 5 paddle 0.33 0.8 0.2 0.0 0.8 paddle 6 paddle 0.31 0.9 0.1 0.0 0.9 paddle

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments.

10: Sensor unit
20: Signal processor
30:
x (t): Vibration signal measured by the sensor
x '(t): 90 ° phase delayed vibration signal
D1 (i): Distance from the center to the envelope with respect to the main axis
D2 (i): Distance from the center to the envelope for the minor axis
Z: Bearing condition monitoring factor
Prob (Z): Probability for Bearing Condition Monitoring Factor

Claims (5)

A system for diagnosing defects in bearings of rotating equipment,
A sensor unit for measuring a vibration signal of the bearing;
A filter for extracting a phase delay signal with respect to the measured vibration signal; an envelope setting unit for setting an envelope according to the data distribution of the vibration signal and the phase delay signal, and extracting a monitoring factor based on the distance from the main axis and the auxiliary axis to the envelope; A signal processing unit including a signal processing unit for determining whether a bearing is defective or not; And
And a warning display unit including a display device for indicating whether or not the bearing is defective and an alarm device for generating an alarm when a defect is generated in the bearing. A method for diagnosing a defect occurring in a bearing of a rotary facility,
(a) measuring a vibration signal of the bearing;
(b) generating a phase delay signal for the vibration signal;
(c) extracting a monitoring factor (Z) from the vibration signal and the phase delay signal;
(d) determining whether or not the bearing is defective based on the extracted monitoring factor (Z). 3. The method of claim 2, wherein step (b)
And generating a phase delay signal whose phase is delayed by 90 ° with respect to the vibration signal. 3. The method of claim 2, wherein step (c)
(c1) displaying the data distribution by assigning the vibration signal and the phase delay signal to a horizontal axis and a vertical axis of a two-dimensional plane;
(c2) setting an envelope including the displayed data;
(c3) an envelope distance in the range of ± 22.5 ° around the main axis and the auxiliary axis, with respect to the auxiliary axis defined by the main axis defined by the vibration signal axis and the phase delay signal axis and the axis rotated by 45 ° with respect to the main axis D1 (i), D2 (i));
(c4) extracting a ratio of the sum of the envelope distance D2 (i) to the sub axis and the sum of the envelope distance D1 (i) to the main axis. delete

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