JPS6031036A - Diagnostic method of rolling bearing - Google Patents

Abstract

PURPOSE:To make the diagnosis of a bearing easy and highly accurate, by computing the frequency characteristics of each part of the outer race, inner race and rolling element of a rolling bearing and the ratio between the value of the root of the sum of square of the intensity of the harmonic component and the effective value of the vibration intensity of the entire frequency region. CONSTITUTION:A vibration sensor 11, which detects vibration, is attached to a rolling bearing 10 to be inspected. The detected result is amplified by a vibration processing circuit 12 and inputted to a frequency analyzing part 13. In the frequency analyzing part 13, frequency analysis is performed based on an expression representing the frequency characteristics of the outer race, inner race and rolling element of the rolling bearing. The ratio between the value of the root of the square of the intensity of the harmonic component and the effective value of the vibration intensity of the entire frequency region is computed as a deterioration index at each part. Thus the diagnosis of the rolling bearing can be performed readily and highly accurately.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for diagnosing abnormal conditions of rolling bearings.

Rolling bearings are general bearings used in the rotating parts of various machines, and have circular outer and inner raceways, and between them, rollers, balls, etc. are used as rolling elements to incorporate rolling motion. Although low friction has been achieved, there is still some sliding motion, which may increase the friction of the bearing, and the rolling surface may be contaminated with flaking due to rolling fatigue or foreign matter such as dirt. There is a risk of damage due to intrusion, poor lubrication, etc., and even secondary failure.

For this reason, various diagnostic methods have been adopted to detect and deal with damage to rolling bearings at an early stage.

An effective method for diagnosing the condition of rolling bearings is the vibration method, which detects the degree of abnormality by capturing the vibration caused by the abnormality when damage or other abnormality occurs in the rolling bearing. In the vibration method as well, various methods with improved accuracy are being developed.

The conventional vibration method measures the peak value, effective value, and average value of acceleration vibration due to damage to rolling bearings, calculates the ratio of the peak value to the effective value, or the ratio of the peak value to the average value, and calculates the value at this value. Common methods include determining abnormality based on series changes, and normalizing the effective value or average value by correcting it by the shaft diameter or rotational speed of the rolling bearing.

Furthermore, recently, as a highly accurate monitoring method, a method has been developed that uses the fourth-order moment of vibration of the rolling bearing to determine abnormalities in the rolling bearing.

This is because the normal vibration of a rolling bearing fluctuates irregularly, but its probability distribution follows a Gaussian distribution. probability density function P
Since (x) is related to the fourth power mean by the fourth moment, damage to the bearing is determined by the value obtained by normalizing the fourth power mean obtained from the probability density function P(X) by the standard deviation. It is something to do.

That is, the probability density function P (x) is expressed as T: mean value and σ: standard deviation, and since the fourth power mean Y7 is obtained by the fourth moment, this fourth power mean 7 is normalized by the standard deviation. As a result, a value related to the vibration of the rolling bearing called the Kurtosis value is calculated, and the degree of damage to the bearing is determined based on this Kurtosis value. The foot sis value will normally be 3.0 if the rolling bearing is correct, and if an abnormality occurs in the rolling bearing, the foot sis value will be greater than 3.0 (so the 10
It becomes possible to judge the extent of the injury.

The types of damage that occur in rolling bearings are generally divided into local defects that occur in the outer ring, inner ring, and rolling elements, such as flaking, and global defects, such as poor lubrication and wear on the rolling surfaces. be done. However, although the method of determining an abnormality using the footosis value described above is effective for general defects, it cannot accurately evaluate local defects.

This is because in the case of a total defect, the frequency component of the vibration does not change much and increases over the entire area.
Although it is possible to accurately determine the state of a defect, in the case of a localized defect, the frequency of vibration generated in a rolling bearing changes greatly due to variations in the characteristic frequency components of the outer ring, inner ring, and rolling elements. This is because it is not possible to accurately determine the extent of damage.

The present invention has been made in view of the above circumstances, and provides a rolling bearing that accurately evaluates the degree of abnormality occurring in each part by focusing on the characteristic frequency components of the outer ring, inner ring, and rolling elements of vibration caused by abnormality. The purpose is to provide a diagnostic method for

The present invention measures the vibration of a rolling bearing and analyzes the frequency of the measured vibration waves to determine the outer ring of the rolling bearing.

Calculate the ratio of the square root of the sum of squares of the intensity of the characteristic frequency and harmonic components of each part of the inner ring and rolling elements to the effective value of the vibration intensity in the entire frequency range as a deterioration index for each part,
The method is characterized in that the deterioration probability of each part is calculated from each deterioration index.

The present invention will be explained in detail below based on the drawings.

FIG. 1 is a cross-sectional view of the rolling bearing, and FIG. 2 is a vertical cross-sectional view thereof. In the figure, 1 is an inner ring located on the inside and is usually attached to a shaft, 2 is an outer ring on the outside and is usually attached to a housing, and between the inner ring 1 and the outer ring 2 are rolling elements 3 using a plurality of balls, 3... are separated by a predetermined interval by a retainer (not shown), and the inner ring 1. It is arranged so as to roll between the outer rings 2.

Now, the diameter of the pitch circle (the circle formed by the center of the rolling element) is 1]
, the diameter of the rolling element is d, the contact angle is α, and the rotation frequency of the inner ring (shaft) is fa, then the frequency fO at which one point of the outer ring contacts the rolling element of IIIJ is expressed by the following equation.

Similarly, the frequency fj at which one point of the inner ring contacts one rolling element
The frequency fb at which one point of the rolling element contacts the inner ring or the outer ring is expressed by .

Now, when the outer ring 2 has a scratch, the characteristic frequency F of the vibration generated in the outer ring when the scratch comes into contact with the rolling elements 3. is expressed by equation (3), where Z is the number of rolling elements, and similarly, for inner ring 1. The characteristic frequencies Fi and Fb of vibrations caused by scratches occurring on the rolling element 3 are respectively...(5
)′.

Therefore, if there is an abnormality in the outer ring, the characteristic frequency of vibration caused by each abnormality can be calculated theoretically using equation (3)2, and if there is an abnormality in the inner ring or rolling elements, using the +41' and f55 equations.

Normally, the vibration of the entire rolling bearing involves the outer ring and inner ring.

The vibrations of the rolling elements are superimposed and are irregular as shown in FIG. However, the characteristic frequency of vibrations caused by abnormalities in the outer ring, inner ring, and rolling elements is theoretically calculated by - (31', (41', (51') as described above), so the vibration of the entire bearing can be reduced to the outer ring.

If frequency analysis is performed based on the characteristic frequencies of vibrations caused by abnormalities in the inner ring and rolling elements, the vibration intensity at the characteristic frequencies of each part will be calculated. In other words, by performing frequency analysis using a predetermined method on the vibration of the entire bearing shown in Figure 3, it is possible to extract the intensity of harmonic components caused by abnormalities in each part, and the harmonic components at this characteristic frequency can be extracted. The intensity is the share of the overall vibration intensity of the bearing, in other words, the square root of the sum of squares of the intensity of harmonic components and the vibration 0J of the entire frequency range.
If the ratio to the effective value of the strength is calculated, this becomes a deterioration index representing the degree of abnormality in each part of the rolling bearing.

That is, the respective component intensities of the third harmonics of the characteristic frequency components of the outer ring are set as Sll, S12 . S13, this root-sum-of-squares value is expressed as Sll +S12 +S13, and if the effective value of the vibration intensity of the entire bearing is S rms,
The deterioration index F41 of the outer ring is as follows.

Similarly, each component intensity of the third harmonic of the characteristic frequency component of the inner ring is set to 521. S22. S23, the intensity of each component of the third harmonic of the characteristic frequency component of the rolling element is 831°332, respectively.
, 333, each deterioration index of the inner ring and rolling element is F42
．． P43 is as follows. In addition, when calculating the square root of the sum of squares value, we decided to use the component intensity of the third harmonic, but this is not limited to the component intensity of the fourth or higher harmonic, or the component intensity of the second harmonic. May be used.

Roughly speaking, in the present invention, the probability of deterioration is calculated from the deterioration index, and the degree of abnormality of the rolling bearing is evaluated based on this. Generally, in reliability theory, random failure probability R (
t) is expressed as -λt R(t)=1−e, and is assumed to follow an exponential distribution. So book 1
As a result of experiments, the inventor obtained the following formula (9).

That is, let the deterioration probability be Pi(x) and the deterioration index be Fli (however, i = l to 3, and when i = l, the outer ring,
When i = 2, it shows the deterioration index of the inner ring, and when t = 3, it shows the deterioration index of the rolling element, respectively), and the deterioration when 11JL/Lo:N is considered not to occur (Pi (x) - 〇). Maximum value of index Mo: Life (Pi (x) = 1.0) (D Maximum value of deterioration index (determined by).When formula (9) is expressed in a graph, it becomes as shown in Fig. 5.

Therefore, by substituting the deterioration index of each part of the rolling bearing into equation (9), the probability of deterioration can be calculated, and the degree of abnormality of each part of the rolling bearing can be reliably evaluated numerically.

FIG. 6 is a block diagram of the apparatus used to carry out the method of the invention. A vibration sensor 11 for detecting vibration is attached to the rolling bearing 1o to be inspected, and the detection result is amplified by a vibration processing circuit 12 and input to a frequency analysis section 13. In the frequency analysis section 13, the above-mentioned (3
]', +41', (Based on formula 51', find the theoretical values of the characteristic frequencies of vibrations caused by abnormalities in the outer ring, inner ring, and rolling elements, and calculate the vibration of the entire bearing 10 as described above based on each characteristic frequency. The frequency is analyzed to extract the intensity of harmonic components at the characteristic frequency of each part of the bearing, and the extraction results are sent to the calculation unit 1.
4, and the calculation unit 14 calculates the above (61, (71, (
The deterioration index is calculated based on Equation 81, and the probability of deterioration is calculated based on Equation (9).
Display at.

Next, the results of implementing the method of the present invention will be shown. If a 6206 specification bearing is used as the rolling bearing to be diagnosed, and the condition of the rolling bearing is f+1 normal, (2) 4.1mmX on the outer ring.
If there is a spot defect of 2.1mm x 0.4mm depth, (3) 4.1mm x 5.2n + m x depth 0 on the outer ring.
．． A case where a spot defect of 6 mm was present was diagnosed by the method of the present invention. Characteristic frequencies Fo and Fi of vibrations caused by abnormalities in the two rolling elements of the outer ring and inner ring of this rolling bearing.

Fb is Fn=3, where the rotation speed of the inner ring (shaft) is fa.
．． 67fa, Fi =5.33fa, Fb =5.23
It becomes fa.

The deterioration index is easily 1′! Therefore, the square root of the sum of squares of the vibration intensity at the second harmonic was used. The respective results are shown below.

In the case of (1), 511 = 1.25xlO' 512 = 5.27xlO-
5S rn+s = 1.038
In case 511=2.049 xlO' 512=2.022
xlO-'Srm5 = 6.581
o-'S rrns = 1.07 X 1O-2F4
1=4.906 xlO' P+ (x) =0.775 +11. The results of (21, (31) are shown in the graphs of Figures 7, 8, and 9, respectively.

2. From various experiments, it has been found that when the probability of deterioration of the outer ring is 0.1 or higher, some kind of abnormality has occurred in the outer ring.
In the above-mentioned implementation results, it is 0.1 or more in normal times and 0.1 or less in abnormal times.

The above-mentioned i11. (
The case of 21, +31 is expressed as follows.

(In the case of 11 (at the time of consolidation) Average value = 0.1g Peak value = 1.5g (2) (
Spot defect 4.1x2.1 xO, 4) Average value -1,
5g Peak value -25g In the case of (3) (spot defect 4.1x5.2 xo, 6
) Average value - 3.0 g Peak value - 130 g It can be seen that each value increases in proportion to the size of the defect, but it is difficult to estimate the extent of damage in which part. Furthermore, these values had to be corrected based on the rotational speed, shaft diameter, etc., making it impossible to accurately grasp the condition of the bearing.

However, according to the method of the present invention, since abnormalities in rolling bearings are expressed as probabilities for each part, it is possible to accurately grasp the condition of each part of the bearing, and diagnosis of rolling bearings can be performed easily and with high precision. I can do it.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of the rolling bearing, Figure 2 is its longitudinal cross-sectional view, Figure 3 is a graph showing the vibration of the rolling bearing, Figure 4 is a graph showing the results of frequency analysis based on the characteristic frequency, and Figure 5 is a graph showing the vibration of the rolling bearing.
Figure 6 is a graph showing the relationship between the deterioration index and the probability of deterioration; Figure 6 is a block diagram of the device used to implement the method of the present invention;
9 is a graph showing the relationship between the deterioration index and the deterioration probability in an embodiment of the method of the present invention. ■...Inner ring 2...Outer ring 3...Rolling element 10.
...Rolling bearing 11...Vibration sensor patent Applicant Sumitomo Metal Industries Co., Ltd. Agent Patent attorney Noboru Kono 5 Figure 3 Figure 4-196-T6 Il-O Banbon Figure 9

Claims (1)

[Claims] 1. The outer ring of the rolling bearing is determined by measuring the vibration of the rolling bearing and frequency analysis of the measured vibration waves. Calculate the ratio of the square root of the sum of squares of the intensity of the characteristic frequency and harmonic components of each part of the inner ring and rolling elements to the effective value of the vibration intensity in the entire frequency range as a deterioration index for each part,
A method for diagnosing a rolling bearing, characterized by calculating the probability of deterioration of each part from each deterioration index.