JP2672773B2 - Shaft core vibration detection method and rotating shaft abnormality determination method using vibration of the shaft core - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a detecting method for detecting a shaft vibration of a rotating shaft and a method of judging an abnormality of a rotating shaft based on the shaft vibration.

[0002]

2. Description of the Related Art A rotating machine such as a generator makes high-speed rotary motion around a shaft. However, in this kind of rotating machine, there is an abnormal situation such as damage to a bearing supporting the shaft or lack of lubricating oil. In order to deal with this, means for detecting the vibration of the shaft during operation and monitoring the occurrence of an abnormality by the change in the vibration is provided.

The conventional shaft vibration is detected by measuring the displacement of the shaft surface with a distance sensor or the like and determining the abnormality by using the measured value as the vibration displacement of the shaft. That is, in the conventional method, it is assumed that the shape of the shaft cross section is a perfect circle, and the measured value of the displacement amount of the shaft surface is directly used as the vibration displacement amount of the shaft core. Looking for.

[0004]

However, the actual shape of the cross section of the shaft is not a perfect circle, which causes a difference between the measured displacement amount and the vibration displacement amount of the shaft core. ing.

For example, when the center of the shaft in cross section and the center of rotation of the shaft, that is, the shaft center are deviated from each other, if the displacement of the shaft surface is changed with time, as shown in FIG. The fundamental wave of the axis rotation period T appears on the curve (where
In the figure, 1 is an axis, 2 is an axis center, and 3 is a distance measuring device. ).
When the cross section of the axis is elliptical, triangular, or polygonal, a harmonic having a frequency that is an integral multiple of the fundamental wave appears, as shown in b, c, and d of FIG. 13, respectively. When there is a misalignment of the shaft core or any irregularities on the shaft surface, each point on the shaft surface rotates on its own circumference around the shaft core, and the displacement of the shaft surface is measured. In that case, the above-mentioned deviations and irregularities are directly reflected in the measured values.

[0006] Therefore, in the detection of the conventional axial vibration, for axis vibration apparent is Wa current can not be detected vibrations accurate axis, on determining the abnormality of the rotation shaft from the shaft vibration However, there is a problem that a sufficiently satisfactory accuracy cannot be obtained.

The present invention has been made to solve the above problems, and a first object thereof is to provide a detection method capable of accurately determining the vibration displacement amount of the shaft core from the displacement amount of the shaft surface. It is to be.

A second object of the present invention is to provide a judging method capable of judging abnormality of the rotating shaft with high accuracy from a measured value of vibration of the rotating shaft.

[0009]

To solve the above problems BRIEF SUMMARY OF THE INVENTION, vibration detection method of the axis of the invention, the distance between the plurality of points and the shaft outside the reference position of the shaft surface of the rotating time Measured later, from this measured value over multiple rotations of the same point
The measured values are averaged for each point above to obtain the average distance, and the same
The deviation of the measured values over multiple rotations of the point with respect to the average distance
The difference is obtained, and the method of using the value of the above deviation arranged in time as the vibration displacement amount of the shaft core is adopted.

Further, in the above detection method, marks are provided at one or more points on the shaft surface, the shortest distance between the shaft surface and the reference position is periodically measured, and based on the time when the mark passes the reference position. The time when a plurality of points on the shaft surface pass the reference position can be obtained, and the distance between each point on the shaft surface and the reference position can be obtained from this time and the measured value.

On the other hand, according to the method for determining abnormality of the rotating shaft of the present invention, the vibration displacement amount of the shaft core obtained by the above detection method or the vibration characteristic value obtained from the shaft core vibration is compared with an arbitrarily set allowable value. However, when the vibration displacement amount or the vibration characteristic value exceeds the allowable value, it is determined as an abnormality.

[0012]

[Operation] Assuming that the shaft core is fixed and rotating at the same position, each point on the shaft surface will have its own circumference around the shaft center due to the displacement of the shaft core and the unevenness of the shaft surface. To rotate. From this state, if the shaft core is now vibrating with an amplitude within a certain range, each point on the shaft surface will rotate while vibrating with the same amplitude inside and outside the circumference. Therefore, the deviation of the displacement amount at each point with respect to the circumference becomes the vibration value of the shaft core with the effects of the shaft core displacement and the surface irregularities removed.

According to the detection method of the present invention, the average distance of the displacements of the respective points on the surface of the shaft with respect to the reference position is calculated to obtain the circumference unique to the respective points, and the deviation of the displacements of the respective points from the average distance is calculated. By obtaining it, an accurate vibration displacement amount of the shaft center is calculated.

Specifically, the detection position of a distance detector provided outside the shaft is used as a reference position, and the shortest distance between the shaft surface and the reference position is periodically measured for a certain period of time. ,
The distance between each of the points and the reference position is calculated from the time when a plurality of points on the shaft surface pass the reference position. Next, the average distance to the reference position for each point is calculated from this calculated distance to obtain the rotation locus unique to each point, and the deviation of each point from this locus is calculated for each passing time to determine the axis center. Detect vibration.

Further, according to the abnormality determining method of the present invention, since the determination is made based on the shaft center vibration detected as described above, the determination of the abnormality of the rotating shaft is influenced by the displacement of the shaft center and the unevenness of the shaft surface. Can be carried out accurately without any trouble, and the accuracy of abnormality detection of the rotating machine can be remarkably improved.

[0016]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows a measuring structure for detecting vibration of a shaft core. Reference numeral 1 is a shaft which rotates around a shaft core 2 and 3 is a non-contact type distance measuring device such as an optical sensor. The distance measuring device 3 is arranged at a fixed position near the surface of the shaft 1, measures the distance between the distance measuring device 3 and the surface of the shaft 1, and outputs it as a signal.

The output signal of the distance measuring device 3 is input to the AD converter 4, converted into a digital signal, and input to the arithmetic unit 5 such as a computer. The arithmetic unit 5
Is configured to detect the shaft center vibration based on the output of the distance measuring device 3.

Next, the procedure of detecting the shaft core vibration using the above-described measurement structure will be described. When the distance is measured cyclically, generally, there is a difference between the measurement time and the time when a plurality of points on the surface of the shaft pass directly below the distance measuring device 3. When it is constant,
The processing procedure will be described separately for the case where the rotation speed changes.

(I) Processing procedure when the rotation speed of the shaft is constant In FIG. 2, one point on the surface of the shaft is provided with a depression as a mark, the mark and the shaft core 2 are connected by a straight line, and this straight line is connected. As a reference, a straight line passing through the shaft core 2 is drawn at an angle of θ = 2π / M at equal angles, and M points Pi (i = 1, 2, ...
M) is set. Here, P1 is a mark point.

Assuming that the rotation cycle of the shaft is T, if the distance is measured at a cycle of T / M from the time when the mark point passes directly below the distance measuring device 3, the rotation speed is constant and M Since the points Pi of 1 are equiangularly spaced at the angle θ, the distance is inevitably measured at the time when each point Pi passes directly under the distance measuring device 3.

In FIG. 3, the measured distance value at the j-th rotation at the time when the point Pi passes directly below the distance measuring device 3 is xij (j = 1,
2, ..., N), the time change of xij is schematically shown.

4A and 4B show the distance value xi of FIG.
Each j is connected by a line to make it easy to see the change over time in the distance value. Further, FIG. 5 schematically shows how the points P1 and P2 rotate on the circumference having distance values H1 and H2, respectively, when the axes are fixed at the same position and are rotating.

When the shaft center is vibrating around this position, the distance value x1j of the point P1 as shown in FIG. 4 (a).
The value of (j = 1, 2, ..., N) changes around the average distance H1. Similarly, as shown in FIG. 4B, the distance value x2j (j = 1, 2, ..., N) of the point P2 also becomes
The value changes around the average distance H2.

Here, the average distance Hi of each of the M points Pi is obtained from the following equation (1).

[0025]

(Equation 1)

In FIG. 4C, the respective average distances Hi are translated so that the distance becomes zero, and the deviation (xi) of the distance value xij from the average distance Hi is calculated for each of M points.
j-Hi) is plotted on a graph.

This deviation becomes the shaft core vibration value from which the apparent value caused by the shaft core shift and the shaft surface unevenness is removed.

(II) Processing Procedure when Rotational Speed of Axis Changes FIG. 6A shows a case where distances are measured at equal time intervals with respect to an axis having M points Pi set, as in FIG. It shows the instantaneous state at the measurement time. As shown in this figure, when the rotation speed changes and the measurement cycles are at equal time intervals, the distance measuring device 3 measures the distance between the points Pi and Pi + 1.

Therefore, it is necessary to calculate the time when each point Pi passes directly under the distance measuring device 3 and the distance at this time. The calculation method will be described below.

(II-i) Method for calculating time when mark point passes directly under the distance measuring device. FIG. 6 (b) shows a case where the rotation speed changes and the measurement cycle is at equal time intervals. It is a diagram schematically showing the change over time of the distance value. Here, since the depression on the shaft surface is used as the mark point, it may be considered that the maximum point of the measured distance value corresponds to the mark point. Therefore, the measurement times t1, t2,
Let the measured distance values at t3 be x1, x2, and x3, respectively, and let T be the time at which the mark point passes directly below the distance measuring device 3.
1. Measured values (t1, x1), (t2, x using the parabolic interpolation method, where X is the distance at this time.
2) Consider that (T1, X) is calculated from (t3, x3).

FIG. 6C shows three points (t1, x1), (t
2, x2), (t3, x3) and the coordinates of the maximum point are (T
1, X), and the following equation (2) is established.

[0032]

(Equation 2)

By using the equation (2), it is possible to calculate the approximate value of the time T1 when the mark point passes directly under the distance measuring device 3.

(II-ii) A method of calculating the shaft core vibration assuming that the rotation speed of the shaft is constant during one rotation from when the mark point passes immediately below the distance measuring device to when the mark point passes next. Then, assuming that the rotation speed is constant during one rotation, the time when each of the M points Pi passes directly under the distance measuring device 3 and the method for calculating the distance at this time will be described.

FIG. 7 (a) schematically shows how the rotational speed f (t) continuously changes with time. In this figure, when the passing times of the mark points calculated in (II-i) are T1, T2, and T3, the rotation cycles are (T2-T1) and (T3-T2), respectively. Is shown to change.

Here, the rotational speed f that changes with time
The average rotation speed in the section [T1, T2] of (t) is represented by a straight line AB, and it is assumed that the rotation speed is constant during one rotation of the section [T1, T2]. Consider approximation with AB.

Assuming that Δt1 = (T2−T1) / M, the time at which the (e + 1) th and (e + 2) th points P _{e + 1} and P _{e + 2} pass immediately below the distance measuring device 3 based on this assumption. Are (T1 + eΔt1) and (T1 + (e + 1) Δt, respectively.
1).

FIG. 7B shows measurement times tk at equal time intervals.
Measured distance values x at -1, tk, and tk + 1
Based on k-1, xk, xk + 1, the time (T1 + eΔt1) and (T1 + (e
+1) A method of calculating the distance values x ′ _e and x ′ _{e + 1} in Δt1) is shown. Therefore, the distance value x ′ _e ,
_{x'e + 1} can be calculated by the following equation (3).

[0039]

(Equation 3)

In this way, the time at which each of the M points Pi passes directly below the distance measuring device 3 and the distance at this time are calculated, and then the procedure similar to (I) is followed.
The average distance and the deviation of the distance from this average distance are calculated for each of these points, and the shaft core vibration value is obtained by removing the apparent values caused by the shaft core shift and the shaft surface irregularities.

However, as shown in FIGS. 7 (a) and 7 (c), the shaft core vibration value calculated in this way is Δt1 = (T2-T1) / M in the interval [T1, T2]. In the interval [T2, T3], Δt2 = (T3-T
2) / M, since values are obtained at time intervals, it is unsatisfactory when performing frequency analysis on this axial vibration value. Therefore, it is necessary to calculate the axial vibration values at equal time intervals.

[0042] in FIG. 7 (b), the time (T1 + e △ t1) and the axis vibration value at (T1 + (e + 1) △ t1) y 'e, y' on the basis of _{e + 1,} using the interpolation method with a linear Then, a method of calculating the axial vibration value y ″ k at the measurement time tk will be described. Therefore, the axial vibration value y ″ k can be calculated by the following equation (4).

[0043]

(Equation 4)

In this way, the measurement times t at equal time intervals
Obtain the axial vibration value at k.

This calculation method is suitable when the change in the rotation speed is small, and a highly accurate result can be obtained with a small amount of calculation.

(II-iii) A method of calculating the shaft center vibration on the assumption that the rotation speed of the shaft is uniformly accelerated during one rotation from when the mark point passes immediately below the distance measuring device to when the mark point passes next. Assuming that the rotation speed is uniformly accelerated during one rotation, a time when each of the M points Pi passes directly under the distance measuring device 3 and a method for calculating the distance at this time will be described.

FIG. 8A schematically shows how the rotation speed f (t) continuously changes with time. In this figure, when the passing times of the mark points calculated in (II-i) are T1, T2, and T3, the rotation cycles are (T2-T1) and (T3-T2), respectively. Is shown to change.

Here, the rotational speed f which changes with time
The average rotational speeds in the sections [T1, T2] and the sections [T2, T3] of (t) are represented by straight lines AB and CD, respectively, and the midpoint between points B and C is G. Similarly, the section [T
1, T2], the point E is obtained from the average rotation speed in the section before, and the midpoint between the points A and E is F, and a straight line FG is obtained.

FIG. 8B shows the straight line FG obtained in FIG.
The method of calculating the time at which each of the M points Pi passes immediately below the distance measuring device 3 based on In this figure, the straight line HJ passes through the midpoint I of the straight line AB and the straight line FG.
It is a straight line with the same slope as. Here, the section [T1, T
It is considered that the rotation speed f (t) is approximated by a straight line HJ on the assumption that the rotation speed is uniformly accelerated during one rotation of [2].

Since the M points Pi are set on the surface of the shaft at equal angles for each angle θ, trapezoid HKML and trapezoid L
Area S1, S2, S of MON and trapezoidal NOQP
3 are all equal and equal to 1 / M of the area S of the trapezoid HKRJ. That is, the following expression (5) is established.

[0051]

(Equation 5)

From the condition of this equation (5), the time when the (e + 1) th point P _{e + 1} passes directly below the distance measuring device 3 is T1.
+ T (e), the lengths of the straight line HK and the straight line JR are f
Assuming 1 and f2, the following equation (6) is obtained.

[0053]

(Equation 6)

Therefore, the time when the (e + 1) th point P _{e + 1} passes directly below the distance measuring device 3 can be calculated by the equation (6).

Next, in the same manner as (II-ii), the M points Pi are respectively measured by the linear interpolation method on the basis of the measured distance values at the measurement times of equal time intervals. After calculating the distance at the time of passing immediately under 3, the average distance and the deviation of the distance from the average distance are calculated for each of these points. As a result, the shaft core vibration value is obtained by removing the apparent value caused by the shaft core shift and the shaft surface unevenness.

Further, as in (II-ii), M points Pi
Can be obtained by using the linear interpolation method based on the axial vibration values at the time when each passes just below the distance measuring device 3, respectively.

This calculation method is suitable when the change of the rotation speed is large, and the calculation amount is a little large, but a highly accurate result can be obtained.

The methods of detecting the shaft center vibration have been described above. Next, an example of detecting the shaft center vibration of the rotating shaft connecting the water turbine and the generator by using these methods will be shown.

FIG. 9 shows a measurement block diagram for detecting the shaft center vibration of the rotating shaft. In this figure, the shaft core 2
The distance measuring devices 3X and 3Y are arranged at two locations near the surface of the shaft 1 that rotates around the center of the axis 1 and the gaps between the distance measuring devices 3X and 3Y and the surface of the shaft 1 are set in two directions, the X direction and the Y direction, respectively. Measure the distance. The output signals of the distance measuring devices 3X and 3Y are input to AD converters 4X and 4Y, respectively, and the AD converters 4X and 4Y convert these signals into digital signals at the same time and periodically, and the arithmetic unit 5 Enter in '. In this arithmetic unit 5 ', the axial core vibration is detected based on the outputs of the distance measuring devices 3X and 3Y.

FIG. 10 is a graph showing the change over time in the measured distance values in the X and Y directions obtained by the measuring method of FIG. 9 for the rotating shaft connecting the water turbine and the generator. According to this figure, when the measured distance value is used as the shaft core vibration value as it is, an apparent shaft core vibration due to the displacement of the shaft core and the unevenness of the shaft surface appears. In particular, the arrow in the figure indicates that a sharp peak appears in the waveform of the measured distance value due to a deep depression (scratch) on the surface of the shaft.

FIG. 11 shows the indentation on the surface of the shaft indicated by the arrow in FIG. 10 as the mark point, and the method of (II-i) and (II-iii) is used, based on the measured distance value shown in FIG. And the Y-direction are the time waveforms of the axis-core vibration obtained by performing the calculation processing separately. According to this figure, the waveform of the arrow in FIG. 10 disappears, and the time waveform of the shaft center vibration in which the apparent value caused by the shaft center shift and the shaft surface irregularity is removed is obtained.

Further, FIG. 12 is a graph of a shaft core vibration Lissajous figure drawn based on the time waveforms of the shaft core vibrations in the X and Y directions shown in FIG.

In the above embodiment, the rotation speed of the shaft is constant during one rotation from the time when one mark point passes directly below one distance measuring device to the time when it passes next, or
The axial center vibration was calculated on the assumption that the acceleration is uniform, but the rotation speed is calculated every moment using a plurality of mark points, and the time at which each of the M points Pi passes directly under the distance measuring device. Alternatively, the distance at this time may be calculated.

If a light reflector is provided at each of the M points Pi on the surface of the shaft and the distance is measured at the time when the light reflection is detected, the time at which each point Pi passes directly under the distance measuring device. Further, since the error due to the distance calculation at this time is eliminated, the shaft center vibration can be detected with higher accuracy even when the change in the rotation speed is large.

[0065]

As described above, in the shaft core vibration detecting method of the present invention, the average distance for each point on the shaft surface with respect to the reference position is obtained from the distance between the shaft surface and the reference position, and the rotation unique to each point is obtained. Since the vibration displacement amount of the shaft core is calculated based on the locus,
Apparent vibration of the shaft core due to the displacement of the shaft core or the unevenness of the shaft surface can be removed, and an accurate vibration value of the shaft core can be obtained.

Further, in the method for determining abnormality of the rotating shaft according to the present invention, since the abnormality is determined based on the accurate vibration value of the shaft core, the criterion for determination becomes highly reliable, and the abnormality of the rotating machine can be detected. There is an advantage that the accuracy can be remarkably improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a vibration measuring structure according to an embodiment.

FIG. 2 is a diagram showing a detection method according to an embodiment.

[Fig. 3] Chart showing measured distance values

4A and 4B are charts showing changes in distance value, and FIG. 4C is a chart showing deviation from an average distance.

FIG. 5 is a diagram showing a rotation locus of mark points.

6A is a diagram showing a detection method, and FIGS. 6B and 6C are diagrams showing a method of calculating the time when a mark point passes directly under a distance measuring device.

7 (a), (b) and (c) are diagrams showing an example of a method of calculating a shaft center vibration.

8A and 8B are views showing another example of a method of calculating shaft core vibration.

FIG. 9 is a block diagram showing a measurement structure for detecting axial core vibrations in X and Y directions.

10 (a) and 10 (b) are charts showing changes with time of measured distance values of a rotating shaft connecting a water turbine and a generator.

11 (a) and 11 (b) are charts showing time waveforms of axial vibration of the rotary shaft of the same.

FIG. 12 is a diagram of a shaft vibration Lissajous of the above rotary shaft.

FIG. 13A is a diagram showing an apparent shaft core vibration waveform caused by deviation of the shaft center, and FIGS. 13B, 13C and 13D, respectively, showing apparent shaft center vibration waveforms.

[Explanation of symbols]

 1 axis 2 axis core 3, 3X, 3Y distance measuring device 4, 4X, 4Y AD converter 5, 5'calculator

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Fumio Shirai, Kamitakase 2002, Takase-cho, Mitoyo-gun, Kagawa Prefecture 2 (72) Inventor Fumio Hyodo 2--12, Ueno-cho, Takamatsu-shi, Kagawa Prefecture

Claims (3)

(57) [Claims] 1. The distance between a plurality of points on the surface of a rotating shaft and a reference position outside the shaft is measured over time, and the measured value is obtained.
The measurements for each of the respective points over a longer multiple rotation of the same point
Average the average distance and measure it over multiple rotations of the same point.
Calculate the deviation of the fixed value from the average distance , and follow the time
A method for detecting vibration of a shaft, wherein the values of the above-mentioned deviations arranged are used as the amount of vibration displacement of the shaft. 2. Marking at one or more points on the shaft surface, periodically measuring the shortest distance between the shaft surface and the reference position,
The time when a plurality of points on the shaft surface pass the reference position is obtained based on the time when the mark passes the reference position, and the distance between each point on the shaft surface and the reference position is obtained from this time and the measured value. A method for detecting vibration of a shaft core according to. 3. A vibration displacement obtained by comparing the vibration displacement amount of the shaft core obtained by the detection method according to claim 1 or 2 or the vibration characteristic value obtained from the shaft core vibration with an arbitrarily set allowable value. Abnormality determination method for rotating axis that determines abnormality when the quantity or vibration characteristic value exceeds the allowable value.