Bearing abnormity reason estimation method and device

Abstract

The invention provides a bearing abnormality cause estimation method and device. The method comprises the following steps: a measuring step: measuring spindle vibration; an analysis step (S1) for calculating the magnitude of the vibration with respect to the frequency from the obtained vibration; an average vibration value calculation step (S2-S5) for calculating an average vibration value by removing the effect of the rotational speed with respect to the magnitude of vibrations having the same ratio of the frequency to the rotational frequency on the basis of the frequency analysis result; a bearing-induced vibration value extraction step (S6) for extracting a bearing-induced vibration value at a characteristic ratio frequency, which is the ratio of the rotation frequency to an integral multiple of the frequency caused by the vibration of the bearing, from among the vibration average values; an abnormality determination step (S7) for determining the presence or absence of an abnormality on the basis of the bearing-caused vibration value; and an abnormality occurrence cause estimation step (S8-S10) for estimating an abnormality occurrence cause on the basis of the relationship between the bearing-caused vibration values at an integral multiple of the characteristic ratio frequency caused by the vibration of the bearing when it is determined that the bearing is abnormal.

Description

Technical Field

[0001] The present disclosure relates to a method and apparatus for estimating a cause of a bearing abnormality for estimating a cause of a bearing abnormality based on a bearing abnormality detected according to vibration data. Background Art

[0002] In a machine tool that processes a workpiece while rotating a tool or workpiece mounted on a spindle, the bearing may sometimes wear out due to aging, resulting in loss of preload, or damage due to the mixing of foreign matter, poor lubrication, etc., which may cause poor operation accuracy, abnormal noise during operation, and other undesirable conditions. When this happens, processing defects such as poor shape of the workpiece, poor properties and shape of the machined surface may occur, which may have an adverse effect on production. In addition, when a failure such as spindle adhesion occurs, the spindle may not rotate, and the machine tool may even be unable to operate.

[0003] In a rolling bearing that supports a rotating body, vibrations are generated when abnormalities such as damage to the inner ring occur. In order to use this to diagnose the bearing status, a method using a vibration sensor is known. Patent document 1 discloses the following method: the vibration is measured and envelope processing and frequency analysis are performed, and the characteristic frequency values ​​of the inner ring, outer ring, and rolling element are extracted based on a prescribed relationship, and different thresholds are used for diagnosis in the inner ring, outer ring, and rolling element.

[0004] Patent Document 2 discloses a method of measuring vibrations at a plurality of rotational frequencies, averaging the amplitudes of vibrations having the same ratio of frequency to the rotational frequency, and performing diagnosis based on the average value.

[0005] Patent document 3 shows the following method: using a classifier that has learned the characteristics of vibration data of a rolling bearing filled with grease having an oil content different from that of normal grease, the vibration data measured during monitoring is classified into a poor lubrication state and a bearing damage state for diagnosis.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent No. 5146008

[0009] Patent Document 2: Japanese Patent No. 6511573

[0010] Patent Document 3: Japanese Patent No. 6997054 Summary of the invention

[0011] Problems to be solved by the invention

[0012] According to Patent Documents 1 and 2, it is possible to carry out repairs before a major failure such as bearing adhesion in which the main shaft cannot rotate occurs. On the other hand, in order to determine who will bear the cost, such as the insurance application during the repair, and to determine countermeasures to prevent the failure from recurring, it is required to diagnose the cause of the bearing abnormality.

[0013] As the cause of the failure, various factors are considered, such as overload caused by collision, tool damage during cutting, foreign matter mixing due to improper management of lubricating oil, poor lubrication, etc., and there are many items to be confirmed. In particular, in the case of mechanical abnormalities related to production, repairs are given priority, making it difficult to conduct a sufficient investigation and sometimes failing to find the cause of the failure.

[0014] In addition, poor lubrication of grease listed as an abnormality to be diagnosed in Patent Document 3 is also one of the causes of failure, but the change in the state of the bearing caused by poor lubrication in the case of oil-gas lubrication progresses rapidly. Therefore, there is a case where the bearing is damaged when the diagnosis is performed.

[0015] Therefore, an object of the present disclosure is to provide a method and apparatus for estimating the cause of bearing abnormality, which can estimate the cause of abnormality caused by a change in the bearing state while performing measurements for diagnosing the bearing state.

[0016] Means for solving problems

[0017] In order to achieve the above-mentioned purpose, the first structure of the present disclosure is a method for estimating the cause of bearing abnormality, which estimates the cause of bearing abnormality when a bearing supporting a rotating body has an abnormality, and is characterized in that it includes: a measuring step, measuring the vibration when the rotating body is rotated at a constant speed at multiple rotational speeds; an analyzing step, calculating the magnitude of the vibration for the frequency based on the vibration obtained in the measuring step through frequency analysis; a vibration average value calculating step, removing the influence of the rotational speed and calculating the average value of the vibration for the magnitude of the vibration with the same ratio of frequency to rotational frequency based on the frequency analysis results obtained by the analyzing step at multiple rotational speeds; a bearing-caused vibration value extraction step, extracting the bearing-caused vibration value at a characteristic ratio frequency from the vibration average value, wherein the characteristic ratio frequency is the ratio of an integer multiple of the frequency generated by the vibration of the bearing to the rotational frequency; an abnormality judgment step, judging whether the bearing has an abnormality based on the bearing-caused vibration value; and an abnormality cause estimation step, estimating the cause of the abnormality based on the relationship between the bearing-caused vibration values ​​at integer multiples of the characteristic ratio frequency generated by the vibration of the bearing when the bearing is judged to be abnormal in the abnormality judgment step.

[0018] Another mode of the first structure is characterized in that, in the above structure, in the abnormality cause estimation step, among the bearing-caused vibration values ​​at integer multiples of the characteristic ratio frequency generated by the vibration of the bearing, when only one bearing-caused vibration value is large at the integer multiples of the characteristic ratio frequency, the abnormality cause is estimated to be poor lubrication, and when more than one bearing-caused vibration value is large at the integer multiples of the characteristic ratio frequency, the abnormality cause is estimated to be overload or foreign matter mixing.

[0019] In order to achieve the above-mentioned purpose, the second structure of the present disclosure is a bearing abnormality cause estimation device, which estimates the cause of the bearing abnormality when the bearing supporting the rotating body has an abnormality, and is characterized in that it includes: a measuring unit, which measures the vibration when the rotating body is rotated at a constant speed at multiple rotational speeds; an analyzing unit, which calculates the magnitude of the vibration for the frequency based on the vibration obtained by the measuring unit through frequency analysis; a vibration average value calculation unit, which removes the influence of the rotational speed and calculates the average value of the vibration for the magnitude of the vibration with the same ratio of frequency to rotation frequency based on the frequency analysis results obtained by the analyzing unit at multiple rotational speeds; a bearing-caused vibration value extraction unit, which extracts the bearing-caused vibration value at a characteristic ratio frequency from the vibration average value, wherein the characteristic ratio frequency is the ratio of an integer multiple of the frequency generated by the vibration of the bearing to the rotation frequency; an abnormality judgment unit, which judges whether the bearing has an abnormality based on the bearing-caused vibration value; and an abnormality cause estimation unit, which estimates the cause of the abnormality based on the relationship between the bearing-caused vibration values ​​at integer multiples of the characteristic ratio frequency generated by the vibration of the bearing when the bearing is judged to be abnormal by the abnormality judgment unit.

[0020] Another mode of the second structure is characterized in that in the above structure, in the abnormality cause estimation unit, among the bearing-caused vibration values ​​at integer multiples of the characteristic ratio frequency generated by the vibration of the bearing, when only one bearing-caused vibration value is large at the integer multiples of the characteristic ratio frequency, the abnormality cause is estimated to be poor lubrication, and when more than one bearing-caused vibration value is large at the integer multiples of the characteristic ratio frequency, the abnormality cause is estimated to be overload or foreign matter mixing.

[0021] Effects of the Invention

[0022] According to the present disclosure, it is possible to estimate the cause of abnormality that changes the bearing state while performing measurement for diagnosing the bearing state. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a block diagram showing a configuration in which a device for estimating the cause of bearing abnormality is applied to a main spindle of a machine tool.

[0024] Figure 2This is a flow chart of a method for estimating the cause of bearing abnormality.

[0025] Figure 3 It is a diagram showing an example of a vibration waveform having no prominent N-order component.

[0026] Figure 4 It is a diagram showing an example of a vibration waveform having a prominent N-order component.

[0027] Description of Reference Numerals

[0028] 1: spindle, 2: spindle housing, 3: tool, 4: motor, 5: speed detector, 6: control device, 7: bearing, 8: vibration sensor, 9: A / D conversion unit, 10: storage unit, 11: calculation unit, 12: display unit. DETAILED DESCRIPTION

[0029] Hereinafter, embodiments of the present disclosure will be described based on the drawings.

[0030] Figure 1 This is a block diagram showing a configuration in which a bearing abnormality cause estimation device according to a second configuration of the present disclosure is applied to a main spindle of a machine tool.

[0031] The spindle 1 is rotatably mounted on the spindle housing 2 via a bearing 7 as a rolling bearing, and a tool 3 for machining is fixed thereto. The motor 4 drives the spindle 1. A speed detector 5 is provided on the motor 4, and the measured rotation speed of the motor 4 is input to the control device 6. During machining, the control device 6 controls the current supplied to the motor 4 in such a manner that the rotation speed of the motor 4 measured by the speed detector 5 is maintained at the command rotation speed.

[0032] A vibration sensor 8 as a vibration measuring unit is installed on the spindle housing 2, and the vibration acceleration at multiple rotation speeds is measured by the vibration sensor 8 (measurement step). The measured vibration acceleration is converted into a digital value by the A / D conversion unit 9 and stored in the storage unit 10 together with the rotation speed when the vibration is measured. The storage unit 10 also stores a preset threshold value. The calculation unit 11 is configured to include a CPU, and calculates the degree of abnormality of the bearing 7 based on the bearing specifications stored in the storage unit 10 and the rotation speed and vibration acceleration recorded in the storage unit 10 through measurement, and determines whether it is normal. In addition, when the calculation unit 11 determines that the bearing 7 is abnormal, it infers the reason for the change in the bearing state. The display unit 12 displays the diagnosis result of the calculation unit 11.

[0033] The vibration sensor 8 , the A / D conversion unit 9 , the storage unit 10 , the calculation unit 11 , and the display unit 12 are an example of the abnormality cause estimation device M of the present disclosure.

[0034] The vibration sensor 8 and the A / D converter 9 are examples of a measuring unit of the present disclosure.

[0035] The calculation unit 11 is an example of an analysis unit, a vibration average value calculation unit, an abnormality determination unit, an abnormality generation cause estimation unit, and a bearing-related vibration value extraction unit in the present disclosure.

[0036] Figure 2 This is a flowchart of a method for estimating the cause of bearing abnormality of the first structure of the present disclosure, and shows the process of diagnosing the abnormality of the state of the bearing 7 and estimating the cause of the abnormality when an abnormality occurs in the bearing state, which will be described in detail below.

[0037] The calculation unit 11 receives the rotation speed and the vibration acceleration when the vibration is measured from the storage unit 10, and starts the diagnosis of the bearing 7. The following processes S1 to S3 are performed for each of the plurality of rotation speeds at which the vibration measurement is performed.

[0038] First, the time-series vibration acceleration data at each of the plurality of rotation speeds acquired in the measuring step is Fourier transformed to calculate the vibration amplitude with respect to the frequency ( S1 : analyzing step).

[0039] Next, the angular velocity is calculated from the rotation speed, and the vibration amplitude is divided by the square of the angular velocity (S2). Since it is known that the exciting force caused by the bearing abnormality is roughly proportional to the square of the rotation speed, the vibration amplitude data without the influence of the rotation speed can be obtained through this process.

[0040] Next, the vibration amplitude data is converted from the frequency domain to the frequency ratio (a value obtained by dividing the frequency by the rotation frequency) domain (S3). This process allows vibration acceleration measured at any rotation speed to be processed equally.

[0041] Next, it is determined whether the processing of S1 to S3 has been completed at all speeds (S4). After it is determined in S4 that the processing of S1 to S3 has been completed at all speeds, the average value of the vibration amplitude data obtained at all speeds is calculated at each specific frequency (S5). By performing the processing of S1 to S5, the influence of the size of the transfer function can be eliminated, and random noise without periodicity can be reduced. S2 to S5 are an example of the vibration average value calculation step of the present disclosure.

[0042] After the vibration accelerations at multiple rotation speeds are sorted into an average value of vibration amplitude data for the specific frequency through the processing of S5, the amplitude caused by the abnormality of the bearing 7 is extracted (S6: bearing-caused vibration value extraction step). The vibration generation frequency corresponding to the parts of the bearing 7 such as the inner ring, outer ring, and rolling element can be calculated based on the design specifications of the bearing 7. Formula 1 represents the calculation formula for the specific frequency when the inner ring generates vibration, Formula 2 represents the calculation formula for the specific frequency when the outer ring generates vibration, and Formula 3 represents the calculation formula for the specific frequency when the rolling element generates vibration. Here, fi is the frequency of the inner ring vibration, f o is the frequency of the outer ring vibration, f b is the frequency of rolling element vibration, f r is the rotation frequency, Z is the number of rolling elements of the bearing 7, D is the pitch circle diameter of the bearing 7, d is the rolling element diameter of the bearing 7, α is the contact angle of the bearing 7, and N is the number.

[0043] [Mathematical formula 1]

[0044]

[0045] [Mathematical formula 2]

[0046]

[0047] [Mathematical formula 3]

[0048]

[0049] After the amplitude of the vibration at the specific frequency corresponding to the part of the bearing 7 is extracted in S6, the amplitude of the extracted N-order component (bearing-caused vibration value) is compared with a predetermined threshold value in S7 to diagnose whether the state of the bearing 7 is abnormal (abnormality judgment step). In this embodiment, when the maximum value of the bearing-caused vibration value of all parts of the bearing 7 exceeds the threshold value, it is diagnosed that the state of the bearing 7 is abnormal. In addition, regarding the determination of whether the bearing 7 is abnormal, a threshold value can be set for each part and compared with the maximum value of the bearing-caused vibration value of each part, or a threshold value can be set for each N-order component that is not related to the part and compared with the maximum value of the bearing-caused vibration value under each N-order component, and a diagnosis can also be made by a combination of them.

[0050] When the bearing state is diagnosed to be abnormal, for each bearing part, it is determined whether there is a prominent value in the amplitude of the Nth order component (S8). In the case of abnormal causes such as inner wheel damage and rolling element damage where there are two characteristic ratio frequencies relative to the number of times, the vibration amplitude value is sorted into one for each number of times. As a sorting method, averaging or setting to a smaller value is preferred.

[0051] When there is a prominent value in the amplitude of the Nth order component (when the specific bearing-caused vibration value is large), it is a vibration caused by wide damage, and the abnormal cause is estimated to be poor lubrication (S9). When there is no prominent value in the amplitude of the Nth order component (when the specific bearing-caused vibration value is not large), it is a vibration caused by point-like damage, and the abnormal cause is estimated to be overload or foreign matter mixing (S10). S8 to S10 are an example of the abnormality generation cause estimation step of the present disclosure.

[0052] Next, a method of determining whether or not there is a prominent value in the amplitude of the N-order component will be described.

[0053] Among the vibration amplitudes of the Nth-order component, among the first largest vibration amplitude and the second largest vibration amplitude, when the value obtained by dividing the first largest vibration amplitude by the second largest vibration amplitude is greater than a predetermined threshold value (for example, 1.5), it can be determined that there is a prominent vibration amplitude.

[0054] In addition, the coefficients of the vibration amplitude expressed by an approximate formula after removing the N-order component of the order to be determined and the vibration amplitude expressed by an approximate formula without removing the N-order component of the order to be determined can be compared. When the difference is greater than a predetermined threshold, it is judged that there is a prominent vibration amplitude.

[0055] Furthermore, the estimation of the cause of the abnormality will be described below using specific examples.

[0056] The minimum value Nmin and the maximum value Nmax of the Nth order component that can be measured are determined by the effective frequency band based on the specifications of the vibration sensor 8 and the frequency of vibration generation corresponding to the part of the bearing 7. The frequency of vibration generation corresponding to the part of the bearing 7 is determined by the design of the bearing 7 and the rotation speed condition for performing the vibration measurement. Here, if the effective frequency band of the vibration sensor is set to 10 to 5000 Hz, and the frequency of vibration generation corresponding to the part of the bearing 7 is set to 600×N (Hz) at the highest rotation speed among the rotation speeds for which the vibration measurement is performed, and the frequency of vibration generation corresponding to the part of the bearing 7 is set to 100×N (Hz) at the lowest rotation speed among the rotation speeds for which the vibration measurement is performed, then the Nth order component (maximum value Nmax) of the frequency generation when the maximum rotation speed in the effective frequency band is calculated to be 5000 / 600≈8. In addition, the Nth order component (minimum value Nmax) of the frequency generation when the minimum rotation speed in the effective frequency band is calculated to be 10 / 100≈1. And under the above conditions, it is diagnosed in S7 that the outer ring of the bearing 7 is abnormal, that is, the outer ring is damaged. exist Figure 3 In the amplitude of the N-order components with N=1 to 8, the value obtained by dividing the vibration amplitude of the first largest 8th-order component by the vibration amplitude of the second largest 7th-order component is less than the threshold value of 1.5. Therefore, in the amplitude of the N-order components with N=1 to 8, it is judged that no outstanding value is found. Therefore, the damage to the outer ring is point-shaped damage, and the abnormality is estimated to be caused by overload and foreign matter mixing. On the other hand, Figure 4 In the amplitude of the N-order components of N=1 to 8, the value obtained by dividing the vibration amplitude of the first largest 4th-order component by the vibration amplitude of the second largest 8th-order component is greater than 1.5, which is the threshold value. Therefore, in the amplitude of the N-order components of N=1 to 8, it is judged that the amplitude of the 4th-order component is prominent. Therefore, the outer wheel damage is a wide damage, and the abnormal cause is estimated to be poor lubrication.

[0057] In the above-mentioned method and device for estimating the cause of bearing abnormality, the vibration when the main shaft 1 (an example of a rotating body) is rotated at a constant speed is measured at multiple rotational speeds, and the magnitude of the vibration for the frequency is calculated based on the vibration obtained by the measurement through frequency analysis (S1). Next, based on the frequency analysis results obtained through frequency analysis at multiple rotational speeds, the magnitude of the vibration with the same ratio of frequency to the rotational frequency is removed from the influence of the rotational speed, and the vibration average value is calculated (S2 to S5). Next, the bearing-caused vibration value at the characteristic ratio frequency, which is the ratio of the integral multiple of the frequency generated by the vibration of the bearing 7 to the rotational frequency, is extracted from the vibration average value (S6), and the presence or absence of abnormality is determined based on the bearing-caused vibration value (S7).

[0058] Then, when the abnormality of the bearing 7 is determined, the cause of the abnormality is estimated based on the relationship between the bearing-caused vibration values ​​at integral multiples of the characteristic specific frequency generated by the vibration of the bearing 7 (S8 to S10).

[0059] According to this configuration, it is possible to estimate the cause of abnormality that causes a change in the bearing state while performing measurement for diagnosing the bearing state.

[0060] In the above embodiment, the calculation unit is made to perform the functions of the analysis unit, the vibration average value calculation unit, the abnormality determination unit, and the abnormality generation cause estimation unit of the present disclosure, but each functional unit may be formed separately.

[0061] The present disclosure is not limited to the estimation of the cause of abnormality of a bearing supporting a main shaft of a machine tool, but can also be applied to a rotating body other than a main shaft.

[0062] The present disclosure may be applied to any mechanical device as long as it supports a rotating body using a rolling bearing, and may be applied to devices other than machine tools.

Claims

1. A method for estimating the cause of bearing abnormality, which estimates the cause of bearing abnormality when an abnormality occurs in a bearing supporting a rotating body, characterized in that: Perform the following steps: A measuring step of measuring the vibration of the rotating body when the rotating body is rotated at a constant speed at a plurality of rotation speeds; an analyzing step of calculating the magnitude of the vibration with respect to the frequency based on the vibration obtained in the measuring step by frequency analysis, a vibration average value calculation step, which is to calculate the vibration average value obtained by averaging the magnitudes of the vibrations having the same ratio of frequency to rotation frequency, based on the frequency analysis results obtained by the analysis step at multiple rotation speeds, while removing the influence of the rotation speed; A bearing-caused vibration value extraction step, extracting a bearing-caused vibration value at a characteristic ratio frequency from the vibration average value, wherein the characteristic ratio frequency is a ratio of an integer multiple of a frequency generated by the vibration of the bearing to a rotation frequency; an abnormality determination step, which determines whether the bearing has an abnormality based on the bearing-caused vibration value; as well as The abnormality generation cause estimating step estimates the abnormality generation cause based on the relationship between the bearing-caused vibration values ​​at integer multiples of the characteristic ratio frequency generated by the vibration of the bearing when the bearing is determined to be abnormal in the abnormality determining step.

2. The method for estimating the cause of bearing abnormality according to claim 1, characterized in that: In the abnormality generation cause estimation step, among the bearing-caused vibration values ​​at integral multiples of the characteristic ratio frequency generated by the vibration of the bearing, When only one bearing-caused vibration value is large at an integer multiple of the characteristic ratio frequency, the abnormality is estimated to be caused by poor lubrication. When the vibration value caused by more than one bearing is large at the integral multiple characteristic ratio frequency, the abnormal cause is estimated to be overload or foreign matter mixing.

3. A bearing abnormality cause estimation device for estimating the cause of a bearing abnormality when an abnormality occurs in a bearing supporting a rotating body, characterized in that: include: a measuring unit for measuring vibration when the rotating body is rotated at a constant speed at a plurality of rotation speeds; an analyzing unit that calculates the magnitude of vibration with respect to frequency based on the vibration acquired by the measuring unit through frequency analysis; a vibration average value calculation unit for calculating a vibration average value obtained by averaging the magnitudes of the vibrations having the same ratio of frequency to rotation frequency based on the frequency analysis results obtained by the analysis unit at a plurality of rotation speeds, while removing the influence of the rotation speed; a bearing-caused vibration value extracting unit that extracts, from the vibration average value, a bearing-caused vibration value at a characteristic ratio frequency, wherein the characteristic ratio frequency is a ratio of an integral multiple of a frequency generated by vibration of the bearing to a rotation frequency; an abnormality determination unit for determining whether the bearing has an abnormality based on the bearing-caused vibration value; as well as The abnormality generation cause estimation unit estimates the abnormality generation cause based on the relationship between the bearing-caused vibration value at an integral multiple of the characteristic ratio frequency generated by the vibration of the bearing when the abnormality determination unit determines that the bearing is abnormal.

4. The bearing abnormality cause estimation device according to claim 3, characterized in that: In the abnormality generation cause estimation unit, among the bearing-caused vibration values ​​at integral multiples of the characteristic ratio frequency generated by the vibration caused by the bearing, When only one bearing-caused vibration value is large at an integer multiple of the characteristic ratio frequency, the abnormality is estimated to be caused by poor lubrication. When the vibration value caused by more than one bearing is large at the integral multiple characteristic ratio frequency, the abnormal cause is estimated to be overload or foreign matter mixing.

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