Method and device for estimating cause of bearing abnormality

Abstract

To estimate a cause of an abnormality in which a change in a bearing state occurs alongside measurement for diagnosis of the bearing state due to vibration.SOLUTION: A method includes: a measurement step for measuring a vibration of a main shaft; an analysis step S1 for calculating a magnitude of the vibration with respect to a frequency from the obtained vibration; vibration average value calculation steps S2 to S5 for calculating a vibration average value by removing an influence of a rotational speed for the magnitude of the vibration with a same frequency ratio to a rotational frequency from the frequency analysis result; a bearing-origin vibration value extraction step S6 for extracting a bearing-origin vibration value at a characteristic ratio frequency being the ratio to the rotational frequency of an integer multiple of the frequency at which the vibration due to the bearing occurs in the vibration average value; an abnormality determination step S7 for determining presence / absence of an abnormality on the basis of the bearing-origin vibration value; and abnormality occurrence cause estimation steps S8 to S10 for estimating an abnormality occurrence cause on the basis of a relationship of bearing-origin vibration values in the integer multiple of the characteristic ratio frequency at which the vibration due to the bearing occurs when it is determined that the bearing is abnormal.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a method and device for estimating the cause of a bearing abnormality, which estimates the cause of the occurrence of a bearing abnormality based on a bearing abnormality detected from vibration data. [Background technology]

[0002] In machine tools that process workpieces by rotating tools or workpieces attached to the spindle, the bearings may wear out due to aging and lose preload, or damage may occur due to the inclusion of foreign matter or poor lubrication, resulting in problems such as reduced operating accuracy and abnormal noise during operation. When this occurs, machining defects such as poor shape of the workpiece or poor machining surface properties occur, adversely affecting production. In addition, if a failure such as seizure of the spindle occurs, the spindle may become unable to rotate, and the machine tool may not even be able to operate. When an abnormality such as damage to the inner ring occurs in a rolling bearing that supports a rotating body, vibration occurs. A method that utilizes a vibration sensor to diagnose the bearing condition by utilizing this is known. Patent Document 1 shows a method in which vibration is measured, envelope processing and frequency analysis are performed, and characteristic frequency values ​​of the inner ring, outer ring, and rolling element are extracted based on a predetermined relational expression, and a diagnosis is made using different threshold values ​​for the inner ring, outer ring, and rolling element. Patent Document 2 discloses a method of measuring vibrations at a plurality of rotational frequencies and diagnosing based on the average value of vibration magnitudes that have the same frequency ratio to the rotational frequency. Patent Document 3 discloses a method of classifying and diagnosing vibration data measured during monitoring into poor lubrication and bearing damage conditions using a classifier that has learned the characteristics of vibration data from rolling bearings filled with normal grease and grease with different oil content. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5146008 [Patent Document 2] Patent No. 6511573 [Patent Document 3] Patent No. 6997054 Summary of the Invention [Problem to be solved by the invention]

[0004] While Patent Documents 1 and 2 make it possible to carry out repairs before a serious failure, such as bearing seizure, occurs that renders the spindle unable to rotate, there is an increasing demand to diagnose the cause of failures that have occurred in bearing anomalies in order to determine who will bear the costs, such as insurance coverage for repairs, and to take measures to prevent recurrence. There are many possible causes for failures, including overload caused by collisions or tool damage during cutting, contamination by foreign matter or poor lubrication due to poor management of lubricating oil, and there are many items that need to be checked. In particular, when there is an abnormality in a machine related to production, recovery is given priority, making it difficult to conduct a thorough investigation, and there are cases where the cause of the failure cannot be identified. In addition, poor grease lubrication, which is listed as an anomaly to be diagnosed in Patent Document 3, is also one of the causes of failure, but in the case of oil-air lubrication, changes in the bearing condition due to poor lubrication progress quickly, so bearing damage may already have occurred at the time diagnosis is performed.

[0005] Therefore, an object of the present disclosure is to provide a method and apparatus for estimating the cause of a bearing abnormality that can estimate the cause of the abnormality that has caused a change in the bearing condition, in addition to taking measurements to diagnose the bearing condition. [Means for solving the problem]

[0006] In order to achieve the above object, a first aspect of the present disclosure is a method for estimating a cause of a bearing abnormality when an abnormality occurs in a bearing supporting a rotating body, comprising: a measuring step of measuring vibrations at a plurality of rotation speeds when the rotating body is rotated at a constant speed; an analysis step of calculating a vibration magnitude with respect to a frequency by frequency analysis from the vibration obtained in the measurement step; a vibration average value calculation step of calculating an average vibration value by excluding the influence of the rotation speed for the magnitude of the vibration having the same ratio of the frequency to the rotation frequency from the frequency analysis results obtained in the analysis step at a plurality of rotation speeds; a bearing-induced vibration value extraction step of extracting a bearing-induced vibration value at a characteristic ratio frequency, which is a ratio of a frequency at which vibration caused by the bearing occurs to a rotation frequency that is an integer multiple of the frequency at which vibration is caused by the bearing, from the vibration average value; an abnormality determination step of determining whether or not there is an abnormality based on the bearing-induced vibration value; and when an abnormality is determined in the abnormality determination step, an abnormality occurrence cause estimation step is executed to estimate the cause of the abnormality based on a relationship between the bearing-induced vibration values ​​at integer multiples of a characteristic specific frequency at which vibration caused by the bearing occurs. In another aspect of the first aspect, in the above-mentioned aspect, in the abnormality occurrence cause estimating step, in the bearing-induced vibration value at an integer multiple of a characteristic specific frequency at which vibration caused by the bearing occurs, If only the bearing-induced vibration value of one integer multiple characteristic frequency is large, it is assumed that the cause of the abnormality is poor lubrication. If only the bearing-induced vibration value of one integer multiple characteristic frequency is not large, it is estimated that the cause of the abnormality is an overload or the inclusion of foreign matter. In order to achieve the above object, a second configuration of the present disclosure is an apparatus for estimating a cause of a bearing abnormality when an abnormality occurs in a bearing supporting a rotating body, comprising: a measurement unit that measures vibrations at a plurality of rotation speeds when the rotor is rotated at a constant speed; an analysis unit that calculates a vibration magnitude with respect to a frequency by frequency analysis from the vibration obtained by the measurement unit; a vibration average value calculation unit that calculates an average vibration value by removing the influence of the rotation speed for the magnitude of the vibration having the same ratio of frequency to the rotation frequency from the frequency analysis results obtained by the analysis unit at a plurality of rotation speeds; a bearing-induced vibration value extracting unit that extracts a bearing-induced vibration value at a characteristic ratio frequency, which is a ratio to a rotation frequency that is an integer multiple of a frequency at which vibration caused by the bearing occurs, from the vibration average value; an abnormality determination unit that determines whether or not there is an abnormality based on the bearing-induced vibration value; and an abnormality occurrence cause estimation unit that, when an abnormality is determined by the abnormality determination unit, estimates a cause of the abnormality based on a relationship between the bearing-attributed vibration values ​​at integer multiples of a characteristic specific frequency at which vibration caused by the bearing occurs. In another aspect of the second configuration, in the above configuration, the abnormality occurrence cause estimation unit is configured to estimate the bearing-induced vibration value at an integer multiple of a characteristic specific frequency at which vibration caused by the bearing occurs, If only the bearing-induced vibration value of one integer multiple characteristic frequency is large, it is assumed that the cause of the abnormality is poor lubrication. If only the bearing-induced vibration value of one integer multiple characteristic frequency is not large, it is estimated that the cause of the abnormality is an overload or the inclusion of foreign matter. Effect of the Invention

[0007] According to the present disclosure, in addition to measurements for diagnosing the bearing condition, it is possible to estimate the cause of the abnormality that caused the change in the bearing condition. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a block diagram showing a configuration in which a bearing abnormality cause estimation device is applied to a spindle of a machine tool. [Diagram 2] 4 is a flowchart of a method for estimating the cause of a bearing abnormality. [Diagram 3] 1 is a graph showing an example of a vibration waveform that does not have a prominent Nth-order component. [Figure 4] 1 is a graph showing an example of a vibration waveform having a prominent Nth-order component. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration in which a bearing abnormality cause estimating device according to a second configuration of the present disclosure is applied to a spindle of a machine tool. The spindle 1 is rotatably attached to the spindle housing 2 via a rolling bearing 7, and a tool 3 for machining is fixed to the spindle 1. The motor 4 drives the spindle 1. The motor 4 is provided with a speed detector 5, and the measured rotation speed of the motor 4 is input to a control device 6. During machining, the control device 6 controls the current supplied to the motor 4 so as to keep the rotation speed of the motor 4 measured by the speed detector 5 at a command rotation speed.

[0010] A vibration sensor 8 is attached to the spindle housing 2 as a vibration measuring means, and the vibration acceleration at a plurality of rotation speeds is measured by the vibration sensor 8. The measured vibration acceleration is converted to a digital value by an A / D converter 9 and stored in a memory unit 10 together with the rotation speed at the time of vibration measurement. The memory unit 10 also stores a preset threshold value. The calculation unit 11 is configured including a CPU, and calculates the degree of abnormality of the bearing 7 from the bearing specifications stored in the memory unit 10 and the rotation speed and vibration acceleration recorded in the memory unit 10 during measurement, and judges whether the bearing is normal or not. Furthermore, if the calculation unit 11 judges that the bearing 7 is abnormal, it infers the cause of the change in the bearing condition. The display unit 12 displays the diagnosis result by the calculation unit 11. 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 an abnormality cause estimation device of the present disclosure. The vibration sensor 8 and the A / D conversion unit 9 are an example of a measurement unit in the present disclosure. The calculation unit 11 is an example of an analysis unit, a vibration average value calculation unit, an abnormality determination unit, and an abnormality cause estimation unit of the present disclosure.

[0011] 2 is a flowchart of a method for estimating the cause of a bearing abnormality according to the first configuration of the present disclosure, illustrating the process of diagnosing an abnormality in the state of the bearing 7 by the calculation unit 11 and estimating the cause of the abnormality when an abnormality occurs in the bearing state. This will be described in detail below. The calculation unit 11 receives the rotation speed and vibration acceleration at the time of vibration measurement from the storage unit 10, and starts diagnosing the bearing 7. The processing of S1 to S3 is performed for each of a plurality of rotation speeds. First, the time-series vibration acceleration data is Fourier transformed to calculate the vibration amplitude with respect to frequency (S1: analysis step). Next, the angular velocity is calculated from the rotation speed, and the vibration amplitude is divided by the square of the angular velocity (S2). Because it is known that the exciting force caused by a bearing abnormality is roughly proportional to the square of the rotation speed, this processing makes it possible to obtain vibration amplitude data with the effects of the rotation speed removed. Next, the vibration amplitude data is resampled from the frequency domain to the specific frequency domain (frequency divided by rotation frequency) (S3). This processing allows the vibration acceleration measured at any rotation speed to be treated equally. Next, it is determined whether the processes of S1 to S3 have been completed for all rotation speeds (S4), and if so, the average value of the vibration amplitude data obtained for all rotation speeds is calculated for each specific frequency and added together (S5). By performing the processes of S1 to S5, the influence of the magnitude of the transfer function can be removed and random noise with no periodicity can be reduced. S2 to S5 are an example of a vibration average value calculation step of the present disclosure.

[0012] After combining the vibration accelerations at multiple rotational speeds into one, the amplitude caused by an abnormality in the bearing 7 is extracted (S6: bearing-induced vibration value extraction step). The occurrence frequency of vibration corresponding to the parts of the bearing 7, such as the inner ring, outer ring, and rolling elements, can be calculated from the design specifications of the bearing 7. Equation 1 shows the formula for calculating the specific frequency at which vibration occurs for the inner ring, Equation 2 for the outer ring, and Equation 3 for the rolling elements. Here, fi is the occurrence frequency of inner ring vibration, fo is the occurrence frequency of outer ring vibration, fb is the occurrence frequency of rolling element vibration, fr is the rotational frequency, Z is the number of rolling elements in 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 order.

[0013]

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[0014] In S6, the vibration amplitude of the specific frequency corresponding to the part of the bearing 7 is extracted, and in S7, if the maximum value of the extracted Nth-order component amplitude (bearing-induced vibration value) in all parts exceeds a predetermined threshold value, the bearing 7 is diagnosed as having an abnormality (abnormality determination step). However, the determination of whether the bearing 7 has an abnormality may be performed by setting a threshold value for each part or Nth-order component. If the bearing condition is diagnosed as abnormal, it is determined whether there are any outstanding values ​​in the amplitude of the Nth order component for each bearing part (S8). In the case of an abnormality caused by an inner ring flaw or rolling element flaw that has two characteristic specific frequencies for each order, the vibration amplitude values ​​for each order are aggregated into one. As a means of aggregation, it is preferable to average the values ​​or use the smaller value. If there is a prominent value in the amplitude of the Nth order component (if only the bearing-induced vibration value is large), it is assumed that the vibration is caused by a wide scratch and the cause of the abnormality is poor lubrication (S9). If there is no prominent value in the amplitude of the Nth order component (if only the bearing-induced vibration value is not large), it is assumed that the vibration is caused by a spot scratch and the cause of the abnormality is overload or foreign matter (S10). S8 to S10 are an example of an abnormality occurrence cause estimation step of the present disclosure.

[0015] Next, a method for determining whether there is an outstanding value in the amplitude of the Nth order component will be described. The minimum value Nmin and maximum value Nmax of the measurable Nth order component are determined by the effective frequency band determined by the vibration sensor 8, the vibration occurrence frequency corresponding to the part of the bearing 7 determined by the design of the bearing 7 and the measured rotation speed conditions. Here, an example will be described in which there is outer ring damage, Nmin=1, Nmax=8. Fig. 3 shows an example of a vibration waveform when there is no outstanding value in the amplitude of the Nth order component, and Fig. 4 shows an example of a vibration waveform when there is an outstanding value in the amplitude of the Nth order component. In the vibration amplitude of the Nth order component, if the value obtained by dividing the first largest vibration amplitude by the second largest vibration amplitude is equal to or greater than a predetermined threshold value (e.g., 1.5), it can be determined that there is an outstanding vibration amplitude. In addition, the vibration amplitude of the Nth order component excluding the order to be determined may be expressed by an approximation formula, and the coefficients of the vibration amplitude of the Nth order component not excluding the order to be determined may be compared, and if the difference is large, it may be determined that there is an outstanding vibration amplitude.

[0016] The above-described bearing abnormality cause estimation method and device measures vibration at a plurality of rotation speeds when a main shaft 1 (one example of a rotating body) is rotated at a constant speed, and calculates the magnitude of vibration relative to frequency from the measured vibration by frequency analysis (S1). Next, from the frequency analysis results obtained at the plurality of rotation speeds, calculates an average vibration value by removing the influence of the rotation speed for vibration magnitudes with the same ratio of frequency to rotation frequency (S2-S5). Next, from the vibration average values, a bearing-attributed vibration value at a characteristic ratio frequency, which is a ratio to a rotation frequency that is an integer multiple of the frequency at which vibration caused by bearing 7 occurs, is extracted (S6), and the presence or absence of an abnormality is determined based on the bearing-attributed vibration value (S7). Then, when an abnormality in the bearing 7 is determined, the cause of the abnormality is estimated based on the relationship of the bearing-attributed vibration value at an integer multiple of the characteristic specific frequency at which the vibration caused by the bearing 7 occurs (S8 to S10). According to this configuration, in addition to measurements for diagnosing the bearing condition, it is possible to estimate the cause of the abnormality that has caused the change in the bearing condition.

[0017] In the above embodiment, the calculation unit functions as the analysis unit, the vibration average value calculation unit, the abnormality determination unit, and the abnormality cause estimation unit of the present disclosure, but each functional unit may be formed separately. The present disclosure is not limited to estimation of the cause of an abnormality in a bearing that supports a spindle of a machine tool, but may also be applied to rotating bodies other than a spindle. The present disclosure can be applied to mechanical devices other than machine tools as long as the mechanical devices have a rotating body supported by a rolling bearing. [Explanation of symbols]

[0018] Reference Signs List 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... Memory unit, 11... Calculation unit, 12... Display unit.

Claims

1. A method for estimating a cause of a bearing abnormality when an abnormality occurs in a bearing supporting a rotating body, comprising: a measuring step of measuring vibrations at a plurality of rotation speeds when the rotating body is rotated at a constant speed; an analysis step of calculating a vibration magnitude with respect to a frequency by frequency analysis from the vibration obtained in the measurement step; a vibration average value calculation step of calculating an average vibration value by excluding the influence of the rotation speed for the magnitude of the vibration having the same ratio of the frequency to the rotation frequency from the frequency analysis results obtained in the analysis step at a plurality of rotation speeds; a bearing-induced vibration value extraction step of extracting a bearing-induced vibration value at a characteristic ratio frequency, which is a ratio to a rotation frequency that is an integer multiple of a frequency at which vibration caused by the bearing occurs, from the vibration average value; an abnormality determination step of determining whether or not there is an abnormality based on the bearing-induced vibration value; an abnormality occurrence cause estimating step of estimating a cause of the abnormality occurrence based on a relationship between the bearing-induced vibration value and an integer multiple of a characteristic specific frequency at which vibration caused by the bearing occurs when an abnormality is determined in the abnormality determining step; A method for estimating the cause of a bearing abnormality, comprising:

2. In the abnormality occurrence cause estimating step, in the bearing-induced vibration value at an integer multiple of a characteristic specific frequency at which vibration caused by the bearing occurs, If only the bearing-induced vibration value of one integer multiple characteristic frequency is large, it is assumed that the cause of the abnormality is poor lubrication.

2. The method for estimating the cause of a bearing abnormality according to claim 1, wherein if only the bearing-induced vibration value of one integer multiple characteristic ratio frequency is not large, it is estimated that the cause of the abnormality is overload or foreign matter.

3. A device for estimating the cause of a bearing abnormality when an abnormality occurs in a bearing supporting a rotating body, comprising: a measurement unit that measures vibrations at a plurality of rotation speeds when the rotor is rotated at a constant speed; an analysis unit that calculates a vibration magnitude with respect to a frequency by frequency analysis from the vibration obtained by the measurement unit; a vibration average value calculation unit that calculates an average vibration value by removing the influence of the rotation speed for the magnitude of the vibration having the same ratio of frequency to the rotation frequency from the frequency analysis results obtained by the analysis unit at a plurality of rotation speeds; a bearing-induced vibration value extracting unit that extracts a bearing-induced vibration value at a characteristic ratio frequency, which is a ratio to a rotation frequency that is an integer multiple of a frequency at which vibration caused by the bearing occurs, from the vibration average value; an abnormality determination unit that determines whether or not there is an abnormality based on the bearing-induced vibration value; an abnormality occurrence cause estimation unit that estimates a cause of the abnormality based on a relationship between the bearing-attributed vibration value and an integer multiple of a characteristic specific frequency at which vibration caused by the bearing occurs when the abnormality determination unit determines that an abnormality exists; A bearing abnormality cause estimation device comprising:

4. The abnormality occurrence cause estimation unit estimates, in the bearing-induced vibration value at an integer multiple of a characteristic specific frequency at which vibration caused by the bearing occurs, If only the bearing-induced vibration value of one integer multiple characteristic frequency is large, it is assumed that the cause of the abnormality is poor lubrication.

4. The device for estimating the cause of a bearing abnormality according to claim 3, wherein if only the bearing-induced vibration value of one of the integer multiple characteristic ratio frequencies is not large, it is estimated that the cause of the abnormality is an overload or the inclusion of foreign matter.

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