Bearing diagnostic device, bearing diagnostic method, bearing diagnostic program, and machine tool

Abstract

The purpose of the present invention is to provide a bearing diagnostic device having a low possibility of erroneous determination even when amplitude acceleration is increased over the whole due to external factors such as noise.　A bearing diagnostic device 20 includes: an acquisition unit 31 that acquires vibration acceleration information indicating a vibration acceleration of a bearing 15; a computation unit 32 that executes envelope processing on the vibration acceleration and further executes frequency analysis processing to compute an envelope vibration acceleration; a determination unit 33 that determines whether or not the bearing 15 is abnormal on the basis of the ratio between a maximum value of the envelope vibration acceleration and a representative value of the envelope vibration acceleration; and an output unit 34 that outputs an abnormality signal when it is determined in the determination processing that the bearing is abnormal.

Description

Bearing diagnosis device, bearing diagnosis method, bearing diagnosis program, and machine tool

[0001] The present invention relates to a bearing diagnosis device, a bearing diagnosis method, a bearing diagnosis program, and a machine tool.

[0002] Various techniques for determining abnormalities in bearings are known. For example, Patent Document 1 describes a technique for determining whether the effective value of acceleration and the temperature of a rolling bearing are greater than or equal to a threshold value when the characteristic frequency output of the rolling bearing is greater than a predetermined threshold value. The technique described in Patent Document 1 realizes highly reliable monitoring of the bearing state by executing determination processing based on the effective value of acceleration and the temperature of the rolling bearing in addition to the determination processing based on the characteristic frequency output of the rolling bearing.

[0003] Japanese Patent Application Laid-Open No. 2020-153875

[0004] However, since the technique described in Patent Document 1 compares the acceleration generated from the bearing with a predetermined threshold value, there is a possibility of erroneously determining a normal bearing as abnormal when the amplitude acceleration increases overall due to external factors such as noise.

[0005] The present invention solves such problems, and an object thereof is to provide a bearing diagnosis device with a low risk of misjudgment even when the amplitude acceleration increases overall due to external factors such as noise.

[0006] The bearing diagnosis device according to the present invention includes an acquisition unit that acquires vibration acceleration information indicating the vibration acceleration of a bearing, a calculation unit that executes an envelope process on the vibration acceleration and further calculates an envelope vibration acceleration calculated by executing a frequency analysis process, a determination unit that determines whether the bearing is abnormal based on the ratio between the maximum value of the envelope vibration acceleration and the representative value of the envelope vibration acceleration, and an output unit that outputs an abnormal signal when it is determined that the bearing is abnormal.

[0007] Furthermore, in the bearing diagnosis device according to the present invention, the representative value is preferably the median value.

[0008] Furthermore, in the bearing diagnostic device according to the present invention, the determination unit further performs a first determination process to determine whether the maximum value of the envelope vibration acceleration is equal to or greater than a predetermined acceleration threshold, and the process of determining whether the bearing is abnormal based on the ratio of the maximum value of the envelope vibration acceleration to the representative value of the envelope vibration acceleration is preferably performed after the first determination process has determined that the maximum value of the envelope vibration acceleration is equal to or greater than the acceleration threshold.

[0009] Furthermore, in the bearing diagnostic device according to the present invention, the process of determining whether or not a bearing is abnormal based on the ratio of the maximum value of the envelope vibration acceleration to the representative value of the envelope vibration acceleration preferably includes a second determination process that determines whether or not the ratio is greater than or equal to a predetermined first ratio threshold, and the output unit preferably outputs an abnormality signal when it is determined that the ratio is greater than or equal to the first ratio threshold.

[0010] Furthermore, in the bearing diagnostic device according to the present invention, the process of determining whether or not a bearing is abnormal based on the ratio of the maximum value of the envelope vibration acceleration to the representative value of the envelope vibration acceleration further includes a third determination process that determines whether or not the ratio is greater than or equal to a predetermined second ratio threshold that is smaller than a first ratio threshold, and the output unit preferably outputs a warning signal indicating that the bearing needs to be monitored when it is determined that the ratio is greater than or equal to the second ratio threshold, and outputs a normal signal indicating that the bearing is normal when it is determined that the ratio is not greater than or equal to the second ratio threshold.

[0011] The bearing diagnostic method according to the present invention includes acquiring vibration acceleration information indicating the vibration acceleration of a bearing, performing envelope processing on the vibration acceleration, calculating envelope vibration acceleration by further performing frequency analysis processing, determining whether the bearing is abnormal or not based on the ratio of the maximum value of the envelope vibration acceleration to the representative value of the envelope vibration acceleration, and outputting an abnormality signal when it is determined that the bearing is abnormal.

[0012] The bearing diagnostic program according to the present invention acquires vibration acceleration information indicating the vibration acceleration of a bearing, performs envelope processing on the vibration acceleration, calculates envelope vibration acceleration by further performing frequency analysis processing, determines whether the bearing is abnormal or not based on the ratio of the maximum value of the envelope vibration acceleration to the representative value of the envelope vibration acceleration, and causes the computer to execute a process to output an abnormality signal when it is determined that the bearing is abnormal.

[0013] The machine tool according to the present invention comprises a spindle that rotatably grips a workpiece and has bearings, a tool post that holds a tool for cutting the workpiece, and a bearing diagnostic device that determines whether or not the bearing is abnormal. The bearing diagnostic device comprises an acquisition unit that acquires vibration acceleration information indicating the vibration acceleration of the bearing, a calculation unit that calculates envelope vibration acceleration calculated by performing envelope processing on the vibration acceleration and further performing frequency analysis processing, a determination unit that determines whether or not the bearing is abnormal based on the ratio of the maximum value of the envelope vibration acceleration to a representative value of the envelope vibration acceleration, and an output unit that outputs an abnormality signal when it is determined that the bearing is abnormal.

[0014] The bearing diagnostic device according to the present invention can reduce the risk of misjudgment even when the amplitude acceleration increases across the entire range due to external factors such as noise.

[0015] This is a perspective view of a machine tool according to an embodiment. This is a block diagram of the machine tool shown in Figure 1. This is a flowchart of the bearing diagnostic process performed by the bearing diagnostic device shown in Figure 2. Figure 4(A) shows a waveform indicating vibration acceleration information, and Figure 4(B) shows an envelope waveform. This is a diagram showing an example of the frequency characteristics of vibration acceleration calculated by the frequency analysis process shown in S105 in Figure 3. This is a diagram showing the first determination process in the frequency characteristics of vibration acceleration shown in Figure 5. This is a diagram showing the second and third determination processes in the frequency characteristics of vibration acceleration shown in Figure 5.

[0016] The bearing diagnostic device, bearing diagnostic method, bearing diagnostic program, and machine tool according to the present invention will be described below with reference to the drawings. However, it should be noted that the technical scope of the present invention is not limited to these embodiments, but extends to the invention described in the claims and its equivalents.

[0017] (Configuration and Function of the Machine Tool According to the Embodiment) Figure 1 is a perspective view of the machine tool according to the embodiment, and Figure 2 is a block diagram of the machine tool shown in Figure 1.

[0018] The machine tool 1 has a spindle 12 and a tool post 13 mounted inside a machining chamber 11 covered by a cover 10 having an opening. It can perform cutting operations by cutting a workpiece rotatably gripped by the spindle 12 with a rotating tool held in the tool post 13. The spindle 12 and the tool post 13 are controlled by a numerical control (NC) device 14.

[0019] The rotating mechanism of the spindle 12 for rotating the workpiece and the rotating mechanism of the tool post 13 for rotating the tool have bearings 15, which are rolling bearings that rotatably hold the rotating part of the workpiece or rotating tool. For example, the spindle 12 has a pair of bearings 15, and the rear spindle (not shown) has a pair of bearings 15 similar to the spindle 12. Each of the bearings 15 is positioned adjacent to a vibration accelerometer 16 that detects the vibration acceleration of the bearing 15. Each vibration accelerometer 16 detects the vibration acceleration of the adjacent bearing 15 and outputs a vibration acceleration signal indicating the detected vibration acceleration to a data logger 17 located inside the machine tool 1 and communicated with each of the vibration accelerometers 16.

[0020] The data logger 17 is located near the outside of the machine tool 1 and is communicated to the NC device 14 and the bearing diagnostic device 20 by cables 18. Cables 18 are, for example, LAN (Local Area Network) cables. In response to a request from the bearing diagnostic device 20, the data logger 17 acquires vibration acceleration information indicating the vibration acceleration of the bearing 15 from a vibration accelerometer 16 located adjacent to the bearing 15 that is to be judged in the bearing diagnostic process, over a predetermined detection period. The data logger 17 stores the acquired vibration acceleration information, associating it with the acquisition time and an identifier indicating the corresponding bearing 15.

[0021] The bearing diagnostic device 20 is, for example, an industrial computer and is located near the outside of the machine tool 1. The bearing diagnostic device 20 includes a communication unit 21, a storage unit 22, an operation unit 23, a display unit 24, and a processing unit 30. The bearing diagnostic device 20 performs envelope processing and frequency analysis on the vibration acceleration detected by the vibration accelerometer 16 over a predetermined detection time, and determines whether the bearing 15 is abnormal based on the ratio of the maximum value of the vibration acceleration to the representative value of the vibration acceleration in a predetermined frequency range.

[0022] The communication unit 21 has a communication interface circuit for connecting the bearing diagnostic device 20 to the NC device 14 and the data logger 17 via a cable 18. The communication unit 21 supplies data received from the NC device 14 and the data logger 17 to the processing unit 30. The communication unit 21 also transmits data supplied from the processing unit 30 to the NC device 14 and the data logger 17.

[0023] The storage unit 22 includes, for example, one of a semiconductor memory, a magnetic disk device, and an optical disk device. The storage unit 22 stores operating system programs, driver programs, application programs, data, etc., used for processing in the processing unit 30. For example, the storage unit 22 stores, as driver programs, an input device driver program that controls the operation unit 23, an output device driver program that controls the display unit 24, etc. The storage unit 22 also stores, as an application program, a bearing diagnostic program that causes the processing unit 30 to execute bearing diagnostic processing. The bearing diagnostic program may be installed in the storage unit 22 from a computer-readable portable storage medium such as a CD-ROM or DVD-ROM using a known setup program or the like.

[0024] Furthermore, the storage unit 22 stores various data used in the bearing diagnostic program. For example, the storage unit 22 stores acceleration threshold information, which is the threshold value for vibration acceleration. In one example, the acceleration threshold is 0.65 (m / s²). ２ ) The memory unit 22 also stores first ratio threshold information and second ratio threshold information, which are threshold values ​​for the ratio of the maximum value of the envelope vibration acceleration to the median value that is a representative value of the envelope vibration acceleration, respectively. The first ratio threshold is greater than the second ratio threshold, and in one example the first ratio threshold is 26 and the second ratio threshold is 13.

[0025] The operation unit 23 can be any device that enables operation of the bearing diagnostic device 20, such as a keyboard or touchpad. The operator can input characters, numbers, etc., via the operation unit 23. When the operation unit 23 is operated by the operator, it generates a signal corresponding to that operation. The generated signal is then supplied to the processing unit 30 as an instruction from the operator.

[0026] The display unit 24 can be any device capable of displaying video, images, characters, etc., such as a liquid crystal display or an organic EL display. The display unit 24 displays video corresponding to video data supplied from the processing unit 30, images corresponding to image data, characters corresponding to character data, etc. The display unit 24 may also display a graphical user interface for operating the bearing diagnostic device 20. The operation unit 23 and the display unit 24 may be integrally formed as a touch panel.

[0027] The processing unit 30 comprises one or more processors and their peripheral circuits. The processing unit 30 comprehensively controls the overall operation of the bearing diagnostic device 20 and is, for example, a CPU (Central Processing Unit). The processing unit 30 controls the operation of the communication unit 21, the display unit 24, etc., so that various processes of the bearing diagnostic device 20 are executed in appropriate procedures according to the programs stored in the storage unit 22, the operations of the operation unit 23, etc. The processing unit 30 executes processing based on the programs stored in the storage unit 22. In addition, the processing unit 30 can execute multiple programs in parallel.

[0028] The processing unit 30 includes an acquisition unit 31, a calculation unit 32, a determination unit 33, and an output unit 34. Each of these units is a functional module implemented by a program executed on the processor of the processing unit 30. Alternatively, each of these units may be implemented in the processing unit 30 as firmware.

[0029] (Bearing diagnostic process performed by the bearing diagnostic device according to the embodiment) Figure 3 is a flowchart of the bearing diagnostic process performed by the bearing diagnostic device 20. The bearing diagnostic process shown in Figure 3 is performed mainly by the processing unit 30 in cooperation with each element of the bearing diagnostic device 20, based on a machining program stored in the storage unit 22 in advance. The bearing diagnostic process shown in Figure 3 is performed, for example, when the material feeder that supplies workpieces to the machine tool 1 is started up, for each of the bearings 15 that are designated as targets for diagnostic determination.

[0030] First, the acquisition unit 31 outputs a rotation signal to the NC device 14 indicating that the rotating body supported by the bearing 15 to be judged is to be rotated at a predetermined rotational speed for a predetermined rotational period (S101). For example, when the rotating body supported by the bearing 15 to be judged is the spindle 12, the acquisition unit 31 outputs a spindle rotation signal to the NC device 14 indicating that the spindle 12 is to be rotated at a predetermined rotational speed for a predetermined rotational period. The rotational speed of the spindle 12 is, for example, 4000 rpm, and the rotational time of the spindle 12 should be a time that allows for the start-up time to reach the target rotational speed, in addition to the detection time to detect the vibration acceleration of the bearing 15.

[0031] Next, the acquisition unit 31 outputs a vibration acceleration request signal to the data logger 17 indicating that it will acquire vibration acceleration information showing the vibration acceleration of the bearing 15 to be determined from a vibration accelerometer 16 located adjacent to the bearing 15 to be determined (S102). In response to the input of the vibration acceleration request signal, the data logger 17 acquires vibration acceleration information showing the vibration acceleration from the vibration accelerometer 16 located adjacent to the bearing 15 to be determined over a predetermined detection period. The data logger 17 stores the acquired vibration acceleration information associated with the acquisition time and an identifier indicating the corresponding bearing 15.

[0032] Next, the acquisition unit 31 acquires vibration acceleration information indicating the vibration acceleration of the bearing 15 that is the target of the diagnostic process (S103). The acquisition unit 31 requests the data logger 17 to output a vibration acceleration signal indicating the vibration acceleration of the bearing 15 that is the target of the diagnostic process. In response to the request from the acquisition unit 31, the data logger 17 outputs a vibration acceleration signal corresponding to the vibration acceleration information indicating the vibration acceleration of the bearing 15 that is the target of the diagnostic process. The acquisition unit 31 stores the vibration acceleration information corresponding to the vibration acceleration signal in the storage unit 22. The vibration acceleration information consists of multiple data points indicating the vibration acceleration of the bearing 15 detected by the vibration accelerometer 16 at predetermined sampling times during a predetermined detection period.

[0033] Next, the calculation unit 32 performs envelope processing on the vibration acceleration corresponding to the vibration acceleration information obtained in the process shown in S103 (S104). The calculation unit 32 performs envelope processing to calculate the envelope (envelope waveform) of the vibration acceleration over the detection time by, for example, applying a low-pass filter to the signal obtained by absolute value of the vibration acceleration over a predetermined detection time to remove high-frequency components, then detecting peak values, and smoothly connecting the detected peak values.

[0034] Figure 4(A) shows a waveform representing vibration acceleration information, and Figure 4(B) shows an envelope waveform. The calculation unit 32 stores envelope information representing the envelope of vibration acceleration over the calculated detection time in the storage unit 22. The calculation unit 32 may also perform envelope processing to calculate the envelope of vibration acceleration over the detection time by, for example, performing a Hilbert transform on the vibration acceleration over a predetermined detection time.

[0035] Next, the calculation unit 32 performs frequency analysis processing on the envelope of vibration acceleration calculated by the envelope processing shown in S104 within a predetermined frequency range (S105). The calculation unit 32 performs Fast Fourier Transform (FFT) processing on the envelope of vibration acceleration over the detection time to calculate the frequency characteristics of the envelope vibration acceleration, which is the vibration acceleration processed by the envelope processing. By performing frequency analysis processing, the calculation unit 32 calculates multiple envelope vibration accelerations within a predetermined frequency range. The calculation unit 32 stores the frequency analysis information showing the frequency characteristics of the envelope vibration acceleration in the storage unit 22.

[0036] Figure 5 shows an example of the frequency characteristics of envelope vibration acceleration. In Figure 5, the horizontal axis represents frequency (kHz), and the vertical axis represents envelope vibration acceleration (m / s²). ２Figure 5 shows the following. In Figure 5, fc represents the defect frequency of the cage, also called the retainer; fb represents the defect frequency of the balls, also called the rolling elements; fi represents the defect frequency of the inner ring; and fo represents the defect frequency of the outer ring. 2fc represents the second harmonic of the cage defect frequency; 2fb represents the second harmonic of the ball defect frequency; 4fb represents the fourth harmonic of the ball defect frequency; 2fi represents the second harmonic of the inner ring defect frequency; and 2fo represents the second harmonic of the outer ring defect frequency. The predetermined frequency range for performing the frequency analysis processing shown in S105 is preferably a frequency range that includes at least eight types of defect frequencies: fc, 2fc, 2fb, fo, fi, 4fb, 2fo, and 2fi. In Figure 5, an example of a predetermined frequency range is shown, which is a frequency range from 0 kHz to 2 kHz. Furthermore, Figure 5 shows the envelope vibration acceleration corresponding to each frequency in the frequency range from 0 kHz to 2 kHz, at 1 Hz intervals.

[0037] In the example shown in Figure 5, the envelope vibration acceleration is large at frequencies near the outer ring defect frequency fo and the second harmonic 2fo of the outer ring defect frequency. Therefore, it is presumed that there is a defect in the outer ring in the example shown in Figure 5.

[0038] Next, the determination unit 33 performs a first determination process to determine whether the maximum value of the envelope vibration acceleration is equal to or greater than a predetermined acceleration threshold (S106). First, the determination unit 33 extracts the maximum value of the envelope vibration acceleration within a predetermined frequency range from the frequency characteristics of the envelope vibration acceleration. In the example shown in Figure 5, the peak value of the envelope vibration acceleration in the frequency band near the second harmonic 2fo of the outer ring defect frequency is 0.70 (m / s²). ２ The maximum value of the envelope vibration acceleration is extracted. Here, the frequency band near 2fo is, for example, the frequency band within ±1% of the frequency of 2fo. Next, the determination unit 33 obtains the acceleration threshold corresponding to the acceleration threshold information stored in the storage unit 22. Next, the determination unit 33 determines whether the extracted maximum value of the envelope vibration acceleration is greater than or equal to the obtained acceleration threshold.

[0039] FIG. 6 is a diagram showing a first determination process in the frequency characteristics of the envelope vibration acceleration shown in FIG. 5. In FIG. 6, a straight line L101 indicates an acceleration threshold value. The acceleration threshold value indicated by the straight line L101 is, for example, 0.65 (m / s ２ ).

[0040] In the example shown in FIG. 6, since the vibration acceleration at a frequency near the second harmonic 2f0 of the defect frequency of the outer ring is equal to or greater than the acceleration threshold value indicated by the straight line L101, the determination unit 33 determines that the maximum value of the vibration acceleration is equal to or greater than the acceleration threshold value (S106 - YES).

[0041] When the determination unit 33 determines that the maximum value of the vibration acceleration is not equal to or greater than the threshold value (S106 - NO), the output unit 34 outputs a normal signal indicating that the bearing 15 to be determined is normal to the display unit 24 (S107). In response to the input of the normal signal, the display unit 24 displays an image indicating that the bearing 15 to be determined is normal. Further, the output unit 34 may output a normal signal indicating that the bearing 15 to be determined is normal to a device other than the display unit 24.

[0042] When the determination unit 33 determines that the maximum value of the envelope vibration acceleration is equal to or greater than the acceleration threshold value (S106 - YES), it extracts the median value that is the representative value of a plurality of envelope vibration accelerations in a predetermined frequency range calculated by the frequency analysis process shown in S105 (S108). The determination unit 33 arranges a plurality of envelope vibration accelerations in descending order of magnitude, extracts the median value, and stores the extracted median value in the storage unit 22. In the example shown in FIG. 7, 0.031 (m / s ２ is extracted as the median value of the envelope vibration acceleration.

[0043] Next, the determination unit 33 calculates the ratio of the maximum value of the envelope vibration acceleration to the median value that is the representative value of the envelope vibration acceleration (S109). The determination unit 33 divides the maximum value of the envelope vibration acceleration extracted in the process shown in S106 by the median value of the envelope vibration acceleration extracted in the process shown in S108, thereby calculating the ratio of the maximum value of the envelope vibration acceleration to the median value of the envelope vibration acceleration (0.7 ÷ 0.031 = 22.58). The determination unit 33 stores the ratio information indicating the calculated ratio in the storage unit 22.

[0044] Next, the determination unit 33 executes a second determination process to determine whether or not the ratio (22.58) of the maximum value of the envelope vibration acceleration to the median value that is the representative value of the envelope vibration acceleration calculated in the process shown in S109 is greater than or equal to a predetermined first ratio threshold (S110). First, the determination unit 33 acquires the ratio calculated in the process shown in S109. Next, the determination unit 33 acquires the first ratio threshold corresponding to the first ratio threshold information stored in the storage unit 22. Next, the determination unit 33 determines whether or not the ratio calculated in the process shown in S109 is greater than or equal to the acquired first ratio threshold.

[0045] When it is determined by the determination unit 33 that the ratio calculated in the process shown in S109 is greater than or equal to the first ratio threshold (S110 - YES), the output unit 34 outputs an abnormal signal indicating that the bearing 15 to be determined is abnormal to the display unit 24 (S111). In response to the input of the abnormal signal, the display unit 24 displays an image indicating that the bearing 15 to be determined is abnormal. Further, the output unit 34 may output an abnormal signal indicating that the bearing 15 to be determined is abnormal to a device other than the display unit 24.

[0046] If the determination unit 33 determines that the ratio calculated in the process shown in S109 is not equal to or greater than the first ratio threshold (S110-NO), it executes a third determination process to determine whether the ratio calculated in the process shown in S109 is equal to or greater than a predetermined second ratio threshold (S112). First, the determination unit 33 obtains the ratio calculated in the process shown in S109. Next, the determination unit 33 obtains the second ratio threshold corresponding to the second ratio threshold information stored in the storage unit 22. Next, the determination unit 33 determines whether the ratio calculated in the process shown in S109 is equal to or greater than the obtained second ratio threshold.

[0047] Figure 7 shows the second and third determination processes in the frequency characteristics of the envelope vibration acceleration shown in Figure 5. In Figure 7, the line L201 represents the first ratio threshold, and the line L202 represents the second ratio threshold. The first ratio threshold is set to a value greater than the second ratio threshold. Furthermore, the first ratio threshold is preferably 1.5 times or more and 2.5 times or less the second ratio threshold, and more preferably a value close to 2 times, between 1.9 times and 2.1 times. In the example shown in Figure 7, the first ratio threshold is 26 and the second ratio threshold is 13. The values ​​of the first and second ratio thresholds are the result of statistical processing based on previously measured data.

[0048] In the example shown in Figure 7, the maximum value of the envelope vibration acceleration is smaller than the first ratio threshold shown by the line L201, so the determination unit 33 determines that the ratio of the maximum value of the envelope vibration acceleration to the median value of the envelope vibration acceleration is not greater than or equal to the second ratio threshold (S110-NO). Also, since the maximum value of the envelope vibration acceleration is greater than or equal to the second ratio threshold shown by the line L202, the determination unit 33 determines that the ratio of the maximum value of the envelope vibration acceleration to the median value of the envelope vibration acceleration is greater than or equal to the second ratio threshold (S112-YES).

[0049] If the determination unit 33 determines that the ratio calculated in the process shown in S109 is equal to or greater than the second ratio threshold (S112-YES), the output unit 34 does not determine that the bearing 15 under determination is abnormal, but because there is a high possibility that the determination result is in an unstable state, it outputs a warning signal to the display unit 24 indicating that monitoring of the bearing 15 is necessary (S113). In response to the input of the warning signal, the display unit 24 displays an image indicating that monitoring of the bearing 15 under determination is necessary. The output unit 34 may also output the warning signal indicating that monitoring of the bearing 15 under determination is necessary to a device other than the display unit 24.

[0050] If the determination unit 33 determines that the ratio calculated in the process shown in S109 is not equal to or greater than the second ratio threshold (S112-NO), the output unit 34 outputs a normal signal to the display unit 24 indicating that the bearing 15 to be determined is normal (S114). The display unit 24 displays an image indicating that the bearing 15 to be determined is normal in response to the input of the normal signal. The output unit 34 may also output the normal signal indicating that the bearing 15 to be determined is normal to a device other than the display unit 24.

[0051] (Effects of the bearing diagnostic device according to the embodiment) The bearing diagnostic device 20 determines whether or not the bearing 15 is abnormal based on the ratio of the maximum value of the envelope vibration acceleration to the median value of the envelope vibration acceleration. Therefore, even if the amplitude acceleration increases overall due to external factors such as noise, the risk of misjudgment can be reduced.

[0052] Furthermore, the bearing diagnostic device 20 uses the median value as a representative value of the envelope vibration acceleration to determine whether or not the bearing 15 is abnormal. When determining whether or not the bearing 15 is abnormal using the average value of all envelope vibration accelerations calculated within a predetermined frequency range as a representative value of the envelope vibration acceleration, the average value of the envelope vibration acceleration fluctuates due to fluctuations in the vibration acceleration value caused by the abnormality of the bearing 15. Therefore, the ratio between the maximum value of the envelope vibration acceleration and the average value of the envelope vibration acceleration is prone to fluctuations due to fluctuations in the vibration acceleration value caused by the abnormality of the bearing 15. The bearing diagnostic device 20 uses the median value as a representative value of the envelope vibration acceleration to determine whether or not the bearing 15 is abnormal, so the fluctuation of the median value of the envelope vibration acceleration due to fluctuations in the vibration acceleration value caused by the abnormality of the bearing 15 is reduced, and the ratio used as the basis for determination is less likely to fluctuate. The bearing diagnostic device 20 is unlikely to have its judgment criteria fluctuate due to changes in the vibration acceleration value caused by the bearing 15, and therefore can perform the judgment process without being affected by changes in the vibration acceleration value caused by the bearing 15.

[0053] Furthermore, the bearing diagnostic device 20 performs a first determination process to determine whether the maximum value of the envelope vibration acceleration is equal to or greater than the acceleration threshold, and then performs a bearing diagnostic process based on the ratio between the maximum value of the envelope vibration acceleration and the median value, which is a representative value of the envelope vibration acceleration. By performing a bearing diagnostic process based on the ratio between the maximum value of the envelope vibration acceleration and the median value of the envelope vibration acceleration after performing the first determination process, the bearing diagnostic device 20 can improve the accuracy of bearing diagnosis. Specifically, when the bearing diagnostic device 20 determines that the ratio is equal to or greater than the first ratio threshold, it outputs an abnormality signal, thereby improving the accuracy of bearing diagnosis.

[0054] Furthermore, after executing the first determination process, the bearing diagnostic device 20 performs a bearing diagnostic process based on the ratio of the maximum value of the envelope vibration acceleration to the median value, which is a representative value of the envelope vibration acceleration. This skips the time required to extract the representative value of the envelope vibration acceleration (steps S108 to S114), thereby shortening the time required for the bearing diagnostic process.

[0055] Furthermore, the bearing diagnostic device 20 outputs a warning signal indicating that the bearing needs monitoring when it determines that the ratio is equal to or greater than the second ratio threshold, and outputs a normal signal indicating that the bearing is normal when it determines that the ratio is not equal to or greater than the second ratio threshold. The bearing diagnostic device 20 can further improve the accuracy of bearing diagnosis by performing bearing diagnostic processing using a second ratio threshold that is smaller than the first ratio threshold in addition to the first ratio threshold.

[0056] (Modified form of bearing diagnostic device according to the embodiment) The bearing diagnostic device 20 determines whether the bearing 15 is abnormal based on the ratio of the maximum value of the envelope vibration acceleration to the median value of the envelope vibration acceleration. However, in the bearing diagnostic device according to the embodiment, if the variation in the representative value of the envelope vibration acceleration due to the variation in the value of vibration acceleration caused by the abnormality of the bearing 15 is reduced, the bearing diagnostic device may use a representative value other than the median value to determine whether the bearing 15 is abnormal. The representative value may be the average value of a plurality of envelope vibration accelerations obtained by excluding abnormal values ​​from a plurality of envelope vibration accelerations calculated in a predetermined frequency range, or it may be a trimmed mean value. Abnormal values ​​are also called outliers, and may be values ​​outside the range of σ (1x the standard deviation), 2σ (2x the standard deviation), 3σ (3x the standard deviation), or 4σ (4x the standard deviation), or they may be values ​​determined by tests such as the Smirnov-Grubbs test and the Thompson test.

[0057] Furthermore, the bearing diagnostic device 20 sequentially performs the first diagnostic process, the second diagnostic process, and the third diagnostic process, but the bearing diagnostic device according to the embodiment only needs to perform at least the second diagnostic process. For example, the bearing diagnostic device according to the embodiment may perform a diagnostic process that includes the first diagnostic process and the second diagnostic process, or it may perform a diagnostic process that includes the second diagnostic process and the third diagnostic process.

[0058] Furthermore, while the bearing diagnostic device 20 performs the determination process in the order of first diagnostic process, second diagnostic process, and third diagnostic process, the bearing diagnostic device according to this embodiment may perform the determination process in the order of first diagnostic process, third diagnostic process, and second diagnostic process.

[0059] Furthermore, although the data logger 17 is located near the outside of the machine tool 1, the data logger in this embodiment may be located inside the machine tool.

[0060] Furthermore, although the bearing diagnostic device 20 is located near the outside of the machine tool 1, the bearing diagnostic device according to this embodiment may be located inside the machine tool.

[0061] Furthermore, the bearing diagnostic device 20 determines abnormalities in the bearings 15 of the rotating mechanism of the spindle 12 that rotates the workpiece and the rotating mechanism of the tool post 13 that rotates the machine tool. However, the bearing diagnostic device according to this embodiment may also determine abnormalities in the bearings of the ball screw.

[0062] Furthermore, the machine tool 1 has a data logger 17 that is communicatively connected to each of the vibration accelerometers 16, but the machine tool according to this embodiment does not have to have a data logger 17. When the machine tool according to this embodiment does not have a data logger 17, the function of the data logger 17 may be provided by the bearing diagnostic device.

[0063] Furthermore, in machine tool 1, the data logger 17 and the bearing diagnostic device 20 are arranged as separate devices from the NC device 14, but in the machine tool according to the embodiment, at least one of the data logger 17 and the bearing diagnostic device 20 may be integrated with the NC device. In the machine tool according to the embodiment, the data logger 17 may be integrated with the NC device, and the bearing diagnostic device 20 may be arranged as a separate device from the NC device 14. Also, in the machine tool according to the embodiment, the data logger 17 may be arranged as a separate device from the NC device 14, and the bearing diagnostic device 20 may be integrated with the NC device, and both the data logger 17 and the bearing diagnostic device 20 may be integrated with the NC device.

[0064] Furthermore, in machine tool 1, the bearing diagnostic device 20 has an operation unit 23 and a display unit 24, but in the machine tool according to the embodiment, at least one of the operation unit 23 and the display unit 24 of the bearing diagnostic device 20 may be shared with or integrated with the operation unit and display unit of the NC device 14. In the machine tool according to the embodiment, by sharing with or integrating at least one of the operation unit 23 and the display unit 24 of the bearing diagnostic device 20 with the operation unit and display unit of the NC device 14, operability can be improved and costs can be reduced.

[0065] 1. Machine tool 12. Spindle 13. Tool post 14. NC device 15. Bearing 16. Vibration accelerometer 17. Data logger 20. Bearing diagnostic device

Claims

1. A bearing diagnostic device comprising: an acquisition unit that acquires vibration acceleration information indicating the vibration acceleration of a bearing; a calculation unit that calculates envelope vibration acceleration by performing envelope processing on the vibration acceleration and further performing frequency analysis processing; a determination unit that determines whether or not the bearing is abnormal based on the ratio of the maximum value of the envelope vibration acceleration to a representative value of the envelope vibration acceleration; and an output unit that outputs an abnormality signal when it is determined that the bearing is abnormal.

2. The bearing diagnostic device according to claim 1, wherein the representative value is the median value.

3. The bearing diagnostic device according to claim 1 or 2, wherein the determination unit further performs a first determination process to determine whether the maximum value of the envelope vibration acceleration is equal to or greater than a predetermined acceleration threshold, and the process of determining whether the bearing is abnormal based on the ratio of the maximum value of the envelope vibration acceleration to the representative value of the envelope vibration acceleration is performed after the first determination process has determined that the maximum value of the envelope vibration acceleration is equal to or greater than the acceleration threshold.

4. The bearing diagnostic device according to claim 3, wherein the process of determining whether the bearing is abnormal based on the ratio of the maximum value of the envelope vibration acceleration to a representative value of the envelope vibration acceleration includes a second determination process of determining whether the ratio is greater than or equal to a predetermined first ratio threshold, and the output unit outputs the abnormality signal when it is determined that the ratio is greater than or equal to the first ratio threshold.

5. The bearing diagnostic device according to claim 4, wherein the process of determining whether the bearing is abnormal based on the ratio of the maximum value of the envelope vibration acceleration to a representative value of the envelope vibration acceleration further includes a third determination process of determining whether the ratio is greater than or equal to a predetermined second ratio threshold that is less than the first ratio threshold, and the output unit outputs a warning signal indicating that the bearing needs to be monitored when it is determined that the ratio is greater than or equal to the second ratio threshold, and outputs a normal signal indicating that the bearing is normal when it is determined that the ratio is not greater than or equal to the second ratio threshold.

6. A bearing diagnostic method characterized by: acquiring vibration acceleration information indicating the vibration acceleration of a bearing; performing envelope processing on the vibration acceleration; calculating envelope vibration acceleration calculated by further performing frequency analysis processing; determining whether the bearing is abnormal based on the ratio of the maximum value of the envelope vibration acceleration to the representative value of the envelope vibration acceleration; and outputting an abnormality signal when it is determined that the bearing is abnormal.

7. A bearing diagnostic program characterized by having a computer perform the following processes: acquire vibration acceleration information indicating the vibration acceleration of a bearing; perform envelope processing on the vibration acceleration and then perform frequency analysis to calculate envelope vibration acceleration; determine whether the bearing is abnormal based on the ratio of the maximum value of the envelope vibration acceleration to the representative value of the envelope vibration acceleration; and output an abnormality signal when it is determined that the bearing is abnormal.

8. A machine tool comprising: a spindle having a bearing for rotatably gripping a workpiece; a tool post for holding a tool for cutting a workpiece; and a bearing diagnostic device for determining whether or not the bearing is abnormal, wherein the bearing diagnostic device comprises: an acquisition unit for acquiring vibration acceleration information indicating the vibration acceleration of the bearing; a calculation unit for calculating envelope vibration acceleration calculated by performing envelope processing on the vibration acceleration and further performing frequency analysis processing; a determination unit for determining whether or not the bearing is abnormal based on the ratio of the maximum value of the envelope vibration acceleration to a representative value of the envelope vibration acceleration; and an output unit for outputting an abnormality signal when it is determined that the bearing is abnormal.

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