Bearing state monitoring system

Abstract

The present invention is provided with: an operation state determination means (2) for determining the operation state of a bearing on the basis of an external force detected by a sensor unit (1); a diagnostic speed setting means (3) for setting a precision diagnostic speed on the basis of the rotational speed and vibration of the bearing detected by the sensor unit (1) when the operating state determination means (2) determines that the bearing is in the light-load operating state; and an abnormality diagnosis means (4) that performs precision diagnosis of the bearing by changing the rotational speed of the bearing to a precision diagnosis speed.

Description

Technical Field

[0001] The present invention relates to a condition monitoring system for bearings used at high rotation speeds, such as bearings supporting a main shaft of a machine tool. Background Art

[0002] The bearings supporting the spindles of machine tools are often used at high rotational speeds of tens of thousands of revolutions per minute. To detect damage early, these machine tool bearings are increasingly equipped with condition monitoring systems that detect bearing vibration and perform abnormality diagnosis (see, for example, Patent Document 1).

[0003] Patent Document 1: Japanese Patent Application Laid-Open No. 2009-20090

[0004] However, in bearings used at high rotational speeds, noise, including base vibration associated with spindle rotation and wind noise associated with lubricant spray, is distributed over a wide frequency band, making it difficult to separate the vibration components caused by this noise from those resulting from bearing damage. Therefore, to accurately diagnose abnormalities using a condition monitoring system, it is necessary to use vibration data at rotational speeds that are less susceptible to the influence of vibration components caused by noise.

[0005] In contrast, the rotation speed of the main shaft can be reduced when performing abnormality diagnosis through a condition monitoring system. However, when the bearings used are angular contact ball bearings, tapered roller bearings, or cylindrical roller bearings that are loaded with a fixed position preload, their preload and rolling element load are small. Therefore, as the rotation speed decreases, the vibration emitted from the bearing itself becomes lower, making it difficult to detect damage to the main shaft and bearings with high precision.

[0006] In addition, in the case of machine tools used mainly in the high rotation speed range, if the rotation speed is reduced to the low speed range for abnormality diagnosis, the temperature changes of the main shaft and bearings will become larger, and it will take time to restore the temperature equilibrium state at the original rotation speed, which will lead to a significant decrease in productivity. Summary of the Invention

[0007] Therefore, an object of the present invention is to provide a condition monitoring system capable of accurately diagnosing abnormalities of a bearing used at a high rotational speed without significantly reducing the productivity of a device incorporating the bearing.

[0008] In order to solve the above-mentioned problems, the present invention adopts the following structure (Structure 1), namely: in a bearing status monitoring system, it is provided with: a rotation speed detection unit, which detects the rotation speed of the above-mentioned bearing; a vibration detection unit, which detects the vibration of the above-mentioned bearing; an operating status judgment unit, which judges whether the above-mentioned bearing is in a load operating state or a light load operating state; a diagnostic speed setting unit, which sets the precision diagnostic speed for performing precision diagnosis of the above-mentioned bearing based on the rotation speed detected by the above-mentioned rotation speed detection unit and the vibration detected by the above-mentioned vibration detection unit when the above-mentioned operating status judgment unit judges that the bearing is in a light load operating state; and an abnormality diagnosis unit, which changes the rotation speed of the above-mentioned bearing to the precision diagnostic speed set by the above-mentioned diagnostic speed setting unit to perform precision diagnosis of the bearing.

[0009] According to the above-mentioned structure 1, the diagnostic speed setting unit uses the data of the rotational speed and vibration of the bearing in the light-load operating state to set an appropriate precision diagnostic speed that suppresses the speed reduction of the bearing relative to the normally used rotational speed. At this precision diagnostic speed, the abnormality diagnosis unit performs precision diagnosis, thereby being able to perform bearing abnormality diagnosis with high precision without significantly reducing the productivity of the equipment assembled with the bearing.

[0010] On the basis of the above-mentioned structure 1, the following structure (structure 2) can be adopted, namely: as the above-mentioned abnormality diagnosis unit, it includes: a simple diagnosis unit, when the above-mentioned bearing is running at an arbitrary rotational speed, calculating at least one simple diagnosis value based on the waveform of the vibration detected by the above-mentioned vibration detection unit, and comparing the simple diagnosis value with a specified threshold value, thereby performing a simple diagnosis of the above-mentioned bearing; and a precise diagnosis unit, which changes the rotational speed of the above-mentioned bearing to the above-mentioned precise diagnosis speed, calculates the damage frequency generated when the above-mentioned bearing is damaged based on the rotational speed detected by the above-mentioned rotational speed detection unit, and compares the damage frequency with the frequency components contained in the spectrum data obtained based on the vibration detected by the above-mentioned vibration detection unit, thereby performing a precise diagnosis of the above-mentioned bearing, and only when the abnormality of the bearing is detected by the above-mentioned simple diagnosis unit, the change of the rotational speed of the bearing and the precise diagnosis based on the above-mentioned precise diagnosis unit are performed.

[0011] The diagnostic speed setting unit in the above-mentioned configuration 1 or 2 is capable of setting the precision diagnostic speed based on the number of vibration events per unit time detected by the vibration detection unit (configuration 3). In addition to this configuration 3, the diagnostic speed setting unit preferably includes an event count confirmation unit that confirms whether a pre-assumed number of vibration events per unit time has been achieved during the precision diagnosis (configuration 4). Furthermore, the event count confirmation unit in this configuration 4 preferably estimates the number of vibration events per unit time during the precision diagnosis based on the damage frequency generated when the bearing is damaged (configuration 5).

[0012] Alternatively, as the diagnosis speed setting means in the configuration 1 or 2, a configuration can be adopted in which the precise diagnosis speed is set based on a total value of vibrations detected by the vibration detection means (configuration 6).

[0013] In addition, based on any one of the above-mentioned structures 1 to 6, the following structure can also be adopted, namely: it is also provided with an external force detection unit, which detects the external force loaded on the above-mentioned bearing. When the external force detected by the above-mentioned external force detection unit is less than a specified magnitude, the above-mentioned operating state judgment unit judges that the above-mentioned bearing is in a light-load operating state (structure 7).

[0014] Furthermore, the present invention, in addition to any one of the above-mentioned configurations 1 to 7, can also be effectively applied particularly to a case where the above-mentioned bearing rotatably supports a main shaft of a machine tool.

[0015] As described above, the bearing condition monitoring system of the present invention can perform precise diagnosis at a precise diagnosis speed at which the bearing has a small reduction in speed relative to the rotational speed during normal use, thereby enabling high-precision bearing diagnosis without significantly reducing the productivity of the equipment in which the bearing is assembled. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a longitudinal sectional view of a bearing to be monitored by the condition monitoring system according to the embodiment.

[0017] Figure 2 This is a conceptual diagram of a state monitoring system according to an embodiment.

[0018] Figure 3A Is the high speed rotation Figure 2 A schematic graph illustrating the number of vibration events detected by the vibration sensor of the sensor unit.

[0019] Figure 3B Is the low speed rotation Figure 2 A schematic graph illustrating the number of vibration events detected by the vibration sensor of the sensor unit.

[0020] Figure 4 It means by Figure 2 Graph showing the relationship between the total value ratio (abnormal value / normal value) of vibrations detected by the vibration sensor of the sensor unit and the bearing rotation speed. DETAILED DESCRIPTION

[0021] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Figure 1The figure shows a bearing 30 to be monitored by the condition monitoring system according to the embodiment. This bearing 30 is a deep groove ball bearing in which balls 33, serving as rolling elements, are retained by a retainer 34 between an inner ring 31 and an outer ring 32. One end of the bearing space is sealed by a seal 35, and a sensor unit 1, which forms part of the monitoring system, is mounted on the side opposite to the side sealed by seal 35. The bearing 30 rotatably supports the spindle of a machine tool (not shown).

[0022] The sensor unit 1 comprises a rotation sensor 10, which serves as a rotation speed detection unit for detecting the rotational speed of the bearing 30; a vibration sensor 20, which serves as a vibration detection unit for detecting the vibration of the bearing 30; and a load sensor 21, which serves as an external force detection unit for detecting the external force acting on the bearing 30. The rotation sensor 10 comprises a metal core 11 fitted to the outer circumference of the inner ring 31; a magnetic encoder 12 attached to the metal core 11; an outer ring 13 fitted to the inner circumference of the outer ring 32; and a sensor housing 14 attached to the outer ring 13. A Hall effect IC 15, which faces the magnetic encoder 12 and together with the magnetic encoder 12 constitutes a rotation sensor, and a printed circuit board 16 connected to the pins 15a of the Hall effect IC 15 are fixed to the sensor housing 14 using molded resin 14a. Electrical components 17, which constitute the electronic circuitry, are mounted on the printed circuit board 16. The vibration sensor 20 is an acceleration sensor that detects the vibration of the outer ring 32, which serves as a stationary ring. The portion of the load sensor 21, which utilizes a strain gauge or piezoelectric element, is incorporated into a recessed portion on the outer circumference of the outer ring 32.

[0023] like Figure 2 As shown, the state monitoring system of this embodiment comprises: a sensor part 1 (a rotation sensor 10, a vibration sensor 20 and a load sensor 21), which is arranged at the peripheral part of the above-mentioned bearing 30; an operating state judgment unit 2, which judges the operating state of the bearing 30 based on the external force detected by the load sensor 21; a diagnostic speed setting unit 3, which sets the precision diagnostic speed when performing precision diagnosis of the bearing 30 based on the rotation speed detected by the rotation sensor 10 and the vibration detected by the vibration sensor 20 when the operating state judgment unit 2 judges that the bearing 30 is in a light-load operating state; and an abnormality diagnosis unit 4, which changes the rotation speed of the bearing 30 to the precision diagnostic speed set by the diagnostic speed setting unit 3 to perform precision diagnosis of the bearing 30.

[0024] When the external force detected by the load sensor 21 (the external force applied to the bearing 30) is greater than a specified magnitude, the operating state judgment unit 2 judges that the bearing 30 is in a loaded operating state (the machine tool is processing); when the external force is less than a specified magnitude, the operating state judgment unit 2 judges that the bearing 30 is in a lightly loaded operating state (the machine tool is not processing).

[0025] The diagnosis speed setting unit 3 uses a method of setting a precise diagnosis speed based on the number of vibration events per unit time detected by the vibration sensor 20. Figure 3A 、 Figure 3B As shown, the number of vibration events (hereinafter referred to as "event number") refers to the number of peaks (black circles in the figure) observed in the waveform of the vibration value (acceleration in this example). Of course, the number of events per unit time is higher at low speeds ( Figure 3B ) than when rotating at high speed ( Figure 3A )few.

[0026] Furthermore, conventional bearing abnormality diagnosis involves detecting the peak value of the vibration waveform generated during an abnormality and performing frequency analysis (FFT) to determine the abnormality. While obtaining the required number of waveform peaks, or events, is easier at high rotation speeds, the peaks are often mixed with noise components, making it difficult to identify the characteristics and making determination difficult. Lowering the rotation speed reduces the impact of noise components, but the vibration value also decreases, making it difficult to detect the waveform peak. Furthermore, not only does the diagnostic time required to obtain the required number of events increase, but the temperature fluctuations of the spindle and bearings also increase, increasing the time required to resume machining and resulting in reduced productivity.

[0027] Therefore, in the diagnostic speed setting unit 3, the number of events required for determination is calculated based on the number of events when precise diagnosis was accurately performed in the past, and the rotation speed range in which the required number of events can be obtained within the time when precise diagnosis can be performed (for example, the interval time for workpiece replacement of a machine tool, etc.) is derived, and an appropriate speed within the rotation speed range is set as the precise diagnosis speed.

[0028] Here, the diagnostic speed setting unit 3 preferably includes an event number confirmation unit, which assumes the number of events per unit time during precise diagnosis based on the damage frequency generated when the bearing 30 is damaged, and confirms whether the pre-assumed number of events per unit time is obtained during precise diagnosis.

[0029] The abnormality diagnosis unit 4 includes: a simple diagnosis unit 4a, which performs a simple diagnosis of the bearing 30 when the bearing 30 is running at an arbitrary rotational speed; a precision diagnosis unit 4b, which changes the rotational speed of the bearing 30 to the above-mentioned precision diagnosis speed to perform a precision diagnosis of the bearing 30; and a diagnosis result output unit 4c, which outputs the diagnosis result information of the simple diagnosis unit 4a and the precision diagnosis unit 4b to the control unit 40 of the machine tool and an external device 50 such as a personal computer and a server. Only when an abnormality of the bearing 30 is detected by the simple diagnosis unit 4a, the rotational speed of the bearing 30 is changed and a precision diagnosis is performed based on the precision diagnosis unit 4b.

[0030] The simple diagnostic unit 4a calculates at least one simple diagnostic value based on the vibration waveform detected by the vibration sensor 20 and compares the simple diagnostic value with a predetermined threshold value to diagnose the bearing 30. For example, the time change rate of the effective value of the vibration waveform data can be used as the simple diagnostic value.

[0031] Meanwhile, precision diagnosis unit 4b changes the rotational speed of bearing 30 to the aforementioned precision diagnosis speed (outputting speed change information to machine tool control unit 40). Based on the rotational speed detected by rotation sensor 10, it calculates the damage frequency generated when bearing 30 is damaged. This damage frequency is then compared with the frequency components included in the spectrum data obtained from the vibration detected by vibration sensor 20, thereby diagnosing bearing 30. A specific diagnostic method, for example, can be employed: within the spectrum data (horizontal axis: vibration frequency, vertical axis: vibration level) obtained by envelope processing and frequency analysis of the vibration waveform, the frequency at which the peak of the vibration level appears is compared with the damage frequency of each component of bearing 30. If a match is found, it is determined that the component corresponding to the matching damage frequency has an abnormality.

[0032] The condition monitoring system has the above-mentioned structure. Only when the simple diagnosis unit 4a included in the abnormality diagnosis unit 4 detects an abnormality in the bearing 30, the precision diagnosis unit 4b reduces the rotational speed of the bearing 30 to an appropriate precision diagnosis speed within the speed range that can obtain the number of events that can accurately determine the abnormality and performs precision diagnosis on this basis. Therefore, the precision diagnosis speed can be set as high as possible (for example, the speed reduction of the bearing 30 relative to the rotational speed in normal use is minimized), and high-precision diagnosis can be performed without significantly reducing productivity.

[0033] Furthermore, the diagnosis speed setting unit 3 can set the precision diagnosis speed using a method based on the total value (OA (overall) value) of vibration detected by the vibration sensor 20, in addition to the method based on the number of events per unit time described above. Specifically, Figure 4 As shown, the ratio of the OA value of the bearing that has an abnormality to the OA value of the vibration of the bearing in a normal state (OA value ratio) varies according to the rotation speed. Therefore, the OA value of the bearing 30 in a normal state is pre-stored. When the bearing 30 is used, the rotation speed at which the OA value ratio of the bearing 30 that has an abnormality can be obtained at the corresponding rotation speed is determined as the precise diagnostic speed.

[0034] That is, generally, if an abnormality occurs in a bearing, the OA value ratio becomes greater than 1 due to the influence of the abnormal vibration component. However, in the high-speed rotation range, this abnormal vibration component (peak that coincides with the damage frequency) is mixed with the noise, and the OA value ratio becomes a value close to 1. Therefore, in the rotation speed that is not affected by noise and the OA value ratio is higher than 1 by a certain degree, the rotation speed at which the speed is reduced to the minimum relative to the rotation speed in normal use is set as the precision diagnosis speed (at Figure 4 Even with this method, high-precision diagnosis can be performed at the highest possible precision diagnostic speed. This method is also effective when gradually increasing the spindle speed to the normal operating speed, such as when starting a machine tool.

[0035] In addition, as a variation of the above-mentioned embodiment, the following structure can also be adopted, namely: the load sensor 21 serving as the external force detection unit in the sensor section 1 around the bearing 30 is omitted, and the operating state judgment unit 2 distinguishes between the loaded operating state and the light-load operating state based on information from the sensors possessed by the machine tool itself, or obtains information on non-machining timing from the sequence program of the machine tool and judges it as the light-load operating state.

[0036] The embodiments disclosed herein are to be considered in all respects as illustrative and non-restrictive. The scope of the present invention is indicated by the scope of the present application rather than the above description, and is intended to include all modifications within the meaning and scope equivalent to the scope of the present application.

[0037] For example, in the simple diagnosis of the abnormality diagnosis unit of the embodiment, abnormality judgment is performed by comparing the simple diagnosis value with the threshold value, but as long as the rotation speed of the bearing in normal use is within the allowable range that can implement FFT, even simple diagnosis can perform abnormality judgment based on FFT.

[0038] Furthermore, the simplified diagnosis unit in the abnormality diagnosis unit of the embodiment can be omitted, and precise diagnosis can be performed periodically or at an arbitrary timing.

[0039] Furthermore, the present invention can be particularly effectively applied to a case where a bearing rotatably supports a main spindle of a machine tool as in the embodiment, but is not limited thereto and is widely applicable to a condition monitoring system for bearings used at high rotation speeds.

[0040] Description of Reference Numerals

[0041] 1…Sensor unit; 2…Operation status determination unit; 3…Diagnostic speed setting unit; 4…Abnormality diagnosis unit; 4a…Simple diagnosis unit; 4b…Precision diagnosis unit; 4c…Diagnostic result output unit; 10…Rotation sensor (rotation speed detection unit); 20…Vibration sensor (vibration detection unit); 21…Load sensor (external force detection unit); 30…Bearing.

Claims

1. A bearing condition monitoring system, characterized in that: have: a rotation speed detection unit, for detecting the rotation speed of the bearing; a vibration detection unit, detecting vibration of the bearing; an operating state judging unit for judging whether the bearing is in a loaded operating state or a lightly loaded operating state; a diagnosis speed setting unit for setting a precision diagnosis speed when performing precision diagnosis of the bearing based on the rotation speed detected by the rotation speed detection unit and the vibration detected by the vibration detection unit when the operating state determination unit determines that the bearing is in a light-load operating state; as well as The abnormality diagnosis unit changes the rotational speed of the bearing to the precise diagnosis speed set by the diagnosis speed setting unit to perform precise diagnosis of the bearing.

2. The bearing condition monitoring system according to claim 1, characterized in that: The abnormality diagnosis unit includes: a simple diagnosis unit that calculates at least one simple diagnosis value based on the waveform of the vibration detected by the vibration detection unit when the bearing is running at an arbitrary rotational speed, and compares the simple diagnosis value with a predetermined threshold value, thereby performing a simple diagnosis of the bearing; and A precision diagnosis unit changes the rotational speed of the bearing to the precision diagnosis speed, calculates a damage frequency generated when the bearing is damaged based on the rotational speed detected by the rotational speed detection unit, and compares the damage frequency with a frequency component included in spectrum data obtained from the vibration detected by the vibration detection unit, thereby performing precision diagnosis of the bearing. Only when the simple diagnosis unit detects an abnormality in the bearing, the rotational speed of the bearing is changed and a precise diagnosis is performed by the precise diagnosis unit.

3. The bearing condition monitoring system according to claim 1 or 2, characterized in that: The diagnosis speed setting unit sets the precise diagnosis speed based on the number of vibration events per unit time detected by the vibration detection unit.

4. The bearing condition monitoring system according to claim 3, characterized in that: The diagnosis speed setting unit includes an event number confirmation unit that confirms whether a predetermined number of vibration events per unit time is obtained during the precise diagnosis.

5. The bearing condition monitoring system according to claim 4, characterized in that: The event number confirmation unit estimates the number of vibration events per unit time during the precise diagnosis based on a damage frequency generated when the bearing is damaged.

6. The bearing condition monitoring system according to claim 1 or 2, characterized in that: The diagnosis speed setting unit sets the precise diagnosis speed based on a total value of vibrations detected by the vibration detection unit.

7. The bearing condition monitoring system according to any one of claims 1 to 6, characterized in that: Also features: An external force detection unit detects the external force applied to the bearing. When the external force detected by the external force detection unit is smaller than a predetermined magnitude, the operating state determination unit determines that the bearing is in a light-load operating state.

8. The bearing condition monitoring system according to any one of claims 1 to 7, characterized in that: The bearing rotatably supports a main shaft of a machine tool.

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