JP7515645B1 - Bearing condition monitoring system - Google Patents

Abstract

[Problem] To provide a condition monitoring system capable of accurately diagnosing abnormalities in bearings used at high rotational speeds without significantly reducing the productivity of equipment in which the bearings are installed. [Solution] The system comprises a sensor unit 1 that detects the rotational speed and vibration of the bearing and the external force applied to the bearing, an operating state determination means 2 that determines the operating state of the bearing based on the external force detected by the sensor unit 1, a diagnosis speed setting means 3 that sets a precision diagnosis speed for performing a precision diagnosis of the bearing based on 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 a lightly loaded operating state, and an abnormality diagnosis means 4 that changes the rotational speed of the bearing to the precision diagnosis speed and performs a precision diagnosis of the bearing, so that a precision diagnosis is performed at an appropriate precision diagnosis speed that suppresses a decrease in bearing speed. [Selected Figure] Figure 2

Description

The present invention relates to a condition monitoring system for bearings used at high rotational speeds, such as bearings that support the spindles of machine tools.

Bearings that support the main spindles of machine tools are often used at high rotational speeds of tens of thousands of revolutions per minute. In order to detect damage to such machine tool bearings early, condition monitoring systems that detect bearing vibrations and diagnose abnormalities are increasingly being attached (see, for example, Patent Document 1).

JP 2009-20090 A

However, in bearings used at high rotational speeds, noise including base vibrations caused by the rotation of the main shaft and wind noise caused by the spraying of lubricating oil is distributed over a wide frequency band, making it difficult to separate the vibration components caused by this noise from those caused by damage to the bearing. For this reason, in order 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.

One way to deal with this is to reduce the rotational speed of the spindle when diagnosing abnormalities using a condition monitoring system, but if the bearings used are angular ball bearings, tapered roller bearings, or cylindrical roller bearings that are preloaded in a fixed position, the preload load and rolling element load are small, so as the rotational speed decreases, the vibration emitted by the bearings themselves becomes weaker, making it difficult to accurately detect damage to the spindle or bearings.

In addition, in the case of machine tools that are primarily used in the high rotational speed range, if the rotational speed is reduced to a low speed range to diagnose an abnormality, the temperature change in the spindle and bearings will be large, and it will take time to recover to the temperature equilibrium state at the original rotational speed, resulting in a significant decrease in productivity.

The present invention aims to provide a condition monitoring system that can accurately diagnose abnormalities in bearings used at high rotational speeds without significantly reducing the productivity of the equipment in which the bearings are installed.

In order to solve the above problems, the present invention employs a configuration (configuration 1) for a bearing condition monitoring system, comprising: a rotational speed detection means for detecting the rotational speed of the bearing; a vibration detection means for detecting the vibration of the bearing; an operating state determination means for determining whether the bearing is in a loaded operating state or a light-load operating state; a diagnosis speed setting means for setting a precision diagnosis speed for performing a precision diagnosis of the bearing based on the rotational speed detected by the rotational speed detection means and the vibration detected by the vibration detection means when the operating state determination means determines that the bearing is in a light-load operating state; and an abnormality diagnosis means for changing the rotational speed of the bearing to the precision diagnosis speed set by the diagnosis speed setting means and performing a precision diagnosis of the bearing.

According to the above configuration 1, the diagnostic speed setting means uses the rotational speed and vibration data of the bearing in a light-load operating state to set an appropriate precision diagnostic speed that minimizes any speed reduction from the rotational speed at which the bearing is normally used, and the abnormality diagnosis means performs a precision diagnosis at that precision diagnostic speed, so that it is possible to perform accurate abnormality diagnosis of the bearing without significantly reducing the productivity of the equipment in which the bearing is installed.

In the above configuration 1, the abnormality diagnosis means may include a simple diagnosis means for performing a simple diagnosis of the bearing by calculating at least one simple diagnosis value from the waveform of the vibration detected by the vibration detection means when the bearing is operating at an arbitrary rotation speed and comparing the simple diagnosis value with a predetermined threshold value, and a precision diagnosis means for performing a precision diagnosis of the bearing by changing the rotation speed of the bearing to the precision diagnosis speed, calculating a damage frequency that occurs when the bearing is damaged based on the rotation speed detected by the rotation speed detection means, and comparing the damage frequency with a frequency component included in the spectrum data obtained from the vibration detected by the vibration detection means, and changing the rotation speed of the bearing and performing a precision diagnosis by the precision diagnosis means only when an abnormality in the bearing is detected by the simple diagnosis means (configuration 2).

The diagnostic speed setting means in the above configuration 1 or 2 can set the precision diagnosis speed based on the number of vibration events per unit time detected by the vibration detection means (Configuration 3). In this configuration 3, it is preferable that the diagnostic speed setting means includes an event number confirmation means for confirming whether a predetermined number of vibration events per unit time is obtained during the precision diagnosis (Configuration 4). Furthermore, it is preferable that the event number confirmation means in this configuration 4 assumes the number of vibration events per unit time during the precision diagnosis based on a damage frequency that occurs when the bearing is damaged (Configuration 5).

Alternatively, the diagnostic speed setting means in the above configuration 1 or 2 can be one that sets the precision diagnostic speed based on the overall value of the vibration detected by the vibration detection means (configuration 6).

In addition, in any of the above configurations 1 to 6, a configuration can be adopted in which an external force detection means is further provided for detecting an external force applied to the bearing, and the operating state determination means determines that the bearing is in a light load operating state when the external force detected by the external force detection means is less than a predetermined magnitude (configuration 7).

And in any of the above configurations 1 to 7, the present invention can be particularly effectively applied when the bearing rotatably supports the main shaft of a machine tool.

As described above, the bearing condition monitoring system of the present invention performs precision diagnosis at a precision diagnosis speed that results in minimal speed reduction from the rotational speed of the bearing during normal use, making it possible to perform highly accurate bearing diagnosis without significantly reducing the productivity of the equipment in which the bearing is installed.

FIG. 1 is a vertical cross-sectional view of a bearing to be monitored by a condition monitoring system according to an embodiment of the present invention. Conceptual diagram of a state monitoring system according to an embodiment 3A and 3B are schematic graphs for explaining the number of vibration events detected by the vibration sensor of the sensor unit in FIG. 2, where A is the graph during high-speed rotation and B is the graph during low-speed rotation. Graph showing the relationship between the overall value ratio (abnormal value/normal value) of vibration detected by the vibration sensor of the sensor unit in FIG. 2 and the bearing rotation speed

The following describes an embodiment of the present invention with reference to the drawings. Figure 1 shows a bearing 30 that is the subject of monitoring by the condition monitoring system of the embodiment. This bearing 30 is a deep groove ball bearing in which balls 33 as rolling elements are held by a cage 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 that constitutes part of the monitoring system is attached to the side opposite the side sealed by the seal 35, and the bearing 30 rotatably supports the spindle of a machine tool (not shown).

The sensor unit 1 is composed of a rotation sensor 10 as a rotation speed detection means for detecting the rotation speed of the bearing 30, a vibration sensor 20 as a vibration detection means for detecting the vibration of the bearing 30, and a load sensor 21 as an external force detection means for detecting the external force applied to the bearing 30. The rotation sensor 10 is equipped with a core 11 fitted to the outer peripheral surface of the inner ring 31, a magnetic encoder 12 attached to the core 11, an outer ring 13 fitted to the inner peripheral surface of the outer ring 32, and a sensor housing 14 attached to the outer ring 13. The sensor housing 14 is fixed with molded resin 14a with a Hall IC 15 that faces the magnetic encoder 12 and constitutes a rotation sensor together with the magnetic encoder 12, and a printed circuit board 16 connected to the leg 15a of the Hall IC 15. An electric component 17 that constitutes an electronic circuit is attached to the printed circuit board 16. The vibration sensor 20 is an acceleration sensor and is designed to detect the vibration of the outer ring 32, which is a fixed ring. The load sensor 21 uses a strain gauge or a piezoelectric element and is embedded in a recess on the outer periphery of the outer ring 32.

As shown in FIG. 2, the condition monitoring system of this embodiment includes a sensor unit 1 (rotation sensor 10, vibration sensor 20, and load sensor 21) provided around the aforementioned bearing 30, an operating state determination means 2 that determines the operating state of the bearing 30 based on the external force detected by the load sensor 21, a diagnostic speed setting means 3 that sets a precision diagnosis speed for performing a 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 determination means 2 determines that the bearing 30 is in a light load operating state, and an abnormality diagnosis means 4 that changes the rotation speed of the bearing 30 to the precision diagnosis speed set by the diagnostic speed setting means 3 and performs a precision diagnosis of the bearing 30.

The operating state determination means 2 determines that the bearing 30 is in a loaded operating state (the machine tool is processing) when the external force (external force applied to the bearing 30) detected by the load sensor 21 is equal to or greater than a predetermined magnitude, and determines that the bearing 30 is in a light-load operating state (the machine tool is not processing) when the external force is less than the predetermined magnitude.

The diagnostic speed setting means 3 uses a method of setting the precision diagnostic speed based on the number of vibration events per unit time detected by the vibration sensor 20. The number of vibration events (hereinafter simply referred to as the "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), as shown in Figures 3(a) and (b), and the number of events per unit time is naturally less during low-speed rotation (Figure 3(b)) than during high-speed rotation (Figure 3(a)).

In general bearing abnormality diagnosis, the vibration waveform peaks that occur when an abnormality occurs are detected and frequency analysis (FFT) is performed to determine whether an abnormality exists. During high-speed rotation, the number of waveform peaks required for judgment, i.e. the number of events, is easy to obtain, but the peaks are often hidden by noise components, making it difficult to find their characteristics and making a judgment. In contrast, if the rotation speed is reduced, the influence of noise components is reduced, but the vibration value also decreases, making it difficult to detect the waveform peaks. Also, the diagnosis time required to obtain the number of events required for judgment increases, and the temperature changes in the spindle and bearings increase, making it take longer to resume machining, resulting in reduced productivity.

The diagnostic speed setting means 3 calculates the number of events required for judgment based on the number of events when a precision diagnosis was performed correctly in the past, derives a rotational speed range that can obtain the required number of events within the time in which a precision diagnosis can be performed (for example, the interval time for changing a workpiece in a machine tool), and sets an appropriate speed within that rotational speed range as the precision diagnosis speed.

Here, it is preferable that the diagnostic speed setting means 3 includes an event number confirmation means for estimating the number of events per unit time during precision diagnosis based on the damage frequency that occurs when the bearing 30 is damaged, and for confirming whether the previously estimated number of events per unit time is obtained during precision diagnosis.

The abnormality diagnosis means 4 includes a simple diagnosis means 4a that performs a simple diagnosis of the bearing 30 when the bearing 30 is operating at an arbitrary rotation speed, a precise diagnosis means 4b that changes the rotation speed of the bearing 30 to the precise diagnosis speed described above and performs a precise diagnosis of the bearing 30, and a diagnosis result output unit 4c that outputs the diagnosis result information of the simple diagnosis means 4a and the precise diagnosis means 4b to the control unit 40 of the machine tool and an external device 50 such as a personal computer or server. Only when an abnormality in the bearing 30 is detected by the simple diagnosis means 4a, is the precise diagnosis means 4b used to change the rotation speed of the bearing 30 and perform a precise diagnosis.

The simplified diagnostic means 4a calculates at least one simplified diagnostic value from the vibration waveform detected by the vibration sensor 20, and diagnoses the bearing 30 by comparing the simplified diagnostic value with a predetermined threshold value. The simplified diagnostic value can be, for example, the rate of change over time of the effective value of the vibration waveform data.

On the other hand, the precision diagnosis means 4b changes the rotation speed of the bearing 30 to the precision diagnosis speed (outputs speed change information to the control unit 40 of the machine tool), calculates the damage frequency that occurs when the bearing 30 is damaged based on the rotation speed detected by the rotation sensor 10, and diagnoses the bearing 30 by comparing the damage frequency with the frequency components contained in the spectrum data obtained from the vibration detected by the vibration sensor 20. As a specific diagnosis method, for example, a method can be adopted in which the frequency at which the vibration level peak appears in the spectrum data (horizontal axis: vibration frequency, vertical axis: vibration level) resulting from frequency analysis of the vibration waveform after envelope processing is compared with the damage frequency of each part of the bearing 30, and if there is a match, it is determined that the part corresponding to the matching damage frequency is abnormal.

This condition monitoring system has the above-mentioned configuration, and only when an abnormality in the bearing 30 is detected by the simple diagnosis means 4a included in the abnormality diagnosis means 4, the precise diagnosis means 4b performs a precise diagnosis after lowering the rotation speed of the bearing 30 to an appropriate precise diagnosis speed within the speed range where the number of events that can be accurately determined to be abnormal is obtained. Therefore, by setting the precise diagnosis speed as high as possible (for example, so that the speed reduction from the rotation speed of the bearing 30 during normal use is minimized), it is possible to perform a highly accurate diagnosis without significantly reducing productivity.

The precise diagnosis speed can be set by the diagnosis speed setting means 3 based on the number of events per unit time as described above, or based on the overall value (OA value) of the vibration detected by the vibration sensor 20. Specifically, as shown in FIG. 4, the ratio of the OA value of a bearing in an abnormal state to the OA value of the vibration of a bearing in a normal state (OA value ratio) varies depending on the rotation speed. Therefore, the OA value of a bearing 30 in a normal state is stored in advance, and the rotation speed at which the OA value ratio of a bearing 30 in an abnormal state is obtained at the corresponding rotation speed during the use of the bearing 30 is identified and used as the precise diagnosis speed.

In other words, generally, when an abnormality occurs in a bearing, the OA value ratio becomes 1 or more due to the influence of abnormal vibration components. However, at high speed rotational speeds, the abnormal vibration components (peaks corresponding to the damage frequency) blend in with the noise, and the OA value ratio indicates a value close to 1. Therefore, the precision diagnosis speed is the rotational speed at which the OA value ratio is somewhat higher than 1 without being affected by noise, and at which the speed drop from the rotational speed during normal use is minimized (in Figure 4, this is medium to high speed rotation). Even with this method, accurate diagnosis can be performed at as high a precision diagnosis speed as possible. This method is also effective when gradually increasing the spindle rotational speed to the normal rotational speed, such as when starting up a machine tool.

As a modification of the above-mentioned embodiment, the load sensor 21 as an external force detection means may be omitted from the sensor section 1 around the bearing 30, and the operating state determination means 2 may be configured to distinguish between a loaded operating state and a light-load operating state based on information from a sensor provided in the machine tool itself, or to obtain information on non-machining timing from the sequence program of the machine tool and determine that the machine tool is in a light-load operating state.

The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is indicated by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims.

For example, in the simplified diagnosis in the abnormality diagnosis means of the embodiment, abnormality determination is performed by comparing the simplified diagnosis value with a threshold value, but if the rotational speed of the bearing during normal use is within an allowable range in which FFT can be performed, abnormality determination using FFT may also be performed in the simplified diagnosis.

In addition, the simplified diagnosis means of the abnormality diagnosis means of the embodiment can be omitted, and a detailed diagnosis can be performed periodically or at any timing.

The present invention is particularly effective when the bearing rotatably supports the spindle of a machine tool, as in the embodiment, but is not limited to this and can be widely applied to condition monitoring systems for bearings used at high rotational speeds.

1 Sensor section 2 Operating state determination means 3 Diagnostic speed setting means 4 Abnormality diagnosis means 4a Simple diagnosis means 4b Precision diagnosis means 4c Diagnostic result output section 10 Rotation sensor (rotation speed detection means)
20 Vibration sensor (vibration detection means)
21 Load sensor (external force detection means)
30 Bearing

Claims (8)

In bearing condition monitoring systems,
a rotational speed detection means for detecting a rotational speed of the bearing;
a vibration detection means for detecting vibration of the bearing;
an operating state determination means for determining whether the bearing is in a loaded operating state or a light loaded operating state;
a diagnosis speed setting means for setting a precision diagnosis speed for performing a precision diagnosis of the bearing, based on the rotational speed detected by the rotational speed detection means and the vibration detected by the vibration detection means when the operating state determination means determines that the bearing is in a light load operating state;
a diagnosis speed setting means for setting the rotational speed of the bearing to a precision diagnosis speed set by the diagnosis speed setting means, thereby performing a precision diagnosis of the bearing; The abnormality diagnosis means includes:
simple diagnosis means for performing a simple diagnosis of the bearing by calculating at least one simple diagnosis value from a waveform of vibration detected by the vibration detection means when the bearing is operated at a given rotational speed and comparing the simple diagnosis value with a predetermined threshold value;
a precision diagnosis means for performing a precision diagnosis of the bearing by changing the rotation speed of the bearing to the precision diagnosis speed, calculating a damage frequency that will occur when the bearing is damaged based on the rotation speed detected by the rotation speed detection means, and comparing the damage frequency with a frequency component contained in spectrum data obtained from the vibration detected by the vibration detection means,
2. A bearing condition monitoring system according to claim 1, wherein said precise diagnosis means changes the rotational speed of the bearing and performs a precise diagnosis only when said simple diagnosis means detects an abnormality in the bearing. The bearing condition monitoring system according to claim 1 or 2, characterized in that the diagnostic speed setting means sets the precision diagnostic speed based on the number of vibration events per unit time detected by the vibration detection means. The bearing condition monitoring system according to claim 3, characterized in that the diagnostic speed setting means includes an event number confirmation means for confirming whether a predetermined number of vibration events per unit time is obtained during the detailed diagnosis. The bearing condition monitoring system according to claim 4, characterized in that the event number confirmation means estimates the number of vibration events per unit time during the precision diagnosis based on the damage frequency that occurs when the bearing is damaged. The bearing condition monitoring system according to claim 1 or 2, characterized in that the diagnostic speed setting means sets the precision diagnostic speed based on an overall value of the vibration detected by the vibration detection means. Further, an external force detection means for detecting an external force applied to the bearing is provided.
3. A bearing condition monitoring system as claimed in claim 1 or 2, characterized in that the operating state determination means determines that the bearing is in a light load operating state when the external force detected by the external force detection means is less than a predetermined magnitude. The bearing condition monitoring system according to claim 1 or 2, characterized in that the bearing rotatably supports a main shaft of a machine tool.

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