Bearing condition monitoring system

Abstract

The present invention provides a condition monitoring system for a bearing, wherein the condition monitoring system comprises: an operating condition determination device (2) for determining an operating condition of the bearing based on an external force detected by a sensor unit (1); a diagnostic speed setting device (3) for setting a detailed diagnostic speed based on the rotational speed and vibration of the bearing detected by the sensor unit (1) when the operating condition determination device (2) determines that the bearing is in a lightly loaded operating condition; and an abnormality diagnostic device (4) for changing the rotational speed of the bearing to a detailed diagnostic speed and for performing a detailed diagnosis of the bearing.

Description

Technical field

[0001] The present invention relates to a condition monitoring system for a bearing used at high speeds, for example a bearing that supports the main shaft of a machine tool. State of the art

[0002] A bearing that supports the main shaft of a machine tool is often used at high speeds, for example, several tens of thousands of revolutions per minute. Condition monitoring systems are increasingly being installed in such machine tool bearings to diagnose anomalies by recording bearing vibrations in order to detect damage at an early stage (see patent document 1 cited below). State of the art document(s) Patent document(s)

[0003] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2009-20090 Summary of the invention; Problems to be solved by the invention

[0004] However, in bearings operating at high speeds, the fundamental vibrations and noises caused by the rotation of the main shaft, including wind noise from lubricating oil blowout, are distributed across a wide frequency band. This makes it difficult to separate the vibration components caused by such noise from those caused by bearing damage. Therefore, to accurately diagnose anomalies with the condition monitoring system, it is necessary to use vibration data acquired at speeds where the noise-related vibration components are less pronounced.

[0005] As a countermeasure, reducing the main shaft speed when diagnosing anomalies with the condition monitoring system is being considered. However, if a bearing with a fixed preload is used, such as an angular contact ball bearing, a tapered roller bearing, or a cylindrical roller bearing, the preload or rolling element load is low. Consequently, the vibration level emitted by the bearing decreases with decreasing speed, making accurate detection of damage to the main shaft and bearing more difficult.

[0006] Furthermore, in machine tools primarily used at high speeds, reducing the speed to a lower range leads to increased temperature fluctuations in the main shaft and bearings. Consequently, additional time is required to return to thermal equilibrium at the original high speed, resulting in a significant decrease in productivity.

[0007] In light of the foregoing, an objective of the present invention is to provide a condition monitoring system capable of accurately diagnosing anomalies of a bearing used at high speeds without significantly reducing the productivity of a plant in which the bearing is installed. Means to solve the problems

[0008] To achieve the aforementioned objective, the present invention provides a condition monitoring system for a bearing, wherein the condition monitoring system comprises: a speed sensing device for detecting a rotational speed of the bearing; a vibration sensing device for detecting a vibration of the bearing; an operating state determination device for determining whether the bearing is in a loaded operating state or a lightly loaded operating state; a diagnostic speed setting device for setting a detailed diagnostic speed when a detailed diagnosis of the bearing is performed, based on the rotational speed detected by the speed sensing device and the vibration detected by the vibration sensing device when the bearing is determined by the operating state determination device to be in a lightly loaded operating state;and an abnormality diagnostic device for changing the rotational speed of the bearing to the detailed diagnostic speed set by the diagnostic speed setting device and for performing a detailed diagnosis of the bearing (arrangement 1).;

[0009] With arrangement 1, the diagnostic speed setting device sets a suitable detailed diagnostic speed that reduces the speed drop from the bearing's normally used speed, using data on speed and vibration in the lightly loaded operating condition of the bearing. The abnormality diagnostic device then performs the detailed diagnosis at this detailed diagnostic speed. Accordingly, the bearing fault diagnosis can be carried out accurately without significantly reducing the productivity of the plant in which the bearing is installed.

[0010] In arrangement 1, an arrangement 2 can be used wherein the abnormality diagnostic device comprises a simple diagnostic device for performing a simple diagnosis of the bearing by (i) calculating at least one simple diagnostic value from a waveform of the vibration detected by the vibration detection device when the bearing is running at any rotational speed, and (ii) comparing the at least one simple diagnostic value with a predetermined limit value;and a detailed diagnostic device for changing the rotational speed of the bearing to the detailed diagnostic speed and for performing the detailed diagnosis of the bearing by (i) calculating a damage frequency that occurs when the bearing is damaged, based on the rotational speed detected by the speed detection device, and (ii) comparing the damage frequency with a frequency component contained in spectral data obtained from the vibration detected by the vibration detection device, wherein the change in the rotational speed of the bearing and the detailed diagnosis of the bearing by the detailed diagnostic device are to be performed only when an anomaly of the bearing is detected by the simple diagnostic device.

[0011] In arrangement 1 or 2, an arrangement 3 can be used in which the diagnostic speed setting device is configured to set the detailed diagnostic speed based on the number of vibration events per unit of time detected by the vibration detection device. Arrangement 3 can also use an arrangement 4 in which the diagnostic speed setting device preferably includes an event count confirmation device for verifying whether a preliminary estimated number of vibration events per unit of time is obtained during the detailed diagnosis. Furthermore, arrangement 4 can use an arrangement 5 in which the event count confirmation device is configured to estimate the number of vibration events per unit of time during the detailed diagnosis based on the damage frequency that occurs when the bearing is damaged.

[0012] Alternatively, in arrangement 1 or 2, an arrangement 6 can be used in which the diagnostic speed setting device is configured to set the detailed diagnostic speed based on an overall value of the vibration detected by the vibration detection device.

[0013] Additionally, in each of arrangements 1 to 6, an arrangement 7 can be used, wherein the condition monitoring system further comprises an external force sensing device for detecting an external force exerted on the bearing, wherein the operating state determination device is configured to determine that the bearing is in a lightly loaded operating state when the external force detected by the external force sensing device is less than a predetermined value.

[0014] Furthermore, the present invention can be particularly effectively applied in each of the arrangements 1 to 7 if the bearing rotatably supports a main shaft of a machine tool. Effects of the invention

[0015] As described above, the condition monitoring system according to the present invention performs the detailed diagnosis at a detailed diagnostic speed that is only slightly below the rotational speed during normal use of the bearing.

[0016] Accordingly, highly accurate bearing diagnostics can be performed without significantly reducing the productivity of the plant in which the bearing is installed. Brief description of the drawings Fig. Figure 1 is a longitudinal sectional view of the bearing that is the subject of condition monitoring by the condition monitoring system according to one embodiment. Fig. Figure 2 is a conceptual diagram of the condition monitoring system according to the embodiment. Fig. 3A is a schematic diagram showing the number of vibration events detected by the vibration sensor of the Fig. The sensor unit shown in section 2 can be detected during a high-speed rotation. Fig. 3B is a schematic diagram showing the number of vibration events detected by the vibration sensor of the Fig. The sensor unit shown in point 2 can be detected during a slow rotation. Fig. 4 is a diagram showing the relationship between the total value ratios (i.e., a value in an abnormal state / a value in a normal state) of the vibrations measured by the vibration sensor of the Fig. The sensor unit shown in point 2 detects the bearing speed. Best embodiment of the invention

[0017] One embodiment of the present invention is described below with reference to the accompanying drawings. Fig. Figure 1 shows a bearing 30, which is to be monitored by a condition monitoring system according to the embodiment. The bearing 30 is a deep groove ball bearing in which balls 33 are held as rolling elements by a cage 34 between an inner ring 31 and an outer ring 32, one end of the bearing chamber is sealed with a seal 35, and a sensor unit 1, which forms part of the condition monitoring system, is attached to the side of the bearing opposite the side sealed by the seal 35. The bearing 30 serves for the rotatable support of the main shaft of a machine tool (not shown).

[0018] The sensor unit 1 comprises a rotation sensor 10 as a rotational speed detection device for detecting the rotational speed of the bearing 30, a vibration sensor 20 as a vibration detection device for detecting vibration of the bearing 30, and a load sensor 21 as an external force detection device for detecting an external force exerted on the bearing 30. The rotation sensor 10 comprises a metal core 11 attached to the outer circumferential surface of the inner ring 31, a magnetic encoder 12 mounted on the metal core 11, an outer annular element 13 attached to the inner circumferential surface of the outer ring 32, and a sensor housing 14 mounted on the outer annular element 31.A Hall-effect IC 15, which is opposite the magnetic encoder 12 and together with the magnetic encoder 12 forms the rotation sensor, and a printed circuit board 16, which is connected to a leg 15a of the Hall-effect IC 15, are attached to the sensor housing 14 by means of a molded resin 14a. An electrical component 17, which forms an electronic circuit, is attached to the printed circuit board 16. In addition, the vibration sensor 20 is an accelerometer and is configured to detect vibrations of the outer ring 32, which is the stationary ring. The load sensor 21, in which a strain gauge or a piezoelectric element is used, is arranged in a recess formed in the outer circumference of the outer ring 32.

[0019] As in Fig. As shown in Figure 2, the condition monitoring system of this embodiment comprises the sensor unit 1 (i.e., the rotation sensor 10, the vibration sensor 20, and the load sensor 21) arranged on the circumferential section of the bearing 30; an operating condition determination device 2 for determining the operating condition of the bearing 30 based on the external force detected by the load sensor 21; a diagnostic speed setting device 3 for setting a detailed diagnostic speed when a detailed diagnosis of the bearing 30 is performed, based on the rotational speed detected by the rotation sensor 10 and the vibration detected by the vibration sensor 20, when the bearing 30 is determined by the operating condition determination device 2 to be in a lightly loaded operation;and an abnormality diagnostic device 4 for changing the rotational speed of the bearing 30 to the detailed diagnostic speed set by the diagnostic speed setting device 3 and for performing a detailed diagnosis of the bearing 30.;

[0020] The operating state determination device 2 is configured to (i) determine that the bearing 30 is in a loaded operating state (i.e., the machine tool is in a machining state) when the external force detected by the load sensor 21 (i.e., the external force exerted on the bearing 30) is equal to or greater than a predetermined quantity; and (ii) determine that the bearing 30 is in a lightly loaded operating state (i.e., the machine tool is in a non-machining state) when the external force is less than the predetermined quantity.

[0021] The diagnostic speed setting device 3 is configured to set a detailed diagnostic speed based on the number of vibration events per unit of time detected by the vibration sensor 20. The number of vibration events (hereinafter referred to simply as the "number of events") means, as described in the Fig. 3A and Fig. Figure 3B shows the number of peaks (black circles in the figures) observed in the waveform of the oscillation value (in this example, the acceleration). It is not surprising that the number of events per unit time at low rotational speed ( Fig. 3B) is lower than at high speed ( Fig. 3A).

[0022] In the general diagnosis of bearing abnormalities, the abnormality is determined by identifying peaks in the vibration waveform occurring under abnormal conditions and analyzing them using frequency analysis (FFT). While the number of peaks, i.e., the number of events, in the waveform required for diagnosis can be easily determined during high-speed rotation, situations often arise where the peaks are obscured by noise components, making it impossible to extract their features and thus complicating the diagnosis. Conversely, while the influence of noise components decreases when the rotational speed is reduced, the vibration amplitude also becomes smaller, making peak detection in the waveform difficult.Furthermore, a longer diagnostic time is required to obtain the necessary number of events for determination, and temperature fluctuations in the main shaft or bearing increase. Consequently, more time is needed before machining can be resumed, leading to a reduction in productivity.

[0023] In light of the foregoing, the diagnostic speed setting device 3 is configured to (i) calculate the number of events required for the determination, for example, based on the number of events in past cases where the detailed diagnosis was successfully performed; (ii) derive a speed range that makes it possible to obtain the required number of events within the time available for the detailed diagnosis (e.g., during the interval time for workpiece changes in a machine tool); and (iii) set a suitable speed within the speed range as the detailed diagnostic speed.

[0024] The diagnostic speed setting device 3 desirablely includes an event count confirmation device for estimating the number of events per unit of time during the detailed diagnosis based on a damage frequency that occurs when the bearing 30 is damaged, and for confirming whether the preliminary estimated number of events per unit of time is obtained during the detailed diagnosis.

[0025] The abnormality diagnostic device 4 comprises a simple diagnostic device 4a for performing a basic diagnosis of the bearing 30 when the bearing is operated at any rotational speed; a detailed diagnostic device 4b for changing the rotational speed of the bearing 30 to the detailed diagnostic speed specified above and for performing a detailed diagnosis of the bearing 30; and a diagnostic result output unit 4c configured to output the diagnostic result information obtained by the simple diagnostic device 4a and the detailed diagnostic device 4b to a control unit 40 of the machine tool and to an external device 50, such as a personal computer or a server. The change in the rotational speed of the bearing 30 and the detailed diagnosis are performed by the detailed diagnostic device 4b only if an abnormality of the bearing 30 is detected by the simple diagnostic device 4a.

[0026] The simple diagnostic device 4a is configured to perform a diagnosis of the bearing 30 by calculating at least one simple diagnostic value from the vibration waveform detected by the vibration sensor 20 and comparing the simple diagnostic value with a predefined limit value. The rate of change of the RMS values ​​of the vibration waveform data can be used as a simple diagnostic value, for example.

[0027] On the other hand, the detailed diagnostic device 4b is configured to change the rotational speed of the bearing 30 to the detailed diagnostic speed mentioned above (i.e., to output rotational speed change information to the control unit 40 of the machine tool) and to perform a diagnosis of the bearing 30 by calculating a damage frequency, which occurs when the bearing 30 is damaged, based on the rotational speed detected by the rotation sensor 10, and comparing the damage frequency with a frequency component contained in the spectral data obtained from the vibration detected by the vibration sensor 20.As a specific diagnostic procedure, for example the following method can be used: In spectral data (where the horizontal axis represents the vibration frequency and the vertical axis the vibration level) obtained by performing envelope processing and frequency analysis of the vibration waveform, frequencies at which peaks in the vibration level occur are compared with damage frequencies for corresponding parts of the bearing 30, and if a match is found, the part of the bearing 30 corresponding to the matching damage frequency is determined to be in an abnormal condition.

[0028] In this condition monitoring system with the above arrangement, the detailed diagnostic device 4b is configured to perform a detailed diagnosis by reducing the rotational speed of bearing 30 to a suitable speed within a speed range where the number of events required for accurate abnormality determination can only be achieved if the abnormality of bearing 30 is detected by the simple diagnostic device 4a, which is included in the abnormality diagnostic device 4. Therefore, the detailed diagnostic speed can be set as high as possible (e.g., with a minimal speed reduction compared to the normal rotational speed of bearing 30), thus enabling highly accurate diagnosis without significantly reducing productivity.

[0029] As a method for setting the detailed diagnostic speed by the diagnostic speed setting device 3, in addition to the method based on the number of events per unit of time, a method based on a total value (i.e., the OA value) of the vibration detected by the vibration sensor 20 can also be used. As in Fig. As shown in Figure 4, the ratio between the OA value of the bearing in an abnormal condition and the OA value of the bearing in a normal condition (i.e., the OA value ratio) varies depending on the rotational speed. Accordingly, the OA value of bearing 30 in a normal condition is pre-stored. During operation of bearing 30, a rotational speed is determined at which the OA value ratio of bearing 30, at which an anomaly occurs at the corresponding rotational speed, can be obtained, and this rotational speed is defined as the detailed diagnostic speed.

[0030] This means that if an anomaly occurs in a bearing, the OA value ratio will generally be equal to or greater than 1 due to the influence of anomalous vibration components. However, at high speeds, the anomalous vibration components (i.e., peaks corresponding to the failure frequencies) may be masked by noise components, resulting in an OA value close to 1. Therefore, a speed free from noise influences, allowing the OA value ratio to be significantly greater than 1 with minimal speed reduction compared to the normal operating speed, is defined as the detailed diagnostic speed (i.e., it corresponds to the medium to high speed in the Fig.Even when using this method, it is possible to perform an accurate diagnosis with the highest possible level of detail. This method is also suitable for cases where the main shaft speed is gradually increased to the speed during normal operation, such as when starting up a machine tool.

[0031] Additionally, as a variation of the embodiment described above, an arrangement can be used in which the load sensor 21, which serves as the external force sensing device, is omitted from the sensor unit 1, which is arranged around the bearing 30, wherein the operating state determination device 2 is configured to (i) determine whether the bearing is in a loaded operating state or in a lightly loaded operating state, based on information obtained from a sensor contained in the machine tool itself; or (ii) determine that the bearing is in a lightly loaded operating state by acquiring time information indicating a non-machining state from a sequence program of the machine tool.

[0032] The embodiments described above are in every respect only examples, and the present invention is not limited to them. The scope of the present invention is not defined by the above description but by the claims and should be understood to include all modifications within the meaning and scope that correspond to the scope of the claims.

[0033] For example, in the simple diagnosis performed by the abnormality diagnostic device according to the embodiment, an abnormality is determined by comparing the simple diagnostic value with a limit value. However, if the normal rotational speed of the bearing falls within a permissible range in which the execution of the FFT is possible, the abnormality diagnosis can also be performed using the FFT in the simple diagnosis.

[0034] Furthermore, the simple diagnostic device can be omitted from the abnormality diagnostic device according to the embodiment, and the detailed diagnostic device can be performed at regular intervals or at any time.

[0035] Furthermore, the present invention can be applied particularly effectively to a case in which the bearing rotatably supports the main shaft of a machine tool, as in the embodiment shown. However, the present invention is not limited thereto and can be applied generally to a condition monitoring system for a bearing used at high rotational speeds. Description of the reference symbols 1 sensor unit 2 Operating status determination device 3 Diagnostic speed setting device 4 Abnormality diagnostic device 4a Easy diagnostic setup 4b Detailed diagnostic equipment 4c Diagnostic Result Output Unit 10 Rotation sensor (“speed detection device”) 20 Vibration sensor (vibration detection device) 21 Load sensor (external force detection device) 30 warehouses QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] JP 2009-20090

[0003]

Claims

[1] Condition monitoring system for a bearing, wherein the condition monitoring system comprises: a speed detection device for detecting the rotational speed of the bearing; a vibration detection device for detecting vibrations of the bearing; an operating condition determination device to determine whether the bearing is in a loaded operating condition or in a lightly loaded operating condition; a diagnostic speed setting device for setting a detailed diagnostic speed when a detailed diagnosis of the bearing is being carried out, based on the rotational speed detected by the speed sensing device and the vibration detected by the vibration sensing device, when the operating condition determination device determines that the bearing is in a lightly loaded operating condition; and An abnormality diagnostic device for changing the rotational speed of the bearing to the detailed diagnostic speed set by the diagnostic speed setting device, and for performing a detailed diagnosis of the bearing. [2] The condition monitoring system according to claim 1, wherein the abnormality diagnostic device comprises: a simple diagnostic device for performing a simple diagnosis of the bearing by (i) calculating at least one simple diagnostic value from a waveform of the vibration detected by the vibration detection device when the bearing is operated at any rotational speed, and (ii) comparing the at least one simple diagnostic value with a predetermined limit value; and A detailed diagnostic device for changing the rotational speed of the bearing to the detailed diagnostic speed and for performing the detailed diagnosis of the bearing by (i) calculating a damage frequency that occurs when the bearing is damaged, based on the rotational speed detected by the speed detection device, and (ii) comparing the damage frequency with a frequency component contained in spectral data obtained from the vibration detected by the vibration detection device. where the change in the rotational speed of the bearing and the detailed diagnosis of the bearing by the detailed diagnostic device are only to be carried out if an abnormality of the bearing is detected by the simple diagnostic device. [3] The condition monitoring system according to claim 1 or 2, wherein the diagnostic speed setting device is configured to set the detailed diagnostic speed based on the number of vibration events per unit of time detected by the vibration detection device. [4] The condition monitoring system according to claim 3, wherein the diagnostic speed setting device includes an event count confirmation device to confirm whether a preliminary estimated number of vibration events per unit of time is obtained during the detailed diagnosis. [5] The condition monitoring system according to claim 4, wherein the event count confirmation device is configured to estimate the number of vibration events per unit of time during detailed diagnostics based on the damage frequency that occurs when the bearing is damaged. [6] The condition monitoring system according to claim 1 or 2, wherein the diagnostic speed setting device is configured to set the detailed diagnostic speed based on an overall value of the vibration detected by the vibration detection device. [7] The condition monitoring system according to any one of claims 1 to 6, further comprising an external force detection device for detecting an external force exerted on the bearing, wherein the operating state determination device is configured to determine that the bearing is in a lightly loaded operating state when the external force detected by the external force detection device is less than a predetermined quantity. [8] The condition monitoring system according to any one of claims 1 to 7, wherein the bearing rotatably supports a main shaft of a machine tool.

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