DE102009044509A1 - Operation monitoring device for spindle motor of hard disk drive of computer, has signal processing unit for outputting operating condition of bearing based on result of comparison of analysis of detected spectrum with expected spectrum - Google Patents

Abstract

The device has a vibration sensor for detecting vibrations of a spindle motor (16), and a signal processing unit (26) for analyzing a spectrum of the detected vibrations. A sliding bearing is integrated into a base plate of the spindle motor and supports a rotor of the spindle motor relative to a stator. The processing unit compares the result of the analysis of the detected spectrum with an expected spectrum and outputs an operating condition of the sliding bearing based on the result of the comparison. The vibration sensor is attached to the base plate of the spindle motor. Independent claims are also included for the following: (1) a spindle motor comprising a rotor supported relative to a stator by a sliding bearing (2) a method for monitoring operating of a spindle motor.

Description

The invention relates to an apparatus and a method for monitoring the operation of a spindle motor, in particular a spindle motor, which uses at least one sliding bearing to support a rotor relative to a stator.

Such spindle motors are preferably used in hard disk drives, wherein one or more plain bearings are used to ensure a minimum bearing friction.

As plain bearings in particular hydrodynamic plain bearings, also called fluid bearings, used in which a liquid friction prevails, but z. B. also air bearings. These can be combined with one or more magnetic bearings. Not for use in the invention, however, come ball and other bearings.

In hydrodynamic plain bearings, a lubricating film of oil or grease is produced during operation between a bearing bush and the shaft guided therein, wherein the shaft slides without direct contact with the bearing bush. To generate a controlled pressure build-up in the bearing gap pressure-generating grooves are formed on the surface of the shaft and / or at its front end, which have a pumping action. Alternatively, the pressure generating grooves may be formed on the bearing surfaces of the bearing sleeve.

During operation of the spindle motor, the bearing characteristics may deteriorate. Apart from impacts on the spindle motor, there are the following three main causes of deterioration in bearing characteristics: The bearing fluid vaporizes during the life of the bearing, so that more and more air is drawn into the bearing. When the motor starts and stops, a bearing surface contact occurs, which generates abrasion on the bearing surfaces. This abrasion can settle like sediment in the bearing, even in the bearing grooves, so that the hydrodynamic bearing can only build up a reduced bearing pressure. Due to manufacturing tolerances of the surfaces which define the bearing gap, a negative pressure is generated in areas of the bearing so that air can outgas from the bearing fluid and accumulate in the bearing gap.

These phenomena reduce the rigidity of the bearing so that the shaft in the bearing no longer runs smoothly. The number of NRROs (Non Repeatable Run Out) and the amplitude of RROs (Repeatable Run Out) are increasing. The term RRO is used to describe the impact of the rotor resulting from the deviations of the actual axis of rotation. The RRO is a measure of the deviation of the actual axis of rotation due to external centering and tilting as well as for the surface defects or shape deviations caused by production processes. Superimposed on the RRO is the NRRO, ie the random or stochastic deviations, which occur irregularly in contrast to the RRO, both in terms of phase position and in terms of their amplitude. The cause is irregularities resulting from the storage system. The increase in such concentricity errors can be used as an indication of an imminent bearing failure.

Due to the described disturbances also results in a higher bearing friction, which in turn accelerates the wear and thus the failure of the bearing.

The EP 1 826 735 A2 describes a device for monitoring the rolling bearings of electric motors. The device uses a vibration sensor and thus monitors a wear-related increase in the rolling bearing typical frequency components to allow an assessment of the rolling bearings in terms of their remaining life. The monitoring device makes use of the fact that rolling bearings generate a discrete vibration excitation in the event of a defect, namely, z. B. every time a ball rolls over the defect. Such error monitoring is not readily possible with fluid bearings and other plain bearings; because the friction, which should usually occur in fluid bearings usually only in the inlet and outlet of the engine, does not produce a discrete excitation, but rather a broad excitation spectrum that manifests itself as a kind of noise in a broad frequency band. The detection of a "bearing typical frequency component" is not possible.

Systems for self-monitoring, analysis and status reporting of computer hard disks are also known from the state of the art under the name SMART (self-monitoring, analysis and reporting technology). SMART monitors hard disk manufacturer-defined limits for individual parameters such as mileage and temperature. For this purpose, built-in sensors and chip functions are used. In addition, SMART monitors non-recoverable disk read errors, corrected read bit errors, and disk drive surface corrected errors, disk drive start / stop, used spare and park operations, and more generally data throughput and mileage the hard drive. These quantities are evaluated to detect an indication of hard disk wear, disk surface problems, or drive motor and bearing problems. In general, SMART estimates that around 60% of disk failures are predictable. It is also known from SMART that the highest selectivity for hard disk drives during the first year of operation and that thereafter up to a regular replacement of the hard drive after, for example, four years of failure no longer represent a significant problem.

It is an object of the invention to provide an apparatus and a method for monitoring the operation of a spindle motor, with which an imminent failure of a sliding bearing of the spindle motor can be predicted with the greatest possible accuracy. If possible, the 40% of failures not recognized by S.M.A.R. T. should become predictable.

This object is achieved by a device having the features of claim 1 and by a method according to claim 13.

The invention provides a device for monitoring the operation of a spindle motor in which a rotor is mounted relative to a stator by at least one sliding bearing before. The device comprises a vibration sensor for detecting vibrations of the spindle motor and a signal processing unit for analyzing the spectrum of the detected vibrations. The result of this analysis is compared with an expected spectrum to derive an operating condition of the sliding bearing. The invention is based on the realization that it is not possible for plain bearings to specify a bearing-specific frequency component, because the vibration spectrum of plain bearings manifests itself rather as a kind of noise in a broad frequency band, but that damages and disturbances of the bearing on the rigidity of the Bearing and thus have an effect on the concentricity of the bearing. However, round-trip deviations can be detected if, for example, the number of NRROs and the amplitude of the RROs increase. Such an increase may be detected as a vibration of the spindle motor at a frequency that does not occur in normal operation. Accordingly, if oscillations of the spindle motor with a frequency and amplitude which would not occur in a vibration spectrum to be expected during normal operation are detected by the vibration sensor, it is possible to conclude that the plain bearing is malfunctioning and thus an imminent failure of the bearing and thus of the spindle motor.

In a preferred embodiment of the invention, the vibration sensor is vibration-mounted on the sliding bearing or on a base plate of the spindle motor, in which the sliding bearing is integrated attached. It is important that vibrations due to a non-circular running of the shaft in the sliding bearing are detected as directly as possible, so that a direct vibration coupling between the sliding bearing and the vibration sensor is sought.

According to the invention, the vibration sensor preferably comprises an acceleration sensor, for. As a piezoelectric acceleration sensor or a micro-electro-mechanical system (MEMS). However, the invention is not limited to this and may also include other classical acceleration sensors, e.g. B. strain gauges use.

In addition to or alternatively to the detection of vibrations of the spindle motor, the monitoring of the operation of the spindle motor according to the invention can also be based on a detection of the phase current passing through the stator windings of the spindle motor. In brushless DC motors and other permanent magnet motors, the phases of the stator are supplied via a motor control unit with a control current. The control current varies depending on the load, starting and stopping of the motor and the speed. For sensorless speed control, the phase currents of the respectively non-energized phases are monitored in such motors (mutual induction voltage), so that many spindle motors themselves already have means for detecting the phase currents of the spindle motor. The invention uses these means to compare the detected phase current with a predetermined current threshold and / or current gradient and to derive an operating state of the spindle motor from the result of the comparison. This additional or alternative monitoring is based on the finding that disturbances of the bearing lead to an increased bearing friction and thus to an increase in temperature and an increased power consumption. The detection of the phase current can be used as a measure of the increased bearing friction. It has the advantage that the phase currents are not subject to any external influences - such as the temperature.

In particular, a sudden increase in power consumption is a clear indication of surface wear of the plain bearing and an imminent failure of the bearing and thus the spindle motor. But other disturbance and wear phenomena can lead to increased power consumption and thus be recognized according to the invention.

For example, when the spindle motor is operated in a high humidity environment, moisture is bound in the bearing fluid, whereby the bearing fluid has a less good lubricating effect; the friction of the bearing increases and the power demand increases exponentially until the bearing fails. Even with a decrease in the magnetic force of the permanent magnets of the rotor over its life increases the power demand. In conventional permanent magnets of a spindle motor, the magnetic force during continuous operation over five years reduces by up to 30%. In this case, the increase in power consumption is steady and shallow.

In the detection of the phase current in particular sudden and steep current changes are of interest because they can give an indication of an imminent failure of the camp. According to the invention, therefore, the phase current is repeatedly detected at defined time intervals in order to derive a change in the phase current and to compare this with a predetermined current gradient. The check of the phase current should preferably be used when the absolute value of the phase current is greater than a nominal current of the spindle motor at maximum load; For example, even at startup of the engine, a large current gradient can occur without this being an indication of a bearing damage.

Different gradients of the rising phase current allow a conclusion on different causes of the error as well as a prognosis of the probability of failure.

Thus, while according to the first discussed aspect of the invention vibrations of the sliding bearing are detected, which are caused by concentricity errors, the second aspect of the invention based on a current detection, in particular to detect an increased bearing friction due to bearing damage. The two aspects of the invention can be used in combination.

In addition to the two monitoring devices described, the invention may optionally include a temperature sensor for detecting the temperature of the spindle motor, wherein the detected temperature compared with a predetermined temperature threshold and / or a temperature gradient and the result of the comparison in the derivation of the operating state of the spindle motor is taken into account. For example, the temperature sensor may be integrated into the spindle motor as a separate temperature transducer or as a transistor within an IC. When using a transistor whose temperature-dependent characteristic is recorded for detecting the temperature. The temperature sensor should possibly be heat coupled to the sliding bearing of the spindle motor.

The temperature measurement allows a conclusion to a disturbance of a bearing, because with an increase in power consumption and bearing friction always accompanied by a temperature increase. By correlating the temperature measurement and the measurement of current consumption and including atypical oscillations of the spindle motor, it is possible to detect malfunctions of the sliding bearing of the spindle motor to determine possible causes of failure to forecast a probability of failure of the bearing, and to point out in due time an impending failure of the bearing.

The device according to the invention can output an alarm signal when determining an operating state which deviates from a normal operation.

The invention also provides a spindle motor with one or more of the described monitoring devices and a method for monitoring the operation of the spindle motor.

The invention is explained in more detail below with reference to a preferred embodiment with reference to the drawings. In the figures show:

1 a block diagram of a device according to the invention for monitoring the operation of a spindle motor;

2a a sectional view through a spindle motor according to the invention; and

2 B an enlarged view of the section A of in 2a shown spindle motor.

1 shows a block diagram of an inventive device for monitoring the operation of a spindle motor in combination with the spindle motor. The figure shows functional units that need not be structurally separated. The arrangement includes a power supply 10 , an engine control unit 12 , a current detection unit fourteen , the spindle motor 16 with stator phases 18 and a warehouse 20 , an acceleration sensor 22 , a temperature sensor 24 and a signal processing unit 26 ,

The spindle motor 16 is, for example, a brushless DC motor with a hydrodynamic fluid bearing 20 , The motor has a permanent magnet rotor (in 1 not shown) and a stature with three stator phases U, V, W, 18 , on. The stator phases are via the engine control unit 12 controlled and supplied with electricity. For speed control, the current detection unit detects fourteen the phase currents of each de-energized phases. The engine control unit 12 gets its power from the power supply 10 , In that regard, the belongs in 1 shown prior art arrangement and is not described here in more detail.

According to the invention, the acceleration sensor 22 in the spindle motor 16 so appropriate and arranged that he is with the camp 20 vibrational coupled, as with respect to the 2a and 2 B is explained. The acceleration sensor 22 detects vibrations of the spindle motor 16 , in particular vibrations caused by the operation of the warehouse 20 caused. The output signal of the acceleration sensor 22 becomes the signal processing unit 26 fed.

Furthermore, according to the invention, the output signal of the current detection unit fourteen , So the detected phase currents of each energized phases, the signal processing unit 26 fed. As explained above, the acceleration sensor 22 and the current detection unit fourteen be used according to the invention alternatively or in combination. In addition, according to the invention, the temperature sensor 24 the temperature of the spindle motor 16 , especially of the warehouse 20 , Capture and this temperature also the signal processing unit 26 respectively.

The engine control unit 12 , the current detection unit fourteen and the signal processing unit 26 can be realized as discrete components or together in an integrated circuit (IC). The temperature sensor 24 is an optional component and may be implemented, for example, as a separate temperature sensor or as a transistor within the integrated circuit (IC).

According to the invention, the signals of the acceleration sensor 22 from the signal processing unit 26 evaluated and the frequency spectrum generated by the vibrations of the spindle motor is evaluated by fundamental frequencies and harmonics and amplitude to determine whether the vibration behavior of the spindle motor 16 Is "normal", ie whether the vibration spectrum corresponds to the expected in normal operation vibration spectrum due to the electric motor design, or whether atypical frequency spectra indicate a lack of concentricity of the bearing and thus damage or disturbance of the bearing. By evaluating the frequency spectra, it is initially possible to detect a malfunction of the bearing in the sense of a yes / no decision, but also to predict a failure probability of the bearing. Since the frequencies and amplitudes of the frequency spectrum are also dependent on the respective design of the bearing and the spindle motor, no concrete limits can be specified here, but in some cases by the expert z. B. be determined empirically.

Alternatively or additionally, it is also possible to determine the current consumption of the stator phases 18 of the spindle motor 16 to a fault or damage to the bearing 20 be inferred. In particular, an increased bearing friction leads to a higher load and thus an increase in power consumption. In the preferred embodiment of the invention, current sensing and temperature sensing are employed in addition to detecting and evaluating the vibrations of the spindle motor to provide accuracy in detecting bearing failures 20 and increase in predicting a selection probability. The correlation of current limit values and gradients to individual errors and failure probabilities can also be determined empirically.

The 2a and 2 B show sectional views through a spindle motor with the vibration monitoring according to the invention. The engine includes a stator 30 with a stator core 32 and stator windings or phases 34 that with a base plate 36 the spindle motor is firmly connected. The rotor 38 of the spindle motor comprises a rotor magnet 40 that's about a hub 42 with a wave 48 rotatably coupled.

The rotor 38 is opposite the stator 30 via a plain bearing 44 , z. B. a fluid dynamic bearing (FDB) stored. The plain bearing 44 is formed by a bearing sleeve 46 in the base plate 36 is pressed, and one on the inner surface of the bearing sleeve 46 formed pressure generating groove structure 50 , Upon rotation of the shaft 48 in the bearing sleeve 46 creates the groove structure 50 a pumping action and thus builds a pressure in the bearing fluid 52 on, wherein the spindle motor of 2a additional compensation channels, fluid seals, a fluid reservoir and the like, which are not relevant to the invention, however. The hub 42 is with the wave 48 rotatably connected. For biasing the rotor 38 is in the in 2a spindle motor also shown a ferromagnetic ring 54 provided, the front end of the rotor magnet 40 and is attracted to it.

According to the invention is in the base plate 36 a space for receiving an acceleration sensor 56 educated. The acceleration sensor 56 is with the base plate 36 over an adhesive or a cast resin 58 vibrationally connected. The glue or the cast resin 58 may be the same material, for example, also for sealing vias of the winding terminals of the stator windings 34 is used. This results in a particularly simple and compact structure that requires no additional materials. In the embodiment shown, the acceleration sensor is soldered directly to a flexible printed circuit board (FPC).

The acceleration sensor 56 is so to the base plate 36 Tied that he also with the sliding bearing 44 , in particular the bearing sleeve 46 . is vibration coupled. He can thus through the plain bearing 44 Capture vibrations directly. As explained, vibrations generated by the operation of the bearing are generally not detected, but the effects of bearing damage or bearing failure on the rigidity of the bearing are detected. A reduced bearing stiffness leads namely to a faulty concentricity of the plain bearing 34 which usually generates vibrations that can be detected by detecting a simple frequency peak. If such frequency peaks deviating from normal operation are detected, damage to the bearing and imminent bearing failure can thus be deduced. From this again a probability of failure can be derived.

LIST OF REFERENCE NUMBERS

10

power supply

12

Engine control unit

14

Current detection unit

16

spindle motor

18

stator phases

20

camp

22

accelerometer

24

temperature sensor

26

Signal processing unit

30

stator

32

stator core

34

Stator windings, stator phases

36

baseplate

38

rotor

40

rotor magnet

42

hub

44

bearings

46

bearing sleeve

48

wave

50

groove structure

52

bearing fluid

54

Ferromagnetic ring

56

accelerometer

58

Glue or cast resin

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 1826735 A2 [0008]

Claims (21)

Device for monitoring the operation of a spindle motor ( 16 ), in which a rotor ( 38 ) relative to a stator ( 30 ) by at least one sliding bearing ( 44 ) is mounted with a vibration sensor for detecting vibrations of the spindle motor ( 16 ) and with a signal processing unit ( 26 ) for analyzing the spectrum of the detected vibrations and comparing the result of the analysis with an expected spectrum and deriving an operating condition of the sliding bearing from the result of the comparison. Apparatus according to claim 1, characterized in that the vibration sensor on the plain bearing ( 44 ) is mounted vibrationally coupled. Apparatus according to claim 1, characterized in that the vibration sensor on a base plate ( 36 ) of the spindle motor ( 16 ) into which the plain bearing ( 44 ) is integrated, vibration coupled is appropriate. Device according to one of the preceding claims, characterized in that the vibration sensor comprises an acceleration sensor ( 22 ). Device according to one of the preceding claims, characterized in that the signal processing unit ( 26 ) is set up to check the spectrum of the detected vibrations at frequencies that occur during a non-circular running of the slide bearing ( 44 ) arise. Device for monitoring the operation of a spindle motor ( 16 ), in particular according to one of the preceding claims, wherein the spindle motor ( 16 ) an engine control unit ( 12 ) having a control current for driving the spindle motor ( 16 ) with means for detecting a phase current of the spindle motor ( 16 ) and with a signal processing unit ( 26 ) for comparing the detected phase current with a predetermined current threshold and / or gradient and for deriving an operating state of the spindle motor ( 16 ) from the result of the comparison. Apparatus according to claim 6, characterized in that the means for detecting the control current are adapted to detect the phase current repeatedly in defined time intervals and to derive therefrom a change of the phase current and to compare this change with the predetermined current gradient. Apparatus according to claim 6 or 7, characterized in that the current threshold value is greater than a rated current of the spindle motor ( 16 ) at maximum load. Device according to one of claims 6 to 8, characterized in that the signal processing unit ( 26 ) is set up, depending on a determined deviation of the detected phase current from the predetermined current threshold value and / or gradient, a fault cause in the spindle motor ( 16 ) to investigate. Device according to one of the preceding claims, characterized by a temperature sensor for detecting the temperature of the spindle motor ( 16 ), wherein the signal processing unit ( 26 ) is adapted to compare the detected temperature with a predetermined temperature threshold and / or gradient and the result of the comparison in the derivation of the operating state of the spindle motor ( 16 ). Device according to one of the preceding claims, characterized in that the signal processing unit ( 26 ) is set to output an alarm signal upon detection of an operating condition which deviates from a normal operation. Spindle motor ( 16 ), in which a rotor ( 38 ) relative to a stature ( 30 ) via at least one sliding bearing ( 44 ) is mounted with a device for monitoring the operation of a spindle motor ( 16 ) according to one of the preceding claims. Method for monitoring the operation of a spindle motor ( 16 ), in which a rotor ( 38 ) relative to a stature ( 30 ) by at least one sliding bearing ( 44 ), wherein vibrations of the spindle motor ( 16 ) and the spectrum of the detected vibrations are analyzed and the result of the analysis is compared with an expected spectrum in order to determine an operating state of the plain bearing ( 44 ) derive from the result of the comparison. A method according to claim 13, characterized in that the vibrations directly on the sliding bearing ( 44 ). A method according to claim 13 or 14, characterized in that the spectrum of the detected vibrations is checked for frequencies which in a non-circular running of the plain bearing ( 44 ) arise. Method for monitoring the operation of a spindle motor ( 16 ), in particular according to one of claims 13 to 15, wherein the spindle motor ( 16 ) an engine control unit ( 12 ) having a control current for driving the spindle motor ( 16 ), wherein the control current of the spindle motor ( 16 ) is detected and compared with a predetermined current threshold and / or gradient to an operating state of the spindle motor ( 16 ) derive from the result of the comparison. A method according to claim 16, characterized in that the control current is detected repeatedly at defined time intervals and derived therefrom a change in the control current and this change is compared with predetermined current gradients. A method according to claim 16 or 17, characterized in that the current threshold is greater than a rated current of the spindle motor ( 16 ) at maximum load. Method according to one of claims 16 to 18, characterized in that depending on a determined deviation of the detected control current from the predetermined current threshold and / or gradient causes a fault in the spindle motor ( 16 ) is determined. Method according to one of claims 13 to 19, characterized in that the temperature of the spindle motor ( 16 ) and compared with a predetermined temperature threshold and / or gradient and that the result of the comparison in the derivation of the operating state of the spindle motor ( 16 ) is taken into account. Method according to one of claims 13 to 20, characterized in that when determining an operating condition which deviates from a normal operation, an alarm signal is output.

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