Device and method for monitoring the operation of a spindle motor

Abstract

Device for monitoring the operation of a spindle motor (16) of a hard disk drive in combination with the spindle motor (16) comprising a stator (30), a rotor (38) and at least one fluid dynamic sliding bearing (44) rotatably supporting the rotor (38) relative to the stator (30), wherein the sliding bearing (44) has a bearing sleeve (46) and a pressure-generating groove structure (50) is formed on the inner surface of the bearing sleeve (46), which, when a rotor shaft (48) rotates in the bearing sleeve (46), generates a pumping action and thus builds up pressure in a bearing fluid (52), wherein the monitoring device comprises: a vibration sensor for detecting vibrations of the spindle motor (16) and 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 a motor control unit (12) which outputs a control current for controlling the spindle motor (16), with means (14) 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 gradient; and means for deriving an operating state of the slide bearing (44) from the result of the comparisons.;

Description

[0001] The invention relates to a device 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.

[0002] Such spindle motors are preferably used in hard disk drives, where one or more plain bearings are used to ensure minimal bearing friction.

[0003] The following are used as plain bearings: hydrodynamic plain bearings, also called fluid bearings, in which fluid friction predominates, but also, for example, air bearings. These can be combined with one or more magnetic bearings. Ball bearings and other rolling bearings are not used in the invention.

[0004] In hydrodynamic plain bearings, a lubricating film of oil or grease forms during operation between a bearing bushing and the shaft guided within it, with the shaft sliding without direct contact with the bearing bushing. 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 end face, creating a pumping effect. Alternatively, the pressure-generating grooves can be formed on the bearing surfaces of the bearing sleeve.

[0005] During operation of the spindle motor, the bearing properties can deteriorate. Aside from impacts to the spindle motor, there are three main causes for this deterioration: The bearing fluid evaporates during operation, leading to an increasing amount of air being drawn into the bearing. During motor start-up and shut-down, contact occurs between the bearing surfaces, causing abrasion. This abrasion can settle in the bearing like sediment, including in the bearing grooves, reducing the hydrodynamic bearing's ability to generate sufficient bearing pressure. Manufacturing tolerances of the surfaces defining the bearing gap create a vacuum in certain areas of the bearing, allowing air to escape from the bearing fluid and accumulate in the bearing gap.

[0006] These phenomena reduce the bearing's stiffness, causing the shaft to run out of true within the bearing. The number of NRROs (Non-Repeatable Run-Outs) and the amplitude of RROs (Repeatable Run-Outs) increase. RRO refers to the rotor runout resulting from deviations in the actual axis of rotation. RRO is a measure of the deviation in the actual axis of rotation due to off-centerness and tilting, as well as surface defects or form deviations caused by manufacturing processes. Superimposed on RRO is NRRO, which represents random or stochastic deviations that, unlike RRO, occur irregularly in both phase and amplitude. These are caused by irregularities originating from the bearing system itself. An increase in such runout errors can be considered an indicator of impending bearing failure.

[0007] Furthermore, the described disturbances result in higher bearing friction, which in turn accelerates wear and thus bearing failure.

[0008] EP 1 826 735 A2 describes a device for monitoring the rolling bearings of electric motors. The device uses a vibration sensor to monitor for wear-related increases in the frequency components typical of rolling bearings, thus enabling an assessment of the remaining service life of the bearings. The monitoring device utilizes the fact that rolling bearings generate a discrete vibration excitation when defective, for example, each time a ball rolls over the defect. Such fault monitoring is not readily possible with fluid bearings and other plain bearings; the friction, which in fluid bearings should generally only occur during the start-up and shut-down of the motor, does not generate a discrete excitation, but rather a broad excitation spectrum that manifests itself as a kind of noise across a wide frequency band. Detecting a "bearing-specific frequency component" is therefore not possible.

[0009] Systems for self-monitoring, analysis, and status reporting of computer hard drives are also known from the prior art under the name SMART (Self-Monitoring, Analysis and Reporting Technology). SMART monitors limit values ​​for individual parameters, such as usage and temperature, as defined by the hard drive manufacturers. Built-in sensors and chip functions are used for this purpose. Furthermore, SMART monitors uncorrectable errors when reading from the hard drive, corrected bit errors during reading, corrected errors when checking the hard drive surface, the number of start / stop operations of a drive, the used reserve sectors, and the number of park operations, and more generally, the data throughput and usage of the hard drive. These parameters are evaluated to detect indications of hard drive wear, problems with the disk surface, or problems with the drive motor and bearings.It is generally assumed that SMART can predict around 60% of all hard drive failures. SMART also shows that the highest selection probability for hard drives occurs during the first year of operation, and that subsequently, until a scheduled replacement of the hard drive after, for example, four years, failures no longer pose a significant problem.

[0010] It is an object of the invention to provide a device and a method for monitoring the operation of a spindle motor with which an impending failure of a spindle motor's sliding bearing can be predicted with the greatest possible accuracy. If possible, the 40% of failures that are not detected by SMART should be predictable.

[0011] This problem is solved by a device having the features of claim 1 and by a method according to claim 13.

[0012] 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 plain bearing. 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 plain bearing. The invention is based on the understanding that, although it is not possible to specify a bearing-specific frequency component for plain bearings because the vibration spectrum of plain bearings manifests itself more as a kind of noise in a broad frequency band, damage and malfunctions of the bearing do affect its stiffness and thus influence its concentricity.However, deviations in concentricity can be detected if, for example, the number of NRROs (Non-Return Oscillations) and the amplitude of the RROs increase. Such an increase can be recognized as a vibration of the spindle motor at a frequency that does not occur during normal operation. Therefore, if the vibration sensor detects vibrations of the spindle motor with a frequency and amplitude that would not occur in a vibration spectrum expected during normal operation, this indicates a malfunction of the plain bearing and thus an impending failure of the bearing and consequently of the spindle motor.

[0013] In a preferred embodiment of the invention, the vibration sensor is vibration-coupled to the sliding bearing or to a base plate of the spindle motor into which the sliding bearing is integrated. It is important that vibrations due to uneven running of the shaft in the sliding bearing are detected as directly as possible, so that direct vibration coupling between the sliding bearing and the vibration sensor is sought.

[0014] According to the invention, the vibration sensor preferably comprises an acceleration sensor, e.g., a piezoelectric acceleration sensor or a microelectromechanical system (MEMS). However, the invention is not limited to this and can also use other conventional acceleration sensors, e.g., strain gauges.

[0015] In addition to or as an alternative to detecting spindle motor vibrations, the monitoring of spindle motor operation can, according to the invention, also be based on detecting the phase current flowing through the stator windings of the spindle motor. In brushless DC motors and other permanent magnet motors, the stator phases are supplied with a control current via a motor control unit. The control current varies depending on the load, the motor's starting and stopping phases, and the speed. For sensorless speed control, the phase currents of the currently unenergized phases are monitored in such motors (back EMF), so that many spindle motors already inherently possess means for detecting the spindle motor's phase currents.The invention utilizes 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 understanding that bearing malfunctions lead to increased bearing friction and thus to a temperature increase and increased power consumption. 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 external influences – such as temperature.

[0016] In particular, a sudden increase in current draw is a clear indication of surface wear on the plain bearing and an imminent failure of the bearing and thus of the spindle motor. However, other malfunctions and wear phenomena can also lead to increased current draw and can therefore be detected according to the invention.

[0017] For example, if the spindle motor is operated in a high-humidity environment, moisture is absorbed into the bearing fluid, reducing its lubricating properties. This increases bearing friction and, consequently, the current draw rises exponentially until the bearing fails. Similarly, a decrease in the magnetic force of the rotor's permanent magnets over its lifespan also increases current draw. With conventional permanent magnets in a spindle motor, the magnetic force can decrease by up to 30% during continuous operation over five years. In this case, the increase in current draw is gradual and flat.

[0018] When measuring the phase current, sudden and steep current changes are of particular interest because these can indicate an imminent bearing failure. According to the invention, the phase current is therefore repeatedly measured at defined time intervals in order to detect changes in the phase current and compare them with a predetermined current gradient. The phase current monitoring should preferably begin when the absolute value of the phase current is greater than the rated current of the spindle motor at maximum load; for example, a large current gradient can also occur during motor start-up without indicating bearing damage.

[0019] Different gradients of the increasing phase current allow conclusions to be drawn about different causes of failure as well as a prediction of the probability of failure.

[0020] While the first aspect of the invention detects vibrations of the plain bearing caused by runout errors, the second aspect of the invention is based on current detection, particularly to detect increased bearing friction due to bearing damage. The two aspects of the invention can be used in combination.

[0021] In addition to the two monitoring devices described, the invention can optionally include a temperature sensor for detecting the temperature of the spindle motor, wherein the detected temperature is compared with a predetermined temperature threshold and / or a temperature gradient, and the result of the comparison is taken into account when deriving the operating state of the spindle motor. The temperature sensor can, for example, be integrated into the spindle motor as a separate temperature transducer or as a transistor within an integrated circuit. When using a transistor, its temperature-dependent characteristic curve is recorded to detect the temperature. The temperature sensor should optionally be thermally coupled to the spindle motor's sliding bearing.

[0022] Temperature measurement allows conclusions to be drawn about a bearing malfunction, because an increase in current consumption and bearing friction is always accompanied by a temperature increase. By correlating the temperature measurement with the current consumption measurement and taking into account atypical vibrations of the spindle motor, it is possible to detect malfunctions in the spindle motor's plain bearing, determine possible causes of the malfunction, predict the probability of bearing failure, and provide timely warning of an impending plain bearing failure.

[0023] The device according to the invention can issue an alarm signal when an operating state is detected that deviates from normal operation.

[0024] 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.

[0025] The invention is explained in more detail below with reference to a preferred embodiment and the drawings. The figures show:

[0026] Fig. 1 a block diagram of a device according to the invention for monitoring the operation of a spindle motor;

[0027] Fig. 2a a sectional view through a spindle motor according to the invention; and

[0028] Fig. 2b an enlarged representation of section A of the in Fig. 2a spindle motor shown.

[0029] Fig. Figure 1 shows a block diagram of a device according to the invention for monitoring the operation of a spindle motor in combination with the spindle motor. The figure shows functional units that do not necessarily have to be structurally separated. The arrangement includes a power supply. 10 , an engine control unit 12 , a current sensing unit 14 , the spindle motor16 with stator phases 18 and a warehouse 20 , an accelerometer 22 , a temperature sensor 24 and a signal processing unit 26 .

[0030] The spindle motor 16 For example, a brushless DC motor with a hydrodynamic fluid bearing 20 The motor has a permanent magnet rotor (in Fig. 1 not shown) and a stat with three stator phases U, V, W, 18 The stator phases are controlled by the motor control unit. 12 It is controlled and powered. The current sensing unit is used for speed control. 14 The phase currents of the respective unenergized phases. The motor control unit 12 It receives its electricity from the power supply. 10 In that respect, the Fig. The arrangement shown is a state of the art and is not described in further detail here.

[0031] According to the invention, the acceleration sensor 22 in the spindle motor 16 so attached and arranged that it is in contact with the storage area 20 is vibration-coupled, as detailed with reference to the Fig. 2a and Fig. 2b is explained. The accelerometer 22 detects vibrations of the spindle motor 16 , in particular vibrations caused by the operation of the bearing 20 caused by the output signal of the accelerometer. 22 the signal processing unit 26 supplied.

[0032] According to the invention, the output signal of the current detection unit is further 14 , i.e., the detected phase currents of the respective unenergized phases, of the signal processing unit 26 supplied. As explained above, the accelerometer 22 and the current sensing unit 14According to the invention, the temperature sensor can be used alternatively or in combination. Additionally, according to the invention, the temperature sensor can be used 24 the temperature of the spindle motor 16 , especially the warehouse 20 , detect and also send this temperature to the signal processing unit 26 supply.

[0033] The engine control unit 12 , the current sensing unit 14 and the signal processing unit 26 They can be implemented as discrete components or together in an integrated circuit (IC). The temperature sensor 24 is an optional component and can be implemented, for example, as a separate temperature sensor or as a transistor within the integrated circuit (IC).

[0034] According to the invention, the signals from the accelerometer are 22 from the signal processing unit 26The frequency spectrum generated by the vibrations of the spindle motor is evaluated according to fundamental frequencies and harmonics as well as amplitude, in order to determine whether the vibration behavior of the spindle motor is suitable. 16 The question is whether the vibration spectrum is "normal," meaning whether it corresponds to the vibration spectrum expected during normal operation due to the electric motor design, or whether atypical frequency spectra indicate a lack of bearing concentricity and thus damage or malfunction. Evaluating the frequency spectra allows for a simple yes / no assessment of bearing malfunction and can also predict the probability of bearing failure. Since the frequencies and amplitudes of the frequency spectrum also depend on the specific design of the bearing and the spindle motor, no concrete limit values ​​can be specified here, but these can be determined empirically by a specialist in individual cases.

[0035] Alternatively or additionally, the current consumption of the stator phases can also be used. 18 of the spindle motor 16 a malfunction or damage to the bearing 20 This can be deduced. In particular, increased bearing friction leads to a higher load and thus an increase in current consumption. In the preferred embodiment of the invention, current and temperature sensing are used in addition to the detection and evaluation of the spindle motor's vibrations to improve the accuracy of bearing malfunction detection. 20 and to increase the probability of selection. The correlation between current limits and gradients and individual faults and failure probabilities can also be determined empirically.

[0036] The Fig. 2a and Fig. Figure 2b shows sectional views through a spindle motor with the vibration monitoring according to the invention. The motor comprises a stator. 30 with a stator core 32 and stator windings or phases 34 , which has a base plate 36 the spindle motor is firmly attached. The rotor 38 The spindle motor includes a rotor magnet. 40 , which has a hub 42 with a wave 48 is coupled in a rotationally fixed manner.

[0037] The rotor 38 is opposite the stator 30 via a plain bearing 44 e.g., a fluid dynamic bearing (FDB). The plain bearing 44 is formed by a bearing sleeve 46 , which are embedded in the base plate 36 is pressed in, and one on the inner surface of the bearing sleeve 46 formed pressure-generating groove structure 50 . When the shaft rotates 48 in the bearing sleeve 46creates the groove structure 50 a pumping effect, thus building up pressure in the bearing fluid. 52 up, whereby the spindle motor of the Fig. 2a additionally features compensating channels, fluid seals, a fluid reservoir and the like, which, however, are not relevant to the invention. The hub 42 is with the wave 48 Connected in a rotationally fixed manner. For pre-tensioning the rotor. 38 is in the Fig. The spindle motor shown in 2a also includes a ferromagnetic ring. 54 provided for, which is located at the end of the rotor magnet 40 opposite and is attracted to it.

[0038] According to the invention, the base plate 36 a space to accommodate an accelerometer 56 trained. The accelerometer 56 is with the base plate 36 via an adhesive or a casting resin 58 Vibration-coupled connection. The adhesive or the casting resin. 58It can be the same material that is also used, for example, to seal the vias of the winding connections of the stator windings. 34 This results in a particularly simple and compact design that requires no additional materials. In the version shown, the accelerometer is soldered directly onto a flexible printed circuit board (FPC).

[0039] The accelerometer 56 is attached to the base plate in this way 36 tied so that it also works with the plain bearing 44 , in particular the bearing sleeve 46 , is vibration-coupled. It can therefore pass through the sliding bearing. 44The system directly detects vibrations caused by the bearing itself. As explained, this typically does not detect vibrations generated by the operation of the bearing itself, but rather the effects of bearing damage or malfunction on the bearing's stiffness. Reduced bearing stiffness leads to uneven running of the plain bearing. 34 This typically generates vibrations that can be detected by capturing a simple frequency spike. If such frequency spikes, deviating from normal operation, are detected, it can be inferred that the bearing is damaged and that a bearing failure is imminent. From this, a probability of failure can be derived. Reference symbol list 10 Power supply 12 Engine control unit 14 Current sensing unit 16 spindle motor 18 stator phases 20 warehouses 22 Accelerometer 24 temperature sensors 26 Signal processing unit 30 Stator 32 Stator core 34 stator windings, stator phases 36 Base plate 38 Rotor 40 Rotor magnet 42 hub 44 plain bearings 46 Bearing sleeve 48 wave 50 groove structure 52 Storage fluid 54 Ferromagnetic ring 56 Accelerometer 58 Adhesive or casting resin QUOTES INCLUDED IN THE DESCRIPTION

[0040] 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

[0041] EP 1826735 A2

[0008]

Claims

[1] Device for monitoring the operation of a spindle motor ( 16 ), in which a rotor ( 38 ) relative to a stator ( 30 ) by at least one plain 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 recorded vibrations and comparing the result of the analysis with an expected spectrum and for deriving an operating state of the sliding bearing from the result of the comparison. [2] Device according to claim 1, characterized in that the vibration sensor is mounted on the sliding bearing ( 44 ) is mounted in a vibration-coupled manner. [3] Device according to claim 1, characterized in that the vibration sensor is mounted on a base plate ( 36 ) of the spindle motor ( 16 ), into which the plain bearing ( 44) is integrated, is mounted in a vibration-coupled manner. [4] Device according to one of the preceding claims, characterized in that the vibration sensor includes an acceleration sensor ( 22 ) includes. [5] Device according to one of the preceding claims, characterized in that the signal processing unit ( 26 ) is designed to check the spectrum of the detected vibrations for frequencies that occur during uneven running of the plain bearing ( 44 ) arise. [6] 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 ) has a control current for controlling the spindle motor ( 16 ) emits, with means for detecting a phase current of the spindle motor ( 16 ) and with a signal processing unit ( 26) to compare the measured phase current with a predefined current threshold and / or gradient and to derive an operating state of the spindle motor ( 16 ) from the result of the comparison. [7] Device according to claim 6, characterized in that the means for detecting the control current are configured to repeatedly detect the phase current at defined time intervals and to derive a change in the phase current from it and to compare this change with the predetermined current gradient. [8] Device according to claim 6 or 7, characterized in that the current threshold is greater than a rated current of the spindle motor ( 16 ) at maximum load. [9] Device according to one of claims 6 to 8, characterized in that the signal processing unit ( 26) is set up to identify a fault in the spindle motor depending on a determined deviation of the detected phase current from the specified current threshold and / or gradient ( 16 to determine. [10] 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 set up to compare the measured temperature with a predefined temperature threshold and / or gradient and to use the result of the comparison to derive the operating state of the spindle motor ( 16 ) to be taken into account. [11] Device according to one of the preceding claims, characterized in that the signal processing unit ( 26 ) is set up to issue an alarm signal when an operating condition is detected that deviates from normal operation. [12] Spindle motor ( 16 ), in which a rotor ( 38 ) relative to a stature ( 30 ) via at least one plain bearing ( 44 ) is mounted, with a device for monitoring the operation of a spindle motor ( 16 ) according to one of the preceding claims. [13] Method for monitoring the operation of a spindle motor ( 16 ), in which a rotor ( 38 ) relative to a stature ( 30 ) by at least one plain bearing ( 44 ) is mounted, whereby vibrations of the spindle motor ( 16 ) are recorded and the spectrum of the recorded vibrations is analyzed and the result of the analysis is compared with an expected spectrum in order to determine an operating condition of the sliding bearing ( 44 ) to derive from the result of the comparison. [14] Method according to claim 13, characterized in that the vibrations are transmitted directly to the sliding bearing ( 44) are recorded. [15] Method according to claim 13 or 14, characterized in that the spectrum of the detected vibrations is checked for frequencies that occur during an uneven running of the sliding bearing ( 44 ) arise. [16] 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 ) has a control current for controlling the spindle motor ( 16 ) emits, whereby the control current of the spindle motor ( 16 ) is detected and compared with a predefined current threshold and / or gradient to determine the operating state of the spindle motor ( 16 ) to derive from the result of the comparison. [17] Method according to claim 16, characterized in that the control current is repeatedly recorded at defined time intervals and a change in the control current is derived from this and this change is compared with predetermined current gradients. [18] 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. [19] 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, a cause of disturbance in the spindle motor ( 16 ) is determined. [20] Method according to any one of claims 13 to 19, characterized in that the temperature of the spindle motor ( 16) is recorded and compared with a predefined temperature threshold and / or gradient, and that the result of the comparison is used to derive the operating state of the spindle motor ( 16 ) is taken into account. [21] Method according to one of claims 13 to 20, characterized in that an alarm signal is issued when an operating state is detected which deviates from normal operation.

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